Highly porous tungsten oxides for electrochromic applications

• Electrochromic properties of tungsten oxides.
• Hot wire deposited tungsten oxide.
• Highly porous metal oxide films.
• Higher effective surface.
• Improved time stability and cyclic durability.

The electrochromic (EC) properties of porous and highly porous tungsten oxide films deposited by heating a metallic wire in rough vacuum, without and with the injection of oxygen pulses on the filament, respectively, were investigated by proton intercalation using conventional and polymeric electrolytes. It was found that the EC properties like coloration efficiency and cyclic durability of coloration–bleaching process of the hot wire deposited tungsten oxide (HW–WO3) films strongly depend on the deposition environment and growth parameters. The highly porous films are initially very transparent (more transparent than fused silica, for example) and exhibit high coloration efficiency due to easier intercalation of the proton within their structure. These results suggest that the highly porous films obtained with the hot wire method combined with rapid injection of O2 exhibit superior EC performances than denser films deposited by conventional deposition methods.

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