High performance TADF-phosphorescence hybrid warm-white organic light-emitting diodes with a simple fully doping-free device structure

White organic light-emitting diodes (WOLEDs) with doping-free emissive layer (EML) structures have been increasingly attracting attention due to their excellent advantages, such as easier manufacturing process and more flexible structure design. In this paper, a series of highly efficient hybrid WOLEDs is manufactured using a simple doping-free EML structure, which is composed of two blue thermally activated delayed fluorescence (TADF) emitters and an ultrathin (<0.1 nm) orange phosphorescent emitter. Through the thickness optimization of the blue TADF emitters, the optimal device shows a maximum external quantum efficiency, power efficiency, current efficiency, and luminance of 9.1%, 22.7 lm/W, 29.0 cd/A, and 14 530 cd/m2, respectively. When the brightness is increased from 1000 cd/m2 to 10 000 cd/m2, the chromaticity coordinates migrate from (0.44, 0.48) to (0.41, 0.47), and the correlated color temperature changes from 3454 to 3881 K, which belongs to the warm-white light emission zone. The result indicates that the use of a doping-free blue–orange–blue structure provides a common path for fabricating efficient, simple, and low cost WOLEDs.