A Bit of Energetic Enlightenment From Nature

Lycopene, which makes tomatoes red, could also help make biogenic solar panels that work well in cities that don't get much sun.

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In a single hour, more solar energy hits the Earth than all of humankind uses in a year, making solar power an attractive option for renewable energy. But what if you live somewhere like Vancouver, known for its rainy and overcast skies?

Vancouver-based researcher Vikramaditya Yadav, professor of chemical and biological engineering at the University of British Columbia, was inspired by nature to find a way to harness solar energy, even under low light conditions.

Lycopene is the molecule that makes grapefruit and watermelon pink, and it’s that insoluble pigment that stains plastic containers after using them to hold tomato sauce. It’s also an important player in photosynthesis, the process that plants use to turn sunlight into energy.

Carotenoids like lycopene are typically considered accessory photosynthetic molecules, with the iconic green chlorophyll being the primary workhorse during long summer days. But carotenoids are more stable, and they continue to work as the autumn days shorten, becoming visible in leaves and ripening tomatoes as chlorophyll breaks down to reveal their golden and red-orange hues.

Past designs for biogenic solar cells have extracted photosynthetic dyes like lycopene out of the bacteria used to produce them. However, the extraction process is expensive and uses toxic solvents that can degrade the dyes.

Yadav wanted to see what might happen if he skipped the extraction step altogether. He engineered E. coli cells to produce lots of lycopene, and then he left the bacteria intact. He took the pigment‐loaded bacteria and coated them with TiO2 nanoparticles to act as a semiconductor, and applied the mixture onto a glass surface.

This configuration generated a current density of 0.686 milliamps per square centimetre, almost doubling the 0.362 achieved previously by other biogenic solar cells.

“We recorded the highest current density for a biogenic solar cell,” said Yadav in a statement. “These hybrid materials that we are developing can be manufactured economically and sustainably, and, with sufficient optimization, could perform at comparable efficiencies as conventional solar cells.”

Yadav estimates that eliminating lycopene extraction reduces the cost of dye production down to just one tenth of what it was before. Beyond providing effective solar panels for overcast cities, biogenic solar cells might also find potential applications in mining, deep-sea exploration and other low-light environments.

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Karyn Ho is a science animator and engineer who thrives at the interface between science, engineering, medicine, and art. She earned her MScBMC (biomedical communications) and PhD (chemical engineering and biomedical engineering) at the University of Toronto. Karyn is passionate about using cutting edge discoveries to create dynamic stories as a way of supporting innovation, collaboration, education, and informed decision making. By translating knowledge into narratives, her vision is to captivate people, spark their curiosity, and motivate them to share what they learned.