Arm Growth and Facet Modulation in Perovskite Nanocrystals.

Highly emissive isotropic CsPbX (X = Cl, Br, and I) perovskite nanocrystals are typically observed in a six-faceted cube shape. When a unique approach is adopted and the reaction medium is enriched with halides, arm growth on all six facets was carried out and reported. Analysis suggested that these armed nanostructures were obtained from intermediate polyhedron shaped structures having 26 facets, and these were formed under halide-deficient conditions. Surface energy calculations further supported the possible existence of all facets for both of these structures under different halide composition environments. The entire study was first explored for CsPbBr and then extended to CsPbCl; however, for CsPbI nanocrystals, Sr(II) dopant was used for obtaining stable emission. Arm lengths could also be tuned with a function of reaction temperature for CsPbBr. Formation of stable facets in polyhedron shaped nanostructures and their transformation to respective hexapods under halide-deficient and halide-rich conditions add new fundamental concepts for these nanostructures and their shape evolutions.