Passivating Grain Boundaries via Graphene Additive for Efficient Kesterite Solar Cells

Abstract Grain boundaries (GBs)‐triggered severe non‐radiative recombination is recently recognized as the main culprits for carrier loss in polycrystalline kesterite photovoltaic devices. Accordingly, further optimization of kesterite‐based thin film solar cells critically depends on passivating the grain interfaces of polycrystalline Cu 2 ZnSn(S,Se) 4 (CZTSSe) thin films. Herein, 2D material of graphene is first chosen as a passivator to improve the detrimental GBs. By adding graphene dispersion to the CZTSSe precursor solution, single‐layer graphene is successfully introduced into the GBs of CZTSSe absorber. Due to the high carrier mobility and electrical conductivity of graphene, GBs in the CZTSSe films are transforming into electrically benign and do not act as high recombination sites for carrier. Consequently, benefitting from the significant passivation effect of GBs, the use of 0.05 wt% graphene additives increases the efficiency of CZTSSe solar cells from 10.40% to 12.90%, one of the highest for this type of cells. These results demonstrate a new route to further increase kesterite‐based solar cell efficiency by additive engineering.