Exciton Photoluminescence of Strongly Quantum-Confined Formamidinium Lead Bromide (FAPbBr3) Quantum Dots

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.