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Title: Surface Composition, Work Function, and Electrochemical Characteristics of Gallium-Doped Zinc Oxide

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.more » 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.« less

Authors:
; ; ; ; ; ; ;
Publication Date:
Research Org.:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org.:
USDOE Office of Energy Efficiency and Renewable Energy Solar Energy Technologies Program
OSTI Identifier:
1047969
DOE Contract Number:  
AC36-08GO28308
Resource Type:
Journal Article
Journal Name:
Thin Solid Films
Additional Journal Information:
Journal Volume: 520; Journal Issue: 17; Journal ID: ISSN 0040-6090
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; CHEMICAL COMPOSITION; CHEMISTRY; ELECTRIC CONDUCTIVITY; ELECTROCHEMISTRY; ELECTRODES; ELECTRON TRANSFER; ETCHING; HYDRIODIC ACID; HYDROLYSIS; IMPURITIES; INDIUM; IONIZATION POTENTIAL; LIGHT EMITTING DIODES; ORGANIC SOLAR CELLS; OXIDES; OXYGEN; PHOTOELECTRON SPECTROSCOPY; PLASMA; POTASSIUM HYDROXIDES; SPECTRA; SPUTTERING; TIN OXIDES; WORK FUNCTIONS; X-RAY PHOTOELECTRON SPECTROSCOPY; ZINC OXIDES; Solar Energy - Photovoltaics

Citation Formats

Ratcliff, E. L., Sigdel, A. K., Macech, M. R., Nebesny, K., Lee, P. A., Ginley, D. S., Armstrong, N. R., and Berry, J. J. Surface Composition, Work Function, and Electrochemical Characteristics of Gallium-Doped Zinc Oxide. United States: N. p., 2012. Web. doi:10.1016/j.tsf.2012.04.038.
Ratcliff, E. L., Sigdel, A. K., Macech, M. R., Nebesny, K., Lee, P. A., Ginley, D. S., Armstrong, N. R., & Berry, J. J. Surface Composition, Work Function, and Electrochemical Characteristics of Gallium-Doped Zinc Oxide. United States. doi:10.1016/j.tsf.2012.04.038.
Ratcliff, E. L., Sigdel, A. K., Macech, M. R., Nebesny, K., Lee, P. A., Ginley, D. S., Armstrong, N. R., and Berry, J. J. Sat . "Surface Composition, Work Function, and Electrochemical Characteristics of Gallium-Doped Zinc Oxide". United States. doi:10.1016/j.tsf.2012.04.038.
@article{osti_1047969,
title = {Surface Composition, Work Function, and Electrochemical Characteristics of Gallium-Doped Zinc Oxide},
author = {Ratcliff, E. L. and Sigdel, A. K. and Macech, M. R. and Nebesny, K. and Lee, P. A. and Ginley, D. S. and Armstrong, N. R. and Berry, J. J.},
abstractNote = {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.},
doi = {10.1016/j.tsf.2012.04.038},
journal = {Thin Solid Films},
issn = {0040-6090},
number = 17,
volume = 520,
place = {United States},
year = {2012},
month = {6}
}