Dye-sensitized solar cells are flexible and cheap to make, but they tend to be inefficient at converting light into electricity. One way to boost the performance of any solar cell is to increase the surface area available to incoming light. So a group of researchers at Georgia Tech has made dye-sensitized solar cells with a much higher effective surface area by wrapping the cells around optical fibers. These fiber solar cells are six times more efficient than a zinc oxide solar cell with the same surface area, and if they can be built using cheap polymer fibers, they shouldn't be significantly more expensive to make.

The advantage of a fiber-optic solar-cell system over a planar one is that light bounces around inside an optical fiber as it travels along its length, providing more opportunities to interact with the solar cell on its inner surface and producing more current. "For a given real estate, the total area of the cell is higher, and increased surface area means improved light harvesting and more energy," says Max Shtein, an assistant professor of materials science and engineering at the University of Michigan who was not involved with the research.

Fiber-optic solar cells could also be used in ways that aren't possible currently. Zhong Lin Wang, professor of materials science and engineering at Georgia Tech, says fiber solar cells would take up less roof area than planar cells because long lengths of the fibers could be nestled into the walls of a house like electrical wiring.

Dye-sensitized solar cells use dye molecules to absorb light and generate electrons. The Georgia Tech group first removes the cladding from optical fibers and then grows zinc-oxide nanowires along their surface, like bristles on a pipe cleaner. Next, the fibers are treated with dye molecules, which the zinc-oxide structures absorb. The advantage of coating nanowires, rather than a smooth surface, with the dye is that the wires collectively have a very large surface area. The more dye molecules there are over a given area of such a cell, the more light it can absorb, says Wang. The dye-coated fibers are then surrounded by an electrolyte and a metal film that carries electrons off the device. The work is described online in the journal Angewandte Chemie International Edition.