Anisotropic Exciton Transport in a Lamellar CsPbBr₃ Nanocrystal Superlattice

Abstract

Colloidal self-assembly is one strategy for engineering anisotropic properties into otherwise isotropic materials. In this work, we demonstrate anisotropic exciton transport in an A2B-type superlattice containing columns of 5.3 nm CsPbBr3 nanocubes assembled into a hexagonal lattice around 6.5 nm LaF3 nanodisks. Using transient photoluminescence microscopy, we determined that diffusivity along the fast axis of the superlattice is more than twice as large as the slow axis at T = 5 K, but that anisotropy is greatly suppressed at room temperature. Calculations of the diffusivity anisotropy ratio based on Förster theory overestimate the measured values, highlighting the limitations of this theory in completely describing exciton transport. Overall, our results demonstrate how self-assembly of colloidal nanocrystals can be used to engineer directional energy transport, and raise more questions about the microscopic nature of dipole coupling in CsPbBr3 NC superlattices.