Role of zinc tin oxide passivation layer at back electrode interface in improving efficiency of Cu2ZnSn(S,Se)4 solar cells

We report a Cu2ZnSn(S,Se)4 (CZTSSe) solar cell with a modified structure via inserting an intermediate zinc tin oxide (ZTO) layer between Mo electrode and CZTSSe layer in the conventional CZTSSe solar cell. Comparing with the conventional CZTSSe solar cells (without ZTO layer), the best photovoltaic performance is obtained for the solar cells with a modified structure. When an 8-nm-thick ZTO passivation layer is inserted, the corresponding device shows the improvements in performance parameters, including short-circuit current density (JSC), open-circuit voltage (VOC), and fill factor (FF). As a result, we obtained a maximum power conversion efficiency (PCE) of 8.95% for the optimized device with an 8-nm-thick ZTO layer, which is ascribed to the increase of shunt resistance (RSh), decrease of series resistance (RS) and decrease of reverse saturation current density (J0). Our results suggest that the ZTO is a promising passivation material at back electrode interface for optimizing the performance and improving efficiency of CZTSSe-based solar cells.