High absorptance and low emittance AR-coated Ni-Al₂O₃solar absorbers

Ni-Al₂O₃films of various compositions have been deposited by planar magnetron-assisted RF sputtering. The cermet films were deposited by sputtering Ni-Al₂O₃targets containing 32.5 wt.% and 61.6 wt.% nickel. To increase the wt.% of nickel above 61.6, additional nickel pellets distributed uniformly on the target were co-sputtered along with the target containing 61.6 wt.% nickel. The increase in wt.% depends ipon the number of nickel pellets. Al₂O₃and SiO₂have been used as AR coatings and have been found to give similar results. Al₂O₃was sputter deposited from a powder target and SiO₂was sputter deposited from a hot pressed target. The composition of nickel in the cermet films was found out by the EDAX technique. ESCA was used to analyse the nature of nickel and aluminium oxide. A molybdenum or nickel backing layer was used as a high reflecting coating. A 650 AA cermet film containing 0.61 volume fraction of nickel and AR coated with 780 AA Al₂O₃or SiO₂on a nickel-backed glass substrate gives an absorptance of 0.94 (AM 1.5 solar spectrum) and an emittance of 0.07 (at 100 degrees C).