Preparation of selective absorbers based on CuMn spinels by dip-coating method

CuMn-spinel thin films were prepared on aluminum substrates by the so-called dip-coating method. The layers were deposited from alcoholic solutions based on nitrate precursors and subsequently sintered in air at 500°C. Reflectance spectra in the NIR–vis–UV interval were measured for samples with different composition and thickness. The absorber quality of the films was checked by calculating the solar absorptance. The films displaying the best reflectance spectra and the highest solar absorptances (αs>0.87) were deposited from solutions containing molar ratio Cu/Mn=1. The analysis of composition showed that Cu/Mn ratio in the film was very close to the ratio in the dip-in solution and supported the formation of a spinel-like material of stoichiometry Cu1.5Mn1.5O4. Solar absorptance was dramatically improved when a SiO2 antireflective layer was deposited onto the spinel. By optimizing film thickness of both CuMn-spinel and SiO2 layers optical parameter values as good as αs=0.94 and eT(100)=0.06 were achieved.