Quantum-confinement effect on the linewidth broadening of metal halide perovskite-based quantum dots

The linewidth broadening caused by various physicochemical effects does limit the well-known advantage of ultrahigh color purity of metal halide perovskites (MHPs) for use in next-generation light-emitting diodes (LEDs). We have theoretically examined the quantum- and dielectric-confinement effects of a quantum dot (QD) on the degree of photoluminescence linewidth broadening. It is predicted that the linewidth (Δλ_QC) is mainly contributed by the two opposing effects: (i) the linewidth broadening due to the repulsive kinetic energy of confined excitons (ΔλQCKE) and (ii) the overall linewidth narrowing caused by the attractive Coulomb interaction (ΔλQCCoul). It is shown that the relative contribution essentially remains at a constant value and is evaluated asΔλQCCoul/ΔλQCKE=0.42, which is independent of the QD size and the chemical nature of semiconducting emitter. We have computed Δλ_QCfor various QD sizes of the prototypical MHP emitter, MAPbBr₃, where MA denotes a methylammonium (CH₃NH₃) organic cation. The calculated results show that the linewidth broadening due to the quantum confinement (Δλ_QC) increases rapidly beginning at the QD radius approximately equal to 6.5 nm but Δλ_QCis less than 2 nm even atR= 1.5 nm. Thus, Δλ_QCis much narrower than the linewidth caused by the exciton-LO phonon Fröhlich coupling (∼23.4 nm) which is known as the predominant mechanism of linewidth broadening in hybrid MHPs. Thus, the linewidth broadening due to the quantum confinement (Δλ_QC) is not a risk factor in the realization of MHP-based ultrahigh-quality next-generation LEDs.