High-efficiency and Low Roll-Off Red Phosphorescent Organic Light-emitting Diodes Enabled by Phenanthridine-based Bipolar Host Materials

Abstract

In this study, we report the synthesis of two host materials for high-efficiency and highly stable organic light-emitting diodes (OLEDs): 3-[4’-(triphenylsilyl)phenyl)-9H-carbazole]-6-phenylbenzofuro [3,2-k]phenanthridine (BF-PTD-SiCz) and 3-[4’-(triphenylsilyl)phenyl)-9H-carbazole]-6-phenylbenzo [4,5]thieno [3,2-k]phenanthridine (BT-PTD-SiCz). These phenanthridine-based bipolar host materials were synthesized via Ullman and Suzuki coupling reactions, reduction, nucleophilic acyl substitution, and reductive cyclization. Both materials exhibited excellent thermal stability. Red phosphorescent OLEDs (PhOLEDs) fabricated using BF-PTD-SiCz and BT-PTD-SiCz as hosts demonstrated improved roll-off characteristics compared to those of PhOLEDs that employed the conventional 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) host. In particular, the BF-PTD-SiCz-based device exhibited an external quantum efficiency (EQE) of 13.86 %. These results indicate that BF-PTD-SiCz and BT-PTD-SiCz are well suited for use in high-efficiency red PhOLEDs. © 2025 Elsevier Ltd