Gold supraballs boost broadband solar absorption

by Clarence Oxford
Los Angeles CA (SPX) Jan 29, 2026

Sunlight carries a wide range of wavelengths, but many solar harvesting technologies only tap a portion of that spectrum, limiting their efficiency. Researchers have now shown that tiny self-assembled gold spheres, known as supraballs, can capture nearly all wavelengths in sunlight, including those that conventional photovoltaic materials often miss, and can significantly increase solar energy absorption when used as a coating on standard devices.

Gold and silver nanoparticles are attractive for solar applications because they are relatively easy and cost-effective to produce. However, the light absorption of conventional metal nanoparticles is largely confined to visible wavelengths, which means they interact with only a fraction of the total solar spectrum. To move beyond this limitation and access additional wavelengths such as near-infrared light, a team led by Jaewon Lee, Seungwoo Lee and Kyung Hun Rho developed gold supraballs, in which many individual gold nanoparticles clump together into compact spherical structures.

The researchers used computer simulations to design supraballs that would interact strongly with the broad mix of wavelengths present in sunlight. By tuning the diameter of these spheres, they optimized the structures to maximize light absorption across the solar spectrum. The modeling results indicated that properly engineered supraballs could absorb more than 90 percent of the incident solar wavelengths, suggesting strong potential for broadband solar harvesting.

After the simulations, the team fabricated supraball films by drying a liquid solution of the gold spheres onto the surface of a commercially available thermoelectric generator, a device that converts absorbed light into electricity via thermal gradients. The films were prepared under ambient room conditions without specialized clean rooms or extreme processing temperatures, which points to a straightforward and scalable manufacturing route. This approach allows the supraballs to function as a coating that can be added to existing solar-thermal or photothermal components.

Under tests with an LED-based solar simulator, the thermoelectric generator coated with the supraball film achieved an average solar absorption of about 89 percent. In contrast, an otherwise identical generator coated with a conventional film made from single, non-assembled gold nanoparticles reached only about 45 percent average absorption. The supraball layer therefore nearly doubled the absorbed solar energy compared to the traditional nanoparticle coating, confirming the performance predicted by the simulations.

By concentrating many nanoparticles into a single sphere, the supraball design enhances plasmonic interactions that are responsible for light capture at the nanoscale. These collective effects help the structures respond to a wider band of wavelengths than isolated particles can manage. The result is a broadband absorber that can harvest visible and near-infrared light, which is important for technologies that rely on converting sunlight into heat or electricity efficiently.

The researchers describe their approach as a simple route to harvesting the full solar spectrum with a coating that can be applied to realistic devices. "Our plasmonic supraballs offer a simple route to harvesting the full solar spectrum," says Seungwoo Lee. "Ultimately, this coating technology could significantly lower the barrier for high-efficiency solar-thermal and photothermal systems in real-world energy applications." Because the films can be formed by solution processing in standard laboratory or industrial environments, they could be integrated into a range of solar-thermal generators, photothermal converters and hybrid energy systems.

Research Report:Plasmonic Supraballs for Scalable Broadband Solar Energy Harvesting