Effects of Electronic Coupling on Bright and Dark Excitons in a 2D Array of Strongly Confined CsPbBr₃Quantum Dots

In contrast to the weakly confined quantum dots dominated by bright excitons, strongly quantum confined CsPbBr₃QDs exhibit both bright and dark exciton photoluminescence (PL) at cryogenic temperatures, making them a unique source of photons and charges of two very different natures. Here, we investigate the effect of inter-QD electronic coupling on the relative energetics and dynamics of the bright and dark excitons, which dictate the PL properties of the coupled arrays of these QDs at low temperatures. For this purpose, we fabricated 2D close-packed arrays of NaBr-passivated CsPbBr₃QDs with a sub-nanomter facet-to-facet distance, which was necessary to introduce electronic coupling. In addition to the redshift of the PL due to electronic coupling, the electronically coupled array of strongly confined CsPbBr₃QDs exhibited narrowed bright-dark level splitting and an acceleration of the decay of both bright and dark exciton PL at cryogenic temperatures. These observations are qualitatively analogous to the effects of increasing the volume of noninteracting QDs, which can be explained by the delocalization of exciton wave function among the coupled QDs.