Power/Performance Bits: June 10

Quantum dots plus perovskites; high-temp superconductor.


Quantum dots plus perovskites
Researchers at the University of Toronto and KAUST created a hybrid material for solar cells that utilizes both perovskites and quantum dots.

Both quantum dots and perovskites suffer from instability: perovskites degrade quickly and certain types become incapable of fully absorbing solar radiation at room temperature, while quantum dots must be covered with a passivation layer, which can be destroyed at temperatures above 100 C.

However, the team found a way to combine perovskites and quantum dots that stabilizes both.

“Two of the technologies we pursue in our lab are perovskite crystals and quantum dots,” said Ted Sargent, a professor at UT. “Both of these are amenable to solution processing. Imagine a ‘solar ink’ that could be printed onto flexible plastic to create low-cost, bendable solar cells. We can also combine them in front of, or behind, silicon solar cells to further enhance their efficiency.”

“Research has shown the successful growth of hybrid structures that incorporated both perovskites and quantum dots,” said Mengxia Liu, who is now a postdoctoral fellow at Cambridge University. “This inspired us to consider the possibility that the two materials could stabilize each other if they share the same crystal structure.”

The team built two different hybrid materials. One was primarily quantum dots with about 15% perovskites by volume, and is designed to turn light into electricity. The other was primarily perovskites with less than 15% quantum dots by volume, and is better suited to turning electricity into light, such as for LEDs.

The team was able to show that the perovskite-rich material remained stable under ambient conditions (25 C and 30% humidity) for six months, about ten times longer than materials composed of the same perovskite alone. As for the quantum dot material, when heated to 100 C, the aggregation of the nanoparticles was five times lower than if they hadn’t been stabilized with perovskites.

“Perovskite and quantum dots have distinct physical structures, and the similarities between these materials have been usually overlooked,” said Liu. “This discovery shows what can happen when we combine ideas from different fields.”

The team hopes solar cell manufacturers will take the ideas and improve on them even further to create solution-processed solar cells that meet all the same criteria as traditional silicon. “Industrial researchers could experiment by using different chemical elements to form the perovskites or quantum dots,” says Liu. “What we have shown is that this is a promising strategy for improving stability in these kinds of structures.”

High-temp superconductor
Scientists at the University of Chicago, Max Planck Institute for Chemistry, Florida State University, Los Alamos National Laboratory, and Institute of Physical Chemistry PAS discovered a class of materials capable of superconductivity, or zero electrical resistance, at the highest temperatures yet recorded.

Using the material lanthanum hydride (LaH10), superconductivity was observed at temperatures of about minus-23 degrees Celsius (minus-9 degrees Fahrenheit), an increase of about 50 degrees C compared to the previous confirmed record, about minus-73 degrees C.

Achieving superconductivity did, however, require extremely high pressure: between 150 and 170 gigapascals, more than one and a half million times the pressure at sea level.

Analysis of the material was carried out at the Advanced Photon Source at Argonne National Laboratory, where a tiny sample of the material was squeezed between two tiny diamonds to create the necessary pressure before being subjected to the beamline’s X-rays to probe its structure and composition.

The data from the X-rays allowed scientists to build a model of the crystal structure of the material. (Image courtesy of Drozdov et al / University of Chicago)

Still, the team says this is a step that shows room temperature, or at least 0 C, superconductive materials are within reach.

“Our next goal is to reduce the pressure needed to synthesize samples, to bring the critical temperature closer to ambient, and perhaps even create samples that could be synthesized at high pressures, but still superconduct at normal pressures,” said Vitali Prakapenka, a research professor at the University of Chicago. “We are continuing to search for new and interesting compounds that will bring us new, and often unexpected, discoveries.”

Their next focus is examining yttrium hydride, said Mikhail Eremets, a research group leader at Max Planck. “With this material we expect to achieve superconductivity at even higher, ambient temperatures.”

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