Accurate Design of Solar Selective Absorber Based on Measured Optical Constants of Nano-thin Cr Film

Solar selective absorbers have significant applications in various photothermal conversion systems. In this work, a global optimization method based on genetic algorithm was developed by directly optimizing the solar photothermal conversion efficiency of a nano-chromium (Cr) film-based solar selective absorber aiming to work at the specified working temperature and solar concentration. In consideration of the semi-transparent metal absorption layer employed in multilayered solar selective absorbers, the optical constants of ultrathin Cr film were measured by spectroscopic ellipsometer and introduced into the optimization process. The ultrathin Cr film-based solar selective absorber was successfully designed and fabricated by the magnetron sputtering method for the working temperature at 600 K and a solar concentration of 1 Sun. The measured reflectance spectra of the sample show a good agreement with the numerical simulations based on measured optical constants of ultrathin Cr film. In comparison, the simulated results by using the optical constants of bulk Cr film or literature data exhibit a large discrepancy with the experimental results. It demonstrates the significance of considering the actual optical constants for the semi-transparent metal absorption layer in the design of nano-metal film-based solar selective absorber.