Novel green synthesized Cr2O3 for selective solar absorber: Investigation of structural, morphological, chemical, and optical properties

Abstract

Cost-effective and eco-friendly Cr2O3 spectrally selective solar absorber nanocoatings prepared by an entirely green process on polished Copper (Cu) substrate is presented. The green synthesized Cr2O3 was deposited by using drop and spin coatings at rotational speeds (RS) of 600, 800, 1000, and 1200 rpm onto Cu substrate. The crystal structure of the nanocoatings investigated by XRD showed merely Eskolite Cr2O3 crystalline phase, implying no other chromium oxide phases were observed. The topological investigations using AFM showed a columnar growth with an average surface roughness of 16.7 nm and 16.3 nm for the drop coat and spin-coated at 600 rpm samples, respectively. SEM analysis revealed quasi-spherical, nanorod, and meso spherical shaped nanocoatings, corresponding to drop coat and spin coatings, respectively. XPS analysis confirmed the presence of Cr3+ 2p3/2, Cr3+ 2p1/2, and O1s, which represent Cr2O3 in all samples. Raman analysis also revealed vibrational modes corresponding to 5Eg and 1Ag symmetries in Cr2O3, which agrees with previously reported XPS results. The optical properties of the Cr2O3 nanocoatings exhibited a high solar absorptance (α) value of 0.93 and thermal emittance (ε) of 0.23 for the drop coated and spin coated at 600 rpm samples, confirming the two basic characteristics of a spectrally selective solar absorber coating. The obtained optical properties of the Cr2O3 nanocoatings can be attributed to the multiple reflections trapped by the surface morphology and intrinsic phenomena of the nanocoatings. One can observe that this cost-effective and environmentally friendly green synthesized Cr2O3 nanocoatings deposited onto Cu substrate is a potential candidate for spectrally selective solar absorber applications.