The future of solar panels may lie in coffee. Researchers at the University of California, Los Angeles (UCLA) and Solargiga Energy in China recently published the results of research in which they saw improved thermal stability of perovskite solar cells and their efficiency increasing from 17% to 20%. This was achieved by applying caffeine on the perovskite layer.

The idea began as a joke over morning coffee, the researchers said in an interview. “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?” Jingjing Xue, a PhD candidate in Professor Yang Yang’s research group at the Department of Materials Science and Engineering at UCLA, said.

This led to the team using the caffeine in coffee to boost the efficiency and long-term stability of perovskite cells. Previous attempts to achieve these goals have included enhancing the perovskite layer by introducing compounds such as dimethyl sulfoxide, which showed some success in the short term, but wasn’t stable over longer spans of time.

The team added caffeine to the perovskite layer of forty solar cells and used infrared spectroscopy to determine that the caffeine had successfully bonded with the material. They observed that the carbonyl groups (a carbon atom double bonded to an oxygen atom) in caffeine interacted with lead ions in the perovskite layer to create a “molecular lock”. This increased the minimum amount of energy required for the perovskite film to react, boosting the solar cell’s efficiency. The molecular lock continued to occur when the material was heated, which could help prevent heat from breaking down the layer.

Unfortunately, this finding only applies to metal halide perovskite solar cells. Perovskite solar cells already have the advantage of being cheaper and more flexible than their silicon counterparts, but are more thermally unstable. They are also easier to manufacture, as perovskite cells can be fabricated from solution-based precursors as opposed to solid crystal ingots.