Transparent and conducting ITO thin films by spin coating of an aqueous precursor solution

Abstract

An environmentally friendly aqueous sol–gel process has been developed to fabricate thin films of indium tin oxide (ITO). A stable sol was prepared from indium nitrate and tin acetate precursors together with acetic acid and ethylene glycol. The sol transformed into an amorphous gel during heating, which decomposed and crystallized further to nano-crystalline ITO at ∼300 °C. The nano-crystalline ITO powders prepared from the precursor gel were homogeneous and single phase with particle sizes around 15 nm. The aqueous sol was applied for spin coating of ITO films on glass substrates. The deposited thin films were homogeneous and continuous with no cracks or pin-holes and exhibited very good and reproducible optical transparency and electrical conductivity, with a specific resistance of 4.59 × 10⁻³ Ω cm, thereby demonstrating the potential of this Pechini related sol–gel process. Experiments to determine the robustness of the process with respect to the concentration of the precursors and substitution of the organic components with other alcohols or acids were also performed, and some important aspects of the chemistry of the sol–gel process are addressed.