Absorb more than 90% of sunlight! Australia developed a new type of graphene film!

Researchers at the Center for Translational Atomaterials (CTAM) at Swinburne University of Technology in Melbourne, Australia have developed a new graphene film that can absorb more than 90% of sunlight while simultaneously Most of the infrared thermal emission losses are eliminated, and this is the first report of this feat.

This is a highly efficient solar-heating metamaterial capable of rapidly heating to 83 degrees Celsius (181 degrees Fahrenheit) in an open environment with minimal heat loss. Proposed applications for the film include thermal energy harvesting and storage, solar thermal power generation, and seawater desalination.

CTAM Founding Director Prof. Baohua Jia said that while absorbing sunlight while suppressing thermal radiation loss (also known as blackbody radiation) is critical for efficient solar thermal absorbers, it is extremely difficult to achieve. "This is because, depending on the heat absorbed and the properties of the absorber, the emission temperature differs significantly, resulting in a significant difference in its wavelength," she explained. But we have developed a three-dimensional structured graphene metamaterial (structured graphene meta materials, SGM), which is highly absorptive and can selectively filter out blackbody radiation."

This three-dimensionally structured graphene metamaterial consists of a 30-nanometer-thick alternating graphene film and a dielectric layer deposited on a trench-like nanostructure that doubles as a copper substrate for enhanced absorption. More importantly, the substrates are patterned in a matrix arrangement to enable flexible tunability of wavelength selective absorption.

The graphene films are designed to absorb light at wavelengths between 0.28 and 2.5 microns. The structure of the copper substrate allows it to act as a selective bandpass filter, suppressing the normal emission of internally generated blackbody energy. This retained heat can further increase the temperature of the metamaterial. Therefore, SGM can heat up to 83 degrees Celsius quickly. If different temperatures are required for specific applications, new channel nanostructures can be fabricated and tuned to match specific blackbody wavelengths. "In our previous work, we demonstrated a 90-nanometer graphene endothermic material," said Professor Jia. Although it can be heated to 160 degrees Celsius," its structure is more complex, consisting of four layers: a substrate, a silver layer, a silicon oxide layer, and a graphene layer. Our new bilayer structure is simpler and does not require vacuum deposition. The fabrication method Scalable and low cost.”

The new material also significantly reduces the film thickness by a third and uses less graphene, and its thinness helps transfer absorbed heat to other media, such as water, more efficiently. In addition, the film is hydrophobic, which aids in self-cleaning, while the graphene layer effectively protects the copper layer from corrosion, helping to prolong the lifespan of the metamaterial.

"Since the structural parameters of the metal substrate are the main factor controlling the overall absorption performance of the SGM, rather than its inherent properties, different metals can be used depending on the application needs or cost," said Keng-Te Lin, who recently published in Nature Communications (Nature Communications), lead author of a paper on metamaterials and a researcher at Swinburne University. He noted that aluminum foil could also be used to replace copper without compromising performance.

Keng-Te said: “We used the prototype membrane to produce clean water and achieved an impressive solar-steam efficiency of 96.2%. This is very competitive for clean water power generation using renewable energy sources. powerful."

He added that the metamaterial could also be used in energy harvesting and conversion applications, steam power generation, wastewater purification, seawater desalination and solar thermal power generation.

But one challenge that remains is finding a way to make the substrate stretchable.

"We are working with Innofocus Photonics Technology, a private company that has commercialized a coating machine for laying graphene and dielectric layers," said Professor Jia. "We're happy with that. We're now looking for a way to produce copper substrates at scale." One possible approach, she adds, is a roll-to-roll process.

Meanwhile, the researchers continue to fine-tune the nanostructure design to improve the stability and absorption efficiency of the SGM. "As for commercialization," Professor Jia said, "we think it's possible within one to two years."