Spectrally selective absorber coating from transition metal complex for efficient photothermal conversion

Copper–manganese oxide (CuMnOx) thin films are proposed as efficient and thermally stable selective solar absorbers. The coatings were deposited on aluminum, stainless steel, and glass substrates by dip-coating method from the alcoholic solution of the Cu and Mn nitrate. An organic filmogen was introduced in order to get better adherence with the substrate hence to get uniform films even for larger substrates. The coated films were dried and subsequently heat-treated at 500 C. X-ray diffraction spectra of the annealed film showed the formation of pure Cu–Mn oxide spinel structure (Cu1.5Mn1.5O4) in the film. FTIR spectra show complete removal of the organic species after thermal treatment at 500 C. The solar absorptance and thermal emittance were calculated from the hemispherical reflectance spectra in the UV/Vis/NIR and IR range, respectively. The maximum visible absorptance with minimizing the infrared thermal emittance was optimized by controlling the thickness of the films, choosing substrates, and introducing a SiO2 overlayer.