Sol–gel vanadium oxide thin films for a flexible electronically conductive polymeric substrate

Abstract

Vanadium oxide nanocrystalline films were prepared by spin-coating from vanadium (V) oxoisopropoxide sol and thermally treated at 150°C, in order to deposit them on PET–ITO substrates. The sols were made from either isopropanol or its mixture with n-butanol, both exhibiting similar rheological behaviour and a viscosity of the order of magnitude of 10−3Pas. A cross-hatch test revealed the excellent adhesion of these films on the ITO surface and delamination occurred preferentially at the ITO–plastic interface when the films were subjected to deliberate bending. The electrochemical and optical properties of the vanadium oxide films were analysed using in-situ UV–vis absorbance spectroelectrochemistry. The response was correspondingly lower than with films deposited on FTO-glass. Ex-situ IR reflection–absorption spectroscopy showed that vanadyl V–OA and superimposed bridging V–OB–V and 3V–OC bands appear at lower frequencies compared to crystalline V2O5, due to the hydrated nanocrystalline structure. An intercalation induced red-shift of the vanadyl mode and the disappearance of the superimposed V–OB–V and 3V–OC bands, but the spectrum was restored to the initial situation after deintercalation. The modulation of polaron absorption that extends from the near to mid-IR spectral region up to 2000cm−1 was not visible due to transfer of the films from electrochemical cell to the IR spectrometer. The electrochromic properties of the vanadium oxide films deposited on PET–ITO substrate were tested in a liquid electrolyte-based cell with an electrochromically active PEDOT film and 1M LiClO4/propylene carbonate electrolyte.