Right now organic solar cells, although cheap, are too inefficient to compete with silicon-based ones. A team of researchers from Wake Forest University in North Carolina have developed a practical method of doubling the efficiency of organic (or dye-sensitized) solar cells by adding a layer of upright optical fibers acting as sunlight traps.
David Carroll, the team’s leader in this project, has founded a spinoff company called “FiberCell”, trying to develop a manufacturing process that others could use: “We’re on the cusp of having working demonstrators that would convince someone to go into production with this,” said Carroll.
Increasing the efficiency of dye-sensitized solar cells to above 10 percent by tweaking the chemistries of the organic layer isn’t enough, as those cannot catch up to the performance of silicon solar cells. “The answer doesn’t lie in chemistry–it lies in the architecture of the cell itself,” he says. Carroll adds that the dollar-per-watt cost of manufacturing fiber-based organic cells should be about the same cost as for flat organic cells. “But they can be produced in a factory costing one-tenth that of a silicon foundry,” he says. This would make them much cheaper to produce than silicon cells.
Carooll calls his fibers “light pipes”, and they protrude from the surface perpendicularly on the surface of the cell. They are surrounded by organic solar cells applied using a dip-coating process, and a light-absorbing dye or polymer is also sprayed onto the cell. Light can enter the tip of a fiber at any angle. Photons then bounce around inside the fiber until they are absorbed by the surrounding organic cell.
Lab tests demonstrated that the fiber they installed helped the light absorption by half. One factor that also reduces the prices of the whole contraption is the lack of sun tracking devices, because the fibers can receive the light from any angle.