Boosting Solar Efficiency with Passive Light Control—No Solar Tracking Required

What is it about?

One way to improve solar cell efficiency is to combine multiple subcells, each designed to absorb a different part of the solar spectrum with maximum efficiency. The most effective designs stack these subcells vertically—so-called vertical tandem solar cells—and can achieve record efficiencies of up to 47.6%. However, this vertical architecture is expensive and technologically demanding to produce. A promising alternative are lateral tandem solar cells, where the subcells are placed side by side. This layout is easier to manufacture, but it introduces a new challenge: sunlight must be split according to wavelength and guided to the correct subcell. This requires an additional photonic structure called a solar spectral splitter. The problem so far is that existing spectral splitters only work well when sunlight hits them head-on. Even a slight change in the angle of sunlight—as happens naturally throughout the day—can cause a sharp drop in performance. In our work, we addressed this problem. Using inverse design, we propose a new type of spectral splitter that can be fabricated by microstructuring the top and bottom surfaces of a glass block. This design passively guides different wavelengths of sunlight to the appropriate subcell across a wide range of angles. The result is more stable and efficient energy generation throughout the day, without the need for tracking systems or moving parts.

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Photo by Newpowa on Unsplash

Photo by Newpowa on Unsplash

Why is it important?

Thanks to the flexibility of our design approach, the device’s optical response can be tailored to emphasize performance during specific times of day—such as peak energy demand hours—without requiring mechanical sun tracking. This makes solar energy generation more predictable and better aligned with grid needs, enhancing its economic value. Our design strategy combines topology optimization and Fourier optics to create photonic devices that are robust, customizable, and manufacturable. By enabling static optical components for high-performance solar energy systems, our work supports broader, more affordable deployment and contributes directly to energy resilience and climate goals.

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