Linking optical properties and nanostructure of NiCrOx Cermet nanocomposite for solar thermal application

Conversion of solar energy into thermal energy helps reducing consumption of non-renewable energies. Cermets (ceramic-metal composites) are versatile materials suitable, amongst other applications, for solar selective absorbers. The presence of metallic Ni nanoparticles (NPs) in the dielectric matrix is a prerequisite for efficient solar selective absorption in NiCrOx cermets (Zhao and Wackelgard, Solar Energy Mater Solar Cells 90:1861–1874, 2006). By combining comprehensive chemical and structural analyses, but also electronic microscopy, we revealed the origin of the remarkable optical properties of this cermet material. A solar absorber multilayer stack on aluminium substrate using a sputtered NiCrOx layers allows us to achieve solar absorptance as high as α = 96:1% while keeping thermal emissivity as low as ϵ = 2:2% both values are comparable to best values recorded so far (Buhrman, Physics of solar selective surfaces. In: Ber (ed) Advances in solar energy. Springer, New York, pp 207–282, 1986). Determining the origin of sputtered NiCrOx cermets optical properties drives further optimization of solar absorbers.