Tungsten Titanium Thin Films Electrochromic Properties

Electrochromic is the phenomenon that the optical properties of materials change stably and reversibly under the action of applied electric field.

It can cause light penetration through the electric field, changing color with the environment, and no longer need to curtain.

WO₃ thin film is one of the most promising electrochromic materials. WO₃ thin films have been widely used in photochromic, photochromic, filter, dye sensitized solar cells and so on. 

With the implantation and extraction of ions, the dissolution and ion residues of WO₃ thin films will occur, and the electrochromic properties will decline obviously, which limits the wide use of electrochromic devices. TiO₂ has excellent stability, and has excellent transmittance in wide waveband. The doping of electrochromic films with TiO₂ composite WO₃ can improve the stability and lifetime of devices. 

Pure Ti/WO₃ composite films were prepared by radio frequency sputtering method, tungsten titanium alloy with tungsten and titanium content of 5% is used as target material. Indium tin oxide (ITO) conductive glass was selected for thin film substrate. The chamber is pre evacuated to 1 x 10^–5 Pa before entering the gas. High purity argon (Ar) was used as working gas, high purity oxygen (O₂) was used as reaction gas, base pressure was 0.5 Pa, O2/Ar was 0.15, target base distance was 8 cm, sputtering power was 300 W, sputtering time was 40 min. Finally, Ti/WO₃ films were prepared by annealing for 2 hours under N₂ atmosphere.

Electrochemical testing results show that Ti doping can improve the reversibility of ion implantation / extraction and improve the cycle stability of the thin films. At the same time, the response speed and optical modulation performance of the films were also improved. The response time of the doped and bleached thin films was reduced from 9.8 and 3.5 s to 8.4 and 2.7 s, respectively. Therefore, the Ti doped WO₃ thin films had better electrochromic properties.

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