Degradation of co-evaporated perovskite thin film in air

⿢The co-evaporated perovskite thin film has a cubic crystal structure.⿢From XRD, CH3NH3PbI3 converted to PbI2 completely after air exposure for 22 h (76.4 °F, 25% humidity level).⿢The atomic ratio of co-evaporated perovskite observed by XPS is very close to the ideal stoichiometric ratio of CH3NH3PbI3.⿢The degradation process revealed the complete removal of N and substantial reduction of I.⿢The aggregation of PbI2 crystals roughened the film and resulted in a partial exposure of the Au substrate, confirmed by AFM and XPS.