Inhibiting Ion Migration and Stabilizing Crystal‐Phase in Halide Perovskite via Directly Incorporated Fluoride Anion

Fluoride anion (F−) with extremely high electronegativity has been under intensive investigation in perovskite solar cells due to its remarkable defect suppression and greatly improvement of device performance. Nevertheless, these researches only focus on surface, grain boundaries or interface modification, the directly insertion of F− into crystal lattice of regular lead halide perovskite films is still unrevealed. Herein, F− was successfully incorporated into perovskite lattice by overcoming the insolubility of PbF2 via the introduced pyridinium halide as a novel volatile solubilizing ligand. The strong electronegativity of F− can strongly increase the binding energy of all the ions in CsPbI2Br and inhibit their defect formations. A trace amount of F− incorporation not only enhanced the optoelectronic properties but also effectively mitigated the ion migration and phase separation simultaneously. The photovoltaic performance and operational stability of perovskite solar cells were significantly improved with a champion efficiency of 17.78% (38.01%) under AM 1.5G (1000 lux indoor light). Moreover, F− can also be directly inserted into hybrid perovskite lattice and greatly stabilized crystal‐phase, enabling efficient fully MA‐free FAPbI3 devices with 25.10% efficiency. Our strategy sheds light on F‐containing perovskites and provides a promising way to tackle ion migration and stabilize crystal‐phase in halide perovskites.