Polarons are an important nanoscale object: a mobile arrangement between electrons and atoms (called quasiparticles) that exist for just trillions of seconds.
These configurations have unique features that help us understand some of the mysterious behavior of the materials they create internally – and scientists have just seen them for the first time.
Polarons were measured in lead hybrid perovskites, the next-gen solar cell products that promise higher conversion rates than the silicon panels used in most today. Scientists hope that polaron’s ideas will go to some extent to tell us just how perovskites convert sunlight into electricity as well.
To find the polarons, scientists lightly trained single crystals of lead hybrid perovskites, looking at an X-ray mass-electron laser called the Linac Coherent Light Source (LCLS) – capable of do so at the smallest scales over the shortest periods of time, down to trillions of seconds (or picoseconds).
(Greg Stewart / SLAC National Acceleration Laboratory)
Above: Photograph of polarons in lead hybrid perovskite.
“When you charge a material by striking it with light, as in a solar cell, electricity is released, and those free electrons begin to move around the material,” says physics. Burak Guzelturk from Argonne National Laboratory, run by the U.S. Department of Energy.
“Soon they are surrounded and surrounded by a kind of bubble of local distortion – the polaron – that travels with them. Some people have argued that this bubble protects electricity from dispersing deficiencies in the material, and helping to explain why they travel so efficiently. to solar cell communications to flow out like electricity. “
Given the promise of perovskites as a solar panel material, it is not entirely clear why: they have many shortcomings that should limit how well flow can pass through, and they are very fragile. and unstable. Polar bears may give some answers.
These polarities are essentially short-lived motions of the atomic surface structure of the material, and have been shown to move about 10 layers of atoms out. The distortion increased the circumference of the surrounding atoms by about 50 times – to 5 billion meters – over tens of picoseconds.
The minute or bubble distances were greater than scientists expected, with the hybrid perovskite allowed to move with a flexible and soft atomic knee structure. The material in some ways behaves both hard and liquid at the same time.
“These materials have taken the field of solar energy exploration by storm because of their efficiency and low cost, but people are still arguing about why they work,” says materials scientist Aaron Lindenberg from Stanford University.
“The idea that polarons may be involved has been around for a number of years, but our experiments are the first to look directly at the creation of these local spaces, including their size, shape, and how they grow. “
Although perovskites are already used in solar energy production, often in combination with silicon, they are not without their challenges – although we have seen significant efficiency benefits from these materials, they think to be capable of even more.
As the years go by, scientists continue to overcome obstacles that have kept the efficiency of a solar panel lower than it should be, and because we are the depending on rising solar farms, improvements even just a few percentage points can make a big difference.
However, the researchers behind the polaron discovery confirm that they have not yet answered all the questions about these quasiparticles – and there is much more to learn about their effect on perovskites and other substances .
“While this test shows as directly as possible that these objects actually exist, it does not show how they contribute to the efficiency of a solar cell,” says Lindenberg. There is still more work to be done to understand how these processes affect the properties of these materials. “
The research was published in Natural Materials.