Tuning peripheral group density in ternary phosphine oxide hosts for low-voltage-driven yellow PhOLEDs

Fluorene and diphenylphosphine oxide were employed as peripheral groups to construct ternary host materials DBFxPODEFn with benzofuran as a core for yellow phosphorescent organic light-emitting diodes (PhOLEDs). Their peripheral group density and ratio were rationally adjusted to suppress quenching and enhance charge balance. The conjugation of DBFxPODEFn was extended appropriately on the basis of meso- and short-axis linkages to render similar optical properties and a medium first triplet energy (T₁) of 2.58 eV for efficient and comparable energy transfer to yellow phosphors, making the yellow PhOLED performance correspond to the charge flux balance and quenching effects, viz. the correlation between device performance and their functional group density and spatial arrangement. DBFSPODEF with the desired electron-dominant characteristics and the suppressed triplet-triplet annihilation (TTA) effect endowed its devices with a low driving voltage of <3.8 V and favorable efficiencies of 32.7 lm W^-1 and 12.5% at 1000 cd m^-2 for lighting applications. This work indicates that an appropriate functionalization and a rational spatial group arrangement are significant for constructing efficient hosts for low-voltage-driven PhOLEDs.