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Polaron Quasiparticles : Observed For The First Time

A polaron, also known as a quasiparticle is an important nanoscale phenomenon used in condensed matter physics so as to understand the interactions between electrons and atoms in a solid material. Scientists have recently observed polarons for the first time. And this marks a very important step for the physicists as these are configurations having unique characteristics which can help humankind understand some of the mysterious behaviours of the materials they form within. This discovery is remarkable because polarons are extremely hard to observe as they only last for trillionths of a second.

 

As this animation shows, polaronic distortions start very small and rapidly expand outward in all directions to a diameter of about 5 billionths of a meter, which is about a 50-fold increase. This nudges about 10 layers of atoms slightly outward within a roughly spherical area over the course of tens of picoseconds, or trillionths of a second. (Greg Stewart/SLAC National Accelerator Laboratory)

 



Polaron

Polarons were measured in lead hybrid perovskites. Scientists are hopeful with polarons as they may help, at least to some extent, in understanding how perovskites convert sunlight into electricity. Perovskites are basically next-generation solar cell materials that promise to boost the conversion rates of solar energy into electrical energy beyond the silicon panels primarily used in the present world.

How Did The Scientists Find Polaron?

 

Scientists from the Department of Energy’s SLAC National Accelerator Laboratory and Stanford University observed polarons by Linac Coherent Light Source (LCLS), which is a giant X-ray free-electron laser. They trained the light on single crystals of lead hybrid perovskites and then observed it using LCLS. The LCLS is capable of imaging materials not only at the smallest scales but also over the shortest times (picoseconds).

Solar Energy to Electrical Energy

With the advancement of technology and research & development, scientists are overcoming hurdles to tackle the low efficiencies of the solar panels. As, day by day, the world is shifting towards solar energy as it is a non-conventional energy form. Hence, even small improvements would make a big difference.

According to the physicist, Burak Guzellturk, when a material is hit by light then there is the incorporation of a charge into the material, and electrons are liberated from the material. The liberated electrons are then free to move around the material. This is followed by the role of polaron. The electrons are surrounded and engulfed by a kind of bubble of local distortion. This bubble is nothing but a polaron that travels along with the electrons. It has been proposed that the polaron protects electrons from scattering off the defects in the material. Hence, this explains the efficient flow of the electrons to the solar cell’s contact to be transduced into electrical energy.  Polaron also helps facilitate easy travel within the material.

Polaron and Solar Energy

Although perovskites are very promising as solar panel material, they do have many defects which limit the quality of current flow through them. Further, these defects also make perovskites fragile & unstable.

 

As mentioned earlier, polarons are brief traveling distortions of the material’s atomic lattice structure. And, these distortions increased the spacing of the surrounding atoms. Polaron is a material that simultaneously behaves as a solid & a liquid.

According to Aaron Lindenberg from Stanford University, polarons are very suitable for solar energy research due to their high efficiency & low cost. Over years, finally, the formation & evolution of the polarons have been discovered.

Further Research

Observing a polaron is just the beginning of extensive research on the way. There are many questions to be answered and a lot to learn about polarons. There is also a need to know what their impact is on perovskites & other materials.

Lindenberg says, “While this experiment shows as directly as possible that these objects really do exist, it doesn’t show how they contribute to the efficiency of a solar cell. There’s still further work to be done to understand how these processes affect the properties of these materials.”

Reference :

Physicists Observe Fleeting ‘Polaron’ Quasiparticles For The First Time (sciencealert.com)

 

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