Determination of frontier orbital alignment and band bending at an organic semiconductor heterointerface by combined x-ray and ultraviolet photoemission measurements

R. Schlaf, B. A. Parkinson, P. A. Lee, K. W. Nebesny, N. R. Armstrong

Research output: Contribution to journalArticle

66 Scopus citations

Abstract

The alignment of the highest occupied molecular orbitals (HOMO) at the tris (8-hydroxy quinoline) aluminum (Alq3)/N,N-di-(3-methylphenyl)-N,N diphenyl-4,4-diaminobiphenyl (TPD) heterojunction, used in organic light-emitting diodes (OLED), was determined by growing a TPD layer in several steps on a thick Alq3 substrate layer. After each growth step the sample was characterized in situ by x-ray and ultraviolet photoemission spectroscopy. The offset of the HOMO maxima at the interface was determined to be -0.13 eV from Alq3 to TPD. By including the known HOMO-lowest occupied molecular orbital (LUMO) gaps for both molecules into the evaluation, the offset of the LUMO minima was determined to be -0.33 eV from Alq3 to TPD. These values are consistent with previous assumptions that this interface represents a higher barrier for electron injection from Alq3 to TPD than for hole injection from TPD to Alq3.

Original languageEnglish (US)
Pages (from-to)1026-1028
Number of pages3
JournalApplied Physics Letters
Volume73
Issue number8
DOIs
StatePublished - Dec 1 1998

ASJC Scopus subject areas

  • Physics and Astronomy (miscellaneous)

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