Download Electrochemical Reduction of Indium Tin Oxide (ITO)

Electrochemical Reduction of Indium Tin Oxide (ITO): to
Prevent and to Use
Liang Liu1,2, Shai Yellinek1, Ido Valdinger1, Daniel Mandler1,*
Institute of Chemistry, The Hebrew University of Jerusalem, Jerusalem 91904, Israel
2
School of Materials Science and Engineering, Nanyang Technological University,
Singapore 639798, Singapore
Email: [email protected]
1
Indium tin oxide (ITO) is widely applied as a transparent conductive electrode material.
One main issue in the applications of ITO is its stability. Specifically, it is known that
ITO undergoes electrochemical reduction at cathodic potentials, leading to the
irreversible deterioration of its conductivity and transparency. In this work, we
systematically investigated the influence of different solution parameters such as pH,
ions and their concentration on the electrochemical reduction behaviour of ITO. The
visible light absorbance of ITO at 326 nm was used as a measure of the reduction, and
the reduced ITO samples were characterized by SEM, XRD and XPS. We observed
that the onset potential and kinetics for the reduction of ITO is sensitive to the pH and
anions of the solution. The reduction of ITO is favoured at low pH, because protons are
involved in the reduction process. NO3- ions are found to significantly inhibit the
reduction of ITO, although the reason is still unclear. The potential at which ITO
starts irreversible reduction (turns dark) varies between -0.85 V and -1.6 V (vs.
Ag/AgCl) depending on the solution conditions. The results suggest that researchers
should be extremely cautious when applying cathodic potential on ITO and
referring the reduction potential to literature. Moreover, we turned the
“negative” results into useful applications. The electrochemically reduced ITO
shows non-linear optical properties, and the performance can be tuned by
deposition conditions such as potential and time. The optimized sample shows 20%
transmittance (50% of the initial value) with the input fluence of 1 J/cm2 (incite light
532 nm). The reduced ITO has good adhesion to the glass substrate, suggesting that it
may have potential applications in non-linear optics.
ise140135