Simplified phosphorescent organic light-emitting devices using heavy doping with an Ir complex as an emitter

Simplified phosphorescent light-emitting devices with the structure ITO/MoO₃ (3 nm)/4,4′-bis(9H-carbazol-9-yl)biphenyl (CBP): x wt% tris(2-phenylpyridine)iridium(iii) [Ir(ppy)₃] (30 nm)/3-(biphenyl-4-yl)-4-phenyl-5-(4-tert-butylphenyl)-4H-1,2,4-triazole (50 nm)/LiF (1 nm)/Al (100 nm) are demonstrated. The optimized organic light-emitting diode with CBP: 25 wt% Ir(ppy)₃ as a light-emitting layer showed a peak current efficiency of 46.8 cd A^-1, which is 1.64 times that of the reference device with the structure ITO/N,N′'-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (30 nm)/CBP: 8 wt% Ir(ppy)₃ (30 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (10 nm)/(4,7-diphenyl-1,10-phenanthroline) (40 nm)/LiF (1 nm)/Al (100 nm). The improvement in efficiency is attributed to the charge-trapping effect of the heavy doping of Ir(ppy)₃ and the excellent hole-transporting ability of the CBP layer doped with Ir(ppy)₃. When we incorporated bis(4,6-difluorophenyl-pyridine)(picolinate)iridium(iii) into the CBP: 25 wt% Ir(ppy)₃ layer, the device showed a higher efficiency of 71.2 cd A^-1, which is superior to that of previously reported simplified organic light-emitting diodes.