Effects of S and Se contents on the physical and photovoltaic properties of Cu₂ZnSn(S_{: X}, Se_{1- X})₄ thin films: Achieving a PCE of 9.47%

CZTSSe absorbers are synthesized by a one-step annealing process from Cu, SnS and ZnS stacks prepared by sputtering deposition. CZTSSe thin films are fabricated by a selenization process using an optimized precursor stack structure. The selenization temperature has a strong influence on the phase and reactions of the elements in the films. CZTSSe formation is initially triggered by the interaction of Cu with Sn(S, Se) to form CuSn(S, Se) compounds, which then react with ZnS. CZTSSe films obtained at 590 °C exhibit a kesterite structure. Sulfo-selenization is performed using an optimized selenization process. Based on the mass ratio of the chalcogen sources, selenium disulfide and selenium, the effect of the S/(S + Se) compositional ratio on the structural and morphological properties of the as-grown films and the optoelectronic parameters of solar cells fabricated using these absorber films are studied. Using this single-step sulfo-selenization method, CZTSSe devices with conversion efficiencies up to 9.47% are obtained.