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 (ΔλQC) 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 ΔλQCfor 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 (ΔλQC) increases rapidly beginning at the QD radius approximately equal to 6.5 nm but ΔλQCis less than 2 nm even atR= 1.5 nm. Thus, ΔλQCis 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 (ΔλQC) is not a risk factor in the realization of MHP-based ultrahigh-quality next-generation LEDs.
Keywords: exciton; light-emitting diodes; linewidth broadening; metal halide perovskites; photoluminescence; quantum confinement.
© 2021 IOP Publishing Ltd.