Suntech Corporation
Suntech Power is a relatively new Australian-Chinese manufacturing
company in China. The company
has
established conventional screen-printed processing of multicrystalline
and single crystalline silicon solar cells. Suntech Power has
recognised
the importance of achieving higher performance from the solar cells
produced on their production lines. To this extent, they have
indicated
their willingness to support and collaborate in research projects
with UNSW aimed at adapting and implementing many of the high-efficiency
attributes of the buried contact solar cell into a device structure
compatible with manufacturing using the existing infrastructure
and equipment at Suntech Power. In particular, the collaborative
research is targeting the achievement of a selective emitter to
overcome many of the fundamental weaknesses associated with the
design of screen-printed solar cells.
The other body of work encompassed by this collaborative research
involves the design and implementation of innovative rear metal
contacting schemes to overcome the problems associated with screen-printed
solar cells that suffer from high rear surface recombination velocities.
Initial experimentation again shows significant promise with this
work being based on an earlier UNSW patent that predated this collaborative
research agreement.
BP Solar
The Centre continues its long standing research and development
collaboration with BP Solar Pty. on the development of improved
processes and cell designs for high-efficiency Buried Contact
Solar Cells.
Pacific Solar, Sydney
Pacific Solar, a partner in the Centre, was established in 1995
to commercialise thin-film “silicon-on-glass” technology
originally developed by Centre researchers. These researchers continue
to be involved with the company through a consulting arrangement
through Unisearch, the University’s commercial arm. The Centre
also provides characterisation services to the company, particularly
in the areas of transmission electron microscopy, focussed ion beam
cross-sectional analysis and spectral response measurement.
Since the company’s technology is in the process of commercialisation,
little of the associated research activity has yet been published.
However, during 2003, Centre and Pacific Solar researchers co-authored
an invited paper for a Special Issue on Thin-Film Solar Cells
to
appear in the International Journal of Solar Energy in 2004. In
this, a sub-module efficiency of 8.9% is reported for a polycrystalline
silicon film of only 1.6 micron thickness deposited onto glass.
The excellent performance of modules under accelerated life testing
is also documented, suggesting this is the first thin-film technology
to reach this stage of development with stability or durability
likely to be equal to, or better than, wafer-based products.
Max Plank Institute for Microstructure Physics,
Germany
The Max Planck Institute for Microstructure Physics is another
partner in the Centre, and on-going collaboration is expected on
several fronts. Centre Executive Research Director, Martin Green,
has spent several months at the Institute, under a Humboldt Senior
Fellow program, and Dr. Otwin Breitenstein from the Institute spent
2 months at the Centre from September to November, 2003.
In one collaborative project, the temperature distribution from
biased PERL cells on p-and n-type Si substrates made at UNSW were
measured at the Max Planck Institute using a lock-in
thermography method. The very sensitive system set-up allows
detection of very small shunting regions and evaluation of the saturation
current uniformity across the cell emitter. The presence of a non-uniform
boron emitter diffusion was confirmed during these measurements.
During Dr Breitenstein’s visit, abrasion
to the cell surface was used to investigate the local saturation
current increase from PERL cells. Some convincing data have been
collected from these experiments on the nature and properties of
shunts in silicon solar cells.
FOM Institute, Amsterdam
The FOM-Institute for Atomic and Molecular Physics in Amsterdam
is a research laboratory of the Dutch Foundation for the Fundamental
Research on Matter (FOM) and another partner in the Centre. The
Optoelectronic Materials group in the Nanophysics Department of
the Institute headed by Professor Albert Polman is one of the most
highly regarded groups internationally in the area of silicon optoelectronics.
By taking advantage of the experience and facilities of this group
in this area, the Centre of Excellence plans to accelerate progress
on its silicon photonics strand and maximise outcomes for the relatively
small amount of funding available to this strand.
During 2003, the Centre took advantage of the Institute’s
expertise with Rutherford Back Scattering (RBS) as a means of characterising
nanostructures in collaboration with Professor Polman and Dr. J.J.
Penninkhof. The collaboration was part of an internationally dispersed
effort, also involving the Photon Factory in Tsukuba, Japan to clarify
the structural properties of silicon quantum wells fabricated by
the Centre. The Institute was successful using the RBS technique
in putting bounds on the thickness of the silicon layers in these
quantum wells of 2-5 nm thickness.
Institut
für Solarenergieforschung, Hameln/Emmerthal
(ISFH), Germany
The degradation mechanisms for n-type PERL cells (see Annual Report
2003, Section 5.3.2) were investigated jointly with ISFH. Silicon
nitride surface passivation layer was deposited onto these cells
by remote plasma PECVD. LBIC scan mapping again revealed the non-uniform
emitter current collection. Unfortunately, the PECVD nitride could
not achieve a stable surface passivation for these n-type cells,
although a large initial performance improvement was observed immediately
after the nitride deposition. Further stability improvement may
be possible by using heavier emitter boron diffusion.
ENEA, Portici, Italy
Collaborative activities included optical testing of the surface
reflection from UNSW’s solar cells, PV modules with planar,
inverted pyramid, random texturing, porous etching, and honeycomb
surface structures. A new method of applying an integrating sphere
was used for this testing. The light reflection was quantified according
to the surface structure and etching time. Light collection from
a textured cell surface, and module optical degradation were also
measured using a similar testing system.
Australian National University, Faculty of
Engineering IT
The Centre strengthened its collaborative ties with the Australian
National University in the area of solar cell measurement and characterisation,
specifically photoconductance measurement and analysis of silicon
wafers and wafer coatings. In 2004, the collaboration will expand
to include the co-supervision of postgraduate research students
working on collaborative projects.
Sunpower Corporation, USA
During 2003, the Centre hosted Dr. Keith McIntosh, a Visiting Research
Fellow from Sunpower Corporation, USA. Dr. McIntosh collaborated
with Centre researchers in the area of silicon solar cell testing,
characterisation and analysis, including modelling the optics of
high-efficiency commercial solar cells and the development of a
next-generation photoconductance decay tool (with Sinton Consulting).
Fraunhofer-Institute for Solar Energy Systems
ISE
ANU, School of Physical Sciences and Engineering
Samples were obtained from both organisations for the photoluminescent
cooling experiments in the Thermophotonics project (See Annual Report
2003, “Thermophotonics” in Section 5.5) in which high
radiative efficiencies are required to give high luminescence quantum
efficiencies. ANU supplied double heterojunction AlGaAs/GaAs/AlGaAs
samples. Fraunhofer supplied both AlGaAs/GaAs/AlGaAs and InGaP/i-GaAs/InGaP
double heterostructures. All samples were grown epitaxially over
50 nm AlAs release layers on semi-insulating GaAs substrates by
metal organic chemical vapour deposition (MOCVD).
Utrecht University, The Netherlands
During 2003, the Centre has been collaborating with Professor Ruud
Schropp and co-workers at the Debye Institut at Utrecht University,
The Netherlands, in the area of amorphous and crystalline silicon
depositions by hot-wire chemical vapour deposition (HWCVD). HWCVD
is interesting for thin-film photovoltaics because it is an inexpensive
silicon deposition method that is easily unscalable to large area
(~1 m2) solar modules. One project investigated HWCVD
epitaxial thickening of poly-Si seed layers on glass made at UNSW
by aluminium-induced crystallisation (AIC) of amorphous silicon.
Another project was the deposition of amorphous solar cell precursor
structures at Utrecht and subsequent processing of these films into
crystalline solar cells at UNSW.
Universität Karlsruhe, Germany
National Renewable Energy Laboratory NREL, Golden, USA
Collaboration with the above was by way of prolonged visits by
researchers from these institutions.
Prof. Würfel of the Universität Karlsruhe visited the
Centre for two months from May to July, 2003. He was principally
involved in work on Hot Carrier cells and Up/Down Conversion but
also provided useful contributions to other areas of Third Generation
Strand activities (see Annual Report 2003, Section 5.5).
A/Prof. Ohno of NREL visited the Centre for two months from March
to May, 2003. He was involved with work on Selective Energy contacts
for Hot Carrier cells, in particular initiating AC I-V and G-V measurements
(see Annual Report 2003, Section 5.5 ). |
