A new material, classified as a perovskite, can reportedly convert sunlight to electricity as a potentially cheaper and more scalable alternative to today's silicon-based solar cells.

However, the new potential material has one problem: stability at ambient conditions. Out of four possible atomic configurations - or phases - of the material, three of them are already efficient but unstable, quickly reverting to the fourth, non-perovskite phase. This problem severely limits its potential as a photovoltaic material.

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Working Toward Perovskite Utilization

Now, researchers from Stanford University, with the SLAC National Accelerator Laboratory under the Department of Energy, have devised a solution to work around this problem. They placed the inactive phase of the material in a diamond anvil cell and compressed the material under high temperatures. Details of their study are described in the journal Nature Communications, January 19.

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

She adds now that there's an "optimal way" for handling and preparing the material, it now has the potential to be scaled up for industrial production. Additionally, it could also open the way to utilizing other perovskite phases.

Utilizing CsPBI3 Perovskite Materials

Perovskites got their name from the Russian mineralogist Lev Perovski, with the first sample of the minerals found in the Ural Mountains in Russia. In the study, the researchers used a lead halide perovskite - containing a mix of Cesium (Cs), Lead (Pb), and Iodine (I).

One phase of the material - called the "yellow phase" - exhibits a non-perovskite structure that has no photovoltaic applications. Previous work has already established that when processed in specific ways, the yellow phase turns into a black phase with a perovskite structure, and is efficient in converting sunlight to electricity.

"This has made it highly sought after and the focus of a lot of research," said Wendy Mao, a co-author of the study and a professor at Stanford. However, the black phases remain structurally unstable and have a tendency of reverting back to the yellow phase. Also, these perovskite materials also operate only under high temperatures - presenting another challenge before making the materials feasible for solar cell applications.

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Squeezed in Between Diamond

The novel method detailed in the study involved squeezing yellow phase minerals between the tips of diamonds in a diamond anvil cell. With the extreme pressure applied in the cell, the yellow phase materials were heated up to 450 degrees Celsius before cooling them down. With the new method of applying pressure and temperature, researchers report, that yellow-phase materials turned into black phase but did not revert into their former state even after it cooled down. The converted black phase material resisted deterioration from moisture in the air and exhibited stability even under room temperatures from ten to more than thirty days.

Researchers then examined the new substances with X-rays and other techniques, confirming the shift in its crystal structure. SIMES theorists, Thomas Devereaux and Chunjing Jia, offered insight on how pressure changed the perovskite structure and maintained the phase of the material.


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