title: Spectroscopy and control of near-surface defects in conductive thin film ZnO.
abstract: 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.
authors: University of Arizona, Department of Chemistry & Biochemistry, 1306 E. University Blvd., Tucson, Arizona 85721, USA.
authors: Leah L
authors: LL
authors: Kelly
authors: David A
authors: DA
authors: Racke
authors: Philip
authors: P
authors: Schulz
authors: Hong
authors: H
authors: Li
authors: Paul
authors: P
authors: Winget
authors: Hyungchul
authors: H
authors: Kim
authors: Paul
authors: P
authors: Ndione
authors: Ajaya K
authors: AK
authors: Sigdel
authors: Jean-Luc
authors: JL
authors: Brédas
authors: Joseph J
authors: JJ
authors: Berry
authors: Samuel
authors: S
authors: Graham
authors: Oliver L A
authors: OL
authors: Monti