Red phosphorescent polymer light-emitting diodes based on iridium complex and poly[(9,9-dioctylfluorene)-alt-(pyridine)]

Red phosphorescent polymer light-emitting diodes based on bis(2-'(2'-pyridyl)benzo[blthiophene-N,C-3)iridium(III)-acetylacetonate [btp(2)Ir(acac)] and poly [(9,9-dioctylfluorene)-alt-(pyridine)] (PF8-Py) have been investigated. The btp(2)Ir(acac):PF8-Py blend device emitted a rich red phosphorescence from the btP(2)Ir(acac) complex. This is due to the effective energy transfer from the PF8-Py copolymer to btp(2)Ir(acac) enhanced by the pyridine unit in the copolymer. By the addition of a hole transporting material, i.e., N,N'-bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD), to the btp(2)Ir(acac): PF8-Py blend, the driving voltage of the device was dramatically lowered and luminance and efficiency were greatly increased. Device performance can be further improved by introducing a hole transporting layer (HTL). The multilayer device, with a poly[(9,9-dioctylfluorene)-alt-(triphenylamine)] (PF8-TPA) layer as a hole transporting layer, showed a maximum luminance of 2600 cd/m(2), a maximum efficiency of 3.78 cd/A and a maximum external quantum efficiency of 4.92%. These are supposed to be obtained by having a good carrier balance in an emitting layer, an effective energy transfer from PF8-Py to the btp(2)Ir(acac) complex, and a highly-efficient triplet emitter.