Demystifying the Formation of Colloidal Perovskite Nanocrystals via Controlling Stepwise Synthesis

As an emerging optoelectronic material, colloidal lead halide perovskite nanocrystals (PeNCs) have attracted considerable interest, but the fundamental and crucial formation mechanism of PeNCs is still unclear due to the fast speed of the chemical synthesis. Here, we developed a novel stepwise method to explore the formation process of CsPbBr3 PeNCs. Polar alcohol was used to trigger the formation reaction of PeNCs, thereby controlling the reaction speed and achieving stepwise synthesis. Our work found that the synthesis of PeNCs undergoes three formation steps: PbBr3– complexes, PbBr64– octahedrons, and perovskite crystals. The PbBr3– complexes were first formed through the coordination of Pb2+ and Br– ions in the precursor solution and then were transformed into PbBr64– octahedrons by being triggered with the polar alcohol. Finally, the PbBr64– octahedrons reacted with the free-state Cs+ ions to form perovskites. The PbBr64– octahedrons should be formed first, otherwise the Cs+ ions are always in the free state in the precursor solution so that they cannot react with lead bromide complexes to form perovskite crystals. This study provides new insights into the formation process of PeNCs and new thinking for designing and constructing PeNCs.