Nucleation, Growth, and Structural Transformations of Perovskite Nanocrystals

Despite the recent surge of interest in lead halide perovskite nanocrystals, there are still significant gaps in the understanding of nucleation and growth processes involved in their formation. Using CsPbX3 as a model system, we systematically study the formation mechanism of cubic CsPbX3 nanocrystals, their growth via oriented attachment into larger nanostructures, and the associated phase transformations. We found evidence to support that the formation of CsPbX3 NCs occurs through the seed-mediated nucleation method, where Pb° NPs formed during the course of reaction act as seeds. Further growth occurs through self-assembly and oriented attachment. The polar environment is a major factor in determining the structure and shape of the resulting nanoparticles, as confirmed by experiments with aged seed reaction mixtures, and by addition of polar additives. These results provide a fundamental understanding of the influence of the environment polarity on self-assembly, self-healing, and the ability to control the morphology and structure over the perovskite structures. As a result of this understanding, we were able to extend the synthesis to produce other materials such as CsPbBr3 nanowires and orthorhombic CsPbI3 nanowires with tunable length ranging from 200 nm to several microns.