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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 CH<inf>3</inf>NH<inf>3</inf>PbI<inf>3</inf> perovskite-based photoactive layers. When exposed to both light and dry air the mp-Al<inf>2</inf>O<inf>3</inf>/CH<inf>3</inf>NH<inf>3</inf>PbI<inf>3</inf> photoactive layers rapidly decompose yielding methylamine, PbI<inf>2</inf>, and I<inf>2</inf> as products. We show that this degradation is initiated by the reaction of superoxide (O<inf>2</inf>-) with the methylammonium moiety of the perovskite absorber. Fluorescent molecular probe studies indicate that the O<inf>2</inf>- species is generated by the reaction of photoexcited electrons in the perovskite and molecular oxygen. We show that the yield of O<inf>2</inf>- generation is significantly reduced when the mp-Al<inf>2</inf>O<inf>3</inf> film is replaced with an mp-TiO<inf>2</inf> electron extraction and transport layer. The present findings suggest that replacing the methylammonium component in CH<inf>3</inf>NH<inf>3</inf>PbI<inf>3</inf> to a species without acid protons could improve tolerance to oxygen and enhance stability.