Single-step fabrication of a large-scale broadband sunlight absorber based on multiple directional grating structures

Broadband light absorbers have attracted great interest worldwide due to their high efficiency in converting light into heat. However, most absorbers show strong light absorption only in the visible spectrum, and their performance typically declines sharply in the near-infrared region. This work developed a large-scale broadband absorber by sputtering a gold (Au) layer onto a mulberry leaf with submicron parallel grating structures. It was found that the grating structures in the mulberry leaf consisted of many grating domains with different axes, making this grating structure distinct from those previously reported. The 10–20 nm thick Au-coated mulberry leaf absorbed more than 90% of incident light in the wavelength range of 300–700 nm and maintained a high absorption efficiency (75%) in the wavelength range up to 2500 nm. Numerical simulations using the finite-difference time-domain (FDTD) method, including calculations of the absorption spectrum and electric fields, indicated that Au-coated multidirectional grating structures, such as the naturally occurring anisotropic grating structures found on mulberry leaves, exhibit higher light absorption than conventional coaxial grating structures. Based on these findings, artificial anisotropic grating structures inspired by mulberry leaves will be fabricated and explored for future applications such as broadband absorbance substrates.