High-performance hybrid white organic light-emitting diodes with simple emitting structures and low efficiency roll-off based on blue thermally activated delayed fluorescence emitters with bipolar transport characteristics

Abstract

A large density of excitons under high current density is accounted for by the sharp decay of efficiency (called “efficiency roll-off”) in white organic light-emitting diodes (WOLEDs). In this paper, by strategically inserting ultrathin layers of long-wavelength phosphorescent emitters in appropriate positions in blue emitters with bipolar transport characteristics, highly efficient hybrid WOLEDs with simple emitting structures and reduced efficiency roll-off as well as a satisfactory color rendering index (CRI) are well-achieved. Based on our design concept, the exciton distribution zone is very broad, and the nonradiative exciton loss is significantly reduced. The optimized hybrid WOLED exhibits a maximum external quantum efficiency (EQE), a current efficiency (CE), and a power efficiency (PE) of 19.1%, 41.6 cd A⁻¹, and 42.4 lm W⁻¹, and maintains 17.3%, 39.2 cd A⁻¹, and 30.5 lm W⁻¹ at a luminance of 1000 cd m⁻². Systematic studies of the electrical properties and transient electroluminescence decay characteristics are performed to confirm the reasons for the reduced efficiency roll-off and the exciton utilization process in the optimized hybrid WOLEDs.