Science & Technology

Perovskite under pressure: hot electrons cool faster

The artist’s impression that “hot electrons” become faster under pressure. Hot electrons under pressure remove excess energy faster. Credit:

Solar cells lose about two-thirds of the energy of the sun. Half of this loss is due to a process called “hot carrier cooling” that loses excess energy in the form of heat before high-energy photons are converted to electricity. AMOLF scientists have found a way to manipulate the speed of this process with perovskite by applying pressure to the material. This paves the way for making perovskite more versatile, allowing it to be used not only in solar cells, but also in a variety of other applications, from lasers to thermoelectric devices.Researchers do their research Journal of Physical Chemistry Letters April 23.

Perovskite is a promising material for next-generation solar cellBecause they are made from inexpensive ingredients, you can easily change the composition to suit your specific needs, such as solar cells of any color. Researchers in AMOLF’s Hybrid Solar Group are trying to extend the efficiency and life of hybrids Perovskite Semiconductors by clarifying the basic characteristics of perovskite. One of these properties is the so-called high temperature rate. Career Cooling will occur. This is also relevant if perovskite is being used in other applications.

Hot carrier cooling

With solar cells energy The amount of light that matches the bandgap of a semiconductor is converted directly into electricity. This direct route cannot be used for higher energy photons. These photons produce so-called hot carriers. High-energy electrons (and holes) need to be cooled before they can be collected in the form of electrical energy. Hot carrier cooling occurs spontaneously. Hot carriers lose excess energy in the form of heat by scattering until they match the conduction energy level of the semiconductor. Trying to understand this process at Perovskite, PhD. Student Loreta Muscarella faces a variety of challenges, one of which is the timescale. She states: “Hot carrier cooling is very fast and typically takes place on a femtosecond to picosecond timescale, making the process difficult to operate and investigate. Unique with a transient absorption spectrometer (TAS). We are fortunate to be able to set it up and use it in combination with our group of pressure devices, which allows us to measure the electronic properties of perovskite under external stress a few femtoseconds after exposing the material to light. I will. “

Operate with pressure

It is already known that under abundant lighting, hot carrier cooling of perovskite semiconductors is much slower than that of silicon semiconductors. This makes process investigations much more viable on perovskite rather than silicon. Muscarella and her colleagues assumed that the speed of the cooling process could depend on pressure. “Hot carriers lose excess energy due to vibration and scattering. When pressure is applied, the vibration inside the material increases, which should increase the cooling rate of hot carriers,” she says. “We decided to test this assumption and found that we could actually manipulate the cooling time with pressure at 3000 times. Ambient pressure This process is 2-3 times faster. “

Solar cells do not operate at such high pressures, but internal strain has the same effect. Muscarella: “We conducted experiments under external pressure, but perovskite can induce internal strain by chemically altering the material or its growth, as previously shown in our group. is.”

Cooling speed for various applications

Since the cooling rate of hot carriers can be controlled, various applications of perovskite other than solar cells are possible. “The potential to design perovskite in a particular color makes it very interesting not only for colored solar cells, but also for laser and LED technologies. In such applications, as with traditional solar cells. Fast cooling of the hot carrier is essential. On the other hand, when cooled, the perovskite becomes suitable for thermoelectric devices that convert the temperature difference into electricity. Therefore, the cooling rate of the hot carrier can be adjusted, so that the perovskite can be used. It allows for a variety of devices that can be created, “says Muscarella. she is, Negative pressure A material that further slows down the hot carrier cooling process for certain types of solar cells.

“Heat dissipation accounts for almost 30% of the efficiency loss of solar cells, so scientists are looking for ways to harvest hot carriers before they cool. Currently, even” slow “. cooling Perovskite at atmospheric pressure is still too fast for such so-called hot carriers Solar cell..Now these hot carriers Excess energy As heat within picoseconds. However, if you can induce negative strain, you may be able to slow down the process fast enough to apply it to a working device. ”

Utilization of hot carriers for high efficiency solar cells

For more information:
Loreta A. Muscarella et al. Accelerated hot carrier cooling with MAPbI3 Perovskite by pressure-induced lattice compression, Journal of Physical Chemistry Letters, DOI: 10.1021 / clett.1c00676

Quote: Perovskite under pressure: Hot electrons cool faster (April 23, 2021) April 23, 2021 Obtained from cool.html

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Perovskite under pressure: hot electrons cool faster Perovskite under pressure: hot electrons cool faster

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