a Schematic representation of the 3D SGM absorber, characterized by the structural parameters: the depth (d) of trenches, the thickness (t) of the graphene metamaterial layer, the width (w) of the hole, and the period (p) of the structure. Inset shows the structure of the graphene metamaterial. b Absorbance spectrum of ideal solar absorber. Ideal solar absorber is able to efficiently absorb (near-unity) sunlight (shaded red) and minimize energy dissipation through thermal radiation (blue dash line). X indicates the blackbody thermal emission is inhibited. c Simulated spectral reflectance (R), transmittance (T), and absorbance (A) for the SGM absorber featuring a hole width of 0.59 µm, a period of 0.8 µm, a depth of trenches of 1 µm, and a graphene metamaterial film with a thickness of 30 nm.