Synthesis and characterization of smoke-like porous sol–gel indium tin oxide coatings on glass

Abstract

A precursor for porous indium tin oxide (ITO) coatings with smoke-like surface feature was prepared from the hydrated metal [In(III)/Sn(IV)] salts and polyvinyl alcohol (PVA) solvated in a mixed aqueous-organic medium. Films were prepared by dip coating and cured at four temperatures (60 °C, 150 °C, 250 °C and 400 °C) where different surface features and morphological properties were obtained. The thickness of the films ranged from 0.5 to 1.2 μm. After the 60 °C cure, the surface showed a unique “smoke-like” feature of combustion products of PVA-ITO precursor. Increasing the cure temperature to 150 °C led to the development of In(III) and Sn(IV) moieties incorporated in crystalline PVA having the shape close to the hexagonal. Study of thermogravimetric analysis and differential thermal analysis of the material suggests that the gel to oxide transformation occurs by the removal of physisorbed water, PVA and nitrate ion followed by the condensation of hydroxide groups. Electrical parameters such as resistivity, conductivity, sheet resistance were evaluated by two- and four-point probe methods. Field emission scanning electron microscopy and transmission electron microscopy studies of the sample cured at 400 °C showed that the films were a porous network containing 5–40 nm clusters of ITO.