High performance yellow organic electroluminescent devices by doping iridium(III) complex into host materials with stepwise energy levels

In this work, we aim to further improve the electroluminescent (EL) performances of a yellow light-emitting iridium(III) complex by designing double light-emitting layers (EMLs) devices having stepwise energy levels. Compared with single-EML devices, these designed double-EML devices showed improved EL efficiency and brightness attributed to better balance in carriers. In addition, the stepwise distribution in energy levels of host materials is instrumental in broadening the recombination zone, thus delaying the roll-off of EL efficiency. Based on the investigation of carriers' distribution, device structure was further optimized by adjusting the thickness of deposited layers. Finally, yellow EL device (Commission Internationale de l'Eclairage (CIE) coordinates of (0.446, 0.542)) with maximum current efficiency, power efficiency and brightness up to 78.62 cd/A (external quantum efficiency (EQE) of 21.1%), 82.28 lm/W and 72,713 cd/m2, respectively, was obtained. Even at the high brightness of 1000 cd/m2, EL efficiency as high as 65.54 cd/A (EQE=17.6%) can be retained.