Reversible Anion Exchange Reaction in Solid Halide Perovskites and Its Implication in Photovoltaics

Anion exchange reaction is a particularly versatile tool for the synthesis of a large class of nanomaterials. Here we report a low temperature, fast, reversible anion exchange reaction in halide perovskite thin film. Although processed in the solid-state phase, the exchanged hybrid perovskite shows good quality in terms of morphology conservation, phase transformation, and homogeneous composition. The easily exchanged reaction during the crystallization process suggests the robust nature of the Pb–CH₃NH₃ framework and high diffusion ability of halide ions in the perovskite lattice. Furthermore, we show its application in perovskite solar cells; we find that the anion exchange reaction does not induce any remarkable defects resulting from the lattice transformation and morphology reconstruction. In some case, the beneficial exchange of halide species involving simultaneous displacement reaction and crystallization can be used to improve the perovskite solar cell performance. Our work provides new physical insight into understanding the perovskite formation mechanism and the ionic behavior in the perovskite