Synthesis and green phosphorescent OLED device performance of cyanofluorene-linked phenylcarbazoles as host material

Abstract

A series of three isomeric bipolar host materials for green phosphorescent organic light-emitting diodes (PhOLEDs) was synthesized from a combination of cyanofluorene and N-phenylcarbazole moieties. A cyano-substituted fluorene moiety was selected as the n-type unit and an N-phenylcarbazole moiety as the p-type unit. Green PhOLEDs were fabricated using bis[2-(2-pyridinyl-N)phenyl-C](acetylacetonato)iridium(III) [Ir(ppy)₂(acac)] as the doped emitter. From the results of the device performance, a maximum current efficiency of 74.6 cd A⁻¹ and an external quantum efficiency of 20.3% were recorded for the [Ir(ppy)₂(acac)]-based PhOLED, with the m-CF-PhCz host showing the best performance. Furthermore, the PhOLED with the m-CF-PhCz host exhibited a relatively slow efficiency roll-off compared to the devices with o-CF-PhCz and p-CF-PhCz hosts. The color coordinates of the green PhOLEDs at 1000 cd m⁻² were (0.36, 0.61; o-CF-PhCz), (0.34, 0.62; m-CF-PhCz), and (0.34, 0.62; p-CF-PhCz), respectively.