CuZnSn(SxSe1-x)4 Solar Cell Prepared by the Sol-Gel Method Following a Modified Three-Step Selenization Process

In current work, Cu2ZnSn(S,Se)4thin films have been prepared by the sol-gel method based on dimethyl sulfoxide solution followed by a modified three-step selenization process. The key process of this method is to divide the Se evaporation and annealing into two different stages: employ a thermal cracking Se source in the Se evaporation stage and an above-atmospheric pressure in the annealing process. The morphological, structural, elemental distributional, and photovoltaic properties of Cu2ZnSn(S,Se)4thin films prepared with the three-step selenization process were systematically investigated. It was found that through this modified selenization process, the formations of secondary phases (ZnSe, CuSnSe3) and a fine-grain bottom layer, which usually exists in the traditional one-step selenization process, were effectively suppressed. These improvements could further reduce the carrier recombination and improve the solar cell performance. The best solar cell is obtained with a short-circuit current density of 28.16 mA/cm2, open-circuit voltage of 404.91 mV, fill factor of 62.91%, and a power conversion efficiency of 7.17% under air mass 1.5 (100 mW/cm2) illumination.Keywords:CZTSSe solar cell;sol-gel method;selenization;thermal cracking Se;above-atmospheric pressure;secondary phases