Almost all silicon PV panels available on the market today are black. Copper indium gallium (CIGS) cells and panels are often a dark coppery color, largely because those colors absorb more light more readily. But what if you could choose PV panels that match the color of a home or building’s original paint color? That’s one of the things being worked on at the Fraunhofer Institute for Applied Optics and Precision Engineering IOF.
"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 the Fraunhofer. He has been developing nanostructured solar cells that can allow for more flexibility in terms of design.
Füchsel is working with his research team exploring how to make colored solar cells out of paper-thin silicon wafers. The wafers are sandwiched with an insulated layer onto which transparent conductive oxide (TCO) layer is placed. The system is called a SIS (semiconductor-insulator-semiconductor) cell. By tuning the TCO layer it’s color can be changed. “The color comes from changing the physical thickness of the transparent conductive oxide layer, or modifying its refractive index," Füchsel explained. In addition, "TCO has a lower refractive index than silicon, so it works as an anti-reflective coating," Füchsel said.
Despite the colored surface Füchsel said it won’t impact their ability to convert sunlight into electricity. "Giving solar cells color doesn't really affect their efficiency. The additional transparent TCO layer has barely any impact on the current yield," Füchsel said. While certain blends of red, blue and green can affect the efficiency of the cells, the lab said simulations showed that SIS cells could be up to 20 percent efficient.
The researchers are also borrowing some techniques being used in the thin-film world of photovoltaics. For instance, they are looking into replacing the indium tin oxide as a coating material and replacing it with zinc oxide and aluminum. And they’re also researching how to use an inkjet printing process “to contact the conductive TCO later on the silicon wafer,” according to the institute.
If they’re able to do that, SIS solar cells could even become printed billboards that make their own energy to light themselves at night. "This opens up numerous possibilities to use a building to communicate information, displaying the name of a company or even artistic pictures," Füchsel said.