Achieving High-Efficiency Blue Organic Light-Emitting Diodes via Pyridyl-Unit Incorporation for Thermally Activated Delayed Fluorescence Materials Design

Abstract

Thermally activated delayed fluorescence (TADF) materials, which enable 100% exciton utilization via reverse intersystem crossing (RISC), play a pivotal role in advancing organic light-emitting diode (OLED). However, designing blue TADF emitter remains challenging due to the inherent trade-off between short emission wavelength and small singlet-triplet splitting. In this study, a strategy for developing such emitters is proposed as introducing pyridyl groups into triindocarbazole donor to form intramolecular C-H•••N hydrogen bonds. Compared with the phenyl-substituted counterpart TDBA-Ph, the pyridylincorporated TDBA-Pd exhibits a blueshifted emission (453 versus 460 nm in toluene) and a deeper HOMO energy (-5.63 eV vs. -5.58 eV). Both TDBA-Ph and TDBA-Pd achieve high luminescent efficiencies of 94% and 88%, respectively, accompanied by rapid RISC rates of 1.85×10 6 s⁻1 and 1.57×10 6 s⁻1 . Non-doped OLEDs based on these emitters demonstrate impressive performance: TDBA-Ph and TDBA-Pd exhibit maximum luminance (Lmax) of 25,600 and 42,498 cd m⁻2 , and maximum external quantum efficiency (EQEmax) of 12.4% and 11.7%, respectively. In the doped devices, TDBA-Ph and TDBA-Pd show significantly enhanced EQEmax of 23.0% and 21.4%, respectively. Notably, both doped and nondoped devices display alleviated efficiency roll-off. This work confirms that introducing sp2 -hybridized nitrogen atom into donor moiety represents a viable approach for constructing high-efficiency blue TADF emitters.