What determines the iodine oxidation reaction kinetics in halide perovskite solar cells?

Abstract

Perovskite solar cells (PSCs) have garnered significant attention owing to their solution fabrication, cost-effectiveness, and high power conversion efficiency, yet their practical application has been hindered by instability issues. Under operational conditions, redox reactions have been found to be prevalent in perovskite devices, but the underlying mechanism remains very unclear. Here, we systematically investigated the impact of light irradiation, atmosphere and interfacial structures on the redox kinetics in PSCs. Our results show that oxygen acts as a predominant factor driving device degradation, other than the transport layer or spectral components. Spectroscopic results reveal that the formation of iodine-related defects, e.g., triiodide ion (I₃⁻) and iodine (I₂), are dramatically boosted under oxygen-rich conditions, and can be further accelerated by light exposure. These findings provide critical insights into the redox reaction mechanism of perovskite-based materials, and offer a potential direction for enhancing the long-term stability of PSCs.