Band　alignment　modulation　and　defect　passivation　for　organic-inorganic　halide　perovskite　solar　cells　(PSCs)　through　interface　engineering　are　some　of　the　most　effective　methods　to　improve　the　performance.　In　the　present　work,　we　systematically　studied　the　effect　of　formamidinium　bromide　(FABr)　treatment　on　perovskite　films.　Transmission　electron　microscopy　(TEM),　Kelvin　probe　force　microscopy　(KPFM),　and　photoluminescence　(PL)　results　validate　that　nonhomogeneously　distributed　Br-　incorporation　was　formed　in　a　FABr-treated　perovskite　layer,　and　an　absorber　with　gradient　band　alignment　was　achieved.　This　effectively　promotes　the　transport　of　photogenerated　carriers　and　inhibits　the　carrier　recombination　in　PSCs.　As　a　result,　the　power　conversion　efficiency　(PCE)　is　significantly　increased　after　FABr　treatment,　and　the　enhancement　is　mainly　due　to　the　increased　open-circuit　voltage　(V-OC).　This　approach　highlights　a　promising　strate　o　obtain　and　characterize　the　gradient　band　alignment,　and　thus　further　optimizes　the　performance　of　PSCs.