Ultrathin broadband solar absorbers for UV and UV-NIR based on a scalable plasmonic metamaterial

• Applicants: Professorin Tayebeh Ameri, Ph.D.; Professor Dr. Carsten Rockstuhl; Dr.-Ing. Alexander Vahl
• Subject Area: Synthesis and Properties of Functional Materials ; Theoretical Chemistry: Molecules, Materials, Surfaces
• Term: since 2019
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 413974664

In this project, we advance the development and understanding of plasmonic perfect absorbers for solar thermal conversion, a crucial component of our future infrastructure to harvest renewable energy resources. For a broadband absorption of solar radiation, ranging from UV (about 200 nm) to NIR (about 2 µm), we use an ultrathin (typically 20 nm) plasmonic metamaterial scalable in fabrication. The metamaterial consists of a densely packed particulate metal-dielectric nanocomposite with a broad nanoparticle size distribution deposited on a reflective metallic back mirror and a dielectric spacer layer. The absorbers are polarization- and angle-insensitive thanks to multiple phenomena. In the next phase of this project, we aim to deepen our successful collaboration by intertwining experimental and theoretical efforts while focusing on improving broadband absorption and thermal management in plasmonic perfect absorbers. Three aspects are important. First, as a novel and highly promising approach to enhance broadband absorption, we utilize an additional structuring of the metal back mirror surface through substrate dewetting. We complement this method with atmospheric plasma spraying, a scalable and industry-relevant coating technology that creates microscale roughness on the metal back mirror. Impedance matching of the devices will be achieved through a tailored permittivity gradient at the front interface of the device. Second, enhanced absorption in the visible and near-infrared wavelengths is important in the final application. Still, it is also crucial to suppress the emission within the spectral range corresponding to the device's temperature. Therefore, we will consider this aspect additionally in the design to perfectly blend both objective functions. Third, the project focuses on application-relevant operational regimes of nanocomposite absorbers at 450°C and above for solar thermal collectors. Therefore, we must improve the temperature stability of the devices by introducing dense passivation coatings through high-power impulse magnetron sputtering and by utilizing refractory plasmonic nanoparticles in their design. To achieve our goals, we rely on plasma-based physical vapor deposition methods, such as magnetron sputtering and the self-organization of nanostructures through simultaneous co-deposition for the absorber thin film stack. To model the devices, we utilize a T-matrix-based scattering formalism that accommodates the textured substrate surfaces and solves the inverse problem. The development cycle is completed through advanced material and device characterization, which includes spectroscopic ellipsometry, optical spectroscopy in the UV-vis-NIR range, and morphological and compositional characterization via electron microscopy and X-ray photoelectron spectroscopy.

• DFG Programme: Research Grants
• International Connection: Czech Republic
• Cooperation Partner: Professor Dr. Andrey Shukurov