Complete Report - University of New South Wales

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
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