A meta-linkage strategy towards high-performance hosts for efficient blue thermally activated delayed fluorescence OLEDs

The development of high-performance host materials for blue thermally activated delayed fluorescence (TADF) emitters is crucial for realizing efficient blue organic light-emitting diodes (OLEDs). Herein, two star-shaped host materials, tris(3-(diphenylphosphanyl oxide)phenypphosphane oxide (m4PO) and tris(3-(carbazole)phenypphosphane oxide (m3CzPO), containing a triphenylphosphine oxide (TPPO) core and three meta-substituted diphenylphosphine oxide or carbazolyl groups, are designed and synthesized. The comparative study reveals that the meta-linkage strategy significantly improves the performances of the hosts. The two hosts show superhigh triplet energies of over 3.1 eV, along with high thermal stability, good carrier-transporting capability, and high film quality, which establish the basis for being potentially ideal hosts for blue TADF emitters. Based on a conventional blue TADF emitter bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS), the blue TADF-OLEDs realize high performances with maximum external quantum efficiencies (EQEs) beyond 20%, maximum power efficiencies (PEs) over 40 Em W-1, a low turn-on voltage of 2.8 V, and a high luminance of up to 5170 nits.