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An international working group spent months looking for the best semiconductor materials. They decided to focus on oligomers.

The German government is rapidly expanding all forms of regenerative energy as it phases out Russian gas and seeks greater energy resilience. But there are barriers to ramping up solar: global supply chain shortages present a serious production challenge, and the surface area available for solar panels is limited in densely-populated municipalities.

Organic solar cells offer a way out of this conundrum, being easier to manufacture than conventional silicon modules and more versatile. In contrast to crystalline systems, they consist of carbon-based semiconductors carried in solution inside a supporting film. This means the modules are flexible and can be translucent or transparent, which opens up a bigger range of potential applications in urban settings, particularly for use in windows and glass structures.

The international working group led by Christoph Brabec, chair of Materials Science at Friedrich Alexander University of Erlangen-Nürnberg (FAU) and director of the Helmholtz Institute Erlangen-Nürnberg for Renewable Energy (HI ERN), spent months looking for the best semiconductor materials. They decided to focus on oligomers: due to their shorter chains, they can be precisely designed and are more efficient in near-infrared light than longer polymer chains. However, they are also less stable.

After extensive fine-tuning of the molecular structure, the team produced a promising candidate – an oligomer called “OY3”. “OY3 has an average performance efficiency of 15 percent,” says Brabec in a press release. “However, what also impressed us was its excellent photostability.” It retained 94 percent of its original output even after 200 hours of operation. Further measurements showed an operating life of more than 25,000 hours (16 years).

“These parameters are unique for multi-layer organic PV modules and fulfil all requirements for rapid commercialisation. Our strategy of targeted oligomer design takes organic photovoltaics to a new level of efficiency and brings them very close to practical application,” concludes Brabec.