Color is the new black for solar cells
Design is sometimes more style than substance, but solar cell manufacturers cannot afford to lose efficiency just to make solar arrays more stylish. 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) in Jena, Germany, are now giving photovoltaics a makeover by adding color.
“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.
The photomontage shows how the Fraunhofer IAO building in Stuttgart could be fitted with a solar façade. Courtesy of Fraunhofer IOF.
Füchsel has spent the past 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 have developed a simple semiconductor-insulator-semiconductor (SIS) solar cell with a transparent conductive oxide (TCO) outer layer to capture more light. 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. Patents already cover the production of colored cells and the ability to integrate design elements into solar panels and whole modules.
The SIS solar cells could be used to make large billboards that produce their own electricity, the researchers say.
“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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