Nondestructive and controllable anion exchange of halide perovskite films through Finkelstein reaction

Anion exchange of halide perovskite has been successfully demonstrated as an effective route to modulate its optoelectronic properties; however, it generally suffers from the issues of morphology deterioration, incomplete exchange, or harsh reaction conditions toward devices exploration. In this work, we develop a solvothermal anion exchange strategy for halide perovskite films via the Finkelstein reaction, in which the typical anti-solvent of dihalomethane for perovskite works as the halide precursor. Because of the inertia of dihalomethane for perovskites, the anion exchange can be precisely controlled with maintaining the morphology of perovskite films. In order to gain the chemical insight into anion exchange, a Finkelstein reaction mechanism was proposed and discussed according to product examination and theoretical calculation. Moreover we further modulate the reaction progress by stabilizing the dissociated alkyl radicals with radical traps, which can help increase the concentration of generated halide anions and effectively accelerate the reaction speed of anion exchange. As a nondestructive and controllable anion exchange, this strategy can further promote the structure tunability of perovskite in optoelectronic applications.