Scientists at the University of Groningen in the Netherlands have discovered how tin-based perovskite materials allow hot electrons to retain their excess energy for around 1,000 times longer than expected, a finding that could shape the future of solar power.
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that → discover → power
The researchers found that two physical effects, the hot phonon bottleneck and the Burstein–Moss effect, work together to slow electron cooling from picoseconds to nanoseconds.
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effects → find → nanoseconds
Published in ACS Energy Letters, the study addresses a major challenge in solar energy, where excess electron energy is typically lost as heat before it can be converted into electricity.
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it → publish → electricity
The findings could support the development of hot-carrier solar cells designed to reduce thermalisation losses and improve solar conversion efficiency.
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findings → support → efficiency
How Dutch scientists uncovered the secret behind longer-lasting hot electrons
The research began with experiments led by Maria Antonietta Loi, whose team was studying the behaviour of excited charge carriers in tin-based perovskite materials.
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team → uncover → materials
These materials are being investigated for their potential use in solar cells and other optoelectronic technologies.
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materials → investigate → cells
During the experiments, Loi’s team observed that hot electrons retained their excess energy for much longer than expected, with cooling occurring over nanoseconds instead of the picosecond timescale typically associated with hot-carrier relaxation.
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cooling → observe → relaxation
The unexpected results raised questions about the physical processes responsible for the unusually slow cooling.
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results → raise → cooling
L. Jan Anton Koster and doctoral researcher Tim Faber used computer simulations to investigate how electrons transfer energy within the material and determine why the cooling process was taking so long.
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process → use → material
Koster explained the challenge of interpreting the experimental findings, saying, “The measurements were clear, but we didn’t understand the physics behind this.”
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we → explain → this
He added, “We even started to doubt the measurements ourselves.”
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We → add → measurements
The researchers first examined the hot phonon bottleneck, a mechanism that can slow energy loss through interactions between electrons and lattice vibrations.
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that → examine → electrons
However, the process alone could not explain the cooling times observed by Loi’s team.
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process → explain → team
The researchers then incorporated band filling, which is associated with the Burstein–Moss effect, into their simulations.
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which → incorporate → simulations
This combination produced cooling times in the nanosecond range, matching the experimental observations.
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combination → produce → observations
Why hot electrons matter for solar energy
When sunlight strikes a solar-cell material, its energy excites electrons and moves them into higher energy states.
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energy → matter → states
These electrons initially carry more energy than they need to contribute to electricity generation.
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they → carry → generation
In conventional solar cells, much of this excess energy is released as heat before it can be converted into usable electricity.
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it → release → electricity
This energy loss is known as thermalisation.
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loss → know → thermalisation
It is one of the factors that limits the efficiency of traditional single-junction solar cells.
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that → limit → cells
Hot-carrier solar cells are being studied as a possible way to capture excited electrons before they lose their excess energy.
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they → study → energy
By preserving more of the energy absorbed from sunlight, these devices could potentially improve solar conversion efficiency and move beyond the theoretical limits associated with conventional single-junction cells.
How the hot phonon bottleneck affects energy loss
The first mechanism examined by Koster and Faber was the hot phonon bottleneck.
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mechanism → preserve → Koster
When hot electrons release energy, some of it is transferred to vibrations in the material’s crystal lattice.
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some → release → lattice
These vibrations are known as phonons.
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vibrations → know → phonons
As energy accumulates in the lattice, electrons may reabsorb some of the energy previously released through interactions with these phonons.
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electrons → accumulate → phonons
This repeated exchange slows the rate at which electrons lose their excess energy and delays the cooling process.
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electrons → repeat → process
The researchers included this mechanism in their simulations to determine whether it could explain the unusually long cooling times.
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it → include → times
Although the hot phonon bottleneck slowed energy loss, it did not produce cooling times long enough to match the experimental results.
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it → slow → results
Koster explained, “When we added this well-known process called Hot Phonon Bottleneck to the simulations, it slowed the loss of energy, but not enough to explain our measurements.”
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it → explain → measurements
The result suggested that another physical process was contributing to the extended cooling period.
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process → suggest → period
How the Burstein–Moss effect slows electron cooling
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effect → slow → cooling
The researchers next examined band filling, a process associated with the Burstein–Moss effect.
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researchers → examine → effect
Hot electrons lose energy by moving from higher energy states to lower ones.
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electrons → lose → ones
However, when lower energy states are already occupied by other electrons, some of the pathways normally available for energy loss become restricted.
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some → occupy → loss
This limits the ability of hot electrons to move into lower energy states, slowing their cooling.
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This → limit → cooling
In the tin-based perovskite material, band filling worked alongside the hot phonon bottleneck to extend the energy-loss process.
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filling → base → process
When the researchers incorporated both mechanisms into their simulations, the model produced cooling times in the nanosecond range.
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model → incorporate → range
The results were consistent with the observations made during Loi’s experiments.
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results → make → experiments
Koster said, “When we added this process to the simulation as well, we saw that energy loss was now in the nanosecond range, as seen in the experiments by Maria Loi.”
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loss → say → Loi
The combined effect of the two mechanisms helped explain how the material could retain hot electrons for much longer than expected.
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material → combine → electrons
…and 14 more, not listed.
The Aporia
