Synthesis of ultrasmall CsPbBr3 nanoclusters and their transformation to highly deep-blue-emitting nanoribbons at room temperature.

Discretely sized semiconductor clusters have attracted considerable attention due to their intriguing optical properties and self-assembly behaviors. While lead halide perovskite nanostructures have been recently intensively explored, few studies have addressed perovskite clusters and their self-assembled superstructures. Here, we report the room-temperature synthesis of sub-2 nm CsPbBr3 clusters and present strong evidence that these ultrasmall perovskite species, obtained under a wide range of reaction conditions, possess a specific size, with optical properties and self-assembly characteristics resembling those of well-known II-VI semiconductor magic-sized clusters. Unlike conventional CsPbBr3 nanocrystals, the as-synthesized CsPbBr3 nanoclusters spontaneously self-assemble into a hexagonally packed columnar mesophase in solution, which can be further converted to single-crystalline CsPbBr3 quantum nanoribbons with bright deep-blue emission at room temperature. Such a conversion of CsPbBr3 nanoclusters to nanoribbons is found to be driven by a ligand-destabilization-induced crystallization and mesophase transition process. Our study will facilitate the investigation of perovskite nanoclusters and offer new possibilities in the low-temperature synthesis of anisotropic perovskite nanostructures.