Researchers tweak solar-cell efficiency

Solar cells that convert light to electricity are widespread in powering small devices like hand-held calculators and can be an excellent solution to bringing energy to remote locations with abundant sunlight.

Jon Van Chicago Tribune

But the high cost of solar cells made from silicon keeps them from becoming a major contributor to the nation’s overall energy supply. Researchers believe that could change if solar cells made from titanium dioxide become more efficient.

Titanium dioxide solar cells are cheaper to make than silicon cells, and theoretically could convert more than 30 percent of the light that strikes them into electricity, providing a phenomenal energy output for the investment.

So far, however, commercially produced titanium dioxide cells convert photons to electrons with only about 8 percent efficiency, and even in the laboratory, efficiency tops out at about 11 percent. If researchers could boost efficiencies to 20 percent or so, a titanium dioxide solar cell industry would become an economic powerhouse.

The cells mimic the photosynthesis process used by green plants to produce energy. They even have molecules of synthetic chlorophyll sitting atop nanoparticles of titanium dioxide.

The problem, said Joseph Hupp, a chemistry professor at Northwestern University, concerns defects in the nanoparticles. Those defects allow photons to leak away as heat rather than be converted to electrons.

Researchers are tweaking various aspects of the production process to boost electrical output by reducing defects, but they’re working in the dark, Hupp said.

To aid this effort, a Northwestern team, led by Hupp, has devised a technique using lasers to measure defect reduction rather than improvement in electrical output.

"It could be that something you do reduces defects by 80 percent, but you don’t see any increase in electrical output because you need a 95 percent defect reduction to get that effect," Hupp said.

The new laser measurement scheme can signal to scientists when they’re on the right track, and that will help guide their way to changing processes to boost solar cell efficiency, Hupp said.

"People have been working blindly, but they don’t have to anymore," he said. "We expect that teams around the world will adopt this technology to aid their research."

Sweetening xylitol production: ZuChem Inc., the Chicago firm that produces specialized sugars, is turning its attention to xylitol, the sweetener often used in toothpaste, gum and candy for diabetics.

While demand for xylitol is strong, supplies have been constrained by a shortage of raw materials and escalating costs, said David Demirjian, ZuChem president.

"The xylitol market is poised to expand dramatically if it could be produced inexpensively from readily available raw materials," he said.

Using a research grant from the Biotechnology Research and Development Corp., based in Peoria, and working with U.S. Department of Agriculture scientists, ZuChem hopes to develop a catalytic process that will significantly reduce the price of making xylitol, Demirjian said.

If successful, the effort could prove to be a sweet deal for corn farmers in Illinois and other Midwestern states.

"The new process will be more cost-effective," said Demirjian, "and it opens the production route to a wider range of very inexpensive raw materials, including those derived from corn and corn products.

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