Effect of post annealing on DC magnetron sputtered tungsten oxide (WO3) thin films for smartwindow applications

Tungsten oxide (WO3) thin films were deposited on Fluorine Doped Tin Oxide (FTO) and Corning Glass (CG) glass substrate by DC magnetron sputtering. The annealing temperature was varied to study its effect on surface morphology, structural, electrochromic (EC), and optical properties and these are investigated by Scanning Electron Microscope (SEM), X-ray Diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, Cyclic voltammetry, and ultraviolet (UV) spectroscopy. From SEM analysis WO3 thin films annealed at 27 degrees C, 100 degrees C, 200 degrees C, and 300 degrees C were shown to crack free after that cracked film was observed for 400 degrees C. From the XRD investigation that the WO3 thin films annealed at 27 degrees C, 100 degrees C, 200 degrees C, and 300 degrees C were amorphous and crystallized at 400 degrees C. The optical band gap (Eg) of WO3 films was decreased from 2.98 eV to 2.30 eV with an increase in annealed temperature. The coloration efficiency (CE) was observed at 51.26 cm2/C at 300 degrees C and 35.06 cm2/C at 400 degrees C and the lowest diffusion coefficient was observed at 5.86 x 10-10 cm2/s at 400 degrees C. On coloring efficiency, which can be very important in electrochromic (EC) applications, post-annealing has been seen to have a strong influence.