Sulfo-selenization of metallic thin films of Cu, In and Cu–In

To achieve an optimized adaptation of the semiconductor bandgap to the terrestrial solar spectrum, CIS (CuInSe2, CuInS2) based chalcopyrite absorber materials are usually substituted in the cation and anion lattice to yield mixed pentanary crystals with general composition Cu(In,Ga)(Se,S)2. In the past, in-situ XRD (X-ray diffraction) measurements helped to clarify the phase formation sequences and reaction kinetics while crystallising the ternary chalcopyrites CuInSe2 and CuInS2 from metallic precursors in the presence of Se or S atmosphere. To better understand the reaction paths towards pentanary mixed chalcopyrites, the experiments are now extended to a study of the combined sulfo-selenization of metallic precursors. The experimental results of the simultaneous sulfo-selenization of Cu, In and Cu–In precursor thin films are presented and their relevance for the crystallisation of a mixed CuIn(S,Se)2 phase discussed.The affinity of the metals Cu and In is higher to sulfur. A crystallisation of mixed sulfo-selenides of Cu, In and Cu–In due to exchange reactions between S and Se is observed. Within the Cu–Se–S subsystem a wider solid solution range of S and Se is apparent as compared to the In–Se–S system. The reactions during the chalcopyrite crystallisation for chalcogen ratio [S]:[Se] = 1:1 are similar to those of the pure sulfur system at least within the In–Se–S subsystem.