Bandgap tuning and morphology amelioration of sol-gel derived Cu 2 ZnSnS 4 (CZTS) thin films by selenium incorporation

Solution-based techniques are promising for fabrication of low-cost Cu 2 ZnSnS 4 (CZTS) thin film solar cells (TFSCs). Annealing at high temperature with Se vapor has been widely applied to improve the performance of CZTS TFSCs. However, the mechanisms have been scarcely addressed in literatures. In this work, Se incorporation into sol-gel derived CZTS thin films was accomplished by introducing Se vapor into the annealing chamber in order to investigate the effects of Se incorporation. Our results indicate that increasing the concentration of Se decreases the optical bandgap. Most importantly, the morphology of CZTS thin film was significantly improved with increasing the concentration of Se.