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 great improvement of device performance. Nevertheless, these researches only focus on the surface, grain boundaries, or interface modification, the direct insertion of F^- into the crystal lattice of regular lead halide perovskite films is still unrevealed. Herein, F^- was successfully incorporated into the 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 the 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 the crystal phase in halide perovskites.