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

Abstract

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 O2-plasma-treated ITO (O2–ITO), and their interface dipole energies were quantitatively determined using synchrotron radiation photoemission spectroscopy. The dipole energies of both O2–ITO and IrOx–ITO were same with each other, −0.3eV, 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 0.5eV than that of O2–ITO, resulting in the decrease of the turn-on voltage via reduction of hole injection barrier.