Low-cost dye solar cells possible with zinc

Sara Ver-Bruggen - 03 May 2012

Research by chemists at the University of Basel in Switzerland could enable production of low-cost dye-sensitised solar cells (DSCs) in future.

DSCs consist of a semiconductor, titanium dioxide, which is coated with a coloured dye that absorbs sunlight. Usually the dye material of choice is ruthenium, a rare transition metal in the platinum group, resulting in DSC efficiencies in excess of 10%.

Though very small amounts of ruthenium are used - DSCs are just nanometres in thickness - such a rare and expensive metal could be an obstacle to the industrialisation of low-cost devices in future.

Ruthenium alternatives

A better alternative would be to use a cheaper and more abundant alternative to ruthenium as the dye. In DSCs, the photosensitiser is one of the most important components influencing solar cell performance. Extensive work on the design and synthesis of organic dyes, to achieve performances on par with ruthenium, has been carried out in Japan by National Institute of Advanced Industrial Science and Technology (AIST), and other R&D centres. But organic dyes tend to be less stable, impacting operating lifetimes.

The University of Basel team has focused on organometallic materials, chemical compounds containing bonds between carbon and metal. Promising candidates are copper and zinc, which is one of the more abundant metals and cheap. The researchers have been able to bind coloured compounds to colourless zinc to produce yellow dyes.

Project officer Biljana Bozic-Weber says: 'Ideally it would be good to produce different colours, but yellow is certainly a good start.'

LiLo

Further work is required, especially to achieve efficiencies on par with ruthenium-based DSCs that are typically in the range of 11-12%. Bozic-Weber declines to speculate, but suggests this could take several years. The research is part of the Light in Light Out: Chemistry for Sustainable Energy Technologies project (LiLo), running until 2015.

The Seventh Framework-funded project is focused on three areas; optimising technologies using transition metal complexes, like ruthenium, to increase efficiency in order to use less of the material in devices such as DSCs; exploring alternative metals with luminescence capability, like zinc and copper; and the use of solar derived electrons for water splitting reactions, for making hydrogen for liquid fuels.

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