Effect of the post-selenization time on the structural and optical properties of Cu2MnSn(S,Se)4 thin films synthesized by sol-gel technique

Cu2MnSn(S,Se)4 (CMTSSe) thin films were synthesized by using spin-coating technique and the structure, composition and optical properties have been investigated. XRD patterns and Raman measurements reveal that the crystallinity of the films is significantly dependent on the selenization time. The grain size of the CMTSSe thin films is demonstrated to be improved and the surface comes to compact without any visible cracks and voids with increasing time. Notably, the longer selenization time (>20 min) would lead to the overgrowth of the films and decomposition of the CMTSSe phase. Especially the escape of Sn and S/Se elements in the form of SnS(e) would resulting in a rough surface with few pin holes. The band gap of all these films are between 1.4 and 1.7 eV. The solar cell device with the CMTSSe layer selenized for 20 min achieves the highest open circuit voltage of 338 mV.