Graphene Solar Thermal Film Could Be a New Way to Harvest Renewable Energy
A novel energy-efficient metamaterial can efficiently absorb sunlight while limiting blackbody heat-loss to almost zero
Researchers at the Center for Translational Atomaterials (CTAM) at Swinburne University of Technology in Melbourne, Australia, have developed a new graphene-based film that can absorb sunlight with an efficiency of over 90 percent, while simultaneously eliminating most IR thermal emission loss—the first time such a feat has been reported.
The result is an efficient solar heating metamaterial that can heat up rapidly to 83 degrees C (181 degrees F) in an open environment with minimal heat loss. Proposed applications for the film include thermal energy harvesting and storage, thermoelectricity generation, and seawater desalination.
Suppressing thermal emission loss—also known as blackbody radiation—while simultaneously absorbing solar light is critical for an efficient solar thermal absorber but is extremely challenging to achieve, says Baohua Jia, founding director of CTAM. “That’s because, depending on the absorbed heat and properties of the absorber, the emission temperature differs, which leads to significant differences in its wavelength,” she explains. “But we’ve developed a three-dimensional structured graphene metamaterial (SGM) that is highly absorbent and selectively filters out blackbody radiation.”
The 3D SGM is composed of a 30-nanometer-thick film of alternating graphene and dielectric layers deposited on a trench-like nanostructure that does double duty as a copper substrate to enhance absorption. More importantly, the substrate is patterned in a matrix arrangement to enable flexible tunability of wavelength-selective absorption.
The graphene film is designed to absorb light between 0.28- to 2.5-micrometer wavelengths. And the copper substrate is structured so that it can act as a selective bandpass filter that suppresses the normal emission of internally generated blackbody energy. This retained heat then serves to further raise the metamaterial’s temperature. Hence, the SGM can rapidly heat up to 83 degrees C. Should a different temperature be required for a particular application, a new trench nanostructure can be fabricated and tuned to match that specific blackbody wavelength.
“In our previous work, we demonstrated a 90 nm graphene heat-absorbing material,” says Baohua. Though it could heat up to 160 degrees C, “the structure was more complicated, [comprising] four layers: a substrate, a silver layer, a layer of silicon oxide, and a graphene layer. Our new two-layer structure is simpler and doesn’t require vacuum deposition. And the method of fabrication is scalable and low cost.” [READ MORE]