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Green solvents for a 17%-efficient organic solar cell

Scientists in Sweden and China developed a solution-based process to produce organic solar cells, demonstrating efficiencies better than 17%. The process utilizes paraxylene as a solvent, which the researchers claim is less toxic and more stable than others used to reach high organic solar cell efficiencies, and with more work could be scaled up to produce large area devices.

Organic PV covers a range of different materials that have maintained plenty of interest from researchers, but not yet achieved the levels of performance that would be needed to attract commercial interest, save for a few niche applications.

While organic PV presents opportunities for low cost and low carbon footprint manufacturing, balancing efficiency with long term stability is still a challenge, and the best performing cells in terms of efficiency most often rely on solvents that are highly toxic and difficult to work with in manufacturing.

A collaboration between scientists at Linköping University in Sweden and China’s Soochow University looked to address these issues, working on an organic solar cell made from a material known as Y6. For solution processing of this cell material, they chose paraxylene, which they say has no toxic ingredients and a higher boiling point making it easier to use in manufacturing.

With this solvent, the group was able to manufacture laboratory-sized solar cells with an efficiency better than 17%, as well as a 36cm² device that reached 14% efficiency. The cells are described in the paper A guest-assisted molecular-organization approach for >17% efficiency organic solar cells using environmentally friendly solvents, published in Nature Energy.

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“This is a major step towards large-scale industrial manufacture of efficient and stable organic solar cells, say Linköping University researchers Feng Gao and Rui Zhang. “Our results now open for the manufacture of organic solar cells at larger scales for outdoor use.”

Guest molecule

Key to these achievements, the researchers say, was the addition of a guest molecule ‘BTO’, which served to keep the Y6 molecules closely packed and ordered within the solvents. Keeping the structure uniform in this way benefits the cell efficiency, improves long-term stability and allows for the fabrication of larger area devices.

As well as paving the way for industrial development of organic solar cells, the group says its approach could be applied to other materials. “Our strategy leads to clear design rules for optimising the interaction between organic donors and acceptors in multicomponent blends, meeting the critical requirements for future development of organic photovoltaic technology,” said Professor Yaowen Li, Soochow University.

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Source: pv magazine