Solar Energy

Twisting, flexible crystals key to solar energy production

Published

4 years ago

March 17, 2021

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Twisting, flexible crystals key to solar energy production

Researchers at Duke University have revealed long-hidden molecular dynamics that provide desirable properties for solar energy and heat energy applications to an exciting class of materials called halide perovskites.

A key contributor to how these materials create and transport electricity literally hinges on the way their atomic lattice twists and turns in a hinge-like fashion. The results will help materials scientists in their quest to tailor the chemical recipes of these materials for a wide range of applications in an environmentally friendly way.

The results appear online March 15 in the journal Nature Materials.

“There is a broad interest in halide perovskites for energy applications like photovoltaics, thermoelectrics, optoelectronic radiation detection and emission – the entire field is incredibly active,” said Olivier Delaire, associate professor of mechanical engineering and materials science at Duke. “While we understand that the softness of these materials is important to their electronic properties, nobody really knew how the atomic motions we’ve uncovered underpin these features.”

Perovskites are a class of materials that – with the right combination of elements – are grown into a crystalline structure that makes them particularly well-suited for energy applications. Their ability to absorb light and transfer its energy efficiently makes them a common target for researchers developing new types of solar cells, for example. They’re also soft, sort of like how solid gold can be easily dented, which gives them the ability to tolerate defects and avoid cracking when made into a thin film.

One size, however, does not fit all, as there is a wide range of potential recipes that can form a perovskite. Many of the simplest and most studied recipes include a halogen–such as chlorine, fluorine or bromine – giving them the name halide perovskites. In the crystalline structure of perovskites, these halides are the joints that tether adjoining octahedral crystal motifs together.

While researchers have known these pivot points are essential to creating a perovskite’s properties, nobody has been able to look at the way they allow the structures around them to dynamically twist, turn and bend without breaking, like a Jell-O mold being vigorously shaken.

“These structural motions are notoriously difficult to pin down experimentally. The technique of choice is neutron scattering, which comes with immense instrument and data analysis effort, and very few groups have the command over the technique that Olivier and his colleagues do,” said Volker Blum, professor of mechanical engineering and material science at Duke who does theoretical modeling of perovskites, but was not involved with this study. “This means that they are in a position to reveal the underpinnings of the materials properties in basic perovskites that are otherwise unreachable.”

In the study, Delaire and colleagues from Argonne National Laboratory, Oak Ridge National Laboratory, the National Institute of Science and Technology, and Northwestern University, reveal important molecular dynamics of the structurally simple, commonly researched halide perovskite (CsPbBr3) for the first time.

The researchers started with a large, centimeter-scale, single crystal of the halide perovskite, which is notoriously difficult to grow to such sizes – a major reason why this sort of dynamic study has not been achieved before now. They then barraged the crystal with neutrons at Oak Ridge National Laboratory and X-rays at Argonne National Laboratory. By measuring how the neutrons and X-rays bounced off the crystals over many angles and at different time intervals, the researchers teased out how its constituent atoms moved over time.

After confirming their interpretation of the measurements with computer simulations, the researchers discovered just how active the crystalline network actually is. Eight-sided octahedral motifs attached to one another through bromine atoms were caught twisting collectively in plate-like domains and constantly bending back and forth in a very fluid-like manner.

“Because of the way the atoms are arranged with octahedral motifs sharing bromine atoms as joints, they’re free to have these rotations and bends,” said Delaire. “But we discovered that these halide perovskites in particular are much more ‘floppy’ than some other recipes. Rather than immediately springing back into shape, they return very slowly, almost more like Jell-O or a liquid than a conventional solid crystal.”

Delaire explained that this free-spirited molecular dancing is important to understand many of the desirable properties of halide perovskites. Their ‘floppiness’ stops electrons from recombining into the holes the incoming photons knocked them out of, which helps them make a lot of electricity from sunlight. And it likely also makes it difficult for heat energy to travel across the crystalline structure, which allows them to create electricity from heat by having one side of the material be much hotter than the other.

Because the perovskite used in the study – CsPbBr3 – has one of the simplest recipes, yet already contains the structural features common to the broad family of these compounds, Delaire believes that these findings likely apply to a large range of halide perovskites. For example, he cites hybrid organic-inorganic perovskites (HOIPs), which have much more complicated recipes, as well as lead-free double-perovskite variants that are more environmentally friendly.

“This study shows why this perovskite framework is special even in the simplest of cases,” said Delaire. “These findings very likely extend to much more complicated recipes, which many scientists throughout the world are currently researching. As they screen enormous computational databases, the dynamics we’ve uncovered could help decide which perovskites to pursue.”

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Solar Energy

Scientists Probe Declining Earbud Battery Longevity

Published

1 day ago

February 5, 2025

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Scientists Probe Declining Earbud Battery Longevity

by Clarence Oxford

Los Angeles CA (SPX) Feb 05, 2025

Have you ever noticed how electronic devices, including wireless earbuds, seem to lose battery capacity faster the longer you use them? An international research team from The University of Texas at Austin set out to examine this familiar issue, known as battery degradation, by focusing on the earbuds that many people rely on daily. Through a series of x-ray, infrared, and other imaging approaches, the researchers investigated the hidden complexities behind these tiny devices and revealed why their battery life declines over time.

“This started with my personal headphones; I only wear the right one, and I found that after two years, the left earbud had a much longer battery life,” said Yijin Liu, an associate professor in the Cockrell School of Engineering’s Walker Department of Mechanical Engineering, who led the new research published in Advanced Materials. “So, we decided to look into it and see what we could find.”

Their analysis showed that crucial earbud features – like the Bluetooth antenna, microphones, and circuits – compete with the battery in a very confined space, producing a microenvironment that is less than ideal. This situation results in a temperature gradient that damages the battery over time, with different sections of the cell experiencing variable temperatures.

Real-world factors also complicate matters. Frequent changes in climate, shifts in air quality, and a host of other environmental variables challenge the battery’s resilience. While cells are generally designed to endure harsh conditions, constant fluctuations can take their toll.

These discoveries highlight the importance of considering how batteries interact with devices such as phones, laptops, and even electric vehicles. Packaging solutions, strategic design decisions, and adaptations for user habits may all play a role in extending battery performance.

“Using devices differently changes how the battery behaves and performs,” said Guannan Qian, the first author of this paper and a postdoctoral researcher in Liu’s lab. “They could be exposed to different temperatures; one person has different charging habits than another; and every electric vehicle owner has their own driving style. This all matters.”

In conducting this study, Liu and his team worked closely with UT’s Fire Research Group, led by mechanical engineer Ofodike Ezekoye. They paired infrared imaging methods with their in-house x-ray technology at UT Austin and Sigray Inc. To expand their scope, they then teamed up with some of the world’s most advanced x-ray facilities.

Their collaborators included researchers from SLAC National Accelerator Laboratory’s Stanford Synchrotron Radiation Lightsource, Brookhaven National Laboratory’s National Synchrotron Light Source II, Argonne National Laboratory’s Advanced Photon Source, and the European Synchrotron Radiation Facility (ESRF) in France. These partnerships allowed them to observe battery behavior under more authentic operating conditions.

“Most of the time, in the lab, we’re looking at either pristine and stable conditions or extremes,” said Xiaojing Huang, a physicist at Brookhaven National Laboratory. “As we discover and develop new types of batteries, we must understand the differences between lab conditions and the unpredictability of the real world and react accordingly. X-ray imaging can offer valuable insights for this.”

Looking ahead, Liu says his team will continue analyzing battery performance in the settings people experience every day. They plan to expand their approach to larger batteries, such as those in smartphones, laptops, and electric vehicles, to learn more about their degradation patterns.

Research Report:In-device Battery Failure Analysis

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Solar Energy

Quantum factors elevate plant energy transport efficiency

Published

1 day ago

February 5, 2025

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Quantum factors elevate plant energy transport efficiency

by Robert Schreiber

Munich, Germany (SPX) Feb 05, 2025

For countless engineers, converting sunlight into easily stored chemical energy stands as an enduring goal. Yet nature perfected this challenge billions of years ago. A recent study reveals that quantum mechanics, once thought to be limited to physics, is also essential for key biological processes.

Green plants and other photosynthetic organisms draw on quantum mechanical mechanisms to capture the sun’s energy. According to Prof. Jurgen Hauer: “When light is absorbed in a leaf, for example, the electronic excitation energy is distributed over several states of each excited chlorophyll molecule; this is called a superposition of excited states. It is the first stage of an almost loss-free energy transfer within and between the molecules and makes the efficient onward transport of solar energy possible. Quantum mechanics is therefore central to understanding the first steps of energy transfer and charge separation.”

Classical physics alone cannot completely describe how this phenomenon unfolds throughout green plants and in certain photosynthetic bacteria. Although the exact details remain only partly understood, Prof. Hauer and first author Erika Keil consider their new findings an important step toward uncovering how chlorophyll, the pigment behind leaf coloration, functions. Applying these insights to engineered photosynthesis devices could unlock unprecedented solar energy conversion efficiencies for both power production and photochemical applications.

In their investigation, the researchers focused on two portions of the light spectrum absorbed by chlorophyll: the low-energy Q band (yellow to red) and the high-energy B band (blue to green). In the Q region, two electronic states are quantum mechanically coupled, promoting virtually loss-free energy movement. The system subsequently relaxes via “cooling”, i.e. by releasing energy in the form of heat. These observations demonstrate that quantum mechanical processes can play a major role in shaping key biological functions.

Research Report:Reassessing the role and lifetime of Qx in the energy transfer dynamics of chlorophyll a

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Solar Energy

HZB sets new efficiency record for CIGS perovskite tandem solar cells

Published

2 days ago

February 5, 2025

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HZB sets new efficiency record for CIGS perovskite tandem solar cells

by Robert Schreiber

Berlin, Germany (SPX) Feb 05, 2025

Researchers at Helmholtz Center Berlin for Materials and Energy (HZB) and Humboldt University Berlin have developed a CIGS-perovskite tandem solar cell that has set a new world record for efficiency, achieving 24.6%. The performance of the cell has been officially certified by the Fraunhofer Institute for Solar Energy Systems.

Thin-film solar cells, such as those based on copper, indium, gallium, and selenium (CIGS), require minimal material and energy to manufacture, making them an environmentally friendly alternative to conventional silicon-based solar cells. CIGS thin films can also be applied to flexible substrates, expanding their potential applications.

The new tandem solar cell developed by HZB and Humboldt University combines a CIGS bottom cell with a perovskite top cell. By optimizing the contact layers between these two components, the research team successfully increased efficiency to a record-breaking 24.6%. This milestone was confirmed by the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg, Germany.

This achievement was made possible through a collaborative effort among researchers. The top cell was developed by Thede Mehlhop, a master’s student at TU Berlin, under the supervision of Stefan Gall. The perovskite absorber layer was created in the joint laboratory of HZB and Humboldt University Berlin, while the CIGS sub-cell and contact layers were fabricated by HZB researcher Guillermo Farias Basulto. Additionally, the KOALA high-performance cluster system at HZB was used to deposit the perovskite and contact layers in a vacuum.

“At HZB, we have highly specialized laboratories and experts who are top performers in their fields. With this world record tandem cell, they have once again shown how fruitfully they work together,” said Prof. Rutger Schlatmann, spokesman for the Solar Energy Department at HZB.

HZB has a strong track record in achieving world records in solar cell efficiency, including past accomplishments in silicon-perovskite tandem cells and now in CIGS-perovskite tandem technology.

“We are confident that CIGS-perovskite tandem cells can achieve much higher efficiencies, probably more than 30%,” said Prof. Rutger Schlatmann.