Optical design of Cu/Zr0.2AlN0.8/ZrN/AlN/ZrN/AlN/Al34O62N4 solar selective absorbing coatings

A novel metal-dielectric stacks coating of Cu/Zr0.2Al0.8N/ZrN/AlN/ZrN/AlN/Al34O62N4 as the solar selective absorbing coating was designed. Thin films of Zr0.2AlN0.8, ZrN, AlN and Al34O62N4 deposited by the dual ion beam assisted deposition (DIBAD) were investigated by X-ray diffraction and spectroscopic ellipsometry. XRD results indicate the deposited films of Zr0.2Al0.8N, AlN, and Al34O62N4 are poorly crystallized, whereas, the ZrN film is polycrystalline. The Drude-type dispersion model and Tauc-Lorentz dispersion model are used for determining the complex refractive indices of ZrN and Zr0.2Al0.8N, respectively. For Al34O62N4 and AlN films, Cauchy's dispersion formula is employed to determine their optical constants. A seven-layer stack with alternating ZrN and AlN layers is optimized by optical simulation programme of TFCalc. The optimized coating obtains the solar absorptance of 0.942 and the emittance of 0.12 at 100 °C.