Li/Ag Co‐Doping Synergistically Boosts the Efficiency of Kesterite Solar Cells Through Effective SnZn Defect Passivation

Abstract

AbstractDespite the tremendous progress in the efficiency of Cu2ZnSn(S,Se)4 (CZTSSe) photovoltaic devices, open‐circuit voltage (Voc) deficit, mainly related to the SnZn‐related defects in the absorber, still remains one of the key issues that hinders the cell performance. To overcome this hurdle, here a facile synergistic post‐deposition treatment (PDT) strategy in CZTSSe family via AgF‐PDT after LiF‐PDT in the photovoltaic absorber to suppress SnZn defects, and thus, to promote the Voc and power conversion efficiency (PCE), is reported. Furthermore, a mechanism for improving device efficiency of CZTSSe cell is also proposed. The in‐depth investigation results demonstrate that Li/Ag co‐doping reduces the band tailing characteristic, enlarges the depletion region width, and enhances the carrier transport and collection, resulting in a lower bulk and interface recombination. More importantly, Li/Ag co‐doping strategy provides an effective method for SnZn defect passivation, thereby prolonging minority carrier lifetime in the ensuing devices and leading to enhancement in device performance. Correspondingly, the resulting Li/Ag co‐doped device delivers a champion efficiency of 12.58% with an impressive Voc of 507 mV. This work explores an effective strategy to kill the SnZn‐related defects, thereby overcoming the problems associated with the Voc deficit and lower cell efficiency in Kesterite‐based photovoltaic devices.