Regulating charges and excitons in simplified hybrid white organic light-emitting diodes: The key role of concentration in single dopant host-guest systems

A series of high-performance hybrid white organic light-emitting diodes (WOLEDs) with simplified structures are developed by systematically investigating the influence of dopant concentrations. An ultrahigh color rendering index of 88 and a peak forward-viewing power efficiency of 44.9 lm/W are achieved in the single-emitting-layer WOLED with a low concentration (0.1%) and a moderate concentration (1%), respectively. To investigate the effect of high concentration (4%), a dual-emitting-layer device is realized, achieving an efficiency of 15.8 lm/W (1000 cd/m(2)). Besides, the devices show extremely stable color with a Commission Internationale de L'Eclairage (CIEx, y) variation of Delta(x, y) <= (0.008, 0.008) during a large range of luminance. Furthermore, the origin of the color-stability and working mechanism of the devices are discussed, which can be attributed to the multifunctional dopant which reduces charge mobilities together with a suitable hole transport material which exhibits strong electron-and exciton-blocking ability. (C) 2014 Elsevier B.V. All rights reserved.