Photo-protective iodine chelate enables stable perovskite solar cells under reverse bias

Mitigating irreversible reverse-bias-induced perovskite degradation is paramount for the commercial deployment of perovskite solar modules, especially ensuring their reliability under partial shading scenarios. In n-i-p perovskite solar cells (PSCs), perovskite decomposition under reverse-bias involves the initial iodide re-distribution, followed by its oxidation and subsequent ultraviolet (UV) activation into iodine radicals, finally triggering the degradation within the perovskite. This work presents a delicate iodine chelation engineering to directly restrain this failure mechanism by incorporating a tailored β-cyclodextrin sulfated sodium salt (S-β-CD) at the critical SnO2/perovskite buried interface. This iodine chelating agent simultaneously sequesters the reactive iodine species from perovskites and provides the intrinsic UV-protection at the front side, to interrupt the photolysis cascade, which significantly enhances the reverse-bias robustness of PSCs. We demonstrate an outstanding operational stability after the reverse-bias precondition (T80 = ~ 1000 h, ISOS-L-3), and more encouragingly, deliver a superior cyclic lifetime under the periodic reverse-bias and light soaking stress (T85 = ~ 1600 h, ISOS-V-1). This strategy offers a significant leap towards the reverse-bias reliability required for solar module applications in the real world. Reverse-bias degradation limits the reliability of perovskite modules, especially under shading. The authors introduce an S-β-CD iodine-chelating layer at the SnO₂/perovskite interface to block the decay pathway and greatly boost operational and reverse-bias stability.