Cobalt oxide selective coatings for all glass evacuated collectors

Abstract

Black cobalt deposits were formed on glass substrates for use in all glass evacuated collectors. Glass was made conducting by depositing fluorine doped tin oxide films using spray pyrolysis. The reflectivity of this glass was further improved by electroplating a thin nickel layer (0.35 μm) on it. Cobalt oxide thin films were deposited on these nickel coated conducting glass substrates using spray pyrolysis. The effect of cobalt acetate concentration in the precursor solution on the performance of these multilayer coatings was studied. Solar absorptances as high as 0.93-0.94 and thermal emittances as low as 0.09 were obtained for films deposited with lower concentrations. For films deposited with higher concentrations the selectivity significantly reduces from ˜ 33 to ˜ 3.0. Structural analysis confirms the presence of Co₃O₄.