Efficient Cu(In, Ga)Se 2 Based Solar Cells Prepared by Electrodeposition
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EFFICIENT Cu(In,Ga)Se2 BASED SOLAR CELLS PREPARED BY ELECTRODEPOSITION
D. Guimard, N. Bodereau, J. Kurdi, J.F. Guillemoles, D. Lincot Laboratoire d’Électrochimie et de Chimie Analytique (LECA, UMR 7575 CNRS) Ecole Nationale Supérieure de Chimie de Paris 11 rue Pierre et Marie Curie, 75231 Paris Cedex 05, France Pierre-Philippe Grand, Moez Ben Farrah, Stéphane Taunier, Olivier Kerrec EDF-R&D, CISEL , 6 Quai Watier-BP 49, 78401 Chatou cedex, France P. Mogensen, Saint-Gobain Recherche, Aubervilliers, France ABSTRACT CuInSe2 and Cu(In,Ga)Se2 precursor layers have been prepared by electrodeposition , with morphologies suitable for device completion. These precursor films were transformed into photovoltaic quality films after thermal annealing without any post-additional vacuum deposition process. Depending on the preparation parameters annealed films with different band gaps between 1eV and 1.5 eV have been prepared. The dependence of resulting solar cell parameters has been investigated. The best efficiency achieved is about 10,2 % for a band gap of 1.45 eV. This device presents an open circuit voltage value of 740 mV, in agreement with the higher band gap value. Device characterisations (current-voltage, capacitance-voltage and spectral response analysis) have been performed. Admittance spectroscopy at room temperature indicates the presence of two acceptor traps at 0.3 and 0.43 eV from the valance band with density of the order of 2. 10 17 cm-3 eV1 .
INTRODUCTION CIGS (Cu(In,Ga)Se2) based solar cells have now demonstrated their maturity to provide a new generation of photovoltaic modules for the conversion of solar energy. Present technologies are based on the use of high vacuum deposition techniques for the preparation of the absorber layers. There is an interest to investigate alternative low cost deposition techniques which may be able to improve further the contribution of CIGS modules to the development of public demand for photovoltaics. Electrodeposition is one of these techniques as shown in the case of cadmium telluride solar cells. However in the case of CIGS this technique is much more difficult to use due to the more complex nature of the absorber as compared to CdTe. 6.5% efficient CIGS based solar cells have been prepared from 1994 by a two stage process : electroplating of a precursor film and thermal annealing [1]. More recently, using CuInSe2 absorber, efficiencies of 8.8% were demonstrated [2]. Device analysis showed electrical characteristics close to those of coevaporated materials in terms of recombination mechanisms [2]. We present in this paper cells with improved
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efficiencies above 10%, thanks to an increase of the band gap value of the absorbers up to 1.47 eV. The effect of increasing the band gap of the absorber on device parameters is presented in detail. First analysis of the distribution of electrical traps in these devices is presented, showing the present of two major acceptor peaks at about 0.27 and 0. 45 eV from the valence band.
EXPERIMENTAL The CIGS precursor thi
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