September 2004

Solar-Cell Rollout

Continued from page 2

By Peter Fairley

Shining Startups

At least one startup may beat Siemens to that goal. Konarka is now gearing up to manufacture its novel photovoltaic film, which it expects to start selling next year. Unlike Siemens's, Konarka's films don't use buckyballs, instead relying on tiny semiconducting particles of titanium dioxide coated with light-absorbing dyes, bathed in an electrolyte, and embedded in plastic film. But like Siemens's solar cells, Konarka's can be easily and cheaply made.

Konarka sees a short-term payoff in consumer products. Power-hungry electronics such as cell phones and laptops-and anything else with a battery and access to light-could make good use of Konarka's flexible film, according to executive vice president Daniel McGahn. And the solar films could eliminate the need to run power cords to many other electronic devices installed in homes or businesses, such as the temperature, gas, and process sensors scattered throughout manufacturing plants.

Down the road, researchers hope to boost nano solar cells' power output and make them even easier to deploy, eventually spraying them directly onto almost any surface. Palo Alto, CA-based startup Nanosolar, which has raised $5 million in venture capital, is working on making this idea practical. The company is exploiting the latest techniques for automatically assembling nanomaterials into precisely ordered architectures-all with a higher degree of control than ever before possible.

Nanosolar's approach is disarmingly simple. Researchers spray a cocktail of alcohol, surfactants (substances like those used in detergents), and titanium compounds on a metal foil. As the alcohol evaporates, the surfactant molecules bunch together into elongated tubes, erecting a molecular scaffold around which the titanium compounds gather and fuse. In just 30 seconds a block of titanium oxide bored through with holes just a few nanometers wide rises from the foil. Fill the holes with a conductive polymer, add electrodes, cover the whole block with a transparent plastic, and you have a highly efficient solar cell.

In theory, at least, energized electrons in Nanosolar's columns of plastic need only jump a few nanometers to reach the titanium compounds. From there, the electrons shoot straight through the vertically oriented titanium compounds to an electrode. "It's a fast path out," says Nanosolar's CEO Martin Roscheisen, an Internet entrepreneur who founded the company two years ago.

This technology could enable Nanosolar to spray-paint photovoltaics onto building tiles, vehicles, and billboards, and wire them up to electrodes. At first, the cells would be applied in manufacturing, but eventually they might be sprayed onto existing surfaces. When will this approach become prevalent enough to feed electricity to power grids? Roscheisen won't say, but he vows that by the end of next year, Nanosolar will have prototypes that capture 10 percent of incoming solar energy.