A solution-processable wholly-aromatic bipolar host material for highly efficient blue electroluminescent devices

Abstract

High-performance solution-processable host materials, especially for blue emitters, are greatly desired to develop low-cost and low-energy-consumption phosphorescent and thermally activated delayed fluorescent (TADF) organic light-emitting diodes (OLEDs). Here, we designed a wholly-aromatic bipolar host of 9,9-bis(9-phenyl-9H-carbazol-3-yl)-9H-thioxanthene 10,10-dioxide based on an insulating C(sp³) bridge linked thioxanthone through a facile Friedel–Crafts-type substitution reaction with a total yield of 63%. The π-conjugate-interrupted linkage not only grants excellent thermal stability and good film-forming ability but also maintains the triplet energy at a high level of 3.05 eV. Therefore, two state-of-the-art solution processed blue phosphorescent and TADF OLEDs were achieved, showing that the turn-on voltages are about 5.0 V while the maximum external quantum efficiencies (EQEs) are of 20.5% and 11.2%, respectively. These performances are among the best results of the solution-processed blue OLEDs reported to date, paving the way for the straightforward construction of solution-processable hosts of blue OLEDs through the novel C(sp³) bridge design strategy.