Novel ternary bipolar host material with carbazole, triazole and phosphine oxide moieties for high efficiency sky-blue OLEDs

A novel bipolar host material 9-(3-(5-(4-(diphenylphosphoryl)phenyl)-4-phenyl-4H-1,2,4-triazol-3-yl)phenyl)-9H-carbazole (CTPO) with carbazole, triazole and phosphine oxide moieties was designed and synthesized. CTPO was found to exhibit a high glass transition temperature (Tg = 127 °C), suitable HOMO and LUMO levels (5.65 and 2.42 eV), a high triplet energy (3.06 eV) and excellent bipolar properties. A device with 15 wt% doping concentration showed a low turn-on voltage of 2.5 V and maximum current and power efficiencies of 41.6 cd A−1 and 43.0 lm W−1, respectively. A high efficiency of 40.1 cd A−1 was achieved at the brightness of 100 cd m−2. Even at a high luminance of 1000 cd m−2, the efficiency remained as high as 35.2 cd A−1.