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 (Delta lambda(QC)) is mainly contributed by the two opposing effects: (i) the linewidth broadening due to the repulsive kinetic energy of confined excitons (Delta lambda((KE))(QC)) and (ii) the overall linewidth narrowing caused by the attractive Coulomb interaction (Delta lambda((Coul))(QC)). It is shown that the relative contribution essentially remains at a constant value and is evaluated as Delta lambda((Coul))(QC)/Delta lambda((KE))(QC) = 0.42, which is independent of the QD size and the chemical nature of semiconducting emitter. We have computed Delta lambda(QC) for various QD sizes of the prototypical MHP emitter, MAPbBr(3), where MA denotes a methylammonium (CH3NH3) organic cation. The calculated results show that the linewidth broadening due to the quantum confinement (Delta lambda(QC)) increases rapidly beginning at the QD radius approximately equal to 6.5 nmbut Delta lambda(QC) is less than 2 nm even at R = 1.5 nm. Thus, Delta lambda(QC) is much narrower than the linewidth caused by the exciton-LO phonon Frohlich coupling (similar to 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 (Delta lambda(QC)) is not a risk factor in the realization of MHP-based ultrahigh-quality next-generation LEDs.