Dielectric

Ecology

Materials science

Photodetector

Metamaterial absorber

Optoelectronics

Metamaterial

Broadband

Physics

Molar absorptivity

Nanotechnology

Photovoltaics

Biology

Optics

Absorption (acoustics)

Graphene

Photovoltaic system

Visible spectrum

Tunable metamaterials

Photonics

Nature Photonics

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.

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