Understanding Photo-Induced Degradation in Perovskites: A Kinetic Model Approach

Photo-induced degradation presents a significant challenge for the application of perovskites in solar cells. This study addresses the lack of accurate degradation kinetics models by deriving rate equations for a triple-cation mixed halide perovskite using a two-step reaction model. Our model predicts the temporal evolution of iodine and formamidinium losses, as well as the generation of metallic lead (Pb(0)), under continuous white light illumination and increased bromine content (5-20%). Our X-ray Photoelectron Spectroscopy (XPS) measurements reveal significant differences in degradation pathways between nitrogen (N2) and ultra-high vacuum (UHV) environments, with UHV conditions accelerating Pb(0) formation. Contradicting claims of stability in N2, our results demonstrate that while Pb(0) is absent in XPS measurements, light-induced degradation persists, indicated by the transformation of the perovskite into lead-iodide and the development of granular structures on the surface, as shown by Atomic Force Microscopy (AFM). Through our kinetic model, we elucidate the rates of iodine and formamidinium losses, underscoring the role of ionic migration in our findings. This study not only enhances our understanding of perovskite stability under varying environmental conditions but also contributes essential insights critical for future advancements in perovskite solar cell technology. Keywords: Perovskite, Photodegradation, Kinetic Model, Stability, Environmental Conditions, XPS, AFM.