Binary phase segregation in CuInS2 thin films for efficient solar energy conversion

We investigate Cu-In-S films with Cu/In>1 grown by different preparation techniques such as coevaporation, sulphurization of stacked elemental layers and spray-pyrolysis. Using electron spectroscopy measurements, a preferential segregation of a CuS layer at the front surface of the films can be displayed by the structure of the Cu LVV Auger electron spectrum. This is observed for films grown by coevaporation and sulphurization. The CuS segregation is missing for as-deposited films which are grown by spray-pyrolysis, can however, be induced for these films by additional tempering. The results of the surface analytical study are discussed with respect to the junction performance of CuInS₂/CdS/ZnO solar cells