Influence of H 2S concentration on the properties of Cu 2ZnSnS 4 thin films and solar cells prepared by sol–gel sulfurization

Abstract

Cu 2ZnSnS 4 (CZTS) thin films prepared by a non-vacuum process based on the sulfurization of precursor coatings, consisting of a sol–gel solution of Cu, Zn, and Sn, under H 2S+N 2 atmosphere were investigated. The structure, microstructure, and electronic properties of the CZTS thin films as well as solar cell parameters were studied in dependence on the H 2S concentration. The sulfurization process was carried out at 500 °C for 1 h in an H 2S+N 2 mixed-gas atmosphere with H 2S concentrations of 3%, 5%, 10%, and 20%. As the H 2S concentration decreased from 20% to 5%, the S content of the CZTS thin films decreased. However, when the H 2S concentration was decreased below 3%, the S content of the films began to increase. A CZTS thin film prepared with an H 2S concentration of 3% had grains in the order of 1 μm in size, which were larger than those of films prepared at other H 2S concentrations. Furthermore, the most efficient solar cell, with a conversion efficiency of 2.23%, was obtained from a sample sulfurized at an H 2S concentration of 3%.