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Zn(S,O,OH) Chemical Bath Deposited buffer layers for high efficiencies Cu(In,Ga)(S,Se)2 solar cells : a better understanding of the growth mechanism

Cedric Hubert 1Negar Naghavi 1Olivier-Gabriel Roussel 1Arnaud Etcheberry 2Dimitri Hariskos 3Michael Powalla 3Olivier Kerrec 1Daniel Lincot 1

1. Institut de Recherche et Développement en Energie Photovoltaique, unité mixte EDF-CNRS-ENSCP (IRDEP), 6 quai Watier, Paris 78401, France
2. Institut Lavoisier, IREM, UMR 8637 CNRS-Université de Versailles, Versailles 78035, France
3. Zentrum für Sonnenenergie und Wasserstoff Forschung (ZSW), Baden-Württemberg, Industriestrasse 6, Stuttgart 70565, Germany


In the next few years, one of the major objectives in the field of CuInS2 and Cu(In,Ga)Se2 PV technology is the development and rapid implementation in production line of Cd-free alternative for the currently used CdS buffer layer. Zinc-based buffer layers, prepared by Chemical Bath Deposition (CBD), have already demonstrated their potential to obtain high efficiencies solar cells. However, the understanding of both deposition mechanism and film properties is by far lower than what is the current status of CBD of CdS. We report here a study of the synthesis of zinc-oxy-sulfide films by CBD in a wide and rigorous experimental parameter window.

For industrial applications, the priority is to achieve scalable CBD ZnS buffer layer with efficiencies comparable to CdS using a simple and short deposition time process (lower than 10 min), with minimum of chemicals and which can be easily extended to stable modules.

In this paper first a theoretical approach, with thermodynamic calculations of ZnS, ZnO and Zn(OH)2 solubility are presented taking into account in particular the effect of temperature and the complexing agent such as ammonia over a wide pH range. In parallel in-situ growth studies by quartz crystal microbalance has been made in order to have a better understanding of the growth mechanism and to establish a general equation concerning the deposition growth. Correlations between film properties obtained by XPS, XRF and SEM with deposition conditions are established. Optimized conditions lead to high efficiency devices, competing very well with classical CdS.


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Presentation: Oral at E-MRS Fall Meeting 2007, Symposium B, by Cedric Hubert
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-11 18:35
Revised:   2009-06-07 00:44