Optimization and preparation of Pt–Al2O3 double cermet as selective solar absorber coatings

Abstract

To prepare high performance Pt–Al2O3 double cermet selective solar absorber coatings, a computer simulation programme has been used to calculate the appropriate complex refractive index of the Pt–Al2O3 double cermet structure. Based on the reflectance, the factors which affect the spectral selectivity of the solar absorber surfaces such as the nature of the IR reflecting metal, and the volume fraction as well as the thickness were optimized. A series of Pt–Al2O3 cermet films with different values of volume fraction and thickness were prepared onto glass and stainless steel substrates. The reflectance spectra of all the single films were in a good agreement with the calculated spectra. The measured optical constants as well as those deduced from the fitting were used as a database to optimize the selective solar absorber coating. Based on the optimized parameters, a Pt–Al2O3 double cermet with a layer stratification consisting of Mo ∼100 nm/Pt–Al2O3 ∼ 60 nm (0.39 HMVF)/Pt–Al2O3∼ 40 nm (0.19 LMVF)/Al2O3∼ 80 nm was prepared using a sputtering system at room temperature. The reflectance of the optimized Pt–Al2O3 double selective solar absorber coatings was also consistent with the theoretical calculation, the corresponding absorptance and thermal emittance were excellent: α ∼0.97 and ε ∼0.05, respectively. Considering the literature by enlarge, such experimental results overcome almost all Al2O3 based selective solar absorber coatings realized so far.