Spectrally selective CuS solar absorber coatings on stainless steel and aluminum

CuS and ZrO2/CuS thin films have been deposited at 200 °C in ambient atmosphere by spray pyrolysis onto stainless steel S304 and aluminum AA1050 sheets in order to be used as prospective solar absorbers for thermal energy harvesting. Zirconia has been deposited as a top layer working as an antireflection coating increasing the solar absorption and protecting the underlying copper sulfide layer, which works as the solar light absorbing material. Solar selectivity of the samples was evaluated measuring the total hemispherical reflectivity in the ultraviolet-visible infrared range and calculating solar absorptance and thermal emittance. The solar selectivity was optimized by tuning the film thickness of the coating stack. X-ray diffraction, SEM and X-ray photoelectron spectroscopy analyses have been used to proof crystal phase, coverage, film thickness, and surface contamination of optimized samples, revealing that the copper sulfide film is CuS covellite and the optimized film thicknesses are in the range of 50 nm for the ZrO2 top layer and 140 nm for the CuS layer. Copyright © 2016 John Wiley & Sons, Ltd.