Solar Energy

Solving interface mystery in organic solar cells makes them more efficient

Published

3 months ago

November 19, 2024

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Solving interface mystery in organic solar cells makes them more efficient

by Matt Shipman for NCSU News

Raleigh NC (SPX) Oct 31, 2024

New research from North Carolina State University provides a deeper understanding of precisely what is happening in organic solar cells as light is converted into electricity. Researchers developed a new method which visualizes interfaces where the sunlight’s energy is converted to electrical charges and used the findings to develop a set of design rules that can improve the efficiency of organic solar cells.

Organic solar cells are made with carbon-based polymer materials that have the potential to be low cost, can be made from earth-abundant materials, and have some attractive features – such as the fact that they can be made into semi-transparent or transparent window applications. In addition, as thin film solar cells they have the potential for lightweight and flexible solar applications amenable to roll-to-roll manufacturing – which could also make them easy to transport and install.

However, organic solar cells have not been as efficient as silicon or perovskite solar technologies at converting light into electricity.

“Organic solar cells are made of a mixture of two materials,” says Aram Amassian, co-corresponding author of a paper on the work and a university faculty scholar and professor of materials science and engineering at North Carolina State University.

“Both materials harvest electrons from sunlight. However, one of the materials is a polymer that harvests electrons, but then has to interact with the second material in order to pass those electrons on. The polymer is called a donor material; the other substance, typically a small molecule, is called the acceptor material. We knew that interfaces between donor and acceptor materials were responsible for a voltage loss – which is what currently limits the efficiency of organic solar cells. Our goal with this work was to gain a deeper understanding of what aspects of interfaces were responsible for the voltage loss so that we may improve them.”

To address this challenge, the researchers developed a scanning-probe microscopy method that allowed them to map not only the topographic characteristics of the donor and acceptor blend, but also the energy characteristics of the donor and acceptor materials at the interfaces – such as the energy gradient at the interface and how disordered the donor and acceptor materials are at the interface.

“This technique allowed us to determine how the degree of disorder of donor and acceptor molecules at the interface impacted the energy disorder,” says Daniel Dougherty, co-corresponding author of the paper and a professor of physics at NC State. “Once we had mapped the energetics of all of these interfaces, we were able to compare those findings with the results of conventional methods that characterize the overall performance of an organic solar cell’s voltage loss.”

The team needed to overcome another key challenge. As the scanning-probe microscopy technique does not directly measure voltage loss, the team could not tell which interface was the main culprit.

“Blends of donor and acceptor materials give rise to many different types of interfaces at once and it is not clear which interfaces are responsible for voltage losses,” Amassian says.

“Our study revealed that the functional interface in modern high performance organic solar cells, such as PM6:Y6, is the sharp donor-acceptor interface,” Dougherty says. “The findings imply that this type of interface needs to be targeted to further reduce voltage losses.”

“Once we identified the functional interface associated with voltage loss, we conducted a series of investigations into which factors influenced voltage loss,” Amassian says.

“There has been a longstanding debate in the organic solar cell community between people who argued that voltage loss was driven by energy differential between constituent donor and acceptor materials and people who argued that voltage loss was driven by energetic disorder along interfaces. Our experiments show that both sides are correct – it’s a combination of both factors.”

The researchers successfully demonstrated that it is possible to “fix” the energy differential and tune the disorder at interfaces by changing the way the donor and acceptor are blended during fabrication in such a way as to reduce the voltage loss as much as possible.

“By controlling for one of the drivers of voltage loss, we were actually able to identify engineering solutions that will help the organic solar cell community minimize the other driver of voltage loss,” Amassian says.

“Essentially, voltage losses are reduced by selecting a pair of materials with minimal energy offsets. Practitioners can then further reduce energy losses by identifying a solvent and processing parameters that substantially reduce interfacial disorder. We’re optimistic the design rules we developed using this technique can be used to inform organic solar cell research and development moving forward.”

Research Report:Mapping Interfacial Energetic Landscape in Organic Solar Cells Reveals Pathways to Reducing Nonradiative Losses

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Solar Energy

Scientists Probe Declining Earbud Battery Longevity

Published

10 hours 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

10 hours 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

11 hours 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.