Crystallization and Defect Control at the Buried Interface via Potassium Pyrophosphate for High‐Efficiency and Stable Perovskite Solar Cells

Buried interface imperfections and uncontrolled crystallization dynamics remain critical challenges that hinder the efficiency and long‐term stability of perovskite solar cells (PSCs). In this work, we present a molecular interface engineering strategy using potassium pyrophosphate (KPP) as an interlayer between the titanium dioxide (TiO 2 ) electron transport layer and the perovskite absorber. The bifunctional nature of KPP enables phosphate group anchoring onto TiO 2 and K + ‐mediated passivation of undercoordinated Pb 2+ and I − ions, simultaneously improving interfacial contact and suppressing nonradiative recombination. This interfacial coordination facilitates crystallization of perovskite films with larger grain sizes, reduced surface roughness, and suppressed PbI 2 residue, as confirmed by a series of analyses. As a result, KPP‐modified PSCs exhibit a champion power conversion efficiency of 24.70%, with an enhanced open‐circuit voltage of 1.17 V and minimal hysteresis. Furthermore, the devices maintain 83% of their initial efficiency after 1000 h of continuous operation under AM 1.5G illumination at the maximum power point. This study highlights the potential of buried interface coordination in simultaneously optimizing crystallization, defect passivation, and device stability, offering a promising and scalable approach toward high‐performance perovskite photovoltaics.