Highly twisted biphenyl-linked carbazole-benzimidazole hybrid bipolar host materials for efficient PhOLEDs
Journal
Journal of Materials Chemistry C
Journal Volume
2
Journal Issue
40
Pages
8554-8563
Date Issued
2014
Author(s)
Abstract
Three new highly twisted bipolar host materials (PhczNBI, PhczCBI, and PhczDCBI) comprising of a biphenyl core linking a hole-transport 9-phenylcarbazole (donor) and an electron-transport N-phenylbenzimidazole (acceptor) with different topologies were synthesized, characterized, and applied as host materials for full-color phosphorescent OLEDs. The highly twisted conformations imparted through a 2,2′-biphenyl linkage effectively disrupt the π-conjugation and electronic coupling between the donor and the acceptor, thus giving the bipolar hosts promising properties such as bipolar charge transport features (μh≈ μe≈ 10-6to 10-4cm2V-1s-1) and high triplet energies (ET= 2.55-2.71 eV). The PhOLED device gave a maximum external quantum efficiency (ηext) of 19.6% for the PhczNBI host with a yellow phosphor (Bt)2Ir(acac). A two-color, single-emitting-layer and all-phosphor WOLED hosted by PhczDCBI achieved high efficiencies (13.9%, 34.9 cd A-1, and 24.8 lm W-1) and a CRI up to 65.5.
Type
journal article