AZO-coated refractory nanoneedles as ultra-black wide-angle solar absorbers

Abstract

Nanoneedles fabricated from refractory materials, such as copper cobaltate, are promising materials for solar energy conversion due to their favorable light-trapping properties at high temperatures. We demonstrate that coating these materials with a thin aluminum-doped zinc oxide (AZO) layer improves their optical properties dramatically, leading to a very low ($<1\text{\%}$) reflectance in a wide spectral range, from the ultraviolet to the near-infrared ($0.3-2$ $\mu$m). This advantageous property is present even at very large angles of incidence ($\theta =70°$), which makes this material attractive for increasing the acceptance angle of central-receiver concentrating solar power systems or as an ultra-black diffuse optical component for infrared imaging systems. Finally, the exceptionally high emissivity of this material in the near- and mid-infrared at temperatures up to 600 °C proves that its optical properties are thermally resistant and suggests that the material can be used as a high-temperature alternative to ultra-black coatings made of vertically aligned carbon nanotubes.