Interface Tailoring by Multifunctional Metal–Organic Salts Enables Efficient Perovskite Solar Cells with a Fill Factor Over 86%

Abstract Interfacial non‐radiative recombination in inverted (p‐i‐n) perovskite solar cells (PSCs) critically limits both efficiency and stability of the devices. To address this challenge, a metal–organic salt, potassium perfluorohexyl ethyl sulfonate (PPFES), featuring a multidentate sulfonate (SO ₃ ⁻ ) moiety and a hydrophobic perfluoroalkyl tail, is introduced to regulate the perovskite/electron transport layer (ETL) interface. Comprehensive theoretical and experimental analyses reveal that PPFES modulation synergistically passivates the surface defects of perovskite via sulfonate‐Pb chelation, shields the perovskite against moisture ingress, and optimizes the energy band alignment at the perovskite/ETL interface. As a consequence, the PPFES‐tailored PSCs deliver a champion power conversion efficiency (PCE) as high as 25.32%, with an ultra‐high fill factor of 86.39%, reaching 95.6% of the Shockley‐Queisser limit at a bandgap of 1.55 eV. Moreover, the devices retain 90% and 88% of their initial PCEs after 1200 h of storage in air with 60% relative humidity and 1300 h of maximum power point tracking under AM 1.5G illumination at 35 °C in ambient, respectively. This work establishes a multi‐effect interfacial engineering paradigm that concurrently achieves defect passivation and stability enhancement in PSCs.