Tantalum Doped Tungsten Oxide Thin Films Electrochromic Properties

Tungsten trioxide is a n type semiconductor material, it is the most widely studied photochromic materials, WO3 has excellent electrochromic properties, however, WOX can be dissolved in proton electrolyte, which limits its application in electrolyte for proton conduction layer in electrochromic devices.

The nano composite oxide electrochromic material can improve the stability of the device, shorten the response time and prolong the life of the device. Ta₂O₅ has excellent ionic and proton conductivity, and it has excellent transparency in a wide wavelength range, and has good thermal stability, mechanical stability and chemical stability. Therefore, the combination of Ta₂O₅ and WO₃ can combine the advantages of the two materials to achieve higher mechanical and chemical compatibility, thereby improving the stability and life of the device.

Use metal tungsten target and ceramic Ta₂O₅ as targets. Prepare Ta doped tungsten oxide thin films by double target co sputtering method. Sputter metal tungsten target with direct current power supply. Sputter tantalic oxide by r-f power supply. The substrate is indium tin oxide (ITO) conductive glass and silicon wafer. Before entering the gas, the deposition chamber is pre pumped to below 3 * 10-4Pa, then high purity argon (Ar) is used as the working gas, high purity oxygen (O₂) is used as the reaction gas, and sputter for 20min at room temperature. When the experimental parameters are basically stable, the baffle is opened by the sputtering coating. The Ta doped tungsten oxide thin films with 5%, 10%, 15%, 25% and 35% contents were prepared by adjusting the gas flow rate, sputtering power and sputtering time.

The analysis of XRD and SEM shows that the pure tungsten oxide films deposited at room temperature are amorphous films. The surface of the film is smooth, and the texture is homogeneous and porous. The Ta doped tungsten oxide films are also amorphous. When the amount of tantalum doping is within a certain range, the surface of the film is smooth and uniform. With the increase of the amount of doping, the larger particles are inlaid inside the film. These particles are more compact, which destroys the porosity and uniformity of the film. When the amount of doping reaches 35%, there are even micron grade particles on the surface of the film.

Research shows that Ta doping has obvious effect on improving tungsten oxide thin film electrochromic properties, cyclic stability and acid corrosion resistance, but the doping amount must be controlled within a certain range, the best range is below 15%, if more than that the excessive doping film will crack.

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