Charge Carrier Transport in Neat Thin Films of Phosphorescent Iridium Complexes

The charge carrier transport properties of neat thin films of red-, green- and blue-phosphorescence Ir complexes have been investigated in terms of time-of-flight transient photocurrent measurement. Bis(2-(2'-benzo[4,5-a]thienyl)pyridinato-N,C 3')iridium(acetylacetonate) (btp2Ir(acac)) (red-phosphorescence emitter) and iridium(III) bis[(4,6-di-fluorophenyl)-pyridinato-N,C 2']picolinate (FIrpic) (blue-phosphorescence emitter) thin films exhibit bipolar charge transport. In contrast, the electron and hole transit signals of fac-tris(2-phenylpyridine)iridium(III) (Ir(ppy)3) (green-phosphorescence emitter) thin films are unobservable. The charge carrier transport properties of thin films of an Ir-complex-doped 4,4'-N,N'-dicarbazole-biphenyl (CBP) and the appropriateness of FIrpic as a triplet-exciton and hole blocking layer are shown.