Deposition of multifunctional TiO2 and ZnO top-protective coatings for CSP application

•Deposition of TiO2 and ZnO thin films with homogeneous thickness and flower like morphology using ILGAR deposition technique.•Deposited thin films behave as multifunctional coating combining photocatalytic activity and transparency.•Wettability switching behavior was pointed out for both ZnO and TiO2 deposited thin films under UV radiation.•Deposited multifunctional thin films are potential top-coating candidates for CSP reflectors with self-cleaning properties.

In this work, high quality, transparent multifunctional and smart anatase TiO2 and wurtzite ZnO top protective coatings used for CSP silver-based first-surface thick glass mirrors are studied. The TiO2 and ZnO top-coatings are deposited using chemical spray pyrolysis technique which conserves a very good specular reflectance of the mirrors (94% reflectance in the Near Infrared range). The photocatalytic activity of the prepared top-coatings is evaluated using the methylene blue dye (MB) as a model molecule, and the highest activity is observed for ZnO top-coating, with a degradation efficiency of 42%. Moreover, the effect of post-annealing treatment on the photocatalytic degradation of the top-coatings is pointed out, and is explained in terms of crystallinity and surface morphology. The increase of the photocatalytic activity can be achieved by increasing surface roughness, which is a conflicting requirement with optical transparency needed for concentrated solar power (CSP) top-coating application. Furthermore, it is pointed out that TiO2 and ZnO top protective thin films exhibit a photo-induced switching of their wetting properties only after 30 min of UV exposure, and their usability as multifunctional top-protective layers for CSP application is discussed.