Measure is Treasure: Proper Iodine Vapor Treatment as a New Method of Morphology Improvement of Lead-Halide Perovskite Films

摘要

It is known that exposure of halide perovskites to iodine vapor causes its severe degradation or doping under high or low iodine partial pressures, respectively. In the present study, we show that there exists a range of conditions between these two extreme cases in which the iodine treatment induces recrystallization of halide perovskites, leading to better crystallinity, enhanced morphology, and optoelectronic properties of the material. This happens because of reversible formation of PbI_(2) and liquid recrystallizing medium—reactive polyiodide melts CH_(3)NH_(3)I–x I_(2) (1.5 x < 2.5) that activate the mass transport. A fine control of the iodine partial pressure, temperature of the substrate, and exposure duration allows to apply this method successfully to mixed-cation and mixed-anion perovskites relevant for photovoltaics applications, thus proving the versatility of the iodine treatment approach.