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Solar charged handhelds, phones on the horizon?

German researchers are developing new types of power cells that could eliminate the need to recharge mobile devices.

German researchers are developing new types of power cells that could eliminate the need to recharge mobile devices.

Casio, Siemens and other manufacturers of handheld computers and cell phones are already building prototype devices that use the new power cells, developed at the energy technology department at the Fraunhofer Institute--Germany's answer to MIT.

The plan is to replace rechargeable batteries in mobile devices with a miniature version of the hydrogen fuel cell used to power electric cars. A superefficient solar cell built into the devices would recharge the miniature fuel cell.

Until now, the combination of fuel cells and solar cells was too large to fit into a mobile phone or handheld, Fraunhofer researchers said. And although manufacturers of solar cells continue to raise the efficiency of their products, such cells have been much too expensive for the mass market.

But researchers at the Fraunhofer Institute's Solar Energy Systems ISE in Freiburg are ready to demonstrate next week a high-performance solar module that is integrated in the lid of a Casio handheld and makes the device completely autonomous of external electrical supplies.

"The decisive factor," said Christopher Hebling, head of the Micro-Energy Technology group at the ISE, "is that the device can run on solar power alone even under low lighting levels. At a normal workplace, you have only 3 percent of the brightness of summer sunshine. Even down to a level of 1 percent, the electrical voltage provided by our solar module remains virtually constant. In conventional cell types, it would have long since broken down."

The surfaces of solar cells with such efficiency are coated with an electrically insulating layer of silicon oxide or nitride. This non-conducting material needs to be removed again at specific points to allow attachment of the electrical contacts--a previously complex and expensive process.

But the Fraunhofer researchers have arrived at a new solution: A special laser zaps away the coating from the designated contact points. Such innovations have enabled the researchers to reduce the total number of process steps by 80 percent, making the solar cells cheap enough to become a viable alternative to other sources of energy.

Staff writers reported from Germany.