Scientists Create Transparent Solar Coating for Energy Generation
Scientists have developed a transparent solar coating that can turn ordinary windows into energy-generating surfaces without affecting their clarity, marking a major advance in building-integrated photovoltaics.
Scientists at Nanjing University in China have unveiled a transparent, colorless solar coating that enables standard windows to generate electricity while maintaining their original appearance. The breakthrough, announced on September 10, 2025, addresses longstanding challenges in building-integrated photovoltaics, where previous solar coatings often compromised window transparency or were incompatible with existing glass.
The new coating, known as a colorless unidirectional solar concentrator (CUSC), uses multilayered cholesteric liquid crystal (CLC) films engineered to selectively guide polarized sunlight toward the edges of the window. There, photovoltaic cells convert the concentrated light into electricity. This approach allows the window to remain clear, with an average visible transmittance of 64.2% and a color rendering index of 91.3, meaning the coating does not distort the view or alter the natural light entering a room.
In laboratory tests, a prototype CUSC window was able to directly power a 10 mW fan under sunlight. Modeling suggests that a standard 2-meter-wide CUSC window could concentrate sunlight by up to 50 times, reducing the number of photovoltaic cells required by as much as 75%. The coating is also designed for scalability, with manufacturing methods compatible with roll-to-roll production, making it suitable for retrofitting existing buildings as well as new construction.
Professor Wei Hu, a lead researcher on the project, emphasized the practical implications: "It represents a practical and scalable strategy for carbon reduction and energy self-sufficiency." The team envisions widespread adoption in green buildings, agricultural greenhouses, and transparent solar displays, with the potential to contribute to a global terawatt-scale green energy supply and reduce annual carbon emissions by billions of tons.
How the Technology Works
The CUSC coating is based on cholesteric liquid crystal multilayers with submicron periodicities. These layers are fabricated using photoalignment and polymerization techniques, which are already established in the display industry. By engineering the structure of the CLC films, the system selectively diffracts circularly polarized light, channeling it into the glass waveguide at steep angles. This enables efficient collection of solar energy at the window's edge, where it is converted to electricity by attached photovoltaic cells.
Implications for Urban Sustainability
The transparent solar coating is expected to accelerate the integration of renewable energy into urban environments, where available surface area for traditional solar panels is limited. By allowing windows to double as power generators without sacrificing aesthetics or functionality, the technology could play a significant role in reducing the carbon footprint of cities. The research team is now focusing on enhancing the broadband efficiency of the coating and adapting it for use in agricultural and display applications.
International experts have noted the significance of this advance, highlighting its potential to transform the way buildings contribute to energy generation. The development has been widely reported in both local Chinese and international scientific outlets, underscoring its global relevance.