3-D photovoltaic systems go where the sun don’t shine

The photovoltaic (PV) panels adorning the rooftops of buildings around the world have become a visible sign of the shift towards environmentally friendly solar power. Now researchers have developed a new type of three-dimensional PV system using optical fiber that promises solar generators that are foldable, concealed and mobile, meaning they could be hidden from view and leave rooftops panel-free.

Fabrication of the new system developed at Georgia Tech 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 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.

Sunlight entering the optical fiber passes into the nanowires, where it interacts with the dye molecules to produce electrical current. Each reflection within the optical fiber increases the likelihood that the light will interact with the dye molecules, thereby increasing the efficiency. A liquid electrolyte between the nanowires collects the electrical charges. The result is a hybrid nanowire/optical fiber system that can be up to six times as efficient as planar zinc oxide cells with the same surface area.

Zhong Lin Wang, a Regents professor in the Georgia Tech School of Materials Science and Engineering, and his team have reached an efficiency of 3.3 percent and hope to reach 7 to 8 percent after surface modification. That’s still short of the average of around 12 percent for typical solar panels, (and a long way off the record 41.1 percent efficiency achieved in a lab earlier this year), but Wang says the potentially lower cost of their approach could make it attractive for many applications.

Also, because the optical fibers could be used to conduct sunlight into a building’s walls where the nanostructures would convert it to electricity, much of the system can remain hidden from the outside world, giving architects and designers new options for incorporating PV into buildings, vehicles and even military equipment.

"This will really provide some new options for photovoltaic systems," Wang said. "We could eliminate the aesthetic issues of PV arrays on building. 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."

Wang and his research team have produced generators on optical fiber up to 20 centimeters in length using traditional quartz optical fiber, but they would like to use less expensive polymer fiber to reduce the cost. They are also considering other improvements, such as a better method for collecting the charges and a titanium oxide surface coating that could further boost efficiency.

Though it could be used for large PV systems, Wang doesn't expect his solar cells to replace silicon devices any time soon. But he does believe they will broaden the potential applications for photovoltaic energy.