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.
Yanxiu Li,He Huang,Yuan Xiong,Alexander F. Richter,Stephen V. Kershaw,Jochen Feldmann,Andrey L. Rogach
Semiconductor nanorods (NRs) offer the useful property of linearly polarized light emission. While this would be an attractive functionality for strongly emitting perovskite nanoparticles, to date, there has been limited success in demonstrating a direct chemical synthesis of cesium lead halide perovskite NRs. In this work, we realized the direct synthesis of CsPbBr3 NRs with an average width of around 5 nm and average lengths of 10.8 and 23.2 nm, respectively, in two samples, which show a high photoluminescence quantum yield of 60–76% and reasonably high emission anisotropy of about 0.2 for longer rods. Both CsPbCl3 and CsPbI3 NRs with similar dimensions have then been derived from the CsPbBr3 NRs by anion-exchange reactions. Remarkably, the synthesis of the NRs has been achieved in polar alcohols, a class of solvents not usually found to be beneficial in classical perovskite nanoparticle synthesis. This work not only offers the possibility to control the shape of chemically synthesized perovskite nanocrystals but also constitutes the hitherto less common strategy of synthesizing perovskite nanoparticles in polar rather than nonpolar or only weakly polar solvents.
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