Energy loss near edge structure of sulfur in non-stoichiometric CuInS2

Non-stoichiometric CuInS2 is a novel material for thin film solar cells. El ectron energy loss spectrometry analysis shows that there are considerable lateral inhomogeneities on a scale of less than 100 nm. It is as yet unknow n whether the Cu or In surplus comes in nanoprecipitates irregularly distri buted in the otherwise stoichiometric matrix, or forms supercells where par ticular atoms are replaced by their complements. This question bears import ant consequences for the understanding of the local electronic structure an d the mechanism of undesired recombination processes in the cell. Since the energy-loss near edge structure of ionisation edges (ELNES) mirrors the lo cal density of unoccupied states it should be different in the two cases. W e compare the sulfur L-2,L-3 ELNES of a Cu-rich and of an In-rich specimen with simulations of supercells based on the TELNES/WIEN97 code. Faint diffe rences in the edge shape can be made visible using difference spectra. They agree reasonably well with simulations. The results show that the surplus species exists as a separate non-stoichiometric phase and not merely as a p recipitate of elemental Cu or In. (C) 2000 Elsevier Science Ltd. All rights reserved.