Angular solar absorptance and thermal stability of W/WAlN/WAlON/Al2O3-based solar selective absorber coating

In this paper, we report the solar absorptance property of a new tandem absorber consisting of layers W/WAlN/WAlON/Al2O3 that holds promise for solar thermal energy harvesting. The coating was prepared by DC/RF magnetron sputtering on stainless steel substrate. The performance of the film was investigated by measuring the reflectance spectra in the wavelength range of 250-2500 nm and most importantly by varying the incident angle from 18° to 68°. The effect of thermal annealing on the optical properties, microstructure and morphology of the solar selective absorber coating was also explored. The thermal annealing of the coating at 350 °C till 550 h in air did not result in any significant change in the spectral properties of the absorber coating. The excellent thermal stability and wide range of angular absorptance of this multilayer coating indicate the potential for application as selective coating in mid temperature photothermal conversion systems.