CuO thin films made of nanofibers for solar selective absorber applications

•Thin films of CuO nanofibers on Cu plates are prepared through a simple method.•CuO morphology is controlled by the pH of the reaction medium.•The CuO nanostructures are pure and single phase nature.•They exhibit high UV–vis absorbance as well as high IR reflectance.•The prepared CuO thin films exhibit good solar selectivity values of >13. CuO thin films made of one dimensional (1D) nanostructures, such as, nanofibers and nanoneedles, are prepared through a facile chemical oxidation of copper (Cu) substrate at different pH conditions maintained by changing the concentration of sodium hydroxide (NaOH) in the reaction medium. The effect of pH on the formation of different CuO nanostructures is examined by analyzing their surface morphology, crystalline nature and chemical composition. The optical properties of the CuO thin films are studied through UV–vis and IR reflectance measurements. The X-ray diffraction (XRD) study indicates that the formed CuO nanostructures are highly crystalline and of single phase in nature. All the thin film samples made of 1D CuO nanostructures have good solar-selectivity (>10) with low thermal emittance (95%). The CuO thin films possess high solar-selectivity value of 13.8 and thus could be suitable for selective absorber in solar collectors for thermal energy conversion.