Achieving high-efficiency blue organic light-emitting diodes via pyridyl-unit incorporated thermally activated delayed fluorescence materials

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 diodes (OLEDs). However, designing blue TADF emitters 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 by introducing pyridyl groups into the triindocarbazole donor to form intramolecular C–H⋯N hydrogen bonds. Compared with the phenyl-substituted counterpart TDBA-Ph, the pyridyl-incorporated 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 exhibit high luminescence efficiencies of 94% and 88%, respectively, accompanied by rapid RISC rates of 1.85 × 10⁶ s⁻¹ and 1.57 × 10⁶ s⁻¹. Non-doped OLEDs based on these emitters demonstrate impressive performance: TDBA-Ph and TDBA-Pd exhibit the maximum luminance (L_max) of 25 600 and 42 498 cd m⁻², and the maximum external quantum efficiency (EQE_max) of 12.4% and 11.7%, respectively. In the doped devices, TDBA-Ph and TDBA-Pd show a significantly enhanced EQE_max of 23.0% and 21.4%, respectively. Notably, both doped and nondoped devices display alleviated efficiency roll-off. This work confirms that introducing an sp²-hybridized nitrogen atom into a donor moiety represents a viable approach for constructing high-efficiency blue TADF emitters.