Facet Control of the Lead-Free Methylammonium Bismuth Iodide Perovskite Single Crystals via Ligand-Mediated Strategy

Recently, the influence of crystal anisotropy on the photoelectric performance of oriented halide perovskite polycrystalline and single-crystal (SC) devices has attracted extensive attention. Nevertheless, very little is known about the crystal facet control and its mechanism of such organic and inorganic hybrid perovskite crystals, especially lead-free perovskite crystals. Here, we have developed a facile approach for controlling the shape and the exposed facets of lead-free methylammonium bismuth iodide (MA3Bi2I9) perovskite SCs by ligand-mediated strategy. Results show that butylamine hydroiodide (BAI) ligand can trigger a morphological transition from hexagonal frustum pyramid-shaped SCs to hexagonal prism-shaped SCs enclosed by (001) and (110) while retaining the material composition and crystalline phase. Moreover, density functional theory (DFT) calculation studies demonstrate higher surface absorption energies of BA ion on the (110) facet than the (001) facet, which may contribute significantly to the selective binding of surfactant ligands to the (110) crystallographic facet and ultimately anisotropic growth. Finally, centimeter-scaled (110) facet MA3Bi2I9 SCs that are preferred for commercial applications have also been prepared by a seed-assisted crystallization method.