Wet-process feasible novel carbazole-type molecular host for high efficiency phosphorescent organic light emitting diodes

Abstract

Wet-process organic light-emitting diodes (OLEDs) are crucial to realize cost-effective and large-area roll-to-roll fabrication of high quality displays and lightings. In this study, a wet-process feasible carbazole based host material, 2-[4-(carbazol-9-yl)butyloxy]-9-[4-(carbazol-9-yl)butyl]carbazole (6), is synthesized, and two other carbazole hosts, 2-[5-(carbazol-9-yl)pentyloxy]-9-[5-(carbazol-9-yl)pentyl]carbazole (7) and 2-[6-(carbazol-9-yl)hexyloxy]-9-[6-(carbazol-9-yl)hexyl]carbazole (8) are also synthesized for comparison. All the three host materials exhibit high triplet energy, and possess high solubility in common organic solvents at room temperature. On doping a green phosphorescent emitter fac tris(2-phenylpyridine)iridium (Ir(ppy)₃) into host 6, the device shows an efficacy of 51 lm W⁻¹ and a current efficiency of 52 cd A⁻¹ at 100 cd m⁻² or 30 lm W⁻¹ and 40.7 cd A⁻¹ at 1000 cd m⁻². The high efficiency may be attributed to the host possessing an effective host-to-guest energy transfer, the ability for excitons to generate on both host and guest, and excellent film integrity.