A high performance smart window which controls light and heat is investigated and developed for low energy and low environmental load. It is well known that the glass with an electrochromic material of tungsten oxide (WO3) controls its transmittance by changing its color because of the reversible intercalation and deintercalation of ions in the crystal structure of WO3. However, the absorption-type smart window discharges radiant heat into the room.
Recently, we have developed and demonstrated the all-solid-state switchable mirror as a new smart window. The device changes its optical property reversibly from a transparent state to a reflective one as a result of hydrogenation and dehydrogenation of the films by applying voltage. The heat can be effectively controlled because the reflective state can reflect the light almost completely, and radiant heat can not be discharged into the room. Our reflection-type device had the multi-layer structure of Mg-Ni/Pd/Ta2O5/WO3/ITO/glass. Each material of Mg-Ni, Pd, Ta2O5 and WO3 in the device plays optical switching, proton injector, solid electrolyte and ion storage, respectively. It is one of the key technologies to develop high performance solid electrolyte thin film for fast switching speed and high durability of the device.
In this work, we focused on the reactive DC magnetron sputtering to deposit solid electrolyte of Ta2O5 thin film. The effect of deposition conditions on electrical and proton conductivities of Ta2O5 thin film was investigated. The transmittance at wavelength of 670 nm of the device with Ta2O5 thin film which has high proton conductivity was changed from 0.1% (reflective state) to 46% (transparent state) within 10 s by applying voltage. The device showed the durability over 2000 switching cycles.
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