The influence of dipyridyl amine-carbazole based bipolar host materials for green PHOLEDs

Abstract The series of new bipolar host materials with dipyridyl amine and carbazole moieties connected to the triazine core unit were synthesized for green phosphorescent organic light-emitting diodes (PHOLEDs). Especially, we controlled the hole transporting behaviors by attaching different connectivity of carbazole moieties attached to the triazine core in new synthetic host materials. From this approach, we found that triazine derivatives with dipyridyl amine-carbazole based substituents exhibited moderately high glass temperature above 139 °C as well as relatively high triplet energy (T 1  > 2.78 eV). With those bipolar host materials, we prepared green PHOLEDs. And the new synthetic dipyridyl amine-carbazole based triazine derivative, [4,6-bis(9-phenyl-9 H -carbazol-3-yl)- N,N -di(pyridin-2-yl)-1,3,5-triazin-2-amine ( 3-BCTPy) ] showed relati-vely high device efficiencies, up to 70.6 cd/A and 18.9% (external quantum efficiency, EQE) when we utilized it as a host materials and bis(2-phenylpyridine)(acetyl-acetonato) iridium (III) [Ir(ppy) 2 (acac)] as a dopant.