Squeezing a rock-star material can make it stable enough for solar cells

Scientists at the SLAC National Accelerator Laboratory and Stanford University found that squeezing a promising lead halide material into the diamond anvil cell (left) produces a so-called “black perocyte” (right) that is stable enough for solar energy applications . Credit: Greg Stewart / SLAC National Accelerator Laboratory

Among the materials known as perovocytes, one of the most exciting is materials that can convert sunlight to electricity as efficiently as today’s commercial silicon solar cells and have the ability to be much cheaper and easier to manufacture. is.

There is just one problem: the four possible atomic configurations, or phases, this material can take, three are efficient but unstable at room temperature and normal environments, and they return quickly to the fourth stage, which is purely for solar applications. Is useless.

Now scientists at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory have discovered a novel solution: simply place the useless version of the material in a diamond chamber and squeeze it at high temperatures. This treatment transforms its atomic structure into an efficient configuration and keeps it at room temperature and also in relatively moist air.

Researchers describe their results Nature communication.

Yu Lin, a SLAC staff scientist and investigator at the Stanford Institute for Materials and Energy Sciences (SIMES), said, “This is the first study to use pressure to control this stability, and it really opens up a lot of potential.” is.”

“We have now found the best way to prepare this material,” he said, “is the ability to use this same approach to enhance it for industrial production and to manipulate other pecovite phases.”

Pursuit of stability

Perovites derive their name from a natural mineral with a similar atomic structure. In this case, scientists studied a lead halide percocyte by combining iodine, lead and cesium.

One phase of this material, known as the yellow phase, does not have a correct perovocyte structure and cannot be used in solar cells. However, scientists discovered some time ago that if you process it in some ways, it turns into a dark colored percovasite phase that is extremely efficient at converting sunlight into electricity. “This has led to a lot of research and a lot of research,” said Wendy Mao, a Stanford professor and study co-author.

Unfortunately, these black phases are also structurally unstable and quickly revert to useless configurations. In addition, they only work with high efficiency at high temperatures, Mao said, and researchers must overcome both of those problems before using them in practical devices.

Previous phases attempted to stabilize black phases with chemistry, stress, or temperature, but only in a moisture-free environment, which does not reflect real-world conditions that operate in solar cells. This study combined both pressure and temperature. More realistic work environment.

Pressure and heat do the trick

Mao and Professor Hemmala Karunadasa’s colleagues from Stanford research groups, working with Lin and postdoctoral researcher Fang, designed a setup that squeezed yellow phase crystals between the tips of the diamond, known as a diamond amla cell Gone. With still pressure, the crystals were heated to 450 ° C and then cooled.

Under 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. They were resistant to deterioration from moist air and remained stable and efficient at room temperature for 10 to 30 days or more.

Examination with X-rays and other techniques confirmed a change in the crystal structure of the material, and calculations by SIMES theorists Chunjing Jia and Thomas DeVero provided information on how pressure changed the structure and preserved the black phase.

The pressure required to darken the crystals and keep them that way was about 1,000 to 6,000 times the atmospheric pressure, Lin said — about a tenth of the pressure routinely used in the synthetic diamond industry. A goal for further research would therefore be to see what the researchers learned from their diamond anvil cell experiments and extended the process to bring it into the realm of manufacturing.

First glimpse of poles in promising next-gen energy material

more information:
Fang K et al., Preservation of a strong CsPbI3 perocyte phase via pressure-directed octahedral tilt, Nature communication (2021). DOI: 10.1038 / s41467-020-20745-5

SLAC provided by National Accelerator Laboratory

Quotes: Squeezing a rock-star material can make it sufficiently stable for solar cells (2021, 21 January). Https://phys.org/news/2021-01-rock-star-material-stable-solar- cells.html from 21 January 2021

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