Converting sunlight to electricity might no longer mean large panels of photovoltaic (PV) cells atop flat surfaces like roofs.

Using zinc oxide nanostructures grown on optical fibers and coated with dye-sensitized solar cell materials, researchers at the Georgia Institute of Technology have developed a new type of three-dimensional PV system. The approach could allow PV systems to be hidden from view and located away from traditional locations, such as rooftops.

“Using this technology, we can make photovoltaic generators that are foldable, concealed and mobile,” said Zhong Lin Wang, a regents professor in the Georgia Tech School of Materials Science and Engineering. “Optical fiber could conduct sunlight into a building’s walls where the nanostructures would convert it to electricity. This is truly a three-dimensional solar cell.”

Dye-sensitized solar cells use a photochemical system to generate electricity. They are inexpensive to manufacture, flexible and mechanically robust, but their tradeoff for lower cost is conversion efficiency, which is lower than that of silicon-based cells. But using nanostructure arrays to increase the surface area available to convert light could help reduce the efficiency disadvantage, while giving architects and designers new options for incorporating PV into buildings, vehicles and even military equipment.

Fabrication of the new Georgia Tech PV system begins with optical fiber of the type used by the telecommunications industry to transport data. First, the researchers remove the cladding layer, then apply a conductive coating to the surface of the fiber before seeding the surface with zinc oxide. Next, they use established solution-based techniques to grow aligned zinc oxide nanowires around the fiber, much like the bristles of a bottle brush. The nanowires are then coated with the dye-sensitized materials that convert light to electricity.

The resulting hybrid nanowire/optical fiber system can be up to six times as efficient as planar zinc oxide cells with the same surface area.

“You have multiple light reflections within the fiber and multiple reflections within the nanostructures. These interactions increase the likelihood that the light will interact with the dye molecules, and that increases the efficiency,” Wang said.

Wang and his research team have reached an efficiency of 3.3 percent and hope to reach 7 to 8 percent after surface modification. This efficiency would be useful for practical energy harvesting. If they can do that, the potentially lower cost of their approach could make it attractive for many applications.

“This will really provide some new options for photovoltaic systems,” Wang said. “We could eliminate the aesthetic issues of PV arrays on buildings. We can also envision PV systems for providing energy to parked vehicles and for charging mobile military equipment where traditional arrays aren’t practical or you wouldn’t want to use them.”