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

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 Sn²⁺ 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.