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

Abstract

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.