High efficiency ultra-thin doping-free WOLED based on blue thermally activated delayed fluorescence inter-layer switch

Abstract Choosing an appropriate interlayer (IL) is still a crucial challenge for charge balance and exciton regulation in ultra-thin doping-free white organic light-emitting diodes (WOLEDs). Herein, for the first time, the blue thermally activated delayed fluorescence (TADF) 10, 10, 10-(4, 4, 4-Phosphoryltris (benzene-4, 1-diyl)) tris (10Hphenoxazine) (TPXZPO) was selected as the n-type inter-layer (IL) switch. The monochromatic and white light device achieved maximum external quantum efficiencies (EQE) of 24.47% and 14.96%, respectively. More importantly, all devices exhibited extremely low turn-on voltage and stable electroluminescent spectra, with CIE coordinates Δ (x, y) varying only by (0.01, 0.01) in the luminance range of 100 to 10,000 cd/m2. The results showed that new-type IL plays a crucial role in regulating charge and exciton distribution, which could effectively control of the emission zone and the triplet exciton density. This excellent performance demonstrates that the introduction of TADF IL is a promising prospect in the application of high-performance ultra-thin doping-free WOLEDs.