Harnessing charge and exciton distribution towards extremely high performance: the critical role of guests in single-emitting-layer white OLEDs

Currently, high efficiency, low efficiency roll-off and stable color white organic light-emitting diodes (WOLEDs) are still challenging to realize via simplified structures. Herein, the simplicity/extremely high efficiency/low efficiency roll-off/stable color trade-off has been accomplished in a single-emitting-layer (single-EML) phosphorescent WOLED. The WOLED exhibits total efficiencies of 111.7 cd A(-1) and 75.5 mu m W-1 at a practical luminance of 1000 cd m(-2), these efficiencies are the highest among single-EML WOLEDs. Even at 5000 cd m(-2), the efficiencies remain as high as 101.3 cd A(-1) and 58.8 mu m W-1. Besides, the color variation in the whole range of luminances is (0.00, 0.00), which is the first single-EML WOLED with an extremely stable color. The origin of the high performance is unveiled. Particularly, the role of guests, which is often ignored in single-EML WOLEDs, on the origin of the color-stability is systematically revealed and harnessing charge and exciton distribution by using multifunctional guests is demonstrated to be critical for stabilizing the color. Such marvelous results not only represent a significant step towards the realization of simplified WOLEDs, but also provide a new opportunity to achieve extremely stable colors [DCIE (Commission International de I'Eclairage) = (0.00, 0.00)].