Solar energy absorption rate of 94%-97% is achieved using natural hyperbolic material

Natural anisotropic metamaterials, which have the advantages of combining metallic and dielectric behaviors in different directions, are excellent candidates for solar energy absorbers. Wang et al. developed a broadband solar absorber made of a metal substrate covered by a roughened Bi₂Te₃ layer, with Bi₂Te₃ being a promising natural anisotropic material. The absorber was fabricated using a cost-effective method known as electrochemical deposition.

“If the proposed perfect absorber of solar energy and a thermoelectric generator work together, phonons will be excited directly by the photons from the sun and the barrier to transport of the phonons from the absorber to the thermoelectric generator might be decreased, which would enhance thermoelectric efficiency,” said author Zhaolong Wang.

A nearly perfect absorptance of 94%-97.5% in the wavelength range of 380-1800 nanometers was achieved by controlling the surface characteristics of the Bi₂Te₃. The authors confirmed that if the bottom width of the Bi₂Te₃ nanostructures is fixed, then an increased roughness of the upper layer will increase absorbance. On the other hand, if the roughness remains the same, then the absorbance will be less.

“Our experiments validate all of the previous calculations on absorptance of metamaterials made of anisotropic materials, providing a solid foundation for the similar design of perfect absorbers for solar energy harvesting in the future,” said Wang.

The researchers plan on studying applications of near-perfect absorption for photothermal and industrial processes such as vapor generation, desalination and sterilization. They also plan to investigate thermoelectricity enabled by solar energy by the present absorber.

“The precise control of morphology of the nanostructures made of Bi₂Te₃ should be further studied to enhance the absorptance of solar energy to nearly 100%,” said Wang.

Source: “An experimental study of a nearly perfect absorber made from a natural hyperbolic material for harvesting solar energy,” by Zhaolong Wang, Peiyan Yang, Genggeng Qi, Zhuomin Zhang, and Ping Cheng, Journal of Applied Physics (2020). The article can be accessed at https://doi.org/10.1063/5.0005700 .