Surface composition, work function, and electrochemical characteristics of gallium-doped zinc oxide

Erin L. Ratcliff, Ajaya K. Sigdel, Mariola R. MacEch, Kenneth Nebesny, Paul A. Lee, David S. Ginley, Neal R. Armstrong, Joseph J. Berry

Research output: Contribution to journalArticle

19 Scopus citations

Abstract

Gallium-doped zinc oxide (GZO) possesses the electric conductivity, thermal stability, and earth abundance to be a promising transparent conductive oxide replacement for indium tin oxide electrodes in a number of molecular electronic devices, including organic solar cells and organic light emitting diodes. The surface chemistry of GZO is complex and dominated by the hydrolysis chemistry of ZnO, which influences the work function via charge transfer and band bending caused by adsorbates. A comprehensive characterization of the surface chemical composition and electrochemical properties of GZO electrodes is presented, using both solution and surface adsorbed redox probe molecules. The GZO surface is characterized using monochromatic X-ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy after the following pretreatments: (i) hydriodic acid etch, (ii) potassium hydroxide etch, (iii) RF oxygen plasma etching, and (iv) high-vacuum argon-ion sputtering. The O 1s spectra for the GZO electrodes have contributions from the stoichiometric oxide lattice, defects within the lattice, hydroxylated species, and carbonaceous impurities, with relative near-surface compositions varying with pretreatment. Solution etching procedures result in an increase of the work function and ionization potential of the GZO electrode, but yield different near surface Zn:Ga atomic ratios, which significantly influence charge transfer rates for a chemisorbed probe molecule. The near surface chemical composition is shown to be the dominant factor in controlling surface work function and significantly influences the rate of electron transfer to both solution and tethered probe molecules.

Original languageEnglish (US)
Pages (from-to)5652-5663
Number of pages12
JournalThin Solid Films
Volume520
Issue number17
DOIs
StatePublished - Jun 30 2012

Keywords

  • Electrochemistry
  • Gallium-doped zinc oxide
  • Photovoltaics
  • Ultraviolet photoelectron spectroscopy
  • X-ray photoelectron spectroscopy

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Surfaces and Interfaces
  • Surfaces, Coatings and Films
  • Metals and Alloys
  • Materials Chemistry

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