Strain Relaxation via Lattice Matching Effect for Highly Efficiency Stable Perovskite Solar Cells

Abstract The residual strain and crystallographic defects in perovskite films pose significant challenges to improving the efficiency and stability of perovskite solar cells (PSCs). To address these issues, 3,5‐difluorobenzenesulfonamide (DBF) is introduced as a powerful additive. The spacing of functional groups in DBF molecules is precisely comparable to the bond lengths and angles of the perovskite lattice, a structural feature originating from the geometric compatibility between its benzene ring substituents and the [PbI 6 ] octahedral framework in the perovskite structure. This atomic‐scale structural matching effectively minimizes lattice mismatch, enabling DBF to release residual strain and passivate defects in the perovskite film. The spontaneous interaction between DBF and PbI 2 slows down perovskite crystal growth, improving film quality. The size‐matching effect with the perovskite lattice and strong interactions from F···MA⁺ (FA⁺) hydrogen bonds and ─S═O (─NH 2 )···Pb 2 ⁺ coordination bonds effectively release residual strain and passivate defects. As a result, the DBF‐modified PSCs achieve a champion efficiency of 25.18%. More importantly, these devices demonstrate excellent environmental stability, retaining 97.71% of their initial power conversion efficiency (PCE) after 1600 h in an atmospheric environment (25 °C, 20% RH) without encapsulation. This study provides a simple and effective strategy to enhance the efficiency and stability of perovskite photovoltaics.