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 that this material can take, three are effective but unstable at room temperature and in ordinary environments and quickly return to the fourth phase, which is completely useless for solar applications.
Now scientists at Stanford University and the National Department of Energy’s SLAC Accelerator Laboratory have discovered a new solution: Just put the useless version of the material in a diamond anvil cage 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 Communications.
“This is the first study to use pressure to control this stability and it really opens up a lot of opportunities,” said Yu Lin, a SLAC scientist and researcher at the Stanford Institute of Materials and Energy Sciences (SIMES).
“Now that we have found this optimal way to prepare the material,” she said, “there is potential for increasing it for industrial production and for using the same approach to manipulate other phases of perovskite.”
Search for stability
Perovskites get their name from a natural mineral with the same atomic structure. In this case, scientists have studied lead halide perovskite, which is a combination of iodine, lead and cesium.
One phase of this material, known as the yellow phase, does not have a true perovskite structure and cannot be used in solar cells. However, scientists have discovered some time ago that if you process it in certain ways, it turns into a phase of black perovskite, which is extremely effective in converting sunlight into electricity. “This has made it extremely sought after and the focus of many studies,” said Wendy Mao, a Stanford professor and co-author of the study.
Unfortunately, these black phases are also structurally unstable and tend to quickly return to a useless configuration. In addition, they only work with high efficiency at high temperatures, Mao said, and researchers will have to overcome both problems before they can be used in practical devices.
There have been previous attempts to stabilize the black phases with chemistry, deformation or temperature, but only in a moisture-free environment that does not reflect the real conditions in which the solar cells operate. This study combines both pressure and temperature in a more realistic work environment.
Pressure and heat work
Working with colleagues from Mao’s Stanford research groups and Professor Hemamala Karunadasa, Lin and postdoctoral fellow Feng Ke designed an installation in which yellow phase crystals were squeezed between the diamond tips in a so-called diamond anvil cage. At still pressure, the crystals are heated to 450 degrees Celsius and then cooled.
With the right combination of pressure and temperature, the crystals changed from yellow to black and remained in the black phase after the pressure was released, the scientists said. They are resistant to deterioration from moist air and remain stable and effective at room temperature for 10 to 30 days or more.
X-ray research and other techniques confirmed the change in the crystal structure of the material, and calculations by SIMES theorists Chungjing Jia and Thomas Devereaux gave an idea of how pressure changed the structure and kept the black phase.
The pressure needed to turn the crystals black and stay that way was approximately 1,000 to 6,000 times the atmospheric pressure, Lin said, about a tenth of the pressure routinely used in synthetic diamond production. So one of the goals of further research will be to transfer what we have learned from our experiments with cellular diamond anvils to industry and to expand the process to include it in the field of production.
A first look at the polarons formed in a promising next-generation energy material
Feng Ke et al, Maintaining a stable phase of CsPbI3 perovskite by directional pressure octahedral slope, Nature Communications (2021). DOI: 10.1038 / s41467-020-20745-5
Provided by SLAC National Accelerator Laboratory
Quote: Squeezing material from a rock star can make it stable enough for solar cells (2021, January 21), extracted on January 21, 2021 from https://phys.org/news/2021-01-rock-star-material-stable -solar- cells.html
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