Imagine forgetting to plug in your smartphone, but then not worrying because your clothes could charge it for you. It sounds surreal, but it may one day be reality. An international team of scientists and engineers led by John Badding, a professor of chemistry at Penn State University, have developed a silicon-based optical fiber that acts like a solar cell and offers the promise of fabric that can generate electricity from light.

The origin of the solar-power fiber lies in earlier research by the team, on merging optical fibers with microchips by using high-pressure chemistry to deposit semi-conductors into tiny holes in optical fibers that are finer than a human hair. Effectively, the outer skin of the fiber became its own integrated chip. In the current phase, the team has gone a step further and used the same high-pressure chemistry to form the silicon fiber itself out of crystalline silicon semiconductor materials, so that the fiber becomes a solar cell.

However, there is more to the project than getting a fiber to turn light into electricity. The fibers also have to be long and flexible. "Our goal is to extend high-performance electronic and solar-cell function to longer lengths and to more flexible forms. We already have made meters-long fibers but, in principle, our team's new method could be used to create bendable silicon solar-cell fibers of over ten meters (32.8 feet) in length," Badding said. "Long, fiber-based solar cells give us the potential to do something we couldn't really do before: We can take the silicon fibers and weave them together into a fabric with a wide range of applications such as power generation, battery charging, chemical sensing, and biomedical devices."

A coiled strand of a meter-long solar-cell fiber

Badding also said that a fabric solar collector would be able to collect energy more efficiently because, unlike conventional panels, it offers more than just a flat surface, so it remains exposed to light from many angles. "A solar cell is usually made from a glass or plastic substrate onto which hydrogenated amorphous silicon has been grown," said Badding. "Such a solar cell is created using an expensive piece of equipment called a PECVD reactor and the end result is something flat with little flexibility. But woven, fiber-based solar cells would be lightweight, flexible configurations that are portable, foldable, and even wearable."

The potential of a solar cell that can be woven into fabric is considerable. Imagine being able to charge a smartphone not with panels sewn into a jacket, but with the jacket itself ... or how about laptop cases that charge their contents? In addition, it could be used in wearable electronics for the military or in kevlar anti-meteorite blankets for spacecraft that double as power collectors.

The fibers also can act as photo detectors. According to Pier J. A. Sazio of the University of Southampton, U.K., "Another intriguing property of these silicon-fiber devices is that as they are so compact, they can have a very fast response to visible laser light. In fact, we fabricated fiber-based photodetectors with a bandwidth of over 1.8 GHz."

The results of the research will be posted in an early online edition of Advanced Materials.

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