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 Chalcogenide semiconductors for PV application.
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| Members: Catherine Guillot-Deudon, Alain Lafond, Yves Moëlo, Marc Souilah |
| Objectives : |
World solar photovoltaic (PV) market installations reached a record high of 1,744 megawatts (MW) in 2006. This is a remarkable market but still far away from constituting a noticeable contribution to the world energy consumption.
All photovoltaic devices incorporate a p-n-junction in a semiconductor across which the photovoltage is developed (see Fig. 1).
Beside the silicon-based technology, semiconductors of I-III-VI2 type are very promising materials for the development of high efficiency and low cost solar cells and are closed to large scale production. In these thin film solar cells the absorber layer is made of Cu(In,Ga)Se2 (CIGSe) compounds (see Fig. 2), which adopt the chalcopyrite structure.
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Figure 1: Principle of the photovoltaic effect across a P-N junction.
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Figure 2: Cross section of typical thin film CIGSe-based solar cell.
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Our work is focused on the following goals:
- Improvement of the efficiency of the CIGSe-based solar cell.
The energy conversion efficiency is expected to be maximal for absorber material band gap values of about 1.5 eV. The band gap of the CIGSe increases with the x = Ga/(Ga+In) ratio value from 1.0 eV (x=0) to 1.7 eV (x=1). Therefore, the optimized band gap widths can be achieved for x ³ 0.8. However, all of the research groups have experimentally observed that the efficiency of standard cells, i.e. based on CIGSe/(CBD)CdS junction, effectively increases when x is raised up to 0.3 (Eg~1.2 eV), but for higher gallium content (Eg>1.3 eV) the cells efficiency falls down.
The crystal structure of high Ga-content CIGSe compounds was reinvestigated from both powder and single crystal X-Ray diffraction techniques. It seems, that for specific compositions, a structural modification of the chalcopyrite structure occurs leading to a new atomic arrangement in the cationic planes, derived from the stannite structure (see Fig. 3).
Because this structural modification could induce some modifications in the electronic properties of these compounds, electronic band structure calculations arein progress.
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Figure 3 :
Structure of CIGSe. Chalcopyrite type (a) and derived from stannite type (b) M3+ = In/Ga . |
- Indium free new absorber materials
For a future large-scale production of the CIGSe-based thin film solar cells the challenge could be the replacement of scarce and expensive In and Ga elements.
We are investigating quaternary compounds with general formula Cu2(Sn,Si)Q2 (Q = S, Se). The crystal structure of these compounds is quite close to that of the chalcopyrite structure (Fig. 4) and their photochemical properties show that they are good candidates for PV application.
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Figure 4 : Structure of Cu2(Sn,Si)S3
(space group: Cc). Comparison with the chalcopyrite structure of CuFeS2 |
- Cadmium free buffer layer materials
Because of the toxicity of Cd, efforts are made to replace CdS by another compound as the buffer layer of thin film solar cells. Colleagues from the Laboratory of Materials for Photovoltaics in Nantes have shown that compounds derived from In2S3 work well as buffer material. We are involved in the study of the crystal structure-electronic properties relationship of these compounds. |
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- Structural and optical study of indium-free chalcogenides for photovoltaic applications
J.A. Cody, A. Lafond and C. Guillot-Deudon, European Conference on Solid State Chemistry - Sheffield - 2005
- Modification of the crystal structure of Cu(In,Ga)Se2 photovoltaic absorbers with large Ga-content
M. Souilah, C. Guillot-Deudon and A. Lafond, 11th European Conference on Solid State Chemistry – Caen-France – 2007 |
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- Study of the new b-In2S3 containing Na thin films Part I : Synthesis and structural characterization of the material.
N. Barreau, J.C. Bernède, C. Deudon, L. Brohan, S. Marsillac, Journal of crystal growth 2002, 241, 4-14
- A study of bulk NaxCu1-xIn5S8 and its impact on the Cu(In,Ga)Se2/In2S3 interface of solar cells
N. Barreau, C. Guillot-Deudon, A. Lafond, S. Gall, J. Kessler, Solar Energy materials and solar cells 90, 1840-1848 (2006)
- Syntheses and X-ray diffraction, photochemical and optical characterization of
Cu2SixSn1-xS3 (0.4<x<0.6) for photovoltaic applications
A. Lafond, J.A. Cody, M. Souilah, C. Guillot-Deudon, R. Kiebach and W. Bensch
Inorg. Chem. 46, 1502-1506 (2007).
- Structural study and electronic band structure investigations of the solid solution
NaxCu1-xIn5S8 and its impact on the Cu(In,Ga)Se2/In2S3 interface of solar cells
A. Lafond, C. Guillot-Deudon, S. Harel, A. Mokrani, N. Barreau, S. Gall and J. Kessler
Thin Solid Films 515 (2007) 6020–6023
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Jean-François Guillemoles et Christophe Domain : IRDEP : Institut de recherche et de développement de l'énergie photovoltaïque (unité mixte CNRS-EDF) localisée au centre de R&D d'EdF à Chatou (78)
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John Kessler et Nicolas Barreau : LAMP : Laboratoire des matériaux photovoltaïques de l'Université de Nantes.
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| Contrats |
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| References |
- D. S. Su, W. Neumann and M. Giersig, Thin Solid Films, 361-362, 218-222 (2000).
- M. A. Contreras, K. Ramanathan, J. AbuShama, F. Hasoon, D. L. Young, B. Egaas and R. Noufi, Prog. Photovolt: Res. Appl., 13, 209 (2005).
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Fax : +33 2 40 37 39 95
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Page updated, october, 13, 2008 |
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