Revealing superoxide-induced degradation in lead-free tin perovskite solar cells

The poor stability of lead (Pb)-free tin (Sn)-based perovskites under only oxygen (O-2) exposure has attracted extensive research, while their stability under simultaneous light and O-2 (light/O-2) exposure is unexplored. Herein, we found that the (NH2)(2)CHSnI3 (FASnI(3)) perovskite degrades more severely when exposed to light/O-2 than only O-2, which we attribute to the superoxide generated via the reaction between O-2 and photoexcited electrons. We propose the superoxide-induced degradation routes of FASnI(3). Fluorescent molecular probe results indicate higher yield of superoxide in FASnI(3) than in FAPbI(3). Density functional theory simulation results rationalize that the formation energy of the most preferred sites (iodine vacancy, V-I) for superoxide formation in FASnI(3) is much lower than that in FAPbI(3); meanwhile, superoxide formation at V-I is more energetically favorable in FASnI(3). A targeted strategy by incorporating halide-containing additives is applied to fill the V-I in FASnI(3) to suppress superoxide formation. Combined with superoxide yield measurement, capacitance-dominated characterization can systematically differentiate the reduction of surface and interior V-I after modification. Understanding the degradation mechanism of FASnI(3) upon light/O-2 exposure manifests the fatal effect of superoxide on the stability of Sn-based perovskite solar cells.

Automated summary

Research has shown that the stability of (NH2)2CHSnI3 perovskites degrades more severely under light/O-2 exposure compared to O-2 exposure alone, due to the generation of superoxide from the reaction between O-2 and photoexcited electrons. Strategies to suppress superoxide formation by filling V-I sites in FASnI3 have been proposed to enhance stability. Understanding the fatal impact of superoxide on the stability of Sn-based perovskite solar cells is crucial for further research and development.