Configuration effect of novel bipolar triazole/carbazole-based host materials on the performance of phosphorescent OLED devices

A series of structurally isomeric carbazole/triazole (TAZ)-based bipolar host materials 1-4 were designed and synthesized. These new materials were found to exhibit wide energy gaps (E-g: 3.29-3.52 eV), high triplet energies (E-T: 2.56-2.76 eV), high thermal stability (T-d: 426-454 degrees C), high glass-transition temperatures (T-g: 116-156 degrees C) and excellent film-forming property. Green and blue emitting devices with fac-tris(2-phenylpyridine)iridium (Ir(ppy)(3)) and iridium(III) bis(4,6-(di-fluorophenyl)pyridinato-N,C-2')picolinate (FIrpic) as phosphorescent dopants have been fabricated. The measurements of turn-on voltages, efficiencies and luminance suggested that the practice of combining carbazole's high triplet energy and excellent hole-transporting ability with TAZ's electron-transporting ability at the molecular level was effectively translated into better performance at the device level. The molecular structure of compound 4 is well-correlated with its efficiencies, which (32.7 and 21.1 cd/A for green and blue devices, respectively) were the best among the four materials. (C) 2012 Elsevier B.V. All rights reserved.