Redox‐Buffering PEAI‐CeO x Passivation Suppresses Thermo‐Mechanical Degradation in Perovskite Solar Cells Under Rapid Thermal Cycling

Perovskite solar cells (PSCs) show critical thermo‐mechanical and defect mediated degradation at interfaces, limiting their deployment in terrestrial high‐temperature and space‐like environments. This study presents a dual‐function interfacial passivation strategy that combines nanoparticle cerium oxide (CeO x ) with phenylethylammonium iodide (PEAI) to form a hybrid surface treatment (PC) for poly[bis(4‐phenyl)(2,4,6‐trimethylphenyl)amine (PTAA) based n‐i‐p PSC architecture, where defect passivation is complemented by redox coupling and enhanced thermal stress stabilization. Optimized PC‐treated devices achieved a champion efficiency of 25.3% and exhibited enhanced operational stabilities under continuous 1 SUN light soaking and 85°C/85% RH damp heat respectively. To probe the engineered interface mechanistically, we employed an accelerated thermal shock (TS) cycling to mimic low Earth orbit (LEO) relevant thermal cycling condition. Under realistically simulated TS conditions of cycling temperature between 80°C and −80°C and 16°C/min ramp rate transition, PC‐treated devices retained 95% of initial efficiency after 100 cycles of TS, showing superior stability compared to their counterparts without CeO x . Collectively, this work highlights a new insight into dynamic thermal fatigue in PSCs and introduces a practical route toward thermally resilient, high efficiency perovskite photovoltaics.