Programm Photovoltaik Ausgabe 2009 ... - Bundesamt für Energie BFE

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Large area thin-film silicon cells
The up-scaling path from small area reactor to the large area KAI 1200 reactor of Oerlikon (1.4 m 2 )
goes through an intermediate size, i.e. the KAI-M (45x55 cm 2 electrode size, work done at Oerlikon
and at IMT). The process development of microcrystalline deposition focused this year in exploring the
validity of the effects of ion bombardment and silane depletion on the microcrystalline intrinsic layer
quality. Deposition parameters were adjusted in order to minimize the first and maximize the second.
By doing a significant effort in cell optimization, the efficiency could increased above 8.2% for a 1.3 µm
thick single junction microcrystalline cell deposited at 4 Å/s (Voc=511 mV, FF=73.0%,
Jsc=21.9 mA/cm 2 ).
As far as high rate deposition of microcrystalline silicon, the reduction of the KAI-M inter-electrode gap
distance allowed us to explore higher pressure regime. As a result of these hardware and process
optimization steps, a microcrystalline single junction solar cell (0.25 cm 2 ) with an efficiency of 7.1%
(Voc=503 mV, FF=70.0%, Jsc=20.2 mA/cm 2 ) was obtained at a deposition rate of 1 nm/s (results in the
frame of the OFEN project). Introduction of this cell into a micromorph device led to the highest initial
efficiency of 10.7% (Voc=1.38 V, FF=70.1%, Jsc=11.1 mA/cm 2 ) as displayed in Fig. 5. The cell is current
matched and the light induced degradation has been evaluated to be lower than 12% after 3000 h
of cell degradation, resulting in a stabilized efficiency close to 9.4%. With an optimized process (for the
µc-Si:H) initial efficiencies slightly higher than 11% are expected. Successful transfer of the SiOx intermediate
reflector from small area systems into KAI-M has been achieved which is expected to improve
also the efficiency of micromorph devices fabricated in the KAI-M system. Additional results on
high rate deposition of µc-Si:H may be found in Ref. [2, 3].
Current density (mA/cm 2 )
12
10
8
6
4
2
0
-0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6
Voltage (V)
Fig. 5: Current-voltage curve of the highest efficiency micromorph tandem cell with the bottom cell
deposited at 1 nm/s in the initial state (�=10.7%, Voc=1.38 V, FF=70.1%, Jsc=11.1 mA/cm 2 ).
Large area cluster deposition systems
The second chamber of our double chamber KAI-M system was also put in operation in 2008. This
configuration allows working easily with different reactor geometry (mainly inter-electrode distance).
The system was also upgraded with several plasma diagnostics systems (developed in the framework
of Athlet, as well as other national projects) such as: peak-to-peak voltage measurement, optical
emission spectroscopy, laser scattering measurement for powder formation monitoring and infrared
absorption spectroscopy for silane depletion/silane consumption measurements. The latter should
then be compared to data obtained by simulation by the University of Patras.
Results on ultra-large area (> 1m 2 )
Even though not the topic of this report, it is worth mentioning the improvements at the industrial level
in this project. In particular the company Oerlikon Solar has been able to demonstrate large area micromorph
module (1.3x1.4 m 2 ) with an initial aperture area efficiency of 9.5% and power up to 128 W.
Characteristics of such a module are plotted on Fig. 6 [4]. Mini-modules with efficiency up to 10.8%
have also been fabricated with the same fabrication equipment.
ATLET, N. Wyrsch, Institut de Microtechnique
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