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ST tackles alternative solar cells

30 Sep 2003

The Franco-Italian semiconductor manufacturer is developing alternative materials to make cheaper solar cells.

ST Microelectronics (ST), the semiconductor device manufacturer, is to develop two advanced materials that it believes will substantially reduce the cost of solar-generated electricity.

The company’s research teams, based in Naples and Catania in Italy, believe that alternative materials must be found to make solar cells economically viable.

Salvo Coffa is heading up the solar cell research. He believes that current solar cell technology, which uses either silicon or compound semiconductors like gallium arsenide to convert sunlight into energy, is doomed to failure:

“Although there is much support around the world for the principle of generating electricity from solar power, existing technologies are too expensive to be used on an industrial scale,” said Coffa.

Despite good progress in solar cell efficiencies – US-based Boeing subsidiary Spectrolab recently developed a multi-junction cell capable of 36.9% conversion – ST believes that it makes more sense to produce much cheaper cells an efficiency of around 10%.

The company believes that little can be done to either increase the efficiency of current cells, or to reduce their manufacturing cost.

As a result, the ST researchers are following two alternative approaches. The first is based on a so-called Graetzel cell (a device invented by Michael Graetzel of the Swiss Federal Institute of Technology in 1990), which uses a method similar in principle to photosynthesis. In the Graetzel cell, an organic dye absorbs light, while a nanoporous metal oxide layer transports electrons. Holes are transported in the reverse direction by a liquid electrolyte.

Coffa says that ST is looking to replace these liquid electrolytes with a conductive polymer. “This could lead to further reductions in the ‘cost per Watt’, which is the key to making solar energy commercially viable,” he said.

The second idea that the ST researchers are working on is to use a mixture of fullerene and a copper-based organic compound sandwiched between the cell’s two electrodes.

Michael Hatcher is technology editor of Opto & Laser Europe magazine.

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