Red phosphorescent iridium complex containing carbazole-functionalized β-diketonate for highly efficient nondoped organic light-emitting diodes

A novel red phosphorescent iridium, complex containing a carbazole-functionalized beta-diketonate, Ir(DBQ)(2)(CBDK) (bis(dibenzo[f,h]quinoxalinato-N, C-2) iridium (1-(carbazol-9-yl)-5,5-dimethylhexane-2,4-diketonate)) is designed, synthesized, and characterized. The electrophosphorescence properties of a nondoped device using the title complex as an emitter with a device configuration of indium tin oxide (ITO)/N,N'-diphenyl-N,N'-bis(1-naphthyl)-1,1'-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) (AlO; 30 nm)/ Mg0.9Ag0.1 (200 nm)/Ag (80 nm) are examined. The results show that the nondoped device achieves a maximum lumen efficiency as high as 3.49 lm W-1. To understand this excellent result observed, two reference complexes Ir(DBQ)(2)(acac), where acac is the acetyl acetonate anion, and Ir(DBQ)(2)(FBDK), [bis(dibenzo[f,h]quinoxalinato-N,C-2) iridium (1-(9-methyl-fluoren-9-yl)-6,6-dimethylheptane-3,5-diketonate)], have also been synthesized, and as emitters they were examined under the same device configuration. The maximum lumen efficiency of the former compound is found to be 0.26 lm W-1 while that for the latter is 0.37 lm W-4, suggesting that the excellent performance of Ir(DBQ)(2)(CBDK) can be attributed mainly to an improved hole-transporting property that benefits the exciton transport. In addition, a bulky diketonate group separates the emitter centers from each other, which is also important for organic light-emitting diodes.