A bipolar thiophene substituted 1,3,5-triazine host material for green phosphorescent OLEDs with low onset voltage and current efficiency roll-off

A novel bipolar host material containing 1,3,5-triazine, thiophene and triphenylamine moieties, 4,4'-(6-thiophen-2-yl)-1,3,5-triazine-2,4-diyl)bis(N,N-diphenylaniline) (TTT), was used as a host for three Ir-III complexes in fabricating high efficiency phosphorescent organic light emitting diodes (OLEDs) with low driving voltage. The onset voltages of these three OLEDs having the configuration ITO (indium tin oxides)/TAPC (1,1-bis[4-[N,N-di(p-tolyl)amino]phenyl]cyclohexane, 60 nm)/TIT: Ir-III complex (92:8, 30 nm)/TPBi (2,2',2 ''-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole, 90 nm)/LiF (1 nm)/Al (100 nm), are between 2.9 V and 3.0 V, which is about 0.5 V less than the onset voltages of similar structural OLEDs with mCP as the host material. Maximum current and power efficiencies are more than 30.0 cd A(-1) and 15.0 lm W-1, respectively, with no significant current efficiency roll-off. All the devices exhibit high efficiency at the high brightness of 10,000 cd m(-2). The small roll-off is due to the improved charge balance and the wide charge recombination zone in the emissive layer of these devices. (C) 2017 Elsevier Ltd. All rights reserved.