A University of Houston professor is reporting on a new type of solar energy harvesting system called thermophotovoltaics (STPV) that breaks the efficiency record of all existing technologies. And no less important, it clears the way to use solar power 24/7.

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Rice University engineers say they’ve solved a long-standing conundrum in making stable, efficient solar panels out of halide perovskites. It took finding the right solvent design to apply a 2D top layer of desired composition and thickness without destroying the 3D bottom one (or vice versa). Such a cell would turn more sunlight into electricity than either layer on its own, with better stability. Chemical and biomolecular engineer Aditya Mohite and his lab at Rice’s George R. Brown School of Engineering reported in Science their success at building thin 3D/2D solar cells that deliver a power conversion efficiency of 24.5%. That’s as efficient as most commercially available solar cells, Mohite said.

A discovery by Rice University engineers brings efficient, stable bilayer perovskite solar cells closer to commercialization. The cells are about a micron thick, with 2D and 3D layers

“This is really good for flexible, bifacial cells where light comes in from both sides and also for back-contacted cells,” the scientist said. “The 2D perovskites absorb blue and visible photons, and the 3D side absorbs near-infrared.”

Perovskites are crystals with cubelike lattices known to be efficient light harvesters, but the materials tend to be stressed by light, humidity and heat. Mohite and many others have worked for years to make perovskite solar cells practical. The new advance, he said, largely removes the last major roadblock to commercial production.

Source: https://news.rice.edu/

A race is on in solar engineering to create almost impossibly-thin, flexible solar panels. Engineers imagine them used in mobile applications, from self-powered wearable devices and sensors to lightweight aircraft and electric vehicles. Against that backdrop, researchers at Stanford University have achieved record efficiencies in a promising group of photovoltaic materials. Chief among the benefits of these transition metal dichalcogenides – or TMDs – is that they absorb ultrahigh levels of the sunlight that strikes their surface compared to other solar materials.

Transition metal dichalcogenide solar cells on a flexible polyimide substrate

“Imagine an autonomous drone that powers itself with a solar array atop its wing that is 15 times thinner than a piece of paper,” said Koosha Nassiri Nazif, a doctoral scholar in electrical engineering at Stanford and co-lead author of a study published in the Dec. 9 edition of Nature Communications. “That is the promise of TMDs.”

The search for new materials is necessary because the reigning king of solar materials, silicon, is much too heavy, bulky and rigid for applications where flexibility, lightweight and high power are preeminent, such as wearable devices and sensors or aerospace and electric vehicles.

“Silicon makes up 95 percent of the solar market today, but it’s far from perfect. We need new materials that are light, bendable and, frankly, more eco-friendly,” said Krishna Saraswat, a professor of electrical engineering and senior author of the paper. While TMDs hold great promise, research experiments to date have struggled to turn more than 2 percent of the sunlight they absorb into electricity. For silicon solar panels, that number is closing in on 30 percent. To be used widely, TMDs will have to close that gap.

The new Stanford prototype achieves 5.1 percent power conversion efficiency, but the authors project they could practically reach 27 percent efficiency upon optical and electrical optimizations. That figure would be on par with the best solar panels on the market today, silicon included.

Moreover, the prototype realized a 100-times greater power-to-weight ratio of any TMDs yet developed. That ratio is important for mobile applications, like drones, electric vehicles and the ability to charge expeditionary equipment on the move. When looking at the specific power – a measure of electrical power output per unit weight of the solar cell – the prototype produced 4.4 watts per gram, a figure competitive with other current-day thin-film solar cells, including other experimental prototypes. “We think we can increase this crucial ratio another ten times through optimization,” Saraswat said, adding that they estimate the practical limit of their TMD cells to be a remarkable 46 watts per gram.”

Source: https://news.stanford.edu/

Solar cells are excellent renewable energy tools that use sunlight to drive an electrical current for power. They’ve been used to power homes since the 1980s, and their performance and production cost have improved dramatically since then. The most common solar cells, based on silicon, work well for a long time. They retain more than 80% of their functionality even after 25 years. However, the efficiency—i.e., how much of the incoming sunlight is converted to electrical power—of commercial-scale silicon solar cells is currently only around 20%.

Maximizing solar cells‘ energy conversion efficiency will improve their competitiveness compared to fossil fuels and help optimize them as a sustainable energy source. Researchers have intensively focused on an alternative to silicon: perovskite materials to enhance solar cells’ efficiency. Designs based on such materials must meet certain requirements, such as ease of fabrication on a large scale, and minimize reflected—i.e., wasted—light.

In a recent study published in Nano-Micro Letters, researchers from Kanazawa University applied a thin metal oxide film—reproducible, uniform, and compact—onto a perovskite solar cell. The researchers used a combination of lab work and computational studies to evaluate their solar cell design performance fairly.

(a) Schematic diagram of the perovskite/perovskite tandem solar cell, and (b)  current–voltage characteristic curves of the best-investigated perovskite/perovskite tandem solar cell. Inset shows quantum efficiency for top perovskite and bottom perovskite.

“We used spray pyrolysis to deposit a front contact layer of titanium dioxide onto a perovskite solar cell,” explains Md. Shahiduzzaman, lead and corresponding author. “This deposition technique is common in the industry for large-scale applications.”

Upon finding an optimum thickness for the front contact layer, the researchers measured an energy conversion efficiency of 16.6%, assuming typical sunlight conditions. As mentioned, this isn’t quite as good as commercial silicon-based solar cells. Nevertheless, electromagnetic simulations were a powerful tool for predicting the possible energy conversion efficiency limit by optimizing specific parameters.

“Computational simulations suggest that the energy conversion efficiency of perovskite/perovskite tandem solar cells could go beyond 30% by a multi-layer front contact,” says Md. Shahiduzzaman, lead and corresponding author. “This is close to the theoretical efficiency limit of silicon-based solar cells.”

Source: https://www.kanazawa-u.ac.jp/

A team of scientists is calling for greater research into how sunlight inactivates SARS-CoV-2 after realizing there’s a glaring discrepancy between the most recent theory and experimental results. UC Santa Barbara mechanical engineer Paolo Luzzatto-Fegiz and colleagues noticed the virus was inactivated as much as eight times faster in experiments than the most recent theoretical model predicted.

“The theory assumes that inactivation works by having UVB hit the RNA of the virus, damaging it,” explained Luzzatto-Fegiz.

But the discrepancy suggests there’s something more going on than that, and figuring out what this is may be helpful for managing the virus.

UV light, or the ultraviolet part of the spectrum, is easily absorbed by certain nucleic acid bases in DNA and RNA, which can cause them to bond in ways that are hard to fix.

But not all UV light is the same. Longer UV waves, called UVA, don’t have quite enough energy to cause problems. It’s the mid-range UVB waves in sunlight that are primarily responsible for killing microbes and putting our own cells at risk of Sun damage.

Short-wave UVC radiation has been shown to be effective against viruses such as SARS-CoV-2, even while it’s still safely enveloped in human fluids.

But this type of UV doesn’t usually come into contact with Earth’s surface, thanks to the ozone layer.

“UVC is great for hospitals,” said co-author and Oregon State University toxicologist Julie McMurry. “But in other environments – for instance, kitchens or subways – UVC would interact with the particulates to produce harmful ozone.”

In July 2020, an experimental study tested the effects of UV light on SARS-CoV-2 in simulated saliva. They recorded the virus was inactivated when exposed to simulated sunlight for between 10-20 minutes.

“Natural sunlight may be effective as a disinfectant for contaminated nonporous materials,” Wood and colleagues concluded in the paper.

Luzzatto-Feigiz and team compared those results with a theory about how sunlight achieved this, which was published just a month later, and saw the math didn’t add up. his study found the SARS-CoV-2 virus was three times more sensitive to the UV in sunlight than influenza A, with 90 percent of the coronavirus‘s particles being inactivated after just half an hour of exposure to midday sunlight in summer.

By comparison, in winter light infectious particles could remain intact for days.

Source: https://www.news.ucsb.edu/
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https://www.sciencealert.com/

One prospective source of renewable energy is hydrogen gas produced from water with the aid of sunlight. Researchers at Linköping University (LiU) in Sweden have developed a material, nanoporous cubic silicon carbide, that exhibits promising properties to capture solar energy and split water for hydrogen gas production.

Cubic silicon carbide immersed in water

“New sustainable energy systems are needed to meet global energy and environmental challenges, such as increasing carbon dioxide emissions and climate change”, says Jianwu Sun, senior lecturer in the Department of Physics, Chemistry and Biology at Linköping University, who has led the new study that has been published in the journal ACS Nano.

Hydrogen has an energy density three times that of petrol. It can be used to generate electricity using a fuel cell, and hydrogen-fuelled cars are already commercially available. When hydrogen gas is used to produce energy, the only product formed is pure water. In contrast, however, carbon dioxide is created when the hydrogen is produced, since the most commonly used technology used today depends on fossil fuels for the process. Thus, 9-12 tonnes of carbon dioxide are emitted when one tonne of’ hydrogen gas is produced.

Producing hydrogen gas by splitting water molecules with the aid of solar energy is a sustainable approach that could give hydrogen gas using renewable sources without leading to carbon dioxide emissions. A major advantage of this method is the possibility to convert solar energy to fuel that can be stored. “Conventional solar cells produce energy during the daytime, and the energy must either be used immediately, or stored in, for example, batteries. Hydrogen is a promising source of energy that can be stored and transported in the same way as traditional fuels such as petrol and diesel”, says Jianwu Sun.

It is not, however, an easy task to split water using the energy in sunlight to give hydrogen gas. For this to succeed, it is necessary to find cost-efficient materials that have the right properties for the reaction in which water (H₂O) is split into hydrogen (H₂) and oxygen (O₂) through photo-electrolysis. The energy in sunlight that can be used to split water is mostly in the form of ultraviolet radiation and visible light. Therefore, a material is required that can efficiently absorb such radiation to create charges that can be separated and have enough energy to split the water molecules into hydrogen and oxygen gases. Most materials that have been investigated until now are either inefficient in the way they use the energy of visible sunlight (titanium dioxide, TiO₂, for example, absorbs only ultraviolet sunlight), or do not have the properties needed to split water to hydrogen gas (for instance, silicon, Si).

Jianwu Sun’s research group has investigated cubic silicon carbide, 3C-SiC. The scientists have produced a form of cubic silicon carbide that has many extremely small pores. The material, which they call nanoporous 3C-SiC, has promising properties that suggest it can be used to produce hydrogen gas from water using sunlight. The present study has been published in the journal ACS Nano, and in it the researchers show that this new porous material can efficiently trap and harvest ultraviolet and most of the visible sunlight. Furthermore, the porous structure promotes the separation of charges that have the required energy, while the small pores give a larger active surface area. This enhances charge transfer and increases the number of reaction sites, thus further boosting the water splitting efficiency.

“The main result we have shown is that nanoporous cubic silicon carbide has a higher charge-separation efficiency, which makes the splitting of water to hydrogen much better than when using planar silicon carbide”, says Jianwu Sun.

Source: https://liu.se/

Amid the coronavirus pandemic, people in developed countries are assured of ample supplies of clean water to wash their hands as often as needed to protect themselves from the virus. And yet, nearly a third of the world’s population is not even assured of clean water for drinking. University of Rochester researchers have now found a way to address this problem by using sunlight—a resource that everyone can access—to evaporate and purify contaminated water with greater than 100 percent efficiency.

How is this possible? In a paper in Nature Sustainability, researchers in the laboratory of Chunlei Guo, professor of optics, demonstrate how a burst of femtosecond laser pulses etch the surface of a normal sheet of aluminum into a superwicking (water-attracting), super energy–absorbing material. Using sunlight to boil has long been recognized as a way to eliminate microbial pathogens and reduce deaths from diarrheal infections. But boiling water does not eliminate heavy metals and other contaminants. Experiments by the lab show that their new method reduces the presence of all common contaminants, such as detergent, dyes, urine, heavy metals, and glycerin, to safe levels for drinking.

Solar-based water purification can greatly reduce contaminants because nearly all the impurities are left behind when the evaporating water becomes gaseous and then condenses and gets collected. The most common method of solar-based water evaporation is volume heating, in which a large volume of water is heated but only the top layer can evaporate. This is obviously inefficient, Guo says, because only a small fraction of the heating energy gets used. A more efficient approach, called interfacial heating, places floating, multilayered absorbing and wicking materials on top of the water, so that only water near the surface needs to be heated. But the available materials all have to float horizontally on top of the water and cannot face the sun directly. Furthermore, the available wicking materials become quickly clogged with contaminants left behind after evaporation, requiring frequent replacement of the materials.

The panel developed by the Guo lab avoids these inefficiencies by pulling a thin layer of water out of the reservoir and directly onto the solar absorber surface for heating and evaporation. “Moreover, because we use an open-grooved surface, it is very easy to clean by simply spraying it,” Guo says.

“The biggest advantage,” he adds, “is that the angle of the panels can be continuously adjusted to directly face the sun as it rises and then moves across the sky before setting” —maximizing energy absorption. “There was simply nothing else resembling what we can do here,” Guo says.

Source: https://www.rochester.edu/

Rice University researchers have created an efficient, low-cost device that splits water to produce hydrogen fuel. The platform developed by the Brown School of Engineering lab of Rice materials scientist Jun Lou integrates catalytic electrodes and perovskite solar cells that, when triggered by sunlight, produce electricity. The current flows to the catalysts that turn water into hydrogen and oxygen, with a sunlight-to-hydrogen efficiency as high as 6.7%. This sort of catalysis isn’t new, but the lab packaged a perovskite layer and the electrodes into a single module that, when dropped into water and placed in sunlight, produces hydrogen with no further input. The platform introduced by Lou, lead author and Rice postdoctoral fellow Jia Liang and their colleagues in the American Chemical Society journal ACS Nano is a self-sustaining producer of fuel that, they say, should be simple to produce in bulk.

A schematic and electron microscope cross-section show the structure of an integrated, solar-powered catalyst to split water into hydrogen fuel and oxygen. The module developed at Rice University can be immersed into water directly to produce fuel when exposed to sunlight

“The concept is broadly similar to an artificial leaf,” Lou said. “What we have is an integrated module that turns sunlight into electricity that drives an electrochemical reaction. It utilizes water and sunlight to get chemical fuels.”

Perovskites are crystals with cubelike lattices that are known to harvest light. The most efficient perovskite solar cells produced so far achieve an efficiency above 25%, but the materials are expensive and tend to be stressed by light, humidity and heat.  “Jia has replaced the more expensive components, like platinum, in perovskite solar cells with alternatives like carbon,” Lou commented. “That lowers the entry barrier for commercial adoption. Integrated devices like this are promising because they create a system that is sustainable. This does not require any external power to keep the module running.”

Liang said the key component may not be the perovskite but the polymer that encapsulates it, protecting the module and allowing to be immersed for long periods. “Others have developed catalytic systems that connect the solar cell outside the water to immersed electrodes with a wire,” he explained. “We simplify the system by encapsulating the perovskite layer with a Surlyn (polymer) film.”

The patterned film allows sunlight to reach the solar cell while protecting it and serves as an insulator between the cells and the electrodes, Liang said. “With a clever system design, you can potentially make a self-sustaining loop,” Lou added. “Even when there’s no sunlight, you can use stored energy in the form of chemical fuel. You can put the hydrogen and oxygen products in separate tanks and incorporate another module like a fuel cell to turn those fuels back into electricity.”

Source: https://news.rice.edu/

Harvesting sunlight, researchers of the Center for Integrated Nanostructure Physics, within the Institute for Basic Science (IBS, South Korea) published in Materials Today a new strategy to transform carbon dioxide (CO₂) into oxygen (O₂) and pure carbon monoxide (CO) without side-products in water. This artificial photosynthesis method could bring new solutions to environmental pollution and global warming.

While, in green plants, photosynthesis fixes CO₂ into sugars, the artificial photosynthesis reported in this study can convert CO₂ into oxygen and pure CO as output. The latter can then be employed for a broad range of applications in electronics, semiconductor, pharmaceutical, and chemical industries. The key is to find the right high-performance photocatalyst to help the photosynthesis take place by absorbing light, convert CO₂, and ensuring an efficient flow of electrons, which is essential for the entire system.

Titanium oxide (TiO₂) is a well-known photocatalyst. It has already attracted significant attention in the fields of solar energy conversion and environmental protection due to its high reactivity, low toxicity, chemical stability, and low cost. While conventional TiO₂ can absorb only UV light, the IBS research team reported previously two different types of blue-colored TiO₂ (or “blue titania”) nanoparticles that could absorb visible light.

For the efficient artificial photosynthesis for the conversion of CO₂ into oxygen and pure CO, IBS researchers aimed to improve the performance of these nanoparticles. The resulted  hybrid nanoparticles showed about 200 times higher performance than nanoparticles made of TiO₂ alone and TiO₂/WO₃ without silver.

Source: https://www.ibs.re.kr/

Engineers from Lehigh University (Bethlehem, Pennsylvania)  are the first to utilize a single enzyme biomineralization process to create a catalyst that uses the energy of captured sunlight to split water molecules to produce hydrogen. The synthesis process is performed at room temperature and under ambient pressure, overcoming the sustainability and scalability challenges of previously reported methods.

Solar-driven water splitting is a promising route towards a renewable energy-based economy. The generated hydrogen could serve as both a transportation fuel and a critical chemical feedstock for fertilizer and chemical production. Both of these sectors currently contribute a large fraction of total greenhouse gas emissions.

One of the challenges to realizing the promise of solar-driven energy production is that, while the required water is an abundant resource, previously-explored methods utilize complex routes that require environmentally-damaging solvents and massive amounts of energy to produce at large scale. The expense and harm to the environment have made these methods unworkable as a long-term solution.

Now a team of engineers at Lehigh have harnessed a biomineralization approach to synthesizing both quantum confined nanoparticle metal sulfide particles and the supporting reduced graphene oxide material to create a photocatalyst that splits water to form hydrogen. The team reported their results in an article entitled: “Enzymatic synthesis of supported CdS quantum dot/reduced graphene oxide photocatalysts” featured on the cover of the August 7 issue of Green Chemistry, a journal of the Royal Society of Chemistry. “Our water-based process represents a scalable green route for the production of this promising photocatalyst technology,” says Professor Steven McIntosh, who is also associate director of Lehigh’s Institute for Functional Materials and Devices.

Source: https://engineering.lehigh.edu/