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 cm(2), 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 degrees. The very broad spectral and angular responses of the absorber are ideal for solar thermal applications, as we illustrate by showing heating to 160 degrees C in natural sunlight. These devices open a novel approach to applications of strongly absorbing large-area photonic devices based on two-dimensional materials.