PHOTOVOLTAICS | MATERIALS
conductive polymers can help to improve the performance of photovoltaic cells. Researchers from the University of Osaka have
created ‘mirror-image’ semiconducting polymers that boost solar cell performance. This could help organic solar cells – which are based on plastics – compete with conventional silicon-based equiva- lents.
In an article in Angewandte Chemie Internation- al Edition, the researchers describe how the new polymers improve electron flow and efficiency. This was done by changing the type of symmetry of the ‘acceptor molecules’ – which can improve the efficiency of organic solar cells. “We knew that using electron acceptor mol- ecules that are asymmetric left to right could boost organic solar cell performance by preventing recombination,” said Shuang Li, lead author of the paper. “But chiral acceptors that have vertical asymmetry hadn’t been explored.” Vertical asymmetry means the top and bottom
of the molecule are different, so there are two mirror-image versions of the whole molecule that cannot be superimposed – a property called chirality. Vertical asymmetry has several benefits.
IMAGE: CHALMERS UNIVERSITY OF TECHNOLOGY/HENRIK SANDSJÖ
The acceptor molecule has more difference in charge between the top and bottom. This helps the molecules pack together and mix better with donor molecules, improving the flow of electrons, say the researchers. The creation of a spin-polarised current from the
mirror image molecules led the organic solar cells to show power conversion efficiencies of about 8%, which is three times higher than the non-mirror- image version.
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