Electronic structure of 8-hydroxyquinoline aluminum (Alq3) / metal interfaces studied by UV photoemission

H. Ishii, D. Yoshimura, K. Sugiyama, S. Narioka, Y. Hamatani, I. Kawamoto, T. Miyazaki, Y. Ouchi, K. Seki

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Abstract

The electronic structures of tris(8-hydroxyquinoline) aluminum (Alq3) / metal (Au, Al) interfaces as a model interface of organic electroluminescent (EL) devices were investigated by ultraviolet photoemission spectroscopy (UPS). We found abrupt shifts of the vacuum level of ca. 1 eV at the interfaces in contrast to the traditional assumption with a common vacuum level at the interface. The shift indicates the formation of interfacial dipole with the metal side negatively charged. At Alq3 / Al interface, the estimated energy position of the lowest unoccupied molecular orbital (LUMO) was very close to the Fermi level of the substrate metal, corresponding to the electron-injecting nature of the interface. This is in contrast to the poor electron-injecting character expected by assuming a common vacuum level where Fermi level of the substrate should be around the center of the gap. The electronic structure of Alq3 as a solid is also discussed in comparison with the results by semi-empirical molecular orbital calculation.

Original languageEnglish
Pages (from-to)1389-1390
Number of pages2
JournalSynthetic Metals
Volume85
Issue number1-3
Publication statusPublished - Mar 15 1997
Externally publishedYes

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Keywords

  • Organic semiconductors based on conjugated molecules
  • Organic/inorganic interface
  • Photoelectron spectroscopy

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry

Cite this

Ishii, H., Yoshimura, D., Sugiyama, K., Narioka, S., Hamatani, Y., Kawamoto, I., Miyazaki, T., Ouchi, Y., & Seki, K. (1997). Electronic structure of 8-hydroxyquinoline aluminum (Alq3) / metal interfaces studied by UV photoemission. Synthetic Metals, 85(1-3), 1389-1390.