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-dipheny1-1H-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 degrees 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/MoO3 (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 (eta(c,max)) of 77.6 cd/A, maximum power efficiency (eta(p,max)) of 80.3 lm/W, and maximum external quantum efficiency (eta(EQA,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 eta(c,max) of 57.2 cd/A, eta(EQE,max) of 19.3%, and eta(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.