Influence of H_2S concentration on the properties of Cu _2ZnSnS_4 thin films and solar cells prepared by solgel sulfurization

摘要

Cu_2ZnSnS_4 (CZTS) thin films prepared by a non-vacuum process based on the sulfurization of precursor coatings, consisting of a solgel solution of Cu, Zn, and Sn, under H_2SN_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_2SN_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.