Waste Styrofoam can now be converted into polymers for electronics

University of Delaware and Argonne National Laboratory have come up with a chemical reaction that can convert Styrofoam into a high-value conducting polymer known as PEDOT:PSS. In a new paper published in JACS Au, the study demonstrates how upgraded plastic waste can be successfully incorporated into functional electronic devices, including silicon-based hybrid solar cells and organic electrochemical transistors.

The research group of corresponding author Laure Kayser, assistant professor in the Department of Materials Science and Engineering in UD's College of Engineering with a joint appointment in the Department of Chemistry and Biochemistry in the College of Arts and Sciences, regularly works with PEDOT:PSS, a polymer that has both electronic and ionic conductivity, and was interested in finding ways to synthesize this material from plastic waste.

After connecting with Argonne chemist David Kaphan during an event hosted by UD's research office, the research teams at UD and Argonne began evaluating the hypothesis that PEDOT:PSS could be made by sulfonating polystyrene, a synthetic plastic found in many types of disposable containers and packing materials.

Sulfonation is a common chemical reaction where a hydrogen atom is replaced by sulfonic acid; the process is used to create a variety of products such as dyes, drugs and ion exchange resins. These reactions can either be "hard" (with higher conversion efficiency but that require caustic reagents) or "soft" (a less efficient method but one that uses milder materials).

In this paper, the researchers wanted to find something in the middle: "A reagent that is efficient enough to get really high degrees of functionalization but that doesn't mess up your polymer chain," Kayser explained.

The researchers first turned to a method described in a previous study for sulfonating small molecules, one that showed promising results in terms of efficiency and yield, using 1,3-Disulfonic acid imidazolium chloride ([Dsim]Cl). But adding functional groups onto a polymer is more challenging than for a small molecule, the researchers explained, because not only are unwanted byproducts harder to separate, any small errors in the polymer chain can change its overall properties.

To address this challenge, the researchers embarked on many months of trial and error to find the optimal conditions that minimized side reactions, said Kelsey Koutsoukos, a materials science doctoral candidate and second author of this paper.

"We screened different organic solvents, different molar ratios of the sulfonating agent, and evaluated different temperatures and times to see which conditions were the best for achieving high degrees of sulfonation," he said.

The researchers were able to find reaction conditions that resulted in high polymer sulfonation, minimal defects and high efficiency, all while using a mild sulfonating agent. And because the researchers were able to use polystyrene, specifically waste Styrofoam, as a starting material, their method also represents an efficient way to convert plastic waste into PEDOT:PSS.

Once the researchers had PEDOT:PSS in hand, they were able to compare how their waste-derived polymer performed compared to commercially available PEDOT:PSS.

"In this paper, we looked at two devices -- an organic electronic transistor and a solar cell," said Chun-Yuan Lo, a chemistry doctoral candidate and the paper's first author. "The performance of both types of conductive polymers was comparable, and shows that our method is a very eco-friendly approach for converting polystyrene waste into high-value electronic materials."

Specific analyses conducted at UD included X-ray photoelectron spectroscopy (XPS) at the surface analysis facility, film thickness analysis at the UD Nanofabrication Facility, and solar cell evaluation at the Institute of Energy Conversion. Argonne's advanced spectroscopy equipment, such as carbon NMR, was used for detailed polymer characterization. Additional support was provided by materials science and engineering professor Robert Opila for solar cell analysis and by David C. Martin, the Karl W. and Renate Böer Chaired Professor of Materials Science and Engineering, for the electronic device performance analyses.

One unexpected finding related to the chemistry, the researchers added, is the ability to use stoichiometric ratios during the reaction.

"Typically, for sulfonation of polystyrene, you have to use an excess of really harsh reagents. Here, being able to use a stoichiometric ratio means that we can minimize the amount of waste being generated," Koutsoukos said.

This finding is something the Kayser group will be looking into further as a way to "fine-tune" the degree of sulfonation. So far, they've found that by varying the ratio of starting materials, they can change the degree of sulfonation on the polymer. Along with studying how this degree of sulfonation impacts the electrical properties of PEDOT:PSS, the team is interested in seeing how this fine-tuning capability can be used for other applications, such as fuel cells or water filtration devices, where the degree of sulfonation greatly impacts a material's properties.

"For the electronic devices community, the key takeaway is that you can make electronic materials from trash, and they perform just as well as what you would purchase commercially," Kayser said. "For the more traditional polymer scientists, the fact that you can very efficiently and precisely control the degree of sulfonation is going to be of interest to a lot of different communities and applications."

The researchers also see great potential for how this research can contribute to ongoing global sustainability efforts by providing a new way to convert waste products into value-added materials.

"Many scientists and researchers are working hard on upcycling and recycling efforts, either by chemical or mechanical means, and our study provides another example of how we can address this challenge," Lo said.

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Researchers invent new triple-junction tandem solar cells with world-record efficiency

Scientists from the National University of Singapore (NUS) have developed a novel triple-junction perovskite/Si tandem solar cell that can achieve a certified world-record power conversion efficiency of 27.1 per cent across a solar energy absorption area of 1 sq cm, representing the best-performing triple-junction perovskite/Si tandem solar cell thus far. To achieve this, the team engineered a new cyanate-integrated perovskite solar cell that is stable and energy efficient.

Solar cells can be fabricated in more than two layers and assembled to form multi-junction solar cells to increase efficiency. Each layer is made of different photovoltaic materials and absorbs solar energy within a different range. However, current multi-junction solar cell technologies pose many issues, such as energy loss which leads to low voltage and instability of the device during operation.

To overcome these challenges, Assistant Professor Hou Yi led a team of scientists from NUS College of Design and Engineering (CDE) and Solar Energy Research Institute of Singapore (SERIS) to demonstrate, for the first time, the successful integration of cyanate into a perovskite solar cell to develop a cutting-edge triple-junction perovskite/Si tandem solar cell that surpasses the performance of other similar multi-junction solar cells. Asst Prof Hou is a Presidential Young Professor at the Department of Chemical and Biomolecular Engineering under CDE as well as a Group Leader at SERIS, a university-level research institute in NUS.

"Remarkably, after 15 years of ongoing research in the field of perovskite-based solar cells, this work constitutes the first experimental evidence for the inclusion of cyanate into perovskites to boost the stability of its structure and improve power conversion efficiency," said Asst Prof Hou.

The experimental process that led to this ground-breaking discovery was published in Nature on 4 March 2024.

Fabricating energy-efficient solar cell technology

The interactions between the components of the perovskite structure determine the energy range that it can reach. Adjusting the proportion of these components or finding a direct substitute can help modify the perovskite's energy range. However, prior research has yet to produce a perovskite recipe with an ultrawide energy range and high efficiency.

In this recently published work, the NUS team experimented on cyanate, a novel pseudohalide, as a substitute for bromide -- an ion from the halide group that is commonly used in perovskites. Dr Liu Shunchang, Research Fellow in Asst Prof Hou's team, employed various analytical methods to confirm the successful integration of cyanate into the perovskite structure, and fabricated a cyanate-integrated perovskite solar cell.

Further analysis of the new perovskite's atomic structure provided -- for the first time -- experimental evidence that incorporating cyanate helped to stabilise its structure and form key interactions within the perovskite, demonstrating how it is a viable substitute for halides in perovskite-based solar cells.

When assessing performance, the NUS scientists found that perovskite solar cells incorporated with cyanate can achieve a higher voltage of 1.422 volts compared to 1.357 volts for conventional perovskite solar cells, with a significant reduction in energy loss.

The researchers also tested the newly engineered perovskite solar cell by continuously operating it at maximum power for 300 hours under controlled conditions. After the test period, the solar cell remained stable and functioned above 96 per cent capacity.

Encouraged by the impressive performance of the cyanate-integrated perovskite solar cells, the NUS team took their ground-breaking discovery to the next step by using it to assemble a triple-junction perovskite/Si tandem solar cell. The researchers stacked a perovskite solar cell and a silicon solar cell to create a dual-junction half-cell, providing an ideal base for the attachment of the cyanate-integrated perovskite solar cell.

Once assembled, the researchers demonstrated that despite the complexity of the triple-junction perovskite/Si tandem solar cell structure, it remained stable and attained a certified world-record efficiency of 27.1 per cent from an accredited independent photovoltaic calibration laboratory.

"Collectively, these advancements offer ground-breaking insights into mitigating energy loss in perovskite solar cells and set a new course for the further development of perovskite-based triple junction solar technology," said Asst Prof Hou.

Read more at Science Daily

Record 19.31% efficiency with organic solar cells

Researchers from The Hong Kong Polytechnic University (PolyU) have achieved a breakthrough power-conversion efficiency (PCE) of 19.31% with organic solar cells (OSCs), also known as polymer solar cells. This remarkable binary OSC efficiency will help enhance applications of these advanced solar energy devices.

The PCE (Power-conversion efficiency), a measure of the power generated from a given solar irradiation, is considered a significant benchmark for the performance of photovoltaics (PVs), or solar panels, in power generation. The improved efficiency of over 19% that was achieved by the PolyU researchers constitutes a record for binary OSCs, which have one donor and one acceptor in the photo-active layer.

Led by Prof. LI Gang, Chair Professor of Energy Conversion Technology and Sir Sze-Yen Chung Endowed Professor in Renewable Energy at PolyU, the research team invented a novel OSC morphology-regulating technique by using 1,3,5-trichlorobenzene as a crystallisation regulator. This new technique boosts OSC efficiency and stability.

The team developed a non-monotonic intermediated state manipulation (ISM) strategy to manipulate the bulk-heterojunction (BHJ) OSC morphology, which simultaneously optimises crystallisation dynamics and energy loss of non-fullerene OSCs. Unlike the strategy of using traditional solvent additives, which is based on excessive molecular aggregation in films, the ISM strategy promotes the formation of more ordered molecular stacking and favourable molecular aggregation. As a result, the PCE was considerably increased and the undesirable non-radiative recombination loss was reduced. Notably, non-radiative recombination lowers the light generation efficiency and increases the heat loss.

The research team's findings are described in the study "19.3% Binary Organic Solar Cell and Low Non-Radiative Recombination Enabled by Non-Monotonic Intermediate State Transition" published in Nature Communications . The conversion of solar energy to electricity is an essential technology for achieving a sustainable environment. Although OSCs are promising devices that harness solar energy cost-effectively, their efficiency must be improved if they are to be used widely in practical applications.

Non-fullerene acceptors based organic solar cells represent the frontier of research in the field of organic photovoltaics due to both the materials and morphology manipulation innovations. Nevertheless, non-radiative recombination loss suppress and performance boosting are in the centre of organic cell research.

Prof. Li said, "Challenges in research came from the existing additive-based benchmark morphology control methods, which suffer from non-radiative recombination loss, thus lowering the open-circuit voltage due to excessive aggregation." The research team took about two years to devise a non-monotonic ISM strategy for increasing the OSC efficiency and lowering the non-radiative recombination loss. The publication of the study promises to galvanise OSC research.

Prof. Li said, "The new finding will make OSC research an exciting field, and this will likely create tremendous opportunities in applications like portable electronics and building-integrated PVs." The new door will open when low cost single-junction OSCs can achieve a PCE of over 20%, along with more stable performance and other unique advantages such as flexibility, transparency, stretchability, low weight and tuneable colour.

Prof. Li has been recognised as a Highly Cited Researcher 9 years in a row since 2014, which testifies to his significant impact on global research. His pioneering contributions to research on polymer solar cells since 2005 have brought sustainable influence on printable solar energy development with global recognition.

Underpinning the research on OPV field, Prof LI's study titled, "High-efficiency solution processable polymer photovoltaic cells by self-organization of polymer blends," was published on Nature Materials in 2005. This represented OPV's first generation research breakthrough which has fuelled solar technology from this frontier study.

In 2010, Prof LI's study titled "For the Bright Future -- Bulk Heterojunction Polymer Solar Cells with Power Conversion Efficiency of 7.4%" was published on Advanced Materials.

Prof. Li said, "The latest study shows a record low non-radiative recombination loss of 0.168 eV in a binary OSC with a PCE of over 19%. This is a very encouraging result for the long-standing research on OSCs that I have conducted over the past two decades. We have already achieved better OSC efficiency, and this will subsequently help accelerate the applications of solar energy."

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New method creates material that could create the next generation of solar cells

Perovskites, a family of materials with unique electric properties, show promise for use in a variety fields, including next-generation solar cells. A Penn State-led team of scientists created a new process to fabricate large perovskite devices that is more cost- and time-effective than previously possible and that they said may accelerate future materials discovery.

"This method we developed allows us to easily create very large bulk samples within several minutes, rather than days or weeks using traditional methods," said Luyao Zheng, a postdoctoral researcher in the Department of Materials Science at Penn State and lead author on the study. "And our materials are high quality -- their properties can compete with single-crystal perovskites."

The researchers used a sintering method called the electrical and mechanical field-assisted sintering technique (EM-FAST) to create the devices. Sintering is a commonly used process to compress fine powders into a solid mass of material using heat and pressure.

A typical process for making perovskites involves wet chemistry -- the materials are liquefied in a solvent solution and then solidified into thin films. These materials have excellent properties, but the approach is expensive and inefficient for creating large perovskites and the solvents used may be toxic, the scientists said.

"Our technique is the best of both worlds," said Bed Poudel, a researcher professor at Penn State and a co-author. "We get single-crystal-like properties, and we don't have to worry about size limitations or any contamination or yield of toxic materials."

Because it uses dry materials, the EM-FAST technique opens the door to include new dopants, ingredients added to tailor device properties, that are not compatible with the wet chemistry used to make thin films, potentially accelerating the discovery of new materials, the scientists said.

"This opens up possibilities to design and develop new classes of materials, including better thermoelectric and solar materials, as well as X- and γ-ray detectors," said Amin Nozariasbmarz, assistant research professor at Penn State and a co-author. "Some of the applications are things we already know, but because this is a new technique to make new halide perovskite materials with controlled properties, structures, and compositions, maybe there is room in the future for new breakthroughs to come from that."

In addition, the new process allows for layered materials -- one powder underneath another -- to create designer compositions. In the future, manufactures could design specific devices and then directly print them from dry powders, the scientists said.

"We anticipate this FAST perovskite would open another dimension for high throughput material synthesis, future manufacturing directly printing devices from powder and accelerating the material discovery of new perovskite compositions," said Kai Wang, an assistant research professor at Penn State and a co-author.

EM-FAST, also known as spark plasma sintering, involves applying electric current and pressure to powders to create new materials. The process has a 100% yield -- all the raw ingredients go into the final device, as opposed to 20 to 30% in solution-based processing.

The technique produced perovskite materials at .2 inch per minute, allowing scientists to create quickly create large devices that maintained high performance in laboratory tests. The team reported their findings in the journal Nature Communications.

Penn State scientists have long used EM-FAST to create thermoelectric devices. This work represents the first attempt to create perovskite materials with the technique, the scientists said.

"Because of the background we have, we were talking and thought we could change some parameters and try this with perovskites," Nozariasbmarz said. "And it just opened a door to a new world. This paper is a link to that door -- to new materials and new properties."

Read more at Science Daily

Built to last: The perovskite solar cells tough enough to match mighty silicon

Researchers at Oxford University and Exciton Science have demonstrated a new way to create stable perovskite solar cells, with fewer defects and the potential to finally rival silicon's durability.

By removing the solvent dimethyl-sulfoxide and introducing dimethylammonium chloride as a crystallisation agent, the researchers were able to better control the intermediate phases of the perovskite crystallisation process, leading to thin films of greater quality, with reduced defects and enhanced stability.

Large groups of up to 138 sample devices were then subjected to a rigorous accelerated ageing and testing process at high temperatures and in real-world conditions.

Formamidinium-caesium perovskite solar cells created using the new synthesis process significantly outperformed the control group and demonstrated resistance to thermal, humidity and light degradation.

This is a strong step forward to matching commercial silicon's stability and makes perovskite-silicon tandem devices a much more realistic candidate for becoming the dominant next-generation solar cell.

Led by Professor Henry Snaith (Oxford University) and Professor Udo Bach (Monash University), the work has been published in the journal Nature Materials and is available here.

Oxford University PhD student Philippe Holzhey, a Marie Curie Early Stage Researcher and joint first author on the work, said: "It's really important that people start shifting to realise there is no value in performance if it's not a stable performance.

"If the device lasts for a day or a week or something, there's not so much value in it. It has to last for years."

During testing, the best device operated above the T80 threshold for over 1,400 hours under simulated sunlight at 65°C. T80 is the time it takes for a solar cell to reduce to 80% of its initial efficiency, a common benchmark within the research field.

Beyond 1,600 hours, the control device fabricated using the conventional dimethyl-sulfoxide approach stopped functioning, while devices fabricated with the new, improved design retained 70% of their original efficiency, under accelerated aging conditions.

The same degradation study was performed on a group of devices at the very high temperature of 85°C, with the new cells again outperforming the control group.

Extrapolating from the data, the researchers calculated that the new cells age by a factor of 1.7 for each 10°C increase in the temperature they are exposed to, which is close to the 2-fold increase expected of commercial silicon devices.

Dr David McMeekin, the corresponding and joint first author on the paper, was an Australian Centre for Advanced Photovoltaics (ACAP) Postdoctoral Fellow at Monash University and is now a Marie Skłodowska-Curie Postdoctoral Fellow at Oxford University.

He said: "I think what separates us from other studies is that we've done a lot of accelerated aging. We've aged the cells at 65°C and 85°C under the whole light spectrum."

The number of devices used in the study is also significant, with many other perovskite research projects limited to just one or two prototypes.

"Most studies only show one curve without any standard deviation or any kind of statistical approach to determine if this design is more stable than the other," David added.

The researchers hope their work will encourage a greater focus on the intermediate phase of perovskite crystallisation as an important factor in achieving greater stability and commercial viability.

This work was supported by the Stanford Linear Accelerator Center (SLAC) and the National Renewable Energy Laboratory (NREL).

Background: About Perovskites

Artificially synthesised in laboratory conditions, semiconductor thin films made up of perovskite compounds are far cheaper to make than silicon solar cells, with greater flexibility and a tunable band gap.

They emerged unexpectedly in the last decade and have reached impressive power-conversion efficiencies of over 25%.

However, too much focus has been placed on creating the most efficient perovskite solar cell, rather than resolving the fundamental problems inhibiting the material from being used in widespread commercial applications.

Compared to silicon, perovskites can degrade rapidly in real world conditions, with exposure to heat and moisture causing damage and negatively impacting device performance.

Read more at Science Daily

Once seen as fleeting, a new solar tech proves its lasting power

Princeton Engineering researchers have developed the first perovskite solar cell with a commercially viable lifetime, marking a major milestone for an emerging class of renewable energy technology. The team projects their device can perform above industry standards for around 30 years, far more than the 20 years used as a threshold for viability for solar cells.

The device is not only highly durable, it also meets common efficiency standards. It is the first of its kind to rival the performance of silicon-based cells, which have dominated the market since their introduction in 1954.

Perovskites are semiconductors with a special crystal structure that makes them well suited for solar cell technology. They can be manufactured at room temperature, using much less energy than silicon, making them cheaper and more sustainable to produce. And whereas silicon is stiff and opaque, perovskites can be made flexible and transparent, extending solar power well beyond the iconic panels that populate hillsides and rooftops across America.

But unlike silicon, perovskites are notoriously fragile. Early perovskite solar cells (PSC), created between 2009 and 2012, lasted only minutes. The projected lifetime of the new device represents a five-fold increase over the previous record, set by a lower efficiency PSC in 2017. (That device operated under continuous illumination at room temperature for one year. The new device would operate for five years under similar lab conditions.)

The Princeton team, led by Lynn Loo, the Theodora D. '78 and William H. Walton III '74 Professor in Engineering, revealed their new device and their new method for testing such devices in a paper published June 16 in Science.

Loo said the record-setting design has highlighted the durable potential of PSCs, especially as a way to push solar cell technology beyond the limits of silicon. But she also pointed past the headline result to her team's new accelerated aging technique as the work's deeper significance.

"We might have the record today," she said, "but someone else is going to come along with a better record tomorrow. The really exciting thing is that we now have a way to test these devices and know how they will perform in the long term."

Due to perovskites' well-known frailty, long-term testing hasn't been much of a concern until now. But as the devices get better and last longer, testing one design against another will become crucial in rolling out durable, consumer-friendly technologies.

"This paper is likely going to be a prototype for anyone looking to analyze performance at the intersection of efficiency and stability," said Joseph Berry, a senior fellow at the National Renewable Energy Laboratory who specializes in the physics of solar cells and who was not involved in this study. "By producing a prototype to study stability, and showing what can be extrapolated [through accelerated testing], it's doing the work everyone wants to see before we start field testing at scale. It allows you to project in a way that's really impressive."

While efficiency has accelerated at a remarkable pace over the past decade, Berry said, the stability of these devices has improved more slowly. For them to become widespread and rolled out by industry, testing will need to become more sophisticated. That's where Loo's accelerated aging process comes in.

"These kinds of tests are going to be increasingly important," Loo said. "You can make the most efficient solar cells, but it won't matter if they aren't stable."

How they got here

Early in 2020, Loo's team was working on various device architectures that would maintain relatively strong efficiency -- converting enough sunlight to electric power to make them valuable -- and survive the onslaught of heat, light and humidity that bombard a solar cell during its lifetime.

Xiaoming Zhao, a postdoctoral researcher in Loo's lab, had been working on a number of designs with colleagues. The efforts layered different materials in order to optimize light absorption while protecting the most fragile areas from exposure. They developed an ultra-thin capping layer between two crucial components: the absorbing perovskite layer and a charge-carrying layer made from cupric salt and other substances. The goal was to keep the perovskite semiconductor from burning out in a matter of weeks or months, the norm at that time.

It's hard to comprehend how thin this capping layer is. Scientists use the term 2D to describe it, meaning two dimensions, as in something that has no thickness at all. In reality, it's merely a few atoms thick -- more than a million times smaller than the smallest thing a human eye can see. While the idea of a 2D capping layer isn't new, it is still considered a promising, emerging technique. Scientists at NREL have shown that 2D layers can greatly improve long-haul performance, but no one had developed a device that pushed perovskites anywhere close to the commercial threshold of a 20-year lifetime.

Zhao and his colleagues went through scores of permutations of these designs, shifting minute details in the geometry, varying the number of layers, and trying out dozens of material combinations. Each design went into the light box, where they could irradiate the sensitive devices in relentless bright light and measure their drop in performance over time.

In the fall of that year, as the first wave of the pandemic subsided and researchers to returned to their labs to tend to their experiments in carefully coordinated shifts, Zhao noticed something odd in the data. One set of the devices still seemed to be operating near its peak efficiency.

"There was basically zero drop after nearly half a year," he said.

That's when he realized he needed a way to stress test his device faster than his real-time experiment allowed.

"The lifetime we want is about 30 years, but you can't take 30 years to test your device," Zhao said. "So we need some way to predict this lifetime within a reasonable timeframe. That's why this accelerated aging is very important."

The new testing method speeds up the aging process by illuminating the device while blasting it with heat. This process speeds up what would happen naturally over years of regular exposure. The researchers chose four aging temperatures and measured results across these four different data streams, from the baseline temperature of a typical summer day to an extreme of 230 degrees Fahrenheit, higher than the boiling point of water.

They then extrapolated from the combined data and forecast the device's performance at room temperature over tens of thousands of hours of continuous illumination. The results showed a device that would perform above 80 percent of its peak efficiency under continuous illumination for at least five years at an average temperature of 95 degrees Fahrenheit. Using standard conversion metrics, Loo said that's the lab equivalent of 30 years of outdoor operation in an area like Princeton, NJ.

Berry of NREL concurred. "It's very credible," he said. "Some people are still going to want to see it play out. But this is much more credible science than a lot of other attempts at forecasting."

The Michael Jordan of solar cells

Perovskite solar cells were pioneered in 2006, with the first published devices following in 2009. Some of the earliest devices lasted only seconds. Others minutes. In the 2010s the device lifetimes grew to days and weeks and finally months. Then in 2017, a group from Switzerland published a groundbreaking paper on a PSC that lasted for one full year of continuous illumination.

Meanwhile, the efficiency of these devices has skyrocketed over the same period. While the first PSC showed a power-conversion efficiency of less than 4 percent, researchers boosted that metric nearly tenfold in as many years. It was the fastest improvement scientists had seen in any class of renewable-energy technology to date.

So why the push for perovskites? Berry said a combination of recent advances make them uniquely desirable: newly high efficiencies, an extraordinary "tunability" that allows scientists to make highly specific applications, the ability to manufacture them locally with low energy inputs, and now a credible forecast of extended life coupled with a sophisticated aging process to test a wide array of designs.

Loo said it's not that PSCs will replace silicon devices so much that the new technology will complement the old, making solar panels even cheaper, more efficient and more durable than they are now, and expanding solar energy into untold new areas of modern life. For example, her group recently demonstrated a completely transparent perovskite film (having different chemistry) that can turn windows into energy producing devices without changing their appearance. Other groups have found ways to print photovoltaic inks using perovskites, allowing formfactors scientists are only now dreaming up.

But the main advantage in the long run, according to both Berry and Loo: Perovskites can be manufactured at room temperature, whereas silicon is forged at around 3000 degrees Fahrenheit. That energy has to come from somewhere, and at the moment that means burning a lot of fossil fuels.

Read more at Science Daily

Solar cell keeps working long after sun sets

About 750 million people in the world do not have access to electricity at night. Solar cells provide power during the day, but saving energy for later use requires substantial battery storage.

In Applied Physics Letters, by AIP Publishing, researchers from Stanford University constructed a photovoltaic cell that harvests energy from the environment during the day and night, avoiding the need for batteries altogether. The device makes use of the heat leaking from Earth back into space -- energy that is on the same order of magnitude as incoming solar radiation.

At night, solar cells radiate and lose heat to the sky, reaching temperatures a few degrees below the ambient air. The device under development uses a thermoelectric module to generate voltage and current from the temperature gradient between the cell and the air. This process depends on the thermal design of the system, which includes a hot side and a cold side.

"You want the thermoelectric to have very good contact with both the cold side, which is the solar cell, and the hot side, which is the ambient environment," said author Sid Assawaworrarit. "If you don't have that, you're not going to get much power out of it."

The team demonstrated power generation in their device during the day, when it runs in reverse and contributes additional power to the conventional solar cell, and at night.

The setup is inexpensive and, in principle, could be incorporated within existing solar cells. It is also simple, so construction in remote locations with limited resources is feasible.

"What we managed to do here is build the whole thing from off-the-shelf components, have a very good thermal contact, and the most expensive thing in the whole setup was the thermoelectric itself," said author Zunaid Omair.

Using electricity at night for lighting requires a few watts of power. The current device generates 50 milliwatts per square meter, which means lighting would require about 20 square meters of photovoltaic area.

"None of these components were specifically engineered for this purpose," said author Shanhui Fan. "So, I think there's room for improvement, in the sense that, if one really engineered each of these components for our purpose, I think the performance could be better."

Read more at Science Daily

Templating approach stabilizes 'ideal' material for alternative solar cells

Researchers have developed a method to stabilise a promising material known as perovskite for cheap solar cells, without compromising its near-perfect performance.

The researchers, from the University of Cambridge, used an organic molecule as a 'template' to guide perovskite films into the desired phase as they form. Their results are reported in the journal Science.

Perovskite materials offer a cheaper alternative to silicon for producing optoelectronic devices such as solar cells and LEDs.

There are many different perovskites, resulting from different combinations of elements, but one of the most promising to emerge in recent years is the formamidinium (FA)-based FAPbI3 crystal.

The compound is thermally stable and its inherent 'bandgap' -- the property most closely linked to the energy output of the device -- is not far off ideal for photovoltaic applications.

For these reasons, it has been the focus of efforts to develop commercially available perovskite solar cells. However, the compound can exist in two slightly different phases, with one phase leading to excellent photovoltaic performance, and the other resulting in very little energy output.

"A big problem with FAPbI3 is that the phase that you want is only stable at temperatures above 150 degrees Celsius," said co-author Tiarnan Doherty from Cambridge's Cavendish Laboratory. "At room temperature, it transitions into another phase, which is really bad for photovoltaics."

Recent solutions to keep the material in its desired phase at lower temperatures have involved adding different positive and negative ions into the compound.

"That's been successful and has led to record photovoltaic devices but there are still local power losses that occur," said Doherty. "You end up with local regions in the film that aren't in the right phase."

Little was known about why the additions of these ions improved stability overall, or even what the resulting perovskite structure looked like.

"There was this common consensus that when people stabilise these materials, they're an ideal cubic structure," said Doherty. "But what we've shown is that by adding all these other things, they're not cubic at all, they're very slightly distorted. There's a very subtle structural distortion that gives some inherent stability at room temperature."

The distortion is so minor that it had previously gone undetected, until Doherty and colleagues used sensitive structural measurement techniques that have not been widely used on perovskite materials.

The team used scanning electron diffraction, nano-X-ray diffraction and nuclear magnetic resonance to see, for the first time, what this stable phase really looked like.

"Once we figured out that it was the slight structural distortion giving this stability, we looked for ways to achieve this in the film preparation without adding any other elements into the mix."

Co-author Satyawan Nagane used an organic molecule called Ethylenediaminetetraacetic acid (EDTA) as an additive in the perovskite precursor solution, which acts as a templating agent, guiding the perovskite into the desired phase as it forms. The EDTA binds to the FAPbI3 surface to give a structure-directing effect, but does not incorporate into the FAPbI3 structure itself.

"With this method, we can achieve that desired band gap because we're not adding anything extra into the material, it's just a template to guide the formation of a film with the distorted structure -- and the resulting film is extremely stable," said Nagane.

"In this way, you can create this slightly distorted structure in just the pristine FAPbI3 compound, without modifying the other electronic properties of what is essentially a near-perfect compound for perovskite photovoltaics," said co-author Dominik Kubicki from the Cavendish Laboratory, who is now based at the University of Warwick.

The researchers hope this fundamental study will help improve perovskite stability and performance. Their own future work will involve integrating this approach into prototype devices to explore how this technique may help them achieve the perfect perovskite photovoltaic cells.

"These findings change our optimisation strategy and manufacturing guidelines for these materials," said senior author Dr Sam Stranks from Cambridge's Department of Chemical Engineering & Biotechnology. "Even small pockets that aren't slightly distorted will lead to performance losses, and so manufacturing lines will need to have very precise control of how and where the different components and 'distorting' additives are deposited. This will ensure the small distortion is uniform everywhere -- with no exceptions."

Read more at Science Daily

A safer, greener way to make solar cells: Toxic solvent replaced

Scientists at SPECIFIC Innovation and Knowledge Centre, Swansea University, have found a way to replace the toxic, unsustainable solvents currently needed to make the next generation of solar technology.

Printed carbon perovskite solar cells have been described as a likely front runner to the market because they are extremely efficient at converting light to electricity, cheap and easy to make.

A major barrier to the large-scale manufacture and commercialisation of these cells is the solvents used to control crystallisation of the perovskite during fabrication: this is because they are made from unsustainable materials and are banned in many countries due to their toxicity and psychoactive effects.

SPECIFIC's researchers have discovered that a non-toxic biodegradable solvent called γ-Valerolactone (GVL) could replace these solvents without impacting cell performance.

GVL's list of advantages could improve the commercial viability of carbon perovskite solar devices:
 

• It is made from sustainable feedstocks
• There are no legal issues in its use around the world
• It is suitable for use in large-scale manufacturing processes
• It is non-toxic and biodegradable

Carys Worsley, who led the research as part of her doctorate, said:

"To be truly environmentally sustainable, the way that solar cells are made must be as green as the energy they produce. As the next generation of solar technologies approaches commercial viability, research to reduce the environmental impact of large-scale production will become increasingly important."

Professor Trystan Watson, research group leader, added:

"Many problems need to be resolved before these technologies become a commercial reality. This solvent problem was a major barrier, not only restricting large-scale manufacture but holding back research in countries where the solvents are banned.

We hope our discovery will enable countries that have previously been unable to participate in this research to become part of the community and accelerate the development of cleaner, greener energy."

Read more at Science Daily

Shining a light on the true value of solar power

 Beyond the environmental benefits and lower electric bills, it turns out installing solar panels on your house actually benefits your whole community. Value estimations for grid-tied photovoltaic systems prove solar panels are beneficial for utility companies and consumers alike.

For years some utility companies have worried that solar panels drive up electric costs for people without panels. Joshua Pearce, Richard Witte Endowed Professor of Materials Science and Engineering and professor of electrical and computer engineering at Michigan Technological University, has shown the opposite is true -- grid-tied solar photovoltaic (PV) owners are actually subsidizing their non-PV neighbors.

Most PV systems are grid-tied and convert sunlight directly into electricity that is either used on-site or fed back into the grid. At night or on cloudy days, PV-owning customers use grid-sourced electricity so no batteries are needed.

"Anyone who puts up solar is being a great citizen for their neighbors and for their local utility," Pearce said, noting that when someone puts up grid-tied solar panels, they are essentially investing in the grid itself. "Customers with solar distributed generation are making it so utility companies don't have to make as many infrastructure investments, while at the same time solar shaves down peak demands when electricity is the most expensive."

Pearce and Koami Soulemane Hayibo, graduate student in the Michigan Tech Open Sustainability Technology (MOST) Lab, found that grid-tied PV-owning utility customers are undercompensated in most of the U.S., as the "value of solar" eclipses both the net metering and two-tiered rates that utilities pay for solar electricity. Their results are published online now and will be printed in the March issue of Renewable and Sustainable Energy Reviews.

The value of solar is becoming the preferred method for evaluating the economics of grid-tied PV systems. Yet value of solar calculations are challenging and there is widespread disagreement in the literature on the methods and data needed. To overcome these limitations, Pearce and Hayibo's paper reviews past studies to develop a generalized model that considers realistic costs and liabilities utility companies can avoid when individual people install grid-tied solar panels. Each component of the value has a sensitivity analysis run on the core variables and these sensitivities are applied for the total value of solar.

The overall value of solar equation has numerous components:
 

• Avoided operation and maintenance costs (fixed and variable)
• Avoided fuel.
• Avoided generations capacity.
• Avoided reserve capacity (plants on standby that turn on if you have, for example, a large air conditioning load on hot day).
• Avoided transmission capacity (lines).
• Environmental and health liability costs associated with forms of electric generation that are polluting.

Pearce said one of the paper's goals was to provide the equations to determine the value of solar so individual utility companies can plug in their proprietary data to quickly make a complete valuation.

"It can be concluded that substantial future regulatory reform is needed to ensure that grid-tied solar PV owners are not unjustly subsidizing U.S. electric utilities," Pearce explains. "This study provides greater clarity to decision makers so they see solar PV is truly an economic benefit in the best interest of all utility customers."

Solar PV technology is now a profitable method to decarbonize the grid, but if catastrophic climate change is to be avoided, emissions from transportation and heating must also decarbonize, Pearce argues.

One approach to renewable heating is leveraging improvements in PV with heat pumps (HPs), and it turns out investing in PV+HP tech has a better rate of return than CDs or savings accounts.

To determine the potential for PV+HP systems in Michigan's Upper Peninsula, Pearce performed numerical simulations and economic analysis using the same loads and climate, but with local electricity and natural gas rates for Sault Ste. Marie, in both Canada and U.S. North American residents can profitably install residential PV+HP systems, earning up to 1.9% return in the U.S. and 2.7% in Canada, to provide for all of their electric and heating needs.

Read more at Science Daily

Anti-solar cells: A photovoltaic cell that works at night

Solar panels against night sky background.

What if solar cells worked at night? That's no joke, according to Jeremy Munday, professor in the Department of Electrical and Computer Engineering at UC Davis. In fact, a specially designed photovoltaic cell could generate up to 50 watts of power per square meter under ideal conditions at night, about a quarter of what a conventional solar panel can generate in daytime, according to a concept paper by Munday and graduate student Tristan Deppe. The article was published in, and featured on the cover of, the January 2020 issue of ACS Photonics.

Munday, who recently joined UC Davis from the University of Maryland, is developing prototypes of these nighttime solar cells that can generate small amounts of power. The researchers hope to improve the power output and efficiency of the devices.

Munday said that the process is similar to the way a normal solar cell works, but in reverse. An object that is hot compared to its surroundings will radiate heat as infrared light. A conventional solar cell is cool compared to the sun, so it absorbs light.

Space is really, really cold, so if you have a warm object and point it at the sky, it will radiate heat toward it. People have been using this phenomenon for nighttime cooling for hundreds of years. In the last five years, Munday said, there has been a lot of interest in devices that can do this during the daytime (by filtering out sunlight or pointing away from the sun).

Generating power by radiating heat

There's another kind of device called a thermoradiative cell that generates power by radiating heat to its surroundings. Researchers have explored using them to capture waste heat from engines.

"We were thinking, what if we took one of these devices and put it in a warm area and pointed it at the sky," Munday said.

This thermoradiative cell pointed at the night sky would emit infrared light because it is warmer than outer space.

"A regular solar cell generates power by absorbing sunlight, which causes a voltage to appear across the device and for current to flow. In these new devices, light is instead emitted and the current and voltage go in the opposite direction, but you still generate power," Munday said. "You have to use different materials, but the physics is the same."

Read more at Science Daily

Even short-lived solar panels can be economically viable

A new study shows that, contrary to widespread belief within the solar power industry, new kinds of solar cells and panels don't necessarily have to last for 25 to 30 years in order to be economically viable in today's market.

Rather, solar panels with initial lifetimes of as little as 10 years can sometimes make economic sense, even for grid-scale installations -- thus potentially opening the door to promising new solar photovoltaic technologies that have been considered insufficiently durable for widespread use.

The new findings are described in a paper in the journal Joule, by Joel Jean, a former MIT postdoc and CEO of startup company Swift Solar; Vladimir Bulović, professor of electrical engineering and computer science and director of MIT.nano; and Michael Woodhouse of the National Renewable Energy Laboratory (NREL) in Colorado.

"When you talk to people in the solar field, they say any new solar panel has to last 25 years," Jean says. "If someone comes up with a new technology with a 10-year lifetime, no one is going to look at it. That's considered common knowledge in the field, and it's kind of crippling."

Jean adds that "that's a huge barrier, because you can't prove a 25-year lifetime in a year or two, or even 10." That presumption, he says, has left many promising new technologies stuck on the sidelines, as conventional crystalline silicon technologies overwhelmingly dominate the commercial solar marketplace. But, the researchers found, that does not need to be the case.

"We have to remember that ultimately what people care about is not the cost of the panel; it's the levelized cost of electricity," he says. In other words, it's the actual cost per kilowatt-hour delivered over the system's useful lifetime, including the cost of the panels, inverters, racking, wiring, land, installation labor, permitting, grid interconnection, and other system components, along with ongoing maintenance costs.

Part of the reason that the economics of the solar industry look different today than in the past is that the cost of the panels (also known as modules) has plummeted so far that now, the "balance of system" costs -- that is, everything except the panels themselves -- exceeds that of the panels. That means that, as long as newer solar panels are electrically and physically compatible with the racking and electrical systems, it can make economic sense to replace the panels with newer, better ones as they become available, while reusing the rest of the system.

"Most of the technology is in the panel, but most of the cost is in the system," Jean says. "Instead of having a system where you install it and then replace everything after 30 years, what if you replace the panels earlier and leave everything else the same? One of the reasons that might work economically is if you're replacing them with more efficient panels," which is likely to be the case as a wide variety of more efficient and lower-cost technologies are being explored around the world.

He says that what the team found in their analysis is that "with some caveats about financing, you can, in theory, get to a competitive cost, because your new panels are getting better, with a lifetime as short as 15 or even 10 years."

Although the costs of solar cells have come down year by year, Bulović says, "the expectation that one had to demonstrate a 25-year lifetime for any new solar panel technology has stayed as a tautology. In this study we show that as the solar panels get less expensive and more efficient, the cost balance significantly changes."

He says that one aim of the new paper is to alert the researchers that their new solar inventions can be cost-effective even if relatively short lived, and hence may be adopted and deployed more rapidly than expected. At the same time, he says, investors should know that they stand to make bigger profits by opting for efficient solar technologies that may not have been proven to last as long, knowing that periodically the panels can be replaced by newer, more efficient ones.

"Historical trends show that solar panel technology keeps getting more efficient year after year, and these improvements are bound to continue for years to come," says Bulović. Perovskite-based solar cells, for example, when first developed less than a decade ago, had efficiencies of only a few percent. But recently their record performance exceeded 25 percent efficiency, compared to 27 percent for the record silicon cell and about 20 percent for today's standard silicon modules, according to Bulović. Importantly, in novel device designs, a perovskite solar cell can be stacked on top of another perovskite, silicon, or thin-film cell, to raise the maximum achievable efficiency limit to over 40 percent, which is well above the 30 percent fundamental limit of today's silicon solar technologies. But perovskites have issues with longevity of operation and have not yet been shown to be able to come close to meeting the 25-year standard.

Bulović hopes the study will "shift the paradigm of what has been accepted as a global truth." Up to now, he says, "many promising technologies never even got a start, because the bar is set too high" on the need for durability.

For their analysis, the team looked at three different kinds of solar installations: a typical 6-kilowatt residential system, a 200-kilowatt commercial system, and a large 100-megawatt utility-scale system with solar tracking. They used NREL benchmark parameters for U.S. solar systems and a variety of assumptions about future progress in solar technology development, financing, and the disposal of the initial panels after replacement, including recycling of the used modules. The models were validated using four independent tools for calculating the levelized cost of electricity (LCOE), a standard metric for comparing the economic viability of different sources of electricity.

In all three installation types, they found, depending on the particulars of local conditions, replacement with new modules after 10 to 15 years could in many cases provide economic advantages while maintaining the many environmental and emissions-reduction benefits of solar power. The basic requirement for cost-competitiveness is that any new solar technology that is to be installed in the U.S should start with a module efficiency of at least 20 percent, a cost of no more than 30 cents per watt, and a lifetime of at least 10 years, with the potential to improve on all three.

Jean points out that the solar technologies that are considered standard today, mostly silicon-based but also thin-film variants such as cadmium telluride, "were not very stable in the early years. The reason they last 25 to 30 years today is that they have been developed for many decades." The new analysis may now open the door for some of the promising newer technologies to be deployed at sufficient scale to build up similar levels of experience and improvement over time and to make an impact on climate change earlier than they could without module replacement, he says.

Read more at Science Daily

Breakthrough material could lead to cheaper, more widespread solar panels and electronics

Imagine printing electronic devices using a simple inkjet printer -- or even painting a solar panel onto the wall of a building.

Such technology would slash the cost of manufacturing electronic devices and enable new ways to integrate them into our everyday lives. Over the last two decades, a type of material called organic semiconductors, made out of molecules or polymers, has been developed for such purposes. But some properties of these materials pose a major hurdle that limits their widespread use.

"In these materials, an electron is usually bound to its counterpart, a missing electron known as 'hole,' and can't move freely," said Wai-Lun Chan, associate professor of physics & astronomy at the University of Kansas. "So-called 'free electrons,' which wander freely in the material and conduct electricity, are rare and can't be generated readily by light absorption. This impedes the use of these organic materials in applications like solar panels because panels built with these materials often have poor performance."

Because of this problem, Chan said "freeing the electrons" has been a focus in developing organic semiconductors for solar cells, light sensors and many other optoelectronic applications.

Now, two physics research groups at KU, led by Chan and Hui Zhao, professor of physics & astronomy, have effectively generated free electrons from organic semiconductors when combined with a single atomic layer of molybdenum disulfide (MoS2), a recently discovered two-dimensional (2D) semiconductor.

The introduced 2D layer allows the electrons to escape from "holes" and move freely. The findings have just been published in the Journal of American Chemical Society, a leading journal in chemistry and interfacing areas of science.

Over the last few years, many researchers have been investigating how free charges can be generated effectively from hybrid organic-2D interfaces.

"One of the prevailing assumptions is free electrons can be generated from the interface as long as electrons can be transferred from one material to another in a relatively short period of time -- less than one-trillionth of a second," Chan said. "However, my graduate students Tika Kafle and Bhupal Kattel and I have found the presence of the ultrafast electron transfer in itself is not sufficient to guarantee the generation of free electrons from the light absorption. That's because the 'holes' can prevent the electrons from moving away from the interface. Whether the electron can be free from this binding force depends on the local energy landscape near the interface."

Chan said the energy landscape of the electrons could be seen as a topographic map of a mountain.

"A hiker chooses his path based on the height contour map," he said. "Similarly, the motion of the electron at the interface between the two materials is controlled by the electron energy landscape near the interface."

Chan and Zhao's findings will help develop general principles of how to design the "landscape" to free the electrons in such hybrid materials.

The discovery was made by combining two highly complementary experimental tools based on ultrafast lasers, time-resolved photoemission spectroscopy in Chan's lab and transient optical absorption in Zhao's lab. Both experimental setups are located in the basement of the Integrated Science Building.

In the time-resolved photoemission spectroscopy experiment, Kafle used an ultrashort laser pulse that only exists for 10-quadrillionths (10-14) of a second to trigger the motion of electrons. The advantage of using such a short pulse is the researcher knows precisely the starting time of the electron's journey. Kafle then used another ultrashort laser pulse to hit the sample again at an accurately controlled time relative to the first pulse. This second pulse is energetic enough to kick out these electrons from the sample. By measuring the energy of these electrons (now in a vacuum) and using the principle of energy conservation, the researchers were able to figure out the energy of electrons before they were kicked out and thus reveal the journey of these electrons since they were hit by the first pulse. This technique resolved the energy of the excited electrons as it moves across the interface after the light absorption. Because only electrons near the front surface of the sample can be released by the second pulse, the position of the electron relative to the interface is also revealed with atomic precision.

In the transient optical absorption measurements, Peng Yao (a visiting student) and KU graduate Peymon Zereshki, both supervised by Zhao, also used a two-pulse technique, with the first pulse initiating the electron motion in the same way. However, in their measurements, the second pulse does the trick of monitoring electrons by detecting the fraction of the second pulse that is reflected from the sample, instead of kicking out the electrons.

Read more at Science Daily

Chemists manipulate the quantum states of gold nanoclusters

Carnegie Mellon chemists created a 30-atom gold nanocluster with a hcp structure, which has a quantum lifetime of one nanosecond and a 38-atom gold nanocluster with a bcc structure, which has a quantum lifetime of 4.7 microseconds.

Researchers from Carnegie Mellon University's Department of Chemistry have found a way to control the lifetime of the quantum states of gold nanoclusters by three orders of magnitude, which could lead to improvements in solar cell and photocatalysis technologies. Their study is published in the April 18 issue of Science.

Excited quantum states occur when light is absorbed by a particle and the energy from that light is temporarily stored within the particle, making its energy higher than its ground state. The energy decays quickly and can be lost as heat in the span of a nanosecond, or one billionth of a second. Extending this quantum state could provide researchers with more time and opportunity to harness the stored energy.

Carnegie Mellon Chemistry Professor Rongchao Jin is known for developing precisely sized gold nanoparticles. In this extension of his work, post-doctoral researcher Meng Zhou and Ph.D. student Tatsuya Higaki, who are co-first authors of the paper, studied atomically precise gold nanoclusters containing between 30 and 38 atoms. They altered the structures of clusters by rearranging the atoms into exotic configurations and protecting them with a capping ligand.

The researchers measured the lifetimes of the nanoclusters' quantum states by using femtosecond and nanosecond time-resolved spectroscopy to take snapshots of the nanoclusters from the time when they absorbed energy from light, in this case a femtosecond laser pulse, until they released the energy. Collaborators at University of California, Riverside confirmed the results using density function theory calculations to analyze the molecular orbitals of the nanoclusters.

They found that a 30-atom gold nanocluster, with a hexagonal close-packed (hcp) structure, had a quantum lifetime of one nanosecond. But a 38-atom gold nanocluster with a body-centered cubic (bcc) structure had a much longer lifetime of 4.7 microseconds. Extending the lifetime by three magnitudes gives researchers ample time to extract the absorbed light energy from the nanoclusters -- a finding that has significant implications.

"The strategy of manipulating the excited-state lifetime from very short to very long is exciting. The exceptionally long quantum lifetime of 4.7 microseconds is comparable to that of bulk silicon, which is used for commercial solar cells," said Jin. "It should give us enough time to efficiently extract the energy into external circuits as an electronic current without losing too much energy to heat."

The tailored quantum lifetime can also be used to increase the efficiency of visible light-based photocatalysis used to convert solar energy storage into chemicals, such as converting methanol and ethanol from carbon dioxide.

Read more at Science Daily

Brilliant iron molecule could provide cheaper solar energy

The new molecule.

For the first time, researchers have succeeded in creating an iron molecule that can function both as a photocatalyst to produce fuel and in solar cells to produce electricity. The results indicate that the iron molecule could replace the more expensive and rarer metals used today.

Some photocatalysts and solar cells are based on a technology that involves molecules containing metals, known as metal complexes. The task of the metal complexes in this context is to absorb solar rays and utilise their energy. The metals in these molecules pose a major problem, however, as they are rare and expensive metals, such as the noble metals ruthenium, osmium and iridium.

"Our results now show that by using advanced molecule design, it is possible to replace the rare metals with iron, which is common in the Earth's crust and therefore cheap," says Chemistry Professor Kenneth Wärnmark of Lund University in Sweden.

Together with colleagues, Kenneth Wärnmark has for a long time worked to find alternatives to the expensive metals. The researchers focused on iron which, with its six per cent prevalence in the Earth's crust, is significantly easier to source. The researchers have produced their own iron-based molecules whose potential for use in solar energy applications has been proven in previous studies.

In this new study, the researchers have moved one step further and developed a new iron-based molecule with the ability to capture and utilise the energy of solar light for a sufficiently long time for it to react with another molecule. The new iron molecule also has the ability to glow long enough to enable researchers to see iron-based light with the naked eye at room temperature for the first time.

"The good result depends on the fact that we have optimised the molecular structure around the iron atom," explains colleague Petter Persson of Lund University.

The study is now published in the journal Science. According to the researchers, the iron molecule in question could be used in new types of photocatalysts for the production of solar fuel, either as hydrogen through water splitting or as methanol from carbon dioxide. Furthermore, the new findings open up other potential areas of application for iron molecules, e.g. as materials in light diodes (LEDs).

What surprised the Lund researchers is that they arrived at good results so quickly. In just over five years, they succeeded in making iron interesting for photochemical applications, with properties largely as good as those of the best noble metals.

"We believed it would take at least ten years," says Kenneth Wärnmark.

Read more at Science Daily

Solar panels for yeast cell biofactories

The researcher's model of a yeast cell (magenta) with semiconductor nanoparticles (purple) attached to its surface (left) corresponds with their SEM analysis of the completed biohybrid system (right). The semiconductors capture electrons from light and hand them over to the cell where they drive the shikimic acid metabolic pathway.

Genetically engineered microbes such as bacteria and yeasts have long been used as living factories to produce drugs and fine chemicals. More recently, researchers have started to combine bacteria with semiconductor technology that, similar to solar panels on the roof of a house, harvests energy from light and, when coupled to the microbes' surface, can boost their biosynthetic potential.

The first "biological-inorganic hybrid systems" (biohybrids) mostly focused on the fixation of atmospheric carbon dioxide and the production of alternative energies, and although promising, they also revealed key challenges. For example, semiconductors, which are made from toxic metals, thus far are assembled directly on bacterial cells and often harm them in the process. In addition, the initial focus on carbon-fixing microbes has limited the range of products to relatively simple molecules; if biohybrids could be created based on microorganisms equipped with more complex metabolisms, it would open new paths for the production of a much larger range of chemicals useful for many applications.

Now, in a study in Science, a multidisciplinary team led by Core Faculty member Neel Joshi and Postdoctoral Fellows Junling Guo and Miguel Suástegui at Harvard's Wyss Institute for Biologically Inspired Engineering and John A. Paulson School of Engineering and Applied Sciences (SEAS) presents a highly adaptable solution to these challenges.

"While our strategy conceptually builds on earlier bacterial biohybrid systems that were engineered by our collaborator Daniel Nocera and others, we expanded the concept to yeast -- an organism that is already an industrial workhorse and is genetically easy to manipulate -- with a modular semiconductor component that provides biochemical energy to yeast's metabolic machinery without being toxic," said Joshi, Ph.D., who is a Core Faculty member at the Wyss Institute and Associate Professor at SEAS. Co-author Nocera is the Patterson Rockwood Professor of Energy at Harvard University. As a result of the combined manipulations, yeasts' ability to produce shikimic acid, an important precursor of the anti-viral drug Tamiflu, several other medicines, nutraceuticals, and fine chemicals, was significantly enhanced.

The baker's yeast Saccharomyces cerevisiae naturally produces shikimic acid to generate some of its building blocks for the synthesis of proteins and other biomolecules. However, by genetically modifying the yeast's central metabolism, the researchers enabled the cells to funnel more of the carbon atoms that their main nutrient source, the sugar glucose, contains into the pathway that produces shikimic acid and prevent the loss of carbon to alternative pathways by disrupting one of them.

"In principle, the increased 'carbon flux' towards shikimic acid should lead to higher product levels, but in normal yeast cells, the alternative pathway that we disrupted to increase yields, importantly, also provides the energy needed to fuel the final step of shikimic acid production," said co-first author Miguel Suástegui, Ph.D., a chemical engineer and former Postdoctoral Fellow in Joshi's team and now Scientist at Joyn Bio LLC. To boost the more carbon-effective but energy-depleted engineered shikimic acid pathway, "we hypothesized that we could generate the relevant energy-carrying molecule NADPH instead in a biohybrid approach with light-harvesting semiconductors."

Toward this goal, Suástegui collaborated with Junling Guo, Ph.D., the study's other co-corresponding and co-first author and presently a Postdoctoral Fellow with experience in chemistry and materials science in Joshi's lab. They designed a strategy that uses indium phosphide as a semiconductor material. "To make the semiconductor component truly modular and non-toxic, we coated indium phosphide nanoparticles with a natural polyphenol-based "glue," which allowed us to attach them to the surface of yeast cells while at the same time insulating the cells from the metal's toxicity," said Guo.

When tethered to the cell surface and illuminated, the semiconductor nanoparticles harvest electrons (energy) from light and hand them over to the yeast cells, which shuttle them across their cell walls into their cytoplasm. There the electrons elevate the levels of NADPH molecules, which now can fuel shikimic acid biosynthesis. "The yeast biohybrid cells, when kept in the dark, mostly produced simpler organic molecules such as glycerol and ethanol; but when exposed to light, they readily switched into shikimic acid production mode with an 11-fold increase in product levels, showing us that the energy transfer from light into the cell works very efficiently," said Joshi.

"This scalable approach creates an entirely new design space for future biohybrid technologies. In future efforts, the nature of semiconductors and the type of genetically engineered yeast cells can be varied in a plug-and-play fashion to expand the type of manufacturing processes and range of bioproducts," said Guo.

Read more at Science Daily

Bacteria-powered solar cell converts light to energy, even under overcast skies

Using bacteria that convert light to energy could be a step toward wider adoption of solar power in places where overcast skies are common.

University of British Columbia researchers have found a cheap, sustainable way to build a solar cell using bacteria that convert light to energy.

Their cell generated a current stronger than any previously recorded from such a device, and worked as efficiently in dim light as in bright light.

This innovation could be a step toward wider adoption of solar power in places like British Columbia and parts of northern Europe where overcast skies are common. With further development, these solar cells -- called "biogenic" because they are made of living organisms -- could become as efficient as the synthetic cells used in conventional solar panels.

"Our solution to a uniquely B.C. problem is a significant step toward making solar energy more economical," said Vikramaditya Yadav, a professor in UBC's department of chemical and biological engineering who led the project.

Solar cells are the building blocks of solar panels. They do the work of converting light into electrical current. Previous efforts to build biogenic solar cells have focused on extracting the natural dye that bacteria use for photosynthesis. It's a costly and complex process that involves toxic solvents and can cause the dye to degrade.

The UBC researchers' solution was to leave the dye in the bacteria. They genetically engineered E. coli to produce large amounts of lycopene -- a dye that gives tomatoes their red-orange colour and is particularly effective at harvesting light for conversion to energy. The researchers coated the bacteria with a mineral that could act as a semiconductor, and applied the mixture to a glass surface.

With the coated glass acting as an anode at one end of their cell, they generated a current density of 0.686 milliamps per square centimetre -- an improvement on the 0.362 achieved by others in the field.

"We recorded the highest current density for a biogenic solar cell," said Yadav. "These hybrid materials that we are developing can be manufactured economically and sustainably, and, with sufficient optimization, could perform at comparable efficiencies as conventional solar cells."

The cost savings are difficult to estimate, but Yadav believes the process reduces the cost of dye production to about one-tenth of what it would be otherwise. The holy grail, Yadav said, would be finding a process that doesn't kill the bacteria, so they can produce dye indefinitely.

Read more at Science Daily

A Black Butterfly’s Wings Point the Way Toward Better Solar Cells

Black butterfly

A microscopic pattern on the wings of a butterfly has shown scientists how to capture more of the sun’s energy in solar cells.

The scales of the black-colored common rose butterfly are topped with an irregular lattice of chitin and melanin. Those structures drew the attention of Radwan Siddique, an engineer trying to develop a technique for building 3D nanostructures as part of his doctoral work at Germany’s Karlsruhe Institute of Technology.

Siddique told Seeker he came across a description of the butterfly’s wings in the course of his research. The lattice helps the cold-blooded insect regulate its body temperature, keeping it warm enough to fly in cool weather, he said.

“I was so intrigued that I literally went to a lot of butterfly nurseries and gathered several butterflies,” said Siddique, now a post-doctoral researcher at Caltech. “The black butterfly was one of them. I was putting them under SEM [an electron microscope] and looking at the structures.” It openings are less than a millionth of a meter wide, but they scatter light and help the butterfly absorb more of the sun’s heat.

“They use those nanostructures to improve absorption,” he said. “So I asked, ‘Can we use the same nanostructres in this type of solar cell, which is not highly used because the absorption isn’t that good?’”

Scientists from KIT and Caltech utilize the disordered nanoholes of the black butterfly to improve solar cell performance.

By mimicking the butterfly’s structure in a sheet of hydrogenated amorphous silicon, he and his colleagues at Karlsruhe were able to capture more low-frequency light — at wavelengths near the infrared end of the spectrum — that wouldn’t have been converted to energy otherwise. A layer of polymer pockmarked with circular indentations of various sizes, transferred to a silicon base, was able to pick up about double the amount of energy that a smooth surface produced and convert it to electricity. Angling those indentations might improve those efficiencies even more, he said.

The findings were published Oct. 18 in the research journal Science Advances. They’re part of a growing body of research aimed at improving the efficiency and reducing the size of solar cells.

Scanning electron microscope image of bio-inspired nanoholes

The ability to produce solar power with a thin film, as opposed to the larger, more typical crystal-based cells, holds the promise of making them more useful. They could be used to power personal electronics or for larger-scale applications, such as being incorporated into windows or other building materials.

And Siddique and his colleagues aren’t the first to find inspiration in the natural world: Earlier this year, researchers in Australia etched a fractal pattern inspired by the leaves of a fern onto sheets of graphene to increase the surface area available for storing and conducting energy.

Read more at Seeker

Scientists design solar cell that captures nearly all energy of solar spectrum

A George Washington University researcher helped design and construct a prototype for a new solar cell that integrates multiple cells stacked into a single device capable of capturing nearly all of the energy in the solar spectrum.

The new design, which converts direct sunlight to electricity with 44.5 percent efficiency, has the potential to become the most efficient solar cell in the world.

The approach is different from the solar panels commonly seen on rooftops or in fields. The new device uses concentrator photovoltaic (CPV) panels that use lenses to concentrate sunlight onto tiny, micro-scale solar cells. Because of their small size -- less than one millimeter square -- solar cells that utilize more sophisticated materials can be developed cost effectively.

The study, "GaSb-based Solar Cells for Full Solar Spectrum Energy Harvesting," was published in the journal Advanced Energy Materials.

The stacked cell acts almost like a sieve for sunlight, with the specialized materials in each layer absorbing the energy of a specific set of wavelengths, said Matthew Lumb, lead author of the study and a research scientist at the School of Engineering and Applied Science. By the time the light is funneled through the stack, just under half of the available energy has been converted into electricity. By comparison, the most common solar cell today converts only a quarter of the available energy into electricity.

"Around 99 percent of the power contained in direct sunlight reaching the surface of Earth falls between wavelengths of 250 nanometers and 2,500 nanometers, but conventional materials for high-efficiency multi-junction solar cells cannot capture this entire spectral range," Dr. Lumb said. "Our new device is able to unlock the energy stored in the long-wavelength photons, which are lost in conventional solar cells, and therefore provides a pathway to realizing the ultimate multi-junction solar cell."

Scientists have worked to develop more efficient solar cells for years, however this approach has two novel aspects. It uses a family of materials based on gallium antimonide (GaSb) substrates, which are usually found in applications for infrared lasers and photodetectors. These GaSb-based solar cells are assembled into a stacked structure along with high efficiency solar cells grown on conventional substrates that capture shorter wavelength solar photons. In addition, the stacking procedure uses a technique known as transfer-printing, which enables three dimensional assembly of these tiny devices with a high degree of precision.

This particular solar cell is very expensive, but researchers believe it was important to show the upper limit of what is possible in terms of efficiency. Despite the current costs of the materials involved, the technique used to create the cells shows promise, researchers say. Eventually a similar product enabled by cost reductions from very high solar concentration levels and technology to recycle the expensive growth substrates could be brought to market.

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