A Phosphanthrene Oxide Host with Close Sphere Packing for Ultralow-Voltage-Driven Efficient Blue Thermally Activated Delayed Fluorescence Diodes.

A phosphanthrene oxide host, 5,10-diphenyl-phosphanthrene 5,10-dioxide (DPDPO2 A), with intra- and intermolecular hydrogen bonds achieves spheroidal cis-configuration and close sphere packing. DPDPO2 A realizes effective exciton suppression and excellent and balanced carrier transporting ability, both at the same time, demonstrating favorable photoluminescence quantum yield of 84% from its blue thermally activated delayed fluorescence (TADF) dye, namely bis[4-(9,9-dimethyl-9,10-dihydroacridine) phenyl]sulfone, doped films and high electron and hole mobility at the level of 10-4 and 10-5 cm2 V-1 s-1 , respectively. DPDPO2 A endows its blue TADF devices with record-low driving voltages, e.g., turn-on voltage of 2.5 V, and the state-of-the-art efficiencies with maxima of 22.5% for external quantum efficiency and 52.9 lm W-1 for power efficiency, which is the best comprehensive performance to date of ultralow-voltage-driven blue TADF diodes.