Recently,　perovskite　solar　cells　(PVSCs)　based　on　CsPbI2Br　have　attracted　increasing　attention　owing　to　their　good　balance　between　efficiency　and　stability.　Solution-processed　CsPbI2Br　perovskites　usually　contain　various　defects　which　need　passivation　for　PVSCs　with　high-performance　as　well　as　good　stability.　Since　the　degradation　of　perovskite　films　usually　begins　at　the　grain　boundaries,　here　we　report　a　facile　defect　passivation　strategy　by　spin-coating　a　KF　solution　on　the　CsPbI2Br　perovskite　surface.　The　deposited　KF　salt　mostly　locates　at　the　grain　boundaries　of　the　perovskite　surface,　resulting　in　PVSCs　with　improved　stability.　Both　steady-state　and　time-resolved　photoluminescence　results　suggest　that　the　defects　of　perovskite　were　significantly　passivated　by　KF　treatment.　Consequently,　the　best-performance　PVSC　based　on　CsPbI2Br　with　KF　treatment　shows　an　enhanced　power　conversion　efficiency　(PCE)　of　15.01%　with　a　larger　open　circuit　voltage　(VOC)　of　1.26　V　in　comparison　with　the　pristine　CsPbI2Br-based　counterpart　which　exhibits　an　inferior　PCE　of　14.14%　with　a　VOC　of　1.18　V.　©　2020,　Science　China　Press　and　Springer-Verlag　GmbH　Germany,　part　of　Springer　Nature.