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A promising novel solution-chemistry method to fabricate spectrally selective solar absorber coatings has been investigated. The selectively absorbing film consists of nickel nano-particles embedded in a dielectric matrix of alumina. Ejecting a precursor solution of nickel and aluminum onto an aluminum substrate using a spin-coating technique followed by a heat-treatment, generated the solar absorber samples. Smooth and homogeneous films with a nickel content of 0 to 80 vol.% were produced. The optimal coating had a nickel content of 65%, a thickness of 0.1 μm and a particle size of ∼10 nm. The absorbing layer attained a normal solar absorptance, αsol, of 0.83 and a normal thermal emittance, εtherm, of 0.03. Adding an anti-reflection layer on top of the first absorbing layer further enhanced the performance of the absorber. The optimum anti-reflection coated sample reached a solar absorptance of 0.93 and a thermal emittance of 0.04.

A previously studied solution chemically derived two layer absorber has been improved by adding a third layer. Simulations done with a thin film program showed that the optimized three layer selective absorber should be composed of an 80% nickel-20% alumina film of 100 nm at the base, a 40% nickel-60% alumina film of 60 nm in the middle and finally a 100% silica film of 85 nm at the top. Experimental results confirmed the computer simulated three layer structure. Prepared absorber consisting of the theoretically found optimized layer structure achieved a solar absorptance, alpha(sol), of 0.97 and a thermal emittance, epsilon(therm), of 0.05.

Thin film materials for the use in solar thermal absorbers have been investigated using time-of-flight energy elastic recoil detection analysis (ERDA). The ERDA measurements proved to be very efficient in detecting the elemental depth composition of a selective solar absorber. The three-layer absorber is composed of an 80% nickel-20% alumina film at the base, a 40% nickel-60% alumina layer in the middle and finally an AR film of silica or hybrid-silica film at the top. The difference between solution volume percent and actual volume percent could be investigated when studying individual nickel-alumina films with varying ratios coated on glass substrates. The result showed that there was a maximum difference of 3% between the calculated solution volume percent and the actual volume percentages in the solid films. The ERDA measurements also indicate that about 15% of the nickel found in the nickel-alumina composite films is bound in the form of NiO.