Solar Energy

‘Twisting’ atomic materials may convert light into electricity

Published

4 years ago

May 2, 2021

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‘Twisting’ atomic materials may convert light into electricity

A pair of physicists at the University of California, Riverside, are aiming to convert light falling on atomically thin semiconductor materials into electricity, having received more than $582,000 in funding from the U.S. Department of the Army.

Nathaniel Gabor and Vivek Aji, both associate professors of physics and astronomy, will focus on how the fundamental science of light and its interaction with matter enables new sensing capabilities in layered and twisted vertical structures of stacked monolayer semiconductors. The researchers aim to understand how electronic excitations influence the flow of photo-absorbed energy in ultrasmall semiconducting optoelectronic materials.

“”This research effort has the potential to impact fundamental science and technology, involving physics of quantum processes in light-sensing and deeper knowledge of novel optoelectronic properties in 2D quantum materials,” said Tania Paskova, program manager of the U.S. Army Combat Capabilities Development Command, known as DEVCOM, Army Research Laboratory. “A successful execution will open new opportunities for quantum enhanced sensors that could usher a new era of night vision technology and quantum communication networks, both of significant importance for the Army.”

Gabor and Aji expect their stacking and twisting approach will spawn a new generation of quantum photodiodes that operate at room temperature, next-generation photovoltaics, single photon sensors, and light-emitting diodes, or LEDs. They will be among the first to explore the ability to stack-engineer the interaction between vibrational motion and electronic states, heralding a new era of quantum sensor science.

“We think this project will give us a deep understanding of fast and highly sensitive quantum coherent electron-hole separation in light sensing,” said Gabor, the three-year grant’s principal investigator. “”It also promises rapid future advancement of precisely engineered materials and devices for advanced light-sensing technologies.””

Using theoretical modeling as a tool, Gabor and Aji have already begun experiments with atomically thin semiconductors tungsten diselenide and molybdenum diselenide. When such semiconductors absorb a photon, a bound electron can be freed, leaving behind an electron vacancy, or hole. As the hole behaves like an electron with positive charge, the electron and hole can attract each other to form a bound state called an exciton.

“Today, we understand better even at just the stacking level how these materials behave,” said Aji, a theoretical physicist and the grant’s co-principal investigator. “In twisting, you arrive at a series of ‘magic angles’ where certain aspects repeat. Twisting is the future in this line of research.”

Gabor explained that materials scientists are now easily able to isolate individual atomically thin materials and also control how they’re twisted relative to each other. Engineering the interactions in these “twistronic” materials between atomic motion and excitons, however, is challenging since the interaction strength is fixed by atomic-scale configuration and electronic structure.

“Imagine a layer of red atoms on top of a layer of blue atoms,” Gabor said. “By twisting these against each other, you finely manipulate the distance between the red and blue atoms and the atoms’ allowed vibrations get affected in unusual ways. As you continue to make these twists … their behavior, in turn, becomes more complex, affecting properties such as magnetism, superconductivity, and optical effects.

“With just one layer, you have a very narrow absorption of an exciton. When you start to stack and twist the layers, you can find new ways to absorb light and efficiently generate current from it.”

When stacking tungsten diselenide and molybdenum diselenide layers, an electrical field may form between them. Light shining on this stack forms a bound exciton, which is then converted directly into electrons and holes with remarkable efficiency. Gabor suspects some unique quantum mechanical effects may be occurring in the tungsten diselenide-molybdenum diselenide system. Only a few materials systems behave in this manner, he said.

“It has to do with the way the atoms are vibrating and how that interacts with light,” he added. “We may be seeing vibronic physics here. The ultimate goal from the Army’s perspective is to find such new ways of increasing efficiency that take advantage of quantum mechanical effects. We have a whole suite of semiconductors that behave like tungsten diselenide and molybdenum diselenide to experiment with.”

Aji explained that when light is absorbed in a semiconductor, some excitation is created in the system that often dissipates away.

“But if you could control the electronic properties of the materials systematically, then you could tune the materials to respond to light in just the ways you want,” he said. “The stacking and twisting of semiconducting layers allow just that.”

The researchers acknowledge twisting two semiconductors against each other places their work in the “Stone Age” of this research endeavor.

“Our collaborative work so far has only scratched the surface of this vast landscape,” Gabor said. “”With three, four, or 10 monolayers, we have a humongous parameter space to study. The good news is we will have a lot of work to do, which should keep my lab busy for long. The bad news is with many layers it gets much harder to understand what exactly is happening.”

Unlike other research groups working on stacking and twisting semiconducting materials, Gabor and Aji are interested in demonstrating devices, such as room temperature vibronic sensors, from an experimental perspective.

“We are focusing on semiconductor devices with applications in photo detection and optoelectronics,” Gabor said. “These devices can theoretically operate at speeds inaccessible to LEDs and lasers, promising high-speed communication. One thing worth noting is that the experiments and theory are presently moving at the same pace in this field. This is really unusual in science. What sets us apart from other research groups is that we are already building these semiconductor devices.”

Gabor and Aji will be assisted in the research by two graduate students. The project, titled “Stacking and twisting van der Waals heterostructures for ultrafast and ultrasensitive vibronic sensors,” begins Sept. 1.

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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

1 day 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.