Effect of thin iridium oxide on the formation of interface dipole in organic light-emitting diodes

The 4,4'-bis[N-(1-naphtyl)-N-phenyl-amino]biphenyl was in situ deposited on both iridium-oxide-coated indium-tin-oxide (IrOx-ITO) and O-2-plasma-treated ITO (O-2-ITO), and their interface dipole energies were quantitatively determined using synchrotron radiation photoemission spectroscopy. The dipole energies of both O-2-ITO and IrOx-ITO were same with each other, -0.3 eV, meaning the formation of same amount of interface dipole. The secondary electron emission spectra revealed that the work function of IrOx-ITO is higher by 0.5 eV than that of O-2-ITO, resulting in the decrease of the turn-on voltage via reduction of hole injection barrier. (c) 2005 Americian Institute of Physics.