A systematic study of the synthesis of cesium lead halide nanocrystals: does CsPbBr or CsPbBr form?

Cs 4 PbBr 6 nanocrystals (NCs) have been recently studied as they can enhance the light emitting efficiency and stability of CsPbBr 3 NCs. However, the synthesis of Cs 4 PbBr 6 NCs is often accompanied by the generation of CsPbBr 3 NCs, and less attention has been paid to how to exactly control their formation. Here, we investigated the key factors in deciding the final products in the hot-injection synthesis by a modified amine-free method. We found that the molarity ratio of Cs/Pb dominated the final products, while the amount of bromine had a relatively small effect. In addition, introducing a certain amount of oleylamine into the amine-free reaction leads to the formation of Cs 4 PbBr 6 , instead of CsPbBr 3 NCs. This clearly shows that the protection ligand oleylamine also plays an important role in the formation of Cs 4 PbBr 6 NCs. This well understood and fine control of the synthesis may inspire a new CsPbBr 3 @Cs 4 PbBr 6 core-shell structure, with the same chemical elements but a different crystal phase in the core and the shell. This nanostructure would open a new avenue for enhancing the stability of perovskite nanocrystals. An amine-free method is used to systematically investigate the role of Cs, Pb and Br in hot-injection synthesis.