Highly Efficient Hybrid White Organic Light‐Emitting Diodes with External Quantum Efficiency Exceeding 30% by Integrating Electron‐Trapping Sensitized Structure and Gradient‐Doping System

Abstract

In this work, efficient two‐color (blue and yellow) hybrid white organic light‐emitting diodes (WOLEDs) with high efficiencies are constructed by introducing iridium(III) bis(4,6‐(difluorophenyl) pyridinato‐N,C2’)picolinate (FIrpic) as electron sensitizer. Experimental results demonstrate that FIrpic with the deep lowest unoccupied molecular orbital (LUMO) level enables preferential electron trapping to collect excessive electrons, thus realizing carrier's balance and high recombination probability. The obtained cool WOLED exhibits the maximum external quantum efficiency (EQE), current efficiency (ηc), and power efficiency (ηp) of 31.05%, 76.36 cd A−1 and 69.92 lm W−1, respectively. Moreover, by gradient doping FIrpic into yellow EML, the generated forward built‐in electric field originating from gradient electrons distribution reduces carriers transport resistance and improves the transport of holes; the diffusion effect of gradient electrons distribution promotes electrons’ transport, thus enhancing the utilization probabilities of carriers and excitons. Besides, FIrpic acts also as an energy transfer ladder to facilitate the energy transfer from host to yellow emitter. Consequently, warm WOLED with enhanced yellow emission achieves the maximum EQE, ηc, and ηp of 33.27%, 75.66 cd A−1 and 88.04 lm W−1, respectively.