Complete Report - University of New South Wales

ARC Centre of Excellence for
Advanced Silicon Photovoltaics
and Photonics
Annual Report 2005

Centre of Excellence for
Advanced Silicon Photovoltaics and Photonics
is a Centre of Excellence of
The Australian Research Council

Page
1. DIRECTORS' REPORT 1
2. HIGHLIGHTS 3
3. STAFF LIST 9
4. RESEARCH
4.1 INTRODUCTION TO RESEARCH 13
4.2 FACILITIES AND INFRASTRUCTURE 17
4.3 FIRST GENERATION: WAFER-BASED PROJECTS 25
4.4 SECOND GENERATION: THIN-FILMS 51
4.5 THIRD GENERATION: ADVANCED CONCEPTS 71
4.6 SILICON PHOTONICS 97
4.7 COLLABORATIVE RESEARCH 117
5 EDUCATION 127
6. ORGANISATIONAL STRUCTURE 145
7. PROGRESS AGAINST TARGETS 147
8. FINANCIALS 161
9. PUBLICATIONS 165

DIRECTORS' REPORT
Photovoltaics involve the conversion of light,
especially sunlight, directly into electricity when
falling upon devices known as solar cells. Silicon is
the most common material used to make these cells,
as well as being the material most widely used in
microelectronics.
The Australian Research Council (ARC) Centre of
Excellence for Advanced Silicon Photovoltaics and
Photonics (or, more compactly, the ARC Photovoltaics
Centre of Excellence) offi cially commenced at the
University of New South Wales (UNSW) on 13th June,
2003. The Centre‘s mission is to advance silicon
photovoltaic research on three separate fronts, as
well as to apply these advances to the related fi eld
of silicon photonics. The educational activities of
the former Key Centre for Photovoltaic Engineering
have also been successfully integrated into the new
Centre.
We are in a period of dynamic growth for
photovoltaics, currently the world’s most rapidly
growing energy source, with markets increasing at a
compounded rate of 35%/year over the last decade,
with the pace accelerating further over the last 2
years. Most present sales are of “fi rst-generation”
solar cells made from silicon wafers, similar to the
wafers used in microelectronics. The Centre has a
world-leading program with these “fi rst-generation”
devices, holding international records for the highestperforming
silicon cells in most major categories,
including that for the outright highest-performing
device. First-generation Centre research addresses
the dual challenges of reducing cost and improving
effi ciency. A key goal is to develop technology which
allows silicon wafers doped with boron to be replaced
by phosphorus-doped wafers. The problem with
boron is that, under sunlight, it interacts with trace
quantities of oxygen in the wafers, producing defects
that reduce cell output. Phosphorus does not have
this problem, but presents more challenges to highperformance
cell fabrication. During 2005, the
Centre’s progress in this area was documented
by the demonstration of world-record 22.7% cell
energy-conversion effi ciency using phosphorus-doped
wafers.
Silicon is quite a brittle material so silicon wafers
have to be reasonably thick, about one-quarter of a
millimetre, to be suffi ciently rugged for processing
into solar cells with reasonable yields. Without this
mechanical constraint, the silicon would perform
well even if very thin, over 100 times thinner. Centre
researchers have pioneered an approach where such
very thin silicon layers are deposited directly onto a
sheet of glass with the glass providing the required
mechanical strength. Such a “second-generation”
approach gives enormous potential cost savings
since, not only are the costly processes involved in
making wafers no longer required, but also there is
an enormous saving in silicon material and cells can
be made more quickly over the entire area of large
glass sheets.
The Centre is at the forefront of international
research with this “second-generation”, “silicon on
glass” approach. A partner in the Centre is CSG
Solar, an originally Sydney-based company formed to
commercialise the Centre’s initial approach. During
2005, the company built the fi rst manufacturing
plant for this new technology in Thalheim, Germany,
with ramping-up of production scheduled for the fi rst
half of 2006. Complementary work wholly within
the Centre demonstrated improvements in its EVA,
ALICIA and ALICE thin-fi lm solar cell concepts. A
signifi cant factor behind these improvements was
the acquisition of a major new processing facility, as
a result of a major ARC Centre of Excellence/UNSW
initiative outlined in our 2004 Annual Report.
The silicon thin-fi lm approach has a large cost
advantage over the wafer-based approach, due
mainly to reduced material costs. However, in large
enough production volumes, even these reduced
material costs eventually will dominate the costs of
the thin-fi lm approach. This has led to the Centre’s
interest in advanced “third-generation” thin-fi lm
solar cells targeting signifi cant increases in energyconversion
effi ciency. Higher conversion effi ciency
means more power from a given amount of material,
reducing costs. The Centre’s experimental program
is concentrating on “all-silicon” tandem solar cells,
where high energy-bandgap cells are stacked on
top of lower-bandgap devices. The silicon bandgap
is controlled by quantum-confi nement of carriers
in small silicon quantum-dots dispersed in an
amorphous matrix of silicon oxide, nitride or carbide.
Progress with this approach was recognised by
the award of substantial complementary funding
during 2005 under the Global Climate and Energy
Project managed by Stanford University and funded
by a large international consortium. Other thirdgeneration
approaches are being explored based
on up-conversion or down-conversion of the energy
of photons in the solar spectrum, to manipulate this
spectrum so it is more suitable for conversion by
1

the cell. Cells based on “hot” carriers are also being
investigated since they offer the potential for very high
effi ciency from simple device structures. Although
their implementation poses daunting challenges,
systematic progress on addressing these was made
during 2005.
The fi nal Centre research strand involves silicon
photonics where, as mentioned, the emphasis is
upon using our experience with solar cells, using
light to produce electricity, to the reverse problem
of engineering silicon devices that use electricity
to produce light. Devices of this type would be of
great interest in microelectronics since they would
allow optical processes to be integrated with the
normal electronic functions on the same silicon
chip. The Centre holds the international record for
the light emission performance from bulk silicon,
in both electroluminescent and photoluminescent
devices. Emphasis is now upon incorporating these
improvements into silicon microchip-compatible light
emitting devices using silicon-on-insulator wafers
and upon exploiting our expertise in silicon light
emission to develop new techniques for silicon wafer
characterisation.
In addition to these four research strands, the
activities of the former Key Centre for Photovoltaic
Engineering have been integrated into the ARC
Centre of Excellence. The second cohort of students
from the Bachelor of Engineering (Photovoltaics and
Renewable Energy) program graduated during the
year.
This program has been enormously successful,
attracting some of the best students entering the
University. The Centre’s second undergraduate
program, leading to a Bachelor of Engineering
(Renewable Energy), completed its third year of
operation.
Another notable achievement during 2005 was
completion of the Centre’s major third year review.
The Review Committee very favourably assessed
the Centre on all aspects of its operations. Other
highlights originated from the rapidly growing
commercial interest in photovoltaics as a sustainable
and increasingly marketable energy source. Centre
partner, Suntech Power, a largely Australianowned
and managed company operating in China,
successfully fl oated on the New York Stock Exchange
in December, in the largest technology fl oat of the year.
A second partner and Centre “spin-off”, CSG Solar,
also announced the completion of its manufacturing
facility in Germany, as previously noted, and licensee,
BP Solar, announced signifi cant increases in the
performance of its commercial product.
We thank all those who contributed to the Centre’s
success during 2005, particularly the Australian
Research Council for its on-going support. The present
continues to be a most exciting time for photovoltaics
with time drawing closer to a future where solar cells
provide a signifi cant part of the world’s energy needs,
without the problems and escalating costs associated
with the present mainstream options.
………………………………………………
Professor Stuart R. Wenham,
Director
………………………………………………
Professor Martin A. Green,
Executive Research Director
2

HIGHLIGHTS
Cell Efficiency World Record
The Centre’s high-effi ciency group demonstrated an independently-confi rmed energy
conversion effi ciency of 22.7% for a large area 22 cm2 cell fabricated on an n-type silicon
substrate, equalling the world-record for a cell on such substrates. Other fi rst generation work
within the buried-contact group resulted in further progress in developing low-cost sequences
on such n-type substrates. Highlights include improved energy conversion effi ciency, opencircuit
voltage and levels of surface passivation. Another highlight was the rapid development
of applications of photoluminescence techniques for device and material characterisation, as
a result of strong collaboration with the Centre’s silicon photonics group.
Technology Commercialisation
2005 was another exciting year for
the photovoltaic industry with global
production increasing 45%, building
on the record 67% growth during
2004. Annual sales of BP Solar
of the Centre’s fi rst generation,
buried contact technology again
exceeded the $100 million mark,
with the company announcing a
new, higher performance module
using this technology during 2005.
The increasing international profi le
of photovoltaics has resulted in an
increasingly high visibility on fi nancial
markets. Suntech Power, a largely
Australia-owned company operating
in China and a partner in the Centre
partner, commenced trading on
the New York Stock Exchange in
December, in what became the
largest technology-based initial public
offering of 2005, internationally.
The Centre has been working with
the company to bring high-effi ciency,
fi rst generation cell concepts into
production, including those based
on semiconductor fi nger technology
(below). A second Centre member,
CSG Solar, successfully took Centre
“second-generation” crystallinesilicon-on-glass
technology a
major step closer to large scale
production, with the competition
of the fi rst manufacturing plant in
Germany. The fi rst product is due on
the market in 2006, with production
capacity also expected to approach
the $100 million/year mark by the
end of the year.
Former student, Zhengrong Shi, rings the bell to open the NYSE after the
Suntech IPO (Centre directors Stuart Wenham (right) and Martin Green
(left) are in the background next to the President of the NYSE, Catherine
Kinney and CEO John Thain, respectively)
3

New Semiconductor Finger Technology
The new semiconductor fi nger technology developed jointly between UNSW and Suntech-
Power for screen-printed solar cells has been successfully implemented at the pilot production
level using the same materials and equipment as for standard screen-printed solar cells. The
10% performance gain is achieved without any increase in cell manufacturing cost, with the
new jointly owned technology expected to be in large scale production in 2006. Based on
pilot production experience, cell effi ciencies for the new technology in large scale production
are expected to average about 18%. A particular strength of this new solar cell design is the
ability to achieve extremely good spectral response, particularly for short wavelengths of light,
compared to most commercial cell technologies. This new cell design appears to overcome
the fundamental weaknesses of conventional screen-printed solar cells associated with the
heavily diffused emitter, but while retaining the many benefi ts of screen-printing technology.
This work won “The Best Oral Presentation” award for its area at the International PVSEC-15
Conference in Shanghai in October 2005 and has been selected as an invited paper as part
of the plenary session at the World Conference in Hawaii in May 2006.
Image of a screen-printed
metal line (foreground) in
excellent contact with a
heavily phosphorus-diffused
laser groove running
perpendicular to the metal
line. The region covered with
tiny pyramids is lightly diffused
with phophorus.
Thin-Film Silicon
4
Good progress has been made with the Thin-Film Group’s solar cell technologies EVA, ALICIA
and ALICE. A milestone achieved in 2005 was the realisation of the Group’s fi rst poly-Si
thin-fi lm solar cells on glass with voltages of over 500 mV. The best cell has a voltage of
517 mV obtained with the EVA structure which, to our knowledge, is a new world record
for homojunction poly-Si thin-fi lm solar cells on glass. Another important milestone was
the achievement of an internal quantum effi ciency of over 70%, obtained using the ALICIA
structure. These advances benefi ted signifi cantly from an improved hydrogenator that became
available in 2005 in the Centre’s research facility at Bay Street, Botany. Good progress was
also made with optimising and upscaling of the Group’s AIT glass texturing method and its
AIC seed layer process. As a result of this work, AIT-textured glass sheets and AIC-seeded
glass sheets with a size of 10 x 10 cm 2 are now routinely produced by the Group. Progress
with cell metallisation has improved the effi ciency of ALICIA cells to 3%. The Group was again
active in generating intellectual property, with the fi ling of a provisional Australian patent on
an interdigitated thin-fi lm cell metallisation method (“SAMPL”) and the entering of the national
phase for two recent PCT patent applications. Furthermore, the Group has published one
book chapter, eleven journal papers, and twenty one conference papers. Fifteen of these
papers were presented as talks at international conferences, including four invited talks by
the Group’s leader, Armin Aberle. The Group’s thin-fi lm solar cell technologies are attracting
a signifi cant amount of interest from the solar industry and the venture capital sector. In
response to this interest, the Group has created a commercialisation roadmap involving a
business plan proposal and layouts of a pilot line and a fi rst factory. UNSW’s commercial arm,
NewSouth Innovations Ltd, has entered negotiations with several interested parties.

PhD student Daniel Inns inspecting EVA poly-
Si thin-fi lm solar cell material fabricated on a
planar sheet of glass.
Silicon Quantum Dots in Silicon Nitride
The same technique previously used to make silicon quantum dots (QDs) by deposition of
thin Si rich layers (4nm) interspersed with thin silicon dielectric layers, used in silicon oxide
based materials, has been successfully applied to silicon nitride based materials. The lower
Si 3 N 4 barrier height should give a higher interdot probability for carrier transport, thus
resulting in a higher conductivity material for the same QD density. The concept will next be
applied to SiC with an even lower barrier height. Transfer to nitride is an important proof of
concept of the transferability of the technology to different material systems. Growth has
been accomplished both by the same reactive sputtering technique used for oxide and with
PECVD. On annealing, both these structures produce nanocrystals of Si limited in size by the
thickness of the Si rich layer – as demonstrated by the TEM images shown. Electron density
contrast for the TEM images of QDs in the nitride is lower than in oxide but the crystal planes
in the Si nanocrystals can still be seen. Characterisation of nanostructures is inherently
diffi cult because of the small sizes involved. Hence in 2005 there has been a signifi cant effort
to improve both the resolution and breadth of nanoscale characterisation techniques. This
has resulted in successful XRD of Si nanostructures which nicely complements TEM data. It
both corroborates the presence of Si nanocrystals and highlights some subtle differences in
lattice parameter which are useful in identifying artifacts in both TEM and XRD.
(a)
120kV TEM image of PECVD deposited (a) Si quantum dots in 10 bi-layers of a silicon-rich-
SiNx /SiNx superlattice and (b) 300kV High Resolution TEM image showing lattice planes in
Si nanocrystals.
(b)
5

Stanford University GCEP Grant
The Global Climate and Energy Project (GCEP) managed by Stanford University and fi nanced
by an industrial consortium consisting of Exxon Mobil, General Electric, Sclumberger and
Toyota is a major US$225 million, 10-year effort to seek new solutions to one of the major
energy challenges of this century, supplying energy to meet and needs of a growing world
population in a way that protects the environment. Promising areas for support have been
identifi ed as photovoltaics, hydrogen, biomass, advanced combustion and CO 2 capture,
separation and storage. After requesting proposals in these fi elds from selected institutions,
these underwent review by two independent technology and impact review panels, as well as
by a technical committee formed by the sponsors. The Centre responded to a request for
a “game-changing” proposal in photovoltaics by outlining its activities in the nanostructured
silicon tandem cell area (Section 4.5) and requesting support to accelerate the development
of this approach. This was one of three successful projects chosen in the photovoltaics
fi eld, and the only one awarded to a non-US group. Funding of US$2.4 million over 3 years
has been allocated. Subsequently, Centre Executive Research Director, Martin Green, was
selected as Team Leader for the overall GCEP Photovoltaic Program with responsibilities for
identifying areas under-represented in the GCEP portfolio and in selecting technical experts
for the evaluation of projects solicited in these areas.
Other Awards
Other highlights in 2005 include Mark Griffi n’s Faculty of Engineering Technical Staff Excellence
Award, Axel Straub’s Graduate Student Award at the European Materials Research Society
(E MRS) 2005 Spring Meeting in France, Roland Utama’s best fi nal-year thesis poster award
and best overall thesis mark in Photovoltaic and Renewable Energy Engineering at UNSW in
2005, and the award of a A$156,000 research infrastructure grant by UNSW to Patrick
Campbell et al for a new multi-target reactive sputtering machine. Research student, Supriya
Pillai, was the recipient of fi rst prize in the Faculty of Engineering’s Inaugural Dean’s Awards for
Postgraduate Research, with her work selected as the best overall from about 70 applicants
at a poster presentation at the Scientia in December. Papers presented by research student
Chu-Wei Jiang, Deputy-Director Jianhua Zhao and Director Stuart Wenham all won best
paper in their fi eld awards at the 15th International Photovoltaic Science and Engineering
Conference in Shanghai in October, with Research Director Martin Green presented with a
special award from Jiangsu province after his keynote presentation during the conference
opening ceremony.
Mark Griffi n’s winner of the Faculty of Engineering Technical
Staff Excellence
6

Education
A major highlight of the educational activities has been the Centre’s ability to attract
outstanding high school graduates to join us. The spread of their University Admissions Index
values is skewed to the top end, while it would more commonly be expected to cluster towards
the lower cutoff value.
70
UAI Distribution 2000 - 2005
# Students
60
50
40
30
20
10
3656
3655
3657
3642
0
Below 80 80-84.99 85-89.99 90-94.99 95-100
University Admission Index
Other highlights include a new Co-Op Scholarship for 2006 the Bachelor of Engineering in
Photovoltaics and Solar Energy program, sponsored by Suntech Power Co. Ltd. of Wuxi,
China. This complements the two existing scholarships, sponsored by BP Solar and CSG Solar.
One of our high achieving undergraduate scholars, Nicole Kuepper, received an Australian
fellowship as part of the Goldman Sachs Global Leaders Program. A new edition of the
Centre’s popular text, Applied Photovoltaics, was completed in 2005 and printed in January
2006. This book is destined for rapid translation to Chinese to support staff training for the
booming industry in China. The Centre gained effective access in 2005 to a dedicated rooftop
area for experimental activities in our education programs. Huge effort was expended by
Centre teaching staff during 2006 to facilitate the introduction in 2006 of a new fl exible fi rst
year program throughout the Faculty of Engineering and the associated development of a
Faculty-wide fi rst year Engineering Design and Innovation course, as well as a new admissions
scheme for local students.
7

ARC Centre Review
The Centre was reviewed by an ARC Review Panel on 3 November, 2005 with very
positive outcomes. As well as recommending on-going funding of the Centre, the
Review Panel’s comments included:
“The Review Panel is impressed with the success of the ARC Centre of Excellence for
Advanced Silicon Photovoltaics and Photonics and believes that since its inception in
2003 the Centre has displayed a high level of achievement against all performance
criteria….”;
“The Centre is conducting world leading research in each of the four major areas with
an array of corresponding performance records, the latest world record being in the area
of n-type silicon solar cells, placing it at the forefront internationally”;
“The Review Panel particularly noted that the Centre has proved to be highly innovative
and very successful at commercialisation”;
“The Centre is particularly strong at developing collaborations with industry and
undertaking commercially significant research. Several of its technologies having
been either commercialised or are approaching large scale manufacturing in the near
future”;
“The Review Panel found the Centre to be highly organised and fully functional. The
Centre has successfully attracted high-quality staff including four Deputy Directors from
overseas”;
“Review Panel discussions with Centre postdoctoral fellows and students revealed
the Centre to be a highly inclusive, supportive and open environment. Students felt
encouraged and well supported in regard to equipment use and training. Students valued
the Centre’s opportunities for industry and research experience as well as participation
in international conferences”;
“The Review Panel considered the Centre to be performing very well in meeting its
performance targets in the area of international, national and regional links and
networks”;
“The Review Panel was very impressed with the level of support the Centre has attracted
from Collaborating Organisations”;
“The Review Panel concluded that the ARC Centre for Advanced Silicon Photovoltaics and
Photonics has performed extremely well against all Key Result Areas and Performance
measures”.
8

STAFF LIST
Director
Stuart Ross Wenham, BE BSc PhD UNSW, FTS, SMIEEE, FIEAust
(Scientia Professor)
Executive Research Director
Martin Andrew Green, BE MEngSc Qld, PhD McMaster, FAA, FTS, FIEEE
(Scientia Professor and Federation Fellow)
Deputy Directors
Armin G. Aberle, BSc MSc PhD Freiburg, Dr habil Hannover, SMIEEE, MDPG
Gavin Conibeer, BSc MSc London, PhD Southampton
Jeffrey E. Cotter, BEE MSc PhD Delaware
Jianhua Zhao, BE ME Nanjing I.T., PhD UNSW
Business & Technology Manager
Mark D. Silver, BE UNSW, GMQ AGSM
Undergraduate Co-ordinator
Jeffrey E. Cotter, BEE MSc PhD Delaware
Postgraduate Co-ordinator
Alistair B. Sproul, BSc PhD UNSW
Associate Professors
Armin G. Aberle, BSc MSc PhD Freiburg, Dr habil Hannover, SMIEEE, MDPG
Thorsten Trupke, PhD Karlsruhe
Senior Lecturers
Richard Corkish, BEng (Com) RMIT, PhD UNSW
Jeffrey E. Cotter, BEE MSc PhD Delaware
Alistair B. Sproul, BSc Sydney, PhD UNSW
Geoffrey J. Stapleton, BE UNSW
Muriel Watt, BSc N.E., PhD Murdoch
Senior Fellow
Jianhua Zhao, BE ME Nanjing I.T., PhD UNSW
Research Fellows
Robert Bardos, BSc (Hons) PhD Melbourne
Patrick Campbell, BSc BE PhD UNSW
Jiun-Hua “Allen” Guo, BSc MSc Nat.Taiwan U, PhD UNSW
Aihua Wang, BE Nanjing IT, PhD UNSW
Per Widenborg, BSc MSc Stockholm, PhD UNSW
Post-Doctoral Fellows
Gavin Conibeer, BSc MSc London, PhD Southampton
Anita W.Y. Ho, BE PhD UNSW
Dirk König, Dipl. Ing. (EE) Dr. rer. nat. (Ph) Chemnitz
Kuo-Lung Lin, BE Tatung, MSc Liverpool
Bryce Richards, BSc VUW, MEngSc PhD UNSW (until March 2005)
Dengyuan Song, BE ME Hebei, PhD UNSW
9

Adjunct Fellows
Kylie Catchpole, BSc PhD ANU
Didier Debuf, BE ME PhD UNSW
Visiting Professors/Fellows
Roman Horacio Buitrago (UNL Santa Fe, Argentina)
Rulong Chen (Suntech, China)
Jean-François Guillemoles, PhD, Dr. Habil P&M Curie, Paris (IRDEP, Paris)
Hans-Richard Karl Leiner (University College Konstanz, Germany)
Hua Li (Suntech, China)
Peter Würfel, Dipl. Physics PhD Karlsruhe (Karlsruhe University)
Research Associates
Peter Cousins BE PhD UNSW (until January 2005)
Professional Officers
Malcolm Abbott, BE UNSW
Ximing Dai, BSc Zhejiang, PhD UNSW
Yidan Huang, BSc Anhui
Tom Puzzer, BSc PhD UNSW
Bernhard Vogl, BE Regensburg
Guangchun Zhang, BE ME Shandong
Research Assistants
Frederick Bamberg
Wan Lam Florence Chen
Matt Edwards
Peter Klement
Mathieu Larose
Esther Lee
Ly Mai
Shervin Motahar
Edwin Pink
Giuseppe Scardera
Adriana Segovia
Budi Tjahjono
Stefan Vetter
Vincent Vogt
Juergen Weber
Guoxiao Yao
Taste of Research Summer Scholars
Sin Von Chan
Cuong Dang
Alexander Fattal
Brett Hallam
Phillip Hamer
James Rudd
Samantha Wong
Yicheng “Sherman” Zhou
10

Technical Support Staff
Gordon Bates, BA(IndDes) UTS
Bruce Beilby, BSc Monash, PhD UNSW
Kathryn Fisher, BE UNSW
Jamie Green, BE UNSW
Mark Griffi n, BE UNSW
Kian Fong Chin, BE QUT, MEngSc QUT, MEngSc UNSW
Robert Largent, AS USA
Timothy Seary, InstrTradeAdvCertIndElectrElecTrade TAFE
Nicholas Shaw, BE UNSW , PhD UNSW
Jules Z.S. Yang, BSc Eastern China
Alan Yee, BE UTS
Casual Teaching Staff
Anna Bruce, BE UNSW
Robert Passey, BSc UNSW, BAppSc Murdoch, MSc Murdoch, PhD UNSW
Casual Staff
Anja Aberle
Daniel Ball
Roman Balla
Andrew Barson
Jonathan Bocking
Nino Borojevic
Damian Camporeale
Susan Conyers
Joel Courtney
Dawei Di
Brett Hallam
Sue Anne Lit Hunter
Zoe Jennings
Anahita Karpour
Daniel Kong
Nicole Kuepper
Daniel Lagos
Tsu-Tsung Andrew Li
Daniel Mansfi eld
Gavin Pereira
James Rudd
Erdinc Saribatir
Nancy Sharopeam
Adeline Sugianto
Fennalia Tan
Owen The
Belinda Thorne
Roland Utama
Dean Utian
11

Student Administration Manager
Trichelle Burns, BCom UNSW
Financial Officer
Julie Kwan
Computer System Officer
Lawrence Soria, AssocDipCompAppl W’gong
Administrative Staff
Lisa Cahill
Danny Lin Chen, BSc UNSW
Jenny Hansen
Jill Lewis
Ana Naumoska
PhD Students
Malcolm Abbott, BE UNSW
Anna Bruce, BE UNSW
Wan-Lam Florence Chen, BE UNSW
Young Hyun Cho, BSc Hanyang U, MEngSc UNSW
Matthew Edwards, BE UNSW
Thipwan Fangsuwannarak, BEng V’kul, MEng C’korn
Ziv Hameiri BSc BGU
Daniel Inns, BE UNSW
Chu-Wei “Scott” Jiang, BSEE Nat.Taiwan U, MEngSc Qld
Oliver Kunz
Ly Mai, BE UNSW
Supriya Pillai, BTech M.G.U
Giuseppe Scardera, BSc McGill , BASc Ottawa
Avi Shalav, BSc MSc Massey
Dengyuan Song, BSc MSc Hebei
Geoffrey Stapleton, BE UNSW
Axel Straub, BE ME Ulm, PhD UNSW (until July 2005)
Mason Terry, BSEET Oregon IT, MSEE Washington
Budi Tjahjono, BE UNSW
Attachai Ueranantasun, BE KMUTT, T’land, MEngSc UNSW
Timothy Walsh, BSc Melbourne, (Hons) ANU
Guoxiao “James” Yao, BE UT Zhegiang, MS Sweden
Masters Students
Kathryn Fisher, BE UNSW
Bijaya Paudyal
Lei “Adrian” Shi
Bernhard Vogl, BE Regensburg
Juergen Weber
12

4.1 INTRODUCTION TO RESEARCH
Photovoltaics, the direct conversion of sunlight to electricity using solar cells, is recognised
as one of the most promising options for a sustainable energy future. The ARC Photovoltaics
Centre of Excellence commenced in mid-2003, drawing together previous disparate strands
of work, supported under a variety of programs, into a coherent whole addressing the key
challenges facing photovoltaics, as well as “spin-off” applications in microelectronics and
optoelectronics.
The Centre’s photovoltaics research is divided into three interlinked strands addressing nearterm,
medium-term and long-term needs, respectively. The present photovoltaic market is
dominated by “fi rst-generation” product based on silicon wafers, either single-crystalline as in
microelectronics, or a lower-grade multicrystalline wafer (Fig. 4.1.1). This market dominance
is likely to continue for at least the next decade. First-generation production volume is growing
rapidly, with the technological emphasis upon streamlining manufacturing to reduce costs
while, at the same time, improving the energy conversion effi ciency of the product. Other key
issues involve reducing the manufacturing spread on multicrystalline wafer lines caused by
variability in wafer quality (typically 20% spread in cell output) and elimination of the effects of
boron-oxygen defects in both types of wafers. These defects become active under illumination
and reduce the performance of most commercial modules by about 3%. They also constrain
the specifi cation of the starting silicon wafer, restricting cell design possibilities. Also important
is the reduction of the thickness of the starting silicon wafer without losing performance, to
save on material use, and the development of low-cost techniques for reducing refl ection
from multicrystalline cells.
Figure 4.1.1:
“First-generation” waferbased
technology (BP
Solar Saturn Module,
the photovoltaic product
manufactured in the highest
volume by BP in Europe,
using UNSW buried-contact
technology).
The Centre’s fi rst-generation research is focussed on these key issues. Major emphasis is
upon the “buried-contact” solar cell, originally developed by Centre researchers, the fi rst of
the modern high-effi ciency cell technologies to be successfully commercialised (Fig. 4.1.1).
Centre research seeks improvements to these devices to increase effi ciency, particularly
for devices fabricated on thin wafers. Of key interest is the development of buried-contact
sequences for substrates doped with phosphorus, rather than boron, to avoid the boronoxygen
defect problem previously noted.
Wafers are expensive and need quite elaborate and expensive encapsulation, since they
are brittle and also thermally mismatched to the glass coversheet, making fi rst-generation
technology inherently material-intensive. To avoid the associated cost penalties, several
companies worldwide are commercialising “second-generation” thin-fi lm cell technology
based on depositing thin layers of the photoactive material onto supporting substrates or
superstrates, usually sheets of glass (Fig. 4.1.2). Although materials other than silicon are
of interest for these fi lms, silicon avoids problems that can arise with these more complex
compounds due to stability, manufacturability, moisture sensitivity, toxicity and resource
availability issues. CSG Solar, a partner in the Centre, has commercialised an approach
pioneered by Centre researchers that is unique in that it is based on the use of the same high
quality silicon used for fi rst-generation production, but deposited as a thin layer onto glass.
13

Figure 4.1.2:
Example of “second-generation”
thin-fi lm technology (module
fabricated on CSG Solar’s pilotline
in Sydney, based on thin-fi lms
of polycrystalline silicon deposited
onto glass, again UNSWpioneered
technology).
As well as its collaborative activities with CSG Solar, the Centre currently maintains a largely
independent program addressing alternative solutions to those adopted by CSG Solar for
producing high-performance “silicon-on-glass” solar cells. The main emphasis of this program
is on improving the quality of the silicon fi lms by using thin crystallographic templates (formed
by aluminium induced crystallisation) and on the development of lower-cost deposition
approaches (evaporation rather than PECVD)
At the present time, second-generation thin-fi lms are entering the market in increasing
quantities. The successful commercialisation of thin-fi lm product will lead to a completely
different manufacturing cost structure. However, costs again are expected increasingly to
become dominated by material cost as production increases, for example, by the cost of the
glass sheet on which the cells are deposited.
More power from a given investment in material is possible by increasing energy-conversion
effi ciency. This leads to the notion of a third-generation of solar cell distinguished by the fact
that it is both high-effi ciency and thin-fi lm. To illustrate the cost leverage provided by effi ciency,
Fig. 4.1.3 shows the relative cost structures of the three generations being studied by the
Centre. This fi gure plots effi ciency against manufacturing cost, expressed in US$/square
metre. First-generation technology has relatively high production cost per unit area and
moderate likely effi ciencies (10-20%). The dotted lines in Fig. 4.1.3 show the corresponding
cost/watt, the market metric. Values as low as US$1/watt may be feasible by increasing the
effi ciency while reducing manufacturing cost, but this is the likely limit of the fi rst-generation
approach (present manufacturing costs for large manufacturers are as low as US$2-3/
watt).
Second-generation thin-fi lm technology has a different cost structure as evident from this
fi gure. Production costs per unit area are a lot lower, since silicon wafers are a lot more
expensive than glass sheet. However, likely energy-conversion effi ciencies are lower (5-15%).
100
US$0.10/W
US$0.20/W
US$0.50/W
Efficiency, %
80
60
40
20
Thermodynamic
Limit
US$1.00/W
Present limit
US$3.50/W
Figure 4.1.3: Effi ciency
and cost projections for
fi rst-, second- and thirdgeneration
photovoltaic
technology (wafers, thinfi
lms and advanced thinfi
lms, respectively).
0 100 200 300 400 500
Cost, US$/m2
14

Overall, this trade-off produces costs/watt estimated as about 2 to 3 times lower than
those of the wafer product, in large production volumes.
The third-generation is specifi ed as a thin-fi lm technology, which therefore has manufacturing
costs similar to second-generation, but is based on operating principles that do not constrain
effi ciency to the same limits as conventional cells (31% for non-concentrated sunlight for
these). Unconstrained thermodynamic limits for solar conversion are much higher (74% for
non-concentrated light), giving an indication of the potential for improvement. If a reasonable
fraction of this potential can be realised, Fig. 4.1.3 suggests that third-generation costs could
be lower than second-generation by another factor of 2 to 3.
Of the third-generation options surveyed by Centre researchers, “all-silicon” tandem cells
based on bandgap-engineering using nanostructures was selected as the most promising for
implementation in the Centre’s timescale (Fig. 4.1.4). This involves the engineering of a new
class of mixed-phase semiconductor material based on partly-ordered silicon quantum-dots in
an insulating amorphous matrix. Photon up- and down-conversion as a way of “supercharging”
the performance of relatively standard cells forms a second line of research. A third is the
investigation of schemes for implementing hot-carrier cells.
Figure 4.1.4: Conceptual design of an all-silicon
tandem cell based on Si-SiO 2 (or Si-Si 3 N 4 or Si-SiC)
quantum dot superlattices. Two solar cells of different
bandgap controlled by quantum dot size are stacked
on top of a third cell made from bulk silicon.
15

The fourth “spin-off” Centre strand of silicon photonics draws upon elements of all three of
the photovoltaic strands. The aim is to develop silicon light-emitting-diodes (LEDs) that can be
integrated into silicon integrated circuits, with their output capable of modulation at gigahertz
frequencies (Fig. 4.1.5). This strand is closely related to the high-effi ciency cell work in our fi rstgeneration
strand of research, since the associated Centre researchers have demonstrated
the highest-performing LEDs based on bulk silicon by a very clear margin, internationally. The
work also draws upon the expertise in the second-generation strand since thin fi lms of silicon
are integral to the silicon-on-insulator (SOI) wafers used in this work. “Light-trapping” is also
very relevant to both strands. The common interest in quantum-confi nement in silicon also
provides strong links to the third-generation strand. Another objective being pursued in the
silicon photonic strand is the demonstration of the fi rst silicon laser. This is the “holy grail” of
the silicon photonics fi eld.
Figure 4.1.5:
One of the concepts for an
integrated silicon light-emitter/
modulator presently being
investigated experimentally.
Modulation is sought using the
quantum-confi ned Stark effect
in thin silicon-on-insulator (SOI)
layers.
16

4.2 FACULTIES AND INFRASTRUCTURE
The ARC Centre of Excellence for Advanced Silicon Photovoltaics and Photonics is located at
the Kensington campus of the University of New South Wales, about 6 km from the heart of
Sydney and close to its world famous beaches including Bondi, Coogee and Maroubra (Fig.
4.2.1).
Sydney CBD
Kensington
University of
New South Wales
Coogee
Bondi
Sydney Airport
Botany
CSG Solar Pty Ltd
Botany Laboratory
Maroubra
Figure 4.2.1: Centre of
Excellence location in
Sydney.
Organisationally, the Centre of Excellence is located within the Centre for Photovoltaic
Engineering within the Faculty of Engineering. The Centre of Excellence has a large range of
laboratory facilities (Fig. 4.2.2). These include the Bulk Silicon Research Laboratories, the
Device Characterisation Laboratory, the Optoelectronic Research Laboratory, the Thin-Film
Cell Laboratory, the Industry Collaborative Laboratory and Inkjet Processing Laboratory. Off
campus the Centre has a Thin-Film Cleanroom facility at Botany, 5km south-west of the main
campus. Another important resource is the Semiconductor Nanofabrication Facility jointly
operated by the Faculty of Science and the Faculty of Engineering.
A new offi ce accommodation area on the fourth fl oor of the Electrical Engineering building has
consolidated 12 offi ces for up to 19 academic/senior researchers around 28 open plan desk
spaces with supporting meeting rooms and tea room. Whilst not only providing fi rst class
accommodation, the consolidation provides space for personnel previously accommodated in
an adjacent building and permits the conversion of LG offi ce space to a new laser laboratory
for the Optoelectronic Research Laboratory.
Additional equipment commonly used for solar cell work is also available on the University
campus. Included in this category are TEM/SEM electron and focussed ion beam (FIB)
microscopes, X-ray diffraction, Raman spectroscopy, AFM and surface analysis equipment.
TEM, ellipsometry and high-precision I-V equipment are also regularly accessed at Sydney
University.
17

4
3
2
1
G
During 2005 the development and acquisition of laboratory equipment and infrastructure
continued with specifi c details about signifi cant additions found under the laboratory headings
which follow.
4
3
2
1
G
4
3
2
1
Office ARC Centre of Excellence for Advanced
Silicon Photovoltaics and Photonics
Buried Contact Cell Lab
High Efficiency Call Lab
Operations Workshop
Office Accommodation
Student Computer Lab
G
Industry Collaboation Lab.
Thin-Film Cell Lab
Offices for School of Photovoltaic and
Renewable Energy Engineering
InkJet Processing Laboratory
Student Project/Seminar Room
Centre for Photovoltaic Engineering Office
Device Characterisation and Laser Lab
Figure 4.2.2: Layout of laboratories and other facilities within the Electrical Engineering
building, Kensington.
The Centre of Excellence has two computer networks. One is used for research and general
administrative purposes and the other by students enrolled in the Undergraduate Degree
Courses in Photovoltaics and Renewable Energy. In 2005 the Research and Administrative
network grew nearly 30% to consist of 3 servers, 3 Intranet servers, two Internet webservers
and over 90 workstations. An additional 16 computers are dedicated to the
computer control of laboratory and other equipment. The computer resources are used
for modelling/simulations, equipment control, general administrative purposes, document
control, laboratory support, Internet access, and maintaining the Centre’s presence on the
Internet. Each postgraduate research student is allocated a dedicated personal computer in
addition to access to existing shared computers.
The Centre also has a computer controlled SCADA system and PLC network for equipment
control and monitoring of the research laboratories and related infrastructure. The Centre is
soon to install a Linux (Beowulf) cluster with an estimated computational power of about 100
Gigafl ops for Density-Functional-Hartree-Fock and molecular dynamical computations.
The Student Computer network comprises of two computer laboratories of total 83 m2 with
4 servers, a UNSW custom CSE computer based router and 26 workstations. Students
enrolled in the Undergraduate Degree Courses use these computers for computer-related
coursework and Internet access. There is also an Internet capable web-server that gathers
and displays data collected from solar arrays on the roof of the building. These data can be
viewed using a web browser and can be made available for Internet access.
The Laboratory Development and Operations Team develops and maintains core Centre and
laboratory facilities. During 2005, the team, under the leadership of Mark Silver, comprised
an additional 5 equivalent full-time and 11 casual employees, including: electrical and industrial
design engineers, a computer/network manager, electronic and computer technicians, and
administrative staff.
18

Bulk Silicon Research Laboratories
The Centre houses the largest and most sophisticated bulk silicon solar cell research facility
in Australia, incorporating both the High Effi ciency/LED and Buried Contact Cell Laboratories.
Total laboratory processing space of over 500 m 2 is located in the Electrical Engineering
Building and is serviced with fi ltered and conditioned air, appropriate cooling water, processing
gas, de-ionized water supply, chemical fume cupboards and local exhausts. There is an
additional 540 m 2 area immediately adjacent to the laboratories for the accommodation of
staff, research students, school offi ce and laboratory support facilities. Off site, areas totalling
200 m 2 are used for the storage of chemicals and equipment spare parts.
The laboratories are furnished with a range of processing and characterisation equipment
including 26 diffusion furnaces, 5 vacuum evaporation deposition systems, a laser-scribing
machine, rapid thermal annealer, four-point sheet-resistivity probe, quartz tube washer, silver,
nickel and copper plating units, visible wavelength microscopes, 3 wafer mask aligners, spinon
diffusion system, automated photoresist dual-track coater, photoresist spinner, electron
beam deposition system, TiO 2 spray deposition, belt furnace, manual screen printer and a
laboratory system control and data acquisition monitoring system.
Figure 4.2.3: CNC Laser Scribe Tool
The laser scribe tool, shown in Figure 4.2.3, has a 20 watt Nd:YAG laser for infrared operation
(1064 nm) and an optional frequency doubler for green operation (532 nm). The work stage
is CNC controlled allowing 1 micron positional accuracy and table speeds approaching 25
cm/second across an area of 15 cm by 15 cm. The tool is used primarily for Buried Contact
solar cell fabrication, cutting 35-micron wide laser grooves as deep as 100 microns into
silicon wafers. It can also be used to cut other suitable materials, such as stainless steel.
Device Characterisation Laboratory
This laboratory is located on the lower ground fl oor of the Electrical Engineering Building.
Associated with it is the Optoelectronic Research Laboratory, reception area, seminar room,
offi ces for Centre staff interacting with the public and industry, including the Business &
Technology Manager, External Relations Manager and Design Assistance Division Manager
and computer workstations for the device modelling activities of the Centre.
The Device Characterisation Laboratory houses characterisation equipment including “Dark
Star”, the Centre’s station for temperature controlled dark current-voltage measurements,
the Centre’s Fourier-transform infrared spectroscopy system (FTIR), admittance spectroscopy
19

system, microwave carrier lifetime system, ellipsometer, Sinton photoconductance lifetime
equipment, wafer probing station for SOI LED work, open circuit voltage versus illumination
measurement system (Suns-Voc), infrared microscope and equipment for spectral response
and related optical measurements.
In 2005 a new Fourier-transform infrared spectroscopy system (FTIR) was purchased for the
laboratory along with a new 4 point resistivity probing station. Planning is also underway to
provide additional effective workspace by removing the viewing wall partition and redesigning
the associated work bench area.
Optoelectronic Research Laboratory
This facility has two optical benches and several visible and near-infrared semiconductor
diode lasers along with other optical and electrical instrumentation. The facility is used for
photoluminescence and electroluminescence measurements in the visible and infrared
spectral range up to wavelengths of 2500nm, photoluminescence (PL) excitation spectroscopy,
luminescence experiments with simultaneous two-colour illumination, quasi steady state
photoluminescence lifetime measurements and Sinton lifetime testing with the conventional
fl ash-light replaced by a high-power light emitting diode array. An area separate from the
Device Characterisation Laboratory was necessary in order to meet stringent standards for
avoidance of laser eye and skin exposure for users and others. It shares cryogenic cooling
equipment with the Device Characterisation Laboratory.
In 2005 the world’s fi rst photoluminescence imaging system was installed along with a
silicon CCD camera (for sensitive PL measurements) and a second spectroscopic PL system.
Demand for additional laboratory space for the Optoelectronic Research Laboratory has
necessitated the conversion of adjacent lower ground fl oor offi ce space into a future laser
laboratory to accommodate experiments on an additional 4 optical benches.
Figure 4.2.4: Optical characterisation bench.
Thin-Film Cell Laboratory
This 40 m2 laboratory is equipped with a range of equipment for thin-fi lm deposition and
patterning, including a plasma-enhanced chemical vapour deposition (PECVD) system, a
sputtering system, a reactive ion etcher (RIE), a resistively heated vacuum evaporator, and
an optical microscope with digital image acquisition system. Also used by the laboratory is an
electron-beam vacuum evaporator for silicon which is physically located within the Bulk Silicon
Research Laboratory. This Si evaporator is also equipped with an ionizer unit and a sample
heater, enabling fast-rate Si homoepitaxy at temperatures of about 500-600 °C by means of
ion-assisted deposition (IAD). Other equipment of use in thin-fi lm projects is located within the
Semiconductor Nanofabrication Facility.
20

The PECVD system, shown in Fig.4.2.5, has a 40x20 cm 2 process platen and can handle
large-area silicon wafers as well as smaller pieces. Two types of plasma excitation (remote
microwave and direct RF) are available. The machine is used for the low-temperature
deposition of thin dielectric fi lms (silicon nitride, silicon dioxide) and of amorphous silicon. The
dual-cylinder, remote microwave plasma source produces excellent-quality silicon nitride and
silicon dioxide fi lms, with precise control over the stoichiometry at temperatures up to 500°C.
Amorphous and microcrystalline silicon fi lms can also be deposited in the system.
In 2005 a plasma etching machine capable of processing sample areas larger than the
existing RIE was added. The sputtering machine was upgraded with mass fl ow controllers to
improve process repeatability.
Figure 4.2.5: Remote plasma PECVD machine.
Industry Collaborative Laboratory
This 120 m 2 laboratory houses equipment needed for many of the industry-collaborative
research activities in the Buried-Contact Solar Cell group. The laboratory was refurbished
in 1999 and several new pieces of infrastructure have been acquired or constructed since,
including: a belt furnace; a state of the art laser micromachining tool; a new PECVD deposition
system (located in the adjacent thin fi lm solar cell laboratory); and a TiO2 spray deposition
station; a high temperature semiconductor muffl e furnace and manual screen printer. In 2005
a fully automatic production scale screen printer was commissioned in the laboratory.
Inkjet Processing Development Lab
This laboratory, new for 2005, houses the Centre’s
inkjet printing development system. The laboratory
is used to develop solar processing “inks” (chemical
solutions) and for printing them onto a solar wafer
under computer control. The aim is to develop low cost
processing techniques for creating fi ne structures in
solar cells. It is anticipated that the inkjet printing is
capable of replacing processes such as laser scribing
and photolithography for forming fi ne patterns for
contacting but at a cost of at least 10 times cheaper.
Figure 4.2.6: Inkjet development system
21

Semiconductor Nanofabrication Facility
The Centre also owns equipment within, and has access to, the Semiconductor Nanofabrication
Facility (SNF) at the University. This is a joint facility shared by the Faculties of Science and
Engineering and houses a microelectronics laboratory and a nanofabrication laboratory
for e beam lithography. A collaborative project continues with the SNF to e-beam pattern
a photonic crystal on the surface of the Centre’s SOI LED structures for enhanced optical
emission. The SNF provides an Australian capability for the fabrication of advanced nanoscale
semiconductor devices and their integration with microelectronics. SNF research projects
form an integrated effort to fabricate innovative semiconductor nanostructures using the
latest techniques of electron beam patterning and scanning probe manipulation. A major
applied objective of the SNF facility is the development of a prototype silicon nuclear spin
quantum computer.
Thin-Film CleanRoom facility in Bay Street, Botany
During 2003 and 2004 the Centre added a 120 m 2 cleanroom facility in Bay Street, Botany to
its infrastructure, greatly improving its experimental capabilities in the area of thin-fi lms. This
cleanroom is equipped with several fume cupboards, two tube furnaces, an electron-beam
vacuum evaporator, a thermal vacuum evaporator, a glass washing machine, a rapid thermal
processing (RTP) machine, and a 5-chamber cluster tool. The cluster tool presently features
four plasma-enhanced chemical vapour deposition (PECVD) chambers and one lamp-heated
vacuum annealing chamber. The PECVD chambers enable the low-temperature deposition of
dielectric fi lms (silicon oxide, silicon nitride, etc) and amorphous silicon fi lms (either n- or p-
doped or undoped). Furthermore, samples can be hydrogenated by PECVD using a hydrogen
plasma at substrate temperatures of up to 480°C. During 2004 the Centre purchased a
low-pressure chemical vapour deposition (LPCVD) system, an infrared NdYAG laser scriber
and a box furnace for sample annealing. The LPCVD system is capable of depositing doped
crystalline silicon on glass and with its additional remote plasma source is currently engaged
in hydrogenation work. The NdYAG laser is used for scribing silicon fi lms and other suitable
metal and dielectric materials. In 2005 a new state of the art sputtering machine was
ordered and plans are underway for the installation of an additional fume cupboard.
Figure 4.2.7: Bay St Clean Room Cluster Tool Controller.
22

Nancy Sharopean
Mark Silver
and
Nick Shaw
Per Widenborg and Anya Aberle
Jill Lewis
Anita Wing Yi Ho
Kian Chin
Lawrence Soria
Alan Yee
Jules Yang
Gordon Bates
23

4.3 FIRST GENERATION: WAFER-BASED PROJECTS
4.3.1 High Efficiency Cells
University Staff:
A/Prof. Jianhua Zhao (group leader)
Prof. Martin Green
Prof. Stuart Wenham
Research Fellows: Dr. Aihua Wang
Research Assistant: Guangchun Zhang
Technical Staff: Jules Yang
During 2005, a cell effi ciency equalling the world record for n-type silicon cells has been
demonstrated by a new rear emitter PERT cell structure, which was developed by the high
effi ciency group at the Centre. The previous record was set more than a decade ago by
Stanford University. This new cell structure is expected to produce further improvements
in cell effi ciency and, importantly, is also suitable for low cost CZ silicon substrates. This
research work is reported below.
4.3.1.1 Rear Emitter PERT Cell Structure on N-type Silicon Substrates
In 2004, a new rear-boron-emitter PERT (passivated emitter, rear totally-diffused) cell
structure on n-type silicon substrates was developed by the high effi ciency cell group in the
Centre. During the initial experiments, these devices demonstrated high cell effi ciencies
close to 22%, and very stable cell performance under one-sun illumination and after long
term storage in nitrogen. Figure 4.3.1.1 shows the structure of these n-type rear emitter
PERT (re-PERT) cells.
finger
“inverted” pyramids
Figure 4.3.1.1
Rear boron emitter PERT cell
structure on n-type silicon
substrates
double layer
antireflection
coating
n-silicon
rear contact
oxide
High effi ciency processing methods, similar to those used for PERL (passivated emitter, rear
locally-diffused) cells, are used for processing these n-type re-PERT cells. These processing
methods include lithographically defi ned regular inverted pyramids surface for excellent light
trapping, TCA thermal oxide growth and aluminium anneal for high quality surface passivation,
boron tribromide liquid source boron diffusion producing very low surface damage, lift-off metal
scheme combined with electro-chemical silver plating for minimum contact recombination
and very little metal shading and resistance loss, and double layer antirefl ection coatings to
further minimise the surface refl ection loss.
25

Since the rear emitter boron diffusion was over the entire rear surface, the rear emitter cells
have to be scribed into individual cells before measurement, in contrast to standard research
PERL cells which are often measured on the whole silicon wafers without scribing. Hence,
the performances of these scribed rear emitter cells are lower when compared to those unscribed
small-area research cells, due to the extra edge recombination loss and increased
cell area, which is non-optimal for the present silver plated metallisation method. By way
of comparison, the best scribed PERL cell on p-type substrates of the same 22 cm 2 area
demonstrated 23.7% effi ciency [J. Zhao et al, “20 000 PERL Silicon Cells for the ‘1996 World
Solar Challenge’ Solar Car Race”, Progress in Photovoltaics, Vol. 5, pp. 269, 1997], while the
best small 4 cm 2 unscribed cell had a signifi cantly higher effi ciency of 24.7%.
Small-area 4 cm 2 rear emitter cells were initially investigated. However, due to the relatively
larger edge scribing damage contributing to increased total recombination, these small cells
had relatively low Voc around 680 mV. Hence, the present research concentrated upon
large-area rear emitter cells of 22 cm 2 area in an effort to reduce the edge recombination
loss, resulting in high Voc of over 700 mV.
4.3.1.2 Calculated Device Performances with the
Device Simulation Program PC-1D
The device simulation program PC-1D was used to calculate and analyse the cell performance.
The cell Voc and the IQE (internal quantum effi ciency) were the main data to be fi tted in
these calculations. After comparing to the experimental device parameters, the bulk and the
surface recombination parameters were selected as following:
Bulk minority carrier lifetime:
1.1 ms
Front surface recombination velocity: 300 cm/s
Rear surface recombination velocity: 400 cm/s
The substrate resistivity was 0.9 Ω-cm. However, the substrate resistivity was found noncritical
for the calculated device performance if the recombination parameters were not
altered. However, normally the higher substrate resistivity is, the higher the minority carrier
lifetime. In this sense, the substrate resistivity may be very critical to the performance of
the fabricated devices, particularly for these thin cells. Figure 4.3.1.2 shows the calculated
variation of Jsc, Voc and cell effi ciency with the substrate thickness, simulated by PC-1D.
(a) (b) (c)
37.9
716
37.8
714
712
37.7
710
37.6
708
37.5
706
37.4
704
37.3
702
700
37.2
698
37.1
696
37
694
500
400 300 200 100
Cell Thickness, um
0
Jsc, mA/cm2
500
400 300 200 100
Cell Thickness, um
Figure 4.3.1.2: PC-1D simulated variation of (a) J sc , (b) Voc, and (c) cell effi ciency with the
substrate thickness. Reducing the substrate thickness from 400 µm to 200 µm is predicted
to signifi cantly increase all the three parameters.
0
Voc, mV
500
400 300 200 100
Cell Thickness, um
0
22.4
22.3
22.2
22.1
22
21.9
21.8
21.7
21.6
21.5
21.4
Efficiency, %
26

According to the calculated data in Figure 4.3.1.2, when the substrate thickness is reduced
from 400 µm to 200 µm, both Voc and Jsc are expected to increase signifi cantly, due to
the higher minority carrier density at the rear emitter and an increased spectral response.
However, when the substrate thickness is reduced to less than 200 µm, the quantity of silicon
material becomes insuffi cient to absorb all of the incident light, resulting in a reduced IQE
and current density. Hence, the effi ciency reaches a plateau at 200 µm thickness, while
the calculated Voc keeps increasing and the Jsc starts to reduce for thinner substrates. In
experimental devices, the cell Voc would not increase as quickly as the calculation suggested
with reducing substrate thickness, since the surface passivation treatment may become
more and more diffi cult to implement for extremely thin substrates.
4.3.1.3 Experimental Performance of N-type Rear Emitter PERT Cells
During 2005, experimental efforts were concentrated on reducing the thickness of these
n-type re-PERT cells. Different n-type substrate materials with higher resistivity were also
tested, even though the effect of this parameter can not be simulated clearly using PC-1D.
These experiments have demonstrated further signifi cant improvements in the performance
of these re-PERT cells.
In 2005, two successful batches of re-PERT cells, with structures as shown in Figure 4.3.1.1,
were fabricated using phosphorus doped n-type FZ substrates of 1.5 Ω-cm resistivity, 270-
µm and 170-µm thickness, supplied by Wafer World. These wafers had to be etched to
reduce their thickness and then mechanically polished in-house before cell processing, since
there is no suitable supplier of such thin, polished silicon substrates. Table 4.3.1.1 lists the
performance of these cells together with the very fi rst batch of the re-PERT cells, all measured
at Sandia National Laboratories under the global AM1.5 spectrum (100 mW/cm 2 ) at 25ºC.
Table 4.3.1.1. The performance of three batches of scribed 22 cm 2 large area n-type re-
PERT cells as measured at Sandia National Laboratories under 100 mW/cm 2 , AM1.5 global
spectrum at 25ºC (the fi rst cell, Wnrj1-1a, was fabricated during 2004).
Cell ID Thickness Jsc Voc FF Effi c.
(µm) (mA/cm 2 ) (mV) (%)
Wnrj1-1a 400 39.1 0.696 0.774 21.0
Wnrj4-3b 270 40.4 0.705 0.785 22.3
Wnrj7-1a 170 40.1 0.706 0.791 22.4
Wnrj7-2a 170 40.1 0.702 0.805 22.7
Wnrj7-2b 170 40.1 0.701 0.802 22.6
High carrier lifetime and thin substrates have helped to achieve effi cient carrier collection
to the cell rear emitter, and hence improved the short circuit current density and the cell
effi ciency. One of these rear emitter n-type cells demonstrated an excellent Voc of 706 mV,
which is as high as the best p-type PERL cells. The current density is about 1 mA/cm 2 below
the p-type PERL cells, since there is a slight loss during the long transportation path of carriers
to the rear emitter and an increased edge recombination loss. High effi ciencies obtained
with relatively simple processing requirements could make these cells highly attractive for
commercial use. Since high carrier lifetimes of over 5 ms have been demonstrated from
n-type SEH CZ substrates [Jianhua Zhao, et al, “High Effi ciency PERT Cells on N-Type Silicon
Substrates”, 29th IEEE Photovoltaic Specialist Conference, New Orleans, pp.218-221, 2002],
the n-type rear emitter cells fabricated using such inexpensive materials are expected to give
similar performances to these n-type FZ cells.
27

Figure 4.1.3.3 shows the measured I-V curve of the best rear emitter n-PERT cell, Wnrj7-2a,
which has demonstrated an effi ciency of 22.7%. This equals the best reported effi ciency
from n-type silicon substrates [R. King, et al, 21st IEEE PVSC, p.227, 1990, P. Verlinden, 14th
European PVSEC, pp.96, 1997].
1.0
amps
0.8
0.6
0.4
0.2
0.0
Cell ID: Wnrj7-2a
Cell Area: 22.04 cm 2
Temperature: 25.1°C
Voc = 702 mV
Isc = 0.884 A
Jsc = 40.1 mA/cm 2
FF = 0.805
Eff = 22.7%
0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
volts
Figure 4.3.1.3: I-V curve of a rear emitter
n-type cell as measured at Sandia National
Laboratories under 100 mW/cm 2 , AM1.5
global spectrum at 25ºC.
It is seen that the cells on thinner substrates demonstrate improved effi ciencies. Also, limited
emitter areas were defi ned by lithography for the last batch, Wnrj7. The emitter boron
diffusion area was terminated about 200 µm from the scribed cell edge. This has signifi cantly
improved the cell fi ll factors to over 80% and hence improved the cell effi ciencies.
4.3.1.4 Spectral Response Measurement and Analysis
The spectral response of the best n-type re-PERT cell, Wnrj7-2a, was measured at Sandia
National Laboratories, with results shown in Figure 4.3.1.4. This cell has internal quantum
effi ciency (IQE) around 98%, compared to 100% for the standard front emitter PERL cells
on p-type substrates. Hence, its current density is only about 1 mA/cm 2 lower compared
to the best p-type PERL cells. The previous 400 µm thick cells had a much lower IQE of only
around 93% and a short-circuit current density about 2 mA/cm 2 lower than the best PERL
cells. It is clear that the 170 µm thin substrates and the modest resistivity of 1.5 Ω-cm have
helped this cell to increase its IQE and Jsc. The IQE for the second batch cell, Wnrj4-3b,
was very close to that from the 170 µm thin cell. Hence, the 270 µm cells and 170 µm thin
cells had similar experimental short-circuit current densities. However, the long wavelength
refl ection from the 170 µm thin cell had been signifi cantly increased compared to that from
the thicker cells. This gives evidence that the 170 µm might be too thin already for the best
light absorption.
Reflectance, EQE, and IQE (%)
100
90
80
70
60
50
40
30
20
10
0
300 400 500 600 700 800 900 1000 1100 1200
Wavelength (nm)
Figure 4.3.1.4: Spectral response of
the best n-type re-PERT cell, Wnrj7-2a,
on a 1.5 µ-cm resistivity, 170 µm thin
n-type substrate.
28

It is seen that the measured IQE in Figure 4.3.1.4 initially increases for the longer wavelength
light. This corresponds to the fact that the weakly absorbed longer wavelength light generates
minority carriers closer to the rear emitter, and hence it has a lower recombination loss
during carrier transportation.
In this work, the device simulation program, PC-1D, was used to simulate and to fi t the
performance of the re-PERT cells. The bulk and the surface recombination parameters
listed in Section 4.3.1.2 are also used for this PC-1D simulation and give a close match to
the experimental cell performance. The reduced IQE in the very short wavelength range
below 500 nm is due largely to the absorption in the 50 nm thick ZnS in the double layer
antirefl ection coating. The PC-1D simulation neglects this ZnS absorption but allows a good
fi t to the rest of the IQE curves, as shown in Figure 4.3.1.5.
Figure 4.3.1.5: Thickness effect on IQE
simulated from PC-1D.
As expected from the simulation, the 170 µm thin device gives a clear advantage in its IQE.
Hence, it also demonstrated a higher short-circuit current density. However, the increased
long wavelength refl ection for the 170 µm thin cell gives evidence that the material absorption
is decreasing signifi cantly. Hence it is believed that the 170 µm cell is a little too thin, since
the 270 µm device gave a slightly higher current density, as shown in Table 4.3.1.1. The
optimum thickness may be around 200 µm.
4.3.1.5 Improved Cell Stability
One of the major problems with our previous front emitter n-type PERT cells was their instability
under one-sun illumination, and even during storage in a nitrogen box. However, it is found
that the rear emitter n-type PERT cells have very stable and even improved performance
under one-sun illumination by an ELH lamp light source for many hours. Figure 4.3.1.6 shows
these results.
29

Voc, mV
705
703
701
699
697
695
693
691
Wnrj1-2b
Wnrj1-1a
Wnrj1-1b
Wnrj1-2a
Wnrj7-1b
0 5 10
One - sun Illumination Time, hr
Jsc, ma/cm2
40.0
39.8
39.6
39.4
39.2
39.0
38.8
Wnrj1-2b
Wnrj1-1a
Wnrj1-1b
Wnrj1-2a
Wnrj7-1b
38.6
0 5 10
One - sun Illumination Time, hr
FF, %
80.0
79.5
79.0
78.5
78.0
77.5
77.0
Wnrj1-2b
Wnrj1-1a
Wnrj1-1b
Wnrj1-2a
Wnrj7-1b
Efficiency, %
22.5
22.0
21.5
21.0
Wnrj1-2b
Wnrj1-1a
Wnrj1-1b
Wnrj1-2a
Wnrj7-1b
76.5
0 5 10
One -sun Illumination Time, hr
20.5
0 5 10
One -sun Illumination Time, hr
Figure 4.3.1.6: The performance of rear boron emitter n-type PERT cells during 1–2 days
one-sun illumination by ELH lamp. The edge recombination may have been reduced by the
illumination process.
For the cells in the fi rst batch, Wnrj1, with scribed and cleaved through emitter edges,
effi ciencies improved by 0.2% to 0.4% absolute after illumination. Most of these gains
came from Jsc improvements, which is a sign of reduced total recombination loss. The high
recombination at the scribed edges may have been reduced during illumination, possibly due
to slight oxidation of the cleaved edge surfaces.
However, the cells in the latest batch, Wnrj7, did not show this increase to the same extent
under one-sun illumination. Separating the emitter from the cleaved exposed edges with the
limited-area emitter design has stabilised cell performance, as well as improving the cell fi ll
factors. Fortunately, cleaved emitter edges for larger area commercial cells will have much
less effect on the fi nal cell performance.
It is clear that moving the light sensitive boron diffused emitter from the front to the rear
surface has signifi cantly improved the cell stability.
4.3.1.6 Recent Design Without Cell Scribing
Recently, the n-type re-PERT cells have been redesigned into one cell on a single wafer
structure. This will eliminate the need for cell scribing. In this case, the edge recombination
loss from the scribed and the cleaved edge surfaces will be eliminated. This structure is
designed to test the recombination contribution from the scribed edges. It will also allow
investigation of the full potential of such n-type re-PERT cell structures. We are confi dent that
such device structures with minimum edge recombination contribution will further improve
the cell effi ciency to a new level above the present world record, as demonstrated by the
scribed re-PERT cells.
30

The re-PERT cells on n-type CZ substrates will also be investigated in the near future. Since
high carrier lifetimes of over 5 ms have been demonstrated from n-type SEH CZ substrates,
the n-type CZ rear emitter cells are expected to give similar performance to the n-type FZ
cells.
4.3.1.7 High Efficiency Group’s Journal Publications:
G. Kumaravelu, M.M. Alkaisi, D. Macdonald, J. Zhao, B. Rong and A. Bittar,
“Minority carrier lifetime in plasma-textured silicon wafers for solar cells”, Solar
Energy Materials and Solar Cells, Vol. 87, pp. 99-106, 2005.
4.3.1.8 High Efficiency Group’s Conference Papers:
J. Zhao and A. Wang, “High Effi ciency Rear Emitter PERT Solar Cells on N-type FZ
Single Crystalline Silicon Substrates” (oral presentation), 20th European
Photovoltaic Solar Energy Conference and Exhibition, Barcelona, Spain, pp.
806- 809, 6-10, June, 2005.
Guoxiao Yao, Jianhua Zhao and Jeffery E. Cotter, “Hybrid stencil-print/buriedcontact
solar cells” (oral presentation), 20th European Photovoltaic Solar Energy
Conference and Exhibition, Barcelona, Spain, pp. 749-752, 6-10, June, 2005.
Jianhua Zhao, “The foundation and the strategy of Photovoltaic Industry in China”,
China Power Conference, Beijing, China, 10-12, August, 2005.
J. Zhao and A. Wang, “Rear Emitter N-Type Silicon Cells with Stable High
Performance” (invited talk), Technical Digest of the 15th International
Photovoltaic Science and Engineering Conference, Shanghai, 10-15, October, pp.
122-123, 2005.
J. Zhao, “High Effi ciency Silicon Solar Cell Technologies Ready for Production”
(invited talk), Technical Digest of the 15th International Photovoltaic Science and
Engineering Conference, Shanghai, 10-15, October, pp. 310-311, 2005.
J. Zhao, “High Effi ciency Silicon Solar Cells for Mass Production” (invited talk),
Sino Euro Workshop, the 15th International Photovoltaic Science and Engineering
Conference, Shanghai, 10, October, 2005.
J. Zhao, “Manufacturing Technologies for High Effi ciency Crystalline Silicon Solar
Cells” (invited talk), PV Industrial Workshop, the 15th International Photovoltaic
Science and Engineering Conference, Shanghai, 12, October, 2005.
31

4.3.2 BURIED CONTACT SOLAR CELL GROUP
University Staff:
Dr. Jeffrey Cotter
Prof. Stuart Wenham
Project Scientists and Technicians:
Dr. J. H. Allen Guo
Jamie Green
Kate Fisher
Fennalia Tan
David Di
Brett Hallam
Adeline Sugianto
Research Associates:
Dr. Robert Bardos
Dr. Tom Puzzer
Dr. Alistair Sproul
Ted Szpitalak
Postgraduate Students:
Malcolm Abbott
Florence Chen
Matthew Edwards
Kate Fisher
Guoxiao “James” Yao
Attachai “Tao” Ueranantason
Undergraduate Thesis Students:
Nino Borojevic
Andrew Li
Jonathon Bocking
Undergraduate Summer Scholars:
Brett Hallam
Neil Bennett
The Buried-Contact Solar Cell Group aims to develop new solar cell structures and novel
process technologies specifi cally for commercially relevant silicon wafers. The group has
a broad spectrum of research and development activities that address the evolving nature
of commercial silicon solar cells. The Group’s main activities are focused on developing higheffi
ciency, thin-wafer Buried Contact solar cells, developing of low-cost processing technologies
and related device designs, and transferring BC technology to industrial and technical
collaborators.
4.3.2.1 N-Type vs. P-Type Wafers for High Efficiency
Silicon Solar Cells
N-type Czochralski and multicrystalline silicon as materials for solar cells have received
considerable attention recently due to emerging evidence that they are electrically superior to
p-type material. Several groups have reported very high pre- and post-processing lifetimes in
both cast multicrystalline and Czochralski materials. There appears to be excellent potential
for commercial grade, n-type silicon wafers as a basis for high-effi ciency commercial solar
cells.
33

In silicon wafers that have naturally occurring defects, such as dislocations, grain boundaries
and chemical impurities, the choice of wafer doping type can play a key role in mitigating
the effect that the impurities have on the electrical quality of the wafer. For example, Figure
4.3.2.1a shows the predicted injection-dependent normalized recombination rate for two
Shockley-Read-Hall (SRH) defect species in p-type and n-type materials. Curves A and B
predict the behaviour in p-type material: (A) for a defect located at a single energy level within
the bandgap and (B) the behaviour for a defect distributed over a continuum of energy levels
within the bandgap. Curve C predicts the behaviour for the same defects in n-type material,
while curve D predicts the behaviour of both n-type and p-type material in the absence of
the defect. When viewed along the 1-sun operating loci (“1-sun Vmp”), it is clear that for a
given defect species, the effective recombination rate depends signifi cantly on the doping
type of the wafer. In this case, the recombination in the n-type wafer is one or two orders of
magnitude lower than the p-type wafer.
Figure 4.3.2.1: (a) Predicted injection-dependent normalized recombination rate for n-type
and p-type silicon wafers in the presence or absence of SRH defects; (b) Predicted effect of
SRH defects on the illuminated IV curve for the cases presented in (a).
The signifi cance of the SRH behaviour in n-type and p-type wafers is highlighted in Figure
4.3.2.1b, which shows the predicted illuminated IV curve for the four cases shown in Figure
4.3.2.1a. The strong SRH recombination behaviour degrades the IV performance in the p-
type material signifi cantly, reducing the operating point voltage by as much as 120 mV. The IV
performance is hardly affected in the n-type material.
The DSBC solar cell design, shown in Figure 4.3.2.2a, is ideal for making a direct comparison
of solar cell terminal characteristics of solar cells made side-by-side on n-type and p-type
silicon wafers. The DSBC processing sequence can be applied to either p-type or n-type
wafers without signifi cant changes in the processing sequence - diffusions, oxidations, even
metallisation processes can be applied with good effect to both types of wafers processed in
split batches. Also, the DSBC process uses a heavy boron contact diffusion that is known to
introduce diffusion induced misfi t dislocations into the bulk of the wafer. Such misfi t dislocations
behave similarly to the SRH defects used in the simulations of Figure 4.3.2.1a. Figure 4.3.2.1b
shows a comparison of terminal characteristics of p-type and n-type DSBC solar cells that
were fabricated using the nearly identical fabrication sequences and processed in a split
batch.
34

Figure 4.3.2.2: (a) DSBC solar cell design for p-type silicon wafers; (b) Illuminated IV curves for
p-type and n-type DSBC solar cells.
The characteristic behaviour of SRH recombination attributed to boron-diffusion-induced
misfi t dislocations is apparent in the terminal characteristics of all three p-type solar cells,
as can be seen in the degraded fi ll factor and open-circuit voltage. The n-type solar cell is not
affected.
The case of the 1 Ωcm p-type and 1 Ωcm n-type solar cells is interesting. While the fi ll factor
of both solar cells looks comparable, the detrimental effect of the SRH recombination on the
p-type solar cell is not immediately apparent by examining the fi ll factor alone. However, the
voltage characteristics of this solar cell are degraded by SRH recombination - the open-circuit
voltage of the p-type solar cell is 20 mV lower than its n-type counterpart, yet, based on the
relative doping levels (the p-type wafer has a factor of three higher doping level), one would
expect the p-type solar cell to reach open-circuit voltages about 25 mV higher than the n-type
solar cell.
The performance bias toward n-type wafers in the above device comparison is attributed
to the electronic nature of the defect species – diffusion induced misfi t dislocations have a
relatively high electron capture cross section and low hole capture cross section. Many defect
studied at UNSW also display similar electronic nature, including laserinduced
defects, surface defects and chemical contaminants. Figure
4.3.2.3 shows a comparison of the recombination rates of a split
batch of n-type and p-type wafers that were unintentionally subjected
to contamination during a high temperature process sequence.
All of the p-type wafers show high and varied recombination rates,
compared to the n-type wafers which show much lower and less
varied recombination.
Figure 4.3.2.3: Photoconductance measurements of p-type and n-
type silicon wafers unintentionally contaminated during a phosphorus
diffusion and thermal oxidation process sequence. The dash-dot line
shows the approximate one-sun operating point for a high-effi ciency
solar cell.
35

Based on our fi ndings, we consider n-type silicon wafers to present a signifi cant opportunity
for commercial, high-effi ciency silicon solar cells. The growing list of defects that exhibit high
hole lifetime and low electron lifetime, and the impact that the associated SRH recombination
has on the terminal characteristics of solar cells, suggests that n-type silicon wafers are
better suited for high-effi ciency, commercial silicon solar cells. Overall, in terms of the
electrical requirements of a solar grade wafer for industrial high-effi ciency silicon solar cells,
n-type wafers seem to hold a signifi cant advantage over p-type wafers.
Given the demonstrated potential of n-type silicon wafers for high-effi ciency commercial
silicon solar cells, UNSW is focusing considerable effort on developing technologies for n-type
silicon solar cells, including high-effi ciency interdigitated backside buried contact silicon solar
cells, screen printed n-type silicon solar cells, laser diffused n-type silicon solar cells and silicon
nitride based n-type silicon solar cells.
4.3.2.2 N-TYPE SILICON SOLAR CELLS
High Efficiency IBBC SILICON Solar Cells
In 2004, we demonstrated the use of laser grooved BC technology to fabricate high-effi ciency
Interdigitated Backside Buried Contact (IBBC) solar cells, as well as the more conventional
n-type Double-sided Buried Contact (DSBC) solar cells.
Three key obstacles to effi ciency were overcome in the IBBC process and in device design
during 2004-parasitic shunt resistance at the diffusion overlap regions, simultaneous
metallization of n++ and p++ contact regions, and optimization of the diffused regions. An
effi ciency of 19.2% was achieved on the n-type FZ IBBC solar cell design, demonstrating
the high-effi ciency potential of buried contact silicon solar cells and of n-type silicon wafers.
Moreover, all types of Buried Contact solar cells made on Czochralski and multicrystalline
phosphorus-doped n-type silicon wafers showed no light-induced degradation.
In 2005, we focused on the further development of the IBBC solar cell design and process,
with signifi cant improved in 2005 due to developments in both processing and design aspects.
Further improvements in diffusions, especially the boron emitter, has led to near elimination
of the shunting in the diffusion overlap regions and improvements in open circuit voltage. A
passivated junction edge along the cell perimeter of the solar cell signifi cantly reduces the
edge recombination, which previously had limited fi ll factor and open circuit voltage. Combined,
these developments have led to increases in fi ll factor, open circuit voltage and effi ciency.
Table 4.3.2.1 summarizes a typical batch result as of the end of 2005.
textured passivated AR coated
n+type FSF
n+type base
n++-type
groove
p+type emitter
36
Figure 4.3.2.4: IBBC solar cell design for n-type wafers.

TABLE 4.3.2.1: Electrical output of the IBBC solar cells (unverifi ed) under both front and rear
illumination.
Front Illumination
Rear Illumination
Cell Voc Jsc FF η Voc Jsc FF η
ID (mV) (mA/cm 2 ) (%) (mV) (mA/cm 2 ) (%)
D2-4 672.9 36.99 0.7743 19.27 670.9 31.79 0.7813 16.66
D2-5 674.1 37.12 0.7805 19.54 670.8 31.66 0.7890 16.76
D2-8 676.5 37.12 0.7911 19.87 670.9 31.70 0.7908 16.82
D2-9 672.6 37.06 0.7773 19.43 672.6 31.85 0.7875 16.87
Detailed modelling indicates improvements in both the front and rear surface recombination
velocities – about 200 cm/s (improved from 600 cm/s in 2004) and 6000 cm/s (improved
from 10000 cm/s in 2004) respectively. Saturation current density due to edge-junction
recombination (J 02 ) has been reduced by about 1 order of magnitude (3.3 pA/cm2 versus
40 pA/cm2 in 2004) due to the incorporation of an edge junction passivation technique.
Figure 4.3.2.5 shows the illuminated J-V curve of the best solar cell (device D2-8). Compared
to the results reported in 2004, open-circuit voltage and fi ll factor are increased by 12 mV
and 2.7% respectively. In these devices, short circuit current is reduced by typically 0.9 mA/
cm2 due to a lower bulk lifetime, the cause of which is currently under investigation. Overall,
the effi ciency best has increased by 0.65% to about 19.85%.
Figure 4.3.2.5: Light J-V curve of IBBC solar cell D2-8.
In 2005, we also introduced statistical process control (SPC) techniques to ensure that
the process fl uctuation is well monitored and controlled and to enhance cell and process
development efforts. Overall, the distribution of results from batch to batch, and across any
batch are much tighter, indicating the fabrication process is under control.
The effi ciency of IBBC solar cell is expected to achieve 20.3% after improving the postprocessing
lifetime to currently expected values. Further research on reducing series
resistance and other key loss mechanisms is currently in progress
Screen Printed N-Type Silcion Solar Cells
The use of n-type Czochralski silicon wafers and stencil-print metallisation has the potential
to improve the performance (Cz) of commercial silicon solar cells, but little work has been
done in investigation of print pastes and fi ring conditions for boron-diffused, p-type emitters.
To investigate the formation of low-cost, good-quality metallization on n-type Cz silicon, several
commercially available print pastes and fi ring cycles were evaluated on p-type emitters by
characterizing the junction shunting and contact resistance.
37

Conductive Paste Firing Tests
Basic cell test structures (Figure 4.3.2.6) were fabricated with a diffused, 100 Ω/sq front
boron emitter. A bare silicon surface was used to avoid added complexities from having to fi re
through an insulating layer. The front grid metallisation was formed by metal stencil printing of
thick-fi lm metal pastes, using stainless steel foil stencil techniques developed in 2004. These
stencils are capable of printing high defi nition contact patterns with fi ngers as narrow as
60 µm in width and up to 30 µm in height. The stencil-printed front contacts were fi red with
varying peak temperatures and durations in a four-zone belt furnace with peak temperature
varied between 700°C and 900°C.
Screen-printed Al contact
p-type emitter
n-type bulk
n+ back surface field
Screen-printed Ag contact
Figure 4.3.2.6: Test structure used for evaluation of front contact shunt resistance.
Figure 4.3.2.7a shows shunt-resistance results obtained for the case of aluminium paste, fi red
with a peak time of 10 s. Results clearly show acceptable shunt resistance for a wide range
of peak temperatures ranging between 720oC and 870oC. Acceptable shunt resistances
were also obtained using silver paste (Figure 4.3.2.7b), however perhaps surprisingly, shunt
resistances obtained for aluminium pastes were often higher than those in cells fabricated
with silver.
Figure 4.3.2.7: Shunt resistances after fi ring a) Ferro 5540 aluminium and b) Ferro 33-466
silver thick-fi lm conductive paste. Peak fi ring time was 10 s.
38

To measure contact resistance to the boron-diffused layer, a stencil with a specially formed
contact pattern consisting of vertical lines spaced progressively further apart was fabricated,
and contacts printed on similar test structures to that shown in Figure 4.3.2.6. Contact
resistances were measured using the transmission-line method, and are shown in Figure
4.3.2.8.
(a)
(b)
Figure 4.3.2.8. Results of contact resistance measurements with a) Ferro 5540 aluminium
and b) Ferro 33-466 silver thick-fi lm conductive paste fi ngers. Peak fi ring time was 10 s.
For aluminium paste fi red at peak temperature for 10 s, area-specifi c contact resistances as
low as 3.85 mΩ.cm2 were obtained, as shown in Figure 4.3.2.8. For silver-aluminium paste
fi red for 10 s, area-specifi c contact resistances were as low as 13.8 mΩ.cm2. Aluminium
was found to be superior in forming ohmic contact to a boron-diffused layer, however, it was
observed that the benefi t of low contact resistance when using aluminium was sometimes
outweighed by the higher bulk resistivity of these pastes.
Paste rheology in stencil printing is critical, and it was found that the lower viscosity of
commercially available aluminium pastes designed for the formation of the rear contact in
p-type cells led to inferior print quality compared to silver pastes, which generally have a
higher viscosity. This leads to fi ll factor degradation in fi nished cells that were stencil printed
with low-viscosity aluminium. Since the inferior contact resistance of silver paste also leads
to fi ll factor degradation, high viscosity aluminium is an ideal choice of paste for use in stencil
printed n-type solar cells.
Fabrication of n-Type Solar Cells with Stencil Printed Contacts
Optimised printing and fi ring parameters for aluminium stencil-printed front contacts on
boron emitters were applied to full solar cell structures. Figure 4.3.2.9 shows results for
a typical cell. It was found that while high fi ll factors were achievable, overall cell effi ciencies
were relatively low due to poor blue response and high front surface recombination velocities.
Passivation of the boron-diffused surface was found to be very diffi cult. Collaboration with
the Universitat Politecnica de Cataluña (UPC) is underway to devise an effective passivation
scheme for the front surface of our cells using either a silicon nitride or silicon carbide layer.
39

Figure 4.3.2.9: Illuminated IV curve and quantum effi ciency characteristics for a typical 4 cm 2
n-type cell fabricated with stencil printed Al contacts. The above cell has fi ll factor of 75% and
effi ciency of 10.1%. Shunt resistance was 8 kΩ and series resistance was 0.38Ω.
Laser Diffused N-Type Silcion Solar Cells
Laser diffusion has been investigated as a technique for the formation of high-effi ciency IBBC
and DSBC solar cell structures. Currently the formation of the contact regions on these
devices requires an estimated 50% of the total fabrication time and requires several hightemperature
processing steps. This intensive high-temperature processing is not compatible
with high-throughput manufacturing or with commercial wafer materials such as CZ and
mc-Si wafers. Laser diffusion offers good potential to simplify the processing of high-effi ciency
bifacial silicon solar cells.
The laser diffusion performed in this work occurs through a process of laser-induced surface
melting and liquid-state diffusion of dopant atoms. A thin layer of dopant fi lm is applied to
the wafer surface over an existing silicon dioxide layer, then diffused by a series of laser
pulses incident on the surface. Each laser pulse causes the underlying silicon to melt, then
recrystallize, without any signifi cant increase in temperature away from the target area.
Dopant atoms diffuse quickly in the liquid phase and are incorporated in electrically active
lattice sites during recrystallization. During the laser diffusion process the silicon dioxide is
locally removed, leaving a mask in the non-doped regions for subsequent electroless metal
plating. The heavily diffused regions are formed selectively, at room temperature and without
the need for any NaOH etching to remove laser damage or oxide deglazing to remove the
silicon dioxide layer.
During 2005, the diffusion process was optimised to achieve the heavy surface concentration
(>10 19 ) and deep junction (> 1 µm) required to form ohmic contact between silicon and metal
contacts. The diffused contact regions were then integrated into a simplifi ed version of the
DSBC solar cell to investigate issues with device fabrication.
Figures 4.3.2.10 shows typical images of the laser diffused contact regions. Laser diffusion
was found to be compatible with the other cell fabrication processes including the electroless
plating of metal contacts.
40

Figure 4.3.2.10: Micrographs of laser diffused contacts; (a) plan view of intersection between
contact fi nger with end of busbar; (b) plan view of contact pad area; and (c) a fi nger after
electro-less copper plating.
The electrical results of the best cell, shown in Figure 4.3.2.11, are very promising with the
highest open-circuit voltage of 672 mV, a fi ll factor of 78% and short-circuit current of typically
33 mA/cm2 demonstrated on an untextured, n-type, FZ wafer. It is concluded that laser
diffusion is a promising alternative to furnace diffusions on IBBC and DSBC devices. Further
work will focus on further optimisation of the process to increase the fi ll factor and integrate
the laser diffusion process with IBBC cells.
Figure 4.3.2.11: Illuminated IV characteristics of
the best n-type planar double-sided solar cell with
laser doped contacts (unconfi rmed).
Silicon Nitride Based n-type Silcion SolarCells
It is well-established that silicon nitride (SiN) fi lms have excellent anti-refl ection and passivation
properties, with a wide range of achievable refractive index, large amount of hydrogen for
passivation, and positive fi xed charges that creates inversion/accumulation layer to enhance
the passivation. While extensive work has been done on SiN for p-type solar cell applications (in
particular, excellent passivation is demonstrated on p-type bare surface and on phosphorus
diffused emitter) little literature is available on SiN for n-type solar cell applications. In 2005,
we investigated the application of SiN fi lms for n-type wafers and solar cells.
Our work shows that PECVD SiN deposited using a Roth&Rau AK400 PECVD system is
particularly well suited for surface passivation of n-type silicon wafers and solar cells. In
particular, the passivation quality on bare planar silicon surfaces, and boron diffused planar
surfaces on n-type, 1 Ωcm, FZ wafers is exceptional. Furthermore, since SiN creates an
accumulation layer rather than inversion layer on n-type surfaces, problems caused by the
inversion layer on p-type surface such as shunting through the inversion layer are avoided.
41

Silicon Nitride Passivation of Bare, n-type Silicon Surfaces
Figure 4.3.2.12 shows the effective surface recombination velocity (SRV) versus injection level
curves for three different refractive index fi lms on FZ wafers. For comparison purpose, the
effective SRV of a sample that had a 100 ohm/sq phosphorus diffusion and oxidation are
also plotted on the same graph. The two dotted lines on the graphs that cross the effective
SRV curves represent the locus of the 1-sun open-circuit voltage and approximate maximumpower
voltage operating points for a high-effi ciency, 200-micron thick solar cell.
As illustrated in the graph, the surface passivation quality of as-deposited SiN is exceptional,
achieving better recombination than the baseline phosphorus diffused and oxidized surface.
In our work, silicon-rich fi lms give the best surface passivation at as-deposited conditions.
Table 4.3.2.2 summarizes the extracted SRV and implied open
circuit voltages for various as-deposited silicon nitride fi lms.
Figure 4.3.2.12: The effective surface recombination velocity vs.
minority carrier density plots of various SiN on 1 ohm.cm n-type FZ
wafer.
Table 4.3.2.2: The best effective SRV, effective SRV at 1-sun Voc, and
implied voltage at 1-Sun Voc operating points of various SiN fi lms on
planar n-type surface of a 200-micron thick wafer.
Refractive index Wafer type Best SRVeff (cm/s) SRVeff at Voc (cm/s) Imp Voc (mV)
2.00 n-FZ 7.01 13.34 723
2.35 n-FZ 2.29 10.74 732
2.75 n-FZ 1.96 9.53 739
Phos and oxide n-FZ 5.23 15.48 709
A voltage test structure device was prepared to further demonstrate the exceptional
passivation quality provided by our SiN fi lms on n-type wafers. The device has two very small
diffused contact regions, one was phosphorus diffused and the other boron diffused. A lowindex
(nr = 2.00) SiN fi lm was deposited on both sides of the wafer in the as-deposited condition.
Small openings made photolithographically in the contact regions allowed the measurement
of the open-circuit voltage at approximately 1-sun, 25ºC of 719 mV. Further improvement
is expected during 2006, with open-circuit voltages approaching 725 mV expected for test
structures and 700 mV in fully fabricated silicon nitride passivated solar cells.
Silicon Nitride Passivation of Boron Diffused Emitters
42
The ability of silicon nitride to passivate a boron-diffused emitter is important for making higheffi
ciency n-type silicon solar cells. Our results show that for some diffusion sheet resistances,
boron diffusion process, and subsequent thermal treatment, SiN is particularly well-suited for
passivating boron-diffused surface on n-type silicon. Figure 4.3.2.13a shows the implied open
circuit voltages (extracted from photoconductance measurements) of various passivation
fi lms on boron-diffused emitters with sheet resistances ranging from roughly 45 ohm/sq to
250 ohm/sq, including silicon dioxide and various silicon nitride fi lms. The results illustrate
that at the as-deposited condition for the sheet resistance range studied in this work, SiN
provides poorer passivation compared to silicon dioxide. Interestingly, it appears that, at the
as-deposited condition, the three different SiN fi lms provide roughly the equivalent passivation
quality and have similar trend across the range of sheet resistances studied.

The SiN fi lms with nr = 2.35 were annealed at 450°C in an N2 ambient for a total duration of
240 minutes. The evolution in implied open-circuit voltage of the annealed samples is plotted
in Figure 4.3.2.13b. After 5 minutes of annealing, the relationship between the implied Voc
and sheet resistance of boron emitter resembles that of as-deposited condition. However,
after 30 minutes of annealing, the relationship has changed, with the implied open-circuit
voltage increasing with increasing boron emitter sheet resistance. It is likely that the implied
open-circuit voltage at low sheet resistance range is limited by the emitter recombination,
whereas, at the high sheet resistance range, the surface recombination dominates. After
240 minutes of annealing, an implied open-circuit voltage of 683 and 718 mV on 135 and 215
ohm/sq boron emitter respectively was achieved. Dark emitter saturation current densities
as low as 5 fA/cm2 per side was achieved by fully annealing the SiN fi lms. The results also
indicate that the passivation quality provided by the annealed fi lms is superior to that by oxide
for sheet resistance above around 100 ohm/sq.
Figure 4.3.2.13: (a) The implied open-circuit voltage of various SiN fi lms at as-deposited
condition on boron emitters across range of sheet resistances; (b) the implied open-circuit
voltage of the nr = 2.35 SiN fi lm after various annealing times; (c) the extracted emitter
saturation current density of the fully annealed nr = 2.35 SiN fi lms.
4.3.2.3. PHOTOLUMINESCENCE AND PHOTOCONDUCTANCE TECHNIQUES FOR
SILICON SOLAR CELL CHARACTERIZATION AND DEVELOPMENT
Photoluminescence Techniques
Photoluminescence characterization techniques have recently emerged in other Centre
work as an accurate, fast, powerful tool for developing high-effi ciency silicon solar cells.
The related PL techniques – spatially averaged PL lifetime, Suns-PL and PL imaging – offer
unprecedented quality and quantity of information that is benefi cial for a wide spectrum
of solar cell development and fabrication purposes. As PL techniques are fast (especially
imaging), contact-less and provide complementary spatial and injection level dependent
information about recombination, they are very powerful techniques relevant to both well
controlled laboratories and high-throughput solar cell factories.
In 2005, we demonstrated the application of multiple PL techniques to several important
aspects of high-effi ciency solar cell development at UNSW: wafer handling, furnace
contamination, process-induced defects, cell design and cell process monitoring. In only a few
months, photoluminescence (PL) techniques have greatly enhanced our solar cell fabrication
sequences and designs, identifying problems that, in some cases, existed in our fabrication
sequences for over ten years. With measurement times of 1 second per wafer (regardless
of area) the power of this technique is as relevant to high-throughput mass-production as it is
to laboratory cell research and development.
43

Wafer Handling
PL imaging was used to characterize a long-standing traditional technique of wafer drying
at UNSW. In practice, wafers were dried using pressurized N 2 while holding the wafer by its
edges with cleaned plastic tweezers. PL imaging quickly revealed the impact of this drying
technique on electrical quality. Figure 4.3.2.14 shows PL images of two wafers that have been
dried by two different techniques prior to high-temperature processing. In the images, bright
areas correspond to a strong PL signal, indicating regions of good local lifetime. The dark
areas indicate regions of poor lifetime where recombination has been locally increased. The
image in Figure 4.3.2.14a shows four very dark spots on the four edges of the wafer, where
it was held with the tweezers whilst drying with a nitrogen gun. The image in Figure 4.3.2.14b
shows a wafer that was dried in a furnace in nitrogen ambient with no wafer handling by the
edges, indicating no such dark spots on the edges.
Figure 4.3.2.14: 1. sun photoluminescence
image of an n-type CZ wafer that was processed
in two successive high-temperature diffusion/
oxidation processes: (a) Dried using tweezers
to hold the wafer by the edges; (b) dried in a
furnace with no edge handling. The location of
tweezers during the drying process is marked
as (X) before the fi rst high-temperature step
and (+) before the second high-temperature
step.
Furnace Contamination
Contamination during high-temperature furnace processes can reduce bulk lifetime and
lead to poor electrical properties of fi nished cells. PL monitoring can be used to identify an
individual contaminated wafer and identify furnace equipment that requires cleaning. Figure
4.3.2.15 demonstrates the case with which PL is able to detect furnace contamination. The
wafer top left (labeled a) was contaminated (unintentionally) during the preparation for high
temperature processing. This contamination was able to spread to the adjacent wafers
(labeled b and c) in the direction of the gas fl ow, whereas other wafers in the same furnace
tube (d, e and f), but upstream of the gas fl ow were unaffected by the contamination.
Figure 4.3.2.15. 1 Sun photoluminescence
images of samples after phosphorus diffusion:
a) CZ sample; with worst contamination; b) CZ
sample in slot next to contaminated sample, c) CZ
sample further down furnace tube in direction of
gas fl ow; ; d-f) FZ samples successively upstream
from the contaminated wafer.
44

Solar Cell Design
PL was used to characterize a new method of edge isolation for our n-type cells that involves
a laser formed isolation trench through the emitter and around the solar cell’s edge. Several
test wafers were prepared, half including the new edge isolation technique and the other
half employing the traditional technique of laser-cleaving the edge. Figure 4.3.2.16 shows
the results of Suns-PL and PL imaging used to analyze the effectiveness of the edge isolation
technique. The image in Figure 4.3.2.16a shows the sample in high injection, revealing where,
in order to create a recombination active area, we have deliberately scratched the surface
outside the isolation trench with a diamond pen. Figure 4.3.2.16b shows the same sample in
lower injection, demonstrating the effectiveness of the new process in providing isolation of
the main solar cell area from the edges and scratches.
Figure 4.3.2.16: Photoluminescence images of
1 Ωcm, 240µm thick, n-type wafers with phosphorus
diffusion on the rear side and boron diffusion on
the front side with isolation trench after various
processing steps: a) at ~ 1 Sun ; b) ~ 0.1 Suns
Figure 4.3.2.17 shows the pseudo dark IV and dark local ideality factor of
the samples shown in Figure 4.3.2.16. The curves were generated using the
Suns-PL technique. All of the curves labeled a) have the new trench isolation
technique applied. These curves compare to the non-isolated cases b), c)
and d) in which the effect of edge enhanced junction recombination and edge
shunting are apparent. In this case, PL techniques provided almost immediate
feedback in assessing the effectiveness of the new edge isolation process.
Figure 4.3.2.17: (top) Pseudo dark I-V curves obtained from QSS-PL
measurements on a 1 Ωcm, 240µm thick, n-type wafer with phosphorus
diffusion on the rear side and boron diffusion on the front side after various
processing steps (see text for details); (bottom) corresponding local ideality
factor.
Silicon Nitride – Wafer Handling and Preparation
PL imaging is particularly powerful for developing silicon nitride as a passivation layer because,
unlike thermal oxide fi lms, silicon nitride fi lms show a rich variety of spatially resolved effects,
even in samples with exceptional quality passivation layers.
In 2005, we investigated the application of PL imaging to the development of improved quality
silicon nitride fi lms. We found that PL imaging can be used to understand the deposition
process, to identify and address key manual handling issues, to characterize thermal annealing
processes, and to study the effect of post-deposition chemical processing.
PL imaging can be used to help identify how sample handling can affect the passivation
quality of the SiN fi lms. Figure 4.3.2.18 shows a few PL images that highlight handling related
issues.
45

(a) (b) (c)
Figure 4.3.2.18: SiN samples showcasing poor sample handling: a) sample with micro-cracks;
b) sample with micrometer marks; c) sample with intentionally induced scratches.
Figure 4.3.2.18a shows how PL imaging can detect micro-cracks that are not visible to the
naked eye. The PL image in Figure 4.3.2.18b reveals that the micrometer used to measure
the wafer thickness, either before or after the SiN deposition, can also lead to localized regions
of higher recombination. Note the four perfectly round dark circles in Figure 4.3.2.18b. Figure
4.3.2.18c illustrates the impact of scratches on passivation quality. In this case, two very light
scratches were deliberately made on the sample, one before and one after the SiN deposition.
The image suggests that even very light scratches, both before and after deposition, can be
resolved by the PL imaging technique.
Silicon Nitride – Process Monitoring
At UNSW, the passivation quality of the samples in the same deposition run is occasionally
inconsistent from sample to sample. Occasionally, a particularly bad sample may be included
in a batch run. Since the PL imaging technique is fast (typically 1 second for the samples
studied here), it is a powerful tool for process monitoring and control in cases like these.
Figure 4.3.2.19 shows two samples prepared identically in the same deposition runs. One
sample is clearly better passivated than the other, as indicated by a comparison of the PL
intensity of both samples.
Figure 4.3.2.19: PL images of two
samples prepared identically in
the same batch and deposition
run.
(a)
(b)
This observation from PL imaging also agree with QSS-PC measurement, as the sample on
the left hand side has an extracted implied open-circuit voltage of 670 mV and the one on the
right hand side has an implied open-circuit voltage of 725 mV.
46

Photoconductance Techniques
During 2005, we developed a new LED-based light source for our heavy use photoconductance
testing system. It uses seven high-luminosity light emitting diode (LED) arrays, consisting of
over 400 individual LEDs, to illuminate wafers instead of the traditional fl ash lamp. This LED
array is PC controlled and can generate arbitrary waveforms over more than 4 orders of
magnitude and optical intensities of up to 10 suns. The control system allows the intensity
and shape of the light pulse be be very accurately controlled to induce near perfect steady
state or transient conditions. More importantly, the control system, along with computer
data acquisition electronics, allows the system to repeat a measurement thousands of times
to obtain high quality data that is free from spurious noise. Figure 4.3.2.20 shows the LED
assembly.
Figure 4.3.2.20: LED assembly above a test wafer
on a Sinton Consulting Photoconductance Tester.
The control software is written in LabView.
It presents a user-friendly graphical user
interface which allows the users to easily alter
all the settings to suit their needs. As results are
acquired, they are displayed on the screen in real
time. Once fi nished and results are averaged, a
series of theoretical curves can be overlayed on
the graph to determine key wafer parameters.
One of the most useful features of this software
is that it supports a database that allows users
to store the results of a single wafer test, or the
results of a multitude of tests made on several wafers in a batch tested at multiple stages
of fabrication, in a single database fi le. The database also stores all measurement settings
for every test, allowing users to recall and retest wafers with ease. This database is stored
in an excel workbook fi le, which can easily be accessed by the user for editing or to create
customized graphs and tables. The user interface is shown in Figure 4.3.2.21.
Figure 4.3.2.21: LabView user interface
for the upgraded photoconductance
tester.
The system will be upgraded in early
2006, doubling the number of LEDs and
optimising their arrangement in order to
reach intensity levels of up to 30 suns.
47

4.3.2.4 Process Engineering – Contact Silicide Formation
Contact resistance and contact adhesion is important for the formation of high-effi ciency
silicon solar cells. In 2005, we studied the formation of nickel silicide for n-type silicon solar
cells. High effi ciency n-type solar cells use both heavy boron contact diffused (BCD) and heavy
phosphorus contact diffused (PCD) regions to form the metal semiconductor regions. Effective
metallization requires the simultaneous deposition of electroless nickel and formation of nickel
silicide in both BCD and PCD regions.
In this study, we form arrays of small-area contacts, formed by laser drilling a small hole
in an oxidized silicon wafer. The resulting inverted, square-based pyramid “pits” are then
diffused with either a BCD or PCD, which are subsequently deglazed with an HF-based etch.
The diffused pits are then subjected to an electroless nickel deposition process, followed by a
350°C sintering process in nitrogen. The small pits afford a better view of the nucleation and
sintering processes compared to grooves.
Figure 4.3.2.22 shows two diffused and nickel plated pits that were formed with insuffi cient
diffusion glass deglazing. Figure 4.3.2.22a shows poor deposition in a poorly deglazed PCD
contact pit, while Figure 4.3.2.22b shows poor nucleation on a BCD pit.
Figure 4.3.2.22: Nickel plated to a pits in a silicon wafer
with (a) PCD and (b) BCD pits.
(a)
(b)
An improved deglazing process leads to improved plating
in the PCD pit, exhibiting a smooth, conformal layer of
nickel plated over the entire contact surface, as shown
in Figure 4.3.2.23a. The nucleation in the BCD is still poor, as shown in Figure 4.3.2.23b, due
to the poor affi nity of the alkali-based nickel solution to plate p-diffused surfaces.
Figure 4.3.2.33: Properly deglazed pits with a heavy a)
PCD and b) BCD.
(a)
(b)
The samples in Figure 4.3.2.22 were sintered in a
furnace at 350°C for 10 minutes in nitrogen to form
a nickel silicide at the interface between the nickel and
the heavily diffused silicon. The un-reacted nickel was
completely removed by etching and the surface of the pits examined (Figure 4.3.2.24). There
is clearly interaction between the silicon and the nickel as is evidenced by the roughening of
the surface on the PCD pit. The nickel was so badly nucleated on the BCD pit that the Si has
been drawn out from the interface such that it almost fi lls the whole pit, forming a poor-quality
physical metal-semiconductor interface.
Figure 4.3.2.24: Pits on the same sample as that shown
in Figure 4.3.2.20 after sintering and nickel removal.
(a)
(b)
Palladium activation is effective in increasing the
nucleation density of electroless nickel plating on both
p++ and n++ diffused silicon surfaces. Figure 4.3.2.25
shows PCD and BCD pits that have been well deglazed,
activated with a palladium solution and subsequently plated with electroless nickel. The
electroless nickel plate is more uniform in the palladium activated BCD pit compared to
without palladium activation.
48

Figure 4.3.2.25: Properly deglazed pits with palladium
activation: a) PCD and b) BCD.
(a)
(b)
The palladium activated pit samples were sintered at
350°C for 10 minutes and the un-reacted nickel was
removed. Figure 4.3.2.26 shows a much improved
interface in the BCD pits with palladium activation, and the roughening of the surface indicates
that a thin, fairly uniform layer of silicide has been formed at the interface. The morphology of
the PCD interface is also improved by the inclusion of the palladium activation process.
Figure 4.3.2.26: Pits on the same sample as that shown
in Figure 4.3.2.23 after sintering and nickel removal.
(a)
(b)
49

4.4 SECOND GENERATION: THIN-FILMS
University Staff:
A/Prof. Armin Aberle (group leader)
Dr. Alistair Sproul
Technical Staff:
Mark Griffi n
Dr. Bruce Beilby (part-time)
Jürgen Weber (part-time)
Research Fellows/Associates:
Frederick Bamberg (since 11/05)
Dr. Patrick Campbell (part-time)
Peter Klement (since 08/05)
Dr. Dengyuan Song
Dr. Per Widenborg
Visiting Research Fellows:
Prof. Roman Buitrago (08/05 to 11/05)
Postgraduate Research Students:
Daniel Inns (PhD)
Oliver Kunz (PhD)
Lei “Adrian” Shi (Masters, since 08/05)
Mason Terry (PhD)
Timothy Walsh (PhD)
Jürgen Weber (Masters, since 07/05)
Axel Straub (PhD, until 07/05)
Ferdi Ferdiansjah (Masters, until 12/05)
Research Assistants:
Anja Aberle
Daniel Ball
Sin Von Chan
Suzie Hunter
Daniel Kong
Undergraduate Thesis Students (4th year):
Sin Von Chan (since 07/05)
Robyn Hyslop
Matthew Linney
Roland Utama
Visiting Undergraduate Thesis Students (final year):
Stefan Vetter (10/05 to 03/06)
Mathieu Larose (06/05 to 09/05)
Vincent Vogt (02/05 to 09/05)
Shervin Motahar (until 03/05)
Undergraduate Project Students (2nd year):
Peter Gress
James Holgate
Tokushin Tanaka
Chee Hong Thoo
Undergraduate Taste of Research Summer Scholars (3rd year):
Sin Von Chan (2004/05)
Cuong Dang (2005/06)
Alexander Fattal (2005/06)
Yicheng “Sherman” Zhou (2005/06)
51

4.4.1 Summary
The primary aim of the Centre’s Thin-Film Group (or “Second-Generation Group”) is to
develop polycrystalline silicon (poly-Si) thin-fi lm solar cells on glass, an approach that is widely
recognised as being a pathway towards substantially lowering the cost of photovoltaic (PV)
solar electricity. Previous work by the Group has led to the invention of three poly-Si thinfi
lm solar cells on glass (ALICIA, EVA, ALICE), a glass texturing method (AIT), and a solar cell
metallisation and interconnection method. Based on these earlier results, the Group’s main
areas of research in 2005 have been:
• Optimisation and upscaling of the Aluminium-Induced Texture (AIT) glass texturing
method
• Optimisation and upscaling of poly-Si seed layers formed on glass by the Aluminium-
Induced Crystallisation (AIC) method
• Improvement of the open-circuit voltages of the Group’s solar cells
• Optimisation of optical absorption in our solar cells
• Optimisation of the Group’s cell metallisation and interconnection methods
• Improvement of the effi ciency of the Group’s solar cells
Voc [mV]
600
500
CSG
400
7%
8%
4%
300
200
EVA
100
ALICIA
0
Jan-00 Jan-01 Jan-02 Jan-03
Year
9%
ALICE
Jan-04 Jan-05 Jan-06
Progress with the voltages of the Group’s
thin-fi lm solar cells during 2005 has been
very good, as shown in Figure 4.4.1. A
momentous milestone that was achieved in
2005 was the realisation of our fi rst poly-Si
thin-fi lm solar cells on glass with voltages
of over 500 mV. The best cell has a voltage
of 517 mV which, to our knowledge, is a
new world record for homojunction poly-Si
thin-fi lm solar cells on glass. This result was
obtained with the EVA structure. Another
important milestone was the achievement
of an internal quantum effi ciency of over
70%, obtained using the ALICIA structure.
These advances benefi ted signifi cantly
from an improved hydrogenator (remote
plasma machine) that became available
in early 2005 in the Centre’s cleanroom
facility at Botany.
Figure 4.4.1: Evolution of the open-circuit voltages Voc of the poly Si thin-fi lm solar cells on
glass (ALICIA, EVA, ALICE) under development in the Centre’s Thin-Film Group. Also shown, for
comparison, is the Voc of CSG Solar’s poly-Si on glass technology.
Good progress was also made in 2005 with optimising and upscaling of both our AIT glass
texturing method and our AIC seed layer process. As a result of this work, AIT-textured glass
sheets and AIC-seeded glass sheets with a size of 10x10 cm 2 are now routinely produced by
the Group.
Compared to solar cells on planar glass superstrates, the use of AIT-textured glass has been
shown in 2005 to drastically improve the absorption of infrared light. This is due to two
effects, reduced refl ection losses at the illuminated cell surface and trapping of infrared light
due to the oblique path of light within the cells. The current gain possible from this improved
optical absorption is larger than 30%.
52

Another highlight of the Group in 2005 was the establishment of the Device Fabrication
Team. This step has resulted from the good progress with device voltages and the growing
need for fully metallised solar cells. This has helped to improve the effi ciency of ALICIA solar
cells to 3% in 2005.
The Group was again active in generating intellectual property, with the fi ling of provisional
Australian patent 2005901285 on an interdigitated thin-fi lm cell metallisation method
(“SAMPL”) and the entering of the national phase for two recent PCT patent applications.
Furthermore, the Group has published one book chapter, 11 journal papers, and 21
conference papers in 2005. Fifteen of these papers were presented as talks at international
conferences, including four invited talks by group leader Armin Aberle.
The Group’s thin-fi lm solar cell technologies are attracting a signifi cant amount of interest
from the solar industry and the venture capital sector. In response to this interest, the Group
has created a commercialisation roadmap in 2005 involving a business plan proposal and
layouts of a pilot line and a fi rst factory. UNSW’s commercial arm, NewSouth Innovations Ltd,
has entered negotiations with several interested parties.
4.4.2 Background Information on Thin-Film PV
It is widely agreed that thin-fi lm photovoltaics has the potential to generate solar electricity at
much lower cost ($/kWh) than is possible with a silicon wafer based technology. Silicon thin
fi lms on foreign supporting materials are particularly interesting due to their non-toxic nature,
the abundance of silicon, the huge technological experience with silicon in the microelectronics
industry, and silicon’s well-matched bandgap energy with respect to photovoltaic conversion
of sunlight. Various high-temperature as well as low-temperature approaches are currently
being investigated internationally to explore how suitable silicon thin-fi lms can be fabricated
on foreign supporting materials [4.4.1 - 4.4.5] or can be transferred onto such materials
[4.4.6 - 4.4.8]. The silicon thin-fi lm materials presently being explored for PV applications
include amorphous silicon (a-Si:H), microcrystalline silicon (µc-Si:H; grain size g < 1 µm),
polycrystalline silicon (poly-Si; g > 1 µm) and single crystalline silicon. Glass is a particularly
promising supporting material as it is cheap, transparent (enabling superstrate and/or
bifacial modules), long-term stable, and readily available. The drawback with glass sheets
is their limited thermal stability, excluding the use of lengthy high-temperature (> 650°C)
processing steps during solar cell fabrication.
The Thin-Film Group’s work focuses on polycrystalline silicon fi lms because we believe that, on
a life-cycle basis, PV modules using this material will, in the not-too-distant future, produce the
cheapest PV electricity. This assessment is based on the assumption that poly-Si thin-fi lm PV
modules will have the same excellent long-term stability as today’s standard Si wafer-based
PV modules. One of the advantages of poly-Si over a Si:H and µc-Si:H materials is the much
higher (orders of magnitude) lateral conductance of (heavily) doped thin fi lms. Therefore,
no transparent conductive oxide (TCO) is required on the illuminated solar cell surface for
cell metallisation, enabling potentially very inexpensive metallisation and interconnection
methods.
53

The most effi cient poly-Si thin-fi lm solar cells made as yet at low temperature on a foreign
supporting material have an effi ciency of 9% and were made by solid phase crystallization
(SPC) of PECVD-deposited amorphous silicon [4.4.9, 4.4.10]. The CSG technology [4.4.10] of
UNSW spin-off company CSG Solar is particularly attractive as it uses glass as the supporting
material and has already been tested extensively at the pilot line level. Pilot sized CSG modules
(aperture area of about 600 cm 2 ) have effi ciencies of over 8% and open-circuit voltages of
close to 500 mV/cell. The CSG devices have excellent light trapping properties, enabling
25 mA/cm 2 of short-circuit current with 1.5 µm thin Si fi lms [4.4.10]. This shows that poly-
Si thin-fi lm solar cells on glass merely require a minority carrier diffusion length of a few
microns in the absorber region to achieve over 8% effi ciency. The CSG technology is ready
for mass production and the fi rst factory has its offi cial opening in March 2006 in Thalheim,
Germany.
4.4.3 Motivation Behind Group’s Work
The Thin-Film Group’s research aims at the realisation of novel poly-Si thin-fi lm solar cells on
glass. One aim is to establish potentially cheaper Si deposition methods than PECVD ( ~ 30
€/m 2 for 1.5 µm thick SPC poly-Si fi lms [4.4.10]) for such cells. Another aim is to realise poly-
Si fi lms with better electronic quality (larger grain size, longer diffusion length, etc) compared
to the existing technologies, enabling higher cell effi ciency. Cell thickness is generally in the
range 1-3 µm.
4.4.4 Challenges with C-SI Thin-film Cells
The main challenges associated with crystalline silicon thin-fi lm solar cells on glass are:
• Glass is the ideal supporting material (cheap, long-term stable, transparent), but
doesn’t permit lengthy high-temperature steps. Thus, a low-thermal-budget Si
formation method is required that is cheap but nevertheless gives good-quality
c-Si.
• Glass is amorphous and hence c-Si on glass is polycrystalline. Thus, a cheap and
effi cient method for passivating grain boundaries (and bulk defects) is required.
• Crystalline silicon is a rather poor absorber of infrared light. To maintain a high
current in thin cells, an excellent light trapping scheme is required.
• The fabricated thin-fi lm material needs to be scribed into individual cells and
these need to be metallised and interconnected. Thus, an inexpensive cell
metallisation and interconnection method is required.
4.4.5 How We Tackle These Challenges
While tempered soda lime glass is the cheapest PV-compatible glass (about 10 €/m 2 ), we
use a more expensive fl oat glass (Borofl oat33 from Schott AG, Germany, about 25 €/m 2
[4.4.11]) because this glass has a better thermal stability and a thermal expansion coeffi cient
that is better matched to silicon. As a consequence, cell processing can occur at higher
temperatures and/or with higher thermal budget, providing scope for signifi cantly improved
Si material quality. To achieve light trapping, we texture the Si-facing surface of the glass plate
with the AIT (Aluminium-Induced Texture) method recently invented by us (patent application
WO 2004/089841 A1).
Low-temperature poly-Si formation on glass is realised using three different methods we
have developed. The resulting solar cells are called ALICIA, EVA, and ALICE. The fi rst two cells
are made by vacuum evaporation of Si in a non-ultra-high vacuum (non-UHV) environment,
54

whereas ALICE cells can be made by either vacuum evaporation or PECVD. Evaporation
in a non-UHV environment is interesting for PV as it is a particularly fast and potentially
inexpensive Si deposition method. It also has an excellent Si source material usage and avoids
the use of toxic gases. Because our Si evaporator is not equipped with a vacuum annealer,
no evaporated ALICE cells have been made in 2005 and instead PECVD was used for ALICE
work. For comparative reasons, we are also making solar cells by SPC of PECVD-deposited
a-Si (“PLASMA” cells). These are structurally identical to EVA cells, however, they are made by
PECVD instead of evaporation.
Rapid thermal annealing is used to
reduce the density of point defects in
our cells and to increase the fraction of
electrically active dopants. Grain boundary
and bulk defect passivation is realised by
hydrogen passivation, using either direct
plasma excitation (parallel-plate reactor)
or remote plasma excitation.
A range of methods is being explored
by us for cell metallisation and interconnection,
including shadow mask
evaporation of aluminium and the use of
photolithographic lift-off processes.
Figure 4.4.2 shows an overview of the
fabrication sequence of the thin-fi lm
solar cells on glass investigated by us in
2005.
a-Si
EVA
PLASMA
glass
SiN
Crystallisation
RTA
a-Si
ALICE
Seed
(AIC)
c-Si
(by IAD)
ALICIA
Figure 4.4.2: Process sequence of
the poly-Si thin-fi lm solar cells on glass
investigated by the Thin-Film Group
in 2005. All cells are designed for
the superstrate confi guration, i.e. the
sunlight enters the solar cells through
the glass.
Hydrogenation
Metallisation
4.4.6 Glass Texturing
We are aiming at producing polysilicon thin-fi lm solar cells on a glass superstrate, with
evaporation as a possible silicon deposition method. Thus, a glass texturing method that
produces a surface morphology that is compatible with “line-of-sight” silicon deposition is an
advantage. Use of a textured conducting oxide is ruled out because of the high temperatures
involved in our cell fabrication process. We are using Schott Borofl oat33 glass because
its thermal expansion matches that of silicon quite well. Recently we have invented a glass
texturing process called Aluminium-Induced Texture (AIT), in which an Al fi lm evaporated onto
planar glass is annealed in an inert atmosphere. High temperature transfers oxygen in a
redox reaction from the glass, largely as SiO 2 , to the aluminium. A surface texture is imparted
to the glass according to the nucleation conditions provided during this anneal. Careful control
of the HF-nitric acid based oxidation-dissolution process used to remove the reduced silicon
also affects texture morphology, since dissolution consumes both the freshly oxidised silicon
and SiO 2 in the glass.
55

During 2005, we have devoted signifi cant effort to optimising and upscaling of the AIT glass
texturing process. We found that considerable freedom is available for varying conditions
used in the AIT process, and that these conditions affect the morphology of the resulting
texture. Prime determinants are the Al layer thickness, anneal temperature profi le, as well
as HF-nitric acid ratio and immersion time. For example, Fig. 4.4.3 shows FIB microscope
images of the surface (plus cross section) of 2.3 µm thick SPC poly-Si fi lms deposited by
PECVD onto three different AIT-textured glass sheets. All were AIT-annealed at a maximum
temperature of 630°C, with differing temperature profi les. The Al thickness and HF-nitric
mixture are varied as follows: 200 nm and 1:20 for sample (a), 400 nm and 1:1 for sample
(b), 600 nm and 1:20 for sample (c). The HF-nitric immersion time was kept to the minimum
needed to remove the silicon residue.
All samples had a similar Voc of about 400 mV after the same SPC crystallisation, rapid
thermal anneal (RTA) and hydrogenation steps, despite the large variation in surface
morphology. In another experiment, AIC seed layers were prepared on the above three AIT
textures. The Al was evaporated, whereas the a-Si was deposited by sputtering. Only sample
(b) was free of pinholes, indicating its promising potential for general use with evaporated
silicon solar cells.
Sample (a) Sample (b) Sample (c)
Figure 4.4.3: Microscope images (with milled trenches to reveal the samples’ cross sections)
of 2.3 µm thick PECVD-based SPC poly-Si fi lms on three AIT-textured glass sheets. The
samples’ structure is: 3.3 mm glass /70 nm SiN /100 nm n++ /2100 nm p- /100 nm p+.
Figure 4.4.4 shows the total measured optical absorption 1-R-T (where R is the sample’s
refl ection and T is its transmission) for the three poly-Si samples, along with that for a planar
PECVD-based poly-Si fi lm with the same layer structure and treatment, in the superstrate
confi guration. These curves are compared with a randomising texture with zero refl ection
at the glass-silicon interface and no back refl ector (top curve; calculated with the software
WVASE). In these measurements, light was collected by an integrating sphere and the
Edwards mount was used. In this arrangement, the sample is placed in the centre of the
integrating sphere and the beam is collimated to illuminate only a small, central area of the
sample. All light emerging from the sample is collected, including R, T, and light from the
edges of the glass (the latter can be signifi cant for textured samples at weakly absorbed
wavelengths, particularly with thick glass). Because edge leakage reduces coupling of light
with the sample, the absorption measured at these wavelengths for the textured samples
underestimates what would be absorbed in a larger solar cell module. Thus, we can say that
the centremount-derived curves in Fig. 4.4.4 represent a conservative estimate of the true
absorption for the textured samples.
56

To illustrate the signifi cance of edge leakage, an absorption curve is also shown in Fig. 4.4.4
for sample (a), based on separate R and T measurements with the beam similarly illuminating
a small central area only. Here, edge leakage is not collected by the sphere and absorption is
overestimated. The true value of absorption therefore lies between these two limits.
Figure 4.4.4: Measured absorption
in the three 2.3 µm thick AITtextured
poly-Si samples shown in
Figure 4.4.3. Absorption attained
in decreasing order in the midband
range (around 800 nm) is for
sample (a) (separate R and T scans),
then (a), (c) and (b) (combined R+T
scans). Also shown is absorption
of a planar control sample
(lowest curve, combined R+T
scan) and calculated absorption
with random scatter (top curve).
Absorption
1
0.8
0.6
0.4
0.2
planar
0
400 500 600 700 800 900 1000 1100 1200
Wavelength (nm)
Random scattering
(calculated)
Comparisons of absorption in the measured samples are only relevant where the Si fi lm
absorbs signifi cantly more than the glass sheet. In the random model, the silicon and glass
absorb equally at around 950 nm. This means that comparisons of absorption for each
texture are best limited to the band 500-900 nm. Here, our AIT-textured samples absorb
midway between the planar and random values, see Fig. 4.4.4. Although absorption can be
seen to increase with sample roughness, the difference is not very large. This is important
because crystallisation tends to favour a low level of roughness with evaporated material. At
long wavelengths, the textured samples appear to absorb more than the random model. We
assume this is due to the WVASE modelling relying upon a T scan which includes only a small
amount of absorption at these wavelengths. This high uncertainty in absorption measurement
is passed on to the k value of the silicon, and this uncertainty is further magnifi ed by pathlength
enhancement in the random model. Long-wavelength absorption measured in the samples
is attributed to either defects and grain boundaries, or modifi cation of the glass properties
during RTA and/or hydrogenation.
As an overall estimate of the benefi t from texturing, we have calculated the 1-Sun Jsc available
from the absorption in the wavelength range 400-900 nm. For the planar sample in Fig. 4.4.4
this is 17.3 mA/cm 2 , whereas sample (b) provides 22.4 mA/cm 2 , a boost of 30%. It should
be noted that these estimations of current densities are obtained without a back refl ector.
In summary, good progress has been obtained in 2005 with fi nding AIT process parameters
that provide a texture topography that is well suited for both PECVD-based and evaporationbased
poly-Si fi lms. Furthermore, good progress has been made with upscaling of the process
to larger glass sheets. As a result of this work, AIT-textured glass sheets with a size of 10x10
cm 2 are now routinely produced by the Group.
57

4.4.7 Optimisation of AIC Seed Layers
One method to produce a poly-Si seed layer on glass that has received a lot of attention
recently is the UNSW-developed Aluminum-Induced Crystallization (AIC) method [4.4.12,
4.4.13], where Al is used as a catalyst for a low-temperature crystallization of amorphous
silicon (a-Si). Our AIC bi-layer process on glass is performed by vacuum evaporating Al onto
SiN-coated glass, followed by an exposure to air for oxide and hydroxide growth on the Al
surface. Amorphous silicon is then deposited by sputtering or PECVD onto the oxidized Al
layer. The sample is then annealed for about 12 hours at about 450°C, followed by a patented
surface preparation method that removes the Al, the Al oxide/hydroxide, and the island-like
silicon regions formed on top of the continuous AIC poly-Si fi lm.
In 2005, we performed a detailed optimisation study of AIC seed layers formed from PECVDdeposited
a-Si:H. We found that a pure silane plasma for a-Si:H deposition results, during
the AIC anneal, in blisters in the a-Si:H fi lm and localised peeling-off of the fi lm. The problem
with blistering in a-Si:H fi lms, believed to be connected to hydrogen out-gassing during
crystallisation, was minimised by the use of an argon-diluted silane plasma.
Figure 4.4.5 shows an AIC poly-Si fi lm deposited with an argon-diluted silane plasma, after Al
removal and surface preparation. A grain-induced contrast is visible in this FIB microscope
image, indicating a grain size in the order of 20 µm. Figure 4.4.6 displays the UV refl ectance
measured on this sample, together with that of a polished single crystalline Cz silicon wafer.
[Remark: Optical simulations show that for a poly-Si fi lm thicker than 70 nm, the interference
effect will not affect the measurements at 367 nm, the position of the E1 peak in c-Si.] This
poly-Si fi lm has the highest UV refl ectance fi gure of merit ever reported for an AIC poly-Si fi lm
on glass (98.9%, compared to 100% for perfect c-Si material).
Furthermore, good progress has been made with upscaling of the AIC process to larger glass
sheets. As a result of the work in 2005, high-quality AIC seeded glass sheets with a size of
10x10 cm 2 are now routinely produced by the Group.
Figure 4.4.5: FIB microscope image of a state-ofthe-art
AIC poly-Si seed layer on glass. The sample
structure is glass / SiN / AIC poly-Si (100 nm).
75
Reflectance (%)
70
65
60
55
Cz Si wafer
AIC poly-Si
Figure 4.4.6: Measured UV refl ectance of
the AIC poly-Si sample of Fig. 4.4.5. Also
shown for comparison is the measured UV
refl ectance of a polished Cz Si wafer.
50
45
210 240 270 300 330 360 390
Wavelength (nm)
58

4.4.8 Optimisation of Evaporated Solar Cells
A. EVA solar cells
EVA solar cells are made by “solid phase crystallisation of EVAporated silicon”. The deposition
of the amorphous silicon occurs at about 200°C in a non-ultra-high vacuum environment
( ~ 10-7 Torr) onto silicon nitride (SiN) coated Borofl oat33 glass sheets. To realise the
desired dopant profi les, phosphorus, boron and/or gallium are added in-situ (i.e., during the
deposition) via high-temperature effusion cells. After the silicon evaporation, the amorphous
structure is crystallised at 600°C in a nitrogen-purged tube furnace. The grain size of the
resulting cells is in the order of 1 µm, and the Si thickness is in the range of 1.5 to 2 µm.
A schematic of a crystallised EVA cell is shown in Fig. 4.4.7. A rapid thermal anneal (RTA)
process (at about 900°C for several minutes) activates dopants and anneals point defects,
and a hydrogen passivation (at about 600°C for about 15 minutes) decreases the defect
density drastically both inside the grains and at grain boundaries, and thereby enhances the
electrical performance signifi cantly (see Section 4.4.10 for more details).
p+
p-
n+
SiN
Glass
Fig. 4.4.7: Structure of an EVA solar cell on glass (not to scale).
Fig. 4.4.8: PhD student Daniel Inns
inspecting EVA poly-Si thin-fi lm solar cell
material fabricated on a planar sheet of
glass.
In 2005, the voltage of EVA solar cells has
been improved by optimisation of several
process variables. First, an increase of
the substrate temperature during the
hydrogenation step to about 600°C has
led to higher hydrogen concentrations in
the fi nished fi lms, which clearly increases
the voltages. Second, boron was used for
the base doping instead of gallium. Third,
preliminary experiments were performed
towards improved crystal growth via precrystallisation
treatments.
59

As a result of these modifi cations, the open-circuit voltage of EVA cells has been improved to
517mV in 2005. This is believed to be a new world record for homojunction poly-Si thin-fi lm
solar cells on glass. The light intensity versus open-circuit voltage characteristics (“Suns-Voc
curve” [4.4.14]) of the 517-mV poly-Si thin-fi lm solar cell is displayed in Fig. 4.4.9 (left). A twodiode
model fi t (oblique straight lines in the graph) reveals that the cell is clearly limited by n=2
recombination. The Suns-Voc curve can be converted into a “pseudo current-voltage curve”,
as shown in the graph on the right hand side of Fig. 4.4.9. This curve has a good fi ll factor FF
of 0.71.
Fig. 4.4.9: Suns-Voc curve of the 517-mV EVA solar cell (left) and the equivalent pseudo
current-voltage curve (right).
The dopant concentration of the a-Si in our research-style silicon evaporator depends
strongly on the location of the sample within the evaporator during the deposition. This would
be undesirable in solar cell manufacturing lines, but can be exploited in the laboratory for
optimising the dopant concentrations in the fi nished solar cells. As an example, Fig. 4.4.10
compares the contour plots of the emitter dopant concentration (left) and the measured
open-circuit voltage of fi nished EVA cells (right). The black squares indicate the positions where
measurements were taken. A clear correlation can be seen, suggesting that the emitter
doping level in these EVA solar cells needs to be reduced to enhance the voltage of the cells.
This is very likely due to poorer crystallisation, since high dopant concentrations are known to
cause an increased nucleation rate and thus a smaller grain size. A corresponding analysis
of the boron base doping has revealed that the best Voc performance was obtained for the
highest boron doping investigated in this set of experiments.
position y
30
a
b c d
20 0.8
1.0 2.0 3.0
3.0
10
3.4
h
f
e
g
0
-10
i j k l
-20
m n o p
-30
-30 -20 -10 0 10 20 30
position x
position y
30
20
10
0
-10
-20
470
440
-30
-30 -20 -10 0 10 20 30
position x
410
380
Fig. 4.4.10: Contour plots of (left) the relative emitter doping density (as determined by SIMS
and sheet resistance measurements) and (right) the measured Voc of the resulting EVA solar
cells.
60

Secondary ion mass spectroscopy (SIMS) measurements were performed externally to
investigate the dopant and impurity profi les in a fi nished EVA cell, see Fig. 4.4.11. The dopant
profi les for both boron and phosphorus are satisfying; however, despite the good voltage
of the cell, the impurity levels of carbon (C) and oxygen (O) are surprisingly high. Tails of
contaminants close to the air-cell interface indicate high carrier recombination in this region,
and thus a small diffusion length. This will most severely affect the minority carrier collection
and hence the short-circuit current of the cell. More work is required to fi nd and eliminate the
source of these contaminants, and to thereby further improve these solar cells.
1E21
Cell-SiN interface
Fig. 4.4.11: SIMS analysis of the
dopants (B, P) and the contaminants
O, C, and N in a recent EVA solar
cell.
concentration (atoms/cm -3 )
1E+2
1E+1
1E+1
1E+1
N
C
O
B. ALICIA Solar Cells
B
P
1E16
0 0.2. 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
ALICIA stands for “ALuminium-Induced Crystallisation Ion-Assisted deposition” [4.4.15]. The
idea behind the patented ALICIA solar cell technology is to directly (i.e., epitaxially) grow the
crystalline absorber layer on a hydrogen-terminated seed layer made by Aluminium-Induced
Crystallisation (AIC) on glass. The AIC precursor structure is glass / SiN (100 nm) / Al
( ~ 200 nm, evaporated) / a-Si ( ~ 300 nm, sputtered). This structure is annealed for 12 hours
at about 450°C in a tube furnace at atmospheric pressure and then the Al and the excess Si
are removed. The resulting average grain size is about 10 to 20 µm. For low-temperature Si
epitaxy we use IAD (Ion-Assisted Deposition) because this method is capable of high-rate Si
growth at low (i.e., borosilicate glass compatible) temperatures of about 600°C. Figure 4.4.12
schematically shows a Mesa-type ALICIA solar cell. The two IAD-grown poly-Si layers have
a combined thickness of about 2 µm and are deposited in less than 30 minutes (this time
includes sample heating, Si deposition, cooling and unloading of the sample). In recent years
we have developed an IAD process that is capable of achieving good-quality epitaxial Si in a non
-UHV environment [4.4.16]. This makes IAD Si epitaxy potentially suitable for the PV industry.
p+ layer
Rear metal
n+ layer
Absorber
layer
Seed layer
Glass
Sunlight
V, I
Front metal
SiN
One limitation of the ALICIA cell to date has been poor
light absorption. Due to the fl at surfaces of the planar
glass superstrates used so far, a great deal of light
refl ects from the front surface of the cell, and this is
a severe limitation for the cell’s effi ciency. In addition,
a large fraction of low-energy light which does enter
the cell reaches the back side, and can be transmitted
through. An aluminium fi lm has been used to date to
refl ect this light back into the cell. This should allow light
which is usually transmitted to refl ect back through
the cell before being lost, giving an increase in light
absorption and cell current.
Figure 4.4.12: Schematic of a Mesa-type ALICIA solar
cell realised by shadow-mask epitaxy (not to scale).
61

In order to trap additional light, texturing is required. This enables light to be scattered so
that it travels diagonally through the cell, giving a longer pathlength before and after the light
hits the back surface. The AIT glass texturing method (see Section 4.4.6) has been used for
making textured glass substrates. The rough surface of the resulting textured AIC seed layer
made on such glass can be seen in fi gure 4.4.13(A). Also shown (see plot B) is a cross section
of the fi nished ALICIA cell, which was grown on top of the textured seed layer.
Using the textured glass sheets gives a large decrease in refl ection, particularly for infrared
light, as shown in the left graph of fi gure 4.4.14. Considering that the rear surface of both
cells is completely covered by Al, no light can be transmitted through the cell. The increase
in external quantum effi ciency (EQE) from the texture is shown in the right graph of fi gure
4.4.14, where the longer-wavelength light is collected better by the textured cell. Figure 4.4.14
also shows that the short-wavelength EQE is better for planar cells – this is due to the planar
cell having a thinner emitter. In this case, the texture added 12% to the short-circuit current
compared to the planar device. Modelling suggests that if the emitter of the textured cell
were as thin as that of the planar cell, this texture would have given a current improvement
of 35%. A diffuse refl ector at the rear of the cell would boost the current further, as the
pathlength of long-wavelength light would be increased further.
Future work will continue to focus on the use of textures with other light trapping features like
diffuse back refl ectors.
Figure 4.4.13 A) Microscope
image (with cross section) of a
textured AIC poly-Si seed layer
on glass. The viewing angle is
about 45°. The SiN fi lm glows
white, and the grey silicon fi lm is
seen to follow the rough glass
surface. The texture dimples can
be seen on the top surface. B)
Microscope image of the cross
section of the resulting textured
ALICIA cell.
Figure 4.4.14: Comparison
of the refl ection and
external quantum effi ciency
(EQE) of a planar and a
textured ALICIA cell. The
texture reduces refl ection
at the illuminated surface
and boosts light trapping in
the Si fi lm. As a result, the
long-wavelength EQE of the
textured cell is better than
that of the planar cell.
Reflection (%)
100
80
60
40
20
0
Planar
Textured
400 600 800 1000 1200
Wavelength (nm)
EQE (%)
50
40
30
20
10
0
Textured
Planar
400 500 600 700 800 900 1000 1100
Wavelength (nm)
62
In addition to the work on textured surfaces, variation of the doping in the absorber region
of ALICIA cells has been investigated in 2005. The natural doping of the absorber region of
these cells was found to be n-type, due to a background phosphorus and oxygen content in the
silicon evaporator. Boron has been added to reduce the n-type base doping in the device, and
the effi ciency of ALICIA cells has been improved to 3% using this approach. The measured
current-voltage and power-voltage curves of this device are shown in fi gure 4.4.15. The best
voltage of ALICIA cells has been improved to 441 mV in 2005.

Current Density (mA/cm 2 )
16
14
12
10
8
6
4
2
Jsc = 14.8mA/cm 2
Voc = 403mV
FF = 0.51
Eff. = 3.0%
4
Power density (mW/cm 2 )
3
2
1
Figure 4.4.15: Current-voltage
and power-voltage curves of
the best ALICIA solar cell made
as yet. The glass substrate is
planar.
0
0
0 100 200 300 400 500
Voltage (mV)
4.4.9 Optimisation of PECVD Alice Solar Cells
ALICE stands for “ALuminium-Induced Crystallisation solid-phase Epitaxy”. The idea behind the
patented ALICE solar cell technology is to deposit the absorber onto an H-terminated AIC
seed layer at very low temperature ( ~ 200°C) as amorphous material and then to crystallise
the amorphous material in a thermal annealing step at elevated temperature (570-600°C).
This method is related to solid-phase crystallisation (SPC), however, because of the presence
of a crystalline seed layer, it is actually a solid-phase epitaxy (SPE) process. The key feature
in the ALICE process is a crystallographic transferral of information during a thermal anneal
from the seed layer into the crystallising a-Si overlayer [4.4.17]. The SPE process is a twostage
process where the fi rst step is an a-Si deposition at around 200-300°C substrate
temperature onto a hydrogen-terminated AIC poly-Si seed layer, followed by the second step
which is a thermal anneal at about 570°C substrate temperature during which the a-Si
crystallises via solid phase epitaxy. It seems possible that, compared to SPC solar cells (which
do not feature a seed layer), the epitaxial growth feature in SPE solar cells improves the
crystal quality and hence the effi ciency of the resulting solar cells.
During 2005, we investigated the structural quality as well as the diode properties of poly-Si
thin-fi lm solar cell fabricated by the SPC and SPE methods, utilizing PECVD a-Si:H precursor
material. Two post-deposition treatments, rapid thermal annealing (RTA) and hydrogenation,
were used to increase the voltages of the cells. The poly-Si fi lms were characterized with
Raman, UV refl ectance, and Suns-Voc measurements. All samples were deposited onto 3
mm thick Borofl oat33 glass substrates (Schott AG). A conventional 13.56 MHz parallelplate
PECVD machine was used for the SiN and the doped a-Si:H layers. Phosphine and
diborane-doped silane gas was used as the doping gas for the deposition of n-type and p-
type a-Si:H fi lms, respectively. SPC and SPE crystallisation anneals were performed ex-situ
in a conventional nitrogen-purged atmospheric-pressure tube furnace. The SPC anneal was
performed iso-thermally at about 600°C for 15 hours, whereas the SPE anneal had a 2-step
anneal (15 hours at 570°C, followed by 6 hours at 600°C). RTA was done at 900°C for 4
minutes. Hydrogenation was performed in a parallel-plate reactor at 13.56 MHz, using a
hydrogen plasma for 1 hour at a glass temperature of about 470°C. Table 4.4.1 summarizes
the different sample structures used in this study.
Table 4.4.1: Structures of the investigated samples.
Sample Final structure
SPE-A Glass / ~ 70 nm SiN / 200 nm p++ AIC poly-Si / 1200 nm n- SPE poly-Si /100 nm n+ SPE poly-Si
SPE-B Glass / ~ 70 nm SiN / 200 nm p++ AIC poly-Si / 1200 nm p- SPE poly-Si / 100 nm n++ SPE poly-Si
SPC Glass / ~70 nm SiN / 200 nm n++ SPC poly-Si / 1200 nm p- SPC poly-Si / 100 nm p+ SPC poly-Si
63

The main Raman peak at 520 cm -1 broadens in damaged and disordered crystalline silicon
due to relaxation of the momentum conservation in the Raman scattering process. Hence, the
full width at half maximum (FWHM) of the main Raman peak at around 520 cm -1 is a quantity
that measures the amount of crystal disorder in our poly-Si fi lms. Raman measurements
were performed with a red laser (λ = 633 nm) on samples SPE-A and SPC. As a reference,
a polished Si wafer was also analysed. The Raman peak at ~ 520 cm -1 was fi tted with a
mixed Lorentzian-Gauss function. The measured FWHM values are displayed in Fig. 4.4.16.
This shows that our poly-Si material grown on an AIC seed layer has a signifi cantly improved
crystal quality compared to SPC poly-Si fi lms grown on SiN-coated glass.
5.5
5.0
FWHM [1/cm]
4.5
4.0
3.5
Figure. 4.4.16: Raman measurements on a Si
wafer, on sample SPE-A and on a SPC sample.
The error bars are calculated with 95%
confi dence.
3.0
Si wafer SPE - PECVD SPC -PECVD
UV refl ectance can be used for evaluating the crystal quality. The total hemispherical
refl ectance was measured with our double-beam spectrophotometer (Varian Cary 5G) and
an integrating sphere, in the wavelength range 220–400 nm. The reproducibility of the UV
measurements was very good (± 0.1 absolute %). As can be seen in Fig. 4.4.17, SPE poly-Si
has a signifi cantly better UV refl ectance response than SPC poly-Si. Hence Raman and UV
refl ectance are in agreement with respect to the Si fi lm quality.
75
Si Wafer
70
SPE
Reflection (%)
65
60
55
50
SPC
Figure 4.4.17: UV refl ectance of a polished
singlecrystalline Cz Si wafer (top curve),
sample SPE-A (middle curve), and sample
SPC (lowest curve).
45
210 240 270 300 330 360 390
Wavelength (nm)
Suns-Voc measurements were performed on samples SPE-A, SPE-B and SPC at room
temperature, using illumination of the samples from the glass side (“superstrate confi guration”)
for sample SPE-A and SPC and air-side illumination for sample SPE-B. The measured Suns-Voc
characteristics were fi tted with a 2-diode model (using fi xed diode ideality factors n of 1 and
2) and a shunt resistance (Rsh). For each sample, the shunt resistance was high enough to
not affect the measured Suns-Voc curve. Figure 4.4.18 shows the measured Suns-Voc curve
for sample SPE-A, together with the 2-diode model analysis. We found that the 1-Sun Voc of
SPE-A and SPE-B are both dominated by the n=1 diode, whereas the Voc of sample SPC also
has some infl uence from the n=2 diode. As displayed in Table 4.4.2, the SPC solar cell has a
signifi cantly better 1 Sun-Voc (463 mV) than the SPE solar cells (423 and 393 mV). The 1-
Sun Voc of the SPE diodes are completely dominated by the n=1 diode.
64

The fact that the SPE diodes are n=1 limited strongly suggests that the voltage problem is
not associated with grain boundaries or the p-n junction depletion region. Investigation of
the active doping levels in the base and emitter regions of the SPE cells is in progress, but it
should be noted that the 393-mV SPE diode had no intentionally different doping level from
that of the 463-mV SPC diode.
From the results obtained in this study it is clear that SPE poly-Si material grown on AICseeded
glass has a signifi cantly better crystal quality compared to SPC poly-Si material grown
on bare (i.e., non-seeded) glass. So far, this advantage has not been translated into superior
photovoltaic performance. Analysis of Suns-Voc curves indicates that the problem lies in the
absorber region and/or the emitter region of the SPE diodes.
10..0
2-diode model
Light Intensity (suns)
1.0
0.1
n=1
Exp. data
n=2
Figure 4.4.18: Suns-Voc data
(symbols) and 2-diode model analysis
(solid lines) of sample SPE-A.
0.0
0.36
0.38 0.40 0.42 0.44 0.46 0.46
Voltage (V)
Table 4.4.2: Suns-Voc data of samples SPE-A, SPE-B and SPC.
Sample p-n junction location 1-Sun Voc n=1 Voc n= 2 Voc
SPE-A glass side 423 424 561
SPE-B air side 393 401 499
SPC glass side 463 474 523
4.4.10 Optimisation of the Rapid Thermal Annealing and Hydrogenation
Processes
Due to the fabrication process and structure of poly-Si thin-fi lm solar cells, defects are
present in the material. These defects can drastically reduce the open-circuit voltage (Voc)
and the short-circuit current (Jsc) of the device. As such, the removal of these defects is
essential and is typically done via thermal annealing and subsequent hydrogen passivation. An
additional concern is achieving complete activation of dopants within the device.
Thermal annealing is well known to dramatically reduce defects and also to activate dopants.
Traditionally this annealing has been done in a tube furnace. Rapid thermal annealing (RTA)
has replaced the tube furnace in many applications. RTA processes are ideally suited for
poly-Si thin-fi lm solar cells on glass substrates [4.4.18 - 4.4.21] as precise control of the
thermal profi le the device receives can be achieved. It is well known that hydrogen passivation
(hydrogenation) is crucial in passivating defects. In thin-fi lm devices this hydrogenation is
typically done using an RF or microwave plasma. The Voc is typically more than doubled and
the Jsc is tripled by the hydrogenation step [4.4.18 - 4.4.21]. The combination of these two
processes is critical in drastically improving poly-Si thin-fi lm solar cells.
65

In 2005, an optimisation of the RTA and hydrogenation processes was performed for three
related poly-Si thin-fi lm solar cells, using planar glass. These cell technologies are EVA, PLASMA
(“solid-phase crystallised PLASMA-enhanced chemical vapor deposited a-Si”), and ALICIA. The
fi rst two cell types are closely related, yet use different a-Si deposition methods. Both have a
grain size of about 1.5 µm, as seen in Figure 4.4.19. The third cell type features a seed layer
formed via aluminium-induced crystallization [4.4.12, 4.4.13]. The remaining cell structure is
grown on this seed layer via ion-assisted deposition. The grain size of ALICIA cells is typically
about 20 µm. Figure 4.4.20 shows a cross section of an ALICIA solar cell as measured with
an electron microscope.
Figure 4.4.19: Transmission electron
microscope image of an EVA cell showing the
crystallographic structure and grain size.
Figure 4.4.20: Transmission electron
microscope image of an ALICIA cell showing
the crystallographic structure.
Figures 4.4.21 and 4.4.22 show the change in Voc following RTA and hydrogenation as a
function of RTA time for EVA and PLASMA at 900°C plateau temperature and ALICIA at
1000°C plateau temperature, respectively. As expected, the Voc increases with longer times,
reaches a maximum and then falls off. This fall-off in Voc is believed to be due to drastic
smearing of the junction space charge region due to excessive dopant diffusion along grain
boundaries.
Figure 4.4.21: Voc as a function of time
at 900°C plateau temperature for EVA
and PLASMA solar cells following RTA and
hydrogenation.
Figure 4.4.22: Voc as a function of time at
1000°C plateau temperature for ALICIA solar
cells following RTA and hydrogenation.
66

The current response of the cell as a function of the wavelength of the incident light (internal
quantum effi ciency, IQE) provides valuable information on the performance of the solar cell.
Figures 4.4.23 and 4.4.24 illustrate the effect of the variation in RTA times at 1000°C and
hydrogenation on the IQE, respectively. With a 15-sec 1000°C RTA the peak IQE and Jsc
increase from 16% to 40% and 1.92 mA/cm 2 to 6.11 mA/cm 2 , respectively. Following
hydrogenation the peak IQE and Jsc increase further to 70% and 10.95 mA/cm 2 , a total
gain of factors 4.4 and 5.7, respectively. Hydrogenation alone without an RTA results in a gain
in peak IQE and Jsc to 41% and 6.43 mA/cm 2 , respectively.
The maximum Voc achieved in this RTA and hydrogenation study were 491 mV, 436 mV
and 435 mV for EVA, PLASMA and ALICIA, respectively. Improved understanding of defect
removal and passivation paves the way towards all three cells having a Voc well over 500 mV
and a Jsc greater than 15 mA/cm 2 on planar glass.
Figure 4.4.23: Measured IQE of ALICIA
cells before and after the 1000°C RTA
process step. RTA plateau times are 10
and 15 sec.
4.4.11 Cell Metallisation
Figure 4.4.24: IQE of hydrogenated
ALICIA cells as a function of the 1000°C
RTA plateau time. RTA plateau times are
1, 10, 15 and 30 sec. Also shown, for
comparison, are the IQE of the as-grown
cell and a hydrogenated cell that did not
receive a RTA step.
During 2005, the Thin-Film Group’s metallisation efforts took major strides forward with the
formation of the Device Fabrication Team (DFT) within the Thin-Film Group. The DFT’s purpose
is the development and implementation of metallisation and interconnection schemes for the
Group’s thin-fi lm poly-Si solar cells.
In 2005, our patented self-aligning maskless photolithography (SAMPL) technique [4.4.22]
has been applied to fabricate large-area ( ~ 4 cm 2 ) interdigitated solar cell structures (see Fig.
4.4.25). The process used to make the large-area solar cells is as follows: First, a comb-like
air-side electrode is deposited on the surface of the solar cell by evaporation or sputtering
of metal (aluminium) through a shadow mask. Next, the regions of silicon fi lm which are not
covered by the air-side electrode are etched away by a plasma process. Finally, the comb-like
glass-side electrode is formed in the etched regions using the SAMPL process.
Large-area (4 cm 2 ) thin-fi lm solar cells with reasonable effi ciencies have been fabricated with
this method. In addition, research is underway to improve the effi ciency of these devices by
optimising the electrode geometry. This is being realised by narrowing the glass-side fi ngers
by defi ning the air-side electrode using a photolithographic technique.
67

Figure 4.4.25: Schematic representation of a metallised interdigitated solar cell
(not to scale).
Furthermore, we have developed a method for interconnecting these large-area solar
cells to form mini-modules. The method is schematically illustrated in Figure 4.4.26. The
interconnection of the large-area solar cells is achieved by using a simple stencil-printing
technique: First, adjacent cells are separated by scribing through the glass-side busbar with
a laser. Next, a layer of isolating polymer is printed across the edge of the busbar. Finally, a
layer of conductive silver paste is printed over the insulating polymer to connect the glass-side
busbar of each cell with the air-side busbar of the adjacent cell. Three-cell series-connected
poly-Si thin-fi lm mini-modules with reasonable effi ciency were fabricated in this way in 2005.
glass - side
contact
air - side
conta ct
series
connection
printed busbar
~ 4 cm
cells isolated
by laser
cutting
p +
p -
n +
printed busbar
isolation
layer
p
+
p -
n +
glass
glass - side glass - side
contact contact
Cell n
Cell n+1
4 mm
air -side
contact
Si
Figure 4.4.26: Schematic
diagram of series connection
of thin-fi lm cells (not to scale).
Three interdigitated solar cells
are connected in series (left,
top view). The cross section
on the right shows a detailed
view of the interconnection
region.
68

4.4.12 References for Section 4.4
4.4.1 H. Keppner, J. Meier, P. Torres, D. Fischer, and A. Shah, Appl. Phys. A 69, 169-177
(1999).
4.4.2 T. Kieliba, S. Bau, D. Osswald, and A. Eyer, Proc. 17th European Photovoltaic Solar
Energy Conference, Munich, 2001, p. 1604.
4.4.3 K. Yamamoto, A. Nakajima, M. Yoshimi, T. Sawada, S. Fukuda, K. Hayashi, T. Suezaki,
M. Ichikawa, Y. Koi, M. Goto, H. Takata and Y. Tawada, Proc. 29th IEEE Photovoltaic
Specialists Conference, New Orleans, 2002, p. 1110.
4.4.4 P.A. Basore, Proc. 3rd World Conference on Photovoltaic Solar Energy Conversion,
Osaka, 2003, p. 935.
4.4.5 A.G. Aberle, P.I. Widenborg, A. Straub, and N. P. Harder, Proc. 3rd World
Conference on Photovoltaic Energy Conversion, Osaka, 2003, p. 1194.
4.4.6 C. Berge, R.B. Bergmann, T.J. Rinke, and J.H. Werner, Proc. 17th European
Photovoltaic Solar Energy Conference, Munich, 2001, p. 1277.
4.4.7 K. Feldrapp, R. Horbelt, R. Auer and R. Brendel, Progress in Photovoltaics 11, 105-
112 (2003).
4.4.8 A. Blakers, K. Weber, V. Everett, S. Deenapanray, J. Babaei, and M. Stocks, Proc.
19th European Photovoltaic Solar Energy Conference, Paris, 2004, p. 431.
4.4.9 T. Matsuyama, N. Terada, T. Baba, T. Sawada, S. Tsuge, K. Wakisaka and S. Tsuda, J.
Non-Cryst. Solids 198-200, 940 (1996).
4.4.10 P.A. Basore, Proc. 19th European Photovoltaic Solar Energy Conference, Paris,
2004, p. 455.
4.4.11 http://www.us.schott.com/hometech/english/products/borofl oat/
4.4.12 O. Nast, T. Puzzer, L.M. Koshier, A.B. Sproul, and S.R. Wenham, Applied Physics
Letters 73, 3214-3216 (1998).
4.4.13 P.I. Widenborg and A.G. Aberle, Journal of Crystal Growth 242, 270-282 (2002).
4.4.14 R.A. Sinton, A. Cuevas, Proc. 16th European PV Solar Energy Conference, Glasgow,
2000, p. 1152.
4.4.15 A.G. Aberle, A. Straub, P.I. Widenborg, A.B. Sproul, Y. Huang, and P. Campbell,
Progress in Photovoltaics 13, 37-47 (2005).
4.4.16 A. Straub, N.-P. Harder, Y. Huang and A.G. Aberle, Journal of Crystal Growth 268,
41-51 (2004).
4.4.17 P.I. Widenborg, A. Straub and A.G. Aberle, Journal of Crystal Growth 276, 19-28
(2005).
4.4.18 M.L. Terry, A. Straub, D. Inns, D. Song, and A.G. Aberle, Applied Physics Letters 86,
172108 (2005).
4.4.19 M.L. Terry, P.I. Widenborg, O. Kunz, and A.G. Aberle, Tech. Digest 15th International
Photovoltaic Science and Engineering Conference, Shanghai, 2005, p. 905.
4.4.20 M.J. Keevers, A. Turner, U. Schubert, P.A. Basore and M.A. Green, Proc. 20th
European Photovoltaic Solar Energy Conference, Barcelona, 2005, p. 1305.
4.4.21 A. Straub, D. Inns, M.L. Terry, Y. Huang, P.I. Widenborg, and A.G. Aberle, Journal of
Crystal Growth 280, 385-400 (2005).
4.4.22 T.M. Walsh, D. Song, S. Motahar, and A.G. Aberle, Tech. Digest 15th International
Photovoltaic Science and Engineering Conference, Shanghai, 2005, p. 706.
69

4.5 THIRD GENERATION STRAND: ADVANCED CONCEPTS
University Staff:
Dr. Gavin Conibeer (group leader)
Dr. Richard Corkish
Prof. Martin Green
Research and Postdoctoral Fellows:
Dr. Ximing Dai
Dr. Tammy Humphrey (part time to Feb 2005)
Dr. Dirk König (from June, 2005)
Dr. Kuo-Lung Lin (to Jan 2005)
Dr. Tom Puzzer (part time)
Dr. Bryce Richards (to March 2005)
Research Associates:
Yidan Huang
Edwin Pink
Dr. Didier Debuf (adjunct fellow)
Higher Degree Students:
Young Hyun Cho
Thipwan Fangsuwannarak
Chu-Wei “Scott” Jiang
Supriya Pillai
Giuseppe Scardera
Avi Shalav
Visiting Researchers:
Dr. Jean-Françoise Guillemoles
(IRDEP: joint EDF/CNRS/ENSCP lab, Paris, April to Oct 2005)
Prof. Peter Würfel (Karlsruhe University, Oct to Dec 2005)
Visiting Students:
James Rudd (U/grad thesis student 2005)
Theo Comino (U/grad thesis student 2005)
Owen The (U/grad thesis student 2005)
In 2005, work in the Third Generation Strand has continued to build on the work of 2004,
2003 and of the earlier Third Generation Special Research Centre. The concept of third
generation photovoltaics is to signifi cantly increase device effi ciencies whilst still using thin
fi lm processes and abundant non-toxic materials. This can be achieved, for example by using
multiple energy threshold approaches.
In 2005, each of the three principal project areas has shown signifi cant development: with
transfer of technology to nitride dielectrics in Si nanostructures; further quantum effi ciency
improvements in Up-conversion and application of carrier cooling theory in Hot Carrier Cells
to include sensitivity to some of the non-idealities found in real materials. Also there have been
advances in subsidiary project areas, with demonstrated increased luminescence effi ciency
using Surface Plasmon coupling; development of more robust windows based limiting effi ciency
programs; and a small resurgence of theoretical work on Quantum Antennas.
71

The parallel project with Toyota on high effi ciency thermoelectrics has made good progress,
with important developments in modelling and characterisation, which also link to the work on
Hot Carrier cells. In addition, a very signifi cant development is the successful proposal to the
Global Climate and Energy Program (GCEP) at Stanford University, for a project to develop the
Si nanostructure work to a prototype Si based tandem cell over the next three years.
4.5.1 Third Generation Photovoltaics
“Third generation” approaches aim to achieve high effi ciency for photovoltaic devices but
still use “thin fi lm” second generation deposition methods. The concept is to do this with only
a small increase in areal costs and hence reduce the cost per Watt peak [4.5.1]. Also, in
common with the silicon based second generation thin fi lm technologies, abundant and nontoxic
materials will be used. Thus these “third generation” technologies will be compatible with
large scale implementation of photovoltaics. The approach differs from “fi rst generation”
fabrication of high quality and hence low defect single crystal photovoltaic devices, which have
high effi ciencies, approaching the limiting effi ciencies for single band gap devices, but which
use energy and time intensive techniques. Third Generation aims to decrease costs to below
US$0.50/W, potentially to US$0.20/W or better, by dramatically increasing effi ciencies
but maintaining the economic and environmental cost advantages of thin fi lm deposition
techniques (see Figure 4.1.3). To achieve such effi ciency improvements, the targetted devices
aim to circumvent the Shockley-Queisser limit for single band gap cells that limits effi ciencies
to the “Present limit” indicated in Fig. 4.1.3 of between 31% to 41% (for one sun and maximum
concentration respectively). One approach multiple energy threshold devices such as the
tandem or multi-colour solar cell. We are investigating a number of approaches to achieve
such multiple energy threshold devices. [4.5.1, 4.5.2]
The two most important power loss mechanisms in single-bandgap cells arise from the inability
to absorb photons with energy less than the bandgap (1 in Figure 4.5.1) and thermalisation
of photon energy exceeding the bandgap, (2 in Figure 4.5.1). These two mechanisms alone
amount to the loss of about half of the incident solar energy in solar cell conversion to electricity.
Multiple threshold approaches can utilise some of this lost energy. Such approaches avoid
the Schockley-Queisser limit, by the exploitation of more than one energy level - in some form
– for which the limit does not apply. The limit which does apply is the thermodynamic limit
shown in Figure 4.1.3, of 67% to 86.8% (again depending on concentration).
There have been proposed three families of approaches for avoiding the Schockley-
Queisser limit [4.5.2]: (a) increasing the number of bandgaps; (b) capturing carriers before
thermalisation; and (c) multiple carrier pair generation per high energy photon or single carrier
pair generation with multiple low energy photons. Of these, tandem cells, an implementation
of strategy (a), are the only ones which have as yet been realised with effi ciencies exceeding
the Shockley-Queisser limit.
Figure 4.5.1: Loss processes in
a standard solar cell: (1) nonabsorption
of below band gap
photons; (2) lattice thermalisation
loss; (3) and (4) junction and contact
voltage losses; (5) recombination
loss.
72

In the Third Generation Strand, we are implementing strategy (a) by fabricating a tandem
cell based on silicon and its oxides, nitrides and carbides using reduced dimension silicon
nanostructures to engineer the band gap of an upper cell material. We are also tackling
strategy (b) by investigating the “Hot Carrier solar cell” in which carrier cooling is slowed such
that carriers can be extracted before thermalisation. This requires both an absorber with
slowed carrier cooling properties and collection of carriers over a limited range of energies,
such that cold carriers in the external contacts do not cool the hot carriers . Finally we are
investigating implementation of strategy (c) by up-conversion in a layer behind the Si cell. Rare
earth doped phosphors in the up-converter absorb below band gap photons and up-convert
two or more to above band gap photons which are then incident on the Si cell.
Hence all Third Generation approaches are based on tackling one or both of the “below band
gap” or “thermalisation” loss mechanisms mentioned above, as detailed below.
4.5.2 Si-Based Nanostructure tandem cells
Researchers:
Young Cho, Gavin Conibeer, Martin Green, Thipwan Fangsuwannarak, Chu-Wei Jiang, Dirk
König, Tom Puzzer, Giuseppe Scardera
Tandem cells are stacks of individual cells with different energy thresholds each absorbing
a different band of the solar spectrum, usually connected together in series. We aim to
engineer a new silicon-based material to form a top cell above a silicon cell, see Fig. 4.1.4.
This material is ‘engineered’ using a quantum dot nanostructure of silicon in a silicon based
dielectric matrix. The confi ned energy levels in the quantum dots will increase the lowest
absorption edge of the material compared to bulk silicon. If the quantum dot density is high
enough, the wavefunctions of the quantum dots will overlap to create true superlattice
minibands and increase the effective band gap of the material.
The main challenge for a nanostructure engineered material for a tandem cell is to achieve
suffi cient carrier mobility and hence a reasonable conductivity. For a nanostructure, this
generally requires formation of a superlattice with overlap of the wavefunction for adjacent
quantum wells or quantum dots; which in turn requires either close spacing between QWs or
QDs or low barrier height. Another requirement for a tandem cell element is the presence
of some form of junction for carrier separation. This can either be a grown or diffused p-n
junction or a p-i-n junction formed in the superlattice as the i-region.
As reported elsewhere [4.5.3, 4.5.4], such Si quantum dots have been fabricated by cosputtering
deposition of silicon rich layers interspersed with stoichiometric SiO 2 layers (an
application of the method of Zacharias et al. [4.5.5] to photovoltaics). On annealing at 1100°C
silicon precipitates from the super-saturated solid solution to form nanocrystals. For layers
of thickness less than about 4nm, the precipitation enters a regime of 2D diffusion in which
the dot size is accurately controlled by the layer thickness.
The increased strength of optical processes in confi ned structures due to localisation of
electrons and holes is highly advantageous for solar cell structures, as it means that only
very thin layers of these 100nm dots are required for strong absorption. With an appropriate
light-trapping scheme, thin 100nm fi lms of unconfi ned bulk Si to give high solar absorption.
Quantum dot devices of only 100nm thickness seem feasible given the increased optical
strength of the confi ned processes.
73

4.5.2.1 Alternative matrices for Si quantum dots:
Transport properties are expected to depend on the matrix in which the silicon quantum dots
are embedded. As shown in Figure 4.5.2, different matrices produce different transport
barriers between the Si dot and the matrix, with tunnelling probability heavily dependent on
the height of this barrier. Si 3 N 4 and SiC give lower barriers than SiO 2 allowing larger dot
spacing for a given tunnelling current.
Figure 4.5.2: Bulk band alignments
between crystalline silicon and its
carbide, nitride and oxide.
The barrier to tunnelling between
quantum dots is reduced for a lower
barrier height material. Considering
the tunnelling probability for electrons
in a square potential well (e.g. [4.5.6]
p244):
1.9 eV
c-Si
0.5 eV
1.1 eV c-Si 1.1 eV c-Si
0.9 eV
2.3 eV
3.2 eV
1.1 eV
4.7 eV
where m* is the bulk effective mass in the conduction band of the matrix, d is the spacing
between dots and ∆E is the energy difference between the conduction band and the fi rst
confi ned minband energy level in the quantum dot superlattice. Hence the important
parameter in determining the degree of interaction between quantum dots is m*∆Ed 2 . As
barrier height decreases, the barrier thickness for a given tunnelling probability increases,
thus requiring lower dot density for a given conductivity or higher conductivity for a given
dot density. (In addition as dot size decreases ∆E also decreases, thus increasing T e and
enhancing the effect further for smaller quantum dots) [4.5.7]. A simialr argument applies
for tunnelling probability of holes in the valence band.
Hence, transport between dots can be signifi cantly increased as the barrier height decreases
with alternative matrices. The spacing of dots would have to be closest in the oxide, nitride and
carbide, in that order. Similar deposition and quantum dot precipitation approaches should
work for all three material systems.
4.5.2.2 Si quantum dots in a nitride matrix
For the above reason, we have explored application of similar techniques to those described
in Section 4.5.2 for SiO 2 , to the growth of Si nanocrystals in silicon nitride by both sputtering
and PECVD [4.5.8]. For sputtering, growth parameters are very similar to the oxide but
with co-sputtering from a Si and Si 3 N 4 target rather than from an oxide one. Results from
HRTEM show crystalline nanocrystals in the nitride matrix.
74
In addition two separate PECVD machines have been used for the growth of Si nanocrystals
in nitride, with a regime similar to that used in oxide, of growing alternate Si rich and
stoichiometric nitride layers. Annealing is carried out again at 1100°C but with a pre-anneal
at 500°C to drive off hydrogen incorporated from the PECVD process. Again HRTEM
images showing even clearer nanocrystals have been obtained, Figure 4.5.5 [4.5.8]. The
two machines are a non-automated single plasma cluster tool and an automated dual mode
RF/microwave plasma Roth and Rau machine, thus demonstrating the transferability of the
approach both to other material systems and to other thin fi lm processes.

Further optical and electrical characterisation is underway on these nitride materials.
Other authors [4.5.9] have published data on Si QD in Si 3 N 4 demonstrating crystallinity and
increased PL energy but not using the close control of QD size that we have employed using
the layering method. To the best of our knowledge this is the fi rst time layered Si QDs in nitride
samples have been prepared using either type of PECVD growth. The automated system
also allows the possibility of growing large numbers of multilayers, which is important for
several characterisation techniques. The technique is also being investigated for large area
uniformity.
4.5.3 Characterisation
Researchers:
Young Cho, Gavin Conibeer, Martin Green, Thipwan Fangsuwannarak, Yidan Huang, Chu-Wei
Jiang, Dirk König, Edwin Pink, Tom Puzzer, Giuseppe Scardera, Thorsten Trupke
In 2005 several new techniques have been implemented to improve characterisation of
Si nanostructures. Complementary information from a range of techniques is necessary
because the very small sizes of the nanostructures involved push the resolution of the
techniques to the limit. Also complementary information on physical structure, optical and
electronic properties is required in order to optimise processing.
4.5.3.1 Physical characterisation
Recent work has continued characterisation using high resolution transmission electron
microscopy (HRTEM) and compared it with the complementary technique of secondary ion
mass spectrometry (SIMS). The latter is carried out at ANSTO, Lucas Heights, NSW, as part
of a grant supplied by AINSE.
Figure 4.5.3a is a medium resolution TEM at 120kV showing the multilayer Si nanostructure
in SiO 2 . Figure 4.5.3b is a HRTEM at 300kV showing the crystal planes in Si nanocrystals.
Figure 4.5.4 is a SIMS plot of the Si nanostructure with detail of the Si and O traces on
the right. It clearly shows the alternation of the Si and O concentrations in the multilayer
structure.
Figure 4.5.3: a) TEM image of multilayer Si
nanostructure in a-SiO2 matrix; b) HRTEM
image of Si quantum dots - highlighted by
ellipses.
Figure 4.5.4: SIMS profi le of
SiQDs/SiO2 multilayer structure
on quartz.
75

4.5.3.1.1 TEM of SiQDs in nitride
HRTEM images showing even clearer nanocrystals have been obtained, as shown in Figure
4.5.5.
(a)
(b)
Figure 4.5.5: TEM image of PECVD deposited (a) Si quantum dots in 10 bi-layers of SRN/SiNx
superlattices and (b) HRTEM lattice image.
4.5.3.1.2 TEM Sample Preparation
Transmission Electron Microscopy (TEM) remains a crucial characterisation technique for
nanostructures. TEM sample preparation, however, has traditionally been diffi cult and time
consuming. Great efforts have been made at the Centre to improve the turn around time for
TEM sample preparation. A very promising technique being explored involves a dual beam
Focused Ion Beam (FIB) system. Figure 4.5.6 shows a cross sectional TEM specimen prepared
using a FEI Nova Nanolab 200 Dualbeam FIB, the fl agship instrument at UNSW’s Electron
Microscopy Unit. This same specimen was used to produce the image shown in Figure 4.5.7.
The sample preparation time for this sample was approximately one hour, signifi cantly faster
than traditional techniques.
Figure 4.5.6: TEM Si QD specimen prepared using a dual beam FIB.
Figure 4.5.7: TEM image of Si QDs in a nitride matrix grown by dual-mode PECVD.
76

4.5.3.1.3 Grazing Incidence X-Ray Diffraction (GIXRD)
During 2005 X-ray diffraction (XRD) analysis has been developed for the Si nanostructure
samples. This gives information on crystallinity, nanocrystal size and crystal fraction and
potentially on nanocrystal size distribution, shape and any preferred orientation. The
technique is complementary to TEM analysis and has the advantage that very little sample
preparation is required.
Two approaches have been used: analysis using X-ray tube diffractometers in the School of
Materials Science at UNSW and analysis using synchrotron XRD at the Australian Nuclear
Beamline Facility, Tsukuba, Japan.
In both cases the experiments aimed to measure XRD from the thin-fi lms at grazing
Incidence (GIXRD). Figure 4.5.8 shows a result using X-ray tube for a sample with 62 bilayers
of alternating 4.5nm SRO/SiO 2 layers (sample DK24) [SRO refers to silicon rich oxide]. It
confi rms that (at least for this sample):
• The lattice constant given by the {111} peak does not vary from the bulk silicon value
by more than 0.2%.
• The average Si nanocrystal size is 4.5nm - thus for this sample, the SRO layer
thickness controlled the size of the nanocrystals.
• There was no measurable microstrain present in the nanocrystals (i.e. no small
variations of lattice constant from dot to dot).
• The crystal orientations of the dots were perfectly random.
Figure 4.5.8: X-ray tube
XRD of a 62 bi-layer,
4.2nm, SRO/SiO2
sample.
An important aspect of the analysis is comparison of X-ray tube with synchrotron XRD data
and comparison of both with information from TEM. Figure 4.5.9 shows two-theta plots of
the same Si QD in nitride sample for which the TEM is shown in Figure 4.5.7. The sample has
20 bilayers of 10nm Si rich nitride layers. It shows that:
• The average Si nanocrystal size is 4.3nm – thus for this sample the SRO layer
thickness was too thick to control the nanocrystal size.
• Lattice parameter has less than 0.1% deviation from bulk value.
• Deviation of intensities from random orientation are less than 10%.
The presence of crystalline Si is clear from these plots. In terms of quantitative analysis, the
viability of both techniques for extracting average size, strain and lattice parameters of the
nanocrystals is being examined.
77

Figure 4.5.9: Two Theta Plots
of the Si QDs in nitride sample
shown in Figure 4.5.7, using (a)
synchrotron radiation and (b) a
conventional x-ray tube source.
The peak positions and shapes
are very similar between a) and
b) in Figure 4.5.9 (except for the
peak at about 50°, which is due
to substrate), indicating that information that can be extracted from X-ray tube measurements
is similar to synchrotron, at least at present. This is particularly true for the fi rst peak at
{111}. Information on average nanocrystal size is contained in the integral breadth or FWHM
of the peaks. The less rapidly decreasing intensity with 2θ for the synchrotron is because
synchrotron X-rays are polarised. The usefulness of this for detailed analysis of high index
planes is being investigated.
There are still issues that need to be resolved in order to extract better information from
XRD. Approximate corrections to data were made to remove the effects of instrumental
FWHM broadening and other effects. However future work will involve de-convolution (the
mathematically correct procedure) of the diffractogram to remove machine-induced effects
and the subsequent Fourier transformation to obtain the full Radial Scattering Distribution
Function (RDF) for both the dots and the amorphous matrix. This represents the most
complete information that can be obtained from XRD for small crystals and disordered
materials such as amorphous silicon dioxide.
4.5.3.2 Optical Characterisation – Photoluminescence (PL)
Photoluminescence (PL) is a key technique in assessing the energy levels within quantum dot
structures. The highest PL intensities will be from the lowest radiative recombination states
within the illuminated area close to the surface. Thus it is a tool which can assess whether
quantum confi ned energy levels, greater than the band gap energy, are present. The fact that
it can be applied to samples without contacts and with minimal preparation lends it to a quick
turnaround feedback technique for processing. However, additional information with more
careful analysis and at reduced temperatures can also be obtained. This can yield specifi c
detailed information on the stability of energy levels with temperature and their relative
luminescence intensities.
4.5.3.2.1 PL on Si QDs In Si 3 N 4
Figure 4.5.10 is a comparison of PL from Si QDs in a SiO 2 matrix for various layer thicknesses
and hence QD size with Si QDs in a Si 3 N 4 matrix for a fi xed layer thickness of 4nm but
with varying numbers of layers. PL measurements were carried out at room temperature
(300 K) using excitation by a laser operating at 405nm and 50mW with detection by a
thermoelectrically cooled Si CCD detector.
78

These results are discussed further elsewhere [4.5.8] and provide tentative evidence for
quantum confi ned energy levels in Si QDs in nitride at a higher energy than in equivalent sized
QDs in oxide. However these are as yet early data. PL on different sized QDs in nitride has
not yet been obtained. These would show whether the 1.8eV peak increases or not with
decreasing dot size, an increase indicating a true confi ned energy level, no increase indicating
a fi xed defect in the interface or matrix. In addition, the intensity of the nitride peaks is
not high, probably indicating a low radiative transition probability. Nonetheless, the fact that
intensity increases with the number of SiQD layers is encouraging. Further data are being
generated.
Figure 4.5.10: Comparison of the PL spectra of
Si QDs in nitride and oxide (300K). Peaks on
the left-hand side are in the nitride matrixes and
higher peaks on the right-hand side are from the
oxide matrixes.
4.5.3.2.2 PL on Si QDs in SiO 2 - Analysis
PL spectra have been used to identify radiative
recombination energy levels in Si QD in SiO 2
nanostructures. In the model used, radiative
contributions are considered to come from one
of three sources: from quantum confi nement
(Q); from SiQD/SiO 2 interfaces (I) and from
amorphous Si clusters (α). The relative strengths of these assumed processes have been
determined by deconvoluting the spectral peaks. The 3 Gaussian deconvolutions of the PL
spectra for Q, I and α are shown in Figure 4.5.11. Initial comparison with similar measurements
on other samples suggests that the position of the Q peak depends on the size of the QDs
whereas the position of the I peak seems to be independent of QD size. Possible mechanisms
for these transitions are being assessed, including a possible recombination due to an oxygen
defi ciency that is at 6.3eV above the valence band of SiO 2 or at 1.65-1.70eV above the
conduction band of the SiQD in the ground state, see Figure 4.5.12.
Figure 4.5.11: Gaussian deconvolution of
PL spectrum for a SiQD/SiO2 sample:
peaks labelled Q, I and α are attributed to
quantum confi nement, interface states and
a-Si clusters, respectively.
Figure 4.5.12: Schematic model of the Q
and I radiative mechanisms.Also shown are
possible hopping conduction mechanisms.
Additional data on the change of the ratio of Q:I peak intensity with the degree of excess
Si in SRO samples and with anneal time are being assessed and promise more detailed
information on these mechanisms.
79

4.5.3.3 Electrical characterisation
In 2005 (as in 2004), electrical characterisation concentrated on lateral conductivity
measurements. Although vertical measurements are the more relevant for structures of
interest, lateral measurements are easier to model because they involve transport only
within layers containing Si nanocrystals whereas vertical measurements include both intralayer
and inter-layer transport across the intervening oxide layers.
Contacting for lateral conductivity measurement has been achieved by using a technique of
using Al contacts to ‘punch’ through the surface oxide, by annealing evaporated Al at 500°C
for 15 hr. This induces non-uniform spiking through the upper layers of oxide and provides
a very large surface area contact to the QD layers, as shown in Figure 4.5.13. This in turn
results in a voltage drop across the contact about a factor of 10 lower than the voltage drop
across the active region of the SiQD SLs, thus resulting in a small relative contact resistance,
Rc .
AL electrode
SiQDs/Sio 2 SL layers
Keithley 617
Electrometer
w=200-400mm
Quartz substrate
Figure 4.5.13: Schematic of sample
structure for lateral conduction
measurements.
Figure 4.5.14 shows current densities vs. applied voltage in the dark for a range of Si
concentrations in the SRO layers. It shows that conductivity generally increases as Si
concentration increases, probably because of an increase in carrier transport as the average
distance between neighbouring Si QDs decreases. Such transport would either be via a direct
tunnelling mechanism through the oxide or by hopping via defects in the oxide, as shown
schematically in Figure 4.5.12. This has been investigated further by measuring conductivity
against temperature. The slopes of the data in Figure 4.5.15 show activation energies in the
range 0.31 to 0.64eV. The variation of conductivity with Si concentration is more diffi cult to
determine. Pre-exponential factors seem to vary from 0.01 to 100Scm -1 , but extrapolation
of the slopes is not very conclusive. Work using this technique is continuing.
Figure 4.5.14:
J-V characteristics of SiQDs
superlattice samples with
various %Si concentrations.
Al contact spacing is 300 µm.
(All samples had 20 bilayers
of 5nm SRO and 10nm SiO2
layers.)
Figure 4.5.15:
Plot of conductivity vs.
temperature showing activation
energy and pre-exponential
factors for another set of
samples with nominally the
same parameters.
80

4.5.4 Modelling
Modelling is important for the interpretation of characterisation data and for designing new
structures and experiments. In 2005 modelling techniques have been developed further,
with additional improvements expected to continue.
4.5.4.1 Modelling of Si nanostructures
Researchers:
Martin Green, Thipwan Fangsuwannarak, Chu-Wei Jiang, Dirk Kőnig
Effective mass approximation approaches are being used to model expected confi ned energy
levels in experimental structures. However as the QD size decreases towards the Bohr
radius, the effective mass approximation will become increasingly inaccurate. Work is
underway to calculate the energy levels using ab-initio calculations based on density functional
theory (DFT). These will be compared to experimental data and effective mass solutions. The
ab-initio calculations are expected to be a powerful tool in modelling a wide range of potential
structures.
4.5.4.2 Simulation of HRTEM and Electron Diffraction of Si nanoparticales
Researchers:
Tom Puzzer, Giuseppe Scardera
Nanoscale structured materials and systems play a central role in the development of
Third Generation solar cell structures. The physical parameters determining the ultimate
nanoparticle properties are the elemental composition, size, external shape and internal
structures. Characterising these materials and their nanostructures is an essential part of
the research project. Although other techniques, such as X-ray diffraction and selected-area
electron diffraction, can provide accurate structural information (averaged over the excited
sample volume), they are incapable of providing information on the structure of individual
nanoparticles. The information contained in the diffraction pattern, however, extends much
further in reciprocal space than is accessible to HRTEM. Since the various types of microscope
aberrations do not infl uence electron diffraction, high resolution electron diffraction data can
be obtained without imaging artefacts.
Despite the diffi culties involved with HRTEM, it remains the most powerful technique to
examine these materials at sub-nanometre resolution. It is important to remember,
however, that the image formation system of the TEM is not perfect. The contrast
transfer function contains zeros and inversions meaning that some spatial frequencies
present in the sample are not observed in the images and other spatial frequencies
are imaged with reversed contrast. Therefore, there is a problem with unambiguous
interpretation of individual high-resolution images and only under well-defi ned conditions
may high-resolution images be naively interpreted in terms of the projected potential of
the atomic columns aligned along the beam direction.
In the past, the standard approach to extracting structural information from HRTEM
images of periodic objects is to match a series of experimental and simulated images,
usually as a function of the objective lens focus setting – a through-focus series.
Computer simulations, based on the multislice algorithm [4.5.10], have been developed
to a relatively mature level and now may be routinely used to simulate images of largearea
(semi-infi nite) uniform crystalline material for comparison with experimentally
acquired images. The calculation has two main parts, a determination of the electron
wave-function at the exit-surface of the specimen followed by propagation through the
imaging system to the fi nal image plane. 81

Generating a description of the sample in a suitable form for the multislice algorithm
can be the most diffi cult part of the simulation problem. The scattering potential of
many crystalline materials, oriented along a high-symmetry direction with respect to
the electron beam, can be described as a repetitive sequence of a small number of
identical layers and is a comparatively straightforward problem. The problem is more
diffi cult for nanoparticles, as the scattering potential is no longer strictly periodic in the x-
y plane and the number of atoms in each slice varies along the z-, or beam direction. The
particle also needs to be embedded in a suffi ciently large supercell to avoid the effects
of wraparound errors. Similar problems are encountered when simulating images of
defects and crystal surfaces.
To examine the image simulation process, a large number of images of particles of
various sizes, shapes and orientations have been performed and a library of images is
being generated. This will form the basis of an image-matching system which will be able
to identify particular crystal structures found in experimentally acquired images. As an
example, a series of images along high-symmetry orientations has been simulated for a
32Å wide truncated cubeoctahedral Si nanoparticle containing 1251 atoms. The atomic
coordinates are based on a bulk Si lattice which has been truncated along 8 sets of {111}
planes and 6 sets of {100} planes. For the (110) and (111) orientations, the particle
is rotated about the z-axis, followed by a tilt around an axis perpendicular to the z-axis.
Coordinate data is generated using Mathematica [4.5.11] and centred in a 100Å x
100Å x 60Å supercell, hardsphere
images are rendered
using the VMD package
[4.5.12] and the simulated
images are generated
using the Kirkland Multislice
code [4.5.10] at electron
beam energy of 200kV
and Cs=1mm for defocus
settings of 613 (Scherzer),
900 and 1200Å. The effects
of beam divergence, beam tilt
and defocus spread are not
included. A contrast reversal
occurs between 613Å and
900Å and the particle
appears to be at least 1
fringe larger at 1200Å than
at 613Å. The apparent
particle size is approximately
10% larger than the actual
size.
Figure 4.5.16: The highsymmetry
orientations of
the truncated cuboctahedral
Si nanoparticle. The fi rst
panel shows a hard-sphere
structural image in real space
of a particle viewed along
the (100), (110) and (111)
directions. The second panel
shows the corresponding
simulated HRTEM images.
82

4.5.5 Up-conversion
Researchers:
Avi Shalav, Bryce Richards, Thorsten Trupke, Peter Würfel, Martin Green
A photovoltaic Up-conversion (PV-UC) device is shown schematically in Figure 4.5.17. The
concept aims to absorb sub-bandgap photons in an Up-converting layer behind a bifacial solar
cell. This layer has the property of radiatively absorbing two or more long wavelength photons
and emitting a photon of higher energy above the bandgap of the bifacial solar cell. Thus the
current in the device is boosted by photons which would not normally be absorbed. It tackles
loss (1) in Figure 4.5.1 and strategy (a) discussed above in Section 4.5.1).
Figure 4.5.17: Schematic of an
Up-conversion layer, designed to
capture sub-bandgap light, behind
a bifacial solar cell.
Incident light
bifacial solar cell
up-converter
reflector
The response of such a device
depends primarily on the
luminescent quantum effi ciency
(LQE) of the up-conversion (UC)
phosphors. Using EQE measurements, the average response between 1480 and 1580nm is
about a third the maximum response at 1523nm. The best case scenario for a PV-UC device
is to assume there are minimal losses. In this case, the measured EQE will be approximately
equal to the LQE (at sub-bandgap wavelengths). Using these idealised values for the EQE, it
is possible to calculate the near infraredNIR effi ciency enhancement η uc of the PV-UC device
at NIR wavelengths under AM1.5 conditions. The total effi ciency for such a device will be
the energy conversion effi ciency of the solar cell, η, plus that of the UC enhancement η uc .
Figure 4.5.18 shows the calculated η uc values using the average value for the LQE from 1480-
1580nm for various solar AM1.5 concentrations. One of the primary reasons for this low
effi ciency enhancement is because only a narrow range of wavelengths are utilised (1480-
1580nm). Even if the PV-UC device had a LQE of 100% for this wavelength range, the value
of η uc would only be 2.4%. A number of methods to improve the spectral sensitivity (or
robustness) of PV-UC devices are being investigated. The methods include co-doped rareearth
systems and quantum dots.
4.0
0.10
Figure 4.5.18: Average LQE
and NIR PV-UC effi ciency
enhancement, η uc , versus
AM1.5G solar concentration.
The solar concentration was
calculated using the broad
absorption properties of the
phosphors (1480-1580nm).
LQE [%]
3.5
3.0
2.5
2.0
1.5
theoretical limit (46200x)
0.09
0.08
0.07
0.06
0.05
0.04
0.03
1.0
0.02
0.5
0.01
0.0
0
0.00
20000 40000 60000 80000 100000
number of suns (concentration)
83

Many lanthanide energy levels are below about 10000 cm -1 (with emission wavelengths less
than about 1000nm) making them potential UC luminescent centres for silicon PV-UC devices.
Unfortunately, closely spaced energy levels result in very large non-radiative relaxation.
Investigation of the Dieke diagram suggests that the only promising co-doped ETU system
that may improve the spectral robustness of a silicon PV-UC device is one based on Dy 3+
and Er 3+ ions. This is illustrated in Figure 4.5.19. The 6 H 7/2 and 6 F 9/2 levels of Dy 3+ can
be excited using 1100-1120nm photons, the 6 H 9/2 and 6 F 11/2 by 1290-1320nm photons,
the 6 H 9/2 by 1700-1730nm photons. These excited ions quickly non-radiatively relax down
to the 6 H 13/2 energy level. This level can also be excited by 2800-2900nm photons, but the
number of photons at these wavelengths from the solar spectrum is negligible. Nevertheless,
the 6 H 13/2 level becomes highly populated from the non-radiative relaxation from the higher
levels. This energy level is resonant with the 4 I 11/2 - 4 I 13/2 of Er 3+ . This implies that energy
transfer up-conversion (ETU) from the 4 I 13/2 to the 4 I 11/2 from the Er 3+ ions is likely if the
Er 3+ are in their fi rst excited state. This fi rst excited state can occur with 1480-1580 nm
photons (in the NaYF 4 host). Due to the rapid non-radiative relaxation of higher energy levels
in the Dy 3+ ions, and non-resonant conditions between the Dy3+ and Er3+ ions, higher order
UC processes or cross-relaxation are unlikely. A signifi cant amount of the sub-bandgap NIR
spectral irradiance can be utilised in this co-doped system.
Figure 4.5.19: ETU between Dy 3+ and
Er 3+ ions. Solid up arrows represent
GSA. The wavy lines represent rapid nonradiative
relaxation. The dotted arrows
represent the ETU mechanism. The solid
down arrow represents the resulting UC
luminescence.
In the above case, the Dy 3+ ions ‘downshift’
higher energies to lower ones which
better match the resonant conditions of
the Er 3+ ions. Although this is an energy
loss mechanism, improved UC responses
will most likely result.
Quantum dots (QDs) could also be used to down-shift higher energy photons to lower energy
photons which are within the absorption range of the UC phosphors. ZnS-passivated CdSe
and PbSe quantum dots have ideal absorption and emission properties for PV-UC QD devices
and are readily commercially available (for example from Evident Technologies). These
quantum dots have large EQE’s (over 50% for the CdSe) and high indices of refraction
compared to the phosphors, making them better matched for Si devices. Figure 4.5.20
shows typical absorption and emission spectra for PbSe quantum dots. The energy transfer
will probably occur by radiative emission (from the quantum dot) followed by absortpion by the
UC phosphor. Direct coupling between the PbSe and UC phosphors resulting in ETU may also
occur and may prove to be a dominant UC mechanism.
84

absorption
emission
absorption, emission [au]
Figure 4.5.20:
Absorption/emission
from three different PbSe
quantum dot samples. The
emission of the quantum
dots coincide with the
absorption of Er 3+ doped
phosphors.
1200 1300 1400 1500 1600 1700
wavelength [nm]
4.5.6 Hot Carrier Cell
The concept underlying the hot carrier solar cell is to slow the rate of photoexcited carrier
cooling, caused by phonon interaction in the lattice, to allow time for the carriers to be
collected whilst they are still at elevated energies (“hot”) and thus allow higher voltages to be
achieved from the cell [4.5.13]. This approach thus tackles the major PV loss mechanism of
thermalisation of carriers (loss (2) in Figure 4.5.1 and strategy (b) discussed above in Section
4.5.1). In addition to an absorber material that slows the rate of carrier relaxation, a hot
carrier cell must allow extraction of carriers from the device through contacts which accept
only a very narrow range of energies (selective energy contacts).
Within the Third Generation Strand, the parallel project, funded by Toyota, on thermoelectric
and energy conversion devices has strong parallels with the Hot Carrier cells project. They
both require the selective energy contacts discussed below but in addition the Hot Carrier
cell requires an absorber in which carrier thermalisation is very signifi cantly slowed from the
picosecond timescale of normal semiconductors, to closer to the nanosecond timescale of
carrier recombination.
Experimental work in the Third Generation Strand is currently focussed on selective energy
contacts using resonant tunnelling structures based on a similar Si quantum dot approach
to that discussed in Section 4.5.2. Theoretical work is directed at investigating mechanisms
for slowing carrier cooling by modifying phononic band structures in nanostructure
superlattices.
85

4.5.6.1 Selective Energy Contacts
Researchers:
Dirk König, Chu-Wei Jiang, Gavin Conibeer, Martin Green
For the hot carrier cell to be effective “hot” carriers, as described above, must be collected
from the absorber over a very small energy range with selective energy contacts. This is so
that only a small amount of their excess energy above the band edge is lost in cooling to the
contact temperature. In thermodynamic terms, the carriers are thus collected with a very
small increase in entropy. Ideally this collection would be isoentropic using mono-energetic
contacts.
Double barrier resonant tunnelling contacts are being investigated as selective energy
contacts, with quantum dots providing a discrete energy level between two insulating barriers.
This will give conduction strongly peaked at the discrete energy level. The total energy fi ltering
of a quantum dot based structure is required of a selective energy contact rather than 1D
energy fi ltering because the 1D energy fi ltering in a quantum well resonant tunnelling device
is only effective for carriers with momenta entirely perpendicular to the plane of the well
[4.5.14]. Carriers with components of momenta away from this normal can be transmitted
even if their total energy is outside the range of the energy fi lter. Hence work in the Centre
is focussed on resonant tunnelling structures using quantum dots or other discrete total
energy confi ned centres as the resonant centres. These would give the required total energy
fi ltering. Such a fi lter should exhibit negative differential resistance (NDR).
A signifi cant proof of concept was achieved in 2004 (as reported in the 2004 annual
report) with negative differential resistance observed at room temperature for a double
barrier quantum dot structure [4.5.15]. The device structure is based on our Si quantum dot
technology discussed previously.
In addition, modelling of the 1D resonant tunnelling has been carried out with a model
developed for perturbations in the position of a defect in an oxide barrier [4.5.16]. The theory
is being extended to a 2D model.
4.5.6.1.1 Conductive atomic force microscopy
In 2005, further characterisation of the resonant tunnelling structures has been carried out
using conductive atomic force microscopy (CAFM) through a collaboration with Dr Chris Pakes
at Melbourne University. CAFM is a powerful tool for investigating the transport properties
of nanostructures. Data are obtained by modifying the local band profi le - on a scale of a few
nanometres - using an applied bias at the conductive probe tip. This technique can be used to
map the current-voltage characteristics of a single layer of Si quantum dots, below an oxide
layer of a few nanometres, at a very high areal resolution. Hence it can be applied to the
mapping of resonant tunnelling sites on a sample. The results so far indicate that CAFM is
useful for verifying the location and density of quantum dots non-destructively. Samples with
thinner oxide layers are now being produced to increase the tunnelling current to allow lower
bias CAFM scans and hence to estimate the resonant energy levels more accurately.
4.5.6.1.2 Optically assisted I-V
Conventionally, tunnelling IV measurements on a MIS structure involve a strong bias fi eld so
as to obtain hot electrons at the Selective Energy Contact / Si interface, which increases
the tunnelling current density such that it can be detected. For a resonant structure, the
resulting dI/dV characteristic would show a blurred negative differential resistance (NDR)
feature.
86

However with a monochromatic optical excitation of high intensity, this shortcoming can be
circumvented. If hot carriers can be generated near to the barrier, a hot carrier population is
created at the Selective Energy Contact. This also requires that the optical generation rate
within the semiconductor is high enough and/or that the current is measured within a few
picoseconds of the massive generation of hot carriers. Using a tuneable monochromatic
light source the energy range of the hot carrier population can be chosen for probing the
relevant energetic portion of the Selective Energy Contact. In addition, in order to collect the
electrons on the metal electrode, a weak bias fi eld may be necessary. By keeping this fi eld
weak, the band bending of the barrier is minimized, resulting in a maximum overlap of the
subband DOS on both sides of the barrier.
As a proof of concept, measurement has so far only been carried out with a broad band
Xenon light source. It comprises:
• A quartz halogen illumination source.
• Short pass fi lter (= 1000 nm): cutting off IR in order to minimize heating of sample
• Long pass fi lter ( = 495 nm): preventing optically assisted thermionic emission of
electrons over the oxide barrier (which would falsify the IV measurements)
• Plane-convex lens
• Faraday box used for IV measurements with a lid with a quartz window.
Figure 4.5.21: Optically assisted
I-V measurement apparatus.
A mesa sample with a single layer of Si QDs, with no p-n junction, was measured, as shown
in Figure 4.5.22. The area of each mesa = 1/16 cm 2 and this contains about 10 10 Si QDs.
The sample is nominally the same as those used to obtain negative differential resistance in
normal I-V during 2004 (see 2004 Annual report).
Figure 4.5.22: Sample
structure for optically
assisted I-V measurements
(the same as that
used in earlier dark I-V
measurements).
The enhanced current at all biases shown in Figure 4.5.23a for optically assisted
measurements as compared to dark I-V, is evidence for an enhanced hot carrier population
near the contact. The increase cannot be explained purely by an increase in Fermi-distribution
with temperature as the temperature increase above room temperature is calculated to be
only a few tens of degrees, suggesting a non-equilibrium hot carrier population exists. There is
also tentative evidence for a resonance in the data in the dark at a bias of about 3.5V (Figure
4.5.23b) which, under illumination, both increases in magnitude and decreases in required
87

ias to about 2.2V (Figure 4.5.23c). This is further tentative evidence for the collection of
hot carriers, as the energies appropriate for collection by the contact are generated at lower
bias voltages with optical assistance. However it should be pointed out that measurements
are made at present without the presence of additional fi lters to control the spectrum of
light illuminating the sample. In subsequent measurements, such fi lters - either providing a
narrow range of energies or a variable sharp long wavelength pass cut-off – will allow more
distinct quantitative data to be collected.
Figure 4.5.23: a) Dark and illuminated, or optically assisted, I-V measurements.
Detail of b) dark and c) illuminated I-V traces.
4.5.6.2 Slowed carrier cooling
Researchers:
Gavin Conibeer, Jean-Francois Guillemoles, Martin Green
Slowing of carrier cooling has been observed in bulk semiconductors by several authors, but
only at very high illumination intensities – typically equivalent to 250 to 2500 suns [4.5.17].
However, the reduced dimensionality in nanostructures offers a promising route for such a
role as this restricts the number of acoustic phonon modes available. because of the Brillouin
zone folding that occurs as a result of the periodicity of the superlattice. Slowed carrier
cooling in QW superlattices has been demonstrated experimentally [4.5.17, 4.5.18] and is
described as an enhancement of the phonon bottleneck effect. Some of the current authors
describe the likelihood of an increased effect in QD superlattices elsewhere [4.5.19]. This
work is principally theoretical at present.
4.5.6.2.1 Modelling of phononic band structures
Investigation in this area is currently focussed on obstructing the phonon decay mechanisms
for carrier cooling. This potentially has relevance to any device which relies on reducing
thermal transport, including thermoelectrics.
The current work [4.5.19] stems from the realisation that hot carriers lose their energy by
scattering with optical phonons which in turn build up a hot non-equilibrium population. Thus,
the critical feature in the overall carrier cooling is the rate of decay of the hot optical phonons.
It has been identifi ed by other workers that the principal and perhaps only mechanism for this
is the decay of an optical phonon into two longitudinal acoustic (LA) phonons of energy half
that of the optical phonon and of equal and opposite momenta.
In some bulk semiconductors, with a large difference in their anion and cation masses, there
can be a large gap between the highest acoustic phonon energy and the lowest optical phonon
88

energy. In a few cases – such as InN – this gap can be larger than the highest acoustic energy
and hence prevent operation of the optical phonon decay mechanism described above, see
Figure 4.5.24.
Figure 4.5.24: Phonon dispersion for InN
[4.5.20] in which E LO >2E LA such that LO
→ 2LA (only) is forbidden. (E LO ; LA ) denote
longitudinal optical and acoustic phonon
energies.)
The current work is investigating achieving a similar effect in less exotic materials possibly
based on silicon, by exploiting the refl ection that occurs at the mini-Brillouin zone boundaries
of nanostructure superlattices. This opens up mini-gaps in the phonon dispersion for those
acoustic phonon energies which satisfy the Bragg condition. Figure 4.5.25 and Figure 4.5.26
show phonon dispersions modelled using a nearest neighbour elastic continuum model
based on Rytov calculations, for quantum well (QW) and quantum dot (QD) superlattices
respectively.
Figure 4.5.25: Acoustic phonon dispersion
and DOS calculated using an elastic
continuum model based on the Rytov
formulation for QW and barrier thicknesses
of 5 lattice spacings and ratio of acoustic
impedances of 4.
Figure 4.5.26: Acoustic phonon dispersion
for multiple QD array showing a folded
dispersion with mini-gaps in all directions
in real and reciprocal space, hence giving
true mini-gaps in the DOS.
89

The phonon dispersions show that if the superlattice structure is engineered correctly, the
mini-gaps can in principle be arranged such that they prevent the decay of optical phonons by
interrupting the same mechanism. However the density of states (DOS) in Figure 4.5.25 and
Figure 4.5.26 indicate that complete gaps in the DOS for all directions in reciprocal space
only occur for the QD superlattice. Hence this mechanism of slowing carrier cooling should
only be present in QD structures. Experimental evidence for this in the literature is being
assessed and effects on effi ciencies calculated. However, to achieve such effects in practice,
the structure would need to be fi nely tuned.
A further effect under investigation is that of the QD interface with the matrix, on phonon
dispersion. Figure 4.5.27 shows that with a soft interface the mini-gaps group into doublets
with a larger gap in the centre. This would improve the ease of fi ne tuning the QD superlattice
such as to block the optical phonon decay. Further work on modelling such interfaces is
underway.
Figure 4.5.27: Dispersion curve of
acoustic phonons for 1nm3 QDs in a
superlattice with 1nm spacing between
QDs – incorporating soft interface modes
between QDs and matrix.
Finally, some progress has been made
towards predicting the effi ciencies that a
Hot Carrier cell might achieve using the
non-ideal properties of existing materials
[4.5.21]. Preliminary computations show
that, at the illumination level used for the
experiments in [4.5.17, 4.5.18] (equivalent to about 2500 suns), effi ciencies of 50% could be
achievable. This is in spite of thermal losses in state of the art materials such as the multiple-
QW structures discussed elsewhere [4.5.17, 4.5.18], even though these have a non optimal
band gap of 1.5 eV. This result compares to a calculated 54% effi ciency at these concentrations
without any thermalisation losses at all [4.5.13]. Hence, at these concentrations the loss to
thermalisation for existing materials is not large. However, these fi gures assume perfect
energy selection at the contacts. Therefore, as operation at lower concentrations would be
preferable and because of the diffi culties in the fabrication of optimal contacts, it is desirable
to search for further reduction in carrier cooling and/or a reduction in the threshold injection
levels at which this occurs. Phononic band gap engineering in superlattices seems a potential
route to achieving this.
4.5.7 Supporting project areas
There are three projects associated with Third Generation Strand work but not directly
concerned with either of Si nanostructures, Up-converters or Hot Carrier cells. These are
continuing work on limiting effi ciency computer programs, coupling of light with surface
plasmons and quantum antennae.
90

4.5.7.1 Limiting efficiency programs
Researchers:
James Rudd, Gavin Conibeer, Jean-Françoise Guillemoles
In the 2004 annual report progress on development of these programs was reported to the
stage of initial fabrication of a graphical user interface (GUI). In 2005 this GUI was developed
further and tested for a range of cell types. This work was carried out in a Taste of Research
project and in an undergraduate thesis project. Screenshots of the resulting GUI are shown
in Figure 4.5.28.
Figure 4.5.28: GUI for limiting effi ciency programs.
The programs were originally written in C++. The thesis work has transferred this to C.net
and tidied up much of the code. The program works on a particle balance approach which
equates the number of incident photons with the electron current plus the number of emitted
photons. These calculations are performed using the generalised Planck expression for
photon fl uxes:
Solving this equation requires use of numerical integration methods as the -1 term in the
denominator introduces a singularity preventing the use of simple integration routines, such
as Simpson’s rule [4.5.22].
91

In addition the thesis project investigated ways to automate the input parameters to the
program – a signifi cant challenge for multi-energy level cells – and developed empirical
relationships based on previously run scenarios. The formulae used to describe these
relationships are in turn giving indications of the physical processes behind the calculations.
The program is now at the stage of testing by members of the Third Generation strand.
4.5.7.2 Surface Plasmons
Researchers:
Supriya Pillai, Kylie Catchpole, Thorsten Trupke
Surface plasmons are the oscillation of conduction electrons in metal particles. The excitation
of surface plasmons is a promising way of increasing light absorption in thin-Si based devices.
According to the generalised Kirchoff’s law, enhanced absorption can also lead to enhanced
emission. Thus the work is also of interest in Si light emission for effi cient light emitting diodes
and is discussed in Section 4.6.
Silver particles are formed on the surface by evaporation followed by annealing. As reported
in Section 4.6, the seven fold enhancement in electroluminescence and spectral response
(Figure 4.5.29 and Figure 4.5.30 respectively) is very promising for signifi cant enhancement
of absorption in the visible range. Work is continuing on optimisation of silver particle size
and shape and of shifting the peak of absorption to more appropriate wavelengths, using an
overlayer of a high refractive index layer such as ZnS.
EL / Photocurrent Enhancement
8
7
6
5
4
3
2
1
EL
SR
0
300 400 500 600 700 800 900 1000 1100 1200 1300
Wavelength(nm)
Enhancement
8
7
6
5
4
3
2
1
with Ag
with Ag+ZnS
0
900 1000 1100 1200 1300
Wavelength (nm)
Figure 4.5.29: Enhancement plots showing absorptance and emission from 95nm thin SOI
devices.
Figure 4.5.30: EL enhancement plot showing the shift in the peak using ZnS overcoating.
Enhancement of absorption is likely to be of key importance in Si based nanostructure devices.
This is because the devices will be thin and hence adequate absorption will be challenging
even if the materials behave as direct bandgap devices, which is likely due to localisation of
electrons and holes due to quantum confi nement. Hence the approach is currently being
investigated for Si nanostructure materials.
92

4.5.7.3 Antenna Collection of Solar Energy
Researchers:
Richard Corkish, Samantha Wong, Gavin Conibeer
Research on the potential use of antennae for conversion of solar energy to direct current
electricity was revived during 2005, with a focus on the ultimate effi ciencies that could be
achieved.
Coherent, polarised, narrow-band radio waves may already be received and converted to
direct current by rectifying antennae, or “rectennas” but the conversion of broad spectrum,
incoherent, unpolarised solar radiation is more challenging. This work has continued to derive
insights from the fi eld of radio astronomy, where the accurate detection of such radiation is
well established. In particular, we have used the model of the “Dicke radiometer” to show that
the electrical noise output of an antenna receiving solar radiation can be represented as that
of a resistor at the sun’s black body temperature.
The effi ciency of conversion of the noise power from a resistor has been studied already
by others but our attempts to reproduce published results in a key paper repeatedly failed
and discussions with the author led to a correction (http://summa.physik.hu-berlin.de/
~ sokolov/).
That work investigated the rectifi cation by a diode, at one temperature, of the electrical noise
from a resistor at a higher temperature. Using the detailed balance method, the calculation
showed that the effi ciency of a system with a diode rectifi er as a heat engine must always be
less than the Carnot effi ciency. The reason for this thermodynamic irreversibility is that even
when no work is done, heat transport takes place between the heat baths.
The Carnot effi ciency increases with temperature. For an assumed black body temperatures
of 6000K for the sun and 300K for the receiver, the Carnot effi cieny equals 0.95. Figure
4.5.31 is a plot of the effi ciency of an ideal rectenna against the current drawn from the
device, with a peak effi ciency at 48.81%. (Dimensionless current is shown as this does not
depend on geometrical factors.)
Camot Efficiency = 0.95
Figure 4.5.31: Rectenna effi ciency vs.
dimensionless current for a Carnot effi ciency
of 95%.
0.5
0.4
While signifi cant practical challenges
remain for the possible implementation of
solar rectennas, the Centre’s work has now
developed a model to predict their ultimate
effi ciency.
Efficiency
0.3
0.2
-0.1
0
-4.5 -4 -3.5 -3 -2.5 -2 -1.5 -1 -0.5 -0
Normalised Current (dimensionless)
93

4.5.8 Concluding remarks for the Third Generation section
The preceding sections show the signifi cant advance in all the Third Generation projects in
2005. Advances include the successful transfer of Si nanostructure technology from Si QDs
in oxide matrix to a nitride matrix – both for sputtering and for PECVD - and preparation for
transfer to a silicon carbide matrix. This should facilitate signifi cant improvements in electrical
transport bringing the goal of a wider band gap Si based material much closer. This work has
also been instrumental in leveraging signifi cant additional funding via the Global Climate and
Energy Project, which started at the end of 2005.
Up-conversion has moved beyond the proof of concept of 2004, to demonstrate improved
quantum effi ciencies and progress towards sensitising the devices to photons between the Si
bandgap energy and the absorption energy of erbium at 1500nm. Proof of concept of these
is expected in 2006 as are moves towards other Up-conversion approaches.
Hot Carrier cells have advanced in the characterisation of selective energy contacts using
conductive AFM and optically assisted I-V. This work has been in parallel with the Toyotafunded
thermoelectric and energy conversion project. There has also been development of
more sophisticated theory on reduction of carrier cooling in nanostructure superlattices.
This work has started to fi nd application in prediction of hot carrier cell effi ciencies in real
non-ideal material systems.
The associated projects have continued to develop with the limiting effi ciency computer
programs advancing to the testing stage, seven fold enhancement of electroluminescence
from surface plasmons and an ideal effi ciency for quantum antennae of 48% predicted.
94

References for Section 4.5
4.5.1 M. A. Green, “Third Generation Photovoltaics: Ultra-High Effi ciency at Low Cost”
(Springer-Verlag, 2003).
4.5.2 J. Nelson, “The Physics of Solar Cells”, Imperial College press, 2003.
4.5.3 E-C. Cho, Y.H. Cho, T. Trupke, R. Corkish, G. Conibeer, M.A. Green, Proc. 19th
European Photovoltaic Solar Energy Conference (Paris, June 2004) 235.
4.5.4 E-C. Cho, Y.H. Cho, R. Corkish, J. Xia, M.A. Green, D.S. Moon, Asia-Pacifi c
Nanotechnology forum, (Cairns, 2003).
4.5.5 M. Zacharias, J. Heitmann, R. Scholz, U. Kahlere, M. Schmidt, J. Blasing, Appl. Phys.
Lett. 80 (2002) 661.
4.5.6 K. Boer, “Survey of Semiconductor Physics”, van Nostrand Reinhold, 1990.
4.5.7 M.A. Green, E-C. Cho, Y. Cho, Y. Huang, E. Pink, T. Trupke, A. Lin, T. Fangsuwannarak,
T. Puzzer, G. Conibeer, R. Corkish, Proc. 20th European PVSEC, p3 (Barcelona, June
2005).
4.5.8 Y. Cho, E-C. Cho, Y. Huang, C-W. Jiang, G. Conibeer, M.A. Green, Proc. 20th
European PVSEC, p47 (Barcelona, June 2005).
4.5.9 B-H. Kim et al, Appl Phys Lett, 86 (2005) 091908.
4.5.10 Kirkland, E. J., “Advanced Computing in Electron Microscopy” Plenum Press, New
York (1998).
4.5.11 Wolfram Research, Inc., Mathematica, Version 5.2, Champaign, IL (2005).
4.5.12 Humphrey, W., Dalke, A. and Schulten, K., “VMD- Visual Molecular Dynamics” J.
Molec. Graphics 14 (1996) 33-38.
4.5.13 P. Würfel, “Solar Energy Conversion with Hot Electrons from Impact Ionisation”, Sol.
Energy Mats. and Sol. Cells. 46 (1997) 43.
4.5.14 G.J. Conibeer, C-W. Jiang, M.A. Green, N. Harder, A. Straub, Proc. 3rd World Conf.
on Photovoltaic Solar Energy Conversion, Osaka, Japan (2003).
4.5.15 C-W. Jiang, E-C. Cho, G. Conibeer, M.A. Green, Proc. 19th European Photovoltaic
Solar Energy Conference (Paris, June 2004) 80.
4.5.16 C-W. Jiang, M.A. Green, E-C. Cho, G. Conibeer, J Appl Phys, 96 (2004) 5006.
4.5.17 A.J. Nozik, C.A. Parsons, D.J. Dunlary, B.M. Keyes, R.K. Ahrenkiel, Solid State
Comm. 75 (1990) 247.
4.5.18 D.J. Westland et al, Solid Sate Eelectronics, 31(1988)431
4.5.19 G.J Conibeer, J-F. Guillemoles, M.A. Green, “Phononic band gap eng. for Hot Carrier
solar cell absorbers”, Proc. 20th EPVSEC (Barcelona, June 2005) p35.
4.5.20 Davydov et al., Appl Phys Lett, 75 (1999) 3297.
4.5.21 J-F. Guillemoles, G.J. Conibeer, M.A. Green, “Phononic Engineering with
Nanostructures for Hot Carrier Solar Cells”,Proc. 15th PCSEC (Shanghai,
Oct 2005).
4.5.22 J. Rudd, G. Conibeer, J-F. Guillemoles, “User Friendly Software for Calculation
of Limiting Cell Effi ciencies for Research on Multijunction Solar Cells”, Proc. “Solar
2005” Australia and NZ Solar Energy Society conf. (Dunedin NZ, Nov 2005).
95

4.6 SILICON PHOTONICS RESEARCH GROUP
University Staff
A/Prof. Jianhua Zhao (group leader: integrated LEDs)
A/Prof. Thorsten Trupke (group leader: silicon laser)
Prof. Martin Green
Prof. Stuart Wenham
Research Fellows
Dr. Aihua Wang
Adjunct Fellow
Dr. K. Catchpole
Research Staff
Dr. Robert Bardos
Dr. Tom Puzzer
Research Assistant
Guangchun Zhang
Research Student
Supriya Pillai
Technical Staff
Jules Yang
Collaborators
Susan Angus, Dr. Fay Hudson, A/Prof. Andrew Dzurak, Centre of Excellence for Quantum
Computing, UNSW
Prof. Peter Würfel, University of Karlsruhe
4.6.1 Thick SOI LED Devices
Research on Silicon On Insulator (SOI) Light Emitting Diodes (LEDs) continued in the Centre
during 2005. Originally most of these SOI LEDs were fabricated on thin silicon layers aiming
for a few nanometre silicon thickness to achieve quantum confi nement effects. The benefi t
of such quantum confi nement is the increased light emission and absorption effi ciencies, and
the ability to emit shorter wavelength light than the band-edge emission. However, no such
quantum confi nement has been demonstrated to date due to the diffi culties in precise control
of the processing conditions.
In 2005, emphasis was changed to the fabrication of SOI LEDs on thicker silicon layers of
about 1.3 µm thickness. This was expected to result in better electrical performance for
these LEDs, and also increased electroluminescence (EL) effi ciency. Figure 4.6.1 shows a
schematic diagram of the cross sectional view of the light emitting diode design.
97

Figure 4.6.1:
Cross sectional view of the SOI
light emitting diode.
These thick silicon LEDs gave stronger EL signals, which allow more accurate measurement
due to the limited sensitivity of our infrared sensors. Images of these SOI LEDs were taken
using the Olympus microscope in combination with a CCD camera, in which the silicon CCD
can catch the light up to 1 µm wavelength, enough to see the short wavelength end of the
emitted infrared light from the SOI LED. From these images, we observe the EL distribution
and the direction of light travel in these SOI LEDs.
Figure 4.6.2(a) is the illuminated top view of a thick SOI LED, LED016-1-B2-D1, which has a
small 300 µm by 24 µm SOI silicon island area with about 1.3 µm thick active silicon layer. The
device is formed by the middle rectangular silicon island (dark) and the two aluminium contact
pads (bright) apparent in Figure 4.6.2(a). The gate aluminium line was deliberately removed
for the EL observation. Figure 4.6.2(b) shows the infrared image of the EL distribution of the
same device. As seen in Figure 4.6.2(b), the light is totally blocked in areas which are covered
by aluminium fi lm, seen in Figure 4.6.2(a) as the white areas.
(a)
(b)
Figure 4.6.2: (a) the illuminated top view of a SOI LED and (b) the infrared images of the EL
distribution of the same LED at 190 mA bias current.
98
Due to the resistance in the narrow aluminium lines towards both ends of the silicon island,
the current density was reduced in these areas. This resulted in a uniform bright centre
luminescence and gradually darker areas toward both ends as seen in Figure 4.6.2(b).
However, it is also observed that one end of LED is brighter than the rest of the areas in
this fi gure. The other end of the silicon island is shaded by an aluminium pad, and hence is
completely dark in Figure 4.6.2(b). It is clear that some light travels along the device and is
emitted out at the end of the device. The light travelling towards the end but not coming out of
the top surface of the silicon island, it should be mostly travelling in a direction parallel to the
surface. However, some of the light parallel to the surface may be scattered up towards the
observer at the end of the silicon island. It is also seen that the end light spot is stronger than
the centre part. This indicates that the light parallel to the surface has a higher concentration
than the vertically emitted light, since light is accumulated along the silicon island. The device
seems to be a good emitter for light parallel to the surface.

Some of these SOI LEDs were designed into larger 1 mm2 devices for easier detection by
the infrared sensor. Figure 4.6.3 shows the EL distribution from one of such large device,
LED016-1-E1-D4. Unfortunately, this design had a little too narrow line width and line spacing.
This resulted in very narrow and uneven metal lines in the fabricated devices, which increased
resistance of the metal lines. Hence, the EL distribution is rather non-uniform as apparent in
Figure 4.6.3. Some of the metal lines were even broken, and resulted in the completely dark
spots in the centre of the device.
Figure 4.6.3: EL distribution of a 1 mm2 large-area LED at
100 mA bias current.
The EQE (external quantum
effi ciency) of the SOI LEDs with
the thick silicon layer were
measured with a Ge photodiode.
The Ge sensor has 0.25 cm
diameter and was placed 1.5
cm away from the SOI LED. The
highest EQE in fi ve measured
devices was about 1.9x10-5 for the small LEDs. The 1 mm2 large LEDs were designed for
higher and more accurate EQE measurement. Unfortunately, the above-mentioned processing
non-uniformity problem caused lower average EL effi ciency.
Figure 4.6.4:
Measured EQE
of SOI LEDs.
8.0E-05
LED016-1-E1-D4
Current(A)
7.0E-05
6.0E-05
5.0E-05
4.0E-05
3.0E-05
2.0E-05
1.0E-05
0.0E+00
0.00
0.10 0.20 0.30 0.40 0.50 0.60 0.70
Vo(V)
Figure 4.6.5: Illuminated I-V of large
LED under one sun.
4.6.2 Illuminated I-V Characteristics of SOI
LEDs
The illuminated I-V characteristics of some
1 mm2 large SOI LEDs were tested on the
Centre’s I-V measurement system, Dark-Star,
under standard one sun illumination conditions.
A typical measured I-V curve from a large SOI
LED is shown in Figure 4.6.5.
Our standard high effi ciency PERL solar cells
have very low metal contact areas of only 0.25% and low metal grid
shading areas of 2% of the total cell area. However, the large SOI
LEDs have 20% metal contact areas and 50% metal shading loss.
Hence, it was not a surprise that the SOI LED had relatively low Voc
of 582 mV due to the signifi cantly increased contact recombination
and shading losses. However, the SOI LED had a rather high shortcircuit
current density of 7 mA/cm 2 , for a 1.3 µm thin and fl at silicon
layer without any light trapping and antirefl ection coating.
99

4.6.3 Design of SOI Silicon Waveguide
One of the goals at the LED group is to demonstrate light propagation within an all-silicon
circuit by using a SOI silicon waveguide. The design of such a SOI waveguide is shown in Figure
4.6.6. The purple T shaped structure in Figure 4.6.6 is the silicon waveguide with 6 µm silicon
waveguide width. At each end of the T-shaped waveguide, there is a SOI LED diode, with the
same structure as the ones shown in Figures 4.6.1 and 4.6.2.
1
2
3
4
5
6
7
8
9
Silicon Island
Boron Diffision
Phosphorus Diffusion
Silicon Thinning
Contact Holes
Metalization
Metalization
Silicon formation
Phosphorus isolation lines
Figure 4.6.6: SOI silicon waveguide
design. The purple line represents
the silicon layer. One of the LEDs is
used to emit light into the T-shaped
silicon waveguide, while the other 2
diodes are used to detect the light
received. The dimensions are in
microns.
4010
As shown in Figure 4.6.6, one LED is used to emit light into the silicon waveguide, while the
other 2 diodes are used to detect the light transmitted through the silicon waveguide. Other
controlling structures are also incorporated along the SOI waveguide, such as control gates
and pn-junction isolation rings. These devices are designed to cut-off electrical signals to
make sure that any signal detected is optical.
The fi rst silicon waveguide devices were fabricated in 2005. Figure 4.6.7 shows an image
of the T-shaped silicon waveguide and the LED or the detector at the end of the waveguide.
Each of these LED and detector devices had good electrical performance if independently
measured. However, when the LED is forward biased and emitting light, no signal could
be detected by the reverse-biased photo detector at the end of the waveguide. Given the
relatively low effi ciency of light emission and of light collection as well as the high absorption in
the silicon waveguide for the emitted infrared light, it is believed that the signal arriving at the
detector may be too small, in the pA range, to be measured by our equipment at present.
100

(a)
(b)
Figure 4.6.7: (a) Top view of the T-shaped intersection of silicon waveguide; (b) top view of a
LED (or a detector) at one end of the waveguide.
Again the infrared CCD camera was used to take photos of the light pattern in this waveguide
system. Figure 4.6.8 shows some of these photos. Here, the LED in the waveguide unit was
also forward biased. Similarly to the image in Figure 4.6.2(b), Figure 4.6.8(a) shows infrared
light emission from the left-side LED. However, no light was observed within the waveguide
in this photo.
(a)
(b)
Figure 4.6.8: The emitted infrared light images (a) for the LED at 100 mA forward bias; (b)
for the entire silicon waveguide system with prolonged signal accumulation, and with a low
external illumination to show the aluminium patterns.
In Figure 4.6.8(b), a very long accumulation period for the image was selected, which gave
a very brightly glowing LED emitter on the left. A low bias illumination was also added in to
show the aluminium patterns, which indicate the location of the LED and detectors. In Figure
4.6.8(b), the light from LED travelling inside the silicon waveguide could not be observed.
However, a bright spot at the T-intersection of the waveguide is observed. This indicates that
the light is indeed travelling along the silicon waveguide.
In future research, we plan to improve the light emission and detection effi ciencies for these
LED and detectors. These may be achieved using photonic crystals or plasmon structures.
The light absorption in the waveguide should also be reduced. This may be achieved by using
SiNx as the waveguide material rather than absorptive silicon.
101

4.6.4 Photonic Crystals in SOI LEDs
Photonic crystals are geometric structures in which the refractive index varies periodically
on a length scale that is comparable to the wavelength of light, i.e. on the order of several
hundreds of nanometers. One dimensional (1D), two-dimensional (2D) and three dimensional
(3D) photonic crystals are distinct in the number of directions the refractive index varies
periodically. An example of a very simple 1D photonic crystal is a Bragg mirror, often used
in laser cavities, which is a one dimensional periodic structure of laterally extended layers of
different refractive indices.
The photonic density of states in a vacuum is continuous, similar to the electronic density of
states in a vacuum. In a photonic crystal structure, the photonic density of states is modifi ed,
resulting in allowed and forbidden energy bands, respectively, similar to the well known
electronic bands in a semiconductor. In this sense photonic crystals can be considered the
optical analogues to semiconductors. The modifi ed photonic density of states has a dramatic
infl uence on the optical properties of the photonic crystal, i.e. on its absorptance, refl ectivity
and emissivity. In the SOI LED project we aim to utilise the properties of photonic crystal to
enhance the light emission effi ciency from SOI light emitting diodes.
Due to the thickness of these devices of typically only a few hundred nanometers, 2D photonic
crystals are the method of choice. The idea is to texture the active area of SOI LEDs with a
regular array of holes in order to enhance the photonic density of states in the wavelength
range around 1150nm, (where spontaneous emission from silicon is most effi cient), which
should enhance the spontaneous emission probability. Combined with scattering effects, this
should lead to a dramatically enhanced external luminescence quantum effi ciency of these
devices. Figure 4.6.4.1 shows a theoretically calculated photonic band structure for such an
array of air holes in silicon. Whether the enhanced photonic density of states falls within the
emission band of silicon thus critically depends on the size of the holes and the periodicity
of the photonic crystal lattice. Experimentally a seventy fold enhancement of the emission
from 2D photonic crystal structured SOI layers has been demonstrated at low temperatures
(T=80K) by Zelsmann et al. [Zelsmann, M., et al., Appl.Phys.Lett. 83, 2542 (2003)]. We aim
to demonstrate a similar improvement of our light emitting diodes at room temperature.
Fig. 4.6.4.1: Theoretical photonic band structure
for a two dimensional array of air holes in silicon
with a lattice parameter a [after Zelsmann et
al.].
102

The photonic crystal processing of SOI LEDs is carried out in collaboration with the Centre
of Excellence for Quantum Computing, UNSW, where a fi rst photonic crystal array was
successfully produced on the surface of a bulk silicon wafer. In that process a PMMA photo
resist is deposited on the surface of an oxidised polished silicon wafer. Electron Beam
Lithography (EBL) was used to write the desired holes pattern into the PMMA resist and the
pattern was then transferred successively into the top SiO2 layer end then into the silicon
using Reactive Ion Etching (RIE). The etched holes were more than 200nm deep. An AFM
image and an SEM image of this test structure are shown in Fig.4.6.4.2 and Fig.4.6.4.3,
respectively.
Fig. 4.6.4.2: AFM image of a photonic
crystal test structure on the surface of
a polished bulk silicon wafer.
Fig. 4.6.4.3: SEM image of the photonic
crystal test structure on the surface of
a polished bulk silicon wafer.
For initial photoluminescence measurements on these test structures, larger patterned
areas of deeper holes are ideally required. Attempts to create larger areas highlighted some
practical experimental problems with the EBL patterning process as a result of the so called
proximity effect. The latter is a result of the increased effective dose that high density features
receive due to back-scattering of the incident beam. The negative impact of the proximity
effect on large area test structures is shown in Fig 4.6.4.4: the circles on the edge of the
patterned area are clearly distinct features but due to an increased dose the features have
joined together in the centre of the pattern. The proximity effect may be alleviated by using
lower accelerating voltages during the EBL. Figure 4.6.4.5 shows an example of a larger
patterned area written with a lower (5kV) accelerating voltage.
103

Additional experimental diffi culties were encountered in the attempt to increase the depth
of the holes to about 1µm, which is the thickness of the thickest and currently most effi cient
SOI LEDs. Different attempts are currently being made to achieve structures with a higher
aspect ration. In this context a number of different RIE recipes have been investigated and
alternatively the possibility to use a chromium mask in order to transfer the EBL pattern
into to the silicon layer has been investigated with some success. First photoluminescence
studies on SOI layers textured with photonic crystals are planned for the near future.
A further interesting aspect of the photonic crystal work within the SOI group is the recent
observation by S.G. Cloutier et al. [S.G. Cloutier et al.,Nature Materials 4, 887 (2005)] that
optical gain associated with a so called A-centre could be observed at a wavelength of
1278nm at lower temperatures from silicon on insulator samples patterned with photonic
crystal structures. Given the signifi cance that a successful demonstration of optical gain in
an electrically pumped silicon device would have, we will carefully investigate whether this
emission is also observed from photonic crystal structured SOI LEDs.
Fig. 4.6.4.4: Negative impact of the proximity
effect on larger area photonic crystal
structures.
Fig. 4.6.4.5: Improved periodicity
and reduced proximity effects due to
reducing the acceleration voltage during
the EBL patterning of the PMMA.
104

4.6.5 Improved SOI LEDs Using Surface Plasmons.
A very effective way to enhance the external luminescence quantum effi ciency from silicon light
emitting diodes is the application of light trapping schemes. Light trapping is conventionally
used in photovoltaic devices to increase the average optical path for incident light, resulting
in better absorption of weakly absorbed light. According to Kirchhoff’s law, an enhanced
absorption corresponds to an enhanced emission. Light that is trapped within a planar device
due to total internal refl ection can be coupled out after multiple paths through a textured
device. The benefi cial effect of light trapping schemes on LED performance has been
demonstrated in high effi ciency bulk silicon light emitting diodes [M.A. Green et al., Nature
412, 805 (2001)].
However, for thin silicon on insulator devices, traditional light trapping methods such as
texturing with pyramids, cannot be used. The excitation of surface plasmons is a promising
alternative way of increasing light absorption and emission from thin-Si based devices. An
eighteen fold absorption enhancement at 800nm wavelength of silicon on insulator (SOI)
devices was reported by Stuart and Hall [H.R. Stuart and D.G. Hall, Appl.Phys.Lett. 73, 3815
(1998)]. Our work aims at increasing the absorption / emission form thin fi lm Si devices at
longer wavelengths.
Surface Plasmon effects are observed on thin silicon layers covered with an array of
nanometer sized metal islands deposited on the surface and separated from the active silicon
layer by a very thin ( ~ 30nm) spacer layer (SiO2). A simple method of silver deposition followed
by annealing is used to deposit Ag nanoparticles on silicon-on-insulator (SOI) light emitting
devices. The fact that the entire island deposition is a low temperature process allows metal
islands to be deposited onto fi nished fully processed devices. Fig.4.6.5.1 shows a typical SEM
image of the nanometer sized silver islands.
Figure 4.6.5.1: SEM photo of the deposited
nanometre silver islands for the surface plasmon
effect.
Changes in the optical device performance were
monitored experimentally by measuring the
spectral electroluminescence (EL) emission and
the spectral response (SR) of SOI LEDs before and
after island deposition. The optical enhancement
is calculated as the ratio of the SR and EL
signals, respectively after and before deposition
of the islands. This combination of EL and SR is
ideal because it provides information about the
optical path lengths enhancement in different
spectral ranges above (SR) and near and below
(EL) the band-gap of silicon. As reported earlier,
our initial proof of concept studies showed only
a 30% enhancement in the electroluminescence
measurements from our Silicon-on-insulator
devices.
105

With further optimisation of the experimental conditions, specifi cally a much thinner isolation
layer between the islands and the silicon layer, a 7 fold enhancement in the electroluminescence
and spectral response measurement has been demonstrated. Fig.4.6.5.2 shows the spectral
emission (EL) from the same SOI LED before and after island deposition.
10
9
8
with Ag islands
without Ag islands
EL Signal (a.u)
7
6
5
4
3
2
1
0
900 950 1000 1050 1100 1150 1200 1250 1300
Wavelength (nm)
Figure 4.6.5.2: Electroluminescence
spectra from the same 95nm thin
SOI LED measured under identical
experimental conditions before (red)
and after (blue) deposition of the silver
islands.
The resulting EL enhancement is shown together with the SR enhancement of the same
device in Fig.4.6.5.3. The enhanced emission intensity due to surface plasmon effects is also
very clearly visible in an electroluminescence image taken with a very sensitive silicon CCD
camera (see Fig. 4.6.5.4) from a device which was partially covered with silver islands on
the left hand side. The image clearly shows the much brighter emission from that half of the
device.
Figure 4.6.5.3: Enhancement of the
spectral electroluminescence intensity
(red curve), calculated as the ratio of
the two spectra shown in Fig.4.6.5.2.
The enhancement of the photocurrent
response is shown for comparison (black
curve).
EL / Photocurrent Enhancement
8
7
6
5
4
3
2
1
EL
SR
0
300 400 500 600 700 800 900 1000 1100 1200 1300
Wavelength(nm)
Figure. 4.6.5.4: Electroluminescence image of a ~ 95nm
thick 1mm x 1mm SOI LED under forward bias. The left
hand side of the device was coated with silver islands.
Clear evidence for enhanced emission from the coated
area is observed.
106

Another interesting aspect of the Plasmon work is the shifting of the enhancement peak by
using a layer of high refractive index material (ZnS) overcoating on the metal nanoparticles,
as shown in Fig.4.6.5.5. Our results show a 70nm shift in the enhancement peak at longer
wavelengths as calculated from the results of the EL measurements. The enhancement in EL
could have signifi cant benefi ts in increasing the effi ciency of Si LEDs and the additional shift
observed would lend more tunability to the operating wavelength of the LEDs. Absorption in
metals is a source of concern for these applications, but the results presented here already
account for the absorption in metals and hence look encouraging. One of the major advantages
of this approach is that the Ag islands can be deposited at the fi nal stage of device processing
and hence no processing incompatibilities are involved.
Enhancement
8
7
6
5
4
3
2
1
with Ag
with Ag+ZnS
0
900 1000 1100 1200 1300
Wavelength (nm)
Figure 4.6.5.5: EL enhancement plot
showing the shift in the enhancement
peak due to application of a ZnS
overcoating.
107

108

4.6.6 Photoluminescence-Based Characterisation of Silicon
Researchers:
Robert Bardos, Thorsten Trupke
Collaborators (internal):
Malcolm Abbott, Florence Chen, Jeff Cotter, Aihua Wang, Jianhua Zhao
Collaborators (external):
Daniel MacDonald, Andres Cuevas, ANU, Canberra
Adam Lorenz, Evergreen Solar
Thomas Roth, Martin Schubert, Stefan Glunz, Wilhelm Warta, ISE, Freiburg Germany
Background
The determination of the injection level dependent effective excess carrier lifetime τ eff (∆n)
by photoconductance (PC) measurements is an important experimental technique that is
used at our Centre and in most photovoltaics research centres around the world for the
characterization of silicon samples. Recently, it has been established theoretically and
experimentally that the PC technique can be subject to signifi cant experimental artefacts
especially at low excess carrier concentrations. Such artefacts can result from excess
charges accumulated in space charge regions via the so called depletion region modulation
(DRM) effect, by temperature variations upon intense illumination and by minority carrier
trapping. These effects can be so dominant, that PC measurements have been claimed to
be unsuitable for the characterization of the effective lifetime e.g. in thin fi lm silicon samples.
In silicon wafers these effects generally make the accurate determination of the effective
lifetime at low to moderate injection levels impossible.
In our photoluminescence (PL) lifetime project we aim to demonstrate that quasi steady state
photoluminescence (QSS-PL) lifetime measurements are advantageous in many regards and
therefore represent a viable alternative to more established techniques such as QSS-PC.
QSS-PL measurements are insensitive to the above mentioned artefacts and also much more
sensitive at low excess carrier concentrations. QSS-PL is thus the most suitable technique to
measure the minority carrier lifetime at low excess carrier densities.
In a separate recent development we have demonstrated that PL imaging is an extremely
sensitive and fast technique that provides spatial information about the material quality in
large area silicon wafers. The response from internal and collaborating external research
groups and from industry partners indicates that within a very short timeframe this technique
is set to revolutionize the characterisation of silicon samples in the PV industry.
Theory
Photoluminescence is the emission of light as a result of an external optical excitation. In
a semiconductor, luminescence is emitted when electrons and holes recombine radiatively,
i.e. by transferring the excess energy released in the recombination process to an emitted
photon (Fig.4.6.6.1). Luminescence is thus the reverse process to photogeneration. In a
simplifi ed model the measured PL signal I PL,rel is given by the product of electron and hole
concentrations, n e and n h respectively and can be written:
I
2
,
= A ⋅ B ⋅ n ⋅ n = A ⋅ B ⋅ n ⋅exp(
∆η
/ kT)
PL rel
i
e
h
i
i
with B the radiative recombination coeffi cient and Ai a scaling factor, which takes into account
that in most cases PL signals are measured in relative units only. On the right hand side, the
luminescence signal is expressed as a function of the separation of the quasi Fermi energies
∆η which, in a good solar cell, is directly linked to the cell voltage V by eV=∆η. This direct
relation between the PL signal and the voltage of a solar cell allows PL measurements to be
interpreted as contact-less voltage (also referred to as implied voltage) measurements (see
also section on Suns-PL further below).
109

Figure 4.6.6.1: Luminescence
is emitted by semiconductors if
electrons from the conduction
band and holes from the valence
band recombine radiatively, i.e. by
giving up the excess energy to an
emitted photon (γ).
Experimental
A very sensitive QSS-PL lifetime system was established in the laser controlled area LG24.
A large area luminescence sensor was incorporated into a commercial Sinton Consulting
PC bridge next to the PC coil, which allows QSS-PL and QSS-PC measurements to be carried
out on the same wafer and under identical experimental conditions and thereby a direct
quantitative comparison of these techniques. A high power LED array, that replaces the
fl ash lamp commonly used in PC testers, is used to illuminate the samples. A photo of that
set-up is shown in Fig.4.6.6.2. Upgrade to a 16-bit data acquisition system allows a large
dynamic range of light intensities (and thus injection levels) to be scanned with one single
shot. Convenient data acquisition and analysis are accomplished by custom built LabView
software. The raw experimental data from a typical quasi steady state photoluminescence
experiment are shown in Fig. 4.6.6.3. The graph highlights two of the main advantages of
using a solid state light source (i.e. an LED array). Firstly, waveforms can be arbitrarily long,
up to tens of seconds, thereby allowing true quasi steady state conditions to be reached even
in high quality material with long carrier lifetimes. Secondly, arbitrary temporal light intensity
profi les can be generated (in this case a triangular waveform), which is particularly important
for the self consistent methods to be described further below. Another advantage of using
a computer controlled solid state light source is that it allows automated repetitive signal
averaging, which results in a better signal to noise ratio.
Figure 4.6.6.2: Experimental set up for
combined PL and PC measurements. The
PL sensor is incorporated into a commercial
photoconductance set up which allows
convenient calibration of relative PL signals
against absolute PC signals.
Figure 4.6.6.3: Typical data set from a PL
lifetime experiment. The PL signal (red) and the
incident light intensity (black) are measured
simultaneously.
110

Surprisingly high sensitivity of PL lifetime measurements
Using PL as a sensitive technique to determine small excess carrier concentrations in silicon
may at fi rst sight appear diffi cult given silicon’s indirect band structure and the resulting low
radiative recombination coeffi cient. However, the automated signal averaging, the geometry
of our PL setup and the use of a home built, low noise, high gain preamplifi er allowed effective
lifetimes to be determined down to injection levels < 10 9 cm -3 in 1 Ωcm p-type wafers (see
Fig. 4.6.6.5) with data acquisition times of only a few seconds [4.6.1], which is orders of
magnitude below the detection limit of a QSS-PC set-up used at our Centre. Using that QSS-
PC set-up, lifetime measurements become extremely noisy and inaccurate at injection levels
< 10 13 cm -3 . Due to this somewhat unexpected sensitivity, PL lifetime measurements can
also be used to determine very low effective lifetimes in quasi steady state mode and are by
no means restricted to high quality fl oat zone silicon.
The development of a computer controlled solid state light source for lifetime measurements
has also improved the sensitivity and accuracy of PC measurements, because the same
averaging techniques as used for PL can also be applied to PC measurements. While these
improvements render PC measurements at low injection levels less noisy they cannot avoid
some more fundamental limitations of PC measurements to be discussed now.
Depletion region modulation effect
In QSS-PC measurements at low to moderate injection conditions, the so-called depletion
region modulation (DRM) effect leads to a sharp artifi cial increase of the apparent minority
carrier lifetime on samples with a diffused or induced junction. Similar effects are expected
in any other experimental technique in which the measured signal is determined by the sum
of the minority and majority carrier concentrations. In contrast, theoretical analysis shows
that QSS-PL measurements should be largely unaffected by the DRM effect [4.6.2]. This was
proven experimentally by investigation of two 1Ωcm p-type wafers, one with Phosphorous
diffusions the other one with Boron diffusions on both sides [4.6.1]. Theoretically the artefacts
due to the DRM effect are expected only for the Phosphorus-diffused sample. Fig.4.6.6.4
shows the lifetimes of the Boron diffused sample determined from PC and from PL. Very good
agreement is observed between PL and PC with no indication in both measurements of an
infl uence of the DRM effect. In contrast, the PC lifetime from the Phosphorus doped sample
shown in Fig.4.6.6.5 increases steeply at injection levels < 5x10 12 cm -3 (up to an apparent
lifetime of 13ms, not shown in Fig.4.6.6.5). This increase is consistent with the theoretically
predicted effects resulting from the DRM effect. As theoretically predicted, the PL lifetime is
unaffected by these effects.
Figure 4.6.6.4: Effective lifetime from
QSS-PL (red) and from QSS-PC (black)
for a 1Ωcm p-type wafer with Boron
diffusions on both sides. Very good
agreement is observed between the
lifetimes from PL and from PC over a
wide injection level range.
111

Figure 4.6.6.5: Effective lifetime
from PL (red and pink) and from PC
(black) for a 1 Ωcm p-type wafer with
phosphorus diffusions on both sides.
The PC data are heavily infl uenced by
the DRM effect at injection levels <
10 13 cm -3 . Very small injection levels

Fig.4.6.6.6: Analysis of
experimental (coloured curves)
and corresponding simulated
(black lines) QSS-PL lifetime data
for different calibrations of the
relative PL signal into absolute
values for ∆n(t). Only the correct
calibration (red curve) gives
consistent results for the rising
and the falling branches of the
waveform, thereby allowing a very
accurate calibration of ∆n(t).
Variation of a calibration constant in the analysis of experimental data until hysteresis
effects vanish in τ eff (∆n) plots are thus a very convenient way to calibrate QSS-PL lifetime
measurements. The self consistent calibration approach is particularly useful for QSS-PL
measurements, where the calibration of the generation rate G(t) is fairly straightforward
because a spectrally narrow light source is used. The self consistent calibration of relative
QSS-PL data into absolute ∆n(t) now allows QSS-PL measurements to be carried out
independently from other experimental techniques. The previous requirement of a separate
QSS-PC calibration measurement is thereby avoided. Our work on self consistent calibration
methods has also improved the accuracy of PC lifetime measurements.
Suns-PL a contactless alternative to Suns-Voc
Because the luminescence signal is directly linked to the open circuit voltage via the separation
of the quasi Fermi energies, PL measurements can be interpreted as a contactless voltage
measurement. We have shown that based on this idea simultaneous measurements of the
incident light intensity and of the PL signal yield the equivalent of Suns-Voc measurements,
with the advantage that these so called Suns-PL measurements can be performed on wafers
at any stage of the processing sequence and are not restricted to solar cell structures. To
demonstrate the validity of this approach, we investigated a shunted bifacial double sided
buried contact silicon solar cell and simultaneously measured the open circuit voltage, the
PL and the varying incident light intensity [4.6.6]. Fig.4.6.6.7 shows the resulting Suns-Voc
and Suns-PL curves, i.e. the incident light intensity plotted as a function of the open circuit
voltage (Suns-Voc) of the cell and as a function of the separation of the quasi Fermi energies
(the latter determined from PL). The two prominent features from the Suns-Voc curve, i.e.
the shunt at low voltages and a kink in the curve at larger voltages are both reproduced in
the Suns-PL measurement. Very good overall agreement between the curves is observed,
which demonstrates the feasibility of the method. In a recent project the Suns-PL technique
was applied extensively during the development and the testing of an edge isolation method
for small area solar cells [4.6.7] highlighting the strong infl uence of edge recombination
especially at low voltages.
113

Fig 4.6.6.7: Comparison of a
Suns-Voc measurement with
a Suns-PL measurement on
a bifacial silicon solar cell. The
good agreement between
the curves demonstrates the
feasibility of using the Suns-
PL technique to obtain implied
IV curves on unfi nished solar
cells.
PL imaging
QSS-PL or QSS-PC lifetime
measurements only provide
information about the injection
level dependence and/or about
the temperature dependence
of the minority carrier lifetime in a silicon wafer with no information about spatial variations
within the wafer. Photoluminescence imaging is a recent and very exciting development at
UNSW that overcomes this limitation. The idea here is to take a laterally resolved “photograph”
of the luminescent emission from silicon wafers under homogeneous intense illumination
[4.6.8, 4.6.9] in order to obtain an image of local variations in the material quality. The local
luminescence intensity refl ects the local carrier concentration and is directly correlated with
the local minority carrier lifetime. Importantly , the above mentioned robustness of QSS-
PL measurements against artifacts and the high sensitivity of PL, which where previously
demonstrated only for spatially averaged QSS-PL lifetime measurements, apply to PL imaging
in the same way. The worldwide fi rst PL imaging set up suitable to measure large area silicon
wafers was established and successfully demonstrated at UNSW during the second half of
2005. Fig.4.6.6.8 shows a PL image taken on a 8.5x8.5 cm 2 multicrystalline silicon wafer,
measured with a data acquisition time of only one second. In Fig.4.6.6.8, the local PL intensity
was calibrated into an effective minority carrier lifetime. Comparison with a lifetime image
from a Carrier Density Image measured at the Fraunhofer Institute in Freiburg showed very
good agreement between the two independently calibrated measurements. Such quantitative
PL imaging will allow local IV curves to be calculated in analogy to Suns-PL measurements
and it also allows local defect rich areas to be identifi ed. The data also shows that typical
photovoltaic material with lifetime variations on the order of a few tens to hundreds of
microseconds can be imaged in only one second.
Fig 4.6.6.8: Example of a PL image of
a 302µm thick polished 1.2Ωcm SiN
passivated p-type multi-crystalline
silicon wafer. The colour bar gives the
local effective minority carrier lifetime
in µs. This image was taken with a data
acquisition time of only one second!
114

In qualitative PL imaging, only the relative variation of the PL intensity across the sample is
investigated. Such qualitative imaging was applied extensively by the buried contact group of the
Centre and within a short period PL imaging was established as a standard characterisation
technique. In fact the initial PL imaging set-up has been in such heavy demand that setting up
of a second PL imaging system is planned for the fi rst half of 2006. A further improvement
of the data acquisition speed by a factor 50 is anticipated for this new system. Within the
fi rst few months of applying PL imaging as a process monitoring tool especially the buried
contact group identifi ed various serious problems with standard processing sequences,
that had previously been used for years [4.6.10, 4.6.11]. The fact that PL imaging is fast,
simple to use and applicable to unfi nished cells turned out to be an invaluable combination
in this context. Some examples of process induced defects identifi ed with PL images are
shown in Fig.4.6.6.9. Various collaborative research projects with industry partners (see for
example [4.6.12]) aim at demonstrating the capabilities of the system and at increasing the
awareness in the PV community regarding the potential of this new technique. A mid-term
goal is the demonstration of PL imaging as an industrial in-line process monitoring tool. The
data acquisition speed in PL imaging is several orders of magnitude higher than in comparable
imaging or mapping methods, making PL Imaging the only experimental technique that can
provide high resolution images of the material quality from large area wafers in a matter of
seconds.
Figure 4.6.6.9: Examples of effective process monitoring using PL imaging. Problems with
standard processing sequences that could be identifi ed include amongst various others (from
left to right): wafer handling using tweezers, furnace contamination; cracks. Each PL image
is taken with a data acquisition time of only one second. Some more examples of process
induced defects that were identifi ed with PL imaging are shown in Section 4.3.2.
Theoretical work
One complication in the analysis of QSS-PL lifetime measurements arises from the fact
that at high carrier densities (>10 16 cm -3 ) the PL intensity no longer follows the product
of electron and hole concentrations as given by Eq.1. It is well established and theoretically
understood that the Auger coeffi cients in silicon decrease as a function of injection level due
to the reduced Coulomb attraction between electrons and holes at high carrier densities.
The reduced attraction of electrons and holes at high carrier densities also affects radiative
recombination, which leads to an injection level dependence of the radiative recombination
coeffi cient B(T,∆n). While we had earlier described the temperature dependence of B(T) at
low injection levels [4.6.13], a detailed analysis of the injection level dependence has only been
carried out very recently by P.P. Altermatt in collaboration with researchers from this Centre
[4.6.14]. The injection level dependence of B is now used in our QSS-PL lifetime system to
correctly interpret experimental photoluminescence data.
115

Another problem in QSS-PL lifetime measurements can be caused by reabsorption
of spontaneously emitted photons on the way to the surface. It has been argued that, in
cases where the effective lifetime various strongly with injection level, resulting in strong
variations of the carrier density profi le, the reabsorption can cause artefacts in PL lifetime
measurements. A detailed theoretical analysis of this problem reveals that even in the worst
case the artefacts that can be expected as a result of these effects can generally be expected
to be small [4.6.15]. That analysis also revealed various experimental procedures to avoid
even the small artefacts resulting from reabsorption.
4.6.7 References for Section 4.6
116
4.6.1 Trupke, T. and R.A. Bardos, Photoluminescence: A surprisingly sensitive lifetime
technique. 31st IEEE PVSC, Orlando, USA, 2005.
4.6.2 Trupke, T., R.A. Bardos, F. Hudert, P. Würfel, A. Wang, J. Zhao and M.A. Green,
Effective excess carrier lifetimes exceeding 100ms in fl oat zone silicon determined
from photoluminescence. 19th EPVSC, Paris, France, 2004.
4.6.3 Bardos, R.A., T. Trupke, M.C. Schubert and T. Roth, Trapping artifacts in quasi
steady state photoluminescence and photoconductance lifetime measurements
on silicon wafers. Applied Physics Letters, 2006. 88: p. 053504.
4.6.4 Trupke, T. and R.A. Bardos, Self-consistent determination of the generation rate
from photoconductance measurements. Applied Physics Letters, 2004. 85(16): p.
3611-3613.
4.6.5 Trupke, T., R.A. Bardos and M.D. Abbott, Self Consistent Calibration of
Photoluminescence and Photoconductance Lifetime Measurements.
Applied Physics Letters, 2005. 87: p. 184102.
4.6.6 Trupke, T., R.A. Bardos, M.D. Abbott and J.E. Cotter, Suns-photoluminescence:
Contactless determination of the current voltage characteristics of silicon wafers.
Applied Physics Letters, 2005. 87: p. 093503.
4.6.7 Abbott, M.D., J.E. Cotter, T. Trupke and R.A. Bardos, Investigation of edge
recombination effects in silicon solar cell structures using photoluminescence.
Appl. Phys. Lett. 88, 114105, 2006.
4.6.8 Trupke, T., R.A. Bardos, M.C. Schubert and W. Warta, Photoluminescence imaging
of silicon wafers. Applied Physics Letters, submitted, 2006.
4.6.9 T. Trupke, R.A. Bardos, M.D. Abbott, F.W. Chen, J.E. Cotter and A. Lorenz, Fast
photoluminescence imaging of silicon wafers. WCPEC-4, Hawaii, USA, May 2006,
accepted for oral presentation, 2006.
4.6.10 Chen, F.W., J.E. Cotter, T. Trupke and R.A. Bardos, Characterisation of PECVD
silicon nitride passivation with photoluminescence imaging. WCPEC-4, Hawaii, USA,
May, 2006.
4.6.11 Abbott, M.D., J.E. Cotter, T. Trupke, K. Fischer and R.A. Bardos, Application of
Photoluminescence to High-effi ciency Silicon Solar Cell Fabrication. WCPEC-4,
Hawaii, USA, May, 2006.
4.6.12 Bardos, R.A., J.E. Cotter, T.Trupke and A. Lorenz, Comparative analysis of n-type
versus p-type string ribbon silicon wafers. WCPEC-4, Hawaii, USA, May, 2006.
4.6.13 Trupke, T., M.A. Green, P. Würfel, P.P. Altermatt, A. Wang, J. Zhao and R. Corkish,
Temperature dependence of the radiative recombination coeffi cient of
intrinsic crystalline silicon. Journal of Applied Physics, 2003. 94(8): p. 4930-4937.
4.6.14 Altermatt, P.P., F. Geelhaar, T. Trupke, X. Dai, A. Neisser and E. Daub, Injection
dependence of spontaneous radiative recombination in crystalline silicon:
experimental verifi cation and theoretical analysis. Appl. Phys. Lett., submitted.,
2006.
4.6.15 Trupke, T., Infl uence of photon reabsorption on quasi steady state
photoluminescence measurements on crystalline silicon. Journal of Applied
Physics, in press, 2006.

4.7 COLLABORATIVE RESEARCH
University Nacional del Litoral, Argentina
Prof. Roman Buitrago from the University Nacional del Litoral in Santa Fe, Argentina, visited
the Centre for three months from August to November 2005. He was principally involved in
work on solid-phase crystallisation of evaporated amorphous silicon, but also provided useful
contributions to other areas of Second Generation Strand activities.
Materials Science and Engineering, UNSW
A very successful collaboration was initiated with Dr Yu Wang, Materials Science and
Engineering, UNSW. Dr Wang contributed signifi cantly to another trip to the Photon Factory
synchrotron facility at Tsukuba, Japan in December 2005. This trip was funded by AINSE
under the Australian Nuclear Beamline Facility project. Dr Wang has also provided facilities
and expertise for X-ray tube X-ray diffraction. The result of both these experiments has been
very useful and has provided complementary structural information from X-ray diffraction on
the silicon quantum dot nanostructure work.
Aachen University, Germany
A collaboration was established with Dr Andreas Nositschka and Robert Rolver at Aachen
University on time resolved photoluminescence. Initial data on PL on Si nanostructure
samples was very promising. This will be built upon to develop time resolved data which
should elucidate decay mechanisms in the material.
Rudjer Boskovic Institute, Zagreb, Croatia
Dr Branco Pivac and Ivana Kovačević from Zagreb carried out Grazing Incidence Small Angle
X-ray Scattering (GISAXS) measurements on Si nanostructure samples at the synchrotron
facility in Trieste. This gave information on nanocrystal size which complemented TEM data
on the same samples and also gave information on nanocrystal shape – confi rming that they
are spherical.
Fraunhofer-Institute for Solar Energy Systems, Freiburg, Germany
University of Bern, Switzerland
Collaboration has continued on the Up/Down conversion project, see Up/Down-conversion in
Third Generation Strand section. H.U. Güdel and K. Krämer from Bern have provided further
Er doped phosphors and helped to interpret results of absorption and PL measurments. S.
Glunz from ISE, has again provided some of the bifacial cells used in the Up-conversion device
experiments.
School of Physics, University of Sydney
Further collaboration has been established with Dr Nicholas Ekin-Daukes at Sydney University
targetting carrier cooling measurements using a femtosecond pulsed laser, which is soon
to be established. This is part of a successful LIEF proposal which also included pulsed DC
sputtering with Prof. Marcella Bilek at Sydney and pulsed laser deposition with Dr Nagy
Valanoor at UNSW.
117

Magnetic Materials Laboratory, School of Physics, UNSW
Dr Jack Cochrane, Physics, UNSW has been instrumental in providing access and in assisting
in measurements for Hall effect and resistivity vs. temperature measurements. These
measurements are important in elucidating electrical transport mechanisms.
Australian Nuclear Science and Technology Organisation, Lucas Heights, NSW
The Centre was yet again successful in an application to AINSE for time on Secondary Ion
Mass Spectrometry at ANSTO in 2005. Again the grant also included time on Rutherford
Backscattering at ANSTO. Characterisation primarily involved Si nanostructures with high
levels of depth resolution achieved for SIMS, this resolution exceeded that of last year and is
now down to 1.5nm (as independently measured by TEM). RBS was used for calibration of
these data and in addition RBS channelling was used for further structural characterisation
of Si nanostructure samples used in synchrotron experiments.
IRDEP (joint EDF/CNRS/ENSCP lab.), Paris
University of Karlsruhe
Collaboration with the above was by way of prolonged visits by researchers from these
institutions to work on projects in the Third Generation strand.
Dr Jean-Françoise Guillemoles, from the IDREP, Paris, visited the Centre for six months from
March to October, 2005. He was principally involved in work on Hot Carrier cells but also
provided useful contributions to other areas of Third Generation Strand activities.
Prof. Peter Würfel, from Karlsruhe University, visited the Centre from October 2005
to January 2006 having visited previously in 2000 and 2003. He contributed to several
areas of Third Generation work, including establishment of an electro-luminescence mapping
teachnique.
Global Climate and Energy Project (GCEP), Stanford Univeristy, California, USA
The Centre was successful in a proposal to the GCEP for work on Si nanostructures to
develop a wide band gap Si nanostructure based tandem cell element over three years. This
builds on the Si quantum dot nanostructure work in the Third Generation strand and will link
to work in the Thin Film strand. The project offi cially started in September 2005 and initial
work involved recruitment of three new postdoctoral fellows and two new research fellows to
lead the strands on materials processing and characterisation/modelling.
Toyota Central Research Laboratories, Nagoya, Japan and Toyota Future Project
Division, Higashi-Fuji, Japan
The project on Energy Conversion Devices concentrating on high effi ciency thermoelectrics
and application of selective energy contacts started in December 2004. It continued
throughout 2005 with appointment of a postdoctoral fellow. Signifi cant progress was made
on thermoelectric and selective energy contact theory and on experimental measurement
of selective energy contacts including initiation of a new technique of optically assisted I-V
measurement. Mr Nagashima, Dr Motohiro, Dr Takeda and Dr Itoh from Toyota visited in
December 2005 for an annual meeting and progress report.
118

UNSW Centre for Energy and Environmental Markets (CEEM)
The PV Centre is one of the founding members of a new UNSW Centre for Energy and
Environmental Markets. CEEM involves collaboration between the Faculty of Engineering, the
Faculty of Commerce and Economics, and the Australian Graduate School of Management.
It undertakes interdisciplinary research in the design, analysis and performance of energy
and environmental markets and their associated policy frameworks. It was established in
2004, largely as a response to government initiatives to reorganise infrastructure industries
(such as electricity, gas, water and telecommunications) and to rely increasingly on markets
in tradable environmental instruments as a form of environmental regulation.
CEEM brings together researchers in UNSW and partner organisations, contributing to
UNSW’s ability to provide world-class research, advice and education. Dr Muriel Watt is
involved with the research strand focussing on “Policy framework and policy instruments
in energy and the environment”. Other strands are Energy market design, Derivative
markets, Experimental markets, Applications of artifi cial intelligence and Economic valuation
methodologies and their application to energy and environmental issues.
Australian Business Council for Sustainable Energy (BCSE)
PV Centre staff liaise regularly with the BCSE on PV industry development and policy issues.
Dr Muriel Watt and Dr Richard Corkish regularly attend the BCSE PV Directorate meetings.
A number of consultancies and research projects have also been funded and longer term
collaborative arrangements are now under discussion.
CSG Solar Pty. Ltd, Botany, Sydney
CSG Solar AG, Thalheim, Germany
Strong collaboration continued with CSG Solar (formerly Pacifi c Solar), a Centre “spin-off”.
In 2004, the Centre purchased and began using an operational cleanroom facility at Bay
Street, Botany, formerly owned by CSG Solar. CSG Solar provides cleanroom services (gases,
exhausting, gas monitoring, OH&S , etc.) on a user-pays basis, with CSG Solar sharing use
of some of the Centre-owned cleanroom equipment on the same basis. During 2005, the
Centre provided characterisation services for CSG Solar, while CSG Solar provided thin-fi lm
material for the Centre’s metallisation and cell interconnection project. Centre Executive
Research Director, Martin Green, also acted as a consultant to the company during 2005
and served on the German company’s Supervisory Board.
BP Solar Espana, Tres Cantos, Spain
In 2005, UNSW and BP Solar, Pty concluded a major Australian Research Council Linkage
project that spanned 2002 to mid 2005. The project’s aimed to improve the effi ciency of p-
type double sided buried contact solar cells. The main outcomes of the project were a detailed
understanding of the formation of boron diffusion induced defects and their impact on the
voltage and fi ll factor of solar cells, the role of oxidation induced stress on the recombination
in textured silicon wafers, the fi rst conclusive experimental demonstration of Depletion
Region Modulation, an artefact that affects photoconductance measurements and a detailed
accounting of the key loss mechanisms in the double sided solar cell. The project resulted in
5 major journal articles and 7 conference papers.
119

Close collaboration between UNSW and BP Solar Espana continued during 2005 with an 8-
week Postgraduate Industrial Training visit by Malcolm Abbott to the Tres Cantos production
facility. This visit focused on developing BP Solar’s capabilities in advanced characterisation
techniques, especially dark IV and local ideality factor analysis and photoconductance
techniques. Malcolm gained invaluable industrial experience while spending 8 weeks living in
nearby Madrid and absorbing everything Spanish.
Suntech-Power Company, China
Project 1: Innovative Emitter Design and Metal Contact for Screen-printed Silicon
Solar Cells
Research Team
Prof. Stuart Wenham (UNSW – Team Leader)
Anita Ho (Postdoc Fellow – UNSW)
Ly Mai (PhD student – UNSW)
Tjahjono (PhD student – UNSW)
Roland Utama (PhD student – UNSW)
Philip Hamer (undergraduate research scholarship)
Dr Z. Shi (Suntech)
Dr Jingjia Ji (Suntech)
A Zhu (Suntech)
Li Hua (Suntech)
Victor Chen (Suntech)
Aim
The broad aim of this work is to develop the next generation of screen-printed solar cell
for implementation on the Suntech-Power production line. In particular, the fundamental
limitations of the conventional screen-printed solar cell that have limited its performance
for the last 30 years have been identifi ed, and innovative approaches to redesigning the
emitter and front metal contact have been devised and are being developed and analysed
in this work. More specifi cally, the initial aim in this work is to develop and demonstrate an
innovative emitter design for the screen-printed solar cell that overcomes the current and
voltage limitations imposed by the standard design shown in Figure 4.7.1, while retaining
compatibility with existing equipment and infrastructure currently used for the manufacture
of screen-printed solar cells.
The primary aim during 2006 will be to complete the pilot line evaluation of the new technology
in readiness for large scale production by the end of 2006. In particular, effi ciencies in excess
of 18% in large scale production will be targeted following the achievement of effi ciencies
in the range of 18-18.5% in pilot production in 2005 using all the same materials, wafers,
equipment and processes.
Background
Screen-printed solar cell technology dominates commercial photovoltaic manufacturing, with
well over 50% share of international markets. Despite the dominance of this technology, the
solar cell design shown in Figure 4.7.1, has signifi cance performance limitations that constrain
the cell effi ciencies to well below those achievable in research laboratories around the world.
In particular, the front surface screen-printed metallisation necessitates a heavily diffused
emitter to achieve low contact resistance and also to achieve adequate lateral conductivity
in the emitter since the metal lines need to be widely spaced compared to laboratory cells
120

to avoid excessive shading losses. Such cells therefore typically have emitters with sheet
resistivities in the range of 40-50 ohms per square, which inevitably give signifi cantly degraded
response to short wavelength light. To raise this sheet resistivity to above 100 ohms per
square as required for near unity internal quantum effi ciencies for short wavelength light,
serious resistive losses are introduced, both in the emitter and the contact resistance at the
metal to n-type silicon interface.
Furthermore, the conventional design of Figure 4.7.1 has quite poor surface passivation in
both the metallised and non-metallised regions. Even if good ohmic contacts could be made
to more lightly doped emitters, the large metal/silicon interface area would signifi cantly limit
the voltages achievable due to the high levels of recombination in these regions and hence
contribution to the device dark saturation current. These voltage limitations are not of major
signifi cance at the moment due to the limitations imposed by the substrates. However, In the
future as wafer thicknesses are reduced to improve the device economics, the cells will have
the potential for improved open circuit voltages, but only provided the surfaces, including
under the metal, are well passivated.
150-200
p+
n++
p-type
3mm
patterned metal contact
phosphorus
bulk of wafer
rear metal contact
Figure 4.7.1: Conventional screenprinted
solar cell with heavily
diffused emitter and large metal/
silicon interface area for the front
surface metallisation.
metal
Innovative Emitter Design
The new emitter design is shown in Figure 4.7.2. The top surface is diffused to 100 ohms per
square, while the heavily diffused grooves act as semiconductor fi ngers to carry the current
to the screen printed silver fi ngers that run perpendicular to the grooves as shown in Figure
4.7.3. Also not shown in Fig 4.7.2 is the surface passivating dielectric that not only passivates
the lightly diffused surface so as to give near unity internal quantum effi ciencies for short
wavelength light as shown in Figure 4.7.4, but it also isolates the metal from these same
regions to minimise the device dark saturation current. The metal only contacts the silicon
within the heavily diffused grooves, therefore giving a low area contact while still achieving low
contact resistance. Fill factors of 79-80% have been demonstrated with this structure on
large area devices of approximately 150cm 2 , area verifying the effectiveness of this contacting
scheme. Effi ciencies as high as 18.3% (inhouse
measurements) have been achieved,
30 microns
contributed to signifi cantly by the high short
circuit currents gained through the excellent
100 / n-type
spectral response of Figure 4.7.4 and the low
metal and top surface shading losses.
45 microns
Figure 4.7.2: Cross-section of the
investigated innovative emitter design using
semiconductor fi ngers, developed to address
the fundamental limitations of screen-printed
metal contacts with their inability to produce
fi ne lines and make ohmic contact to lightly
diffused emitters.
5 / n++
p-type silicon
n++
rear surface of solar cell
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Figure 4.7.3 : Screen-printed fi ngers running
perpendicular to the heavily diffused grooves
where electrical contact is made. A dielectric/
AR coating passivates the top surface and
isolates the metal from the lightly diffused top
surface.
%
100
90
80
70
60
50
40
30
20
10
S6A-33452
EQE
Reflection
IQE
0
300 400 500 600 700 800 900 1000 1100 1200
Wavelength (nm)
Figure 4.7.4: Excellent IQE achieved through
the use of the innovative emitter design
and low refl ection losses due to AR coated
textured surface and low metal shading
The grooves are typically spaced less
than a millimetre apart so as to minimise
resistive losses within the lightly diffused
emitter, while the screen-printed metal
lines can be spaced signifi cantly further
apart than in normal screen-printed cells of Figure 4.7.1 due to the comparatively excellent
lateral conductivity of the emitter achieved by the very heavy doping within the grooves. This
concept of semiconductor fi ngers does not appear to have ever been used in commercial
solar cells, and has considerable appeal as it facilitates good conductivity within the emitter.
This is acheived without the normal trade-off found in screen printed cells where such regions
of good emitter conduction are located at the top surface and therefore degrade the cell
spectral response and current generating capability, due to the corresponding extremely
short minority carrier diffusion lengths in such regions.
Fig. 4.7.5 shows an SEM of a screen-printed metal line crossing one of the heavily phosphorus
diffused laser grooves. The silicon is only exposed within the grooves, with the screen-printed
metal having been shown to make excellent ohmic contact to the heavily phosphorus
diffused silicon in these regions. Both thick oxides and silicon nitride layers, when used with
appropriate pastes, appear to provide adequate protection to the lightly diffused surface
regions, preventing the screen-printed metal from contacting the silicon.
A simplifi cation of the proposed emitter design is to apply a phosphorus doped passivating
dielectric after lightly diffusing the top surface. The laser scribing conditions for groove
formation are then modifi ed so as to melt the silicon rather than ablate it, thereby allowing
large amounts of phosphorus to penetrate into the molten silicon, producing heavily doped
channels rather then grooves. This avoids the need for etching the grooves and subsequently
122

diffusing the groove walls. The performance of these devices however does not currently
match that of the devices produced using the emitter design of Figure 4.7.2. A further
simplifi cation for producing the semiconductor fi ngers that appears likely to produce the
best results of all three approaches and is arguably the simplest and lowest cost approach,
is under development using ink jet technology. Patent protection is currently being sought for
this work.
Fig. 4.7.5: SEM of a screen-printed
metal line making excellent electrical
contact to one of the heavily
phosphorus diffused laser grooves
running perpendicular to the metal
line. The dark regions are textured
and lightly diffused to 100 Ω/square
and well passivated by a thick
thermally grown oxide
Financial Support
Suntech-Power has been particularly generous, not only funding all the collaborative research
conducted in China, but also fully funding two research positions at UNSW for a period of 12
months through to April 2005. The latter alone is equivalent to a cash contribution in excess
of $50k, while the inkind contribution through the former has been valued in excess of $300k.
In addition, Suntech has provided a cash contribution of approximately $200k in support
of the collaborative research, with a commitment for this to increase to $500k for 2006.
Furthermore, Suntech funded all the living, travel and accommodation expenses for the 12
staff and students who worked at Suntech on the collaborative research.
Suntech Project 2 : High Efficiency cells based on ink jet technology
Research Team
Prof Stuart Wenham (UNSW – Team Leader)
Prof Martin Green (Executive Research Director – UNSW)
Anita Ho (Postdoc Fellow – UNSW)
Ly Mai (PhD student – UNSW)
Tjahjono (PhD student – UNSW)
Roland Utama (PhD student – UNSW)
Nicole Kuepper (research assistant – UNSW)
Alison Lennin (PhD student – UNSW)
Philip Hamer (undergraduate research scholarship – UNSW)
An exciting new research area was established at UNSW during 2005 based on ink jet
technology. Ink jet printing has been applied to a wide range of applications and research
areas in recent years, with CSG Solar pioneering the application of such technology to thinfi
lm solar cell fabrication. Independent research activities have been established at UNSW to
develop new approaches and technologies based on ink jet technology, primarily for application
to wafer based technologies. Several high effi ciency technologies are being developed with
a key factor being the avoidance of any photolithographic or masking processes. It appears
effi ciencies on fl oatzone material above 23% are achievable while more interestingly
effi ciencies above 20% appear feasible with solar grade p-type CZ wafers and likely to peak at
effi ciencies above 22% for CZ n-type wafers.
123

Figure 4.7.6 shows an example of one of the particularly versatile cell structures being
developed by the ink jet printing team for wafer based devices. This work was initially reported
in mid 2005 although limited details are available as patent protection is being sought. This
device structure is of particular interest to Suntech as it can be used as a contacting scheme
for a new thin-fi lm crystalline silicon solar cell technology, or can be applied to either n or p type
wafers for rear contacting, or perhaps most importantly, can be used as an improved rear
surface passivation and contacting approach for existing commercial technology through
the use of a rear fl oating junction by eliminating the n-type contact. This latter rear surface
structure, when applied to the standard PERL front surface, has held the world record for
silicon solar cell voltages for most of the last decade with independently confi rmed opencircuit
voltages in excess of 720mV. The new inkjet printing development system plus several
of the ink jet printing team at UNSW are shown in Figure 4.7.7
dielectric
n- or p-type
p- or n-type
resin
+ or - contact - or + contact
Figure 4.7.6 : Versatile device
contacting scheme under
development using ink jet
technology and applicable to
wafer based devices, thin-fi lm
technologies and for improved
rear surface passivation and
metal contacting for current
commercial cell technologies.
Figure 4.7.7 : New Ink jet printing
development system at UNSW
Centre for Quantum Computer Technology, Melbourne University
A collaboration has been established with Dr Chris Pakes at Melbourne University. Dr Pakes
has used conductive atomic force microscopy (CAFM) on our Si QD resonant tunnelling
structures. CAFM has proved to be a powerful tool for mapping transport properties at a
very high areal resolution.
In 2005 more detailed analysis has been carried out using this technique of the SiO 2 /Si QD/
SiO 2 double barrier resonant tunnelling structures discussed in Section 4.5.6.1. Conductive
atomic force microscopy (CAFM) at Melbourne University has been used to map the
conductivity of single Si QD layer mesa samples containing about 1010 5nm QDs per mesa
or 10,000 QDs per µm 2 . Figure 4.7.8 shows a CAFM scan at a constant voltage of 10V.
The white spots are areas of high conductivity, indicating the high tunnelling probability at a
resonant QD. Figure 4.7.8 also shows a line scan across two of these white spots and shows
the sharp change in conductivity when resonance is achieved.
124

Thus this represents a QD areal mapping technique. However, the voltage used at present is
high because the oxide layers are quite thick at 5nm. Hence the indicated tunnelling regions
may be either from very small QDs or from higher confi ned energy levels within QDs and only
indicate a lower limit on the QD density. Proof that these do indeed indicate QD locations was
obtained by a subsequent anneal of the sample in an ordinary ambient. A subsequent CAFM
scan showed no white regions, thus showing that the Si QDs had been oxidised in the anneal.
Further experiments will use thinner oxide layers and should give a more complete map of the
QD structure. Scans of such structures at various biases may give further information on
QD size and size distribution by effectively mapping the confi ned energy levels at a very high
areal resolution.
Figure 4.7.8: (a) Current image obtained at 10V applied voltage (probe tip grounded); the
white dots indicate areas of higher current conduction (up to 800 pA); (b) line scan of current
profi le in region shown by red arrow in (a).
125

126

Summary
The Centre for Advanced Silicon Photovoltaics and Photonics incorporates the activities of
the former Key Centre for Photovoltaic Engineering. The former Key Centre started in 1999,
after the award of special funding from the Australian Government to promote teaching
and research in the area of photovoltaics. One of the primary new initiatives of this Key
Centre was the establishment of the world’s fi rst undergraduate degree in Photovoltiacs and
Solar Energy. This was one of only eight such Key Centres awarded Australia-wide across all
disciplines, demonstrating the importance the government placed on this new and exciting
fi eld of photovoltaics. In 2003 the Key Centre and its activities were incorporated into the
new Centre of Excellence, awarded to the same team at the University of New South Wales.
The Centre offers undergraduate, postgraduate and research programs encompassing a
range of aspects relating to the photovoltaic and renewable energy industries. These programs
have been developed in consultation with representatives from industry to ensure graduates
are appropriately qualifi ed to enter the fi eld upon completion of their studies. Since 2003,
the Centre has seen a total of 40 students graduate from its undergraduate programs, and
23 students from its postgraduate degrees. These graduates are now taking advantage of
a range of opportunities being created in the booming photovoltaics and renewable energy
industries.
During 2005 there was a signifi cant amount of curriculum development and revision due
to new initiatives of the Faculty of Engineering which aimed at adding value to engineering
programs at UNSW. Throughout the year the Centre continued to attract bright students
to all our educational programs, and we were very excited to be able to offer a new Co-
Op Scholarship sponsored by Suntech Power Co. Ltd. School Offi ce staff also concentrated
on reinvigorating existing promotional material, and utilising new promotional activities to
increase the awareness of Photovoltaics and Renewable Energy Engineering at UNSW.
At the end of 2005 there were 137 undergraduate students, 7 postgraduate coursework
students, and 23 research students enrolled in the Centre’s educational programs.
5.1 Undergraduate Educational Programs
The Centre offers two undergraduate coursework
engineering programs, which can be taken in
combination with a Bachelor of Arts, Bachelor of
Science or a Bachelor of Commerce. These degrees
aim to develop well-educated graduates with the
basic skills, attributes and knowledge required to
practise as professional engineers in the growing
photovoltaics and renewable energy industries.
The photovoltaics program draws on the expertise
of Centre staff in this fi eld and was the fi rst of
its kind internationally. The program focuses on
photovoltaic devices, and includes training in
technology development, manufacturing, quality
control, reliability and life cycle applications, system
design, maintenance and fault diagnosis, marketing,
policy development and the use of other renewable
energy technologies. It has two unique features:– a
project in the second year of the program, and a ‘strand’, a second area of specialisation. Since
2003 a total of 40 students have graduated from the program, as previously mentioned, and
another 10 are expected to graduate in March 2006 after completing their studies at the
end of 2005.
127

The second broader degree in Renewable Energy Engineering was introduced in 2003 and
will see the fi rst students graduate in 2006. At the end of 2005 a total of 42 students were
majoring in this area. In addition to photovoltaic devices, students in this program study solar
architectural technologies, wind energy, biomass, solar thermal, and renewable energy policy
as part of their core curriculum.
Students generally enrol in these programs because they are
interested in working with cutting edge technology, and they are
enthusiastic about making a personal contribution to society and the
environment. Total enrolments increased slightly in 2005 with an
increase in students electing to enrol in combined degree programs.
This can be attributed to the increase in range of combined degree
programs offered by the Centre which, from 2005, includes a
Bachelor of Engineering / Bachelor of Commerce, and a Renewable
Energy Engineering / Bachelor of Science program. The new
combined Commerce program aims to enhance the technical and
scientifi c expertise of Engineering graduates with an understanding
of commercial and fi nancial principles which will assist engineers to
manage projects, obtain fi nance for the commercialisation of new
products, create and manage companies, manage the manufacturing
and marketing of products, and accurately predict and monitor
market and economic trends. The Renewable Energy / Science
combined program allows students to expand their understanding
of scientifi c concepts which form the basis of engineering principles.
Students installing a
solar-powered clean water
system in Sri Lanka
At the end of 2005, 27% of enrolled students were women. This is
unusual when compared to other Engineering programs which typically
have a participation rate by women, of about half this. The women
enrolled in our undergraduate degree programs are more inclined to
enrol in a single degree program, and in particular the Photovoltaics and
Solar Energy program. Women who elect to enrol in a combined degree,
are more likely to choose a combined Photovoltaics and Solar Energy /
Arts program.
Students using a
computer lab
Graduates of our undergraduate programs are gaining employment
within a variety of organisations, and increasingly in the area of energy
effi ciency and sustainable design. Each year a number of graduates elect
to expand upon their undergraduate degree by undertaking a research
program with our internationally recognised research groups, whilst
others are employed in industry by solar cell and equipment manufacturers, system
design and integration companies, electricity utilities and major end users of products
(such as sustainable design organisations).
5.1.1 The Strand
The strand is unique to the Photovoltaics and Solar
Energy program, and is essentially a second area of
specialisation which complements a student’s study
of photovoltaics. Students can take strands covering
a variety of areas including computing, electronics,
mathematics, physics, mechanical engineering,
civil engineering, and architecture. The aim of the
128

strand is to provide students with broader engineering backgrounds important for the
cross-disciplinary nature of photovoltaic applications. UNSW’s Sunswift Solar Car project
is one example of the cross-disciplinary nature of photovoltaic applications, requiring the
skills of mechanical engineers, biomedical engineers, and electrical engineers in addition
to photovoltaic engineers. Since the commencement of the program, the Electronics and
Physics strands have been the most popular, with Architecture, Mechanical Engineering and
Computing also popular choices among students.
5.1.2 Goldman Sachs Recipient
One of the Centre’s outstanding undergraduate students,
Nicole Kuepper, was one of eight students in 2005 to receive an
Australian fellowship as part of the Goldman Sachs Global Leaders
Program. Nicole received a New South Scholarship for achieving
a UAI of 100, and is heavily involved with community activities
including volunteer projects with indigenous Australians, teaching
English in the Phillipines and fundraising events. She is enrolled in
the Photovoltaics and Solar Energy program and hopes to bring
sustainable improvement to disadvantaged communities through
engineering and education.
The Goldman Sachs Leaders Program, which is run by the Institute
of International Education and the Goldman Sachs Foundation,
acknowledges the outstanding achievements and abilities of
students across a range of disciplines. Nicole joins a group of 100
outstanding students from around the world to be awarded the
fellowship, which recognises academic performance and community
contribution.
Nicole Kuepper with English
student in the Phillipines
5.2 Undergraduate Student Projects
In the second year of the Photovoltaics and Solar Energy program, students have the
opportunity of undertaking a year long project in the photovoltaic or renewable energy areas.
The main emphasis of the second year project course is hands-on “projecteering”, or project
engineering. The course has a lecture component covering projecteering skills and practice,
and each project has a research component, a planning component, a hands-on component
and a reporting component. This course helps to prepare students for their fourth year
thesis, which is generally undertaken by all students enrolled in both the Photovoltaics and
Solar Energy and Renewable Energy Engineering undergraduate programs. While in the past
projects in developing countries have been the most popular among students, in 2005 there
was a swing in popularity towards laboratory-based projects with the introduction in 2005 of
a new project on Screen Printed Solar Cells.
5.2.1 Biodiesel Trailer
The Biodiesel Project aims to construct a small-scale, portable chemical factory to convert
used vegetable oil, from UNSW’s food outlets, into diesel fuel for UNSW’s fl eet of diesel cars.
The project has now been running for four years and is at a stage where completion is in
sight. In 2005, four second-year students who undertook the Biodiesel Project implemented
two key subsystems:- the pneumatic fl uid handling mixing subsystem, and the fl uid handling
129

system for the solar thermal hot water. One of the key challenges was handling potentially
explosive vapours and fl ammable liquids, and this necessitated a completely pneumatic fl uid
mixing and pumping system instead of the more common electrical pumping and mixing
systems. Another challenge was investigating, designing and implementing the hot water
system, which required extensive research into codes and best practices for the plumbing.
The students spent several full days on the construction effort on campus, learning the
not-so-easy art of bending and fi tting rigid stainless steel and copper tubing. The hot water
system was completed, but not tested. The pneumatic pumps and motors were fi tted and the
stainless steel plumbing was started, but more work is needed.
5.2.2 Developing Countries
The Centre has been involved
with projects in the developing
countries for the last fi ve years.
The application of photovoltaics
and other renewable energy
technologies can make the
greatest difference to people’s
lives and living standards in
these places. Students involved
with this project in the past have
installed photovoltaic systems in
villages in Nicaragua and Nepal.
Students installing a solar-powered clean water system in Sri Lanka
A student investigating solar-powered water
pumping
In 2005, this second-year project group of six students
worked on a variety of technologies which included
assembling a micro-hydro testing system, a water
purifi cation system, a small solar powered system and
low cost passive solar design for houses in developing
countries. The culmination of this work resulted in some
students travelling to Sri Lanka over the summer break
to install PV powered clean water systems in a small
village called Seenigama, which was badly affected by
the Tsunami that struck the region in 2005. Skills that
the students had developed throughout the year were
put to good use in the fi eld. Invaluable lessons were
gained regarding project management of activities
in developing countries, as students had to face and
overcome many technical and non-technical issues in
implementing the project.
130

5.2.3 Screen-printed Solar Cells
Screen-printed solar cells are the workhorse of today’s solar cell industry and will likely remain
the dominant technology for the foreseeable future. Screen-printed modules are bringing
renewable electricity to people in both developing countries and the developed world. UNSW
researchers are developing new printed solar cell technologies to improve effi ciency and
cost of commercial technologies. This project aims to give undergraduate students broad
exposure to the fi eld by engaging them in laboratory infrastructure development projects.
In 2005, students undertook a variety of engineering projects around key equipment and
infrastructure, including designing and implementing a shuttering system for our CNC laser
machine, installing and commissioning a thermal muffl e furnace, repairing and upgrading
a quartz furnace stack and receiving, commissioning and testing a new production screen
printer. After completing this project, the student’s interest in laboratory research,
development and infrastructure activities was such that they were placed for summer R&D
employment at UNSW (as part of the Taste of Research Summer Scholarship program), at
BP Solar (as part of UNSWs Co-op Scholarship Placement) or at Suntech Solar (as part of an
ongoing summer exchange program). This highlights the success of this project at engaging
students in laboratory or production activities.
5.2.4 Thin Film Solar Processing Equipment
This project aims to give students a broad experience in establishing and maintaining a worldclass
thin-fi lm solar cell research laboratory. This is achieved through a two-stage process.
Firstly students develop a base level understanding of equipment and systems within the
thin-fi lm lab, which include vacuum systems, gas delivery systems, leak testing equipment
and plasma processing. The second stage involves the students integrating what they have
learnt by applying it to a specifi c project in the thin fi lm laboratory. In 2005, four secondyear
students undertook this project. They were split into two groups and worked on two
independent equipment upgrade projects. One group converted a decommissioned PECVD
machine into a fully working plasma etching system, while the other group developed a control
interface for a reactive ion etcher. Both groups undertook leak testing work on their system
to achieve a better base pressure, and improved existing equipment safety and operation
documentation.
5.2.5 Fourth Year Thesis
The thesis is generally carried out in the last two sessions of an
engineering undergraduate student’s studies. Students undertake
directed laboratory and research work on an approved subject under
guidance of the Centre’s academic staff. Typically, the thesis involves
the design and construction of experimental apparatus together
with practical tests. Each student is required to present a seminar,
submit a written report, and present a poster as part of an Open Day.
It is a chance for students to demonstrate what they have learned
throughout their studies.
Theses submitted during 2005 were of a very high quality. Contrary
to 2004 where application-based photovoltaic and renewable energy
topics were the most popular with students, in 2005 laboratorybased
research topics were the most popular. Theses in this area
covered topics such as the “Saturn 7” light source for solar cell
measurements, the quantum effi ciency of polycrystalline thin-fi lm
solar cells, texturing of GaAs solar cells by nanosphere lithography,
2005 Thesis Poster-Presentation
Prize winners receiving their award
from Dr Richard Corkish, Head of
School. Session 1 winner: Andrew
Coffey; Session 2: Roland Utama
131

and the determination of dopant profi les in crystalline silicon using wet chemical layer
removal technique. However, students did investigate other topics such as life cycle analysis
of alternative fuels for transport, energy and water effi ciency in schools, sustainability in
commercial offi ce buildings, a solar thermal hot water heater, solar home systems in Sri
Lanka, and renewable energy policy.
One outstanding thesis submitted received both the 2005 Photovoltaics Thesis Prize as well
as the Poster Presentation Prize for session 2. This thesis by Roland Utama titled ‘Capacitance
Voltage Analysis of Polycrystalline Silicon Thin Film Solar Cell’, investigates the applications
of a novel capacitance-voltage measurement using impedance analysis to determine the
active doping concentration of boron-doped ALICIA solar cells. Roland examined the infl uence
of defects and two post-deposition treatments (RTA and hydrogenation) on the active base
doping concentration, as well as the effect of varying boron doping concentration on the base
doping type. His thesis has also been nominated for the 2005 Wal Read Memorial Prize
presented by the Australia New Zealand Sustainable Energy Society (ANZSES).
5.3 Postgraduate Educational Programs
The Centre for Photovoltaic Engineering offers one postgraduate coursework
program, a Master of Engineering Science, and three research programs:- a
Master of Philosophy, Masters by Research and a Doctor of Philosophy. These
degrees are intended to provide students with an exceptional basis in advanced
concepts and research in the photovoltaic area.
The one-year coursework program was developed to build on the previous
engineering education of engineers from other engineering disciplines who are
currently being attracted to the photovoltaics and renewable energy industries.
Students study courses chosen from the areas of photovoltaic devices, photovoltaic
systems and applications, and renewable energy technologies. Enrolments in the
program have been steady with total enrolments of 7, and 2 graduates in 2005.
At the end of 2005, the Centre had 23 students enrolled in postgraduate research
degrees, 18 in a Doctor of Philosophy, and 5 in a Masters by Research. Research
topics available to these students cover the entire photovoltaic sector, but with
greatest emphasis on device theory, device and module design, balance of system
components, and photovoltaic systems and applications. Research students are
involved across all the Centre’s research groups and play an important role in the
Centre’s activities. In 2005 the Centre saw 6 research students graduate, the
largest number so far to graduate from these research degrees.
5.3.1 Dean’s Award for Excellence in Postgraduate
Research
One of the Centre’s research students was the recipient
of fi rst prize in the Faculty of Engineering’s inaugural
Dean’s Awards for Postgraduate Research. Supriya
Pillai’s work was selected as the best overall from about
70 applicants at a poster presentation at the Scientia
in December.
Supriya Pillai - First prize winner of the Dean’s
Award
132

5.4 Scholarships
The undergraduate programs at the Centre attract very bright students from across
Australia. Even though the UAI cut off for the programs has been approximately 80 over
the last few years, almost half the students have a UAI over 90 with 40% of these students
having a UAI over 95. The Co-Op Scholarship Program and the Faculty of Engineering’s Rural
Scholarship Program help to attract these bright students, while the Taste of Research
Summer Scholarship Program provides bright students with experience in the Centre’s
laboratories and encourages them to pursue research careers. The Centre’s very high
international profi le also allows it to attract high quality research students evidenced by the
number of doctoral students undertaking research programs at the Centre who have been
awarded either an APA or EIPRS Scholarship.
5.4.1 Co-Op Scholarship Program and New Industry Sponsor
The Co-Op Program is an industry-linked scholarship program where students obtain a year of
work experience with industry sponsors as part of their undergraduate studies. In addition to
their outstanding academic achievements, students are selected based on their involvement
in school and community activities, their demonstrated leadership skills and their ability to
communicate. Participation in this program enables students to apply the knowledge they
have gained during their studies. This program is also benefi cial to industry sponsors, who
have access to excellent students, can observe these students in their workplace, and have
the fi rst opportunity of recruiting the best new graduates.
Two organisations, BP Solar and CSG Solar, have sponsored scholarships for the
undergraduate Photovoltaics and Solar Energy program since 2001. However, in 2005
the Centre was fortunate enough to obtain a 3rd industry sponsor, Suntech Power Co. Ltd.
Suntech is a partly Australian-owned company located in China and, as a result, this becomes
the fi rst international Co-Op Scholarship at the University of New South Wales. Suntech
is an extremely successful and rapidly growing manufacturer of multicrystalline and single
crystalline silicon solar cells, and this scholarship has further strengthened the existing
research and educational relationship between this organisation and the Centre.
In 2005, the Centre also experienced an increase in good quality applicants applying for the
scholarship program. In 2004 industry sponsors and academics interviewed 17 students,
however, in 2005 they interviewed 24. Feedback received from applicants regarding the
interview process was also very positive to the effect that the interviews were the best
organised that they had experienced as the students knew what was going on, where it was
happening, and who could help.
5.4.2 Rural Scholarship Program
The Faculty of Engineering established the Rural
Scholarship Program in 2001 to encourage highachieving
students living in rural and isolated areas
to study engineering. The scholarships are valued
at approximately $8,500 per annum for four years
of full-time study which eases the fi nancial hardship
of relocating to and living in Sydney. Due to the high
standard of applicants in 2005, the Centre funded
an extra scholarship in addition to the Faculty-funded
scholarship. These students will commence studying
with the Centre in 2006.
David Uncle is a rural scholar who commenced his studies in 2005. In March he formally
received his scholarship from the Dean of Engineering, Professor Parker.
133

5.4.3 Taste of Research Summer Scholarship Program
The Taste of Research Summer Scholarship Program is primarily for high achieving 3rd
year students and, in exceptional cases, 2nd year students may be considered. As part of
the program, engineering schools offer 10 week projects for students to complete during
their summer break. These projects provide students with scholarship support to gain
experience working as part of a research team, for example in the world class laboratories
at the Centre. From December 2005 to March 2006, the Centre hosted seven students
working on projects, three with the thin-fi lm group on crystalline silicon thin-fi lm solar cells
on glass, two with the buried contact group on high effi ciency n-type silicon solar cells, one
on innovative research with industry to improve commercial solar cell performance, and
another on antenna collection of solar energy. David Bennett, an undergraduate student
attracted to the Centre by the Taste of Research program from ANU, was awarded one of
the six Engineering Undergraduate Research Prizes for the best poster and presentation at
the end of the program.
Participation in these projects helps students further develop their technical skills as well
as their written and oral communication as students have to write a report and present a
poster on the outcomes of their research.
5.4.4 Research Scholarships (APA and EIPRS)
Through hands-on laboratory-based projects and theses, and scholarship programs such as
the Taste of Research Summer Scholarship program, the Centre aims to encourage good
quality undergraduate students into research. Being an internationally recognised research
organisation, the Centre attracts very high quality students to its research programs where
students have the opportunity to work with leaders in this fi eld. The fact that 11 of our
doctoral students are in receipt of very competitive APAs (Australian Postgraduate Award)
or an EIPRS (Endeavour International Postgraduate Research Scholarship) is testament to
the quality of these students. To be awarded an APA the student must be a local student
and ranked near the top of the fi rst class honours graduates, while the EIPRS is available to
international students and appear to demand an even higher standard than the APAs.
.
5.5 Curriculum Development
134
Throughout 2005 students indicated through
UNSW’s course evaluation process, CATEI, that
they were satisfi ed with the Centre’s courses.
On average, at least 88% of students were
satisfi ed or very satisfi ed with the content,
structure, and teaching of our courses. Whilst
no new courses were offered by the Centre, the
Faculty undertook several initiatives in 2005 to
attract undergraduate students to Engineering
at UNSW, each of which involved Centre staff.
These include the introduction of a new fl exible
fi rst year program, the development of a Facultywide
fi rst year Engineering Design and Innovation
course, and a new admissions scheme for local
students. Furthermore, in order to try to increase
the number of courses offered each year to
students, the Centre trialled a semi-distance
mode of delivery for a core course on Sustainable
and Renewable Energy Technologies.

5.5.1 New Flexible First Year
In 2005 the Faculty undertook a revision of all Engineering programs to increase fl exibility for
students in their fi rst year, and ensure a broad base in mathematics, science and engineering
fundamentals. Prospective students had indicated that there was value in delaying their choice
of specialisation, and this new program exposes students to the various engineering schools
and enables them to make an informed choice at the end of their fi rst year. However, students
who already know which fi eld of engineering they would like to enter, can enter directly into
that specialisation in their fi rst year. The Centre’s educational programs were involved with
this revision and academic and administrative staff were involved with the process that will
see these new style programs effective from 2006.
5.5.2 New Engineering Design and Innovation Course
Along with the rationalisation of fi rst year courses for all engineering programs for the fl exible
fi rst year, a new common course on Engineering Design and Innovation was created. Staff
members from each School met periodically throughout the year to establish the aims and
structure of the course, and to write a course outline. The course aims to give students fi rst
hand experience with designing and building creative solutions to problems which are limited
by budget, time and resources. The key engineering skills it aims to develop in students include
concept development, critical thinking and evaluation skills, clear communication, research
and information literacy skills, and teamwork. Dr Jeff Cotter is one of the leaders in the
development and implementation of the new course, and is teaching the course in 2006.
5.5.3 First Year Course on Sustainable Energy
With the introduction of the new fl exible fi rst year program and the opportunity for fi rst year
students to take electives, the Centre decided to offer a new fi rst year course on Sustainable
Energy as part of the elective pool. This new course will introduce students to the concept
of energy in its different forms through a range of demonstrations which will introduce
the concepts of energy storage, energy effi ciency, energy conversion and sustainability. An
overview of renewable and nuclear energy sources will be given with particular emphasis
on photovoltaic technology including interesting case histories and fascinating mistakes
and disasters. One lecture each week will be given by guest lecturers who are experts from
industry, end-user groups, research and government. The course will fi rst be offered in 2006
to all students enrolled in the Faculty of Engineering.
5.5.4 Multiple Criteria Entry for Undergraduate Programs
Generally, admission to undergraduate programs for local Australian citizens and permanent
residents is through the Universities Admissions Centre based solely on a prospective
student’s UAI result as part of the Higher School Certifi cate. However, in 2005 the Faculty
of Engineering introduced the Multiple Criteria Entry admissions scheme which recognises
that there are a number of factors not measured in high school assessment, which indicate
the potential of a student to succeed in engineering programs. In addition to their UAI, these
factors include a student’s attitude, commitment, interest in engineering and the type of
subjects taken for their HSC. Students who anticipated receiving a UAI less than 85, but
higher than 75, were encouraged to apply for an interview with members of the Faculty’s
academic staff. At the interview students have the opportunity to exchange information,
demonstrate their suitability to engineering and ask questions of Engineering staff.
135

The main round of interviews for this admissions scheme was held during the week
of the 26th to the 30th September. Five of the Centre’s academic staff members
were involved with interviews during this week. In addition to this, one academic
conducted tours of our school for prospective photovoltaic and renewable energy
engineering students, and one general staff member coordinated the regional
interviews in Canberra on behalf of the Faculty. This program was deemed to be
very successful and will be further refi ned and administered again in 2006.
5.5.5 Semi-distance Delivery Mode Trial
The Centre has recognised that by being a small School, it is limited in the number
of courses that it can teach each year. In an attempt at increasing the number of
yearly course offerings, a second year core course, Sustainable and Renewable
Energy Technologies, was delivered in a semi-distance mode in 2005. This course
was available to students who had previously failed the course, missed taking the
course in the previous year, or were on the Co-Op Scholarship. Lecture material
was delivered via the web, and students attended a one hour tutorial one night a
week, submitted assignments, and sat an examination at the end of the session.
Students appreciated the evening classes, and having the opportunity to take the
course in a year when it wasn’t typically offered. The Centre is investigating this
mode of delivery with more courses in 2006.
5.6 Educational Resources
5.6.1 New Edition of Applied Photovoltaics
In 2005, revisions to the Centre’s book titled Applied Photovoltaics were fi nalised
and it was re-printed ready for distribution in 2006. This book was originally
published by Stuart Wenham, Martin Green, and Muriel Watt in 1995, and the
revisions were the result of experience teaching a course on applied photovoltaics
as part of the Centre’s undergraduate and postgraduate programs. The book
examines the characteristics of sunlight, how photovoltaic devices work, and
various applications for the devices including stand-alone photovoltaic systems,
grid-connected photovoltaic systems, remote area power supply, and water
pumping.
5.6.2 Virtual Survivor game
The online Virtual World Solar Challenge game,
developed Jeff Cotter in 1999, is a highly successful
game-based learning tool (http://wsc.pv.unsw.edu.
au/) that has been played over 50,000 times by highschool
students and solar racing car enthusiasts
across Australia and around the world. It has been
used numerous times by the School for Photovoltaic
Engineering and the Faculty of Engineering for
promotion and education purposes since 1999. This
successful game-based learning tool grew out of a
simple on-paper exercise developed for the general
education course Solar Racing Cars.
136
The Virtual Survivor game-based learning tool comes from similar origins – an on-paper
exercise developed for SOLA2053 - Sustainable and Renewable Energy Engineering. The
on-paper exercise was very popular and engaging with students, and it is presently under
development as a web-based tool.

The main purpose of this tool is to expose students to the issues related to sustainable
development, including management of dynamic resources, Tragedy of the Commons, the
Precautionary Principle, negotiation and policy, and more. When completed, the learning tool
will consist of an online, multiplayer simulator and a series of supporting activities to enhance
learning in sustainable development.
In short, each of many students (as independent agents) inhabits a small Easter-Island-like
island, playing the role of Chief of a small tribe. They can harvest the natural resources and
expand their individual tribes. They climb and fall in rank ordering among all tribes, based on
population, collected commodities, and the number of stone-head statues they construct.
However, they do not know in advance that their environment has limited capacity to sustain
growth and expansion. Occasionally, droughts, famine, confl ict, external trade fl uctuations and
other factors will strain the islands ability to sustain its inhabitants. In this setting, students
will struggle to sustain their virtual society and, especially, learn and debate about issues
confronting their virtual society – resource management, sustainable development, policy
development and more. To make things more interesting, external factors will be applied, for
example, trade fl uctuations, war with neighbouring islands, drought, etc.
The game will eventually feature, among other things:
A Polynesian setting – limited resources, isolation, external factors affect sustainability
Multiplayer mode – each student plays as an independent agent
Dynamic resource models – natural resources behave like dynamic systems
Internal factors – confl ict, competition for resources, communication by in-game email
External factors – such as trade fl uctuations, war, drought, pestilence, famine
Online help
Game history – software will “write, record and publish” the history of every game played
5.6.3 New Outdoor Experimental Area
During 2005, with support from the Faculty of Engineering, the Centre gained effective
access to a reserved section of new roof over an extension of the fourth fl oor of the Electrical
Engineering building. This concrete roof area, comprising approximately 425 m 2 , has
been specially engineered to allow attachments without compromising the integrity of the
waterproof membrane and is already the home for a 38 m 2 battery room and a mounting
frame for more than 4 kW of solar photovoltaic modules. Modules that were previously
mounted on the UNSW property at Little Bay have been moved to the new roof for installation.
That array will be used both as a grid connected solar power station and an experimental
facility and will be operated in collaboration with staff from the School of Electrical Engineering
and Telecommunications.
The outdoor area will be used for
students’ experiments and projects that
require solar access and for regular
community outreach activities such as
the Indigenous Australian Engineering
Summer School that is hosted by the
UNSW Faculty of Engineering each
January. Work is proceeding on the
design of a dedicated experimental jig
to teach about the effects of partial
shading of arrays and modules and the
effects of blocking and bypass diodes in
photovoltaic systems.
A picture of this new area on top of the Electrical
Engineering Building.
137

Staff and students enjoying the
PVSOC annual dinner.
5.7 PVSOC
One characteristic of the Centre
which has led to the success of the educational programs is the
friendly atmosphere that is engendered by being a small school
with highly motivated academic and general staff. Students appreciate being able to form
friendships and support networks with fellow students, as well as feeling comfortable and
familiar with academic and administrative staff. PVSOC is a social committee established by
the students which fosters this atmosphere with organised social events and activities to
encourage student interaction. In 2005 the committee organised barbeques, pubcrawls, a
soccer match, student participation in Solar House Day (organised by ANZSES), and fi nally the
PVSOC Annual Dinner. More than 120 students and staff attended this dinner in November
2005 where fi nal year students were farewelled, staff thanked, and the 2006 PVSOC
committee was elected. This dinner epitomised the sense of community that exists between
students and staff within the Centre.
5.8 Promotional Activities
The Centre regularly participates in promotional activities
organised by the Faculty of Engineering and Student
Recruitment at UNSW. These events are important
for increasing awareness and interest in the Centre’s
educational programs. In 2005 in addition to these annual
events, staff in the School Offi ce also undertook a revision
of promotional material for prospective students, and ran
an Australia-wide Virtual World Solar Car Challenge for
high school students.
Two concepts used in the revision of
promotional material for the Centre’s
educational programs.
5.8.1 Print Media
In order to increase the awareness of the Centre’s educational programs, in 2005, the Centre
increased the number of advertisements in relevant Sydney Morning Herald publications.
Colour advertisements were placed in the Earth and Environmental Science HSC Study Guide,
the HSC Survival Magazine, the HSC Change of Preference Guide, and the HSC Universities
Advisory and Information Day Guide.
5.8.2 Promotional Material
Recognising that the Centre’s printed promotional material was inappropriate for attracting
the attention of prospective students in the competitive tertiary marketplace, School
Offi ce staff developed new promotional booklets which contained information pertinent to
undergraduate, postgraduate, and research prospective students. These new colourful and
eye-catching booklets were developed in consultation with current students, and contain
student and graduate profi les, information on the Centre, its research and educational
activities, and photovoltaic specifi c cartoons developed by a current research student. The
feedback from current and prospective students on this promotional material has been very
positive.
138

5.8.3 UNSW Information Day
Local undergraduate students must apply for admission to UNSW programs through UAC,
and the 5th January 2005 was the last day students could change their preferences for
university degrees. Therefore the university hosted an information day on the 5th January
to assist students obtain information to fi nalise their preferences. Centre administrative
and academic staff attended this event and talked to many prospective students who were
unsure of their career direction. Students received information on our programs and had the
opportunity to ask questions of staff.
5.8.4 UNSW Courses and Careers Day
UNSW Courses and Careers Day is the annual information day for prospective students
to obtain information about programs and student life at the university. As part of this
day academic and administrative staff from the Centre attended information desks in the
Roundhouse to provide advice, and information to prospective students. During the day Dr
Alistair Sproul also presented two lectures about the Centre’s programs as part of the
lecture series organised centrally by the university.
In order to increase the awareness of photovoltaic
technology the Centre organised another couple
of activities on the day. BP Solar was kind enough to
lend the Centre a Solar Powered Ice-Cream Cart for
the day which was used to distribute free ice-blocks to
members of the public. Alongside the ice-cream cart
the Centre displayed a solar cooker and a solar-powered
water pump. Students staffed this display and talked
about our educational programs. In addition to this the
Centre, in collaboration with the Energy Management
Unit at UNSW, also conducted tours of the inverter
room for the recently installed photovoltaic array on
the Quadrangle Building.
The solar-powered ice-cream cart and solar-powered
water pump display at Courses and Careers Day.
The student-built solar cooker baking pumpkin and
potato using only the sun and engineering.
139

5.8.5 Faculty of Engineering Information Day for High School Students
Each year the Faculty of Engineering organises an information day to give high school students
an opportunity to learn about engineering and the programs offered at UNSW. As part of the
day students visit three engineering schools of their choice and engage in interactive activities
aimed at demonstrating the relevant engineering area. In 2005 the demand to attend this
event was so great that two High Schools Days were coordinated, one in April and another
in October. In 2003 59 students attended the Centre, in 2004, 40 attended, however in
2005 over the two days 114 students visited. 26% of the students attending the day visited
Photovoltaic Engineering which was an increase from 18% in the previous year. Due to this
large number of students, the Centre ran two tours for the day in April and 3 on the day in
October when only one was conducted in prior years. As part of these tours students used the
solar-powered water pumps in the Centre’s teaching laboratory, watched the charging and
discharging of a capacitor with solar energy, and gained exposure to the Virtual Production
Line, a computer simulation of a real life photovoltaic manufacturing line.
Students using the solar-powered water pumping equipment in the Centre’s teaching
laboratory.
5.8.6 Honeywell Engineering Summer School
The Honeywell Engineering Summer School is an event held in December and is conducted by
Engineers Australia. As part of the summer school high school students from across NSW and
the ACT about to enter their fi nal year take part in a week of activities which involves industry
visits and lectures / demonstrations at a number of universities. In 2005 approximately
30 students visited the Centre where they constructed a capacitor using PET bottles, salt
water and aluminium foil under the supervision of Mr Rob Largent. At the conclusion of Rob’s
demonstration of charging and discharging the student-built capacitors, the students were
issued with information on the Centre’s educational programs.
5.8.7 Sunsprint and Minisprint
140
In conjunction with the UNSW Faculty of Science, the Centre for Photovoltaic
Engineering co-sponsored the 2005 UNSW Sunsprint Model Solar Car
Challenge. This was the NSW state competition of the annual Australian
International Model Solar Challenge and involved 15 schools and nearly
100 high school students. The top teams from this competition went on to
compete for the national title in Adelaide. Participants spent, on average,
four months designing and building their model solar racecar.

For the fi rst time in 2005, UNSW Minisprint
was also held alongside Sunsprint and involved
24 model solar cars. Minisprint is especially
designed for primary school students.
Where a competitive model solar car for the
high school competition takes four months to
design and build, the Minisprint model solar
racecar is bult from raw materials supplied
as a kit and can be assembled by primary school
students, with a bit of help, in an afternoon.
The thrill of the competition is tremendous for
these students and the feedback from teachers
regarding teaching outcomes and student
motivation shows the effectiveness of this
competition.
5.8.8 Virtual World Solar Car Challenge
Every two years a World Solar Car Challenge is held where teams race solar cars from
Darwin to Adelaide. This event was held from the 25th September to the 2nd October 2005
and in association with this the Centre conducted a Virtual World Solar Car Challenge, using
a computer program that had been developed as part of the fi rst year teaching curriculum.
As part of the Virtual World Solar Car Challenge, students design a virtual solar car within
budgetary constraints and race it in a simulated race from Darwin to Adelaide. This
competition was conducted throughout September and marketed to all high schools across
Australia. Over the month the website experienced 5621 hits from 1440 students from high
schools in every state and territory of Australia. The most number of entries came from QLD
and WA and the Centre was contacted by several high school teachers seeking permission to
use the game as part of their Engineering Studies curriculum. At the end of the competition
the Centre presented a winner and runner-up prize, with Dr Corkish attending Normanhurst
Boys High to present the winner Edmund Tse with his plaque and winner’s cheque.
The fl yer sent to every high school around
Australia promoting the Virtual World Solar
Car Challenge.
Edmund Tse receiving his plaque from
Dr Richard Corkish
141

5.9 Educational Collaboration
A range of collaborations have been established between the Centre and other educational
institutions and organisations. These collaborations involve the development and
implementation of educational programs and courses, the provision of support for student
projects and theses, and the exchange of students and staff.
5.9.1 BP Solar Sydney
BP Solar manufactures, designs, markets and installs solar systems for residential,
commercial and industrial sectors. The Australian branch of BP Solar is located at Sydney
Olympic Park and staff from this company kindly donated the use of their Solar Powered Ice-
Cream Cart to the Centre for use on Courses and Careers Day to increase the awareness of
photovoltaics in a novel manner.
5.9.2 Edwards Hot Water
Edwards Hot Water produces hot water systems for domestic and commercial purposes
using a variety of energy sources which includes solar. This organisation has supported the
second year biodiesel trailer over the last few years and provided ongoing advice and support
to students working in the project in 2005.
5.9.3 The Foundation of Goodness
Based in tsunami-affected Seenigama, Sri Lanka, The Foundation of Goodness is a nongovernment
organisation which assists villagers in Seenigama and neighbouring areas with rebuilding
housing, infrastructure and livelihoods, and providing medical care, welfare, education
and skills development. The organisation has been active for 6 years and students and staff
involved with the second year developing countries project liaised with this organisation in
preparation for travel to Sri Lanka in 2006 to install photovoltaic powered water pumping
and water fi ltration systems.
5.9.4 Fowlers Gap UNSW Arid Zone Research Station
In 2005 a fourth year thesis student collaborated with staff
at UNSW’s Fowlers Gap Research Station, 110 kilometres
north of Broken Hill in the state’s far west. The aim of the
project was to test and maintain an existing photovoltaic
pumping system, and to design and install a new water
pumping system suitable for stock watering. The student’s
work was deemed a success in that repairs she made to
the array increased output by more than 33 percent which
provided the homestead with suffi cient water and hence a
new and expensive array was not required.
Shelley Bambrook at Fowlers Gap Station
5.9.5 Kyocera Solar
Kyocera Solar produces and supplies solar energy products and in 2005 donated mounting
frames for the fourth year thesis conducted in collaboration with the UNSW Fowler’s Gap
Arid Zone Research Station.
142

5.9.6 Murdoch University Western Australia
Scientia Professor Wenham was awarded an adjunct appointment at Murdoch University to
help the university implement a new undergraduate degree in Renewable Energy Engineering
which commenced in 2001. Prof Wenham still holds this appointment and is also a member of
the Murdoch University Renewable Energy Engineering Board. This collaboration is important
for the exchange of educational material for both institutions.
5.9.7 Queensland Sustainable Energy Industry Development Group (QSEIDG)
The Queensland Sustainable Energy Industry Development Group was formed in 2004 to
enhance collaboration between government, education, industry, and community organisations
involved in sustainable energy and energy effi cient projects in Queensland. This organisation
has developed mobile training facilities to raise awareness of sustainable energy. Each trailer
has working examples of photovoltaic systems, wind energy systems, solar hot water heating
and water pumping. The organisation has allowed the Centre to use their design for this
trailer to build our own mobile display unit suitable for the annual Courses and Careers Day.
5.9.8 Randwick City Council
The Centre is in collaboration with the Randwick City Council on a fourth year thesis which
is investigating the potential application of high-profi le, public renewable energy projects in
the Randwick City Council area. Feasibility studies are to be conducted as part of this project
which commenced in July 2005 and will be completed mid-2006.
5.9.9 Suntech Power Corporation
Suntech, a partly Australian-owned company operating in China, has been actively involved
in assisting UNSW with the development, testing and evaluation of educational material in
the PV area such as in the development, testing and evaluation of a software package called
the Virtual Production Line. Signifi cant numbers of UNSW undergraduate students also
participate in industrial training at Suntech. These students fi nd their time in China an extremely
valuable educational and cultural experience. This collaboration has also resulted in members
of Suntech visiting the Centre and obtaining experience in the Centre’s laboratories.
143

Dean of Engineering
Other Schools
School of Photovoltaic and Renewable
Energy Engineering
Head: Dr Richard Corkish
School Administration
Trichelle Burns
Centre Excellence in
Advanced Silicon Photovoltaics
and Photonics
Undergraduate
Education
Advisory Committee
Director: Prof. Stuart Wenham
Res. Director: Prof Martin Green
Management Committee
Administrative
Support
Jenny Hansen
Research Programs
Business and
Operations Support
Mark Silver
Photovoltaics
and Solar Energy
Renewable
Energy
Engineering
Postgraduate Education
- Coursework and Research
Dr Jeff Cotter & Dr Alistair Sproul
Wafer-Based Projects
Manager: Dr Jeff Cotter
Silicon Thin Films
Manager: A/Prof. Armin Aberle
Third Generation
Manager: Dr Gavin Conibeer
Silicon Photonics
Manager: A/Prof. Jianhua Zhao
144

The Management structure of the Centre and how it fi ts into the University system is shown
below. When the Key Centre for Photovoltaic Engineering was awarded in 1999, it was
established as an autonomous Centre within the Faculty of Engineering of UNSW, becoming
independent from the School of Electrical Engineering within which the photovoltaic activities
had been previously located. At that time, the Key Centre was given the same operational
independence and rights as the other Engineering schools, with the Director Stuart Wenham
being given the same status and authority as other Heads of Schools. With the awarding of
the Centre of Excellence in 2003, the University made the commitment that the Key Centre
for Photovoltaic Engineering would become the School of Photovoltaic Engineering, within
which the ARC Photovoltaics Centre of Excellence would be located. This transition occurred
in January 2006.
Within the Centre of Excellence, Deputy Directors have been appointed for each of the major
strands of research as shown. Each Deputy Director is of the highest calibre, and would
make worthy Directors or Research Directors in almost any major research Centre in this
fi eld internationally. In fact when establishing the Centre of Excellence, it was noted that three
of the four Deputy Directors, along with the Centre’s Director and Research Director, have
all held prior positions as Directors or Deputy Directors of ARC Special Research Centres.
All four Deputy Directors were originally from overseas (USA, Germany, China and the UK),
being attracted to Australia by the opportunity of being involved in the photovoltaic research
activities at UNSW.
The Management Committee of the Centre comprises the six Directors and Deputy Directors,
along with the Head of School, the Head of Characterisation and the Business and Operations
Manager. This committee meets fortnightly on the 1st and 3rd Fridays of each month, with
each Deputy Director giving a report on the activities in his or her area over the preceding
fortnight. This committee takes responsibility for decision making within the Centre that
affects the Centre as a whole, while the individual Deputy Directors receive their own annual
budgets to allow them to make and implement decisions that impact only their own laboratory
areas and research activities.
The Advisory Committee for the Centre comprises the Centre Directors, the Head of School
for Photovoltaic Engineering, leading academics from other institutions, industry leaders such
as CEO’s of various companies involved in the fi eld, and research leaders. This committee
provides high level advice, feedback and recommendations in relation to the Centre’s
activities and their relevance. The Advisory committee meets annually, taking into account the
geographical separation of its members (Australia, USA, China, Italy, Germany), although more
frequent correspondence takes place when necessary with individual committee members
either by email or telephone. The membership of the Advisory Committee includes:
145

• Professor Stuart Wenham, Centre Director
• Professor Martin Green, Centre Executive Research Director
• Associate Professor Armin Aberle, Deputy Director of the Centre (2nd Generation
PV research)
• Associate Professor Jianhua Zhao, Deputy Director of the Centre (Photonics)
• Dr Jeff Cotter, Deputy Director of the Centre (1st Generation PV Research)
• Dr Gavin Conibeer, Deputy Director of the Centre (3rd Generation PV Research)
• Professor Allen Barnett: world leading academic in the fi eld; recipient of many
prestigious international prizes such as the William Cherry Award; former
President of AstroPower, one of the world’s largest solar cell manufacturers,
before being purchased by GE.
• Dr Zhengrong Shi: CEO of Suntech-Power, another of the world’s largest solar cell
manufacturers; recipient of various industry prizes; former Deputy Research
Director of Pacifi c Solar; major collaborator of the Centre.
• David Hogg: CEO of CSG Solar AC, Germany; former CEO of Pacifi c Solar, Australia;
• Mr. David Jordan, Manager of New Technology, BP Solar International;
• Prof. Andres Cuevas, ANU;
• Prof. Peter Würfel, Institut fur Angewandte Physik der Universität Karlsruhe;
• Dr Francesca Ferrazza, Chief Scientifi c Offi cer, Enitechnologie.
Also within the Management structure and a member of the Centre’s Management Committee
is the Centre’s Business, Technology and Operations Manager Mark Silver, given the extensive
involvement of Centre staff with industry, large number of collaborative research projects,
and the high level of success of the Centre in generating, marketing and commercialising
technology. The Head of Administrative Support for the Centre is Jenny Hansen. Not shown
in the Management Structure is the Financial Offi cer Julie Kwan who looks after the Centre
Accounts, interfaces with the University Financial System, advises the Centre Directors and
Deputy Directors on budgeting and fi nancial matters, and generally assists with sourcing
of funding, purchasing, reporting, writing grant applications, and advising on business
opportunities.
A primary responsibility of the Director in the Centre is to ensure the Management structure
as shown functions effi ciently and effectively, with appropriate support and resources to
facilitate the Centre’s achievement of its milestones and performance targets. An important
aspect of this is managing the Centre’s fi nances to ensure suitable levels of funding are
made available for supporting the four major research strands, while simultaneously
ensuring adequate funding is available for repair and maintenance of existing facilities and
the purchasing of appropriate new infrastructure and equipment. Another important aspect
relates to how the Centre has been assimilated and functions within the university system, and
how the Centre interacts with industry, other research and teaching institutions, the various
levels of government and the broader community. The Director also has a signifi cant role in
the appointment of new staff, the establishment and operation of the Centre’s Management
Committee, and the establishment and operation of the Advisory Committee to facilitate
quality feedback and guidance for the Centre’s Management Committee.
The Director works closely with the Centre’s Executive Research Director to assist in setting
high level research direction and priorities for the Centre’s programs. In the teaching area,
with the Key Centre for Photovoltaic Engineering and its activities being incorporated into
the Centre of Excellence, the Director also takes signifi cant responsibility in ensuring the
successful development and implementation of the Centre’s educational programs, both
at undergraduate and postgraduate levels. In this area, the Director works closely with Dr
Richard Corkish, the Head of School.
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7.1 PROGRESS AGAINST CENTRE DESIGNATED MILESTONES
In its initial application, the Centre proposed 18 challenging research milestones for its
5-year program, as well as 4 teaching milestones, 4 “linkage” milestones and 5 governance
milestones. Progress towards these milestones is reported below.
Research Milestones
A.1
Efficiency improvement of standard p-type silicon cells to 26% or n-type cell to 24%.
With the growing industry interest in n-type wafers for solar cell manufacturing, the Centre
has focused on developing its highest performance solar cells to suit this type of wafer.
Excellent progress has been made, particularly in recent months, with the Centre equalling
the world record of 22.7% effi ciency for this type of wafer, held for more than a decade by
Stanford University.
Importantly, the Centre’s new high effi ciency designs for the n-type wafers are still far from
optimised with the expectation that the Centre will set more world records in this area during
the next couple of years, thereby establishing a clear lead over competitors internationally.
A.2
Efficiency improvement of Si cell boosted by an up- or down- converter to 28%.
This milestone is linked to A10. An increase in spectral response in the range 1480 to
1580nm (i.e. well below the band edge of Si) for a bifacial Si cell has beendemonstrated
representing a very small increase in current, which nonetheless represents a proof of
concept.
Further work on increasing the sensitivity to light between 1250 & 1480nm which should in
turn increase this up-conversion current, is being carried using two approaches (see Section
4.5.5). PbSe quantum dots absorb photons between 1250 & 1480nm, which then undergo
non-radiative transitions and are re-emitted at longer wavelengths, inside the absorption
range of the erbium (Er) in the Up-conversion phosphors. Alternatively, addition of dysprosium
(Dy) to the erbium.doped phosphors, provides energy levels for absorption of photons between
1250 & 1480nm. Again these decay non-radiatively in the Dy atoms to be re-emitted within
the Er absorption band.
A patent application has been fi led on a new up-conversion approach.
A.3
Demonstration of large-area buried contact silicon solar cell of efficiency above 21% and/or
multicrystalline buried contact solar cell above 18%.
The link between boron diffusion induced dislocations and a key recombination mechanism
limiting solar cell performance for p-type buried contact silicon solar cells has been
identifi ed.
The boron diffusion induced dislocation has been identifi ed as one of the major effi ciency
limitations of double-sided buried contact solar cells, which have now reached effi ciencies as
high as 18.6% on FZ(Boron) and 18.6% on Cz(Ga) despite this limitation.
The signifi cance of defects in n-type and p-type silicon wafers using side by side comparison of
similar n-type and p-type solar cells has been demonstrated.
We have achieved cell effi ciencies as high as 19.2% on textured FZ(Phosphorus), and
performance levels almost as high on Cz(Phosphorus) n-type wafers.
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A.4
A.4.1
Demonstration of at least three new promising technologies for use in conjunction
with commercial buried contact solar cells.
Stencil printed solar cells
We have developed and demonstrated single and double level stencils for the printing of fi neline
metallisation lines on silicon solar cells, which can be used to print the metallisation for
buried contact solar cells.
We have demonstrated precision alignment of both the stencil and the surface grooves of
a selectively diffused emitter for a buried contact solar cell. This type of buried contact solar
cell captures many of the benefi ts of printed solar cells yet has the potential to improve both
current and voltage of these cells.
We have already demonstrated solar cell effi ciencies of over 16% with the stencil print
technology, comparable with the best commercially manufactured screen-printed solar cells
fabricated using the conventual structure (typically 16.0-16.5% effi ciency).
A.4.2
Hybrid buried contact/screen-printed solar cells
An innovative emitter structure for screen-printed solar cells incorporating semiconductor
fi ngers, has been developed in conjunction with Suntech-Power company and is described in
the section on industry collaborative research.
Improvements during 2005 have increased effi ciencies from about 15% in 2004 to above
18% effi ciency, now well ahead of conventional screen-printed solar cells that are typically
16-16.5% effi ciency.
This new design addresses the fundamental limitations of screen-printed metallisation
schemes that have limited the performance of screen-printed solar cells for more than 30
years. The approach captures the performance advantages of buried-contact solar cells with
a selective emitter, low top surface shading losses, and a well passivated and lightly diffused
top surface, while simultaneously retaining the simplicity and manufacturability of screenprinted
solar cells including the use of all the same equipment and infrastructure.
A.4.3
Micro-contact Silicon Solar Cell
An improved rear surface design for the buried contact solar cell that minimises the electrode
diffusion/contact area, has been developed and demonstrated. This new technology appears
to have the potential for high effi ciency.
Test devices have demonstrated a large reduction in the recombination associated compared
to the standard laser-groove contact used in the buried contact process, with open-circuit
voltages approaching 685 mV achieved. This indicates the potential for achieving high
effi ciency once the remainder of the structure is optimised to minimise optical and parasitic
resistive losses.
A.5
A.5 Demonstration of optical pathlength enhancement > 30 in a silicon thin-film.
Recent collaborative work with CSG Solar has resulted in optical pathlength enhancement
above 20 in the thin crystalline layers deposited onto textured glass. Further improvement is
expected in the near future.
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In parallel, the AIT glass texturing method (AIT = Aluminium-Induced Texture) is being
developed at UNSW. Patent protection has been sought for the AIT method (Glass texturing,
International PCT patent application PCT/AU2004/000339, priority date 7/04/2003).
A.6
Demonstration of series interconnection of silicon thin-film solar cells without the use
of metal interconnects and improved durability and performance for such devices.
Good progress has been made in developing new cell designs that minimise the requirement
for metal contacts. Conventional cell designs require a metal grid on the light receiving
surface and then another metal contact on the opposite surface, to collect current and
conduct it parallel to the cell surface to a point or region where the current is subsequently
transported to the adjacent solar cell. The new cell design completely alleviates the need for
such metal, with the only remaining metal being used to conduct the generated current a
short distance of only 40 microns across the isolation region produced by the laser between
series connected cells. This cell interconnection approach is achieved with the SAMPL, a
self-aligned maskless photolithography method. Patent protection has been sought for this
cell interconnection method (Thin-fi lm solar cell inter¬connection, International PCT patent
application PCT/AU2005/000734, priority date 4/06/2004).
The latest cell designs will aim to eliminate the fi nal metal components by utilising doped
semiconductor material to conduct the current the short distance of 40 microns between
juxtaposed cells.
A.7
Demonstration of 11% efficient silicon thin-film cell deposited onto glass.
Work towards this goal progresses along two paths. One is the involvement of senior Centre
staff as Consultants for UNSW’s spin-off company CSG Solar Pty Ltd (formerly Pacifi c Solar
Pty Ltd), aiming at the improvement of the company’s CSG (crystalline silicon on glass)
technology from 8.2% effi ciency in 2003 to 11% by the end of 2007. Good progress is being
made through this collaboration, with the best CSG Solar modules now having effi ciencies of
over 9%.
The second path is the independent research performed in the Centre’s Thin-Film Group. As
outlined in Section 4.4, three novel poly-Si thin-fi lm solar cells on glass are being developed
(EVA, ALICIA, ALICE). The focus in 2005 was on improving the voltages and the quantum
effi ciency of these cells, and on making functioning mini-modules. Good progress has been
made with all three cell technologies, with open-circuit voltages now in the range 440-517
mV and internal quantum effi ciencies of up to 70%. The 517-mV result is, to our knowledge,
a new world record for homojunction poly-Si thin-fi lm solar cells on glass. Simple solar cells
(“Mesa cells”) with effi ciencies of up to 3% have so far been made from these novel solar
cell materials. First functioning mini-modules have also been realised. The present research
focuses on boosting the short-circuit current of these cells to above 20 mA/cm2 and the
cell effi ciency to over 5%.
A.7
Demonstration of 10% photoluminescent efficiency in silicon and above 98% in GaAs,
sufficient to produce device refrigeration.
The fi rst part of this milestone was achieved in 2003. In photoluminescence (PL) testing
using oxide passivated FZ silicon wafers with textured front surfaces, we have demonstrated
EQE (external quantum effi ciency) up to 10.2% at T = 130K and 6.1% at room temperature.
[T. Trupke, J. Zhao, A. Wang, R. Corkish and M.A. Green, Appl. Phys. Lett. 82, 2996, (2003)].
The IQE (internal quantum effi ciency) is also estimated to be over 20%. The results of this
work were also used to measure the radiative recombination coeffi cient B(T) [T. Trupke et
al. J.Appl.Phys. 94, 4930 (2003)]. Further improvement in the PL effi ciency is expected
from thinning substrates with textured surfaces, and improving the light-trapping surface
structures.
149

Progress towards the second milestone has been good with 96% effi ciency for GaAs devices
demonstrated in the Centre’s fi rst year of operation (Section 5.5 of 2003 report). PL EQE
measurements were carried out on an 800 nm sample of GaAs, sandwiched in a double GaInP
heterojunction structure so that carriers are confi ned in the GaAs. Two measurements were
used: a calibrated PL technique which gave 90% EQE for planar samples and a combined
thermal/PL measurement that gave 92% ± 3% EQE (a reasonable agreement). Further
calibrated PL measurements with the ZnSe dome to couple light out of the sample gave an
increase from 90% to 96% EQE.
Further progress predicted to increase the EQE towards the 98% for GaAs was achieved in
2004, with development of the texturing technique required for the back surface. Modelling in
2004 showed that this would bring the 96% with a ZnSe dome to a 97.5% external quantum
effi ciency – remarkably close to the 98% fi gure calculated to be required for PL cooling.
As the primary aim of this task was to improve insight into the physics and technology of
improved radiative emission, rather than to achieve radiative cooling itself, no further work
has been carried out or is planned in this milestone area.
A.9
Efficiency improvement for a silicon based tandem cell over a single cell baseline.
Signifi cant progress has been made in demonstrating an enhanced band gap material for
the top cell for a Si based tandem (see Section 4.5.2). Both Si/SiO2 quantum-well (QW)
and quantum-dot (QD) structures have been fabricated. These have also been grown in the
multilayer structures that will be required for the superlattice structures of an enhanced
band-gap material.
Photoluminescence (PL) at enhanced energies has been demonstrated. The enhancement
in PL energy is in general agreement with quantum confi nement calculations based on the
dimensions for QW and QD structures observed in TEM (within the approximately 20%
errors in the size measurements). X-ray diffraction and work on the artefacts present in TEM
of such small structures is improving the quantitative validity of these calculations.
A PL energy at 1.7 eV has been observed for 1-2 nm QDs; this being the ideal band gap for
an upper cell material on Si. Further evidence for quantum confi nement in the Si QDs comes
from the greatly enhanced PL intensity indicative of localisation in the QDs.
This work includes initial measurement of the electrical properties, with promising, although
still high, resistivities. It has been demonstrated that these can be reduced to about 103
Ω.cm with hydrogen passivation. Further information on resistivity variation with temperature
has been obtained in 2005 which is giving an indication of the activation mechanisms.
Furthermore, there has been success with the fabrication of the analogous structure of
Si QDs in Si3N 4 , with TEM evidence of nano-crystals by both sputtering and PECVD. The
advantage of the nitride matrix is that the lower barrier height should improve conductivity
for a given QD density, although optical and electrical properties are still being tested. PL
evidence for enhanced energy levels in these Si QDs in Si3N4 matrix has been achieved with
preliminary evidence for higher energies than for similar sized dots in oxide – although this
remains to be confi rmed.
This technique is now starting to be applied to Si QDs in silicon carbide (SiC). SiC having an
even lower barrier height and hence expected higher tunnelling probability between QDs and
hence higher conductivity.
150

A.10
Demonstration of photon down-conversion quantum efficiency above 50% and/or
up-conversion efficiency above 10% and demonstration of performance improvement
in a baseline cell by either approach.
Work to date has concentrated on up-conversion (see Section 4.5). For a luminescent
phosphor, NaYF4: 20% Er 3+ supplied by the University of Bern, an external quantum effi ciency
(EQE) of more than 3.5% has been measured. Furthermore small improvements in below
band gap photoresponse have been measured for bifacial cells with luminescent phosphors
on the underside. Although only very small current increases are observed, these are very
promising results for non-optimised materials. A baseline test cell has been established using
bifacial cells for up-conversion comparative tests.
Properties of down-conversion luminescent materials have been surveyed in the literature
and form the subject of a review paper by authors from the Centre [Richards BS, Solar
Energy Materials (2005) submitted]. For some mechanisms these can be up to 1.2 EQE,
i.e., 1.2 low energy photons out for one high energy photon in, and hence useful for effi ciency
increase. However, in such materials there are many other mechanisms operating in parallel
which bring the overall EQE to about 0.9. Nonetheless these fi gures are promisingly close to
an EQE of 1, i.e., 50% of the ideal performance and hence close to the threshold useful for
increased effi ciency from down-conversion.
Ideal quantum effi ciency for a down-conversion process is 2, i.e., two low energy photons out
(above the cell band gap) for each high energy photon in. The milestone refers to achieving
50% of this ideal performance, this being the effi ciency above which real gains in PV effi ciency
are achieved.
A.11
Demonstration of two key elements required for hot carrier cell implementation:
energy selective contacts and enhancement of radiative recombination rates relative
to relaxation rates of photogenerated carriers.
The luminescence from QDs mentioned under Milestone A.9, is consistent with enhanced
band gap emission from QD superlattices. There has also been experimental evidence of
resonant tunnelling in these structures. The radiative effi ciency improvements for GaAs
mentioned under Milestone A.8 are also relevant for improved understanding of hot carrier
absorbers.
Experimental progress has been made towards selective energy contacts. This has been
achieved with the demonstration of negative differential resistance (NDR) in samples
containing a single layer of quantum dots sandwiched between two oxide layers (see Fig. 4.102
in 2004 Annual Report). This indicates resonance in the tunnelling current across the two
oxide barriers – this being a necessary pre-requisite for selective energy contacts. Further
work on improving the quality factor of this NDR response is in progress. In addition. in 2005,
characterisation of these structures has been improved with two additional techniques.
Firstly conductive atomic force microscopy (CAFM) in collaboration with Melbourne University,
gives much greater spatial resolution of resonant tunnelling centres (Section 4.5.6.1.1). The
technique requires thinner oxide layers than at present but has already demonstrated detailed
mapping of a resonant tunnelling structure. Secondly, a technique of optically assisted I-V has
been established, which uses optical excitation of carriers retaher than a bias fi eld (Section
4.5.6.1.2). This has already demonstrated more direct evidence for hot carrier generation
and collection.
151

The theory of hot carrier absorbers has been extended to include a greater understanding of
phononic transport and a recognition of similarities to the required properties of thermoelectric
materials (see “Hot Carrier Absorbers” in Section 5.5 in 2003 Annual Report). In particular
the specifi c mechanisms which can slow cooling by enhancing the “phonon bottleneck effect”
in QW and QD superlattices are being identifi ed. Experimental evidence of such reduced
cooling in QW superlattices has been identifi ed in the literature. (See section “Hot Carrier
Absorbers” in section 4.5 in 2004 Annual Report). This work has been extended further in
2005 with modelling of the specifi c phonon mechanisms and quantum dot conditions that
can give an enhanced ‘phonon bottleneck effect’ in QD nanostructured materials.
A.12
Demonstration of the quantum confined Stark effect in silicon as the basis of a highspeed
silicon modulator).
Devices of an appropriate structure were fabricated during 2003, but silicon layers needed
to be thinner to demonstrate this effect. Progress was made in 2004 and 2005 in reducing
the thickness of these layers, that are now close to the desired value.
A.13
Evaluation of the optical constants of quantum confined silicon SOI devices as a
function of layer thickness.
Relevant data have been reported in section 5.5 of the 2003 Annual Report and section 4.6
of the 2004 report. Photoluminescence properties have been characterised. Conversion
to optical constants requires accurate knowledge of the dimensions of the confi ned material.
Measurement of these produces some experimental challenges, presently being addressed.
The most accurate method seems to be by identifying photoluminescence features
corresponding to regions differing by the presence of one additional atomic plane in the
region under test. However, fi nding an independent technique that is able to confi rm this
interpretation of the data has provided a challenge.
Other work quantifying the evidence for QDs and their dimensions is continuing. This includes
analysis of HRTEM, high resolution SIMS and synchrotron XRD.
A.14
Improvement of light emission efficiency of silicon diodes above levels already
demonstrated, to maintain Australian leadership and as a test bed for integrated
devices.
Australia retains leadership in the bulk silicon luminescence fi eld, although efforts during the
last 12 months have concentrated on integrated devices.
A.15
Demonstration of high light emission efficiency in silicon LEDs integrated into
microelectronic chips.
Effi ciencies of 2x10 -6 have been demonstrated, although further improvements are expected
as devices become thinner.
A.16
Demonstration of high speed modulation of output of silicon light emitting diodes.
Modulation has been demonstrated, but not yet at high speed.
152

A.17
Demonstration of operational microelectronic circuits communicating at high data
rates using silicon light emission and detection.
This is a target for the fi nal year of the program. To date, we have demonstrated the targeted
communication between bulk silicon devices, probably for the fi rst time, but data rates
are slow, as expected. Test structures for demonstrating this at the chip level have been
designed.
A.18
Investigate the feasibility of obtaining lasing action in both bulk and quantum-confined
silicon and, if feasible, demonstrate the first laser in these materials.
Several new mechanisms for demonstrating lasing in bulk silicon continue to be investigated.
Teaching Milestones
C.1
At least 50 honours students completing their degrees by 2007
The Centre of Excellence has performed particularly well in the educational areas with 31
students having completed their degrees and graduated with honours in the last 2 years.
The Centre has already achieved, throughout its duration, an average of more than the
required 10 honours graduates per year, despite the time-lag associated with producing the
fi rst graduates.
Based on the performance and the numbers of students enrolled in the Centre’s degree
programs, there will be a further 30-40 students graduating with honours by the end of
2007. This will therefore give a total of 60-70 students graduating with honours, exceeding
the Centre’s target number of 50.
C.2
At least 20 new postgraduate students involved by 2007
Nineteen new postgraduate research students have enrolled in the Centre since 2003,
making the Centre well on track towards achieving this milestone.
Importantly, the rate of enrolments have been steadily increasing since the establishment
of the ARC Photovoltaics Centre of Excellence with 4 new postgraduate research students
enrolling in 2003, 7 in 2004, followed by 8 in 2005.
C.3
The involvement of at least 10 postdoctoral research fellows by 2007
The Centre of Excellence has already achieved this 5-year target with the involvement of 15
postdoctoral research fellows since 2003. These include Dr. Robert Bardos, Dr. Andrew
Brown, Dr. Kylie Catchpole, Dr. Eun-Chel Cho, Dr. Gavin Conibeer, Dr. Didier Debuf (Adjunct
Fellow), Dr. Tammy Humphrey, Dr. Dirk Kőnig, Dr. Kuo-lung Lin, Dr. Bryce Richards, Dr. James
Xia. Dr. Per Widenborg, Dr. Thorsten Trupke , Dr.Anita Ho and Dr Peter Cousins.
C.4
The development of at least 4 courses on photovoltaics suitable for internet-based
delivery with at least 1 such internet-based course offered each year
Two courses have now been developed for internet delivery, with both being run during session
2, 2005.
153

The fi rst course, based on the postgraduate course Photovoltaics SOLA9001, has been
completed and successfully run on multiple occasions, with course enrolments from many
countries.
The second is based on the undergraduate course Sustainable and Renewable Energy
Engineering SOLA2053. The latter is currently being offered electronically on-line via Web CT
for local students enrolling during session 2, 2005, to demonstrate suitability for internetbased
delivery internationally.
A third course is under development for on-line delivery and is based on the course Solar Cell
Technology and Manufacturing SOLA9006. A CD has been produced that contains all the
necessary teaching material, assignments and simulation software for project work, with this
likely to be offered over the internet internationally during 2006.
“Linkage” Milestones
G.1
Total Average Cash and equipment Contribution of at least $600,000 p.a. from
UNSW
As documented in the fi nancial section within Centre Annual Reports for 2003, 2004 and
2005, UNSW has made cash contributions to the Centre of approximately $1 million each
year, well above the target allocation of $600k.
In addition, with the Centre receiving “school” status, EFTSU income has been awarded to the
Centre with additional earnings of close to $3 million.
G.2
Allocation of at least 70m 2 office space and 180m 2 laboratory space by UNSW
The Centre’s space needs for new offi ces have been signifi cantly greater than expected due
to the growth in numbers of PhD students, post doctoral researchers and visiting Fellows/
Academics associated with the Centre of Excellence. UNSW has responded well as the need
has arisen, with 385m 2 having now been made available.
Regarding Laboratory space, an additional 200m 2 of space has been made available for the
Centre of Excellence, primarily to accommodate the new state-of-the-art facilities at Bay St,
Botany.
G.3
Support for at least 4 academic staff affiliated with the centre from EFTSU or related
income
UNSW has again exceeded its targeted support during 2004 through the provision of staff
funded from EFTSU generated income or related sources. The staff supported either partially
or fully are listed in the Annual Report and include: Dr J. Cotter; Dr A. Sproul; Professor S.
Wenham; Dr R. Corkish; Dr M. Watt; Dr B. Richards; Dr A. Ho; Ms A. Bruce; Dr G. Stephenson;
and M. Kobacker.
G.4
Average of at least 3 weeks per year of interchange between collaborating
organisations
This target has been comfortably exceeded as documented in the section on collaborative
research in Section 4.7.
154

Governance Milestones
H.1
Establishment of Advisory and Management Committees during 2003.
As was reported in the 2003 Annual Report, this milestone has been achieved.
The Advisory Committee of the ARC Centre of Excellence has met in June 2004 and June
2005.
The Management Committee meets fortnightly. The membership of the latter includes the
Centre Director (S. Wenham), the Executive Research Director (M. Green), the 4 Deputy
Directors (G. Conibeer, J. Zhao, J. Cotter and A. Aberle), the Head of Characterisation (A.
Sproul), the Head of School for the Centre for Photovoltaic Engineering (R. Corkish) and the
Centre’s Business and Technology Manager (M. Silver).
H.2
Formation of the School of Photovoltaic and Renewable Energy Engineering and the
appointment of a Head of School during 2003.
Richard Corkish offi cially appointed as Head of School in August 2003, indicating impending
recognition of School status
UNSW Council meeting in July 2005 approved the offi cial formation on 1 January 2006 of
the School of Photovoltaic and Renewable Energy Engineering
H.3
Establishment of the Management Structure of Figure H.1 of the initial application
by June, 2003, with appropriate documentation of responsibilities of all staff and
managers.
The Management structure of Section 6 was successfully established in early 2003 as was
reported in the 2003 Annual Report. Since initially being established, the following changes
have been made:
Dr J. Cotter has taken over as Manager of the wafer-based projects in C. Honsberg’s
absence, with his automatic inclusion in the Management Comittee
Head of School, Richard Corkish, was appointed Aug. 2003
G. Conibeer replaced R. Corkish as manager of the Third Generation strand.
T. Burns took over responsibility for School Administration
The roles and responsibilities for most staff are defi ned, in most cases, in their offi cial Position
Descriptions, held by Human Resources Department. These are routinely reviewed and
revised at times of appointments and reappointments.
In special cases, such as for the Head of School who is responsible to the Dean of Engineering,
additional documentation exists: http://www.hr.unsw.edu.au/poldoc/hos.htm. Management,
staff and student responsibilities for occupational health and safety are documented by the
UNSW Risk Management Unit
H.4
Consolidation of New Centre Strategic Plan in New Document by June, 2003.
Following the achievement of this milestone in 2003, the strategic plan is regularly reviewed
in consultation with the Head of School and the Dean of Engineering.
A copy of the Centre’s Strategic Plan is held by the School of Photovoltaic Engineering
155

H.4
H.5 Document Management and Advisory Committee Meetings at least monthly
and annually, respectively.
Advisory Committee meetings have been held annually in June 2004 and June 2005.
Management meetings are scheduled fortnightly. At the latter, reports have been written for
each meeting to document progress in each of the research areas.
Monthly overview meetings are also held for the entire Centre for information dissemination
and the presentation of brief (6 minute) reports from each area of activity including the Lab
Operations Team, External Affairs and Teaching.
In addition to the overview meetings, members of the Management team also hold
meetings with the respective staff and students from their particular area in relation to the
corresponding research and other activities. Such meetings are normally held either on a
fortnightly or monthly basis, except for teaching meetings which involve most staff and are
only held every few months.
8.2 Progress Against ARC Designated Performance Indicators
Subsequently to the initial application, the ARC also designated an additional set of performance
indicators. Progress against these is documented below.
Quality of publications – the Centre has achieved its target of 30% of its publications in
refereed journals each year, with 31.5% in 2003 and 35.6% in 2004 and 33.6% in 2005.
The Centre’s 2005 publications are listed towards the end of this report.
Number of publications – the Centre has easily achieved its target of 50 publications per year
with 89 in 2003, 101 in 2004 and 113 in 2005.
Number of patents per year – the Centre’s programs have led to more than the expected 1
new patent per year. In fact there were 2 in 2003, 4 in 2004 and 7 in 2005. The patents are
reasonably well distributed between the three generations of PV technology with 4 in the 1st
generation PV area, 5 in the 2nd generation PV area, 3 in the 3rd generation PV area and 1
in the characterisation area.
Invitations to address and participate in International Conferences – the Centre has easily
achieved its target of 2 per year with more than 40 of such invitations having been received
since 2003.
Invitations to visit leading international laboratories – quite a few Centre staff regularly receive
invitations to visit leading international laboratories with almost 30 such invited visits taking
place. This is well above the target number of 2/year.
Number and nature of commentaries about the Centre’s achievements – the target number
of 2 media articles per year has been well exceeded with more than 50 examples of such
media interaction documented.
Number of postgraduates recruited – the Centre has recruited 25 postgraduate students
since 2003, well ahead of the target of 4 per year. The new enrolments include 19 postgraduate
research students and 14 postgraduate coursework students.
156

Number of postgraduate completions – the Centre has achieved 23 postgraduate completions,
comprising 14 postgraduate research students and 9 postgraduate coursework students.
Most of the former commenced their research degrees before the Centre commenced,
with completion numbers expected to increase over the next couple of years due to the
increased numbers of enrolments since being awarded the Centre. Despite this, the numbers
of completions are well ahead of the target value of 3 per year.
Number of honours students – despite the challenging target of producing 10 honours
students per year and the delay in producing the fi rst graduates, the success of the Centre’s
new undergraduate program has enabled it to comfortably exceed this average with 32
honours graduates to date primarily in 2004 and 2005.
Number of professional courses – the Centre on average has run more than 8 such courses
per year, ahead of the target fi gure of 6 per year.
Participation in professional courses – there has been 25 professional courses run by the
Centre since 2003. The target fi gure of 20 enrolments per course has been comfortably
achieved with the course average being above 50.
Number and level of undergraduate and high school courses in the priority area(s) – the
Centre has run a large number of undergraduate courses in the priority area. The average
number run each year exceeds 16, exceeding the target number of 12 per year.
Number of international visitors – the Centre has received approaching 100 international
visitors in the last 3 years well ahead of the target number of 10 per year.
Number of national and international workshops – the Centre has achieved its target of 3
workshops per year with participation in 16 such workshops internationally during the period
2003-2005.
Number of visits to overseas laboratories – these were listed in chronological order in the
documentation produced for the ARC during the Centre’s review in late 2005. The total
number comfortably exceeds the target number of 10 per year.
Examples of relevant Social Science and Humanities research supported by the Centre – as
described above, staff and students from the Centre have been actively involved in developing
countries projects involved in providing renewable energy power sources to materially
disadvantaged people who have in many cases never previously had access to electricity. Six
Centre staff and more than 30 Centre students have participated in these projects including
travelling to locations such as Nepal, Sri Lanka and Nicaragua to live briefl y with the locals,
provide technical expertise to local technicians, design and install PV systems, and train locals
in the use and maintenance of the new technology. This work is usually done in conjunction
with Aid Organisations or local institutions.
Number and nature of commercialisation activities – the Centre has engaged in 15 technology
transfers which have in general been to companies who have licensed or purchased Centre
technology, in some cases prior to the establishment of the Centre of Excellence in 2003. In
addition, with the rapid growth of the PV industry, Centre staff are often also heavily involved
in assisting companies in expanding or setting up new manufacturing facilities. These activities
have exceeded the Centre’s target of 4 such technology transfers per year.
157

Number of government, industry and business briefi ngs – the Centre target of 2 such
briefi ngs has been exceeded with more than 20 such briefi ngs since the commencement
of the Centre. The high fi gure has resulted from the extraordinary rate of growth in the
industry (67% sales growth in 2004; 45% in 2005), with relatively large numbers of business
briefi ngs by Centre staff in particular being sought by the industry
Number of Centre associates trained/ing in technology transfer and commercialisation –
although the target number for this was set at 5, the diversity of Centre technology coupled
with the recent high demand from the rapidly growing industry, has necessitated the Centre
train additional staff and associates in the various areas where there is commercial interest
in the Centre’s technologies. The Centre now has 15 staff and/or research students at a
stage where they feel confi dent in their training for technology transfer. Those trained in
technology transfer often become particularly valuable to industry and are often offered
good employment opportunities. For example, two of the staff listed below have within recent
months accepted offers to work for newly established companies wishing to set up new
manufacturing.
Number and nature of Public Awareness programs – the Centre conducts extensive public
awareness programs, particularly amongst high school students. This has been particularly
important with the Centre developing and establishing the world’s fi rst undergraduate
engineering degree in Photovoltaics and Solar Energy which is only able to attract students
provided students become aware of its existence and relevance. There have been well over
50 examples of activities in which the Centre has been engaged that increase the public
awareness of the Centre’s program and of the photovoltaics fi eld in general.
Annual cash contributions from Collaborating Organisations – the target of $0.5 million per
year has been easily exceeded as documented in the Financial section
Annual in-kind contributions from Collaborating Organisations – the target of $0.5 million
per year has been easily exceeded with most collaborating organisations and companies
preferring to make signifi cantly larger in-kind contributions than cash contributions.
Number of new organisations recruited to or involved in the Centre – more than 20 new
collaborators have been recruited to the Centre, well ahead of the target of 2 per year.
Level and quality of infrastructure provided to the Centre – the Centres infrastructure and
facilities were already world class at the time the Centre was awarded. Since this time the
Centre has further developed its infrastructure and capabilities through acquiring state-ofthe-art
facilities from Pacifi c Solar, using funding of well over $1 million from the University
and State Government of NSW.
Breadth and experience of the members of the Advisory Board – the Centre’s Advisory Board
comprises members recognised as industry leaders including manufacturers, end-users,
academia and research institutes. In particular it includes several Heads of organisations
such as CEO’s of major international companies. The membership is listed in Section 6 on
Organisational Structure.
158
Frequency and Effectiveness of Advisory Board Meetings – the Advisory Board has met
annually as planned. To be effective, a particular challenge for such an Advisory Board, with
membership from 6 different countries, is to achieve adequate meeting attendance. The last
meeting was held in Barcelona in conjunction with one of the major international conferences,
with members from all six countries being in attendance with only two Australian members
being unable to be present. Feedback and advice from Advisory Board members have been
valuable for the Centre’s Management Team in effecting improvements in some areas,
particularly with regard to content in teaching programs and commercial signifi cance of
some of the research.

Quality of the Centre Strategic Plan – the Centre’s strategic plan is of high quality following
several iterations.
The adequacy of the Centre’s Key Performance Indicators – the Centre’s performance
criteria/milestones outlined in the original grant application are proving to be effective in
guiding the research and its focus. Few, if any, have needed modifi cation. In general they
are quite challenging and ambitious. For example, the Centre has made excellent progress
in developing new high effi ciency solar cell technology to suit n-type wafers, with the recent
achievement of equalling the world record with 22.7% effi ciency. Despite this success, the
aim is to achieve the ambitious 24% effi ciency target by the end of 2007. Regarding the ARC
designated performance indicators, their breadth and their direct links to the objectives of
the ARC Centres of Excellence program ensure the Centre adequately addresses all areas
of importance and signifi cance in contributing to the achieving of the program’s aims and
objectives.
Measures of expansion of Australia’s capability in the priority area – the growth rate of
manufacturing capacity in Australia has greatly outstripped the targeted 15% per annum in
recent years, with the largest manufacturer BP Solar signifi cantly expanding their production
capability while Origin Energy is establishing new manufacturing capacity in Adelaide. The
increase in capacity has been so great that locally manufactured product now exceeds
demand in Australia by a factor of 5 (i.e. Australia now exports 80% of its manufactured
product in this industry).
Case studies of economic, social, cultural or environmental benefi ts – the Centre has met its
target of one such case study per year. In 2003, Centre staff were involved in a case study
on Policy Support for Renewables in Australia from the perspective primarily of the social and
environmental impact of photovoltaics. This case study was published in January 2004:
M. Watt, Hugh Outhred and Iain MacGill, “Policy Support for Renewables in Australia
with PV as a Case Study”, Technical Digest, 14th International Photovoltaic Science and
Engineering Conference (PVSEC-14), Bangkok, Thailand, January, 2004, p.1061-1062.
A second case study in which Centre staff have been involved, focused on where PV is heading
in the future, and considered economic, employment, markets, social and environmental
benefi ts. This study culminated in producing for Australia a PV Roadmap with the following
publication stemming from the work in 2004:
M. Watt (2004) “Development of the Australian PV Roadmap”, presented on behalf of
the Australian Business Council for Sustainable Energy at the IEA-PVPS Workshop for
Industry at the 19th European Photovoltaic Solar Energy Conference and Exhibition,
Paris, France, 7-11 June, 2004.
As described elsewhere, the Centre runs projects involving the use of PV in developing
countries. These projects directly impact the economic, social, cultural and environmental
well-being of those being helped. For example, the Solar Sisters program specifi cally aims to
provide PV power to facilitate new opportunities for women such as for educational radio/
television, lighting at night to engage in craft work to earn income, etc. Studies have been done
to identify the social and economic benefi ts of these projects. In 2005, these case studies
are being extended to the indigenous population in Australia for inclusion in the Centre’s
“Developing Countries Projects”. Thesis student Gavin Periera under the supervision of Dr
Richard Corkish, is currently conducting this case study.
Another study being conducted at present by the Centre is a review by Centre staff of
the Federal Government organisation Bushlight. Bushlight is also involved in studying and
capitalising on the social, cultural and economic benefi ts able to be offered by PV and other
renewable energy technologies in providing for the needs of our indigenous communities. At
completion, thesis student Long Seng To, under the supervision of Dr Muriel Watt, will publish
material from this case study.
159

160

Centre 2005 Income
The total income for 2005 for the Australian Research Council (ARC) Centre of Excellence
in Advanced Silicon Photovoltaics and Photonics was $4.67 million. This does not include
funding approaching $1 million from the Host Institution based on EFTSU and related income.
This latter income has been generated by the Centre through its educational activities by
virtue of the fact that it is now equivalent to a School within the Faculty of Engineering. This
income has been used for the development of new courses and teaching materials and to
fund the salaries of most of the academic staff associated with the Centre.
ARC Centre Grant
Other ACR grants
State Government Funds
Industry/Private Funds
Host Institution Support
Other Income
Sources/Interest
Figure 8.1: Centre income by source of income.
The largest component of the Centre’s income was from the ARC totalling $2.6 million, while
the second largest cash component of income was Host Institution support, with UNSW
contributing $0.9 million excluding EFTSU and related income. This was well above the
targeted $600k, and excludes the direct funding of seven full-time or part-time academic
staff who have been actively involved in the Centre’s activities.
The next largest cash component of income was $304k from the State Government through
the Department of State and Regional Development (DSRD). This funding is particularly
important for the purchase of new equipment and the development of facilities, and has
contributed signifi cantly to the acquisition and development of the new state-of-the-art
research facilities at Botany.
161

The 2005 income from industry grew sharply over 2004 levels with cash contributions
totalling $850k and even larger in-kind contributions for collaborative research. The largest
overall contributor in 2005, as in the previous two years, was Suntech-Power Company who,
in addition to their cash contribution of almost $200k, continued to fund two full-time research
positions in the Centre’s laboratories for several months, while simultaneously supporting the
collaborative research at their own facilities. Including the funding of collaborative research
costs, scholarships, royalties, consulting and rental of facilities, the major cash contributors
to the Centre’s 2005 income from industry were BP Solar with $306k, CSG Solar with a
contribution of $262k, Suntech-Power with $187k and Toyota Motor Corporation with $90k.
Other cash or in-kind contributions have been made by the Max Plank Institute, FOM Institute,
Eurosolare, ANSTO, Ian Potter Foundation, the Australian CRC for Renewable Energy, the
Australian Business Council for Solar Energy, the Fraunhofer Institute, SunPower, ENEA, the
Paul Scherrer Institute and the Australian National University. These organisations contribute
to the Centre through the expertise and experience they offer in collaborative research areas
and the in-kind support they provide through access to equipment, facilities and personnel not
available at UNSW.
CSG Solar
BP Solar
Suntech - Power
Other Industry/Private
Funds
Figure 8.2: Industry contributions
Other Centre contracts, consulting work and technology transfers are conducted through
NewSouth Innovations, the commercial arm of the University. These are handled on behalf of
the Centre of Excellence and its staff through the NewSouth Innovations accounts and are
not included in this fi nancial report.
The Centre also earns income through the sale of educational CDs, books and computer
software, with a combined income for 2005 of $24k.
162

Centre 2005 Expenditure of ARC Grant
The total expenditure of ARC grant monies during 2005 was $2.56 million, close to the
$2.60 million awarded. By far the largest component of this expenditure was on salaries,
with the employment of 18 full-time staff and a further 53 part-time or casual staff, including
student scholarships. The combined expenditure on salaries and scholarships during 2005
was $1.71 million. This included 11 full-time researchers: D. König, A. Ho, M. Abbott, K. Fisher,
A. Wang, G. Zhang, R. Bardos, G. Conibeer, X.M. Dai, K. Lin and B. Richards. To support the
research activities, 7 technical support staff were employed by the Centre during 2005,
namely M. Silver, M. Griffi n, L. Soria, A. Yee, J. Green, J. Yang and R. Largent. One parttime
and one full-time administrative staff member were also employed by the Centre during
2005, J. Hansen and J. Kwan. The latter is the Financial Offi cer for the Centre of Excellence,
while the former carries out secretarial, administrative and receptionist duties.
Equipment expenditure from the Centre grant was kept relatively small for 2005 at $209k
due to the support from the State Government through DSRD and the host institution UNSW.
These provided signifi cant levels of funding specifi cally targeting equipment and infrastructure
development. The majority of equipment expenditure from these latter sources was for a
sophisticated sputtering machine and in equipping the new Botany facilities with a range of
processing capabilities. This freed-up Centre funds so that they could be used primarily for
small laboratory equipment items such as hotplates, temperature controllers, a small muffl e
furnace, tuneable laser, pumps, a small processing furnace, specialised computing facilities,
test equipment and a range of spare parts.
The total expenditure from the ARC grant on consumables and maintenance for 2005 was
$472k. These costs are strongly dominated by laboratory consumables to support the device
research, such as high purity gases, chemicals and general laboratory supplies.
The expenditure on travel during 2005 from the ARC grant was $163k. The primary purposes
for this travel were for staff and students participating in collaborative research projects
with overseas industry partners such as BP Solar in the USA, UK and Spain and Suntech-
Power in China, and for the attendance at international conferences such as the PVSEC-15
Conference in Shanghai, China and the IEEE Photovoltaic Specialists Conference in Orlando
in the United States.
Salaries & Scholarships
Equipment
Accommodation
Travel
Materials/Consumables
Figure 8.3: Expenditure of ARC income by expenditure category.
163

164

BOOKS
Stuart R. Wenham, Martin A. Green, Muriel E. Watt, Richard P. Corkish, “Applied Photovoltaics”
(Second Edition), Centre for Photovoltaic Engineering, 2005 (printed February 2006 and to
be translated into Spanish and Chinese).
BOOK CHAPTERS
A.G. Aberle, “Progress in crystalline silicon thin-fi lm solar cells”, in: Progress in Solar Energy
Research (Nova Science Publishers, Hauppauge, NY, USA), in press (invited).
R. Corkish, “Photovoltaic Materials”, in “Encyclopedia of Chemical Processing”, Vol. 4, DOI:
10.1081/E-ECHP-120007896, Taylor & Francis, 2006, p.2129-2138 (invited).
R. Corkish, “Howard keeps us stuck in the coal age”, in “Renewable Energy”, Volume 229
in the Spinney Press series on social issues, “Issues in Society”, ed. Justin Healey, ISBN 1
920801 39 1, for Australian secondary school students (http://www.spinneypress.com.
au/229_book_desc.html). (Reprinted from Sydney Morning Herald, 16 June 2004, p. 15.)
M.A. Green, “Photovoltaic Applications of Nanostructures”, in A.A. Baladin and K.L. Wang
(eds.), “Handbook of Semiconductor Nanostructures and Devices”, 2005 (invited).
M.A. Green, “High Effi ciency Silicon Solar Cell Concepts” in “Solar Cells: Materials, Manufacture
and Operation”, T. Markvart and L. Castener (eds.), Elsevier, Oxford, 2005, p.190-214
(invited).
M.A. Green, “Eureka!” in “The Ideas Book”, L. Carroli (ed.), Brisbane, University of Queensland
Press, 2005.
M.A. Green, “Very High-Effi ciency in Silico Photovoltaics” in “Artifi cial Photosynthesis: From
Basic Biology to Industrial Application”, A.F. Collings and C. Critchley (eds.), Wiley-VCH,
Weinheim, 2005, p.169-185 (invited).
M.A. Green, “Futuristic Photovoltaics”, in “Renewable Energy 2005”, D. Flin (Ed.), Sovereign
Publications, London, 2005, p.52-55, ISBN 19 03605 652 (invited).
M.A. Green, “Materials for Solar Cells” in “Materials for Energy Conversion Devices”, C.C.
Sorrel, S. Sugihara and J. Notvotny (Eds.), Woodhead Publishing, Cambridge, 2005, pp.1-62
(invited).
M.A. Green, “Third Generation Photovoltaics” in “Solar Photovoltaic Batteries”, K. Misawa
(Ed.), Nikkan Kougyo Simbun Ltd, Japan, 2006, p.186-196 (invited; translated into Japanese).
M.A. Green, “Photovoltaics in Deserts”, in “Global Environment Outlook -Deserts”, Global
Environment Outlook Series, United Nations Environment Programme, 2006.
B.S. Richards and M.A. Green, “Photovoltaic Cells”, in “Encyclopaedia of Biomedical Engineering”,
Wiley, 2005 (invited).
165

PATENTS, PATENT APPLICATIONS
A.G. Aberle, T. Walsh, and D Inns, “Photolithography method for contacting thin-fi lm
semicon¬ductor structures”, Australian Provisional Patent Application 2005901285 (fi led
on 16 Mar 2005), International PCT patent application in preparation.
M.A. Green, “Up- and Down-Conversion using Quantum Dot Arrays”, August 2005.
M.A. Green, “Resonant Defect Enhancement of Current Transport in Semiconducting
Superlattices”, Australian Provisional Patent Application No. 2005902712, (fi led on May
2005).
T. Trupke and R. Bardos, “Method and System For Inspecting Indirect Bandgap Semiconductor
Structure”, September 2005.
T. Walsh, A.G. Aberle and S.R. Wenham, “Thin-fi lm solar cell interconnection”, International
PCT patent application PCT/AU2005/000734 (fi led on 23 May 2005, priority date 04 June
2004), international publication number WO 2005/119782 A1, international publication date
15 Dec 2005). National patent applications fi led in key countries for photovoltaic technology.
S.R. Wenham and M.A. Green, “Ink Jet Printing for High Performance Solar Cells”, October
2005.
S.R. Wenham and L. Mai, “Low Area Screen Printed Metal Contacts”, October 2005.
S.R. Wenham, L. Mai and B.S. Tjahjono, “Transparent Conductors for Silicon Solar Cells”, June
2005.
PAPERS IN SCIENTIFIC JOURNALS
M.D. Abbott and J.E. Cotter “Optical and Electrical Properties of Laser Texturing for High
Effi ciency Solar Cells,” Progress in Photovoltaics: Research and Applications, Vol. 14(3)
p. 225-235, 2006.
M.D. Abbott, J.E. Cotter, T. Trupke, R.A. Bardos, “Investigation of Edge Recombination Effects in
Silicon Solar Cell Structures using Photoluminescence”, Applied Physics Letters (in press).
A.G. Aberle, “Progress with polycrystalline silicon thin-fi lm solar cells on glass at UNSW”,
Journal of Crystal Growth, Vol. 287, p.386-390, 2006.
A.G. Aberle, “Fabrication and characterisation of crystalline silicon thin-fi lm materials for solar
cells”, Thin Solid Films (in press).
A.G. Aberle, A. Straub, P.I. Widenborg, A.B. Sproul, Y. Huang and P. Campbell, “Polycrystalline
Silicon Thin-Film Solar Cells on Glass by Aluminium-Induced Crystallisation and Subsequent Ion
Assisted Deposition (ALICIA)”, Progress in Photovoltaics, Vol. 13, p.37-47, 2005.
P.P. Altermatt, F. Geelhaar, T. Trupke, X. Dai, A. Neisser and E. Daub, “Injection dependence of
spontaneous radiative emission in crystalline silicon: Experimental verifi cation and theoretical
analysis”, Applied Physics Letters (submitted).
166

R.A. Bardos, T. Trupke, M. Schubert, T. Roth, “Trapping artefacts in quasi steady state
photoluminescence and photoconductance lifetime measurements on silicon wafers”, Applied
Physics Letters, Vol. 88, 053504, 2006.
G. Conibeer, M. Green, R. Corkish, Y. Cho, E.-C. Cho, C.-W. Jiang, T. Fangsuwannarak, E. Pink, Y.
Huang, T. Puzzer, T. Trupke, B. Richards, A. Shalav, K.-L. Lin, “Silicon nanostructures for third
generation photovoltaic solar cells”, Thin Solid Films, 2005 (submitted, refereed).
R. Corkish, S.R. Wenham, M.A. Green, A.B. Sproul, J. Cotter, A.G. Aberle, A. Bruce, “Materials
Engineering Education in Two New Engineering Degree Programs at the Centre for Photovoltaic
Engineering”, Journal of Materials Education (accepted).
J.E. Cotter, J.H. Guo, P.J. Cousins, M.D. Abbott, F.W. Chen and K.C. Fisher, “p-type vs. n-type
Silicon Wafers: Prospects for High-effi ciency, Commercial Silicon Solar Cells”, IEEE Transactions
on Electron Devices (submitted 2005).
P.J. Cousins and J. Cotter, “Minimising lifetime degradation associated with thermal oxidation
of upright randomly textured silicon surfaces”, Solar Energy Materials and Solar Cells
(accepted April 2005).
P.J. Cousins, A. Guo and J. Cotter, “Infl uence of diffusion-induced misfi t dislocations on high
effi ciency silicon solar cells”, IEEE Transactions on Electron Devices (accepted May 2005).
P.J. Cousins, N. Mason and J. Cotter, “Loss Analysis of double-sided buried contact solar cells
on FZ(B), MCZ(B), CZ(Ga) and CZ(B) wafers”, IEEE Trans. Electron Devices. (accepted August
2005).
L.V. Dao, X. Wen, M.T.T. Do, P. Hannaford, E.-C. Cho, Y.H. Cho, Y. Huang, “Time-Resolved and
Time-Integrated Photoluminescence for Studies of State Filling and Quantum Confi nement of
Silicon Quantum Dots”, Journal of Applied Physics, Vol. 97(1), 013501, 2005.
M.A. Green, K. Emery, D.L. King, S. Igari and W. Warta, “Solar Cell Effi ciency Tables (Version
25)”, Progress in Photovoltaics: Research and Applications, Vol. 13(1), p.49-54, 2005.
M.A. Green, “Price/Effi ciency Correlations for 2004 Photovoltaic Modules”, Progress in
Photovoltaics: Research and Applications, Vol. 13(1), p.85-87, 2005.
M.A. Green, K. Emery, D.L. King, S. Igari and W. Warta, “Solar Cell Effi ciency Tables (Version
26)”, Progress in Photovoltaics: Research and Applications, Vol. 13(5), p.387-392, 2005.
M.A. Green, “Silicon Photovoltaic Modules: A Brief History over the First 50 Years”, Progress
in Photovoltaics, Vol. 13, p.447-455, 2005.
M.A. Green, “Improved Estimates for Te and Se Availability from Cu Anode Slimes and Recent
Price Trends”, Progress in Photovoltaics (in press).
M.A. Green “Consolidation of Thin-Film Photovoltaics Technology: The Coming Decade of
Opportunity”, Progress in Photovoltaics (invited).
M.A. Green, K. Emery, D.L. King, S. Igari and W. Warta, “Solar Cell Effi ciency Tables (Version
27), Progress in Photovoltaics, Vol. 14, pp. 45-51, 2006.
167

J.H. Guo and J.E. Cotter, “Metallization Improvement on Fabrication of Interdigitated Backside
and Double-sided Buried Contact Solar Cells,” Solar Energy Materials and Solar Cells, Vol.
86(4), p.485-498, 2005.
J.H. Guo and J.E. Cotter, “Optimizing the Diffused Regions of Interdigitated Backside Buried
Contact Solar Cells,” Solar Energy Materials and Solar Cells (in review).
J.H. Guo, P.J. Cousins, and J.E. Cotter, “Investigations of Parasitic Shunt Resistance in N-type
Buried Contact Solar Cells,” Progress in Photovoltaics: Research and Applications, Vol. 14,
p.95-105, 2006.
A.W.Y. Ho and S.R. Wenham, “Innovative Contacting Scheme for Electron Devices”, IEEE
Transactions on Electron Devices (submitted October 2005).
A.W.Y. Ho, S.R. Wenham, “Fabrication of Silicon Solar Cells with Rear Pinhole Contacts”,
Progress in Photovoltaics: Research & Applications (submitted).
C.-W. Jiang and M.A. Green, “Silicon Quantum Dot Superlattices: Modelling of Energy Bands,
Densities of States and Mobilities for Silicon Tandem Solar Cell Applications”, Journal of
Applied Physics, JR05-2773. (submitted August 2005).
D. König, R. Scholz, D.R.T. Zahn, G. Ebest, “Band diagram of the AlF_3/SiO_2/Si system”,
Journal of Applied Physics, Vol. 97, 093707, 2005
G. Kumaravelu, M.M. Alkaisi, D. Macdonald, J. Zhao, B. Rong and A. Bittar, “Minority carrier
lifetime in plasma-textured silicon wafers for solar cells”, Solar Energy Materials and Solar
Cells, Vol. 87(1-4), Vol. 14(2), p.99-106, 2005.
K.R. McIntosh, J.E. Cotter and D. Swanson, “A Simple Ray Tracer to Compute the Concentration
of a Photovoltaic Module”, Progress in Potovoltaics: Research and Applications, p.167-177,
2006
S. Pillai, K. Catchpole , T. Trupke , G. Zhang , J. Zhao , M.A. Green, “Enhanced Emission from Si
based LEDs using Surface Plasmons”, Applied Physics Letters (submitted December 2005).
B.S. Richards, “Luminescent layers for enhanced silicon solar cell performance: Down
conversion”, Solar Energy Materials and Solar Cells (in press).
B.S. Richards and G. Conibeer, “A Comparison of Hydrogen Storage Technologies for Solar-
Powered Stand Alone Power Supplies”, Special Issue of Int. Journal of Hydrogen Energy
(submitted).
B.S. Richards and A. Shalav, “The Role of Polymers in the Luminescence Conversion of Sunlight
for Enhanced Solar Cell Performance”, Synthetic Metals, Vol. 54(22), Issues 1-3, p.61-64,
2005.
B.S. Richards, A. Shalav, K.W. Kramer and H.U. Gudel, “Up-conversion Photovoltaic Devices:
Enhancing the Near Infrared Spectral Response of Silicon Solar Cell Response”, IEEE Electron
Device Letters (submitted December 2005).
A. Shalav, B.S. Richards, T. Trupke, K.W. Kramer and H.U. Gudel, “The Application of NaYF4:
Er3+ Up-Converting Phosphorus for Enhanced Near Infrared Silicon Solar Cell Response”,
Applied Physics Letters, Vol. 86(1), 013505, 2005.
168

D. Song, D. Inns, A. Straub, M.L. Terry, P. Campbell, and A.G. Aberle, “Solid phase crystallized
polycrystalline thin-fi lms on glass from evaporated silicon for photovoltaic applications”, Thin
Solid Films (in press).
A.B. Sproul, “Solar Geometry using Vector Analysis”, Renewable Energy (submitted).
J. Stradal, G. Scholma, H. Li, C.H.M. van der Werf, J.K. Rath, P.I. Widenborg, P. Campbell, A.G.
Aberle and R.E.I. Schropp, “Epitaxial Thickening by Hot Wire Chemical Vapor Deposition of
Polycrystalline Silicon Seed Layers on Glass”, Thin Solid Films (in press).
A. Straub, R. Gebs, H. Habenicht, S. Trunk, R.A. Bardos, A.B. Sproul, and A.G. Aberle, “Impedance
analysis - A powerful method for the determination of the doping concentration and built-in
potential of nonideal semiconductor p-n diodes”, Journal of Applied Physics, Vol. 97, 083703,
2005.
A. Straub, D. Inns, M.L. Terry, R. Gebs, and A.G. Aberle, “The infl uence of defects and postdeposition
treatments on the free carrier density in lightly phosphorus-doped large-grained
polycrystalline silicon fi lms”, Journal of Applied Physics, Vol. 98(2), 023507, 2005.
A. Straub, D. Inns, M.L. Terry, Y. Huang, P.I. Widenborg, and A.G. Aberle, “Optimisation of lowtemperature
silicon epitaxy on seeded glass substrates by ion-assisted deposition”, Journal
of Crystal Growth, Vol. 280(1-2), p.385-400, 2005.
A. Straub, D. Inns, M.L. Terry, Y. Huang, P.I. Widenborg, and A.G. Aberle, “Homoepitaxial silicon
growth in a non-ultra-high vacuum environment by ion-assisted deposition on Si wafer and
seeded glass substrates”, Thin Solid Films (in press).
M.L. Terry, A. Straub, D. Inns, D. Song, and A.G. Aberle, “Large open-circuit voltage improvement
by rapid thermal annealing of evaporated solid-phase-crystallized thin-fi lm silicon solar cells on
glass”, Applied Physics Letters, Vol. 86, 172108, 2005.
T. Trupke, “Infl uence of reabsorption on quasi steady state photoluminescence measurements
on crystalline silicon”, Journal of Applied Physics (in press).
T. Trupke, R.A. Bardos et al, “Photoluminescence imaging of silicon wafers”, Applied Physics
Letters (submitted).
T. Trupke, R.A. Bardos, M.D. Abbott, “Self-Consistent calibration of photoluminescence and
photocoductance lifetime measurements”, Applied Physics Letters, 87, 184102, 2005.
T. Trupke, R.A. Bardos, M.D. Abbott and J.E. Cotter, “Suns-photoluminescence: Contact-less
determination of current-voltage characteristics of silicon wafers”, Applied Physics Letters,
Vol. 87(9), 093503, 2005.
T. Trupke, A. Shalav, B.S. Richards, P. Würfel, M.A. Green, “Effi ciency enhancement of solar cells
by luminescent up-conversion of sunlight”, Solar Energy Materials & Solar Cells (in press).
P.I. Widenborg, A. Straub and A.G. Aberle, “Epitaxial thickening of AIC poly-Si seed layers on
glass by solid phase epitaxy”, Journal of Crystal Growth, Vol. 276, p.19-28, 2005.
P. Wuerfel, A.S. Brown, T.E. Humphrey and M.A. Green, “Particle Conservation in the Hot-
Carrier Solar Cell”, Progress in Photovoltaics: Research and Applications, Vol. 13, p.277-285,
2005.
169

CONFERENCE PROCEEDINGS
M.D. Abbott, P.J. Cousins, F.W. Chen and J.E. Cotter, ”Laser-induced defects in crystalline
Silicon solar cells’’, 31st IEEE Photovoltaic Specialists Conference, Orlando, USA, 3-7 January
2005, p.1241-1244.
M.D. Abbott, J.E. Cotter and K. Fisher, “N-Type Bifacial Solar Cells with Laser Doped Contacts”,
IEEE 4th World Conference on Photovoltaic Energy Conversion (WCPEC-4), Hawaii, 7-12 May
2006 (accepted).
M.D. Abbott, J.E. Cotter, T. Trupke, K. Fisher and R.A. Bardos, “Application of Photoluminescence
to High-effi ciency Silicon Solar Cell Fabrication”, IEEE 4th World Conference on Photovoltaic
Energy Conversion (WCPEC-4), Hawaii, 7-12 May 2006 (accepted).
A.G. Aberle, “Progress in Evaporated Crystalline Silicon Thin-Film Solar Cells on Glass”, IEEE
4th World Conference on Photovoltaic Energy Conversion (WCPEC-4), Hawaii, 7-12 May
2006 (accepted).
A.G. Aberle, “Crystalline silicon thin-fi lm solar cells on glass - Cheap electricity from the Sun?”,
Proc. 16th Australian Institute of Physics Congress, Canberra, February 2005, see Book of
Abstracts (CD), p.237 (invited).
A.G. Aberle, P.I. Widenborg, D. Song, A. Straub, M.L. Terry, T. Walsh, A. Sproul, P. Campbell,
D. Inns, B. Beilby, M. Griffi n, J. Weber, Y. Huang, O. Kunz, R. Gebs, F. Martin-Brune, V. Barroux,
and S.R. Wenham, “Recent advances in polycrystalline silicon thin-fi lm solar cells on glass at
UNSW”, 31st IEEE Photovoltaic Specialists Conference, Orlando, USA, 3-7 January 2005,
p.877-882 (invited review talk).
A.G. Aberle, “Crystalline Silicon Thin-Film Solar Cells: Where are We? Where to Go from
Here?”, 20th European Photovoltaic Solar Energy Conference, Barcelona, Spain, 6-10 June
2005, p.1108-1111.
P.P. Altermatt, F. Geelhaar, T. Trupke, X. Dai, A. Neisser and E. Daub, “Injection dependence of
spontaneous radiative recombination in c-Si: Experiment, theoretical analysis and simulation”,
5th International Conference on Numerical Simulation of Optoelectronic Devices, NUSOD,
Berlin, September 2005.
R.A. Bardos and T. Trupke, “Self consistent determination of the generation rate in
photoluminescence and photoconductance lifetime measurements”, 31st IEEE Photovoltaic
Specialists Conference, Orlando, USA, 3-7 January 2005, p.899-902.
R.A. Bardos, J.E. Cotter, A.Lorenz, T. Trupke, “Comparison of n and p type ribbon grown multi
crystalline silicon wafers using photoluminescence imaging”, IEEE 4th World Conference on
Photovoltaic Energy Conversion (WCPEC-4), Hawaii, 7-12 May 2006 (accepted).
N. Borojevic, F.W. Chen, J.E. Cotter, “Properties of PECVD Silicon Nitride Films for Antirefl ection
Coatings”, 43rd Australian and New Zealand Solar Energy Society (ANZSES) Annual
Conference, Dunedin, New Zealand, 28-30 November 2005.
P. Campbell, P.I. Widenborg, and A.G. Aberle, “Surface textures for large-grained poly-silicon
thin-fi lm solar cells on glass using the AIT method”, 15th International Photovoltaic Science
and Engineering Conference (PVSEC-15), Shanghai, China, 10-15 October 2005, p.859-860.
170

F.W. Chen, J.E. Cotter, A. Cuevas, S. Winderbaum, K. Roth, “Anomalous Thermal Behaviour of
Surface Passivation by PECVD Silicon Nitride on P-type Silicon”, 20th European Photovoltaic
Solar Energy Conference, Barcelona, Spain, 6-10 June 2005, p.1419-1422.
F.W. Chen, J.E. Cotter, T. Trupke, R.A. Bardos, “Characterization of PECVD Silicon Nitride
Passivation with Photoluminescence Imaging”, IEEE 4th World Conference on Photovoltaic
Energy Conversion (WCPEC-4), Hawaii, 7-12 May 2006 (accepted).
F.W. Chen, T.A. Li, J.E. Cotter, “PECVD Silicon Nitride Surface Passivation for High-Effi ciency
N-type Silicon Solar Cells”, IEEE 4th World Conference on Photovoltaic Energy Conversion
(WCPEC-4), Hawaii, 7-12 May 2006 (accepted).
Y.H. Cho, M.A. Green, E.-C. Cho, Y. Huang, T. Trupke, G. Conibeer, “Silicon Quantum Dots in
SiNx Matrix for Third Generation Photovoltaics”, 20th European Photovoltaic Solar Energy
Conference, Barcelona, Spain, 6-10 June 2005, p.47-50.
N. Chuangsuwanich, P. Campbell, P.I. Widenborg, A. Straub, and A.G. Aberle, “Light trapping
properties of evaporated poly-silicon fi lms on AIT-textured glass substrates”, 31st IEEE
Photovoltaic Specialists Conference, Orlando, USA, 3-7 January 2005, p.1161-1164.
G. Conibeer, M.A. Green, R. Corkish, Y. Cho, E.-C. Cho, T. C.-W. Jiang, T. Fangsuwannarak, E. Pink,
Y. Huang, T. Puzzer, T. Trupke, B. Richards, A. Shalav, K.-L. Lin, “Silicon nanostructures for third
generation photovoltaic solar cells”, Symposium on Thin Film and Nanostructured Materials
for Photovoltaics THINC-PV2, Strasbourg, France, May / June 2005 (invited).
G.J. Conibeer, J.F. Guillemoles and M.A. Green, “Phononic Band Gap Engineering for Hot Carrier
Solar Cell Absorbers”, 20th European Photovoltaic Solar Energy Conference, Barcelona,
Spain, 6-10 June 2005, p.35-38.
G.J. Conibeer, M.A. Green, R. Corkish, Y. Cho, E-C. Cho, C-W. Jiang, E. Pink,B. Richards, A.
Shalav, T. Fangsuwannarak, Y. Huang, T. Puzzer, T. Trupke, “Third Generation Photovoltaics:
routes to high effi ciency that retain the advantages of thin fi lm”, 43rd Australian and New
Zealand Solar Energy Society (ANZSES) Annual Conference, Dunedin, New Zealand, 28-30
November 2005.
R. Corkish, S.R. Wenham, A.B. Sproul, J. Cotter, C.B. Honsberg, M.A. Green, A.G. Aberle, G.
Conibeer, “Education and Research at the Centre for Photovoltaic Engineering, University of
New South Wales”, International Rio 5 World Climate and Energy Event, Rio de Janeiro, Brazil,
15-17 February 2005, p. 481-487.
R. Corkish, S.R. Wenham, M.A. Green, J.E. Cotter , A. Sproul, A.B. Aberle, J. Zhao, G. Conibeer,
G. Stapleton, M. Watt, E. Spooner, A. Bruce, A.W.Y. Ho, M. Kobacker, “Education and Research
at the Centre for Photovoltaic Engineering, UNSW”, 15th International Photovoltaic Science
and Engineering Conference (PVSEC-15), Shanghai, China, 10-15 October 2005, p.455-456.
R. Corkish, G. Conibeer, M. A. Green, Y. Cho, E.-C. Cho, T. Fangsuwannarak, E. Pink, Y. Huang,
T. Puzzer, T. Trupke, A. Shalav, K.-L. Lin, “Silicon Nanostructures for Third Generation
Photovoltaics”, Material Research Society (MRS) Fall Meeting, Boston, USA, 28 Nov-2 Dec
2005.
171

R. Corkish, S.R. Wenham, M.A. Green, A.B. Sproul, J. Cotter, A.G. Aberle, A. Bruce, “Materials
Engineering Education in Two New Engineering Degree Programs at the Centre for
Photovoltaic Engineering”, Material Research Society (MRS) Fall Meeting, Boston, USA, 28
Nov-2 Dec 2005 (invited).
J.E. Cotter, “RaySim 6.0 - A Free Geometrical Ray Tracing Program for Silicon Solar Cells”,
31st IEEE Photovoltaic Specialists Conference, Orlando, USA, 3-7 January 2005, p.1165-
1168.
J.E. Cotter, G. Yao and B. Eggleston, “Laser-formed Stencils for Printed Silicon Solar Cells”,
31st IEEE Photovoltaic Specialists Conference, Orlando, USA, 3-7 January 2005, p.1169-
1172.
J.E. Cotter, J.H. Guo, P.J. Cousins, M.D. Abbott, F.W. Chen and K.C. Fisher, “p-type vs. n-type
Silicon Wafers: Prospects for High-effi ciency, Commercial Silicon Solar Cells”, 15th workshop
on Crystalline Silicon Solar cells & Modules: Materials and Processes, Vail, USA, 7-10 August
2005 (invited).
P.J. Cousins and J.E. Cotter, “Misfi t dislocations generated during non-ideal boron and
phosphorus diffusion and their effect on high-effi ciency silicon solar cells”, 31st IEEE
Photovoltaic Specialists Conference, Orlando, USA, 3-7 January 2005, p.1047-1050.
P.J. Cousins, N.B. Mason and J.E. Cotter, “Manufacturing and design issues for thin silicon
solar cells on FZ(B), MCZ(B), CZ(Ga) and CZ(B) wafers”, 31st IEEE Photovoltaic Specialists
Conference, Orlando, USA, 3-7 January 2005, p.987-990.
P. J. Cousins, M. D. Abbott and J. E. Cotter, “Impact of Furnace Transients on the Lifetime
of Upright Randomly Textured Wafers Evaluated using Photoconductance Lifetime
Measurements” 20th European Photovoltaic Solar Energy Conference, Barcelona, Spain, 6-
10 June 2005, p.1182-1185.
A. Cuevas, F.W. Chen, J. Tan, S. Winderbaum, K. Roth, “FTIR Analysis of Microwave Silicon
Nitride”, IEEE 4th World Conference on Photovoltaic Energy Conversion (WCPEC-4), Hawaii,
7-12 May 2006 (accepted).
D. Debuf, “Multiple-level-defect measurements using Fundamental Frequency Deep Level
Transient Spectroscopy: A new measurement technique”, 20th European Photovoltaic Solar
Energy Conference, Barcelona, Spain, 6-10 June 2005, p.132-135.
M.B. Edwards, G. Yao, F. W. Chen, J. E. Cotter, “Metallisation
for n-type, stencil-printed silicon solar cells”, 15th International Photovoltaic Science and
Engineering Conference (PVSEC-15), Shanghai, China, 10-15 October 2005, p.710-711.
T. Fangsuwannarak, E. Pink, Y. Huang, Y. H. Cho, G. Conibeer, T. Puzzer and M.A. Green,
“Conductivity of self-organized silicon quantum dots embedded in silicon dioxide”, Proceeding
of SPIE 2005 International Symposium on Microelectronics, MEMS and Nanotechnology,
Brisbane, Australia, 11-14 December 2005, Vol.6037, 60370T.
K.C. Fisher, J.E. Cotter, “Investigation of Low Molarity Alkaline Texturing Solutions”, 15th
International Photovoltaic Science and Engineering Conference (PVSEC-15), Shanghai, China,
10-15 October 2005, p.622-623.
172

M.A. Green, “Photovoltaics – Electricity’s Future?”, Local Government Manager, Accent on
Energy, Dec 2004-Jan 2005, p.8 (invited).
M.A. Green, “Renewable Energy and Its Future”, International Rio 5 World Climate and Energy
Event, Rio de Janeiro, Brazil, 15-17 February 2005.
M.A. Green, “State-of-the-Art of Solar Cell Development”, International Rio 5 World Climate
and Energy Event, Rio de Janeiro, Brazil, 15-17 February 2005.
M.A. Green, “Status of Silicon on Glass, a New Production Technology”, 2nd Photovoltaic
Science Applications and technology Conference, Loughborough, U.K., April 2005 (invited).
M.A. Green, E.-C. Cho, Y. Cho, Y. Huang, E. Pink, T. Trupke, A. Lin, T. Fangsuwannarak, T. Puzzer, G.
Conibeer, R. Corkish, “All-Silicon Tandem Cells based on “Artifi cial” Semiconductor Synthesised
using Silicon Quantum Dots in a Dielectric Matrix”, 20th European Photovoltaic Solar Energy
Conference, Barcelona, Spain, 6-10 June 2005, p.3-7 (opening plenary).
M.A. Green, “Third Generation Photovoltaics and Feasibility of Realisation”, 15th International
Photovoltaic Science and Engineering Conference (PVSEC-15), Shanghai, China, 10-15
October 2005, p.7-10 (invited opening ceremony paper).
M.A. Green, “Bulk Silicon for Photonics Applications”, IEEE Laser and Electro-Optics Society
(LEOS), Sydney, Australia, 23-27 October 2005 (invited talk).
M.A. Green, “All-Silicon Tandem Solar Cells”, Joint Scientifi c Workshop on the Utilization of the
Solar Spectrum, Ispra, Italy, 23-24 November 2005 (invited).
MA Green, “Thin-Film Solar Cells: Review of Technologies and Commercial Status”, 43rd
Australian and New Zealand Solar Energy Society (ANZSES) Annual Conference, Dunedin,
New Zealand, 28-30 November 2005.
M.A. Green, “Solar and Wind: An Update”, Boat House III - Technology Futures, Paris, France,
3-5 April 2006 (invited paper).
M.A. Green, “Nanostructure Silicon Quantum Dot Tandem and Hot Carrier Solar Cells”,
Materials Research Society (MRS) Spring Symposium, San Francisco, California, 17-21 April
2006 (invited paper).
M.A. Green, “Recent Developments and Future Prospects for Third Generation and Other
Advanced Solar Cells”, IEEE 4th World Conference on Photovoltaic Energy Conversion
(WCPEC-4), Hawaii, 7-12 May 2006 (invited keynote paper).
M.A. Green, “Composite Semiconductors Based on Silicon Quantum Dots”, ACUN-5
International Composites Conference: Advanced, Infrastructure, Natural and Nanocomposites,
Sydney, Australia, 11-14 July 2006 (invited keynote paper).
J.-F. Guillemoles, G. Conibeer, M. Green, “Phononic Engineering with Nanostructures for Hot
Carrier solar cells” , 15th International Photovoltaic Science and Engineering Conference
(PVSEC-15), Shanghai, China, 10-15 October 2005, p.375-376.
J.-H. Guo, B.S. Tjahjono, and J.E. Cotter, “19.2% Effi ciency N-type Laser-grooved Silicon Solar
Cells,” 31st IEEE Photovoltaic Specialists Conference, Orlando, USA, 3-7 January 2005,
p.983-986.
173

A.W.Y. Ho, S.R. Wenham, “Investigation of the Surface Passivation Quality of Various Novel
Low Temperature Rear Localised Contacting Schemes for PV Devices”, Proc. Of 31st IEEE
Photovoltaic Specialists Conference, Orlando, USA, 3-7 January 2005, p.1189-1192.
D. Inns, A. Straub, M. Terry, Y. Huang, and A.G. Aberle, “Impact of growth and hydrogenation
temperature on the voltage of ALICIA thin-fi lm silicon solar cells on glass”, 15th International
Photovoltaic Science and Engineering Conference (PVSEC-15), Shanghai, China, 10-15
October 2005, p.774-775.
C.-W. Jiang, M.A. Green and G. Conibeer, “Effective Mass Calculations of Energy Bands for
Silicon Quantum Dot Solar Cells in Oxide, Nitride and Carbide Matrices”, 15th International
Photovoltaic Science and Engineering Conference (PVSEC-15), Shanghai, China, 10-15
October 2005, p.158-159.
O. Kunz, A. Straub, A. Sproul and A.G. Aberle, “Determination of the Two-Diode Model
Parameters of Non-Ideal Solar Cells”, 20th European Photovoltaic Solar Energy Conference,
Barcelona, Spain, 6-10 June 2005, p.226-229.
L. Mai, S.R. Wenham, B. Tjahjono, J. Ji, Z. Shi, “New Emitter Design and Metal Contact for
Screen-Printed Solar Cell Front Surfaces”, IEEE 4th World Conference on Photovoltaic Energy
Conversion (WCPEC-4), Hawaii, 7-12 May 2006 (invited paper).
R. Passey, I. MacGill and M. Watt, “Some options for State-based Renewable Obligations
in Australia”, 43rd Australian and New Zealand Solar Energy Society (ANZSES) Annual
Conference, Dunedin, New Zealand, 28-30 November 2005.
S. Pillai, K.R. Catchpole and A. Shalav, “Targeting Better Absorption at Longer Wavelengths
Using Surface Plasmons”, 31st IEEE Photovoltaic Specialists Conference, Orlando, USA, 3-7
January 2005, p.171-174.
S. Pillai, K.R Catchpole, T. Trupke, M.A. Green “Application of Surface Plasmons for Increased
Light Emission from Silicon Based LEDs”, 20th European Photovoltaic Solar Energy Conference,
Barcelona, Spain, 6-10 June 2005, p.369-372.
S. Pillai, K.R. Catchpole, T. Trupke, G. Zhang, J. Zhao, M.A. Green, “Effects of Dielectric
Overcoating on the Absorption Enhancement of SOI LEDs with metal island fi lms”, SPIE
International Symposium on Microelectronics, MEMS, and Nanotechnology, Queensland Univ.
of Technology, Brisbane, Australia, 11–15 December 2005.
M. Pop, M.E Watt, J. Rivier and A. Birch, “Tariff Implications for the Value of PV to Residential
Customers”, 43rd Australian and New Zealand Solar Energy Society (ANZSES) Annual
Conference, Dunedin, New Zealand, 28-30 November 2005.
J.W. Rudd, G.J. Conibeer, J-F. Guillemoles, “User Friendly Software for Calculation of Limiting
Cell Effi ciencies for Research on Multijunction Solar Cells”, 43rd Australian and New Zealand
Solar Energy Society (ANZSES) Annual Conference, Dunedin, New Zealand, 28-30 November
2005.
A. Shalav, B.S. Richards, K.W. Cramer and H.U. Gudel, “Improvements of an Up-Conversion
NaYF4:Er3+ Phosphor-Silicon Solar Cell Device for an Enhanced Response in the Near-
Infrared”, 31st IEEE Photovoltaic Specialists Conference, Orlando, USA, 3-7 January 2005,
p.114-117.
174

A. Shalav, B. Richards, G. Conibeer and M.A. Green, “Two colour excitation up-conversion
effi ciency enhancement for a silicon photovoltaic device using Er3+-doped up-converting
phosphors”, IEEE 4th World Conference on Photovoltaic Energy Conversion (WCPEC-4),
Hawaii, 7-12 May 2006 (accepted).
D. Song, P.I. Widenborg, A. Straub, P. Campbell, N. Chuangsuwanich, Y. Huang and A.G. Aberle,
“EVA polycrystalline silicon thin-fi lm solar cells on textured glass”, 31st IEEE Photovoltaic
Specialists Conference, Orlando, USA, 3-7 January 2005, p.1217-1220.
D. Song, P.I. Widenborg, A. Straub, D. Ins, M. Terry and A.G. Aberle, “Impact of Glass Substrate
Topography on EVA Polycrystalline Silicon Thin-Film Solar Cells on Glass”, 20th European
Photovoltaic Solar Energy Conference, Barcelona, Spain, 6-10 June 2005, p.1104-1107.
D. Song, P.I. Widenborg, M.L. Terry, and A.G. Aberle, “Impact of a SiN barrier layer on EVA
polycrystalline silicon thin-fi lm solar cells”, 15th International Photovoltaic Science and
Engineering Conference (PVSEC-15), Shanghai, China, 10-15 October 2005, p.186-187.
D. Song, T.M. Walsh, and A.G. Aberle, “Monolithically Integrated Polycrystalline Silicon Thin-
Film Mini-module on Glass”, IEEE 4th World Conference on Photovoltaic Energy Conversion
(WCPEC-4), Hawaii, 7-12 May 2006 (accepted).
A.B. Sproul, A.W.Y. Ho, A. Bruce and S.R. Wenham, “Student Installation of a PV Lighting
System in a Rural Health Clinic”, 43rd Australian and New Zealand Solar Energy Society
(ANZSES) Annual Conference, Dunedin, New Zealand, 28-30 November 2005.
J. Stradal, G. Scholma, H. Li, C.H.M. van der Werf, J.K. Rath, P.I. Widenborg, P. Campbell, A.G.
Aberle, and R.E.I. Schropp, “Hot Wire CVD for epitaxial thickening of polycrystalline silicon
seed layers made by AIC on glass”, 31st IEEE Photovoltaic Specialists Conference, Orlando,
USA, 3-7 January 2005, p.1540-1543.
A. Straub, D. Inns, O. Kunz, M.L. Terry, P.I. Widenborg, A.B. Sproul, and A.G. Aberle, “Towards
400 mV ALICIA thin-fi lm silicon solar cells on glass”, 31st IEEE Photovoltaic Specialists
Conference, Orlando, USA, 3-7 January 2005, p.1221-1224.
A. Straub, R. Gebs, A.B. Sproul, R. Bardos, D. Inns, M.L. Terry and A.G. Aberle, “C-V
Measurements by Impedance Analysis on ALICIA Polycrystalline Silicon Thin-Film Solar Cells
on Glass”, 20th European Photovoltaic Solar Energy Conference, Barcelona, Spain, 6-10 June
2005, p.128-131.
Y. Takeda, T. Ito, T. Motohiro, T. Nagashima, D. König, G. Conibeer, “A novel method based
on oblique depositions to fabricate quantum dot arrays”, IEEE 4th World Conference on
Photovoltaic Energy Conversion (WCPEC-4), Hawaii, 7-12 May 2006 (accepted).
Y. Takeda, T. Ito, T. Motohiro, T. Nagashima, D. König, G. Conibeer, “Formation of quantum dot
arrays utilizing oblique depositions”, 2006 Spring the Japan Society of Applied Physics annual
meeting, Tokyo, Japan, March 2006 (accepted).
M.L. Terry, A. Straub, D. Inns, D. Song, and A.G. Aberle, “Voc improvement of evaporated SPC
thin-fi lm Si solar cells on glass by rapid thermal annealing”, 31st IEEE Photovoltaic Specialists
Conference, Orlando, USA, 3-7 January 2005, p.971-974.
175

M.L. Terry, P.I. Widenborg, O. Kunz, and A.G. Aberle, “Effects of rapid thermal annealing and
hydrogen passivation on crystalline silicon thin-fi lm solar cells on glass made by PECVD solidphase
crystallization”, 15th International Photovoltaic Science and Engineering Conference
(PVSEC-15), Shanghai, China, 10-15 October 2005, p.905-906.
M.L. Terry, D. Inns and A.G. Aberle, “Massive improvement through rapid thermal annealing
and hydrogen passivation of poly-Si thin-fi lm solar cells on glass based on aluminum induced
crystallization”, IEEE 4th World Conference on Photovoltaic Energy Conversion (WCPEC-4),
Hawaii, 7-12 May 2006 (accepted).
T. Trupke and R.A. Bardos, “Photoluminescence: A surprisingly sensitive lifetime technique”,
31st IEEE Photovoltaic Specialists Conference, Orlando, USA, 3-7 January 2005, p.903-
906.
T. Trupke and R.A. Bardos, “Photoluminescence: A versatile characterization technique for
crystalline silicon”, 15th workshop on Crystalline Silicon Solar cells & Modules: Materials and
Processes, Vail, USA, 7-10 August 2005.
T. Trupke, R.A. Bardos, M.D. Abbott, F.W. Chen, J.E. Cotter, A. Lorenz, ”Fast photoluminescence
imaging of silicon wafers”, IEEE 4th World Conference on Photovoltaic Energy Conversion
(WCPEC-4), Hawaii, 7-12 May 2006 (accepted).
T.M. Walsh, S.R. Wenham, and A.G. Aberle, “Novel method for the interconnection of thin-fi lm
silicon solar cells on glass”, 31st IEEE Photovoltaic Specialists Conference, Orlando, USA, 3-7
January 2005, p.1229-1232.
T.M. Walsh, D. Song, S. Motahar, and A.G. Aberle, “Self-aligning maskless photolithography
method for metallising thin-fi lm crystalline silicon solar cells on transparent supporting
materials”, 15th International Photovoltaic Science and Engineering Conference (PVSEC-15),
Shanghai, China, 10-15 October 2005, p.706-707.
M. Watt, “Status of Australia’s PV Market”, Sustainable Energy 2005, the BCSE Annual
Conference, 27-29 April 2005, Melbourne.
M. Watt, “National Survey Report of PV Power Applications in Australia – 2004”, Australian
Photovoltaic Power Systems (PVPS) Consortium, May 2005.
M. Watt, S. Healy and R. Passey, “Some considerations when designing a retail energy
market that works for Energy Effi ciency and distributed generation”, BCSE Energy Effi ciency
Conference, Melbourne, Australia, 22-23 November 2005 (invited).
S.R. Wenham, L. Mai, B. Tjahjono, J.Jia and Z. Shi, “Innovative emitter design and metal contact
for screen printed solar cells”, 15th International Photovoltaic Science and Engineering
Conference (PVSEC-15), Shanghai, China, 10-15 October 2005, p.805-805.
P.I. Widenborg, T. Puzzer, J. Stradal, D.H. Neuhaus, D. Inns, A. Straub, and A.G. Aberle,
“Structural quality of smooth AIC poly-Si fi lms on glass substrates”, 31st IEEE Photovoltaic
Specialists Conference, Orlando, USA, 3-7 January 2005, p.1031-1034.
P.I. Widenborg, J. Weber, M.L. Terry and A.G. Aberle, “Solid Phase Epitaxy of PECVD a-Si:H n
AIC Poly-Si Seeded Glass Substrates”, 20th European Photovoltaic Solar Energy Conference,
Barcelona, Spain, 6-10 June 2005, p.1000-1003.
176

P.I. Widenborg, S.V. Chan, D. Inns, and A.G. Aberle, “Fabrication of poly-Si seed layer by
aluminium-induced crystallisation of a-Si deposited by PECVD or sputtering”, 15th International
Photovoltaic Science and Engineering Conference (PVSEC-15), Shanghai, China, 10-15
October 2005, p.814-815.
Per I. Widenborg, J.W. Weber, M.L. Terry, and A.G. Aberle, “A comparative study of poly-Si fi lms
fabricated on glass by crystallisation of PECVD a-Si:H via the SPC and SPE methods”, 15th
International Photovoltaic Science and Engineering Conference (PVSEC-15), Shanghai, China,
10-15 October 2005, p.420-421.
G. Yao, J. Zhao and J.E. Cotter, “Metal Stencil-Printed Selective Emitter Silicon Solar Cell
Fabrication on CZ Wafer”, 20th European Photovoltaic Solar Energy Conference, Barcelona,
Spain, 6-10 June 2005, p.749-752.
G. Yao, S.R. Wenham and J.E. Cotter, “Comparison of Stencil and Screen Printed Solar Cell”,
15th International Photovoltaic Science and Engineering Conference (PVSEC-15), Shanghai,
China, 10-15 October 2005, p.299-300.
J. Zhao and A. Wang, “High Effi ciency Real Emitter PERT Solar Cells on n-type FZ Single
Crystalline Silicon Substrates”, 20th European Photovoltaic Solar Energy Conference,
Barcelona, Spain, 6-10 June 2005, p.806-809.
Jianhua Zhao, “The Foundation and the Strategy of Photovoltaic Industry in China”, China
Power Conference, Beijing, China, 10-12 August 2005.
J. Zhao, “High Effi ciency Silicon Solar Cell Technologies Ready for Production”, 15th
International Photovoltaic Science and Engineering Conference (PVSEC-15), Shanghai, China,
10-15 October 2005, p.310-311 (invited talk).
J. Zhao and A. Wang, “A Novel Rear Emitter N-Type PERT Silicon Cells with Stable High
Performance”, 15th International Photovoltaic Science and Engineering Conference (PVSEC-
15), Shanghai, China, 10-15 October 2005, p.122-123 (invited talk).
J. Zhao, “High Effi ciency Silicon Solar Cells for Mass Production”, Sino-Euro Workshop, 15th
International Photovoltaic Science and Engineering Conference, Shanghai, 10 October 2005
(invited talk).
J. Zhao, “Manufacturing Technologies for High Effi ciency Crystalline Silicon Solar Cells”, PV
Industrial Workshop, 15th International Photovoltaic Science and Engineering Conference,
Shanghai, 12 October 2005 (invited talk).
177

Press
Richard Corkish, “Fusion fallacies”, (letter to editor re nuclear fusion) New Scientist, No. 2528,
p.24, 3 Dec 2005.
Other Reports
R. Corkish, “Photovoltaics and Renewable Energy Education and Research at the University
of New South Wales”, presentation to NSW Department of State and Regional Development,
UNSW, 12 April 2005 (unpublished).
R. Corkish, “Photovoltaics & Silicon Photonics Research at UNSW”, presentation at UNSW-
Singapore Research Collaboration Workshop, A*STAR Institute of Materials Research and
Engineering, Singapore 28 February – 2 March 2005 (invited).
R .Corkish, S.R. Wenham, A.B. Sproul, J. Cotter, C.B. Honsberg, M.A. Green, A.G. Aberle, G.
Conibeer, “Photovoltaics and Renewable Energy Education and Research at the University of
New South Wales”, presentation at The Joint Graduate School of Energy and Environment,
King Mongkut’s University of Technology Thonburi, Bangkok, 25 February 2005. (invited).
R .Corkish, S.R. Wenham, A.B. Sproul, J. Cotter, C.B. Honsberg, M.A. Green, A.G. Aberle, G.
Conibeer, “Photovoltaics and Renewable Energy Education and Research at the University
of New South Wales”, presentation at Department of Physics, Imperial College of Science,
Technology and Medicine, London, 22 February 2005. (invited).
M.A. Green, “Research Opportunities with CSG Solar Material”, Forschungszentrum Jülich,
Germany, February 2005.
R. Passey, M. Watt and K. Nolles, CEEM Submission on the Green Power Options Paper, June
2005.
Dr R. Passey, I. MacGill, H. Outhred, R. Corkish, Submission on “Proposal to increase MEPS
for Room Air Conditioners and harmonise MEPS for single and three-phase units”, Regulatory
Impact Statement, Draft fi nal report – 21 June 2005, Australian Greenhouse Offi ce, July
2005. http://www.ceem.unsw.edu.au/documents/ceem-cpveacmepssubmission.pdf
M. Watt, M. Oliphant, H. Outhred, I. MacGill, E. Spooner and S. Partlin, “Photovoltaics and Peak
Electricity Loads, Summer 2003-04”, Final Report for the BCSE, May 2005.
178

This report is available from:
ARC Centre of Excellence
for Advanced Silicon Photovoltaics
and Photonics
University of New South Wales
Sydney NSW 2052, Australia
Phone:
+61 2 9385 4018
Fax:
+61 2 9662 4240
Email:
s.wenham@unsw.edu.au
Web:
http://www.pv.unsw.edu.au
Director:
Stuart Wenham
Executive Research Director:
Martin Green
Report Coordinators:
Martin Green, Stuart Wenham
and Jenny Hansen
Graphic Artist:
Roman Balla
rballa@bigpond.net.au
Photos, figures and graphs:
Courtesy of Centre Staff