Raman and PL study of defect-ordering in CuInS2 thin films

The efficiency of CuInS2 (CIS) solar cells is determined by the presence of native (extrinsic) lattice defects. These defects introduce energy levels in the band gap, which determine the conductivity type and the minority carrier lifetime. In this study, different characterization methods are applied to elucidate the defect physics and chemistry of CIS. Thin films of CIS are obtained by sulfurization of a CuIn metallic alloy. The process conditions are: reactor pressure 1 bar, substrate temperature between 450 and 500 °C, sulfurization time between 2 and 15 min. The films are investigated with X-ray diffraction, Raman spectroscopy, and photoluminescence spectroscopy. It is found that the deposition parameters such as the sulfur pressure and the reactor temperature determine the concentration and type of lattice defects. In the present investigations, the process conditions are related to the defect chemistry and show how the quality of CIS thin films can be improved.