Electronic structures of organic molecular materials for organic electroluminescent devices studied by ultraviolet photoemission spectroscopy

Kiyoshi Sugiyama, Daisuke Yoshimura, Takayuki Miyamae, Takafumi Miyazaki, Hisao Ishii, Yukio Ouchi, Kazuhiko Seki

Research output: Contribution to journalArticle

134 Citations (Scopus)

Abstract

Electronic structures of evaporated films of five organic light-emitting and carrier-injecting materials for organic electroluminescent devices were studied by ultraviolet photoemission spectroscopy. The compounds examined were (i) light-emitting materials tris(8-hydroxyquinolino) aluminum (Alq3) and 1,2,3,4,5-pentaphenylcyclopentadiene, (ii) a hole-injecting material N,N′ -bis(3-methylphenyl)-N ,N′ -diphenyl-[1,1′ -biphenyl]-4,4′ -diamine, and (iii) electron-injecting materials N,N′ -diphenyl-1,4,5,8-naphthyletracarboxyldiimide and 1,3,5-tris(5-phenyl-1,3,4-oxadiazol-2-yl)benzene. The spectral features corresponding to the top parts of the valence states, which dominate the electric properties of the materials, were assigned by the comparison with the simulated density of states obtained from PM3 molecular orbital calculations. Using these calculations, the evolution of the electronic structure of each molecule from those of constituent parts was discussed. The characters of the unoccupied states obtained by these calculations were also presented. Using these data, the correlation between the ionization threshold energies determined by ultraviolet photoemission spectroscopy and the carrier-injecting and light-emitting properties were discussed.

Original languageEnglish
Pages (from-to)4928-4938
Number of pages11
JournalJournal of Applied Physics
Volume83
Issue number9
DOIs
Publication statusPublished - May 1 1998
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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