Layer of gold nanodots could improve organic solar cell efficiency

LONDON, UK: A layer of gold nanodots on the surface of indium-tin oxide (ITO) coated glass may improve the efficiency of organic photovoltaic cells, according to new research published in the journal, Gold Bulletin. The paper, written by an international team from France and Denmark, explains how a discontinuous film of gold nanodots just 0.5nm thick is sufficient to generate the performance improvement.

Organic photovoltaic cells have strong potential as a low cost means of generating solar power and are currently the focus of significant scientific interest. However, one of the factors limiting the efficiency of these cells at present is the energy alignment between the transparent ITO electrode and the organic semi-conductors responsible for harvesting light and conducting photo-generated charge carriers to the electrodes.

Lead author, Professor Linda Cattin at the University of Nantes commented: "Our earlier work showed that a thin gold film, introduced at the interface between the ITO electrode and organic substrate, provides a strong improvement in the cell efficiency. This new work shows that only fractional coverage with gold (15 percent) on the ITO electrode is required to provide the efficiency improvement. This discontinuous gold layer may provide a viable anode buffer layer for future organic photovoltaic devices."

Dr Ross Hatton, Assistant Professor of Chemistry and Royal Academy of Engineering Research Fellow at the University of Warwick, who specialises in nano-structured electrodes for organic photovoltaics, commented: "The need to improve upon ITO as an electrode material is clear and it is remarkable that such a low coverage of gold is so effective in facilitating charge carrier extraction. The methods reported by Dr Cattin and co-workers for determining fractional surface coverage are key tools for probing this important class of electrode buffer layer.”

Dr Hatton's work has demonstrated an alternative approach to improve organic photovoltaics, by replacing the ITO electrode layer with a continuous, flexible and highly transparent ultra-thin gold film electrode. This technology has been licensed to the Warwick University spin-out Molecular Solar, who have recently been awarded the Lord Stafford Award for Innovation in Development and short listed for The Engineer's Technology and Innovation Awards.

Director of Technology at the World Gold Council and Editor of Gold Bulletin, Dr Richard Holliday, said: "Gold has a strong track record of use in the electronics industry, largely due to its high conductivity, chemical stability and compatibility with other elements. This combination of properties makes gold an ideal candidate for conductive layers in photovoltaics. Through precise control of metal thickness, manufacturers are able to use gold cost-effectively."