Defects Evolution in the Degradation of Metal Halide Perovskite Solar Cells Under Reverse-Bias and Illumination

The efficiency and stability of perovskite solar cells are essentially determined by defects in perovskites, yet their chemical nature and linking with the degradation mechanism of perovskite solar cells remain unclear. Here we uncover the degradation locations and underlying mechanisms in high performance p-i-n perovskite solar cells by identifying the chemical nature of defects in perovskites, and then tracing their evolution in solar cells under illumination or reverse-bias. The light-induced degradation of perovskite solar cells starts with the generation of iodide interstitials at both interfacial regions between perovskites and charge transport layers, while trap-annihilation of two types of iodide defects is observed only at the anode side. This leaves negatively charged iodide interstitials near the cathode side which are shown to be more detrimental to the solar cell efficiency, pointing out future directions for improving the photo-stability of perovskite solar cells by suppressing the generation of iodide interstitial defects at the interfacial regions. The reverse-bias degradation is initialized by the interactions between iodide interstitials and injected holes at the interface between electron transport layer and perovskites, leading to a finding that introducing a hole blocking layer between them suppresses this interaction and significantly improves the reverse-bias stability.