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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.

Coffee makes solar cells more efficien

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.

With further research, the team believes caffeine may facilitate large-scale production of perovskite solar cells. “Caffeine can help the perovskite achieve high crystallinity, low defects, and good stability. This means it can potentially play a role in the scalable production of perovskite solar cells,” they said.

The researchers have been investigating perovskite and other types of solar cells for several years. They recently developed a dual-layer solar cell that generates more energy from sunlight than typical solar panels, and the latest caffeine study has prompted them to start working on their next project. The team plans to further investigate the chemical structure of the caffeine-incorporated perovskite material and to identify the best protective materials for perovskites.

The research was supported by the Air Force Office of Scientific Research, the Office of Naval Research, the University of California Advanced Solar Technologies Institute, the Natural Science Foundation of China, Suzhou Nano Science and Technology’s Collaborative Innovation Center, Jiangsu Higher Education Institutions’ Priority Academic Program Development and Jinzhou Solargiga Energy. The paper “Caffeine Improves the Performance and Thermal Stability of Perovskite Solar Cells” was published in the journal Joule.

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