Pseudomorphic Transformation of Organometal Halide Perovskite Using the Gaseous Hydrogen Halide Reaction

Halide exchange is a facile method of adjusting the band gap and optimizing the performance of organometal halide perovskite. During the halide exchange processes, preserving the crystallinity and morphology of highly crystalline materials will be desirable for preparing novel materials with outstanding performance. In this study, the gasous hydrogen halides were used as reactants for halide exchange processes. The mutual conversions among three halides for condense films were realized. Moreover, perovskite inverse opals and perovskite single crystals were also adopted as substrates to illustrate the morphology preservation and crystallinity preservation, respectively. Powder X-ray diffraction and UV-vis diffuse reflectance spectra demonstrated the segregation when smaller ions were substituted by larger ions. Scanning electron microscopy displayed the direct evidence for morphology preservation during the transformation. For the first time, single crystal X-ray diffraction confirmed the single-crystal-to-single-crystal transformation from bromide to chloride analogy, which demonstrated that the presented method can preserve the crystalline framework of large-sized perovskite during the halide exchange.