Determination of interface dipole energy at the interface of ruthenium-oxide-coated anode with organic material using synchrotron radiation photoemission spectroscopy

Abstract

4,4'-Bis[N-1-naphthyl)-N-phenylamino]biphenyl (alpha-NPD) was deposited in situ on both ruthenium oxide-coated indium-tin oxide (RuOx-ITO) and O-2-plasma-treated ITO (O-2-ITO) anodes, and their interface dipole energies were quantitatively determined using synchrotron radiation photoemission spectroscopy. The dipole energy of RuOx-ITO was lower by 0.2 eV than that of O-2-ITO even though RuOx-ITO had a higher work function. Secondary electron emission spectra after deposition of alpha-NPD on anodes revealed that the work function of RuOx-ITO is higher by 0.2 eV than that of O-2-ITO, resulting in a decrease of the turn-on voltage via reduction of hole injection barrier.