Introducing B-Site Cations by Ion Exchange and Shape Anisotropy in CsPbBr₃ Perovskite Nanostructures

Lead halide perovskite nanocrystals, whether formed by their own nucleation and growth or by ion diffusion into the lattice of others, are still under investigation. Moreover, beyond isotropic nanocrystals, fabricating anisotropic perovskite nanocrystals by design has remained difficult. Exploring the lattice of orthorhombic-phase Cs₂ZnBr₄ with the complete replacement of Zn tetrahedra by Pb octahedra, dimension-tunable anisotropic nanocrystals of CsPbBr₃ are reported. This B-site ion introduction led to CsPbBr₃ nanorods having [100] as major axis, in contrast with all reports on rods/wires where the lengths were along the [001] direction. This was possible by using derivatives of α-bromo ketones, which helped in tuning the shape of Cs₂ZnBr₄ and also the facets of transformed CsPbBr₃. While similar experiments are extended to orthorhombic Cs₂HgBr₄, standard nanorods with [001] as the major axis were observed. From these results, it is further concluded that anisotropic perovskite nanocrystals might not follow any specific rules for directional growth and instead might depend on the structure of the parent lattice.