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  Mainz, R.; Klaer, J.; Klenk, R.; Papathanasiou, N.: Solar cells based on Cu(In,Ga)S₂ prepared by a two-step process. In: The compiled state-of-the-art of PV solar technology and deployment : 22nd European Photovoltaic Solar Energy Conference, EU PVSEC ; proceedings of the international conference, held in Milan, Italy, 3 - 7 September 2007Munich: WIP-Renewable Energies, 2007. - ISBN 3-936338-22-1, p. 2429-2433

Abstract:
In this contribution we report about the development of a two-step process to prepare Cu(In,Ga)S₂ solar cells. The two steps consist of magnetron sputtering of the metal precursors followed by rapid thermal processing (RTP) in sulfur vapor. Based on the well known RTP of CuInS₂ and preceding experiments with a co-evaporation process, we investigated different processes starting with stacked elemental layer (SEL) of In and Cu:Ga with a Cu-rich composition ([Cu]/([In]+[Ga])>1). As variation parameters we chose the temperature profile of the RTP, the sequence of the SEL and the amount of sulfur present in the beginning of the thermal processing. The solar cells are finished by a window layer containing a chemical bath deposited CdS buffer and a sputtered i-ZnO/ZnO:Al emitter. It is possible to obtain solar cell efficiencies of 12.2% with a spectral response cut off similar to CuInS₂ but a much better current collection, j_sc=24.2 mA/cm². Choosing a suitable temperature profile leads to open circuit voltages of 766 mV due to a blue shift of the band gap. First steps are taken to scale up the process for an industrial application by choosing 30x30 cm² substrates.