Bipolar TADF interlayer for high performance hybrid WOLEDs with an ultrathin non-doped emissive layer architecture

Abstract White organic light-emitting diodes (WOLEDs) with non-doped construction have compelling advantages, such as simplifying manufacturing process and reducing costs, thus attracting more attention. To improve the efficiency of non-doped WOLEDs, the selection of suitable interlayer is still a big problem to balance carriers. Here, for the first time, we employed a thermally activated delayed fluorescence (TADF) material with bipolar transport characteristics as the interlayer to modulate the exciton distribution, and fabricated efficient and ultrathin non-doped devices. The optimized monochromatic and white OLED exhibited maximum external quantum efficiencies of 18.1% and 15.6%, current efficiencies of 55.7 cd/A and 46.6 cd/A, as well as power efficiencies of 43.8 lm/W and 41.8 lm/W, respectively. More importantly, the devices adopted an ultrathin non-doped emissive layer architecture, and its thickness was only 3.6 nm, which was beneficial to reduce costs and simplify preparation process. Our results illustrated a new strategy that the bipolar TADF interlayer can suppress triplet-triplet annihilation (TTA) effect and improve the exciton utilization, which presents unprecedented opportunities for fabricating highly efficient, low cost and commercial WOLEDs.