CuS-WO3 Photochromic Film for Smart Window Applications

Among the transition metal oxides, tungsten trioxide (WO3) has attracted much attention and has been widely studied due to its many interesting structures and defect characteristics. The numerous applications of WO3 optical and electronic devices include electrochromic (EC) smart windows, flat panel displays, tunable EC photonic crystals, and gas sensors. However, its higher band gap energy (2.6-3.6 eV) limits its application. Therefore, the low frequency near infrared light (NIR) cannot be blocked.

Copper sulfide (CuS) is a cheap p-type semiconductor, earth-rich material, with low reflectivity in the visible light region and high reflectivity in the NIR region. Coupling copper sulfide on tungsten trioxide is a promising method to improve photoactivity. Therefore, CuS-WO3 film has been successfully prepared by doping copper sulphide on tungsten trioxide to enhance its photochromic properties. The preparation process is as below:

First dissolve 1 gram of Na2WO4.2H2O in 10 ml of deionized water (18.2 MΩ). A yellow precipitate was obtained by adding nitric acid dropwise and mixing to the solution. Wash the precipitate with deionized water several times, then dissolve it with 2ml H2O2, and stir for 2 hours until it becomes clear. The solution was aged with 30 ml of ethanol for 2 days, and then 1 g of polyethylene glycol (PEG; MW2000) was added to the clear solution. The CuS particles were dispersed in ethanol and sonicated for 10 minutes. The obtained precursor is coated on a clean glass plate (size 3x3cm.) by casting technology. The CuS-WO3 film is first coated with CuS, and then coated with WO3 in various molar ratios. The film is dried under various oxygen contents (0-100%) at room temperature.

In summary, WO3 photochromic was widely used in smart window applications. CuS-WO3 photochromic film for smart window applications has been successfully prepared by doping copper sulphide on tungsten trioxide to enhance its photochromic properties. CuS-WO3 photochromic film shows higher coloration than pure WO3 films because CuS-WO3 films gave high photocatalytic activity since CuS added WO3 would assist to increase photochromic efficiency.

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