Conversion of Single Crystalline PbI₂ to CH₃NH₃PbI₃: Structural Relations and Transformation Dynamics

The realization of high-quality optoelectronic properties in halide perovskite semiconductors through low-temperature, low energy processing is unprecedented. Understanding the unique aspects of the formation chemistry of these semiconductors is a critical step toward understanding the genesis of high quality material via simple preparation procedures. The toolbox of preparation procedures for halide perovskites grows rapidly. The prototypical reaction is that between lead iodide (PbI2) and methylammonium iodide (CH3NH3I, abbr. MAI) to form the perovskite CH3NH3PbI3 (MAPbI3), which we discuss in this work. We investigate the conversion of small, single-crystalline PbI2 crystallites to MAPbI3 by two commonly used synthesis processes: reaction with MAI in solution or as a vapor. The single crystal nature of the PbI2 precursor allows definitive conclusions to be made about the relationship between the precursors and the final product, illuminating previously unobserved aspects of the reaction process. From i...