Design optimization of SS-AlN cermet solar selective coatings

In this work, effect of the number of stainless steel-aluminum nitride (SS-AlN) cermet layers and stainless steel (SS) volume fraction in each of cermets on the optical properties of SS-AlN solar selective coatings was theoretically investigated based on the effective medium theory and optical properties of SS and ceramic AlN. Results shows that increasing the number of cermets does not improve the optical performance of solar selective coatings in terms of solar absorptance and thermal emittance at 80 °C, and the two-cermet-layer structure, one having a high metal volume fraction (HMVF) and other having a low metal volume fraction (LMVF), is the most suitable due to better optical performance and easier preparation. Theoretical results also shows that, for double SS-AlN cermets structure selective coatings, optimized LMVF and HMVF are 0.35 and 0.6, respectively, optimized thickness of cermets with LMVF and HMVF are 50 and 60 nm, respectively, and optimized thickness of AlN anti-reflection film is about 60 nm. Comparisons of reflectance of a sample deposited by a pulse magnetron sputtering coater between measured and calculated showed that theoretically predicted reflectance were highly agreed with those experimentally measured, indicating that the theoretical method used in this work can pretty predict the optical properties of SS-AlN cermet solar selective coatings.