Electronic Materials Letters , vol. 1, no. 1, pp.59-62, September, 2005

DOI :

Direct Evidence of Hole Injection Enhanced by O₂ Plasma Treatment on Indium Tin Oxide

Soo Young Kim and Jong-Lam Lee^*
Pohang University of Science and Technology (POSTECH)

Abstract : We have investigated interface dipole energies and the energy alignment between 4,4'-bis[N-(1-naphtyl)-Nphenyl-amino]biphenyl (α-NPD) and bare indium tin oxide (ITO)/O₂-plasma-treated ITO (O₂-ITO) anodes using synchrotron radiation photoemission spectroscopy (SRPES). SRPES spectra showed that the work function of O₂-ITO is 0.6 eV higher than that of ITO. After deposition of α-NPD, the dipole energy and amount of band bending were calculated to be - 0.1 and - 0.5 eV for ITO and - 0.3 and - 0.3 for O₂-ITO, respectively. It is thereupon concluded that the work function of O₂-ITO is still 0.6 eV higher than that of ITO, resulting in a decrease of the turn-on voltage via reduction of the hole injection barrier.

Keyword : organic light emitting diodes, hole injection barrier, x-ray photoemission spectroscopy, O₂ plasma