Novel Graphene Film Offers New Concept for Solar Energy and Solar Seawater Desalination


Ultrathin-graphene-film-for-solar-energy-image-img_assist-400x254

Researchers at Swinburne, the University of Sydney and Australian National University have collaborated to develop a solar absorbing, ultra-thin graphene-based film with unique properties that has great potential for use in solar thermal energy harvesting.

The 90 nanometre material is said to be a 1000 times finer than a human hair and is able to rapidly heat up to 160°C under natural sunlight in an open environment.

The team stated that this new graphene-based material may also open new avenues in:

  • thermophotovoltaics (the direct conversion of heat to electricity)
  • solar seawater desalination
  • infrared light source and heater
  • optical components: modulators and interconnects for communication devices
  • photodetectors
  • colorful display
  • It could possibly lead to the development of ‘invisible cloaking technology’ through developing large-scale thin films enclosing the objects to be ‘hidden’.

The researchers have developed a 2.5cm x 5cm working prototype to demonstrate the photo-thermal performance of the graphene-based metamaterial absorber. They have also proposed a scalable manufacturing strategy to fabricate the proposed graphene-based absorber at low cost.

“This is among many graphene innovations in our group,” says Professor Baohua Jia, Research Leader, Nanophotonic Solar Technology, in Swinburne’s Center for Micro-Photonics.

“In this work, the reduced graphene oxide layer and grating structures were coated with a solution and fabricated by a laser nanofabrication method, respectively, which are both scalable and low cost.”

‌‌“Our cost-effective and scalable graphene absorber is promising for integrated, large-scale applications that require polarisation-independent, angle insensitive and broad bandwidth absorption, such as energy-harvesting, thermal emitters, optical interconnects, photodetectors and optical modulators,” says first author of this research paper, Dr Han Lin, Senior Research Fellow in Swinburne’s Center for Micro-Photonics.

“Fabrication on a flexible substrate and the robustness stemming from graphene make it suitable for industrial use,” Dr Keng-Te Lin, another author, added.

“The physical effect causing this outstanding absorption in such a thin layer is quite general and thereby opens up a lot of exciting applications,” says Dr Bjorn Sturmberg, who completed his PhD in physics at the University of Sydney in 2016 and now holds a position at the Australian National University.

“The result shows what can be achieved through collaboration between different universities, in this case with the University of Sydney and Swinburne, each bringing in their own expertise to discover new science and applications for our science,” says Professor Martijn de Sterke, Director of the Institute of Photonics and Optical Science.

“Through our collaboration we came up with a very innovative and successful result. We have essentially developed a new class of optical material, the properties of which can be tuned for multiple uses.”

Source:  Swinburne
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MIT: Unleashing perovskites’ potential for solar cells


Solar cells made of perovskite have great promise, in part because they can easily be made on flexible substrates, like this experimental cell. Image: Ken Richardson

New results show how varying the recipe could bring these materials closer to commercialization.

Perovskites — a broad category of compounds that share a certain crystal structure — have attracted a great deal of attention as potential new solar-cell materials because of their low cost, flexibility, and relatively easy manufacturing process.

But much remains unknown about the details of their structure and the effects of substituting different metals or other elements within the material.

Conventional solar cells made of silicon must be processed at temperatures above 1,400 degrees Celsius, using expensive equipment that limits their potential for production scaleup.

In contrast, perovskites can be processed in a liquid solution at temperatures as low as 100 degrees, using inexpensive equipment. What’s more, perovskites can be deposited on a variety of substrates, including flexible plastics, enabling a variety of new uses that would be impossible with thicker, stiffer silicon wafers.

Now, researchers have been able to decipher a key aspect of the behavior of perovskites made with different formulations:

With certain additives there is a kind of “sweet spot” where greater amounts will enhance performance and beyond which further amounts begin to degrade it.

The findings are detailed this week in the journal Science, in a paper by former MIT postdoc Juan-Pablo Correa-Baena, MIT professors Tonio Buonassisi and Moungi Bawendi, and 18 others at MIT, the University of California at San Diego, and other institutions.

Perovskite solar cells are thought to have great potential, and new understanding of how changes in composition affect their behavior could help to make them practical. Image: Ken Richardson

Perovskites are a family of compounds that share a three-part crystal structure. Each part can be made from any of a number of different elements or compounds — leading to a very broad range of possible formulations. Buonassisi compares designing a new perovskite to ordering from a menu, picking one (or more) from each of column A, column B, and (by convention) column X.

“You can mix and match,” he says, but until now all the variations could only be studied by trial and error, since researchers had no basic understanding of what was going on in the material.

In previous research by a team from the Swiss École Polytechnique Fédérale de Lausanne, in which Correa-Baena participated, had found that adding certain alkali metals to the perovskite mix could improve the material’s efficiency at converting solar energy to electricity, from about 19 percent to about 22 percent.

But at the time there was no explanation for this improvement, and no understanding of exactly what these metals were doing inside the compound. “Very little was known about how the microstructure affects the performance,” Buonassisi says.

Now, detailed mapping using high-resolution synchrotron nano-X-ray fluorescence measurements, which can probe the material with a beam just one-thousandth the width of a hair, has revealed the details of the process, with potential clues for how to improve the material’s performance even further.

It turns out that adding these alkali metals, such as cesium or rubidium, to the perovskite compound helps some of the other constituents to mix together more smoothly. As the team describes it, these additives help to “homogenize” the mixture, making it conduct electricity more easily and thus improving its efficiency as a solar cell.

But, they found, that only works up to a certain point. Beyond a certain concentration, these added metals clump together, forming regions that interfere with the material’s conductivity and partly counteract the initial advantage. In between, for any given formulation of these complex compounds, is the sweet spot that provides the best performance, they found.

“It’s a big finding,” says Correa-Baena, who in January became an assistant professor of materials science and engineering at Georgia Tech.

What the researchers found, after about three years of work at MIT and with collaborators at UCSD, was “what happens when you add those alkali metals, and why the performance improves.” They were able to directly observe the changes in the composition of the material, and reveal, among other things, these countervailing effects of homogenizing and clumping.

“The idea is that, based on these findings, we now know we should be looking into similar systems, in terms of adding alkali metals or other metals,” or varying other parts of the recipe, Correa-Baena says.

While perovskites can have major benefits over conventional silicon solar cells, especially in terms of the low cost of setting up factories to produce them, they still require further work to boost their overall efficiency and improve their longevity, which lags significantly behind that of silicon cells.

Although the researchers have clarified the structural changes that take place in the perovskite material when adding different metals, and the resulting changes in performance, “we still don’t understand the chemistry behind this,” Correa-Baena says. That’s the subject of ongoing research by the team. The theoretical maximum efficiency of these perovskite solar cells is about 31 percent, according to Correa-Baena, and the best performance to date is around 23 percent, so there remains a significant margin for potential improvement.

Although it may take years for perovskites to realize their full potential, at least two companies are already in the process of setting up production lines, and they expect to begin selling their first modules within the next year or so. Some of these are small, transparent and colorful solar cells designed to be integrated into a building’s façade. “It’s already happening,” Correa-Baena says, “but there’s still work to do in making these more durable.”

Once issues of large-scale manufacturability, efficiency, and durability are addressed, Buonassisi says, perovskites could become a major player in the renewable energy industry. “If they succeed in making sustainable, high-efficiency modules while preserving the low cost of the manufacturing, that could be game-changing,” he says. “It could allow expansion of solar power much faster than we’ve seen.”

Perovskite solar cells “are now primary candidates for commercialization. Thus, providing deeper insights, as done in this work, contributes to future development,” says Michael Saliba, a senior researcher on the physics of soft matter at the University of Fribourg, Switzerland, who was not involved in this research.

Saliba adds, “This is great work that is shedding light on some of the most investigated materials. The use of synchrotron-based, novel techniques in combination with novel material engineering is of the highest quality, and is deserving of appearing in such a high-ranking journal.” He adds that work in this field “is rapidly progressing. Thus, having more detailed knowledge will be important for addressing future engineering challenges.”

The study, which included researchers at Purdue University and Argonne National Laboratory, in addition to those at MIT and UCSD, was supported by the U.S. Department of Energy, the National Science Foundation, the Skolkovo Institute of Science and Technology, and the California Energy Commission.

MIT: Optimizing solar farms with ‘Smart Drones’


mit-raptor-maps-01_0As drones increasingly take on the job of inspecting growing solar farms, Raptor Maps’ software makes sense of the data they collect. Image courtesy of Raptor Maps

MIT spinoff Raptor Maps uses machine-learning software to improve the maintenance of solar panels.

As the solar industry has grown, so have some of its inefficiencies. Smart entrepreneurs see those inefficiencies as business opportunities and try to create solutions around them. Such is the nature of a maturing industry.

One of the biggest complications emerging from the industry’s breakneck growth is the maintenance of solar farms. Historically, technicians have run electrical tests on random sections of solar cells in order to identify problems. In recent years, the use of drones equipped with thermal cameras has improved the speed of data collection, but now technicians are being asked to interpret a never-ending flow of unstructured data.

That’s where Raptor Maps comes in. The company’s software analyzes imagery from drones and diagnoses problems down to the level of individual cells. The system can also estimate the costs associated with each problem it finds, allowing technicians to prioritize their work and owners to decide what’s worth fixing.

“We can enable technicians to cover 10 times the territory and pinpoint the most optimal use of their skill set on any given day,” Raptor Maps co-founder and CEO Nikhil Vadhavkar says. “We came in and said, ‘If solar is going to become the number one source of energy in the world, this process needs to be standardized and scalable.’ That’s what it takes, and our customers appreciate that approach.”

Raptor Maps processed the data of 1 percent of the world’s solar energy in 2018, amounting to the energy generated by millions of panels around the world. And as the industry continues its upward trajectory, with solar farms expanding in size and complexity, the company’s business proposition only becomes more attractive to the people driving that growth.

Picking a path

Raptor Maps was founded by Eddie Obropta ’13 SM ’15, Forrest Meyen SM ’13 PhD ’17, and Vadhavkar, who was a PhD candidate at MIT between 2011 and 2016. The former classmates had worked together in the Human Systems Laboratory of the Department of Aeronautics and Astronautics when Vadhavkar came to them with the idea of starting a drone company in 2015.

The founders were initially focused on the agriculture industry. The plan was to build drones equipped with high-definition thermal cameras to gather data, then create a machine-learning system to gain insights on crops as they grew. While the founders began the arduous process of collecting training data, they received guidance from MIT’s Venture Mentoring Service and the Martin Trust Center. In the spring of 2015, Raptor Maps won the MIT $100K Launch competition.

But even as the company began working with the owners of two large farms, Obropta and Vadhavkar were unsure of their path to scaling the company. (Meyen left the company in 2016.) Then, in 2017, they made their software publicly available and something interesting happened.

They found that most of the people who used the system were applying it to thermal images of solar farms instead of real farms. It was a message the founders took to heart.

“Solar is similar to farming: It’s out in the open, 2-D, and it’s spread over a large area,” Obropta says. “And when you see [an anomaly] in thermal images on solar, it usually means an electrical issue or a mechanical issue — you don’t have to guess as much as in agriculture. So we decided the best use case was solar. And with a big push for clean energy and renewables, that aligned really well with what we wanted to do as a team.”

Obropta and Vadhavkar also found themselves on the right side of several long-term trends as a result of the pivot. The International Energy Agency has proposed that solar power could be the world’s largest source of electricity by 2050. But as demand grows, investors, owners, and operators of solar farms are dealing with an increasingly acute shortage of technicians to keep the panels running near peak efficiency.

Since deciding to focus on solar exclusively around the beginning of 2018, Raptor Maps has found success in the industry by releasing its standards for data collection and letting customers — or the many drone operators the company partners with — use off-the-shelf hardware to gather the data themselves. After the data is submitted to the company, the system creates a detailed map of each solar farm and pinpoints any problems it finds.

“We run analytics so we can tell you, ‘This is how many solar panels have this type of issue; this is how much the power is being affected,’” Vadhavkar says. “And we can put an estimate on how many dollars each issue costs.”

The model allows Raptor Maps to stay lean while its software does the heavy lifting. In fact, the company’s current operations involve more servers than people.

The tiny operation belies a company that’s carved out a formidable space for itself in the solar industry. Last year, Raptor Maps processed four gigawatts worth of data from customers on six different continents. That’s enough energy to power nearly 3 million homes.

Vadhavkar says the company’s goal is to grow at least fivefold in 2019 as several large customers move to make the software a core part of their operations. The team is also working on getting its software to generate insights in real time using graphical processing units on the drone itself as part of a project with the multinational energy company Enel Green Power.

Ultimately, the data Raptor Maps collect are taking the uncertainty out of the solar industry, making it a more attractive space for investors, operators, and everyone in between.

“The growth of the industry is what drives us,” Vadhavkar says. “We’re directly seeing that what we’re doing is impacting the ability of the industry to grow faster. That’s huge. Growing the industry — but also, from the entrepreneurial side, building a profitable business while doing it — that’s always been a huge dream.”

Nanomaterials that ‘self-assemble’ offer pathway to a more efficient, affordable harnessing of Solar Power


more efficient solar selfassembli
In this illustration, DPP and rylene dye molecules come together to create a self-assembled superstructure. Electrons within the structure absorb and become excited by light photons, and then couple with neighboring electrons to share …more

Solar rays are a plentiful, clean source of energy that is becoming increasingly important as the world works to shift away from power sources that contribute to global warming.

But current methods of harvesting solar charges are in large expensive and inefficient—with a theoretical efficiency limit of 33 percent. New nanomaterials developed by researchers at the Advanced Science Research Center (ASRC) at The Graduate Center of The City University of New York (CUNY) could provide a pathway to more efficient and potentially affordable harvesting of solar energy.

The materials, created by scientists with the ASRC’s Nanoscience Initiative, use a process called singlet fission to produce and extend the life of harvestable light-generated electrons. The discovery is described in a newly published paper in the Journal of Physical Chemistry. Early research suggests these materials could create more usable charges and increase the theoretical efficiency of  up to 44 percent.

“We modified some of the molecules in commonly used industrial dyes to create self-assembling materials that facilitate a greater yield of harvestable electrons and extend the electrons’ xcited-state lifetimes, giving us more time to collect them in a solar cell,” said Andrew Levine, lead author of the paper and a Ph.D. student at The Graduate Center.

The self-assembly process, Levine explained, causes the  to stack in a particular way. This stacking allows dyes that have absorbed solar photons to couple and share energy with —or “excite”—neighboring dyes. The electrons in these dyes then decouple so that they can be collected as harvestable solar energy.

Methodology and Findings

To develop the materials, researchers combined various versions of two frequently used industrial dyes—diketopyrrolopyrrole (DPP) and rylene. This resulted in the formation of six self-assembling superstructures, which scientists investigated using electron microscopy and advanced spectroscopy. They found that each combination had subtle differences in geometry that affected the dyes’ excited states, the occurrence of singlet fission, and the yield and lifetime of harvestable electrons. Significance

“This work provides us with a library of nanomaterials that we can study for harvesting solar energy,” said Professor Adam Braunschweig, lead researcher on the study and an associate professor with the ASRC Nanoscience Initiative and the Chemistry Departments at Hunter College and The Graduate Center. “Our method for combining the dyes into functional materials using self-assembly means we can carefully tune their properties and increase the efficiency of the critical light-harvesting process.”

The materials’ ability to self-assemble could also shorten the time for creating commercially viable solar cells, said the researchers, and prove more affordable than current fabrication methods, which rely on the time-consuming process of molecular synthesis.

The research team’s next challenge is to develop a method of harvesting the solar charges created by their new nanomaterials. Currently, they are working to design a rylene molecule that can accept the electron from the DPP molecule after the singlet fission process. If successful, these  would both initiate the singlet fission process and facilitate charge-transfer into a solar cell.

 Explore further: Pathway opens to minimize waste in solar energy capture

More information: Andrew M. Levine et al, Singlet Fission in Combinatorial Diketopyrrolopyrrole–Rylene Supramolecular Films, The Journal of Physical Chemistry C (2019). DOI: 10.1021/acs.jpcc.8b09593

 

Penn State – 3D Imaging Technique Unlocks Properties of Perovskite Crystals – Applications for Perovskite Solar Cells


A reconstruction of a perovskite crystal (CaTiO3) grown on a similar perovskite substrate (NdGaO3) showing electron density and oxygen octahedral tilt. (insert) Artist’s conception of the interface between substrate and film. Credit: Yakun Yuan/Penn State

A team of materials scientists from Penn State, Cornell and Argonne National Laboratory have, for the first time, visualized the 3D atomic and electron density structure of the most complex perovskite crystal structure system decoded to date.

Perovskites are minerals that are of interest as electrical insulators, semiconductors, metals or superconductors, depending on the arrangement of their atoms and electrons.

Perovskite crystals have an unusual grouping of oxygen atoms that form an octahedron, an eight-sided polygon. This arrangement of oxygen atoms acts like a cage that can hold a large number of the elemental atoms in the periodic table. Additionally, other atoms can be fixed to the corners of a cube outside of the cage at precise locations to alter the material’s properties, for instance in changing a metal into an insulator, or a non-magnet into a ferromagnet.

In their current work, the team grew the very first discovered perovskite crystal, called calcium titanate, on top of a series of other perovskite crystal substrates with similar but slightly different oxygen cages at their surfaces. Because the thin film perovskite on top wants to conform to the structure of the thicker substrate, it contorts its cages in a process known as tilt epitaxy.

The researchers found this tilt epitaxy of calcium titanate caused a very ordinary material to take on the property of ferroelectricity, a spontaneous polarization, and to remain ferroelectric up to 900 Kelvin, around three times hotter than room temperature. They were also able to visualize the three-dimensional electron density distribution in calcium titanate thin film for the first time.

“We have been able to see atoms for quite some time, but not map them and their electron distribution in space in a crystal in three dimensions,” said Venkat Gopalan, professor of materials science and physics, Penn State. “If we can see not just where atomic nuclei are located in space, but also how their electron clouds are shared, that will tell us basically everything we need to know about the material in order to infer its properties.”

That was the challenge the team set for itself over five years ago when Gopalan gave his student and lead author of a new report in Nature Communications, Yakun Yuan, the project.

Based on a rarely used x-ray visualization technique called COBRA, for coherent Bragg rod analysis, originally developed by a group in Israel, Yuan figured out how to expand and modify the technique to analyze one of the most complicated, least symmetrical material systems studied to date: the strained three-dimensional perovskite crystal with octahedral tilts in all directions, grown on another equally complex crystal structure.

“To reveal 3D structural details at the atomic level, we had to collect extensive datasets using the most brilliant synchrotron X-ray source available at Argonne National Labs and carefully analyze them with the COBRA analysis code modified for accommodating the complexity of such low symmetry,” said Yakun Yuan.

Gopalan went on to explain that very few perovskite oxygen cages are perfectly aligned throughout the material. Some rotate counterclockwise in one layer of atoms and clockwise in the next. Some cages are squeezed out of shape or tilt in directions that are in or out of plane to the substrate surface.

From the interface of a film with the substrate it is grown on, all the way to its surface, each atomic layer may have unique changes in their structure and pattern.  All of these distortions make a difference in the material properties, which they can predict using a computational technique called density functional theory (DFT).

“The predictions from the DFT calculations provide insights that complement the experimental data and help explain the way that material properties change with the alignment or tilting of the perovskite oxygen cages,” said Prof. Susan Sinnott, whose group performed the theoretical calculations.

The team also validated their advanced COBRA technique against multiple images of their material using the powerful Titan transmission electron microscope in the Materials Research Institute at Penn State.  Since the electron microscopes image extremely thin electron transparent samples in a 2-dimensional projection, not all of the 3-dimensional image could be captured even with the best microscope available today and with multiple sample orientations.

Why Perovskite Solar Cells Are So Efficient

This is an area where 3-dimensional imaging by the COBRA technique outperformed the electron microscopy in such complex structures.

The researchers believe their COBRA technique is applicable to the study of many other three-dimensional low-symmetry atomic crystals.

Additional authors on “Three-dimensional atomic scale electron density reconstruction of octahedral tilt epitaxy in functionals perovskites” are Yanfu Lu, a Ph.D. student in Sinnott’s group, Greg Stone, Gopalan’s former postdoctoral scholar, Ke Wang, a staff scientist in Penn State’s Materials Research Institute, Darrell Schlom and his Ph.D. student Charles Brooks, Cornell University, and Hua Zhou, staff scientist, Argonne National Laboratory.

img_0885-1Penn State University

Funding was provided by the National Science Foundation with additional support provided through the Department of Energy and the Penn State 2D Crystal Consortium, a NSF Materials Innovation Platform, and the Penn State institute for CyberScience.

Contact Venkat Gopalan at vxg8@psu.edu or Hua Zhou at hzhou@aps.anl.gov.

Quantum Dots leader completes deal to manufacture NextGen Cadmium Free QD’s in Asia


A leading US quantum dot and nanomaterials manufacturer has announced a licensing and manufacturing deal in Assam, India.

The company, Quantum Materials Corp (QMC), has a range of products which can be used to make anything from superior Ultra High Definition television displays to ultra-thin solar cells and more efficient batteries.

The agreement will not only lead to significant job opportunities in the locality of Assam, but is also a major step in deploying QMC’s extraordinary technologies in the region.

There is the opportunity to adopt next-generation solar photovoltaic technology in the area, after the implementation of recent tariffs on imported photovoltaics into India.

QMC’s cadmium-free quantum dots offer a less hazardous and eco-friendlier alternative for producers and consumers, providing them with the color benefit without the risks of toxicity or liability.

The incorporation of cadmium in quantum dots has restricted their adoption, keeping manufacturers from leveraging the benefits of the technology. Restriction of Hazardous Substances regulations currently state that 1,000 parts per million (ppm) cadmium can be used, however this exception will soon expire and only 100 ppm of cadmium will be acceptable. In 2015, the European Parliament banned the continued use of cadmium in display and lighting devices.

img_0866Read More: What are quantum dots? The Science and Applications

Furthermore, controls and regulations are growing in Asia, with China implementing new laws of its own.

QMC signed the License and Development Agreement with Amtronics CC to allow for the establishment of large scale, low cost quantum dot production for the development and future commercial manufacture of: ultra-high definition display panels, solid state lighting LEDs and quantum dot driven thin-film solar cells.

The Agreement provides Amtronics CC with the right to manufacture quantum dots and thin-film quantum dot solar cells for commercial supply in India, as well as the right to use the QDXTM trademark and technical data to support its marketing initiatives. Under the terms of the Agreement, QMC receives an immediate upfront license fee of US$1,000,000 in addition to technology development funding, scheduled milestone payments and royalties on all quantum dots/solar cells produced.

The 12,000 square feet nanotech-focused facility is being established as the anchor project within the recently announced Electronics Manufacturing Cluster in the Guwahati Tech City.

“We are extremely pleased to partner with Amtronics CC and Amtron as they establish the necessary infrastructure to support large scale thin-film, quantum dot based solar cell production in Assam India using QMC patented technologies” explained Stephen B. Squires, President and CEO of Quantum Materials Corp.

“India’s recent implementation of tariffs applied to imported solar photovoltaics creates an ideal opportunity to establish QMC’s next generation thin-film photovoltaics for broad adoption in the region. I am highly confident that our technologies will help India fulfill its goal to deploy low cost renewables as a significant step toward energy independence”

Dr. George Anthony Balchin, Managing Director of Amtronics CC added, “We are pleased to be involved and provide the initial US $20,000,000 in funding for this enterprise and are anxious to see these extraordinary technologies deployed in a region that will benefit from both the end product as well as the significant potential for job creation.

The initial capital infusion will be used to build out the facility, purchase all the production and process equipment, including the micro reactors, train the staff and provide the initial working capital. It is very rare and rewarding to be involved with a project that is the culmination of a group of like-minded individuals striving for a common goal that has so much potential to enhance the lives of so many.”

Commenting further QMC CEO Squires stated: “As India represents one of the largest renewable energy and consumer electronics markets in the world, our partnership with Amtronics CC is an important step in expanding the value of the QMC franchise globally. This partnership will allow us to address global challenges such as rising energy costs, energy security, increasing power consumption and environmental quality on a more rapid basis.”

How a ‘solar battery’ could bring electricity to rural areas – A ‘solar flow’ battery could “Harvest (energy) in the Daytime and Provide Electricity in the Evening


New solar flow battery with a 14.1 percent efficiency. Photo: David Tenenbaum, UW-Madison

Solar energy is becoming more and more popular as prices drop, yet a home powered by the Sun isn’t free from the grid because solar panels don’t store energy for later. Now, researchers have refined a device that can both harvest and store solar energy, and they hope it will one day bring electricity to rural and underdeveloped areas.

The problem of energy storage has led to many creative solutions, like giant batteries. For a paper published today in the journal Chem, scientists trying to improve the solar cells themselves developed an integrated battery that works in three different ways.

It can work like a normal solar cell by converting sunlight to electricity immediately, explains study author Song Jin, a chemist at the University of Wisconsin at Madison. It can store the solar energy, or it can simply be charged like a normal battery.

“IT COULD HARVEST IN THE DAYTIME, PROVIDE ELECTRICITY IN THE EVENING.”

It’s a combination of two existing technologies: solar cells that harvest light, and a so-called flow battery.

The most commonly used batteries, lithium-ion, store energy in solid materials, like various metals. Flow batteries, on the other hand, store energy in external liquid tanks.

What is A ‘Flow Battery’

This means they are very easy to scale for large projects. Scaling up all the components of a lithium-ion battery might throw off the engineering, but for flow batteries, “you just make the tank bigger,” says Timothy Cook, a University at Buffalo chemist and flow battery expert not involved in the study.

“You really simplify how to make the battery grow in capacity,” he adds. “We’re not making flow batteries to power a cell phone, we’re thinking about buildings or industrial sites.

Jin and his team were the first to combine the two features. They have been working on the battery for years, and have now reached 14.1 percent efficiency.

Jin calls this “round-trip efficiency” — as in, the efficiency from taking that energy, storing it, and discharging it. “We can probably get to 20 percent efficiency in the next few years, and I think 25 percent round-trip is not out of the question,” Jin says.

Apart from improving efficiency, Jin and his team want to develop a better design that can use cheaper materials.

The invention is still at proof-of-concept stage, but he thinks it could have a large impact in less-developed areas without power grids and proper infrastructure. “There, you could have a medium-scale device like this operate by itself,” he says. “It could harvest in the daytime, provide electricity in the evening.” In many areas, Jin adds, having electricity is a game changer, because it can help people be more connected or enable more clinics to be open and therefore improve health care.

And Cook notes that if the solar flow battery can be scaled, it can still be helpful in the US.

The United States might have plenty of power infrastructure, but with such a device, “you can disconnect and have personalized energy where you’re storing and using what you need locally,” he says. And that could help us be less dependent on forms of energy that harm the environment.

“Harvesting Energy from Light” – ORNL: Multimodal imaging shows strain can drive chemistry in a photovoltaic material –


In a thin film of a solar-energy material, molecules in twin domains (modeled in left and right panels) align in opposing orientations within grain boundaries (shown by scanning electron microscopy in the center panel). Strain can change chemical segregation and may be engineered to tune photovoltaic efficiency. Credit: Stephen Jesse/Oak Ridge National Laboratory, U.S. Dept. of Energy (hi-res image)

OAK RIDGE, Tenn., Sept. 25, 2018—A unique combination of imaging tools and atomic-level simulations has allowed a team led by the Department of Energy’s Oak Ridge National Laboratory to solve a longstanding debate about the properties of a promising material that can harvest energy from light.

The researchers used multimodal imaging to “see” nanoscale interactions within a thin film of hybrid organic–inorganic perovskite, a material useful for solar cells.

They determined that the material is ferroelastic, meaning it can form domains of polarized strain to minimize elastic energy. This finding was contrary to previous assumptions that the material is ferroelectric, meaning it can form domains of polarized electric charge to minimize electric energy.

“We found that people were misguided by the mechanical signal in standard electromechanical measurements, resulting in the misinterpretation of ferroelectricity,” said Yongtao Liu of ORNL, whose contribution to the study became a focus of his PhD thesis at the University of Tennessee, Knoxville (UTK).

Olga Ovchinnikova, who directed the experiments at ORNL’s Center for Nanophase Materials Sciences (CNMS), added, “We used multimodal chemical imaging—scanning probe microscopy combined with mass spectrometry and optical spectroscopy—to show that this material is ferroelastic and how the ferroelasticity drives chemical segregation.”

The findings, reported in Nature Materials, revealed that differential strains cause ionized molecules to migrate and segregate within regions of the film, resulting in local chemistry that may affect the transport of electric charge.

The understanding that this unique suite of imaging tools enables allows researchers to better correlate structure and function and fine-tune energy-harvesting films for improved performance.

“We want to predictively make grains of particular sizes and geometries,” Liu said. “The geometry is going to control the strain, and the strain is going to control the local chemistry.”

For their experiment, the researchers made a thin film by spin-casting a perovskite on an indium tin oxide–coated glass substrate. This process created the conductive, transparent surface a photovoltaic device would need—but also generated strain.

To relieve the strain, tiny ferroelastic domains formed. One type of domain was “grains,” which look like what you might see flying over farmland with patches of different crops skewed in relation to one another. Within grains, sub-domains formed, similar to rows of two plant types alternating in a patch of farmland. These adjacent but opposing rows are “twin domains” of segregated chemicals.

The technique that scientists previously used to claim the material was ferroelectric was piezoresponse force microscopy (“piezo” means “pressure), in which the tip of an atomic force microscope (AFM) measures a mechanical displacement due to its coupling with electric polarization—namely, electromechanical displacement. “But you’re not actually measuring the true displacement of the material,” Ovchinnikova warned. “You’re measuring the deflection of this whole ‘diving board’ of the cantilever.” Therefore, the researchers used a new measurement technique to separate cantilever dynamics from displacement of the material due to piezoresponse—the Interferometric Displacement Sensor (IDS) option for the Cypher AFM, developed by co-author Roger Proksch, CEO of Oxford Instruments Asylum Research.

They found the response in this material is from cantilever dynamics alone and is not a true piezoresponse, proving the material is not ferroelectric.

“Our work shows the effect believed due to ferroelectric polarization can be explained by chemical segregation,” Liu said.

The study’s diverse microscopy and spectroscopy measurements provided experimental data to validate atomic-level simulations. The simulations bring predictive insights that could be used to design future materials.

We’re able to do this because of the unique environment at CNMS where we have characterization, theory and synthesis all under one roof,” Ovchinnikova said.

“We didn’t just utilize mass spectrometry because [it] gives you information about local chemistry. We also used optical spectroscopy and simulations to look at the orientation of the molecules, which is important for understanding these materials. Such a cohesive chemical imaging capability at ORNL leverages our functional imaging.”

Collaborations with industry allow ORNL to have unique tools available for scientists, including those that settled the debate about the true nature of the light-harvesting material. For example, an instrument that uses helium ion microscopy (HIM) to remove and ionize molecules was coupled with a secondary ion mass spectroscopy (SIMS) to identify molecules based on their weights.

The HIM-SIMS instrument ZEISS ORION NanoFab was made available to ORNL from developer ZEISS for beta testing and is one of only two such instruments in the world. Similarly, the IDS instrument from Asylum Research, which is a laser Doppler vibrometer, was also made available to ORNL for beta testing and is the only one in existence.

“Oak Ridge National Laboratory researchers are naturally a good fit for working with industry because they possess unique expertise and are able to first use the tools the way they’re meant to,” said Proksch of Asylum. “ORNL has a facility [CNMS] that makes instruments and expertise available to many scientific users who can test tools on different problems and provide strong feedback during beta testing as vendors develop and improve the tools, in this case our new IDS metrological AFM.”

The title of the paper is “Chemical Nature of Ferroelastic Twin Domains in CH3NH3PbI3 Perovskite.”

The research was supported by ORNL’s Laboratory Directed Research and Development Program and conducted at CNMS, a DOE Office of Science User Facility at ORNL.

UT-Battelle manages ORNL for DOE’s Office of Science. The single largest supporter of basic research in the physical sciences in the United States, the Office of Science is working to address some of the most pressing challenges of our time. For more information, please visit https://science.energy.gov/.

NREL: Envisioning Net-Zero Emission Energy Systems


NREL researchers contribute to a major journal article describing pathways to net-zero emissions for particularly difficult-to-decarbonize economic sectors

As global energy consumption continues to grow—by some projections, more than doubling by 2100—all sectors of the economy will need to find ways to drastically reduce their carbon dioxide emissions if average global temperatures are to be held under international climate targets. Two NREL authors contributed to a recently published article in Science that examined potential barriers and opportunities to decarbonizing certain energy systems that are essential to modern civilization but remain stubbornly reliant on carbon-emitting processes.

Difficult to Decarbonize Energy Sectors Contribute 27% of Carbon Emissions

Many sectors of the economy, such as light-duty transportation, heating, cooling, and lighting, could be straightforward to decarbonize through electrification and use of low- or net-zero-emitting energy sources. However, some energy uses, such as aviation, long-distance transport and shipping, steel and cement production, and a highly reliable electricity supply, will be more difficult to decarbonize. Together, these sectors contribute 27% of global carbon emissions today. With global demand for many of these sectors growing rapidly, solutions are urgently needed, the article’s authors write.

“The timeframes and economic costs of any energy transition are enormous. Most technologies installed today will have a lifetime of perhaps 30 to 50 years and the transition from research to actual deployment can also be quite lengthy,” said Bri-Mathias Hodge, an author on the paper and manager of the Power Systems Design and Studies Group at NREL. “Because of this we need to be able to identify the most pertinent issues that will need to be solved fairly far in the future and get started now, before we find ourselves heavily invested in even more carbon-intensive, long-term infrastructure.”

Diverse Expert Perspectives Informed Study

Discussion of the article’s underlying issues began at an Aspen Global Change Institute meeting in July 2016. “The diversity and depth of expertise at the workshop—and contributing to the paper—were outstanding,” said Doug Arent, the other NREL researcher to contribute to the paper and deputy associate lab director for Scientific Computing and Energy Analysis. “It was great to hear the different perspectives and learn about new areas that are related to our work at NREL, but that I don’t get to hear about every day at NREL,” added Hodge.

Considering demographic trends, institutional barriers, and economic and technological constraints, the group of researchers concluded that future net-zero emission systems will depend critically on integration of now-discrete energy industries. Although a range of existing low or net zero emitting energy technologies exist for these energy services, they may only be able to fully meet future energy demands through cross-sector coordination. Collaboration could speed research and development of new technologies and coordinating operations across sectors could better utilize capital-intensive assets, create broader markets, and streamline regulations.

Research Should Pursue Technologies and Integration to Decarbonize These Sectors

The article’s authors suggest two broad research thrusts: research in technologies and processes that could decarbonize these energy services, and research in systems integration to provide these energy services in a more reliable and cost-effective way.

The Science article concludes by stating, “if we want to achieve a robust, reliable, affordable, net-zero emissions energy system later this century, we must be researching, developing, demonstrating, and deploying those candidate technologies now.”

Long-lasting solar cells from and “unexpected gray area” … U of Wisconsin-Madison Make Surprising Discovery


anunexpectedUW-Madison engineers found a way to dramatically extend the lifespan of solar energy-harvesting devices, which use energy from sunlight to generate hydrogen from water. Credit: iStock

University of Wisconsin-Madison materials engineers have made a surprising discovery that could dramatically improve the lifetime of solar energy harvesting devices.

The findings allowed them to achieve the longest-ever lifetime for a key component of some types of photovoltaic cells called the photoelectrochemical electrode, which uses sunlight to split water into its constituent parts of hydrogen and oxygen.

In a paper published July 24, 2018, in the research journal Nano Letters, a team led by UW-Madison materials science and engineering Ph.D. student Yanhao Yu and his advisor, Professor Xudong Wang, described a strategy that extended the lifetime of a photochemical electrode to a whopping 500 hours—more than five times (5X) the typical 80-hour lifespan.

Usually, these types of electrodes are made of silicon, which splits water well, but is highly unstable and quickly degrades when it comes into contact with corrosive conditions. To protect these electrodes, engineers often thinly coat their surfaces.

It’s a tactic that only delays their eventual breakdown—sometimes after a few days and sometimes within hours.

“Performance varies widely and nobody really knows why. It’s a big question,” says Wang, a professor of materials science and engineering at UW-Madison.

Intriguingly, the researchers didn’t make any changes to the coating material. Rather, they boosted the electrode’s lifetime by applying an even thinner coating of  than usual.

In other words, less really was more!

Key to this exceptional performance was the team’s discovery about the atomic structure of titanium dioxide thin , which the researchers create using a technique called .

Previously, researchers believed that the atoms in titanium dioxide thin films adopted one of two conformations—either scrambled and disordered in a state referred to as “amorphous,” or locked into a regularly repeating and predictable arrangement called the crystalline form.

Crucially, researchers were certain that all the atoms in a given thin film behaved the same way. Crystalline or amorphous. Black or white. No in-between.

What Wang colleagues found, however, is a gray area: They saw that small pockets of an in-between state persisted in the final coatings—the  in these areas was neither amorphous nor crystalline. These intermediates have never been observed before.

“This is a cutting edge of materials synthesis science,” says Wang. “We’re thinking that crystallization is not as straightforward as people believe.”

Observing those intermediates was no easy feat. Enter Wang’s colleague Paul Voyles, a microscopy expert who leveraged UW-Madison’s unique facilities to perform sophisticated scanning transmission electron microscopy measurements, enabling him to detect the tiny structures.

From there, the researchers determined those intermediates lowered the lifetime of titanium dioxide thin films by leading to spikes of electronic current that ate tiny holes in the protective coatings.

Eliminating those intermediates—thus extending the ‘s lifetime—is as simple as using a thinner film.

Thinner films make it more difficult for intermediates to form within the film, so by reducing the thickness by three quarters (from 10 nanometers to 2.5), the researchers created coatings that lasted more than five times longer than traditional coatings.

And now that they’ve discovered these peculiar structures, the researchers want to learn more about how they form and influence amorphous film properties. That’s knowledge that could reveal other strategies for eliminating them—which not only could improve performance, says Wang, but also open new opportunities in other energy-related systems, such as catalysts, solar cells and batteries.

“These intermediates could be something very important that has been overlooked,” says Wang. “They could be a critical aspect that controls properties of the film.”

 Explore further: Discovery brings renewable fuel production one step closer to reality

More information: Yanhao Yu et al. Metastable Intermediates in Amorphous Titanium Oxide: A Hidden Role Leading to Ultra-Stable Photoanode Protection, Nano Letters (2018). DOI: 10.1021/acs.nanolett.8b02559