Luminance efficiency roll-off mechanism in CsPbBr3−xClx mixed-halide perovskite quantum dot blue light-emitting diodes

Abstract

Efficiency roll-off is a significant issue in blue light-emitting diodes (LEDs), but its origin still remains controversial. We report CsPbBr_3−xCl_x/PbBr_y (or PbCl_y) (core/shell) quantum dot LEDs exhibiting the emission peak spanning from λ_peak = 492 to λ_peak = 435 nm by varying the Cl composition (0 ≤ x ≤ 2.21). PLQY and EQE significantly decreased with the increase of the Cl composition. Careful analyses of the composition and the energy structure using EL, PL, TRPL, UPS, XPS and STEM-EDX measurements reveal that the luminance efficiency roll-off in CsPbBr_3−xCl_x LEDs is attributed to the following three combined effects: (1) luminescence quenching by the non-radiative trap-assisted recombination, (2) the hole transfer process at the CsPbBr_3−xCl_x/PbBr_y core/shell, and (3) imbalanced charge injection caused by a high energy barrier for the hole conduction at the PVK/QD heterointerface (Δh′).