UV–O(3) treated annealing-free cerium oxide as electron transport layers in flexible planar perovskite solar cells

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 (CeO(x)) films prepared by the UV–O(3) treatment have been successfully applied as the electron transport layer (ETL) in methylammonium lead halide (CH(3)NH(3)PbI(3)) perovskite-based f-PSCs. Under AM 1.5 G sunlight with 100 mW cm(−2), these cells exhibited an open-circuit voltage (V(oc)) of 0.98 V, a short-circuit current density (J(sc)) 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 CeO(x) ETL (PCE ∼ 9.08%) prepared at a low temperature (80 °C) without the UV–O(3) treatment, and this was ascribed to the improved CeO(x) 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 CeO(x)-based f-PSCs were analyzed as well.