In contrast to the weakly confined quantum dots dominated by bright excitons, strongly quantum confined CsPbBr 3 QDs 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 closepacked arrays of NaBr-passivated CsPbBr 3 QDs with a subnanomter 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 CsPbBr 3 QDs 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.

Despite the versatility of semiconductor nanocrystals (NCs) in photoinduced chemical processes, the generation of stable radicals has been more challenging due to reverse charge transfer or charge recombination even in the presence of sacrificial charge acceptors. Here, we show that cesium lead halide (CsPbX3) NCs can selectively photogenerate either aminium or aminyl radicals from amines, taking advantage of the controllable imbalance of the electron and hole populations achieved by varying the solvent composition. Using dihalomethane as the solvent, irreversible removal of the electrons from CsPbX3 NCs enabled by the photoinduced halide exchange between the NCs and the dihalomethane resulted in efficient oxidative generation of the aminium radical. In the absence of dihalomethane in solvent, the availability of both electrons and holes resulted in the production of an aminyl radical via sequential hole transfer and reductive N–H bond dissociation. The negative charge of the halide ions on the NC’s lattice surface appears to facilitate the aminyl radical production, competing favorably with the reversible charge transfer reverting to the reactant.

Imposing strong quantum confinement in metal halide perovskite (MHP) quantum dots (QDs) not only tunes the exciton transition energy but also alters other photophysical properties that are sensitive to the spatial confinement of the exciton wave function. A recent study of inorganic cesium lead halide QDs in strongly confined regime revealed important exciton properties contrasting to those of weakly confined counterparts, such as the strong emission from the dark exciton and switching of the relative level order of bright and dark states. However, strongly quantum-confined hybrid MHP QDs, with organic A-site cations that are known to have additional pathways to influence the exciton and charge carrier transport properties in bulk, have received less attention. Here, we prepared strongly quantum-confined formamidinium lead bromide (FAPbBr3) QDs of different sizes and studied the photoluminescence, fine structure, and decay dynamics of excitons at varying temperatures and under varying magnetic fields that are affected by quantum confinement. We compared the results from this work with those of CsPbBr3 QDs in the same size range also experiencing strong quantum confinement to examine the similarities and differences between these two QDs.