Improvement of the photovoltaic performance of Ag-alloyed Cu2ZnSn(S,Se)4-based solar cells by optimizing the selenization temperature

(Cu1-xAgx)(2)ZnSn(S,Se)(4) films with Ag content of x = 0 (CZTSSe), 0.05 (CAZTSSe) and the corresponding solar cells were fabricated on soda-lime glass (SLG) substrates by sol-gel method and rapid selenization thermal processing (RTP). As Ag is alloyed into CZTSSe, Cu+ cation in CZTSSe films was replaced by Ag+ cation, leading to the improvement in crystal quality, the decrease of hole concentration and the increase of bandgap. We observed an increase in open-circuit voltage (V-OC) and an accompanying rise in device efficiency from 4.48% to 5.94% as Ag is alloyed into CZTSSe. To further improve the efficiency, we optimized the selenization temperature of the CAZTSSe films. It is found that the optimized selenization temperature is 530 degrees C and the best efficiency of the corresponding CAZTSSe solar cell is 7.91%. The improvement of device performance with selenization temperature is mainly attributed to the optimization of device parameters such as reversion saturation current density (J(0)), diode ideal factor (A) and series resistance (R-s), which are determined by crystal quality and grain size of CAZTSSe films as well as structure of the CAZTSSe/CdS and CAZTSSe/Mo interfaces.