Portable power: Tiny solar cells show promise

So far, they have managed to pull 11 volts of electricity from a small array of the cells, which are each just a quarter of the size of a grain of white rice, said Xiaomei Jiang of the University of South Florida, who led the research.

"They could be sprayed on any surface that is exposed to sunlight — a uniform, a car, a house," Jiang said in a telephone interview.

"Because it is in a solution, you can design a special spray gun where you can control the size and thickness. You could produce a paste and brush it on," she said.

Eventually, Jiang envisions the solar cells being used as a coating on a variety of surfaces, including clothing. They might generate energy to power small electronic devices or charge a cell phone, for example.

Solar cells, which convert energy from the sun into electricity, are in increasing demand amid unstable gas prices and worries over global warming.

Most conventional solar cells are made up of silicon wafers, a brittle substance that limits where they can be placed.

Many teams of scientists are working on different ways to make solar cells more flexible in the hopes of taking better advantage of energy from the sun.

The tiny cells from Jiang's lab are made from an organic polymer that has the same electrical properties of silicon wafers but can be dissolved and applied to flexible materials.

"The main components are carbon and hydrogen — materials that are present in nature and are environmentally friendly," Jiang said.

In research published in the Journal of Renewable and Sustainable Energy, Jiang and colleagues showed an array of 20 of these cells could generate 7.8 volts of electricity, about half the power needed to run a microscopic sensor for detecting dangerous chemicals and toxins.

Her team is now refining the manufacturing process with the hope of doubling that output to 15 volts. "It's a matter of months," Jiang said.