Simple Phenanthroimidazole/Carbazole Hybrid Bipolar Host Materials for Highly Efficient Green and Yellow Phosphorescent Organic Light-Emitting Diodes

By conjugating carbazole moiety to the different positions of the rigid skeleton 1,2-diphenyl-1 H -phenanthro[9,10- d ]imidazole, a series of hybrid bipolar phosphorescent hosts was synthesized, and their photophysical properties were investigated. The introduction of a rigid phenanthroimidazole moiety greatly improves their morphological stability, with high decomposition temperatures ( T d ) and high glass transition temperatures ( T g ) in the range of 394–417 and 113–243 °C, respectively. The highly efficient green and orange phosphorescent organic light-emitting diodes (PhOLEDs) have been achieved by employing these compounds as the phosphorescent hosts. For the device of ITO/MoO 3 (10 nm)/NPB (80 nm)/TCTA (5 nm)/mPhBINCP:9 wt % Ir(ppy) 3 (20 nm)/TmPyPB (45 nm)/LiF (1 nm)/Al (100 nm), a maximum luminous efficiency (η c,max ) of 77.6 cd/A, maximum power efficiency (η p,max ) of 80.3 lm/W, and maximum external quantum efficiency (η EQE,max ) of 21% were obtained. Furthermore, these hosts are also applicable for the orange phosphorescent emitter (fbi) 2 Ir(acac), a yellow PhOLEDs with pPhBICP as host, for which a performance of η c,max of 57.2 cd/A, η EQE,max of 19.3%, and η p,max of 59.8 lm/W was achieved. These results demonstrated that the phenanthroimidazole unit is an excellent electron-transporting group for constructing the bipolar phosphorescent host.