White Organic Light-Emitting Diodes with External Quantum Efficiency of 20.77% at 10000 cd m-2 and Ultra-High Color Stability by Controlling Exciton Distribution.

ABSTRACT

Although brightness and efficiency have been continually improved, the inability to achieve superior efficiency, color stability, and low-efficiency roll-off simultaneously in white organic light-emitting diodes (OLEDs) remains a knotty problem restricting the commercial application. In this paper, emission balance for two different horizontal orientation emitting molecules is maintained by using hole transport materials and bipolar host materials to control carriers' recombination and exciton diffusion. Impressively, the obtained devices exhibit extremely stable white emission with small chromaticity coordinates variation of (0.0023, 0.0078) over a wide brightness range from 1000 to 50000 cd m-2. Meanwhile, the optimal white OLED realizes the power efficiency, current efficiency, and external quantum efficiency up to 70.68 lm W-1, 85.53 cd A-1, and 24.33%, respectively at the practical brightness of 1000 cd m-2. Owing to reduced heterogeneous interfaces and broadening recombination region, this device exhibits a high EQE over 20% under high luminance of 10000 cd m-2, demonstrating slight efficiency roll-off. The operating mechanism of the device is analyzed by versatile experimental and theoretical evidences, which concludes precise manipulation of charges and excitons is the key points to achieve these excellent performances. This work provides an effective strategy for the design of high-performance white OLEDs.