Fabricating　electron　transport　layers　at　low　temperatures　is　challenging　but　highly　desired　in　the　field　of　flexible　perovskite　solar　cells　(f-PSCs).　In　this　study,　highly　uniform　cerium　oxide　(CeOx)　films　prepared　by　the　UV-O3　treatment　have　been　successfully　applied　as　the　electron　transport　layer　(ETL)　in　methylammonium　lead　halide　(CH3NH3PbI3)　perovskite-based　f-PSCs.　Under　AM　1.5　G　sunlight　with　100　mW　cm-2,　these　cells　exhibited　an　open-circuit　voltage　(Voc)　of　0.98　V,　a　short-circuit　current　density　(Jsc)　of　19.42　mA　cm-2,　a　fill　factor　(FF)　of　0.72　and　power　conversion　efficiency　(PCE)　of　14.63%.　The　PCE　was　much　higher　than　that　of　the　control　planar　CeOx　ETL　(PCE　∼　9.08%)　prepared　at　a　low　temperature　(80　°C)　without　the　UV-O3　treatment,　and　this　was　ascribed　to　the　improved　CeOx　film,　enhanced　light　absorption　and　suppressed　charge　recombination.　The　cells　that　bend　at　15　mm　of　radius　showed　excellent　stability　with　less　than　10%　reduction　in　PCE　after　500　cycles　of　repeated　bending　at　ambient　temperature.　The　charge-transmission　kinetic　parameters　and　long-term　stability　of　the　CeOx-based　f-PSCs　were　analyzed　as　well.　This　journal　is　©　The　Royal　Society　of　Chemistry.