Room-temperature synthesis of pure perovskite-related Cs4PbBr6 nanocrystals and their ligand-mediated evolution into highly luminescent CsPbBr3 nanosheets

Currently, all-inorganic cesium lead-halide perovskite nanocrystals have attracted enormous attentions owing to their excellent optical performances. While great efforts have been devoted to CsPbBr 3 nanocrystals, the perovskite-related Cs 4 PbBr 6 nanocrystals, which were newly reported, still remained poorly understood. Here, we reported a novel room-temperature reaction strategy to synthesize pure perovskite-related Cs 4 PbBr 6 nanocrystals. Size of the products could be adjusted through altering the amount of ligands, simply. A mixture of two good solvents with different polarity was innovatively used as precursor solvent, being one key to the high-yield Cs 4 PbBr 6 nanocrystals synthesis. Other two keys were Cs + precursor concentration and surface ligands. Ingenious experiments were designed to reveal the underlying reaction mechanism. No excitonic emission was observed from the prepared Cs 4 PbBr 6 nanocrystals in our work. We considered the green emission which was observed in other reports originated from the avoidless transformation of Cs 4 PbBr 6 into CsPbBr 3 nanocrystals. Indeed, the new-prepared Cs 4 PbBr 6 nanocrystals could transform into CsPbBr 3 nanosheets with surface ligands mediated. The new-transformed two-dimensional CsPbBr 3 nanosheets could evolve into large-size nanosheets. The influences of surface ligand density on the fluorescent intensity and stability of transformed CsPbBr 3 nanosheets were also explained. Notably, the photoluminescence quantum yield of the as-transformed CsPbBr 3 nanosheets could reach as high as 61.6% in the form of thin film. The fast large-scale synthesis of Cs 4 PbBr 6 nanocrystals and their ligand-mediated transformation into high-fluorescent CsPbBr 3 nanosheets will be beneficial to the future optoelectronic applications. Our work provides new approaches to understand the structural evolution and light-emitting principle of perovskite nanocrystals. ᅟ