XPS depth profile study of CZTS thin films prepared by spray pyrolysis

Uniformity of elements distribution in Cu2ZnSnS4 (CZTS) thin films were analyzed using X-ray photoelectron spectroscopy (XPS) to improve of conversion efficiency on solar cells. The films were prepared from CuCl or CuCl2, ZnCl2, SnCl2, and thiourea by spray pyrolysis on quartz glass. The composition on surfaces of the as-grown CZTS films was Cu-poor and near stoichiometric compositions of Zn, Sn and S. In contrast to the surface, Cu-rich and Sn-poor compositions were obtained in the films. An existence of oxygen was observed on the film surface less than 20 nm. With increasing of thiourea concentration in the precursor, internal Cu composition, Cu/(Sn+Zn), was increased. S/metal ratio and Sn/Zn ratio in the films were less influenced by the thiourea concentration in the precursor solution. Cupper composition in the films was also affected a valence of Cu ion in the precursor. (C) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim