Multifunctional phosphorescent iridium (III) complexes based on 2-phenylbenzothiazole derivative for highly efficient organic light-emitting diodes

Abstract

Phosphorescent robust heteroleptic iridium (III) [Ir(III)] complexes based on 2-(4-(9H-carbazol-9-yl)phenyl)benzothiazole integrated with three auxiliary ligand were designed, synthesized and used to fabricate organic light-emitting diodes (OLEDs). The Ir(III) complexes emitted intense phosphorescence with yellow or orange color at room temperature with high quantum efficiencies and relatively short lifetimes. The auxiliary ligand greatly influenced the electronic and photophysical properties of their corresponding heteroleptic Ir(III) complexes. The complexes showed reversible redox characteristics. Hole-only single-carrier devices indicated that three complexes all possessed excellent hole-transporting ability. The phosphorescent OLEDs using three Ir(III) complexes as dopants exhibited turn-on voltages of ca. 4 V, maximum current efficiencies of 22.3–44.2 cd A−1 and maximum power efficiencies of 18.3–23.3 lm W−1, which were superior to the (bt)2Ir(acac)-based device (19.1 cd A−1, 9.3 lm W−1) under the same condition. The elevated devices' performances based on the new Ir(III) complexes as emitters were probably attributed to the hole-transporting rigid carbazole moiety resulting in more balanced electron and hole transportation and recombination in emissive layer.