Among the materials known as perovskites, one of the most exciting is a material that can convert sunlight into electricity as efficiently as today’s commercial silicon solar cells and has the potential to be much cheaper and easier to manufacture.
There is only one problem: Of the four possible atomic configurations or phases this material can take, three are effective but unstable at room temperature and in ordinary environments, and they quickly return to the fourth phase, which is completely useless for solar applications.
Now, researchers at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have found a new solution: Simply place the useless version of the material in a diamond anvil cell and squeeze it at high temperature. This treatment pushes its atomic structure into an efficient configuration and keeps it that way, even at room temperature and in relatively humid air.
The researchers described their results in Nature communication.
“This is the first study that uses pressure to control this stability, and it really opens up a lot of possibilities,” said Yu Lin, an SLAC researcher and researcher at the Stanford Institute for Materials and Energy Sciences (SIMES).
“Now that we’ve found this optimal way to prepare the material,” she said, “there is potential to scale it up for industrial production and to use the same approach to manipulate other perovskite phases.”
A quest for stability
Perovskites get their name from a natural mineral with the same atomic structure. In this case, the researchers examined a lead halide perovskite, which is a combination of iodine, lead and cesium.
A phase of this material, known as the yellow phase, does not have a true perovskite structure and cannot be used in solar cells. However, researchers discovered some time ago that if you treat it in certain ways, it switches to a black perovskite phase that is extremely efficient at converting sunlight into electricity. “This has made it in high demand and in focus for a lot of research,” said Stanford professor and co-author Wendy Mao.
Unfortunately, these black phases are also structurally unstable and tend to quickly fall back into the useless configuration. Plus, they only work with high efficiency at high temperatures, Mao said, and scientists will have to overcome both of those problems before they can be used in practical devices.
There had been previous attempts to stabilize the black phases with chemistry, load or temperature, but only in a moisture-free environment that does not reflect the real conditions in which solar cells operate. This study combined both pressure and temperature in a more realistic work environment.
Pressure and heat do the trick
Working with colleagues at the Stanford Research Group in Mao and Professor Hemamala Karunadasa, Lin and postdoctoral researcher Feng Ke designed a setup in which yellow phase crystals were pressed between the tips of diamonds in what is known as a diamond anvil cell. With the pressure still on, the crystals were heated to 450 degrees Celsius and then cooled.
Under the right combination of pressure and temperature, the crystals turned from yellow to black and remained in the black phase after the pressure was released, the researchers said. They were resistant to deterioration from humid air and remained stable and effective at room temperature for 10 to 30 days or more.
X-ray study and other techniques confirmed the shift in the crystal structure of the material, and calculations by SIMES theorists Chunjing Jia and Thomas Devereaux provided insight into how the pressure changed the structure and retained the black phase.
The pressure required to make the crystals black and hold them that way was about 1,000 to 6,000 times atmospheric pressure, Lin said – about one-tenth of the pressure routinely used in the synthetic diamond industry. So one of the goals of further research will be to transfer what scientists have learned from their diamond anvil cell experiments to industry and to scale up the process of bringing it within the field of production.
First glimpse of polarones formed in a promising next-generation energy material
Feng Ke et al., Preservation of a robust CsPbI3 perovskite phase via pressure-controlled octahedral slope, Nature communication (2021). DOI: 10.1038 / s41467-020-20745-5
Provided by SLAC National Accelerator Laboratory
Citation: Squeezing a rock star material can make it stable enough for solar cells (2021, January 21) retrieved January 21, 2021 from https://phys.org/news/2021-01-rock-star-material-stable-solar- cells .html
This document is subject to copyright. Except for fair trade for private examination or research, no parts may be reproduced without written permission. The content is provided for informational purposes only.