Quasicrystal films: numerical optimization as a solar selective absorber

Abstract

Selective absorbers for solar thermal energy applications have to show high solar absorptance α s and low thermal emittance ϵ h. Stability against oxidation and diffusion is indispensable, especially at high absorber temperatures. The new class of quasicrystalline materials seems to have favourable properties regarding stability. With a genetic algorithm a thin film stack based on dielectric and quasicrystal films was optimized as a selective absorber. A sandwich system dielectric/quasicrystal/dielectric on copper has highly selective properties: α s = 0.86 and ϵ h (400 ° C) = 0.051. Even better results can be achieved, at least in theory, by the use of a cermet. The optical constants of cermets with the quasicrystalline material as the metal were calculated with the Bruggeman theory. A system of a cermet film and an additional antireflective coating on copper shows α s = 0.92 and ϵ h (400 ° C) = 0.048.