Adding Color to Solar Cells

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Fashion sometimes is about style over substance, but to make solar cells stylish, efficiency cannot be sacrificed for design flexibility.

Covering a roof or a façade with standard black or bluish-gray solar cells to generate electricity will change a building’s original appearance — and not always for the better. With the help of thin-film technologies, researchers at the Fraunhofer Institute for Applied Optics and Precision Engineering (IOF) are now giving photovoltaics a makeover, turning them into colorful creations.

“Not enough work has been done so far on combining photovoltaics and design elements to really do the term ‘customized photovoltaics’ justice,” said Kevin Füchsel, project manager at Fraunhofer IOF.

Füchsel has spent the last four years developing nanostructured solar cells suitable for mass production as part of a junior research group funded by Germany’s Federal Ministry for Education and Research. Together with a Fraunhofer team and scientists at the Friedrich-Schiller University, the researchers are looking for cost-effective techniques and manufacturing processes that increase both the efficiency of solar panels and the design flexibility for architects and designers.

The photomontage shows how the Fraunhofer IAO building in Stuttgart could be fitted with an efficient design solar façade.
The photomontage shows how the Fraunhofer IAO building in Stuttgart could be fitted with an efficient design solar façade. Courtesy of ©Fraunhofer IOF.

The investigators developed a simple semiconductor-insulator-semiconductor (SIS) solar cell with a transparent conductive oxide (TCO) outer layer to capture more light and, they say, it could be made in different colors and shapes.

“The color comes from changing the physical thickness of the transparent conductive oxide layer, or modifying its refractive index,” Füchsel said. “Giving solar cells color doesn’t really affect their efficiency. The additional transparent TCO layer has barely any impact on the current yield.”

Simulations showed that SIS cells could be up to 20 percent efficient. In practice, the efficiency depends on the design of the panels and the direction the building faces. Not every color would generate the same amount of electricity, the scientists say. There are restrictions, for example, with certain blends of red, blue and green.

Dye solar modules and flexible organic solar cells have also been used to provide new opportunities in façade design.

Laser-based optical welding processes will be used to connect several solar cells together to create a single module. An inkjet printing process under development could also be used to contact the conductive TCO later on the silicon wafer, enabling faster manufacturing and additional degrees of design flexibility.

SIS solar cells could be used to make large billboards that produce their own electricity, the researchers say. Patents already cover the production of colored cells, as well as the ability to integrate design elements into solar panels and whole modules.

“This opens up numerous possibilities to use a building to communicate information, displaying the name of a company or even artistic pictures,” Füchsel said.

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Published: July 2013
colored solar panelsenergyEuropeFraunhofer Institute for Applied Optics and Precision EngineeringFraunhofer IOFGermanygreen photonicsindustrialKevin FüchselMaterials & ChemicalsphotovoltaicsResearch & Technologysemiconductor-insulator-semiconductorSIS solar cellssolar design flexibilityTCOtransparent conductive oxide

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