Improving the Green Glow of Organic Solar Cells

By switching the solvents used in their production, organic solar cells could become even more environmentally sustainable. Researchers from KAUST have demonstrated that plant-derived substitutes for today’s harmful chlorinated solvents can be used without affecting the performance of the resulting solar cells in capturing light.

organic solar cells, green glow
Organic solvents derived from plant residue, algae or microorganisms could replace the toxic solvents typically used to produce solar cells. Image Credit: KAUST; Hassan Tahini

Organic photovoltaics (OPVs), which emit as little as three grams of CO2 equivalent per KW of energy, are one of the greenest solar cell technologies.

However, their fabrication still relies on halogenated solvents that, on top of being linked to reproductive hazards and cancer, are derived from petrochemical processes. We wanted to find green alternatives to protect the health and safety of workers when these cells are manufactured at a larger scale and to further reduce the carbon footprint of OPVs.

Daniel Corzo, PhD Student, King Abdullah University of Science and Technology

Since solvents form the foundation of the printable inks used to create organic solar cells, they are essential to producing OPVs.

Corzo added, “These inks require the organic active materials to remain in solution during processing and then crystallize under optimized conditions as the ink dries. Solvent choice greatly affects OPV processing and overall device performance.

The team used a framework known as the Hansen solubility formulation to find potential substitute solvents.

This methodology measures how similar molecules are to one another based on their molecular interactions. You can select solvents that are alike at the molecular level but have beneficial properties, including reduced toxicity, or that originate from renewable sources,” Corzo explained.

The method showed that terpenes, plant-based solvents that include the aromatic oils limonene and eucalyptol, could serve as effective substitutes.

Corzo stated, “These solvents can be derived from plant residue, such as eucalyptus leaves or orange peel, or be produced from algae and microorganisms in bioreactors.

These substances were an excellent fit for formulating solvent blends for OPVs.

Corzo added, “We obtained solar cells with efficiencies above 16% using terpene-based inks—essentially the same as from chlorinated solvents—but with an 85% lower carbon footprint and with the potential to become carbon negative in the future.

Derya Baran, associate professor in the Material Science and Engineering Department at the King Abdullah University of Science and Technology, stated, “We believe that multiple industries and tech developers will benefit from terpene solvent development.

The group has made its research accessible in an engaging online library for choosing green solvents.

Baran noted, “This library can go beyond the use of green solvents for organic electronics because terpenes are also used in food and fragrance industries, for instance.

Journal Reference:

Corzo, D., et al. (2022) High-performing organic electronics using terpene green solvents from renewable feedstocks. Nature Energy. doi:10.1038/s41560-022-01167-7.

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