A Universal Thermally Activated Delayed Fluorescence Host with Short Triplet Lifetime for Highly Efficient Phosphorescent OLEDs with Extremely Low Efficiency Roll-off

Triplet-involved quenching processes lead to significant efficiency roll-off in phosphorescent organic light-emitting diodes (OLEDs). Thermally activated delayed fluorescence (TADF) materials can reduce the triplet exciton density in the emitting layer (EML) via the up-conversion of triplet into singlet exciton. However, the effect of triplet lifetime of TADF host on efficiency roll-off is still under-researched. Inspired by the fast spin-flip process in TADF with a small singlet-triplet energy gap, we herein reported a triazine/carbazole hybrid (Trz-PhCz) with short triplet lifetime and extremely low efficiency roll-offs were achieved for green, yellow, orange and red OLEDs with external quantum efficiencies (EQEs) over 20% at 10000 cd m-2. Particularly, the optimized orange device showed a record-high maximum EQE of 31.4%, and 25.5% at 10000 cd m-2. Furthermore, unprecedented high PEmaxs of 111.8 lm W-1 and 98.9 lm W-1 were obtained for Ir(ppy)2(acac) and PO-01 based devices, respectively. Notably, two-color white OLED based on single host Trz-PhCz also showed remarkably high maximum power efficiency (PEmax) of 102.5 lm W-1 with the Commission Internationale de l’Eclairage (CIE) of (0.42, 0.48). So Trz-PhCz hosted phosphorescent OLEDs demonstrated the state-of-the-art device performance, and this work provided an insight about the design of efficient TADF host materials via controlling their triplet lifetime for the practical applications.