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 I2 as products. We show that this degradation is initiated by the reaction of superoxide (O2−) with the methylammonium moiety of the perovskite absorber. Fluorescent molecular probe studies indicate that the O2− species is generated by the reaction of photoexcited electrons in the perovskite and molecular oxygen. We show that the yield of O2− 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. The influence of light and oxygen on the stability of CH3NH3PbI3 perovskite‐based photoactive layers is investigated. Upon exposure to both light and dry air, the mesoporous (mp) Al2O3/CH3NH3PbI3 layers decompose to methylamine, PbI2, and I2. This degradation is initiated by the reaction of superoxide (O2−) with the methylammonium moiety of the perovskite absorber. MA=methyl ammonium, CB=conduction band, VB=valence band.