Organic solar cells ditch ITO for Au

University of Warwick researchers have developed a gold-plated window as the transparent electrode for organic solar cells. The method can be scaled up for large-area applications like solar cells and the resulting electrodes are chemically very well-defined.

April 7, 2011 — Researchers at the University of Warwick have developed a gold-plated window as the transparent electrode for organic solar cells.

Contrary to what one might expect, these electrodes have the potential to be relatively cheap, as the gold layer is 8 billionths of a meter. This ultra-low thickness means that even at the current high gold price, the cost of the gold needed to fabricate one square meter of this electrode is around £4.5. It can also be readily recouped from the organic solar cell at the end of its life.

Gold is widely used to form reliable interconnects in the electronics industry. Organic solar cells have long relied on indium tin oxide (ITO) coated glass as the transparent electrode. ITO is a complex, unstable material with a high surface roughness and tendency to crack upon bending if supported on a plastic substrate. Indium can be expensive to use due to supply shortages.

An ultra-thin film of air-stable metal like gold would offer a viable alternative to ITO, but until now it has not been possible to deposit a film thin enough to be transparent without being too fragile and electrically resistive to be useful.

Research led by Dr Ross Hatton and Professor Tim Jones in the University of Warwick’s department of Chemistry has developed a rapid method for the preparation of robust, ultra-thin gold films on glass. This method can be scaled up for large-area applications like solar cells and the resulting electrodes are chemically very well-defined.

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Researchers at the University of Warwick hold up a sample of their gold transparent electrode.

“This new method of creating gold-based transparent electrodes is potentially widely applicable for a variety of large area applications, particularly where stable, chemically well-defined, ultra-smooth platform electrodes are required, such as in organic optoelectronics and the emerging fields of nanoelectronics and nanophotonics, ” said Dr Hatton.

The full research paper, “Ultrathin Transparent Au Electrodes for Organic Photovoltaics Fabricated Using a Mixed Mono-Molecular Nucleation Layer,” is published in Advanced Functional Materials: http://dx.doi.org/10.1002/adfm.201002021.

The film’s optical properties can be finetuned by perforating it with tiny circular holes using something as simple as polystyrene balls. The University of Warwick research team has also had some early success in depositing ultra-thin gold films directly on plastic substrates.

Molecular Solar Ltd, a Warwick spinout company, is dedicated to commercializing the discoveries of its academic founders in the area of organic solar cells.

This work was supported by the European Regional Development Fund (ERDF) / Advantage West Midlands Science City SCRA AM2 project, the Engineering and Physical Sciences Research Council (EPSRC) and the Royal Academy of Engineering. For further information, visit http://www2.warwick.ac.uk/

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