Plenarvorträge - DPG-Tagungen

Halbleiterphysik Dienstag
HL 18 Hauptvortrag Zacharias
Zeit: Dienstag 14:30–15:15 Raum: H15
Hauptvortrag HL 18.1 Di 14:30 H15
Confinement effects in Si nanostructures — •Margit Zacharias,
Johannes Heitmann, Vadim G. Talalaev, Roland Scholz, Florian
M. Kolb, and Herbert Hofmeister — Max-Planck- Institut
für Mikrostrukturphysik, Weinberg 2, 06120 Halle
Silicon is the main base material for modern microelectronics. Due to
its indirect band structure it is not ideally suited for optoelectronic purposes.
Nevertheless, because of its importance in microelectronics major
research and development efforts have been undertaken to change sili-
HL 19 Symposium 50 Jahre Solarzelle
con into a photonics material. The present lecture will highlight areas in
which silicon promises to have an increasing impact in the area of photonics.
Approaches developed in our group will be presented on how to
transform silicon so that it can be used as an efficient light emitter in the
visible and infrared. Especially the interaction of quantum confinement
and migration effects of the excitons and the energy transfer to doping
materials, i.e. Erbium, is investigated in details. The presented strategies
for size controlled growth of nanocrystals and nanowires play a major
role for the described investigations and perspective applications.
Zeit: Dienstag 15:15–17:45 Raum: H15
HL 19.1 Di 15:15 H15
Slow Solar Ascent — •H. J. Queisser — Max-Planck-Institute for
Solid State Research, D-70506 Stuttgart
Limited attention arose from the miniscule note by Chapin, Fuller,
and Pearson on a new solar cell, as received on January 11, 1954 by the
Journal of Applied Physics. Pentagon engineers sneered at this feeble
power source; trials failed for rural telephony. The initial theory for solar
cells relied on mere extensions for the forward current – voltage relations
of p – n junctions. Later work simply attempted reductions of all loss
mechanisms. The Sputnik shock suddenly rekindled active research. The
optimal semiconductor was to be found. A thermodynamic theory was
proposed on the basis of detailed balance and a restriction to radiative
recombination. Silicon proved to be close to maximal efficiency.
HL 19.2 Di 15:45 H15
Progress in Manufacturable High-Efficiency Silicon Solar Cells
— •R. Hezel — Institut für Solarenergieforschung GmbH, Am Ohrberg
1, 31860 Emmertal
As an important step towards making photovoltaics an economic
source of energy, the efficiency of industrial crystalline silicon solar cells
has to be drastically increased. In this way not only more power is gained
with less silicon, but simultaneously also all other area-related costs of
the PV system are reduced. It is of great importance to bridge the efficiency
gap between the present industrial solar cells with values of 14% to
16% and the sophisticated laboratory cells with a record efficiency close
to 25%. Recently new technologies are emerging or existing ones being
upgraded aiming for the ambitious goal to manufacture silicon solar cells
with efficiency above 20% cost effectively in an industrial environment.
Four different promising approaches of high efficiency silicon solar cells
are presented in this paper, including one with bifacial sensitivity.
HL 19.3 Di 16:15 H15
Second and third generation photovoltaics: dreams and reality.
— •J. H. Werner — Institut für Physikalische Elektronik, Universität
Stuttgart
To more than 90 %, the present world market of solar cells is dominated
by one material: crystalline silicon. Is has become common to term
photovoltaics based on silicon wafers as ”first generation” photovoltaics.
Research on ”second generation” photovoltaics, i.e. on thin film solar
cells started as early as 1956 when the first Cu2S/CdS solar cell was prepared.
Research on this type of cells was essentially given up around 1980
because 10 % efficiency have never been exceeded. At the same time, substantial
research started on amorphous silicon, which now stands at 13 %
(stable) efficiency compared to almost 25 % for the world best cells from
crystalline silicon. Thus, early second generation photovoltaics did not
fulfil the dreams of a cheap, highly efficient thin film technology. Nowadays,
two other materials second generation are going into the production
of commercial modules: CdTe and Cu(In,Ga)Se2. This presentation gives
a critical assessment of these two materials which are highly interesting
for research but as commercial products may suffer either from their toxicity
or from their polycrystallinity. In particular, the inherent structural
inhomogeneity of the polycrystalline films results in an electronic inhomogeneity
which limits the performance of cells and modules in several
ways. As a consequence, even in the case of second generation photovoltaics,
the material of choice probably will be again crystalline silicon.
Only photovoltaic materials which either supplement crystalline silicon
or lead to new principles for the conversion of solar radiation into electricity
seem to be interesting for innovative research. From this point of
view, research on ”third” generation photovoltaics, i.e. solar cells with
potential efficiencies above the classic Shockley/Queisser limit of 30 %,
including recent publications on ZnMnTe, will be critically discussed.
HL 19.4 Di 16:45 H15
Material & Device Concepts for Organic Photovoltaics: Towards
Competitive Efficiencies — •C. J. Brabec — SIEMENS
AG, CT MM1, Innovative Polymers, Paul Gossenstr. 100, D-91052 Erlangen,
Germany
The talk gives an overview on the technology of polymer photovoltaics,
addressing device, production, packaging and business aspects. The focus
is however placed on the function of bulk-heterojunction devices. Even
10 years after the introduction of the bulk-heterojunction concept, basic
physical processes in these devices are still under discussion. A model to
describe bulk heterojunction solar cells in introduced. The performance
potential of state of the art organic bulk-heterojunction photovoltaic devices
is analysed at the hand of this model, and guidelines towards higher
device efficiencies are presented. The concept relies on the identification
and determination of the relevant material parameters (lifetime, mobility,
bandgap, trap density.....) for the pristine components and for the
blended photovoltaic composites. Results from simulation are compared
to experimental device performance. Based on these findings, material
and device parameters for highly efficient bulk heterojunction devices
are presented and a roadmap for the polymer photovoltaic is suggested.
HL 19.5 Di 17:15 H15
The Crystalline Silicon Solar Cell - Its History, Achievements
And Perspectives — •G. Willeke — Fraunhofer ISE, Heidenhofstr.
2, D-79110 Freiburg, Germany
With a long history of successful market deployment, the crystalline
silicon solar cell currently celebrates its 50th anniversary. On this occasion
it is useful and appropriate to analyse the rate of progress in the
past and to highlight its further development potential for the markets
to come. Subsequent to finding a suitable market in space 5 years after
its conception, crystalline silicon developed into the workhorse technology
of the terrestrial power market which was stimulated by the oil crises
25 years ago. In the first 25 years of its existence, all the technological
features were already demonstrated on a lab-scale that are now incorporated
in the mass-manufacturing lines such as a screen printed front
finger grid, textured and passivated surfaces, the back surface field and
even the now very successful block-casting technique was researched then.
The early terrestrial devices in the late 70s took a great benefit from the
space development and first modules were 8 inch single crystalline wafers.
In comparison, today’s product is made from 125mm quasi-square substrates
(150mm full square are currently under development) with module
efficiencies in the range of 11-15 efficiency of 6 technology. The wafer
size here has increased from 10x10 cm 2 to 12.5x12.5 cm 2 (15x15 cm 2 being
introduced into manufacturing). In all these technologies the wafer
thickness has been hardly reduced in this quarter century from 400 m 2
to 300 m 2 . The task of the next decade will be to bring 20 technology
into production, bring the wafer size to 20x20 cm 2 and at the same time
reduce the wafer thickness considerably. That the manufacturing of 50
m 2 thin crystalline silicon wafers into 40 m 2 thin 20 technique LFC, has