Planar-structure　perovskite　solar　cells　have　attracted　more　and　more　attention,　because　their　simple　and　low-temperature　preparation　processing.　However,　the　performance　of　perovskite　solar　cells　is　currently　limited　by　defect-induced　recombination　at　interfaces　between　perovskite　and　charge　transport　layers.　In　this　work,　a　filmy　poly　methyl　methacrylate　(PMMA)　layer　introduced　in　Perovskite/Spiro-OMeTAD　interface　to　passivate　the　interfacial　and　interganular　defects,　by　which　a　high　open-circuit　voltage　(1.18　V)　is　acquired,　and　the　optimal　device　shows　a　steady-state　power　conversion　efficiency　of　20.5%　and　negligible　hysteresis.　Femtosecond　transient　absorption　measurement　confirms　a　significant　reduction　in　non-radiative　recombination　for　passivated　devices.　Mott-Schottky　measurement　indicates　improved　flat　band　potential　and　carrier　density　in　passivated　devices,　consisting　with　the　increased　voltage.　In　addition,　PMMA　film　can　protect　perovskite　film　from　moisture　and　oxygen　erosion.　The　unsealed　device　still　maintains　95%　of　the　initial　efficiency　under　ambient　conditions　with　60%　relative　humidity　for　one　month.　This　approach　solves　one　of　the　main　limitations　of　interfacial　recombination　and　shows　its　potential　to　improve　the　performance　of　perovskite　solar　cells　in　the　future.