Solar energy harvesting using new broadband metamaterial solar absorbers for generation of heat

We have designed and fabricated TiN/SiO2/TiN–HfO2-based new metamaterial microstructures as an absorber of the visible wavelength, in the range of 400–700 nm, with exceptionally high absorption efficiency (>96%) for solar energy harvesting purposes and generation of heat upon absorption of electromagnetic energy. The finite element method-based COMSOL Multiphysics software simulations were used to optimize the structural parameters of the microstructures and visualize the electric field and electromagnetic power loss distribution in the structure. An optimized 2D unit cell of the structure consists of a 4 μm × 160 nm TiN base on a glass substrate covered with a 70 nm thick SiO2 film. A periodic structure of TiN straps (each 90 nm thick and 2 μm wide) is deposited over the SiO2. The straps are capped with a 40 nm thick layer of high-temperature dielectric HfO2 with a periodicity of 4 µm. This unit is symmetric along the other dimension and is repeated periodically along the horizontal direction. Similar optimized parameters were used for 7, 10, and 100 µm periodic structures to investigate the effect of grating structure pitch on the absorption of light. Although these microstructures were optimized for the visible light spectrum, they show absorption efficiency of >92% when integrated over a broadband wavelength spectrum ranging from 400 to 1200 nm. The experimental data show excellent agreement with the simulated results. We observe less than 5% difference between experimental and simulated absorption efficiencies for the investigated microstructures. Furthermore, we should emphasize that, to the best of our knowledge, this is the first study to experimentally report the light to heat conversion in metamaterials with micron-range size patterned structures.