Synergistic Dual‐Interface Engineering in Perovskite Solar Cells via Chloramine Hydrochloride Molecular Bridges

High‐performance perovskite solar cells (PSCs) require synergistic passivation strategies to address defects at the electron transport layer (ETL)/perovskite interface, impacting both efficiency and long‐term stability. This study introduces chloramine hydrochlorides (CAHs) – 2‐Chloroethylamine Hydrochloride (CEA), Bis(2‐chloroethyl)amine Hydrochloride (BCEA), and Tris(2‐Chloroethyl)Amine Hydrochloride (TCEA) – as bifunctional molecular bridges to simultaneously passivate defects at both ETL (SnO2) and perovskite interfaces while controlling crystallization. Density functional theory calculations showed that TCEA forms strong Sn‐Cl bonds, enhancing Sn4+ coordination. In situ characterization revealed that TCEA accelerated perovskite formation, suppressed PbI2, and promoted larger grains, thus minimizing grain boundary defects. This leads to an improved electron extraction efficiency, prolonged hot‐carrier cooling, and a champion power conversion efficiency (PCE) of 25.25% (compared to 23.64% for controls), with negligible hysteresis and 90% PCE retention after 1000 h under ambient conditions. This study establishes a universal molecular design strategy for dual‐interface engineering in high‐efficiency and stable PSCs.