Transparent solar concentrator turns windows into clean energy sources

A team from Nanjing University has developed a transparent, colorless solar concentrator that can be applied directly to ordinary glass windows, enabling buildings to generate electricity without altering their appearance. The innovation, reported in PhotoniX, relies on cholesteric liquid crystal multilayers to redirect sunlight toward window edges fitted with photovoltaic cells.

Conventional luminescent and scattering concentrators often face issues such as distortion, inefficiency, and limited scalability. In contrast, the new concentrator achieves polarization-selective diffraction and waveguiding while preserving clarity, maintaining an average visible transmittance of 64.2% and a color rendering index of 91.3.

"By engineering the structure of cholesteric liquid crystal films, we create a system that selectively diffracts circularly polarized light, guiding it into the glass waveguide at steep angles," explained co-first author Dr. Dewei Zhang. "This allows up to 38.1% of incident green light energy to be collected at the edge."

A one-inch prototype successfully powered a 10-mW fan under sunlight, and modeling predicts that a two-meter-wide window could concentrate sunlight by a factor of 50. This efficiency could reduce the need for photovoltaic cells by up to 75%, particularly when paired with advanced materials such as gallium arsenide.

The films are fabricated through photoalignment and polymerization processes, making them suitable for roll-to-roll manufacturing. They remain stable under extended exposure and can be retrofitted onto existing windows, offering a sustainable solution for urban infrastructure.

"The CUSC design is a step forward in integrating solar technology into the built environment without sacrificing aesthetics," said Professor Wei Hu. "It represents a practical and scalable strategy for carbon reduction and energy self-sufficiency."

Ongoing research will refine broadband efficiency and polarization control, with potential applications ranging from agricultural greenhouses to transparent solar displays. The ultimate goal is to transform passive glass into active, energy-generating surfaces worldwide. Research Report:Colorless and Unidirectional Diffractive-type Solar Concentrators Compatible with Existing Windows