Multifunctional Borate Additive Enables Defect Passivation and Crystallization Control Toward High‐Performance n‐i‐p Perovskite Solar Cells

Metal halide perovskite solar cells (PSCs) represent one of the most promising next‐generation photovoltaic technologies, owing to their exceptional optical absorption coefficient, tunable bandgap, long carrier diffusion length and low‐cost solution processability. However, the performance of PSCs remains constrained by the crystalline quality and high defect density of perovskite thin films. Herein, we report a multifunctional molecular additive, potassium [(tert‐butoxycarbonylamino) methyl] trifluoroborate (denoted as ER). Theoretical calculations and experimental characterizations reveal that the hydroxyl groups generated via ‐BF 3 − hydrolysis and carbonyl oxygen atoms in ER strongly coordinate with undercoordinated Pb 2+ ions. Meanwhile, the tert‐butoxycarbonylamino (‐NH‐Boc) group effectively suppresses iodide migration by anchoring I − through hydrogen bonding. Notably, ER molecules can capture ambient moisture, converting humidity from a detrimental environmental factor into “chemical fuel” that drives in situ defect passivation through a self‐catalyzed molecular transformation process. As a result, the optimized n‐i‐p structured PSCs with ER achieve a champion power conversion efficiency (PCE) of 25.63%. Moreover, the unencapsulated device maintains 93.84% of its initial PCE after for 1778 h of aging under ISOS‐D‐1 conditions. This work provides an effective strategy for synergistically regulating perovskite crystallization and defect passivation via molecular engineering, thereby promoting the development of high‐performance and long‐term stable PSCs.