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Solar power venture focuses on ZnMnTe and InGaN

New "split band" semiconductors based on ZnMnTe alloys could deliver multi-junction solar cell performance.

A new joint venture company is aiming to become the first to commercialize ZnMnTe and InGaN semiconductors for solar energy applications.

Japanese conglomerate Sumitomo Chemical and the US start-up RoseStreet Labs have set up a new company called RSL Energy in Phoenix, AZ, to develop, manufacture and sell what they describe as full-spectrum solar cells.

Having signed exclusive technology licenses from Lawrence Berkeley National Laboratory (LBNL) and Cornell University, RSL Energy believes that the novel materials could be commercialized for solar energy production within three years.

Wladyslaw Walukiewicz and Kin Man Yu have developed the ZnMnTe material system at LBNL. They have found that it is possible to split the conduction band of ZnMnTe by adding oxygen to the semiconductor alloy.

The bands split so that the normally single-band material becomes multi-band, with the energy levels widely spaced to create three energy transitions that fall within the range of the solar spectrum.

This means that by tailoring the exact proportion of oxygen impurities in the alloy, the energy levels can, in theory, be tuned to produce triple-band material capable of more than 50 per cent conversion efficiency.

According to the research team, the energy bands could be further split to yield quadruple-band semiconductors with up to 73 per cent calculated efficiency.

RSL Energy also has a license to commercialize a different approach that was developed through a collaboration between LBNL and Cornell. This has focused on InGaN as a material that can be used in more conventional multi-junction solar cell designs.

The joint venture company believes that the InGaN approach could produce solar cells with practical efficiencies of more than 48 per cent.

The US Defense Advanced Research Projects Agency (DARPA) is currently funding a separate photovoltaics project involving multi-junction cell manufacturer Emcore that is also working to incorporate InGaN in highly-efficient cell designs (see related story).

With a start-up capital of $6.6 million, RSL Energy is 50 per cent-owned by Sumitomo Chemical and 50 per cent owned by RoseStreet Labs. Sumitomo's subsidiary Sumika Electronic Materials has the first right of refusal to produce the compound semiconductor materials required.

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