Science News: 2021 Nat. Commun., 4 steps for High-efficiency Perovskite Crystallization Processes!

　　In September 2021, Nature　Communications (IF 14.919) journal published a study by  Peter Müller-Buschbaum from Technical University of Munich (TUM). Because there are complex phenomena in the formation of perovskite materials, which affect the processing-structure-function relationships. Thin films of methylammonium lead iodide (CH₃NH₃PbI₃, MAPI) are processed by spin coating, antisolvent drop, and annealing of colloidal precursors. The structure and properties of the transient and stable phases formed in this process, as well as data from grazing grazing-incidence wide-angle X-ray scattering and in-situ photoluminescence, are combined. The author proposes ideas for potential transformation mechanisms.

　　The author provides detailed insights on the embryonic stages of organic-inorganic perovskite formation. Through experiments with solar simulators and other instruments, it was found that the physicochemical evolution during the conversion is divided into four steps: i) An instant nucleation of polydisperse MAPI nanocrystals on anti-solvent droplet, ii) the metastable nanocrystals are instantly partially conversion into orthorhombic solvent-complex by cluster coalescence, iii) When the solvent evaporates from the complex, the stable solvent-complex thermally decomposes the lead iodide fragments, iv) the formation of cubic MAPI crystals in thin film (recrystallization) . The final phase of MAPI maintains stability in the cubic symmetry and exhibits the expected structural and photoelectric properties.