Solution Synthesis Approach to Colloidal Cesium Lead Halide Perovskite Nanoplatelets with Monolayer-Level Thickness Control

Abstract

We report a colloidal synthesis approach to CsPbBr3 nanoplatelets. The nucleation and growth of the platelets, which takes place at room temperature, is triggered by the injection of acetone in a mixture of precursors that would remain unreactive otherwise. The low growth temperature enables the control of the plate thickness, which can be precisely tuned from 3 to 5 monolayers. The strong two-dimensional confinement of the carriers at such small vertical sizes is responsible for the narrow PL, the strong excitonic absorption and the blue shift of the optical band gap of more than 0.47 eV compared to that of bulk CsPbBr3. We also show that the composition of the platelets can be varied all the way to CsPbCl3 or to CsPbI3 by anion exchange, with preservation of size and shape of the starting particles. The blue fluorescent CsPbCl3 nanoplatelets represent a new member of the scarcely populated group of blue emitting colloidal nanocrystals. The exciton dynamics were found to be independent of the extent of 2D confinement in these platelets, and this was supported by band structure calculations.