A sample of the conductive polymer used in the organic solar cell. Photo: Thor Balkhed.
A sample of the conductive polymer used in the organic solar cell. Photo: Thor Balkhed.

For the first time, researchers at Linköping University in Sweden have mapped how energy flows in organic solar cells. They report their findings, which could contribute to more efficient solar cells, in a paper in Nature Communications.

“To enable the full potential of organic solar cells to be exploited, there is a need for a clear picture of how they work,” says Mats Fahlman, a professor in the Laboratory of Organic Electronics at Linköping University. “We have now obtained that picture. This provides a better understanding of how to create new efficient and sustainable solar cell materials.”

Today, solar energy only meets around 2% of the world's energy needs, but its potential is far greater. The energy contained in the sun's rays is more than enough to meet our all needs today and in the future. Solar cells that are cheap and environmentally friendly to manufacture are needed to take advantage of this abundant energy source. In addition, solar cells need to be efficient at absorbing a large proportion of the sun's rays and converting them to electrical energy.

Organic solar cells, based on organic semiconductors, are increasingly emerging as a sustainable option. But until just a few years ago, they were unable match the efficiency of traditional silicon-based solar cells. This was due to the energy lost when separating negatively charged electrons from positively charged ‘holes’, which was thought to be unavoidable.

Then, in 2016, a research team at Linköping University, together with colleagues in Hong Kong, showed that it was possible to avoid this energy loss using different donor-acceptor materials that could help electrons escape from their holes more easily, increasing efficiency. The problem was that no one knew exactly how this happened. Scientists could see that it worked, but not why.

Some of the same research team at Linköping University have now solved this mystery, by identifying what energy levels are required to minimize energy losses.

“To find out how the energy flows, we laid nanometer-thick organic semiconducting films in several layers one on top of the other, rather like a strawberry and cream cake,” explains Xian’e Li, a PhD student at Linköping University and principal author of the paper. “After that we measured the energy required to separate the electrons from their holes in each individual layer.”

The researchers were then able to map the mechanism behind the energy-efficient charge separation. This systematic mapping points to a new way forward for the development of organic solar cells.

This story is adapted from material from Linköping University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.