Novel phenanthro[9,10-d]imidazole-zinc complex as a host for high-performance OLEDs

In this work, a novel phenanthro[9,10-d]imidazole-zinc coordination complex (Zn(TPPI) 2 ) is reported. This compound exhibits suitable physical properties for a host material. First, its highest occupied molecular orbital (HOMO) (− 5.33 eV) energy level is favorable for hole injection from transporting layer. Second, its small singlet–triplet splitting (0.31 eV) can reduce the intrinsic energy loss from singlet to triplet excited state and promote the device efficiency. Finally, its good thermal stability (decomposition temperature: 495 °C) favors evaporation preparation of uniform films. As a result, yellow–red and red phosphorescent devices which utilize Zn(TPPI) 2 as host display high efficiencies (yellow–red: 58.35 cd/A, 70.52 lm/W, 20.82%) (red: 15.89 cd/A, 16.09 lm/W and 19.05%). The performance of red device is comparable to the best results of previous publications on corresponding emitter. Meanwhile, the undoped device of Zn(TPPI) 2 exhibits high efficiencies (3.79 cd/A, 3.97 lm/W, 2.47%) in zinc-complex blue emitters. These results demonstrate that Zn(TPPI) 2 is a good blue emitter and host material.