New Spray-on Solar Cells Invented

An inch-long array of some of the tiniest solar cells ever built has been successfully tested as a power source for microscopic machines, a new study reports.

Xiaomei Jiang of the University of South Florida and her colleagues needed a power source for a microscopic sensor that can detect dangerous chemicals and toxins, potentially helping to sniff out chemical leaks. So the team turned to solar cells.

But these aren't the traditional solar cells that you see perched on rooftops. Most solar cells in use now have a brittle backing made of silicon (found in sand, and the same material computer chips are made with).

Instead of using silicon, Jiang and her colleagues turned to a polymer (a long organic molecule made of repeating structural units). The polymer they selected has the same electrical properties as silicon wafers, but can be dissolved and printed onto flexible material.

"I think these materials have a lot more potential than traditional silicon," Jiang said. "They could be sprayed on any surface that is exposed to sunlight — a uniform, a car, a house."

Another type of solar cell scientists are trying to develop are dye-sensitized cells, which so far are slightly less efficient than silicon cells, which convert about 12 percent of the sunlight that hits them into electricity. Typical organic cells only manage about 3 percent, prompting some scientists to caution praise for their use.

Jiang and her colleagues made 20 tiny cells — each the size of a lower case "o" in standard 12-point print — and joined them together in an array to power the microscopic detector.

The detector needs a 15-volt power source to work, and so far Jiang's solar cell array can provide about half of that — up to 7.8 volts in the lab tests she and her colleagues did.

The next step, Jiang said, is to increase the voltage and then combine the tiny solar array to the chemical sensors. Jiang expects to reach the 15-volt goal by the end of the year. The results of her initial experiment are detailed in the inaugural issue of the Journal of Renewable and Sustainable Energy.

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