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

摘要

Two novel iridium complexes both containing carbazole-functionalized P-diketonate, Ir(ppy)_2(CBDK) [bis(2-phenylpy-ridinato-N,C~2)iridium(1-(carbazol-9-yl-5,5-dimethylhexane-2,4-diketonate)], Ir(dfppy)_2(CBDK) [bis(2-(2,4-difluorophe-nyl)pyridinato-N,C~2)iridium(l-(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-diphe-nyl-N,N'-bis(l-naphthyl)-l,l'-diphenyl-4,4'-diamine (NPB) (20 nm)/iridium complex (20 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) (5 nm)/tris(8-hydroxyquinoline)aluminum (A1Q) (45 nm)/Mg_(0.9)Ag_(0.1) (200 nm)/Ag (80 nm) were examined. In addition, a most simplest device, ITO/Ir(ppy)_2(CBDK) (80 nm)/Mg_(0.9)Ag_(0.1) (200 nm)/Ag (80 nm), and two double-layer devices with configurations of ITO/NPB (30 nm)/Ir(ppy)_2(CBDK) (30 nm)/Mg_(0.9)Ag_(0.1) (200 nm)/ Ag (80 nm) and ITO/Ir(ppy)_2(CBDK) (30 nm)/AlQ (30 nm)/Mg_(0.9)Ag_(0.1) (200 nm)/Ag (80 nm) 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 4.54 lm/W and which is far higher than that of Ir(ppy)_2(acac), 0.53 lm/W, the device for Ir(dfppy)_2(CBDK) achieves maximum lumen efficiency of 0.51 lm/W and which is also far higher than that of Ir(dfppy)_2(acac), 0.06 lm/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 p-diketonate was introduced, therefore the carrier transporting property was improved and the triplet-triplet annihilation was reduced.