Improving selectivity of thin film solar absorber by cobalt oxide grafted reduced graphene oxide

Reduced graphene oxide (rGO) modified cobalt oxide (Co3O4) nanocomposite (NC) thin films were prepared on aluminum substrates through dip-coating technique for solar selective absorber. The prepared rGO-Co3O4 NC thin films were characterized by X-ray diffraction, which revealed that the prepared samples have face centered cubic structure. Scanning electron microscopy showed that morphology of prepared thin films is comprised of spherical shaped grains with rough surface. Energy-dispersive X-ray spectra exhibited absence of impurities in the thin films. Raman spectra predicted spinel structure, combined vibrations of tetrahedral site and octahedral oxygen motions in the rGO-Co3O4 NC thin films. Optical properties were investigated by UV–Vis–NIR reflectance spectroscopy. The prepared thin films with a concentration of 1.0 wt% of rGO (1%-rGO-Co3O4) disclosed a highest solar absorptance (α = 89.95) and low thermal emittance (ε = 4.6) with a highest solar selectivity (ξ) of 19.55. These values indicated that the rGO-Co3O4 NC thin film samples can be ideal candidates as solar selective absorbers for solar thermal energy gadgets.