New Boron Nitride Coating for Glass Reduces Heat Loss and Saves Energy

Researchers at Rice University and their collaborators have developed a new coating for glass that can help reduce energy bills by preventing heat loss from leaking windows, particularly during cold seasons. The material—a transparent film made by weaving carbon into the atomic lattice of boron nitride—creates a thin, durable layer that reflects heat, resists scratching, and repels moisture, UV light, and temperature fluctuations.

The researchers simulated how the material would perform in a full-scale building in cities with cold winters such as New York, Beijing, and Calgary, demonstrating a 2.9% increase in energy savings compared to existing alternatives. Given that more than 4 billion square meters of new windows are installed annually in the US alone, the savings could reach significant proportions. According to a study published in Advanced Materials, the coating's durability allows it to be placed on the exterior surface of glass—a major advantage over conventional low-emissivity (low-E) coatings. Emissivity describes a material's ability to emit heat as thermal energy; lower values mean less heat escapes from the glass. Conventional low-E coatings tend to degrade from environmental factors such as moisture and temperature fluctuations, requiring them to be placed on the interior surface of windows.

Pulickel Ajayan, Benjamin M. and Mary Greenwood Anderson Professor of Engineering and Professor of Materials Science and Nanoengineering at Rice, said, "While pure boron nitride shows emissivity almost similar to glass, when you add a small amount of carbon to it, the emissivity drops significantly—and that changes the game completely." To create the coating, the team used pulsed laser deposition, a technique in which short, high-energy laser bursts strike a solid boron nitride target, creating plasma clouds that disperse as vapor and deposit onto a substrate—in this case, glass. Because the process occurs at room temperature, it avoids the high heat typically required to make adhesive coatings.

Abhijit Biswas, lead author of the study and thin-film synthesis specialist, said, "From a synthesis perspective, coating boron nitride onto glass is really amazing and very exciting." Ajayan noted that the same low-temperature boron nitride deposition technique could be adapted for other materials beyond glass, including polymers, textiles, and possibly even biological surfaces. Furthermore, other scalable techniques such as roll-to-roll chemical vapor deposition or sputtering could eventually enable commercial production with proper process optimization. Ajayan added, "This significantly expands the range of applications for boron nitride coatings."

Researchers in Ajayan's group at Rice have been studying boron nitride thin-film growth for years, motivated by interest in the material's superior mechanical, thermal, and optical properties. In terms of raw materials, boron nitride is cheaper than the silver or indium tin oxide used in most commercial low-E glass. However, the researchers caution against direct cost comparisons because the materials differ in durability, processing methods, and technological maturity. Nevertheless, the team sees promise in the coating's long-term performance, particularly in challenging environments where existing materials fall short.

To evaluate the coating's optical clarity and potential for energy savings in buildings, the Rice team partnered with Yi Long, co-responsible author from the University of Hong Kong, whose group focuses on functional materials for smart window technologies. Long emphasized the coating's durability in outdoor conditions as a fundamental distinction from current technologies.

"Resistance to harsh atmospheric conditions makes it the first exterior-facing low-E window coating, with energy-saving capacity that clearly outperforms its interior-facing counterpart," Long said. "It could be an excellent solution for densely built environments.

Shancheng Wang also made significant contributions to the research, particularly regarding energy savings. "The level of transparency and promising low emissivity make carbon-doped coated glass a competitive energy-saving option for cities such as Beijing and New York," Wang said. Beyond Rice and the University of Hong Kong, the scientific team also included collaborators from Arizona State University, Cornell University, and the University of Toronto.

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