Effective Design Strategy for Aggregation-Induced Emission and Thermally Activated Delayed Fluorescence Emitters Achieving 18% External Quantum Efficiency Pure-Blue OLEDs with Extremely Low Roll-Off

High-color purity organic emitters with a simultaneous combination of aggregation-induced emission (ME) and thermally activated delayed fluorescence (TADF) characteristics are in great demand due to their excellent comprehensive performances toward efficient organic light-emitting diodes (OLEDs). In this work, two D-pi-A-structure emitters, ICz-DPS and ICz-BP, exhibiting ALE and TADF properties were developed, and both the emitters have narrow singlet (S-1)-triplet (T-1) splitting (Delta E-ST) and excellent photoluminescence (PL) quantum yields (Phi(PL)), derived from the distorted configurations and weak intra/intermolecular interactions, suppressing exciton annihilation and concentration quenching. Their doped OLEDs based on ICz-BP provide an excellent electroluminescence external quantum efficiency (eta(ext)) and current efficiency (eta(C)) of 17.7% and 44.8 cd A(-1) respectively, with an eta(ext) roll-off of 2.9%. Their nondoped OLEDs based on ICz-DPS afford high efficiencies of 11.7% and 30.1 cd A(-1) with pure-blue emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.15, 0.08) and a low roll-off of 6.0%. This work also shows a strategy for designing AIE-TADF molecules by rational use of steric hindrance and weak inter/intramolecular interactions to realize high Phi(PL) values, fast reverse intersystem crossing process, and reduced nonradiative transition process properties, which may open the way toward highly efficient and small-efficiency roll-off devices.