Spatial Inhomogeneity of Methylammonium Lead-Mixed Halide Perovskite Examined by Space- and Time-Resolved Microwave Conductivity

Reducing the spatial inhomogeneity of solution-processed, multicrystalline methylammonium lead iodide (MAPbI₃) perovskite is of great importance for improving its power conversion efficiency, suppressing point-to-point deviations, and delaying degradation during operation. Various techniques, such as conducting-mode atomic force microscopy and photoluminescence mapping, have been applied for this intriguing class of materials, revealing nonuniform electronic properties on the nanometer-to-micrometer scale. Here, we designed a new space- and time-resolved microwave conductivity system that enables mapping of the transient photoconductivity with resolution greater than ∼45 μm. We examined the effects of the precursor concentration of MAPbI₃ and the mixing of halides (I^– and Br^–) on the charge carrier dynamics, crystal size, and inhomogeneity of the films. The optoelectronic inhomogeneity of MAPbI₃ and MAPb­(I_1–<i>x</i>Br<i>_x</i>)₃ on the sub-millimeter and millimeter scales shows a general correlation with their crystallite sizes, whereas the precursor concentration and halide mixing affect the inhomogeneity in a different way, providing a basis for uniform processing of a multicrystalline perovskite film