Enhancing the Efficiency of CZTSSe Solar Cells by Optimizing K-Doping Concentration and Selenization Temperature

As is well-known, the lower open-circuit voltage (VOC) and fill factor (FF) are two major reasons for the lower efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) solar cells. K-doping has become an effective means of improving the efficiency. In this work, the effect of K-doping on power conversion efficiency (PCE) was studied in a K-doping concentration (K/Cu) of 0 to 15 mol % at a selenization temperature ranging from 490 to 530 °C. As a result of our study, it was found that the optimal K-doping concentration for obtaining the highest PCE decreases with increasing selenization temperature. Through optimizing the K-doping concentration and selenization temperature, the highest PCE of 10.15% is obtained at K/Cu = 10 mol % and 510 °C. It is proved that the increased PCE induced by K-doping at a fixed selenization comes mainly from the decreased reverse saturated current density (J0), then from the photogenerated current density (JL), series resistance (RS), and shunt resistance (RSh).