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

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. • Low Roll-OFF Red Phosphorescent OLED. • Phenanthridine-Based Bipolar Host was demonstrated. • (BF-PTD-SiCz)-based Device Exhibited EQE of 13.86 %. • (BF-PTD-SiCz)-based Device Showed a Narrower FWHM and a Suppressed Shoulder Peak.