Molecular Design and Operational Stability: Toward Stable 3D/2D Perovskite Interlayers

Abstract Despite organic/inorganic lead halide perovskite solar cells becoming one of the most promising next‐generation photovoltaic materials, instability under heat and light soaking remains unsolved. In this work, a highly hydrophobic cation, perfluorobenzylammonium iodide (5FBzAI), is designed and a 2D perovskite with reinforced intermolecular interactions is engineered, providing improved passivation at the interface that reduces charge recombination and enhances cell stability compared with benchmark 2D systems. Motivated by the strong halogen bond interaction, (5FBzAI) 2 PbI 4 used as a capping layer aligns in in‐plane crystal orientation, inducing a reproducible increase of ≈60 mV in the V oc , a twofold improvement compared with its analogous monofluorinated phenylethylammonium iodide (PEAI) recently reported. This endows the system with high power conversion efficiency of 21.65% and extended operational stability after 1100 h of continuous illumination, outlining directions for future work.