Spectral properties and microstructure of sputtered WOx films for solar conversion applications

Tungsten oxides (WOx) films have gained promising attention in terms of selective solar absorption due to its high intrinsic absorption properties. We fabricated a series of single‐layer WOx films on aluminum substrates by a magnetron sputtering system. The optical absorption properties of the film were investigated by spectrophotometer and ellipsometry. We found that the optical properties of the film were very sensitive to the change of the thickness. The result showed the highest α value can reach up 0.82 with the thickness of 26 nm at 0.6 Pa or 70 nm at 1.5 Pa, and both ε values was around 0.05, indicating the high spectral selectivity properties. The different reflectance evolutions presented a wide range of color appearances, such as yellow, reddish, cyan, and blue. Moreover, the surface morphologies and phase structures of single‐layer WOx films were investigated by SEM, XRD, and Raman. A WOx/SiO2 solar selective absorber coating indicated that the as‐obtained WOx film was a promising application in solar‐thermal conversion.