Rapid thermal processing of CuInSe2 electroplated precursors for CuIn(S,Se)2-based thin film solar cells

Abstract : During the elaboration of standard CISEL™cells, electroplated CuInSe2 precursors undergo a rapid thermal processing (RTP) in a sulfur-containing atmosphere to promote grain growth and enable sulfurization of the precursor. The aim of this work is to show how structural and morphological properties of the CuIn(S,Se)2-based solar cells can be modified with RTP parameters, namely temperature, heating rate, and sulfur addition. X-ray diffractograms show that the preferential (112) orientation of the electrodeposited CuInSe2 precursor is maintained after annealing but the coefficient of crystallographic texture can be modified with specific RTP parameters. It is also shown that the quantity of sulfur incorporated in the chalcopyrite lattice can be controlled and reaches almost pure CuInS2 according to the sulfur quantity used during the RTP. Another effect of the RTP annealing is to form a Mo(S,Se)2 layer which can lead to a quasi-ohmic contact between the molybdenum and the absorber. The properties of the Mo(S,Se)2 buffer layer are also studied according to the process parameters and an increase of the annealing temperature or of the sulfur concentration tends to increase the thickness of this layer