Charge carrier transport in an emissive layer of green electrophosphorescent devices

Charge carrier generation and transport in fac tris (2-phenylpyridine) iridium (III) (Ir(ppy)(3)) doped in 4,4(')-N,N-'-dicarbazole-biphenel (CBP) thin films have been studied in terms of time-of-flight and time-resolved photoluminescence spectroscopies. It is found that the excitation energy rapidly transfer from CBP to Ir(ppy)(3), and that the charge carriers are generated on Ir(ppy)(3) sites. With increasing Ir(ppy)(3) concentration, the electron drift mobility is slightly decreased, while the hole transit signals become unobservable. The electron and hole transport properties of Ir(ppy)(3) doped CBP thin films result from the energy levels of the lowest unoccupied molecular orbital and the highest occupied molecular orbital of Ir(ppy)(3) with respect to those of CBP. (C) 2004 American Institute of Physics.