ITO alternative for clear solar cells

Sara Ver-Bruggen - 29 Nov 2010

Using graphene, researchers at Massachusetts Institute of Technology (MIT) have developed transparent organic solar cells.

The MIT research team has developed an alternative transparent conductor to indium tin oxide (ITO) based on doped graphene and used the material as part of the structure of prototype organic photovoltaics (OPV). The technology could be applied to coating windows and glass with energy harvesting potential.

According to the research team alternative transparent conductive layers are lacking for OPVs. The market for ITO - a material commonly used in electronic devices and touchscreens - is already facing problems as demand is outstripping supply. The team also sees an opportunity to develop a clear conductive layer in OPVs that can outperform ITO.

In experiments organic solar cells made with graphene electrodes had power conversion efficiencies comparable to devices made with ITO. Doping the graphene reduced chances of device failure.

Graphene

The researchers 'grew' graphene sheets using chemical vapor deposition with controlled numbers of layers to make alternatives for ITO anodes. Due to its high electron and hole mobility, high current carrying capability, and high mechanical robustness graphene is a good material candidate for anodes, as well as other components electronics. The material's properties allow for ultra-thin layers of it in such a device, which help to achieve transparency.

With further work the research has potential to be spun out from MIT to develop a commercial technology.

The market for ITO alternatives is significant, spanning LCD and other electronic displays, thin-film solar and organic cells, and also emerging printed electronics devices. A few companies are commercialising ITO alternatives in these markets. One of these, California-based Unidym, recently started a joint programme with Tokyo Electron to scale up a coating tool applying Unidym's ITO alternative, which is based on carbon nanotubes, for displays and solar cell electronics. Tokyo Electron is one of the leading suppliers of semiconductor manufacturing equipment.

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