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

9/9
Steps towards multi-junction solar cells
In order to assess the suitability of high Ga content CIGS top cells in tandem structures we measured
the photovoltaic properties of low Ga content (25%) CIGS and CIS bottom cells by applying the wide
gap top cell as an optical filter. The measured current densities were only 3.0 mA.cm -2 and 4.0 mA.cm -2
in the respective bottom cells. The main reason for the low current densities in the bottom cells is a
very low transmittance through the top cell. Thus, improvements in the PV performance and
transmittance of CIGS solar cells with very high Ga content x on TCO are necessary to make them
suitable for efficient multi-junction devices.
Summary – Semitransparent CIGS cells
The microstructure and photovoltaic properties of CIGS solar cells depend on the Ga content, the
electrical back contact, and the substrate temperature during deposition of the absorber layer. Results
have shown that by varying the gallium content of CIGS solar cells, the photocurrent can be adjusted
to achieve current matching in a tandem device.
The use of ZnO:Al as a back contact for a chalcopyrite top cell has shown good results for devices
with low x, a solar cell with 13.5% efficiency (x = 0.24) was obtained using a low temperature process
(450 °C) for the absorber deposition. However, further work is required to achieve efficiently working
devices with higher Ga contents, which would make them suitable as top cells. Furthermore, higher
optical transparency through the complete cell is required for which reduction in parasitic absorption is
necessary.
National and international collaboration
The partners of our ATHLET work packages are: HMI Berlin (D), FU Berlin (D), ZSW Stuttgart (D),
Solarion (D), AVANCIS (D), CNRS-ENSCP (F), ETH Zürich (CH). Collaborations with the electron
microscopy group of ETH Zurich.
Several activities of this project benefit from the projects sponsored by Swiss agencies,
especially the work for flexible and tandem solar cells have some overlap from the projects
supported by the Swiss Federal Office of Energy and CCEM.
Publications and conference presentations
Journal Publications:
[1] S. Seyrling, S. Calnan, S. Bücheler, J. Hüpkes, S. Wenger, D. Brémaud, H. Zogg, A.N. Tiwari, CuIn1-xGaxSe2
photovoltaic devices for tandem solar cell application, Thin Solid Films 25310 (2008).
[2] S. Buecheler, D. Corica, D. Guettler, A. Chirila, R. Verma, U. Müller, T.P. Niesen, J. Palm and A.N. Tiwari, Ultrasonically
Sprayed Indium Sulfide Buffer Layers for Cu(In,Ga)(S,Se)2 Thin-Film Solar Cells, Presented during E-MRS Spring
Meeting 2008, Strasbourg, France, May 26-30, 2008, and accepted for publication in Thin Solid Films.
Conference contributions:
[3] R. Verma, D. Brémaud, S. Bücheler, S. Seyrling, H. Zogg and A. N. Tiwari, Physical vapor deposition of In2S3 buffer on
Cu(In,Ga)Se2 absorber: optimization of processing steps for improved cell performance, Pro. 22nd European
Photovoltaic Solar Energy Conference, Milano, Italy, Sept. 3-7, 2007.
[4] R. Verma, D. Brémaud, A. Chirila, S. Buecheler, S. Seyrling, D. Guettler, H. Zogg and A. N. Tiwari, Flexible Cu(In,Ga)Se2
Solar Cells with In2S3 Buffer Layer Deposited by Physical Vapor Deposition, E-MRS spring meeting, Strasbourg,
France, May 26-31, 2008.
[5] R. Verma, S. Buecheler, D. Corica, A. Chirila, S. Seyrling, J. Perrenoud, D. Guettler, C. J. Hibberd and A. N. Tiwari,
Cu(In,Ga)Se2 Solar Cells with In2S3 Buffer Layers grown by Vacuum Evaporation and Chemical Spray Methods,
23rd European Photovoltaic Solar Energy Conference, Valencia, Spain, Sept. 1-5, 2008.
[6] D. Corica, S. Buecheler, D. Guettler, A. Chirila, S. Seyrling, R. Verma and A.N. Tiwari, Indium Sulfide Buffer Layer for
Cu(In,Ga)Se2 Thin-Film Solar Cells Deposited by Ultrasonic Spray Pyrolysis, Conference Proceedings of 23 rd
European Photovoltaic Solar Energy Conference and Exhibition, Valencia, Spain, Sept 1-5, 2008.
[7] R. Verma, S. Buecheler, D. Corica, A. Chirila, S. Seyrling, J. Perrenoud, D. Güttler, D. Brémaud, C.J. Hibberd, H. Zogg
A.N. Tiwari, Cu(In,Ga)Se2 Solar Cells with In2S3 Buffer Layers grown by Vacuum Evaporation and Chemical Spray
Methods, Conference Proceedings of 23 rd European Photovoltaic Solar Energy Conference and Exhibition, Valencia,
Spain, Sept 1-5, 2008.
[8] R.Verma, S.Buecheler, D.Corica, A.Chirila, S.Seyrling, J.Perrenoud, R.L.Sauaia, D.Güttler and A.N.Tiwari, Cd-free buffer
layers for Cu(In,Ga)Se2 thin-film solar cells, "A look inside solar cells" Workshop, Monte Verità, Ascona, Switzerland,
16-18 November 2008.
113/290
ATHLET - Advanced Thin Film Technologies for Cost Effective Photovoltaics, A. N. Tiwari, ETH Zürich