Cholesteric liquid crystals (CLCs) offer a versatile solution to the aesthetic integration of solar modules into building façades and roofs, enabling both passive colouring and dynamic thermochromic effects without compromising power conversion efficiency (PCE). Researchers at the University of Luxembourg have demonstrated remarkable results, paving the way for the widespread adoption of building-integrated photovoltaics (BIPV) that blend seamlessly into the urban environment.
Arbitrary Coloring Techniques
Conventional approaches to colouring solar cells, such as multi-layer thin film stacks or pigment-based inks, often incur significant PCE losses of up to 68%. In contrast, the self-organized helical modulation of CLCs allows for the generation of structural colour with minimal impact on the underlying solar cells. By strategically adjusting the chiral dopant concentration, researchers have created solar cells with uniform red, green, and blue retroreflection, maintaining 92-96% of the original PCE.
Furthermore, the researchers have demonstrated the ability to pixelate CLC coatings to produce non-spectral colours that effectively camouflage the solar cells into wooden or metallic backgrounds. This approach combines red, green, and blue pixels to generate a blended hue that is indistinguishable from the surroundings at distances greater than 2 meters, while still achieving a relative PCE that is 50% higher than commercially available coloured modules.
Active Coloring Approaches
In addition to permanent coloration, the researchers have developed thermochromic solar cells that can dynamically change colour across the full visible spectrum in response to temperature variations. These cells maintain 88-91% of their original PCE, offering the possibility of adding functional value through active colour-changing capabilities.
Negligible Efficiency Loss
Through meticulous engineering of the CLC coatings, the researchers have overcome the traditional trade-off between colouring and PCE. By leveraging the selective reflection of CLCs, which only affects a narrow band of the solar spectrum, they have achieved remarkably high power outputs compared to other structural colour technologies or pigment-based inks.
Green Building Integration
The ability to colour solar modules without significantly impacting their efficiency opens up new possibilities for the seamless integration of renewable energy generation into the built environment.
Aesthetic Considerations
The versatility of CLC coatings, ranging from arbitrary full-colour images to thermochromic effects, enables solar modules to be aesthetically integrated into building façades and roofs in a way that is fully acceptable to the public. This is a crucial step in overcoming the visual impact barriers that have hitherto limited the widespread adoption of BIPV.
Functional Requirements
Beyond aesthetic considerations, the researchers have demonstrated the thermal stability and environmental durability of their CLC coatings, ensuring that the coloured solar cells can withstand the rigours of real-world operating conditions. This is a critical requirement for the long-term reliability and performance of BIPV systems.
Sustainability Aspects
The minimal efficiency losses associated with CLC coatings contribute to the overall sustainability of BIPV solutions, maximizing the energy generation potential of building-integrated solar modules. This, combined with the ability to blend seamlessly into the urban environment, can further drive the adoption of renewable energy sources and support the transition towards greener, more energy-efficient buildings.
Solar Cell Technology
The research conducted at the University of Luxembourg builds upon advancements in photovoltaic materials and device engineering, leveraging innovative approaches to enhance the visual appeal of solar cells without compromising their core functionality.
Photovoltaic Principles
The researchers have demonstrated the compatibility of their CLC coatings with chalcogenide thin-film solar cells, such as copper indium gallium selenide (CIGSe), which offer high efficiencies and a low-bandgap that is well-suited for coloured solar applications.
Material Innovations
The development of thermochromic CLC mixtures with precisely tuned phase transitions and reactive CLC monomers for pixelated coatings showcase the researchers’ expertise in materials science and their ability to tailor the optical properties of solar cell surfaces.
Performance Optimization
By carefully designing the CLC coatings to selectively reflect only a narrow band of the solar spectrum, the researchers have minimized the impact on the overall power conversion efficiency, paving the way for high-performance BIPV solutions.
Architectural Design
The integration of coloured solar modules into the built environment requires close collaboration between renewable energy specialists and architectural designers, ensuring that the aesthetic and functional requirements are seamlessly met.
Façade Integration
The researchers have demonstrated the ability of their CLC-coated solar cells to blend into a variety of backgrounds, including textured wooden surfaces and metallic plates, effectively camouflaging the solar modules at distances beyond 2 meters. This versatility is crucial for the seamless integration of BIPV into building façades.
Roof Applications
In addition to façade integration, the researchers have also explored the potential of their CLC coatings for roof-mounted solar modules, where the viewing angle and lighting conditions may differ from vertical wall installations. By optimizing the CLC pitch and distribution, the researchers aim to address the angle-dependent nature of structural colour to ensure consistent and appealing aesthetics.
Urban Environments
The successful deployment of BIPV solutions within the urban landscape is essential for the widespread adoption of renewable energy. The researchers’ approach to camouflaging solar modules through pixelated CLC coatings demonstrates a promising pathway for integrating solar energy generation into the built environment in a way that is visually harmonious and acceptable to the public.
The University of Luxembourg’s research on arbitrary and active colouring of solar cells with negligible efficiency loss represents a significant breakthrough in the field of BIPV. By overcoming the traditional trade-offs between aesthetics and performance, the researchers have paved the way for a future where renewable energy generation is seamlessly woven into the fabric of our cities and buildings, driving the transition towards a more sustainable and environmentally-conscious future.