Formation of iminium ions during the processing of metal halide perovskites.

Ammonium ions are a key component of many organic-inorganic metal halide materials. We show that the hexagonal perovskite (MeNH)PbI is rapidly transformed to iminium-based perovskites (MeCNMeR)PbI (R = Me, Et), simply by stirring the material in the respective ketone at room temperature, triggering clear changes in the materials' photophysical properties.