Self-regulated facet stability during solution growth of perovskite crystals

Solution growth of metal halide perovskites has enabled the development of applications including solar cells, light-emitting diodes and detectors, but the crystal growth mechanism remains unclear. Herein we studied the in situ transition of solute to crystals at the solid–liquid interface of methylammonium lead triiodide single crystals in γ-butyrolactone solution using microscopic spectroscopy. By establishing a temperature–bandgap relationship of the precursor solution, we observe a cooler interfacial region (1.5–4 μm from the crystal edge), explained by endothermic particle dissolution. This cooler region serves as a protective layer, hindering the attachment of particles with random orientations, maintaining the crystal facet orientation. The cooler interfacial protective layer is formed by the dissolution of particles driven by latent heat from crystallization and the concentration gradient of monomers at the interface. Disruption of the protective layer results in polycrystals with irregular facets. The understanding of the growth mechanisms of perovskite crystals provides insights for further improving the quality of solution-grown crystals. The in situ growth of methylammonium lead triiodide crystals in γ-butyrolactone is investigated. A cooler interfacial layer that serves as a protective layer to preserve the crystal facet orientation is observed.