Electrochromism in sputtered V2O5 thin films: structural and optical studies

Abstract Vanadium pentoxide thin films were successfully fabricated on indium–tin–oxide-coated glasses by r.f. sputtering in an Ar/O 2 gas mixture. The films gave excellent cyclic voltammograms with a two-step electrochromism, yellow to green, and then green to blue. The effect of the Li + concentration in the electrolyte on the voltammogram cycles was also studied. The thin films were characterized before and after coloration by X-ray diffraction. No significant changes in the crystallographic structure occurred after coloration. The optical properties of films colored at three different potentials were measured in the UV-vis near infra-red (NIR) wavelength range. The results showed that the changes in the optical absorption are consistent with the color changes of the films. In particular, when the potential increased the optical absorption decreased in the wavelength range 500–900 nm, and the optical absorption edge shifted towards lower energies. The optical density of each colored film was monitored continuously when the circuit was opened after coloration for 15 min. The green, yellow and blue colors were relatively stable for several tens of hours.