Caffeine gives solar cells a boost of energy

Scientists at the University of California at Los Angeles (UCLA) and Solargiga Energy in China have discovered that caffeine can help make a promising alternative to traditional solar cells more efficient in converting light into electricity. Their research, published April 25 in the journal Joule, can enable this cost-effective renewable energy technology to compete in the market with silicon solar cells.

The idea started as a joke on morning coffee. "One day, while we were discussing perovskite solar cells, our colleague Rui Wang said," If we need coffee to increase our energy, then what about perovskites? Would they need coffee for better results? ", Recalls Jingjing Xue, Ph.D. candidate in the research group of Professor Yang Yang at UCLA's Department of Materials Science and Engineering.

The spontaneous comment led the team to recall that caffeine in coffee is an alkaloid compound containing molecular structures likely to interact with the precursors of perovskite-based materials, compounds with a structure crystalline particles that form the light-collecting layer in a class of solar cells. Previous attempts to improve the thermal stability of these solar cells have included improving the perovskite layer by introducing compounds such as dimethylsulfoxide, but researchers have struggled to increase long-term efficiency and stability cells. Nobody had tried caffeine.

Realizing that they might be on something, the team set aside their coffee and began investigating further. They added caffeine to the perovskite layer of forty solar cells and used infrared spectroscopy (which uses infrared radiation to identify chemical compounds) to determine if caffeine had successfully bonded to the material.

By performing other infrared spectroscopy tests, they observed that the carbonyl groups (an oxygen-linked double carbon atom) in caffeine interacted with the lead ions in the layer to create a "molecular latch." This interaction increased the minimum amount of energy required for the perovskite film to react, increasing the efficiency of the solar cell from 17% to over 20%. Molecular blockage continued to occur when the material was heated, which could help prevent heat from degrading the layer.

"We were surprised by the results," said Wang, who also holds a PhD. candidate in Yang's research group at UCLA. "During our first attempt at caffeine incorporation, our perovskite solar cells have already achieved the almost optimal efficiency we achieved in the document."

However, while caffeine seems to significantly improve the performance of cells using perovskite to absorb sunlight, researchers do not think it will be useful for other types of solar cells. The unique molecular structure of caffeine only allows it to interact with the precursors of perovskite, which could give this variety of solar cells an edge in the market. Perovskite solar cells already have the advantage of being cheaper and more flexible than their silicon counterparts. They are also easier to manufacture: perovskite cells can be made from solution-based precursors as opposed to solid crystal ingots. After further research, Wang believes that caffeine could facilitate large-scale production of perovskite solar cells.

"Caffeine can help perovskite achieve high crystallinity, low defects and good stability," he says. "It means that it can potentially play a role in the evolutionary production of perovskite solar cells."

In order to continue to improve the efficiency and stability of solar cells, the team then plans to further investigate the chemical structure of perovskite material containing caffeine and identify the best protective materials against perovskites.