Synthesis and characterization of benzo-phenanthridine-based acceptor hosts with enhanced bipolar characteristics for red phosphorescent organic light-emitting diodes

Abstract

Herein, we report the development of highly stable red phosphorescent organic light-emitting diodes (PhOLEDs) that exhibit stable light emission and low efficiency roll-off under high-brightness operation. Typical applications of PhOLEDs include smart phones, TVs, tablets, and automotive displays. Two new acceptor-type host materials, 6-phenyl-3,9-bis(3-(pyridin-3-yl)phenyl)benzo[ k ]phenanthridine ( PBPyP-BPH ) and 3-(3,5-di(pyridin-3-yl)phenyl)-6-phenylbenzo[ k ]phenanthridine ( DPyP-BPH ) were designed and synthesized based on a highly rigid benzophenanthridine core. Owing to this structural rigidity, the two hosts demonstrated excellent thermal stability with high 5 % weight loss temperatures (Td,5 %) of 403°C for PBPyP-BPH and 395°C for DPyP-BPH . These high thermal transition temperatures ensure device reliability for automotive applications, even under harsh driving conditions. When utilized in a bipolar mixed-host system with a thermally stable donor, 4,4′,4″-tri(N-carbazolyl)triphenylamine (TCTA), the developed red PhOLEDs (doped with Bis(2-methyldibenzo[ f , h ]quinoxaline)(acetylacetonate)iridium(III) [Ir(MDQ)2(acac)], TCTA: PBPyP-BPH and TCTA: DPyP-BPH, achieved high maximum external quantum efficiencies (EQEs) of 17.9 and 17.2 %, respectively with significantly suppressed efficiency roll-offs. These results demonstrate that securing high thermal stability through molecular design, combined with controlling charge balance via device structure optimization, is an effective strategy for realizing high-performance red PhOLEDs.