Red Phosphorescent Polymer Light-Emitting Diodes Based on Iridium Complex and Poly[(9,9-dioctylfluorene)-alt-(pyridine)]

概要

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Red phosphorescent polymer light-emitting diodes based on bis(2-(2$'$-pyridyl)benzo[$b$]thiophene-N,C3)iridium(III)acetylacetonate [btp2Ir(acac)] and poly[(9,9-dioctylfluorene)-alt-(pyridine)] (PF8-Py) have been investigated. The btp2Ir(acac):PF8-Py blend device emitted a rich red phosphorescence from the btp2Ir(acac) complex. This is due to the effective energy transfer from the PF8-Py copolymer to btp2Ir(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 btp2Ir(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/m2, 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 btp2Ir(acac) complex, and a highly-efficient triplet emitter.
2006-06-15