Temperature induced thermochromism of m-BiVO4 thin films prepared by sol-gel spin coating technique

Now-a-days, thermochromic materials have gained the interest of scientific community because of their diverse applications. Bismuth vanadate (BiVO4) is a promising candidate for thermochromic application. In the present work, we report on the thermochromism of m-BiVO4 films prepared by a modified citrate-route of simple sol-gel spin coating method, for the first time. X-ray diffraction (XRD) study witnesses the formation of monoclinic structure of BiVO4 films. From the Raman study, the symmetric (Ag) and the anti-symmetric (Bg) of V-O stretching and bending modes of BiVO4 are confirmed. The highest transmittance of 95% is obtained in the near-infrared region. The Urbach energy, steepness parameter and strength of electron-phonon interactions are extracted from the optical data and correlated with other measurements. The films possess the petal-like morphology throughout the substrate. The temperature induced reversible colour change of the films (from yellow to reddish-orange) clearly demonstrates the thermochromic behaviour of BiVO4 films. This may be due to the annealing temperature induced variation in structural distortion of BiVO4 from monoclinic to tetragonal phase.