An international research collaboration that was led by UCLA and included teams from Marmara University in Turkey, Sungkyunkwan University in Korea, Dalian University of Technology and Westlake University in China, Washington State University, UC Irvine and Washington University in St. Louis, has developed a way to use perovskites in solar cells while protecting it from the conditions that cause it to deteriorate.
The scientists added small quantities of neodymium ions directly to the perovskite. They found not only that the augmented perovskite was much more durable when exposed to light and heat, but also that it converted light to electricity more efficiently.
Halide perovskite’s ability to convert light to electricity is due to its structure, that is held together by bonds between ions with opposite charges. But light and heat tend to cause negatively charged ions to pop out of the perovskite, which damages the crystal structure and diminishes the material’s energy-converting properties.
Neodymium is commonly used in microphones, speakers, lasers and decorative glass. Its ions are just the right size to nestle within a cubic perovskite crystal, and they carry three positive charges, which the scientists hypothesized would help hold negatively charged ions in place.
The researchers added about eight neodymium ions for every 10,000 molecules of perovskite and then tested the material’s performance in solar cells. Working at maximum power and exposed to continuous light for more than 1,000 hours, a solar cell using the augmented perovskite retained about 93% of its efficiency in converting light to electricity. In contrast, a solar cell using standard perovskite lost half of its power conversion efficiency after 300 hours under the same conditions.
The team also shined continuous light on solar cells without any equipment drawing power, which accelerates the degradation of perovskite. A device using perovskite with neodymium retained 84% of its power conversion efficiency after more than 2,000 hours, while a device with standard perovskite retained none of its efficiency after that amount of time.
To test the material’s ability to withstand high temperatures, the researchers heated solar cells with both materials to about 180 degrees Fahrenheit. The solar cell with augmented perovskite held onto about 86% of its efficiency after more than 2,000 hours, while a standard perovskite device completely lost its ability to convert light to electricity during that time.
In many previous studies aimed at making perovskite more durable, researchers have experimented with adding protective layers to the material, but that has largely failed. The idea to augment the material itself came from lead author Yepin Zhao, a postdoctoral researcher at UCLA. Zhao said he was inspired by a technique commonly used in the production of silicon semiconductors — adding small amounts of other compounds to modify the material’s properties.
“The ions tend to move through the perovskite like cars on the highway, and that causes the material to break down,” Zhao said. “With neodymium, we identified a roadblock to slow down the traffic and protect the material.”
