Researchers Unveil Self-Generating Power Nanowire

October 22, 2007 by Jeff Shepard

Some Harvard chemists claim that they have built a new wire out of photosensitive materials that is hundreds of times smaller than a human hair. The wire is said to not only carry electricity to be used in small circuits, but to generate power as well.

Charles M. Lieber, the Mark Hyman Jr. Professor of Chemistry, and colleagues created the nanowire out of three different kinds of silicon with different electrical properties. The silicon is wrapped in layers to create the wire. When light falls on the outer material, a process begins due to the interaction of the core with the shell layers, leading to the creation of electrical charges. The work was described in the Oct. 18 issue of the journal Nature.

"The idea of creating nanoscale photovoltaics is not new," Lieber stated, "but prior efforts used organic compounds in combination with semiconductor nanostructures that had lower efficiency and that degraded under concentrated sunlight." The materials are said to be more efficient, converting 3.4% of the sunlight into electricity; they can withstand concentrated light without deteriorating, gaining efficiency up to about 5%; and they are said to be as cheap to make as other related nanoscale photovoltaic devices. "The real question is whether there’s a new geometry that will lead to better photovoltaic technology," Lieber said. "We worked on coaxial geometry."

The most recent development builds on Lieber’s considerable prior work on nanoscale devices. He has developed sensors with potential bioterrorism applications that can detect a single virus or other particle, nanowire arrays that can detect signals in individual neurons, and a cracker-sized detector for cancer. A cheap nanoscale power source broadens the potential applications of such nanoscale devices. Though the tiny photovoltaic cells can generate enough electricity to power a similarly tiny circuit, Lieber states that they’re not yet efficient enough to have applications on the scale of commercial power generation.

Leiber states that commercial solar cells have efficiencies around 20%, compared with 3.4% for his nano-solar cells. One avenue of future research, Lieber said, will be to explore ways to boost efficiency of the nanowire photovoltaics. "If they can reach 10 to 15%, their lower cost of production – they can be made from relatively inexpensive materials and don’t require clean rooms to produce – may make them useful in larger-scale applications. There’s no physical reason it couldn’t be higher. I’m pretty optimistic that we’ll be able to track down the efficiency issue."

Until then, Lieber sees a future for the nanowire photovoltaics in niche applications, such as multiple distributed sensors or durable, flexible devices, possibly sewn into clothing or worn as a patch. "It will have to be unique to be an economically viable application, some place where you want durability and flexibility, where if it gets destroyed, people don’t care."