Regenerative Interfacial Passivation of Inorganic Perovskite via Redox Mediator for High Performance Solar Cells

All‐inorganic perovskites are promising photovoltaic materials for tandem cells owing to their suitable bandgaps and enhanced photothermal stability. However, inverted inorganic perovskite solar cells (PSCs) suffer from efficiency losses and poor operational stability primarily by iodide oxidation, which in turn induces ion migration and defect formation. Traditional defect‐healing processes are often irreversible and static, and selective reduction of iodine and oxidation of Pb 0 are hardly achievable simultaneously. Herein, we target surface halide oxidation and develop a regenerative interfacial passivation strategy via redox mediator to improve power conversion efficiency (PCE) and stability of inverted inorganic PSCs, by judiciously designing a thiol‐containing surface modifier 3‐mercaptopropionohydrazide (MPH). The reversible conversion between thiol and disulfide allows MPH as a self‐regenerating redox mediator, facilitating the removal of I 2 and Pb 0 while suppressing iodide oxidation in a sustainable manner. Meanwhile, hydrazide group provides additional reduction capability, together with multiple coordination sites with undercoordinated Pb 2 + and form hydrogen bonds with halides on perovskite surface, dramatically reducing defect density and inhibiting ion migration. Consequently, MPH‐treated devices achieve a champion PCE of 22.17% with a high open‐circuit voltage of 1.27 V, retaining 91.1% of its initial efficiency after 1100 h of maximum powerpoint tracking, substantially outperforming the control devices.