Chinese scientists develop colorless solar concentrator for PV windows

<p class="p1"><span class="s1">The research team’s semi-transparent solar concentrator can be directly coated onto standard window glass. It uses liquid crystal films to reflect and guide circularly-polarized sunlight to solar cells installed toward the edge of a window. A 1-inch diameter prototype was found capable of directly powering a 10 mW fan under sunlight.</span></p><p>A research team based at China’s <a href="https://www.pv-magazine.com/2024/06/11/perovskite-silicon-tandem-solar-cell-treated-with-n-butanol-achieves-29-4-efficiency/" rel="noopener" target="_blank">Nanjing University</a> has developed a transparent, colorless and unidirectional solar concentrator compatible with existing windows.</p>
<p>Solar concentrators are designed to converge solar energy onto the side of architectural glass. Useful in building-integrated photovoltaics, existing solar concentrators often suffer from setbacks, including low efficiencies, coloring, or a lack of compatibility with existing windows.</p>
<p><span style="font-weight: 400;">The research team's newly developed diffractive-type solar concentrator (CUSC) utilizes cholesteric liquid crystal (CLC) multilayers with submicron lateral periodicities to selectively guide sunlight toward the edge of the window where photovoltaic cells are installed. </span><span style="font-weight: 400;">The team fabricated the multilayered CLC films via photoalignment and polymerization techniques, which are scalable via roll-to-roll manufacturing.</span></p>
<p><span style="font-weight: 400;">Under testing, the CUSC device maintained an average visible transmittance of 64.2% and colour rendering index of 91.3, enabling energy generation without altering the appearance of the window.</span></p>
<p><span style="font-weight: 400;">“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,” said Dewei Zhang, co-first author of the research. “This allows up to 38.1% of incident green light energy to be collected at the edge.”</span></p>
<p><span style="font-weight: 400;">The research paper &#8220;</span><span style="font-weight: 400;"><a href="https://photonix.springeropen.com/articles/10.1186/s43074-025-00178-3" rel="noopener" target="_blank">Colorless and Unidirectional Diffractive-type Solar Concentrators Compatible with Existing Windows</a>,&#8221; available in the journal </span><span style="font-weight: 400;"><em>PhotoniX</em>, details how a 1-inch diameter prototype was found capable of directly powering a 10 mW fan under sunlight.</span></p>
<p><span style="font-weight: 400;">Further modeling found that a typical 2-meter-wide CUSC window could concentrate sunlight by 50 times, reducing the number of photovoltaic cells required by up to 75%. The design also remained stable under long-term exposure and was found suitable for retrofitting onto existing windows, allowing sustainable urban upgrades.</span></p>
<p><span style="font-weight: 400;">Professor Wei Hu commented that the CUSC design is a step forward in integrating solar technology into the built environment without sacrificing aesthetics. “It represents a practical and scalable strategy for carbon reduction and energy self-sufficiency,” Hu added.</span></p>
<p>In the research paper's conclusion, the authors write that the CUSC design would be widely adopted in green buildings, agricultural photovoltaics and other emerging areas. &#8220;It is expected to contribute to a global terawatt-scale green energy supply and reduce annual carbon emissions by billions of tons,&#8221; the paper concludes.</p>
<p><span style="font-weight: 400;">The research team says it is planning to focus future work on enhancing broadband efficiency, polarization control and adapting the technology for agricultural greenhouses and transparent solar displays.</span></p>