Amorphous and crystalline vanadium pentoxide (V2O5) 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-V2O5 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, V2O5 films may be useful as a
passive counter electrode in conjunction with an active working electrode in
complementary electrochromic devices.