Researchers at the University of California, Los Angeles (UCLA) and Solargiga Energy in China have tried to perk up solar panels with coffee. It worked.

Caffeine solar cell.

One of the solar cells the team made using the new method.
Image credits Rui Wang and Jingjing Xue.

The team reports that caffeine can help improve the efficiency with which perovskite solar panels convert light to electricity. The finding could help them a more competitive and cost-effective alternative to silicon solar cells.

Wakey, wakey

“One day, as we were discussing perovskite solar cells, our colleague Rui Wang said, ‘If we need coffee to boost our energy then what about perovskites? Would they need coffee to perform better?'” recalls Jingjing Xue, a Ph.D. candidate at the Department of Materials Science and Engineering at UCLA and co-lead author of the study.

After, presumably, a few rounds of hearty laughs, the team set their cups down and set to work on trying to see if the idea has any value.

The authors have previously worked on improving the thermal stability of perovskite materials — the blue compounds with a particular crystal structure that forms the light-harvesting layer certain solar cells — to make them more efficient at harvesting sunlight. Part of that work involved trying to strengthen the material with additives such as dimethyl sulfoxide, an approach which showed some success in the short term, but wasn’t stable over longer spans of time. Caffeine, however, is an alkaloid compound whose molecular structures could, the team suspected based on their previous experience, interact with the precursors used to make perovskite materials.

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So, they set out to add caffeine to the perovskite layer of forty solar cells and used infrared spectroscopy, an approach that uses infrared radiation to identify a sample’s chemical components, to determine if the materials bonded. They had.

Further infrared spectroscopy tests showed that carbonyl groups (a carbon atom double bonded to an oxygen) in caffeine tied to lead ions in the perovskite layer to form a “molecular lock”. This lock increases the minimum amount of energy needed for the perovskite layer to react to sunlight, boosting the solar cell efficiency from 17% to over 20%. This lock stood firm when the material was heated, which suggests that caffeine could also help to make the solar cells more thermally-stable.

“We were surprised by the results,” says Wang, who is also a Ph.D. candidate in Yang’s research group at UCLA. “During our first try incorporating caffeine, our perovskite solar cells already reached almost the highest efficiency we achieved in the paper.”

The caveat, or caffeat if you so prefer, is that this approach likely won’t work with other types of solar cells. It only works here because it can tie into the unique molecular structure of perovskite precursors. However, it may be enough to give this type of solar cell variety an edge on the market.

Currently, perovskite solar cells are the cheaper and more flexible option available on the market. They’re also easier to manufacture, as they can be fabricated from liquid precursors — their silicon counterparts are cast from solid crystal ingots. Wang believes that caffeine might make them even easier to fabricate on a large scale, in addition to making them more efficient.

“Caffeine can help the perovskite achieve high crystallinity, low defects, and good stability,” he says. “This means it can potentially play a role in the scalable production of perovskite solar cells.”

The team plans to continue their efforts by investigating the chemical structure of the caffeine-infused perovskite crystals and identify what materials would best serve as a protective layer for the solar cells.

The paper “Caffeine Improves the Performance and Thermal Stability of Perovskite Solar Cells” has been published in the journal Joule.