Oxygen breathes new life into solar cell research


Oxygen breathes new life into solar cell research

Molecular Photonics Laboratories at UNSW Sydney Credit: UNSW Sydney / Exciton Science

Scientists in Australia and the United States have been able to ‘convert’ low-energy light into high-energy light, which can be captured by solar cells, in a new way, with oxygen as a surprise secret ingredient. The results are published in Nature Photonics today.

While the efficiencies of the approach are relatively low and more work is needed to achieve commercialization, the research is an exciting development, according to lead author Professor Tim Schmidt of the ARC Center of Excellence at Exciton Science and UNSW Sydney.

“The sun’s energy is not just visible light,” explains Professor Schmidt.

“The spectrum is broad, including infrared light that gives us heat and ultraviolet light that can burn our skin.”

“Most solar cells, charge-coupled device (CCD) cameras, and photodiodes (a semiconductor that converts light into electrical current) are made of silicon, which cannot respond to light with less energy than near infrared.

“This means that some parts of the light spectrum are not used in many of our current devices and technologies.”

To extend the sensitivity range of these devices, and potentially increase the efficiency of solar cells, one strategy is to ‘convert light’, converting low-energy light into more visible and energetic light that can excite silicon.

“One way to do this is to capture multiple smaller energy light photons and stick them together,” says Professor Schmidt.

“This can be done by interacting excitons (united states of electrons and electron holes that can carry energy without carrying a net electrical charge) on organic molecules.”

Until now, this has never been accomplished beyond the silicon band gap, which is the minimum energy required to drive an electron in silicon to a state where it can participate in conduction. However, researchers at UNSW Sydney-based Exciton Science have solved this challenge. And they transformed a familiar enemy, oxygen, into an unlikely friend to achieve their goal.

Together with collaborators from RMIT University and the University of Kentucky, the researchers used semiconductor quantum dots (artificial nanoscale crystals) to absorb low-energy light and molecular oxygen to transfer light to organic molecules.

Oxygen is generally detrimental to molecular excitons, but at such low energies its role changes and can mediate energy transfer, allowing organic molecules to emit visible light, above the silicon band range.

Collaborating author Professor Jared Cole of RMIT University says: “The interesting thing is that often without oxygen, many things work well. And as soon as oxygen is let in, they stop working.”

“It was the Achilles’ heel that ruined all of our plans, but now, not only have we found a way to avoid it, it suddenly helps us.”

Efficiencies are still low, but scientists have strategies to improve this in the near future.

“This is just an early demonstration, and it takes a lot of material development to make commercial solar cells, but this shows us that it is possible,” says Professor Schmidt.

And lead author Elham Gholizadeh, also from UNSW Sydney, is optimistic about the potential of the work to have a rapid positive impact in the field of research.

“Since this is the first time we have been successful with this method, we will face some challenges,” she says.

“But I am very hopeful and I think we can improve efficiency quickly. I think it is quite exciting for everyone. It is a good method of using oxygen to transfer energy.”

“Violanthrone doesn’t have the perfect quantum photoluminescence performance, so the next step will be to look for an even better molecule.”


A path is opened to minimize waste in capturing solar energy


More information:
Photochemical up-conversion of near infrared light from below the silicon band, Nature Photonics (2020). DOI: 10.1038 / s41566-020-0664-3

Provided by the ARC Center of Excellence in Exciton Science

Citation: Oxygen breathes new life into solar cell research (2020, July 20) retrieved on July 21, 2020 from https://techxplore.com/news/2020-07-oxygen-life-solar-cell.html

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