In Situ Interfacial Polymerization Enabling a Dual‐Anchor Surface Binding Interlayer for Efficient and Stable Inverted Perovskite Solar Cells

migration and proton transfer, resulting in structural collapse. This degradation propagates into the bulk via coupled ion and vacancy diffusion, thereby accelerating irreversible performance decay. Conventional surface-passivation methods are often limited by weak intermolecular interactions and suboptimal stability. In this study, we developed an in situ interfacial polymerization strategy that leverages the reaction between amino and acyl chloride groups via room-temperature condensation polymerization. This interlayer enabled multi-anchoring via strong hydrogen and coordination bonds by ─NH and ─C═O groups, which doubled the binding energy for effective defect suppression. Furthermore, Poly-PT interlayer that enables an n-type surface induced favorable band bending and improved morphological contact, facilitating electron transport to achieve excellent device efficiency. Finally, this stable interlayer inhibited environmental ingress and ion migration, conducive to device stability. The resulting inverted perovskite solar cells achieved a high efficiency of 26.12% and demonstrated outstanding stability: unencapsulated devices retaining 85% of their initial efficiency following 2300 h of maximum-power-point tracking under one-sun illumination and 1680 h of storage at 65°C. This study provides a highly effective surface passivation solution and demonstrates the potential of in situ polymerization for durable, high-performance perovskite devices.