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

Abstract Despite the tremendous progress in the efficiency of Cu 2 ZnSn(S,Se) 4 (CZTSSe) photovoltaic devices, open‐circuit voltage ( V oc ) deficit, mainly related to the Sn Zn ‐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 Sn Zn defects, and thus, to promote the V oc 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 Sn Zn 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 V oc of 507 mV. This work explores an effective strategy to kill the Sn Zn ‐related defects, thereby overcoming the problems associated with the V oc deficit and lower cell efficiency in Kesterite‐based photovoltaic devices.