Dot-Wire-Platelet-Cube: Step Growth and Structural Transformations in CsPbBr3 Perovskite Nanocrystals

While the classical mechanism for the growth of colloidal chalcogenide nanocrystals is largely understood, fundamental insights for the growth of perovskite nanocrystals still remain elusive. Using nanoclusters of nm diameter as monomers and growing to more than 25 nm in a single reaction, herein, the step growth process of perovskite CsPbBr3 nanocrystals is reported. This is performed with a step-rise of the reaction temperature with correlating annealing time. The growth is so precise that similar to 0.6 nm (nearly one unit cell) increments were successively monitored in parallel with the conversion of clusters to nanowires and then to thickness tunable platelets and finally to size-tunable cube-shaped nanostructures. The entire reaction was monitored optically and microscopically, and their step growths were correlated. From these observations, the possible growth mechanism for perovskite nanocrystals along with their shape transformations was proposed.