Programm Photovoltaik Ausgabe 2009 ... - Bundesamt für Energie BFE
Programm Photovoltaik Ausgabe 2009 ... - Bundesamt für Energie BFE Programm Photovoltaik Ausgabe 2009 ... - Bundesamt für Energie BFE
5/6 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 67/290
Fig. 6: 1.4 m 2 micromorph p-i-n tandem module with 125.8 W initial efficiency fabricated by Oerlikon Solar in Kai 1200 PECVD reactors [4]. Conclusion Despite the large size of the Athlet consortium, the organization in sub-projects allows relative good research efficiency and fruitful collaborations. These collaborations comprise the exchange of layers, cells, measurement results, services, but also discussions and experience exchanges during project meetings. Significant progress have been made toward the final objectives of 14% stable efficiency on small area and 10% stable efficiency on 1.4 m 2 micromorph modules. National and international collaborations Beside the strong partnership between OC Oerlikon and IMT, this Athlet project allows a fruitful collaboration with the Jülich Forschungszentrum, the Institute of Physics of the Academy of Science of Prague, the University of Patras (Greece), Schott Solar in Germany, Saint-Gobain Research, among the most important ones. Evaluation for year 2008 and perspectives for 2009 In 2008, all project deliverables were met in time. Development of micromorph cells in KAI-M system are progressing according to schedule and the project goal should be achieved by the end of 2009. For the development of small area devices, the progresses, especially in term of stable efficiency are slower than expected. Introduction of SiOx based intermediate reflectors have allowed significant improvement in term of device open circuit voltage at a price of reduced device stability. The origin of the effect is not yet understood and will be the subject of detailed analysis in 2009. Nevertheless, the very ambitious goal of 14% stable device seems difficult to achieve experimentally with a tandem micromorph device in the time frame of the present project, even though numerical simulation show higher potential. Such a high efficiency may need the use of triple junction cells as so far studied by companies such as Unisolar in the US or Kaneka in Japan. References [1] D. Dominé et al., Proc. of the 23 rd EU PV Solar Energy Conference, 2008, Valencia, pp. 2091-2095. [2] A. Feltrin et al., Proc. of the 23 rd EU PV Solar Energy Conference, 2008, Valencia, pp. 2447-2450. [3] F. Meillaud et al., Proc. of the 23 rd EU PV Solar Energy Conference, 2008, Valencia, pp. 2396-2399. [4] J. Meier et al., Proc. of the 23 rd EU PV Solar Energy Conference, 2008, Valencia, pp. 2057-2061. ATLET, N. Wyrsch, Institut de Microtechnique 68/290 6/6
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Fig. 6: 1.4 m 2 micromorph p-i-n tandem module with 125.8 W initial efficiency fabricated by Oerlikon<br />
Solar in Kai 1200 PECVD reactors [4].<br />
Conclusion<br />
Despite the large size of the Athlet consortium, the organization in sub-projects allows relative good<br />
research efficiency and fruitful collaborations. These collaborations comprise the exchange of layers,<br />
cells, measurement results, services, but also discussions and experience exchanges during project<br />
meetings. Significant progress have been made toward the final objectives of 14% stable efficiency on<br />
small area and 10% stable efficiency on 1.4 m 2 micromorph modules.<br />
National and international collaborations<br />
Beside the strong partnership between OC Oerlikon and IMT, this Athlet project allows a fruitful collaboration<br />
with the Jülich Forschungszentrum, the Institute of Physics of the Academy of Science of<br />
Prague, the University of Patras (Greece), Schott Solar in Germany, Saint-Gobain Research, among<br />
the most important ones.<br />
Evaluation for year 2008 and perspectives for <strong>2009</strong><br />
In 2008, all project deliverables were met in time. Development of micromorph cells in KAI-M system<br />
are progressing according to schedule and the project goal should be achieved by the end of <strong>2009</strong>.<br />
For the development of small area devices, the progresses, especially in term of stable efficiency are<br />
slower than expected. Introduction of SiOx based intermediate reflectors have allowed significant improvement<br />
in term of device open circuit voltage at a price of reduced device stability. The origin of the<br />
effect is not yet understood and will be the subject of detailed analysis in <strong>2009</strong>. Nevertheless, the very<br />
ambitious goal of 14% stable device seems difficult to achieve experimentally with a tandem micromorph<br />
device in the time frame of the present project, even though numerical simulation show higher<br />
potential. Such a high efficiency may need the use of triple junction cells as so far studied by companies<br />
such as Unisolar in the US or Kaneka in Japan.<br />
References<br />
[1] D. Dominé et al., Proc. of the 23 rd EU PV Solar Energy Conference, 2008, Valencia, pp. 2091-2095.<br />
[2] A. Feltrin et al., Proc. of the 23 rd EU PV Solar Energy Conference, 2008, Valencia, pp. 2447-2450.<br />
[3] F. Meillaud et al., Proc. of the 23 rd EU PV Solar Energy Conference, 2008, Valencia, pp. 2396-2399.<br />
[4] J. Meier et al., Proc. of the 23 rd EU PV Solar Energy Conference, 2008, Valencia, pp. 2057-2061.<br />
ATLET, N. Wyrsch, Institut de Microtechnique<br />
68/290<br />
6/6
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