Programmable precise kinetic control over crystal phase, size, and equilibrium in spontaneous metathesis reaction for Cs-Pb-Br nanostructure patterns at room temperature.

Growth kinetics involved in spontaneous random clustering of perovskite precursors to a particular cesium-lead-bromide (Cs-Pb-Br) nanocrystal (NC) is a poorly understood phenomenon and its spectroscopic investigation is highly challenging. There is scarcely any method that has been optimized yet in which perovskites and their related NCs of a particular size can be grown, viewed, or tuned to another by reaction handling. Here, for the first time, we shed light on the largely overlooked process of growth kinetics of these transformations throughout the reaction trajectory of anionic [PbBr] crystallization dictated by Cs cation and report a simple and direct approach to control the metathesis reaction between two precursors (specifically Cs- and PbBr-associated oligomeric complexes) in one solvent at room temperature to monitor the NC growth characteristics in a stepwise manner even in the early stages of nucleation. Altering the molar ratio of the two precursors up to a factor of 10 leads to the formation of three prominent phases (CsPbBr, CsPbBr, CsBr) as dictated by Cs to trigger distinct morphological forms (nanobelts, nanoplatelets, rhombohedral NCs, pseudo-rhombic NCs, spherical CsBr NCs, cubic CsBr NCs) including a transient phase that is formed out of linearly self-assembled CsPbBr clusters. Our results pave the way towards understanding spontaneous crystallization to develop well-defined, hassle-free routes for diverse perovskite NCs in a simple yet controlled manner.