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The Secret To Better Solar Cells Could Be Hiding In A Cup Of Coffee

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Scientists found that like people, perovskite solar cells, an alternative to traditional silicon-based solar cells, enjoy a little caffeine boost.

A team from the University of California, Los Angeles and the China-based firm Solargiga Energy demonstrated how the substance, which is found in cups of coffee and tea, can improve the thermal stability of perovskite solar cells. They believe that the findings could make perovskite solar cells commercially viable one day.

Caffeine Makes Solar Cells Withstand Heat From The Sun

Perovskite solar cells are being tagged as the future of solar cells. Experts believe that they will replace traditional solar cells that are made from silicon because they would eventually cost less to produce.

However, perovskite solar cells are currently not as efficient as the silicon-based solar cells.

"Solar cells need high thermal stability since they are constantly exposed to sunlight, which warms up the devices," explained Yang Yang, a professor of material science and engineering at UCLA. "While perovskites are an attractive option for solar cells, the materials degrade and become less stable over time. We need them to last 20 to 30 years like traditional solar cells."

The idea to use caffeine to improve the thermal stability of perovskite solar cells came from Rul Wang, a graduate student at UCLA while drinking coffee with some colleagues in March 2018. He wondered how caffeine, which has a boiling point of 300 degrees Celsius, would interact with the materials used in perovskite solar cells.

He and the team then made a perovskite film from dimethylformamide, methylammonium iodide, and lead iodide. They added the caffeine and poured the liquid solution on top of an indium tin oxide glass.

They incorporated the perovskite film into a solar cell and placed it on a plate that is heated to 85 degrees Celsius. The researchers conducted the test for two months, measuring its energy output every four days.

The team also tested a perovskite solar cell without caffeine.

They reported in the journal Joule that the caffeinated perovskite solar cells were able to maintain a thermal stability for more than 1,300 hours or 55 days. It also preserved 86 percent of its power conversion efficiency.

Meanwhile, the perovskite solar cells without caffeine and found that it maintained thermal stability of 175 hours or seven days and retained 60 percent of its power conversion efficiency.

What Caffeine Improves Thermal Stability

The researchers also investigated why caffeine improved the thermal stability and power conversion efficiency of perovskite solar cell. They looked at the film infused with caffeine under a transmittance electron microscope and found that there was a strong interaction between the chemical and the perovskite cells' lead ions.

"Parts of caffeine's chemical structure were forming very strong binding with the lead ions and stabilizing the crystals," explained Jingjig Xue, also a graduate student at UCLA and an author of the study.

He added that the interaction also slowed down the growth of perovskite crystals that helped with the alignment and orientation that improved electric charge transfer.

The discovery might just be the key that would make perovskite solar cells commercially viable. While caffeine is the only substance now that is known to improve thermal stability, the researchers hope that further studies will be done to find other chemicals that work better with perovskite solar cells.

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