Abstract
Three novel tripodal bipolar compounds (CNTPA-CZ, CNTPA-PXZ and CNTPA-PTZ) were designed and synthesized, where three functional groups were attached to 1,3,5-positions of the central benzene ring, respectively. In these three compounds, carbazole/phenoxazine/phenothiazine (CZ/PXZ/PTZ) and benzonitrile were applied as electron-donating and electron-withdrawing groups, respectively, to achieve bipolar transport functionality, which was confirmed by the hole-only and electron-only device results. Due to the efficient energy transfer from these compounds to the dopant (Ir(MDQ)2(acac)), the red phosphorescent OLEDs demonstrated high device performance with maximum external quantum efficiency (EQE) over 20%. Particularly, the red OLED hosted by CNTPA-PTZ achieved a maximum efficiency of 42.5 cd/A, 44.3 lm/w and 23.4% with the EQE roll-off ratio of 3.4% from the peak value to that at a brightness of 500 cd/m2.
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