Nuzzo's group used the techniques to make functioning microscopic spherical solar cells, as a proof of the functionality of what he calls "materials origami." Before cutting the silicon into the petal shape, the team treated it to form the conductive regions that make a solar cell work. After the flower had folded up into a sphere, electrical contacts were added. The group used a similar technique to make cylindrical micro-solar cells as well.

These devices convert only about 1 percent of the light that hits them into electricity--a poor return for a solar cell--but this is better than a planar solar cell made using the same relatively crude techniques using the same amount of silicon. The researchers say the technique can be applied to other materials besides silicon, and could be used to make new forms of solar cells. The work is described online this week in the Proceedings of the National Academy of Sciences.

"Folding is very appealing because you can make fantastic, complicated three-dimensional shapes," says George Barbastathis, professor of mechanical engineering at MIT.

There are other ways of improving solar cells' ability to capture light, such as antireflective coatings and surface texturing. The main advantage of the new approach is that it requires less material, says Nuzzo. Planar solar cells just a few micrometers thick can't be textured--there's simply not enough material. And antireflective coatings add more manufacturing costs and complexity. Self-assembly, Nuzzo hopes, could offer an alternative.

The Illinois group will now work to improve the process, and make designs that further improve the cells' light management. "We want to bring forward form factors that rely on high performance materials like silicon but provide a substantial economy" by using as little of these expensive materials as possible, says Nuzzo.