The Role of Oxygen in the Degradation of Methylammonium Lead Trihalide Perovskite Photoactive Layers

In this paper we report on the influence of light and oxygen on the stability of CH3NH3PbI3 perovskite-based photoactive layers. When exposed to both light and dry air the mp-Al2O3/CH3NH3PbI3 photoactive layers rapidly decompose yielding methylamine, PbI2, and I-2 as products. We show that this degradation is initiated by the reaction of superoxide (O-2(-)) with the methylammonium moiety of the perovskite absorber. Fluorescent molecular probe studies indicate that the O-2(-) species is generated by the reaction of photoexcited electrons in the perovskite and molecular oxygen. We show that the yield of O-2(-) generation is significantly reduced when the mp-Al2O3 film is replaced with an mp-TiO2 electron extraction and transport layer. The present findings suggest that replacing the methylammonium component in CH3NH3PbI3 to a species without acid protons could improve tolerance to oxygen and enhance stability.