Flexible, Ultrathin, and Lithographic‐Free Nanocoral Metamaterial Membrane for Omnidirectional UV–vis–NIR Broadband Absorption

Abstract

UV–vis–NIR metamaterial absorbers are key components for devices used in photothermal applications, especially those related to solar energy. Demanded by modern applications using nonplanar devices, they should be flexible, thin, mass producible, easy for integration, and demonstrate strong omnidirectional light absorption over wide spectral ranges. However, there are few ways to achieve these simultaneously. Additionally, most fabrication methods are substrate dependent, limiting integrability, or involve lithography, which can be costly and difficult. Herein, a metamaterial absorber that meets all the requirements above is demonstrated, using a simple substrate‐independent lithographic‐free process. It is composed of 3D randomized gold@SU‐8 hybrid nanocoral structures of ≈2 μm thin on a supporting membrane, which can be different materials to meet various integration needs depending on applications. Benefiting from multilevel hybridizations of plasmon resonance reinforced by strong light‐trapping effect, >90% optical energy ranging from 250 to 2500 nm is omnidirectionally absorbed. The perfect metamaterial absorber exhibits very stable photothermal conversion properties with great reproducibility and durability. The excellent performance, thinness, flexibility, and simple fabrication method grant the presented absorber great potential in modern photothermal applications, especially those requiring nonplanar thin‐film devices.