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

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 (SO₃⁻) 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.