Next-gen solar cells perk up with coffee

Perovskite may become the go-to material for manufacturing solar cells, thanks to a hit of caffeine.

Scientists have discovered that the familiar human pick-me-up boosts the performance of perovskite cells, making them a viable alternative to traditional silicon ones.

Perovskite cells are already cheaper, more flexible and easier to manufacture, the researchers say, because they can be fabricated from solution-based precursors rather than solid crystal ingots. However, their efficiency and long-term stability are below par.

In a recent trial, described in a paper in the journal Joule, a team from the University of California Los Angeles (UCLA), in the US, and China’s Solargiga Energy added caffeine to 40 solar cells and discovered that this made them more efficient at converting light into energy, while remaining stable. 

“We were surprised by the results,” says UCLA’s Rui Wang. “During our first try incorporating caffeine, our perovskite solar cells already reached almost the highest efficiency we achieved in the paper.”

It started as a joke, of course, but then someone recalled that caffeine in coffee is an alkaloid compound containing molecular structures that could interact with the precursors of perovskite materials – compounds with a particular crystal structure that form a  light-harvesting layer in the cells.

Wang and colleagues added caffeine to the perovskite layer of the cells and used infrared spectroscopy to determine that it had successfully bonded with the compounds.

They then observed that carbon atoms double bonded to oxygen atoms – known as  carbonyl groups – in caffeine interacted with lead ions in the layer to create a “molecular lock”.

This increased the minimum amount of energy required for the perovskite film to react, boosting the solar cell efficiency from 17% to more than 20%. The lock continued to occur when the material was heated, which could help prevent heat from breaking down the layer.

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