As cities around the world struggle with rising energy demand, controlling heat from sunlight has become a major challenge.
A large portion of the heat entering buildings comes from near-infrared (NIR) light, an invisible part of sunlight that passes easily through ordinary windows.
Now, researchers in South Korea have developed a promising new material that could help smart windows block this heat more efficiently and at a much lower cost.
The breakthrough comes from a research team led by Assistant Professor Sungyeon Heo at Seoul National University of Science and Technology.
The team focused on a class of materials called hexagonal tungsten oxide nanorods.
These materials are known for their electrochromic properties, meaning they can change transparency and heat-blocking ability when a small electric voltage is applied.
This makes them ideal candidates for smart windows that can adjust automatically to sunlight and temperature.
What makes these nanorods special is their internal structure. They contain tiny hexagonal tunnels that act like channels for ions from an electrolyte.
When ions move in and out of these tunnels, the material can selectively block near-infrared light, reducing heat without significantly darkening the window.
Until now, most high-performance electrochromic systems relied on lithium ions because they are small and can easily fit into the tunnels.
However, lithium is relatively expensive and less abundant. Sodium, on the other hand, is cheap and widely available, but its larger size made it difficult to use. The tunnels were partially blocked by stabilizing dopants needed to maintain the material’s structure, preventing sodium ions from moving freely.
The research team solved this problem with a clever twist.
They introduced special dopants that help form the nanorods during synthesis but can be removed later through a simple heat treatment. Once the dopants are gone, the tunnels are left open and accessible, allowing sodium ions to move in and out efficiently.
As a result, the sodium-based system achieved near-infrared heat blocking performance comparable to lithium-based systems, even with an ultrathin film only 150 nanometers thick. This means smart windows could be made thinner, cheaper, and more sustainable without sacrificing performance.
Another advantage of the new material is its scalability. The nanorods are produced in a single-batch reactor with controlled temperature and pressure, making the process suitable for large-scale manufacturing.
Because the materials are made in a liquid, or colloidal, form, they can also be easily applied as coatings or combined with other materials, expanding their potential uses beyond smart windows.
The technology could be particularly useful in regions with extreme heat, where windows could remain in a constant heat-blocking mode to reduce cooling needs. In areas with seasonal climates, the windows could dynamically adjust to let heat in during winter and block it in summer.
Looking ahead, the researchers believe this innovation could accelerate the adoption of smart windows and energy-efficient buildings within the next decade.
By relying on abundant materials like sodium and scalable production methods, the technology offers a practical path toward lower energy consumption and more comfortable indoor environments.
