The lab-scale, near-white heterojunction solar cell uses nanoclay-based scattering layers combined with dielectric multilayer films to preserve power conversion efficiency while enhancing visual appeal. The researchers report optical losses of less than 1% at a 50% clay volume fraction, which are significantly lower than those observed with textured glass.
Appearance of the solar cell modules fabricated by the research team
Image: Nagaoka University of Technology, Solar Energy Materials and Solar Cells, CC BY 4.0
Researchers from the Nagaoka University of Technology in Japan have fabricated a heterojunction (HJT) solar cell with a near-white appearance for applications in building-integrated photovoltaics (BIPV).
“This is still a lab-scale proof of concept, but the key processes we used such as large-area coating and sputtering-type thin-film deposition have clear industrial equivalents,” the research’s lead author, Noboro Yamada, told pv magazine. “We are not yet working directly with PV manufacturers, and we would welcome partners to evaluate scalability, module integration, and long-term reliability.”
The scientists explained that, although white-toned building materials are commonly used in architectural applications, they achieve a visually white appearance in solar-integrated materials at the cost of reduced efficiency. In white solar cells, for example, increased reflection and scattering of light can lead to power losses of up 41.5%.
To address this limitation, they proposed to use surface texturing of cover glass to increase scattered light. They utilized, in particular, nanosized clay minerals, or nanoclays, as a scattering layer to increase haze while maintaining high transmittance. Furthermore, dielectric multilayer films (DMFs) were used for reflection control.
The nanoclays were based on organically modified smectite, which is a group of clay minerals known for their layered, plate-like structure and exceptional ability to absorb water and swell.
Image: Nagaoka University of Technology, Solar Energy Materials and Solar Cells, CC BY 4.0
Comparing the optical performance of clay films to textured and flat glass, the scientists found that clay films maintain high transmittance across the visible spectrum while achieving substantial scattering. Unlike textured glass, which primarily scatters light at the surface and reduces transmittance, clay films rely on volume scattering within nanosized clay layers, allowing them to increase lightness without significant optical loss.
At a clay content of 50% by volume, clay films achieved near-white appearance with optical loss below 1%, whereas textured glass incurred over 6% loss for comparable whiteness. Moreover, hybrid films combining clay with wavelength-selective DMFs enhanced whiteness while controlling optical loss.
Data on the device’s power conversion efficiency and other electric parameters were not disclosed.
“These results indicate that nanoclay films could be promising whitening materials able to balance the lightness and power performance, in contrast to textured glass, which relies on surface scattering,” the research team stressed. “We then designed DMFs using multi-objective Bayesian optimization and combined them with clay to study hybrid films with lower optical loss and whiter appearance. The optimization targeted reduced optical loss, chroma, and increased lightness.”
“We did not conduct a full cost analysis in this paper,” Yamada added. “However, we made a rough internal estimate and the added materials for the near-white coating are based on widely available, low-cost components, so we do not expect a large solar cell cost increase.”
The new cell design was introduced in “Near-white appearance solar cells enabled by nanoclay-based scattering layers,” published in Solar Energy Materials and Solar Cells. Looking forward, the team intends to create improved techniques to obtain a near-white or fully white appearance, test the materials’ durability under outdoor conditions, establish scalable fabrication methods suitable for large-area manufacturing, and assess the overall cost-effectiveness of the technology.
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