Preparation and properties of transparent conductive indium-tin-oxide/polyimide substrates via a sol-gel process

High temperature, flexible and colorless indium-tin-oxide (ITO) coated plastic substrates have been prepared from a series of thermally stable, high glass transition temperature (T_g) and colorless copolyimide films. The copolyimides were synthesized from 3,3′-diaminodiphenylsulfone, 9,9′-bis(4-aminophenyl) fluorene and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride monomers. Their T_gs were around 285-365 °C. The conductive ITO was synthesized by a sol-gel method, and then deposited onto the copolyimide films by a spin coating process. After thermal treatment at 300 °C under a nitrogen/hydrogen mixture gas for 24 h, the resistivity of the ITO film was 10⁻³ Ω cm, and its transmittance was 75% at the visible light region. Scanning electron microscopy and X-ray diffraction were used to observe the surface and morphology of the ITO films. UV-visible spectroscopy and the four-probe method were used to study their optical and electrical properties. The high performance ITO/plastic substrates can be used in the next generation flexible flat panel displays and solar cell.