Organic solar cells one step closer to commercialisation

UK scientists have discovered that key components of organic solar cells require less electrical conductivity than initially thought — a breakthrough that should bring the devices closer to becoming a commercial reality. Their work has been published in the journal Advanced Functional Materials.

A basic organic solar cell consists of a thin film of organic semiconductors sandwiched between two electrodes which extract charges generated in the organic semiconductor layer to the external circuit. It has long been assumed that 100% of the surface of each electrode should be electrically conductive to maximise the efficiency of charge extraction, but Dr Ross Hatton and his team at the University of Warwick wanted to know whether this was really true.

The researchers developed a model electrode that they could systematically change the surface area of, and found that when as much as 99% of its surface was electrically insulating the electrode still performs as well as if 100% of the surface was conducting, provided the conducting regions aren’t too far apart. The electrodes therefore only need ~1% of their surface area to be electrically conductive to be fully effective.

In addition, high-performance organic solar cells have additional transparent layers at the interfaces between the electrodes and the light-harvesting organic semiconductor layer that are essential for optimising the light distribution in the device and improving its stability, but must also be able to conduct charges to the electrodes. Not many materials meet all of these requirements, but the new discovery means a range of composite materials could be used.

“This new finding means composites of insulators and conducting nanoparticles — such as carbon nanotubes, graphene fragments or metal nanoparticles — could have great potential for this purpose, offering enhanced device performance or lower cost,” said postdoctoral researcher Dr Dinesha Dabera.

“Organic solar cells are very close to being commercialised but they’re not quite there yet, so anything that allows you to further reduce cost whilst also improving performance is going to help enable that.”

Organic solar cells are potentially very environmentally friendly, because they contain no toxic elements and can be processed at low temperature using roll-to-roll deposition, so can have an extremely low carbon footprint and a short energy payback time. Importantly, they are also flexible, with the ability to be applied to curved surfaces such as the body of a car.

“Conventional silicon solar cells are fantastic for large-scale electricity generation in solar farms and on the roofs of buildings, but they are poorly matched to the needs of electric vehicles and for integration into windows on buildings, which are no longer niche applications,” Dr Hatton explained. “Organic solar cells can sit on curved surfaces, and are very lightweight and low profile.

“This discovery may help enable these new types of flexible solar cells to become a commercial reality sooner because it will give the designers of this class of solar cells more choice in the materials they can use.”

Image credit: ©stock.adobe.com/au/Scanrail

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