Fluorosubstitution Boosting 2D Ruddlesden–Popper CsPbI3 with High Stability and Efficiency

Bulky organic cations exhibit significant roles in improving the phase stability of CsPbI 3 by reducing its dimension with higher steric hindrance. However, the insulative properties of organic cations impede the carrier transition and damage the device performance. Herein, a new aromatic cation of 4‐fluorobenzenaminium (FPA + ) in the 2D CsPbI 3 to act as a spacer cation, is reported. Based on the theoretical simulation and experimental characterization for materials properties, film quality, and device performance, the large dipole moment and electronic inductive effect of FPA + cations improve the hydrogen bond between H and I atoms, which is beneficial to realizing controllable crystallization quality. Therefore, the whole quality of 2D CsPbI 3 film is improved with a larger grain size, compact morphology, and low trap density. As a result, the (FPA) 2 Cs 4 Pb 5 I 16 perovskite solar cell delivers a power conversion efficiency of 15.18%, significantly higher than that of PA‐based (14.32%) perovskite solar cells. Herein, an in‐depth understanding of fluoro‐substituted organic cations is provided and is beneficial to the design and synthesis of new organic molecules in 2D perovskite.