Spectroscopy and Control of Near-Surface Defects in Conductive Thin Film ZnO

Leah L. Kelly, David A. Racke, Philip Schulz, Hong Li, Paul Winget, Hyungchul Kim, Paul Ndione, Ajaya K. Sigdel, Jean Luc Brédas, Joseph J. Berry, Samuel Graham, Oliver L.A. Monti

Research output: Contribution to journalArticlepeer-review

17 Scopus Citations


The electronic structure of inorganic semiconductor interfaces functionalized with extended π-conjugated organic molecules can be strongly influenced by localized gap states or point defects, often present at low concentrations and hard to identify spectroscopically. At the same time, in transparent conductive oxides such as ZnO, the presence of these gap states conveys the desirable high conductivity necessary for function as electron-selective interlayer or electron collection electrode in organic optoelectronic devices. Here, we report on the direct spectroscopic detection of a donor state within the band gap of highly conductive zinc oxide by two-photon photoemission spectroscopy. We show that adsorption of the prototypical organic acceptor C60 quenches this state by ground-state charge transfer, with immediate consequences on the interfacial energy level alignment. Comparison with computational results suggests the identity of the gap state as a near-surface-confined oxygen vacancy.

Original languageAmerican English
Article numberArticle No. 094007
Number of pages9
JournalJournal of Physics Condensed Matter
Issue number9
StatePublished - 12 Feb 2016

Bibliographical note

Publisher Copyright:
© 2016 IOP Publishing Ltd.

NREL Publication Number

  • NREL/JA-5K00-66154


  • gap state
  • hybrid organic/inorganic interface
  • two-photon photoemission
  • ZnO


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