Efficient and low roll-off solution-processed sky-blue TADF emitters via hetero-donor and space modification strategies†

Solution-processed thermally activated delayed fluorescence (TADF) organic light-emitting diodes (OLEDs) have traditionally underperformed compared to vacuum-deposited OLEDs, primarily due to low external quantum efficiency (EQE) and severe efficiency roll-off at high brightness. Herein, a strategic molecular design for solution-processable TADF emitters featuring multiple-donor shielded lowest unoccupied molecular orbital (LUMO) structures is proposed by filling rigid bulky phenyl substituents (monophenyl, diphenyl and m-triphenyl) into a hetero-donor TADF core. The introduced bulky units not only effectively suppress the aggregation-caused quenching (ACQ) effect in the solid state, but also accelerate the up-conversion process. The corresponding solution-processed TADF-OLEDs exhibit a maximum external quantum efficiency (EQE_max) exceeding 20% and low efficiency roll-off. Among them, the HCB-3-based device demonstrates the highest performance, with an EQE of 24.1% and maintaining 23.7% at 100 cd m⁻². These results highlight the significant potential for developing high-efficiency and low roll-off solution-processed TADF materials, representing a promising advancement in OLED technology.