Electrochromic properties of Bi ₂O ₃ thin films deposited by RF magnetron sputtering

Bismuth oxide thin films were prepared on ITO glass substrate by radio frequency (RF) magnetron sputtering. X-ray diffraction, atomic force microscopy and X-ray photoelectron spectroscopy were employed to characterize the microstructure, surface morphology, composition and valence state of the thin films. It is indicated that the crystal structure of the thin film annealed at 350°C in air is tetragonal phase and the thin film shows a clear electrochromic change between transparent and dark brown on switching voltage between -1.8V and +3.0V. There are no other valence states (except the trivalent state) for bismuth during the process of coloration and decoloration, which is confirmed by the results of XPS analysis. The measurement of UV-Vis spectrophotometer demonstrates that the average optical modulation in the wavelength range from 400 to 800nm can reach 44%. The electrochromic efficiency at 550nm is 9.6cm /C proved by cyclic voltammetry. The results show that the Bi ₂O ₃ thin films possess well electrochromic property.