High-efficiency endothermic energy transfer in polymeric light-emitting devices based on cyclometalated Ir complexes

We report polymeric light-emitting diodes (PLEDs) made from pinene-substituted iridium(III) phosphorescent dopants: tris(5-(4-difluoro phenyl)-10,10-dimethyl-4-aza-tricycloundeca-2,4,6-triene) iridium (III) [Ir (F-pppy)3] and tris(5-(2,4-difluorophenyl)-10,10-dimethyl-4-aza-tricycloundeca- 2,4,6-triene) iridium (III) [Ir (F2 -pppy)3]. The pinene substitution introduces steric hindrance to molecular structure of the dopant that reduces triplet-triplet annihilation between dopants and consequently enhances device performance. Via endothermic energy transfer from poly(vinylcarbazole) to Ir (F-pppy)3 and Ir (F2 -pppy)3, a peak electroluminescent efficiency of 32.8 cdA or 12.3 cdA at 12 wt % Ir (F-pppy)3 or 15 wt % Ir (F2 -pppy)3 doped and solution-processed PLEDs have been obtained. These values represent significant improvement in performance over previously reported endothermic energy-transfer based electrophosphorescent devices. © 2008 American Institute of Physics.