Researchers at the University of Warwick have developed a cost efficient way toward a more stable organic solar cell using gold.
Though seemingly counter-intuitive, the addition of gold to the makeup of an organic solar cell system should not jack up its price as the amount of gold needed is minimal.
The researchers fashioned an electrode from thin gold film only 8 billionths of a meter. This means that even at the current gold price, the cost of gold needed to fabricate one square meter of this electrode would come to only around £4.5 ($7.3). Organic solar cells are seen as an inexpensive alternative to silicon solar cells as they use carbon-containing compounds instead of highly purified silicon.
However, the most conventional material used to form the organic solar cell's electrode is indium-tin-oxide, which is not very cost-effective as indium is a rare and expensive material. Indium-tin-oxide is also considered complex and unstable, with a high surface roughness and a tendency to crack upon bending if supported by a plastic substrate. It is usually deposited on a glass substrate.
An ultra-thin film of air-stable metal like gold has long been thought to be a viable alternative to indium-tin-oxide but until now it has not proved that it is possible to deposit a film thin enough to be transparent without being too fragile and electrically resistive.
The University of Warwick team, led by Dr. Ross Hatton and Professor Tim Jones of the department of chemistry, developed a method for the preparation of robust, ultra-thin gold films on glass. The glass surface is subjected to derivatization - slight alterations of its chemical structure - by applying a mixed layer of trimethoxysilane before the layer of gold is deposited on it.
Derivatization often creates a product with slightly different or even new chemical properties from its original. In this case, it modifies glass' growth kinetics to produce a highly conductive yet stable film that has applications for organic solar as well as other future technologies.
"This new method of creating gold based transparent electrodes is potentially widely applicable for a variety of target area applications, particularly where stable, chemically well-defined, ultra-smooth platform electrodes are required, such as in organic optoelectronics and the emerging fields of nanoelectronica and nanophotonics," said Dr. Hatton.
A Warwick spinout company, Molecular Solar Ltd, is set to commercialize the innovation. The full research paper on their findings is published in the journal Advanced Functional Materials. Early this year, the Massachusetts Institute of Technology proposed using graphene in lieu of indium-tin-oxide as electrode for organic solar cells.
Graphene is a form of carbon in which atoms form a flat sheet just one atom thick. Much like gold, graphene also posed problems for those seeking to use it as an electrode because it wouldn't "stick" properly to the electrode structure. With graphene, the problem was it repelled water, so the normal deposition techniques didn't work. The researchers solved this by introducing impurities that changed its behavior and allowed it to bond to glass. This also had the additional advantage of improving its electric conductivity.
Work on the graphene electrodes is ongoing and funded by the Eni-MIT Alliance Solar Frontiers Center and a National Science Foundation research fellowship.
source: Apec-vc Korea
