Interfacial Ionic Redistribution Induced by Sulfonate‐Anchored Dipotassium Salts Enables Efficient Buried Interface Engineering in Perovskite Solar Cells

Perovskite solar cells (PSCs) fabricated via two‐step sequential deposition commonly suffer from severe non‐radiative recombination at the buried electron transport layer/perovskite interface, where defect accumulation and unfavorable interfacial energetics limit device performance. Herein, we introduce a bifunctional methanedisulfonic acid dipotassium salt (DPMDS) interlayer to simultaneously regulate interfacial electrostatics and crystallization behavior. The sulfonate groups (–SO 3 − ) strongly coordinate with undercoordinated Sn 4+ sites on the SnO 2 surface, enabling effective passivation of oxygen‐vacancy‐related defects while inducing a positive interfacial dipole that optimizes energy‐level alignment and promotes charge extraction. Meanwhile, partial redistribution of K + ions into the adjacent perovskite layer modulates crystallization kinetics, leading to enlarged grains and reduced defect density. Benefiting from the synergistic effects of defect passivation, dipole‐induced electrostatic regulation, and crystallization control, the optimized PSC achieves a champion power conversion efficiency of 25.76% with an open‐circuit voltage of 1.184 V and retains over 80% of its initial efficiency after 3000 h of storage under dry ambient conditions. This work demonstrates an effective buried‐interface engineering strategy by integrating interfacial dipole formation with ionic regulation for high‐efficiency and stable perovskite solar cells.