Highly efficient white organic light-emitting diodes based on balanced bipolar-transporting blue hybridized local charge transfer fluorophores

Abstract

Fluorescent/phosphorescent hybrid white organic light-emitting diodes (WOLEDs) that combine the blue fluorophore with long-wavelength emissive phosphors have attracted a great deal of attention in the fields of solid-state lighting and full-color display. However, the efficiency and its roll-off at high luminance are still unsatisfactory, resulting from serious exciton-quenching involving long-lived triplet excitons. In this work, we have developed a high-performance hybrid WOLED by integrating a perfect arrangement of emitting layers with a high and balanced hole- and electron-transporting hybridized local charge transfer (HLCT) blue fluorophore. The resulting two-color WOLED with the CIE coordinates of (0.39, 0.43) achieves a high current efficiency of 78.8 cd A⁻¹ and a maximum external quantum efficiency (EQE_max) of 27.1%. More importantly, the value of EQE is maintained as high as 23.8% at 1000 cd m⁻², showing low efficiency roll-off. This efficiency is one of the best results of WOLEDs achieved using blue HLCT materials.