Enhanced Exciton Utilization through Multichannel High-Lying Reverse Intersystem Crossing Enabled by Degenerate Strategy for High-Performance Ultraviolet OLED

Ultraviolet (UV) organic light-emitting diodes (OLEDs) utilizing hybridized local and charge transfer (HLCT) emitters exhibit significant potential, where a favorable high-lying reverse intersystem crossing process is pivotal for attaining both triplet exciton utilization and low efficiency roll-off. Herein, a degenerate strategy induced by multiple donor moieties is proposed to design and synthesize a highly efficient UV HLCT fluorophore, namely 3,6-mCPCNC3. Comparatively, it not only demonstrates exceptional morphological stability and a rapid radiative decay rate but also enriches the reverse intersystem crossing channels from high-lying triplet to singlet states. Consequently, the 3,6-mCPCNC3-based device exhibits an astonishing external quantum efficiency (EQE) of 8.73% coupled with an impressive exciton utilization efficiency of 86.3%. Even at a luminance of 1000 cd m^–2, the EQE still maintains a remarkable value of 8.29%, showcasing an exceptionally low efficiency roll-off. Remarkably, the device emits stable UV light with a peak wavelength at 389 nm and a narrow full-width half-maximum of 41 nm, corresponding to the color coordinates (0.161, 0.021). The record-high EQE achieved at 1000 cd m^–2 represents the state-of-the-art efficiency among the currently reported UV-OLEDs operating at high luminance levels.