Efficient red electrophosphorescence from a fluorene-based bipolar host material

Abstract

We have prepared efficient red organic light-emitting diodes (OLEDs) incorporating 2,7-bis(diphenylphosphoryl)-9-[4-( N, N-diphenylamino)phenyl]-9-phenylfluorene (POAPF) as the host material doped with the osmium phosphor Os(fptz) 2(PPh 2Me) 2 (fptz = 3-trifluoromethyl-5-pyridyl-1,2,4-triazole). POAPF, which possesses bipolar functionalities, can facilitate both hole- and electron-injection from the charge transport layers to provide a balanced charge flux within the emission layer. The peak electroluminescence performance of the device reached as high as 19.9% and 34.5 lm/W – the highest values reported to date for a red phosphorescent OLED. In addition, we fabricated a POAPF-based white light OLED – containing red-[doped with Os(fptz) 2(PPh 2Me) 2] and blue-emitting {doped with iridium(III) bis[(4,6-difluorophenyl)pyridinato- N, C 2′] picolinate, FIrpic} layers – that also exhibited satisfactory efficiencies (18.4% and 43.9 lm/W).