Green and blue-green phosphorescent heteroleptic iridium complexes containing carbazole-functionalized β-diketonate for non-doped organic light-emitting diodes

Abstract

Two novel iridium complexes both containing carbazole-functionalized β-diketonate, Ir(ppy)2(CBDK) [bis(2-phenylpyridinato-N,C2)iridium(1-(carbazol-9-yl)-5,5-dimethylhexane-2,4-diketonate)], Ir(dfppy)2(CBDK) [bis(2-(2,4-difluorophenyl)pyridinato-N,C2)iridium(1-(carbazol-9-yl)-5,5-dimethylhexane-2,4-diketonate)] and two reported complexes, Ir(ppy)2(acac) (acac=acetylacetonate), Ir(dfppy)2(acac) were synthesized and characterized. The electrophosphorescent properties of non-doped device using the four complexes as emitter, respectively, with a configuration of ITO/N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-diphenyl-4,4′-diamine (NPB) (20nm)/iridium complex (20nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) (5nm)/tris(8-hydroxyquinoline)aluminum (AlQ) (45nm)/Mg0.9Ag0.1 (200nm)/Ag (80nm) were examined. In addition, a most simplest device, ITO/Ir(ppy)2(CBDK) (80nm)/Mg0.9Ag0.1 (200nm)/Ag (80nm), and two double-layer devices with configurations of ITO/NPB (30nm)/Ir(ppy)2(CBDK) (30nm)/Mg0.9Ag0.1 (200nm)/Ag (80nm) and ITO/Ir(ppy)2(CBDK) (30nm)/AlQ (30nm)/Mg0.9Ag0.1 (200nm)/Ag (80nm) were also fabricated and examined. The results show that the non-doped four-layer device for Ir(ppy)2(CBDK) achieves maximum lumen efficiency of 4.54lm/W and which is far higher than that of Ir(ppy)2(acac), 0.53lm/W, the device for Ir(dfppy)2(CBDK) achieves maximum lumen efficiency of 0.51lm/W and which is also far higher than that of Ir(dfppy)2(acac), 0.06lm/W. The results of simple devices involved Ir(ppy)2(CBDK) show that the designed complex not only has a good hole transporting ability, but also has a good electron transporting ability. The improved performance of Ir(ppy)2(CBDK) and Ir(dfppy)2(CBDK) can be attributed to that the bulky carbazole-functionalized β-diketonate was introduced, therefore the carrier transporting property was improved and the triplet–triplet annihilation was reduced.