Characterization of Electrochromic Vanadium Pentoxide Thin Films Prepared By Spray Pyrolysis

Abstract

Amorphous and crystalline vanadium pentoxide (V 2 O 5 ) thin films were grown onto heated glass substrates using spray pyrolysis technique.Aqueous solution of ammonium meta-vanadat with different concentrations ranging from 0.1 to 0.5M was used.X-ray diffraction study of c-V 2 O 5 revealed polycrystalline films of orthorhombic structure with a preferred orientation (001).Voigt analysis of single reflection was used to determine crystallite size and microstrain.The refractive index n and the extinction coefficient k have been computed from the corrected transmittance and reflectance over the spectral range 300 to 2500 nm.Analysis of the absorption coefficient versus photon energy revealed allowed direct transitions with energy gap 2.34eV.The electrochromic behaviour has been investigated using three-electrode cell.Upon sodium insertion, the results showed that the changes in the optical absorption are consistent with the colour changes of the film.On applying the voltage the optical absorption in the wavelength range 500 -900 nm increases and the absorption edge shifts towards lower energies.The film colouration showed to be stable over several tens of hours claiming high colouration memory.Due to its limited optical modulation, V 2 O 5 films may be useful as a passive counter electrode in conjunction with an active working electrode in complementary electrochromic devices.