Unveiling the Two-Step Formation Pathway of Cs4PbBr6 Nanocrystals

All-inorganic cesium lead halide perovskites have received much attention, but the study of the formation pathway is relatively little. We report here a new one-step approach for the synthesis of Cs4PbBr6 nanocrystals (NCs), as well as the exploration of its formation process. Mixing three independent precursors of Cs, Pb, and Br in a cuvette, we monitor the evolution of Cs4PbBr6 NCs by in situ absorption spectroscopy, the formation of which features a sharp absorption peak at 313 nm. Based on this model, we further divide the synthesis process into two stages, in which the two precursors react for a certain period before adding the third precursor to the reaction. We find that the absorption peak exhibits a dramatic change from 358 to 313 nm with the addition of Cs precursor to the reaction mixture of Pb and Br precursors. Accordingly, we propose that there might be a two-step formation pathway for CCs4PbBr6 NCs. The formation of the Pb-Br bond is the first step, and then, a new reaction takes place after the Cs precursor is involved, which eventually results in the formation of Cs4PbBr6 NCs. The present study provides a new approach to synthesize the Cs4PbBr6 NCs and understand their formation pathway.