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

• Published in: Nature photonics Vol. 13; no. 4; pp. 270 - 276
• Main Authors: Lin, Han, Sturmberg, Björn C. P., Lin, Keng-Te, Yang, Yunyi, Zheng, Xiaorui, Chong, Teck K., de Sterke, C. Martijn, Jia, Baohua
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group 01.04.2019
• Subjects: Absorption; Absorptivity; Broadband; Electromagnetic absorption; Emitters; Fabrication; Graphene; Metamaterials; Modulators; Near infrared radiation; Photonics; Photovoltaic cells; Photovoltaics; Solar cells; Solar heating; Thin films; Two dimensional materials
• ISSN: 1749-4885; 1749-4893
• DOI: 10.1038/s41566-019-0389-3

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.