Highly Efficient Thermally Activated Delayed Fluorescence via an Unconjugated Donor–Acceptor System Realizing EQE of Over 30%

In this work, two novel thermally activated delayed fluorescence (TADF) emitters, 2tDMG and 3tDMG, are synthesized for high-efficiency organic light-emitting diodes (OLEDs), The two emitters have a tilted face-to-face alignment of donor (D)/acceptor (A) units presenting intramolecular noncovalent interactions. The two TADF materials are deposited either by an evaporation-process or by a solution-process, both of them leading to high OLED performance. 2tDMG used as the emitter in evaporation-processed OLEDs achieves a high external quantum efficiency (EQE) of 30.8% with a very flat efficiency roll-off of 7% at 1000 cd m^-2 . The solution-processed OLEDs also display an interesting EQE of 16.2%. 3tDMG shows improved solubility and solution processability as compared to 2tDMG, and thus a high EQE of 20.2% in solution-processed OLEDs is recorded. The corresponding evaporation-processed OLEDs also reach a reasonably high EQE of 26.3%. Encouragingly, this work provides a novel strategy to address the imperious demands for OLEDs with high EQE and low roll-off.