Multidentate Chelation by Imine‐Linked Covalent Organic Framework Enables High‐Performance Tin‐Based Perovskite Solar Cells

ABSTRACT Tin‐based perovskite solar cells (TPSCs) represent a highly promising photovoltaic technology owing to their eco‐friendliness and near‐ideal bandgap, which approaches the single‐junction efficiency limit. However, the rapid oxidation of Sn ^{2 +} ions in tin‐based perovskites induces high defect densities and hampers charge transport, significantly limiting device performance. In this study, we report the first use of two imine‐linked donor–acceptor covalent organic frameworks (COFs) featuring abundant surface binding groups, BCTB‐BTD‐COF and BCTB‐BSD‐COF, as precursor additives for TPSCs. Both COFs effectively suppress oxidation of Sn ²⁺ ions and passivate defects, while BCTB‐BSD‐COF exhibits superior performance through multidentate chelation, enabling defect passivation, reduced non‐radiative recombination, and optimized interfacial energy‐level alignment. Consequently, the addition of COFs significantly improved the performance of TPSCs, while BCTB‐BSD‐COF‐based TPSCs achieve a champion power conversion efficiency of 16.29% (certified 15.88%) with an open‐circuit voltage of 0.95 V and a fill factor of 79.47%. These devices also demonstrate exceptional stability, retaining 85% of its initial PCE after 35 days of continuous illumination. This work presents a novel strategy for passivating defects in TPSCs and offers a promising pathway toward high‐performance TPSCs.