Buried‐Interface Iodine Redox Regulation for Durable All‐Perovskite Tandem Photovoltaics

Tin–lead (Sn–Pb) mixed perovskites have propelled all‐perovskite tandem solar cells (APTSCs) beyond 30% efficiency, yet buried‐interface instability impedes commercialization. The ubiquitous PEDOT:PSS layer readily facilitates the oxidation of I − , and the subsequent diffusion of corrosive I 2 severely compromises device performance—a fundamental chemical degradation pathway that leaves unresolved. Here, we introduce 6‐amino‐2‐thiouracil (ATU) as a multifunctional additive that chemically targets this degradation pathway. Embedded within the PEDOT:PSS layer, the interaction between ATU and PSS contributes to alleviating the oxidation of I − while its C═S moiety actively reduces corrosive I 2 back to I − , establishing a dynamic iodine‐recycling mechanism that addresses the root chemical cause of instability. Concurrent defect passivation and crystallization modulation further enhance film quality. Benefiting from these synergistic effects, the optimized APTSCs achieve a champion efficiency of 29.29% (certified 28.79%) and exhibit significantly improved stability, maintaining over 85% of their initial efficiency after 500 h of maximum power point tracking. By targeting buried‐interface corrosive I 2 , this work provides a rational framework beyond conventional passivation for durable perovskite photovoltaics.