By Etiido Uko
This supraball (left) is 2,100 nanometers in diameter and is made from hundreds of tiny gold nanoparticles (right) engineered to boost solar energy absorptionAdapted from ACS Applied Materials & Interfaces 2026, DOI: 10.1021/acsami.5c23149
At
any given moment, 89,000 terawatts of solar power hits the Earth’s
surface. While significant advancements have been made in harvesting
this power, existing technologies do not capture the full potential of
the entire solar spectrum. This limitation primarily lies in these
technologies' incomplete absorption of the sun’s ultraviolet, visible,
and infrared radiation.
A
team of researchers at KU-KIST Graduate School of Converging Science
and Technology, Seoul, has now reported a way of absorbing nearly the
full usable solar spectrum in thermal-based devices, using
self-assembling gold nanospheres called plasmonic colloidal supraballs.
Solar
radiation spans ultraviolet (3-5%), visible (40-45%), and infrared
(50-55%) wavelengths. Photovoltaic (PV) cells primarily convert visible
light and part of the near-infrared spectrum into electricity, leaving
much of the remaining energy untapped. Concentrated solar systems
collect broader wavelengths using mirrors, but require large-scale
infrastructure and still depend on receiver materials that are not
perfectly absorbing. Solar-thermal collectors absorb visible and
infrared light relatively well, yet their efficiency is constrained by
surface coatings that rarely achieve near-total absorption.
This is where the plasmonic supraballs come in.
The
new technology starts as a colloidal suspension of gold nanoparticles,
which self-assemble into micrometer-scale spheres in solution. Thousands
of nanoparticles cluster together to form "supraballs" and the liquid
is then drop-cast onto the ceramic surface of a thermoelectric
generator, forming a dense, textured film that efficiently captures
sunlight.
Conventional gold nanoparticle films and dielectric absorber coatings do
already exist that can increase light absorption in specific wavelength
ranges and reduce heat re-radiation. However, the often suffer from
limited infrared absorption, angular sensitivity, high manufacturing
costs, and thermal degradation over long-term thermal exposure.
Plasmonic
supraballs work differently. Localized surface plasmon resonances
(LSPR) at the nanoparticle surfaces, combined with Mie-type resonances
within the spheres, trap photons across UV, visible, and near-infrared
wavelengths, converting much of this energy into heat. This results in
~90% absorption across the solar spectrum, significantly improving
thermal energy capture and creating a stronger temperature gradient that
ultimately generates nearly 2.4 times the power output of conventional
nanoparticle coatings.
The team, comprising Jaewon Lee, Seungwoo Lee, and Kyung Hun Rho, published their research in the journal ACS Applied Materials & Interfaces.
It
is important to note that the plasmonic supraball technology is
primarily designed for thermal-based solar systems, such as
thermoelectric solar generators (TEG systems), solar-thermal collectors,
and thermal management and passive heating systems. They could also
play a role in hybrid PV-thermal (PVT) systems where visible light is
converted to electricity by PV cells, and remaining wavelengths are
harvested as heat.
“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.”
Beyond performance, another major appeal of
the technology is its practicality. The supraballs require
low-complexity fabrication and application via solution processing.
Furthermore, the technology is compatible with existing, commercially
available devices.
Source: American Chemical Society