Miniscule solar cells would enable ultramicroscopic technology

Published 19 October 2007

Harvard team develops solar cells 200 hundred times thinner than a human hair; source of power for ultramicroscopic technology now available; team leaders says one of the first application would be in monitoring bioterrorism

Scientists have developed solar cells 200 hundred times thinner than a human hair. The scientists believe these cells will power the nanoscale gadgetry of tomorrow. From consumer devices to bioterrorism monitors to in-body diagnostics, the ultramicroscopic technology may well take centre stage in less than a decade from now. Finding the sources to power ultramicroscopic technology, however, has been a major obstacle, so the development of the tiny cells is an important breakthrough. Charles Lieber, who leads the Harvard Lieber Research Group, and colleagues at Harvard University describe silicon nanowire they devised that can convert light into electrical energy. Virtually invisible to the naked eye, a single strand can crank out up to 200 picowatts. Now, two hundred billionths of a watt may not seem like much, but at nanoscale it is enough to provide a steady output of electricity to run ultralow power electronics, including some that could be worn on — or even inside — the body. It is also clean, efficient, and renewable. “An individual nanoelectonic device will indeed consume very little power, but to do something interesting will require many interconnected devices and thus the power requirement — even for nanosystems — can be a challenge,” Lieber said. Monitoring bioterrorism threats, for example, would require an entire array of nanosensors, nanoprocessors to analyse the signals received, and nanotransmitters to relay information to a centralised facility, he said. Conventional sources, he added, are “bulky, non-renewable and expensive” by comparison.

The nanowire is not made of metal but of silicon with three different types of conductivity arranged as layered shells. Incoming light generates electrons in the outer shell, which are then swept into the second layer and the inner core along micropores. These “holes,” as they are called, carry an equal, but opposite, charge as electrons, meaning that the two particles move in opposite directions in the presence of an electric field. “The electrically connected core and cladding” — a kind of sheath — “play the same role as the ‘+’ and ‘-’ termini of a battery,” Lieber said.

-read more in Bozhi Tian et al., “Coaxial Silicon Nanowires as Solar Cells and Nanoelectronic Power Sources,” Nature 449 (18 October 2007) (doi:10.1038/nature06181): 885-89