A 90-nm-thick graphene metamaterial for strong and extremely broadband absorption of unpolarized light

Broadband strong light absorption of unpolarized light over a wide range of angles in a large-area ultrathin film is critical for applications such as photovoltaics, photodetectors, thermal emitters and optical modulators. Despite long-standing efforts in design and fabrication, it has been challenging to achieve all these desired properties simultaneously. We experimentally demonstrate a 12.5 cm2, 90-nm-thick graphene metamaterial with approximately 85% absorptivity of unpolarized, visible and near-infrared light covering almost the entire solar spectrum (300–2,500 nm). The metamaterial consists of alternating graphene and dielectric layers; a grating couples the light into waveguide modes to achieve broadband absorption over incident angles up to 60°. The very broad spectral and angular responses of the absorber are ideal for solar thermal applications, as we illustrate by showing heating to 160 °C in natural sunlight. These devices open a novel approach to applications of strongly absorbing large-area photonic devices based on two-dimensional materials. Eighty-five per cent absorptivity of unpolarized light over the wavelength range 300–2,500 nm is realized in a 90-nm-thick, 12.5 cm2 metamaterial.