Single layer WOx films for efficient solar selective absorber

Abstract

Multilayer solar absorber coatings (SSACs) with the gradient optical constant have been widely used for solar thermal harvesting due to their high photothermal conversion efficiency, which involved the multilayer interference stacks and metal-dielectric composites. This complicated multilayer structure severely limited a low-cost and large-scale industrial production. Here, it can be found that a single layer non-stoichiometric WOx film exhibits excellent solar selectivity (solar absorptance of 0.84 and thermal emittance of 0.053). With the aid of a SiO2 anti-reflective layer, the absorptance is significantly raised to 0.92, and the emittance remains unchanged. The spectral selectivity is on par with those of multilayer SSACs. A thermal annealing result indicated that the as-fabricated SSACs possessed outstanding thermal stabilities reaching up 400 °C in vacuum. The simple, low cost and high performance WOx films are promising candidate for efficient solar selective absorber. Keywords: Selective solar absorption, Non-stoichiometric WOx film, Intrinsic selectivity, Thermal annealing