Compatibility of antireflective coatings on glass for solar applications with photocatalytic properties

Antireflective coatings for solar cover glasses and photocatalytic coatings for self-cleaning glasses are two types of nano-functionalized thin films, which are extensively investigated at present. Broadband antireflective coatings typically receive their function by the low refractive index of nano-porous silica (<1.4), whereas the most established photocatalytic coatings consist of high refractive index materials, such as titania (>2.0). Compatibility of these two functional materials was investigated using sol–gel dipcoating-technology. Therefore silica sol, used to prepare nano-porous antireflective coatings, was mixed with different amounts of titanium n-butoxide to achieve titania concentrations in the range from 1 to 50 wt%. The fired coatings on silica glass showed a decrease in solar transmittance and an increase in photocatalytic activity with increasing titania concentration. With respect to applications in solar energy conversion systems compatible SiO2–TiO2 materials of low titania fractions (10 wt%) were established, which combine minor loss in transmittance and exceptional high photocatalytic activity. In comparison to conventional nano-porous silica, the decrease in the solar transmittance was only 0.7%, whereas the degradation rate of stearic acid was 30 times faster.

► Bifunctional quarter-wavelength sol–gel coatings on silica glass.
► Combination of high photocatalytic activity and broadband antireflectance.
► Synthesis based on silica sol and titanium n-butoxide.