High Triplet Energy Phosphine Sulfide Host Materials with Selectively Modulated Electrical Performance for Blue Electrophosphorescence

Bipolar host materials consisting of electron-donating (D) and -accepting (A) moieties are significant advances in broadening the recombination zone to suppress the quenching effects of emissive phosphors in the emission layer for achieving a high-efficiency blue electrophosphorescence device. However, it is still a daunting and challenging issue to design bipolar blue host molecules that have high triplet energy (E_T) and balanced charge transportation simultaneously in the directly linked D-A molecules, owing to their high tendency in forming low-energy charge-transfer (CT) states. Herein, on account of the high-polarization, electron-withdrawing, and insulating features of the acceptor of aryl phosphine sulfide (APS), a series of blue host materials in D-A/D-A-D skeletons with high E_T's are constructed and facilely prepared. Thus, designed host materials show high E_T's up to 3.02 eV, suitable highest occupied molecular orbitals and lowest unoccupied molecular orbitals, and balanced hole/electron flux, which facilitate blue phosphorescent organic light-emitting diodes (PhOLEDs) with a maximum external quantum efficiency of 14.1%, power efficiency of 21.4 lm W^-1, and current efficiency of 27.8 cd A^-1. These findings demonstrate the important role of APS unit in designing and developing host materials with high E_T's and balanced carrier flux for high-performance blue PhOLEDs.