Tag Archives: perovskite

Stronger, longer-lasting perovskite solar panels could be on the way

New research at Soochow University, China, is looking at how and why perovskite materials degrade — with the hope of engineering solar panels with much longer lives.

Image credits Wikimedia / Ken Fields.

Perovskite panels aren’t the only type of solar panels out there, but they are very popular ones. They’re constructed around an active layer of perovskite, which forms crystal structures. Over time, stresses inside the material sandwich can create distortions in these crystals, which reduces their symmetry — essentially wearing them out. Environmental factors like sunlight or temperatures also degrade the layer.

“It is important to understand the degradation mechanisms under different conditions, including light, heat, humidity, electrochemical environment, and intrinsic stability, if you want to improve the durability of perovskite solar cells,” said co-author Zhao-Kui Wang.

“It is important to guarantee that the perovskite and the other layers have the best intrinsic stability and then to do some adjustments for further improving environmental resistance.”

The paper, together with a research update published in the journal APL Materials looked at the factors that influence the degradation of this layer, how degradation influences its performance, and examined possible approaches to making them more resilient.

The update focuses on chemical degradation, caused mainly by the transporting layers (integral parts required for the devices to work which sit in direct contact with the perovskite layer). The authors also analyzed the intrinsic stability of the perovskite layer and how factors such as moisture, oxygen, light, and heat affect it.

One of the most promising ways of reducing degradation seems to be bonding passivation — the removal of tiny gaps formed when assembling the layers together.

The team also points to hydrophobic (water-repelling) and ionic liquids as useful for this purpose under several types of environmental conditions. Ionic liquids can help maintain a stable internal temperature while the panels generate energy, and hydrophobic materials keep moisture out — which further improves the devices’ lifespan. Ionic liquids can be easily modified to possess hydrophobic properties, they add.

“The low volatility means ion liquids can be considered an environmental-friendly solvent for perovskites, yet the efficiency of the device still needs improvement,” Wang said.

“We have proposed the concepts of pure oxygen stability and flexible stability, which are valuable for other researchers to pay attention. Moreover, we hope that these strategies are not only useful in perovskite solar cells but also in other photoelectrical systems, such as organic photovoltaics, photodetectors, and light-emitting diodes.”

As solar power stands poised to take the lead in our energy grids, such research could help dramatically slash operation costs and increase the active lifespans of solar power plants — which would mean less pollution and cheaper energy for us all.

The paper “Durable strategies for perovskite photovoltaics” has been published in the journal APL Materials.

New catalyst nanoparticle turns plastic waste into high-quality hydrocarbons for oils, waxes, cosmetics

New research is looking to give plastic waste a new lease on life as quality motor oil, lubricants, detergents, or even cosmetics.

Electron micrograph of the platinum nanoparticles distributed onto perovskite nanocubes.
Image credits Northwestern University / Argonne National Laboratory / Ames Laboratory.

Let’s not beat around the bush: humanity has a plastic problem. We’re making a lot of it and we’re throwing most away after a single use. Most recycling methods available today can take some of this waste out of the environment, but they also result in cheap, lower-quality plastics than the ones going into the process, which doesn’t make them very lucrative.

In an effort to find a better way of repurposing the mounds of plastic in the wild, a group of U.S. researchers has developed a new catalyst to turn them into high-quality liquid hydrocarbons. These materials can serve as the base for other products or can be useful as-is.

Liquidizing the assets

“Our team is delighted to have discovered this new technology that will help us get ahead of the mounting issue of plastic waste accumulation,” said Kenneth Poeppelmeier, a paper co-author from Northwestern University.

“Our findings have broad implications for developing a future in which we can continue to benefit from plastic materials, but do so in a way that is sustainable and less harmful to the environment and potentially human health.”

The upcycling method relies on a new catalyst the team developed. It is constructed from perovskite nanocubes studded with platinum nanoparticles. Perovskite was chosen because it remains stable under high temperatures and pressures, and is also a very good material for energy conversion (perovskite is the main material used for several types of solar panels). To deposit nanoparticles onto the nanocubes, the team used atomic layer deposition, a technique developed at Argonne National Laboratory that allows precise control of nanoparticles.

Under moderate pressure and temperature conditions, the catalyst breaks down plastics into high-quality liquid hydrocarbons. The team explains that these substances could be used in motor oil, lubricants, or waxes, or further processed to make ingredients for detergents and cosmetics.

It’s the first plastic recycling or upcycling method that is able to reach this end product. Commercially-available catalysts today generate lower quality products with many short hydrocarbons, which are of limited usefulness. Classic melt-and-reprocess recycling results lower-value plastic that is not as structurally strong as the original material.

Plastics are so resilient because on an atomic level, they have a lot of carbon atoms linked to other carbon atoms — and this chemical bond is very strong (has a lot of energy). As a rule of thumb, it takes a greater amount of energy than that contained in a bond to break it. There aren’t many things in nature that can completely break down plastic, but there are enough sources of energy to degrade it into microplastics. Given that we produce around 380 million tons of plastic yearly, and that over 75% is thrown away after one use (ending up in waterways and the ocean), it adds up to a lot of microplastics.

“There are certainly things we can do as a society to reduce consumption of plastics in some cases,” said Aaron D. Sadow, a scientist in the Division of Chemical and Biological Sciences at Ames Laboratory and the paper’s co-lead author. “But there will always be instances where plastics are difficult to replace, so we really want to see what we can do to find value in the waste.”

The team says that their approach produces far less waste than comparable processes, and virtually no emissions compared to recycling methods that involve melting plastic.

The paper “Upcycling Single-Use Polyethylene into High-Quality Liquid Products” has been published in the journal ACS Central Science.

Caffeine solar cell.

Researchers figure out how coffee can boost (some) solar cells

Researchers at the University of California, Los Angeles (UCLA) and Solargiga Energy in China have tried to perk up solar panels with coffee. It worked.

Caffeine solar cell.

One of the solar cells the team made using the new method.
Image credits Rui Wang and Jingjing Xue.

The team reports that caffeine can help improve the efficiency with which perovskite solar panels convert light to electricity. The finding could help them a more competitive and cost-effective alternative to silicon solar cells.

Wakey, wakey

“One day, as we were discussing perovskite solar cells, our colleague Rui Wang said, ‘If we need coffee to boost our energy then what about perovskites? Would they need coffee to perform better?'” recalls Jingjing Xue, a Ph.D. candidate at the Department of Materials Science and Engineering at UCLA and co-lead author of the study.

After, presumably, a few rounds of hearty laughs, the team set their cups down and set to work on trying to see if the idea has any value.

The authors have previously worked on improving the thermal stability of perovskite materials — the blue compounds with a particular crystal structure that forms the light-harvesting layer certain solar cells — to make them more efficient at harvesting sunlight. Part of that work involved trying to strengthen the material with additives such as dimethyl sulfoxide, an approach which showed some success in the short term, but wasn’t stable over longer spans of time. Caffeine, however, is an alkaloid compound whose molecular structures could, the team suspected based on their previous experience, interact with the precursors used to make perovskite materials.

So, they set out to add caffeine to the perovskite layer of forty solar cells and used infrared spectroscopy, an approach that uses infrared radiation to identify a sample’s chemical components, to determine if the materials bonded. They had.

Further infrared spectroscopy tests showed that carbonyl groups (a carbon atom double bonded to an oxygen) in caffeine tied to lead ions in the perovskite layer to form a “molecular lock”. This lock increases the minimum amount of energy needed for the perovskite layer to react to sunlight, boosting the solar cell efficiency from 17% to over 20%. This lock stood firm when the material was heated, which suggests that caffeine could also help to make the solar cells more thermally-stable.

“We were surprised by the results,” says Wang, who is also a Ph.D. candidate in Yang’s research group at UCLA. “During our first try incorporating caffeine, our perovskite solar cells already reached almost the highest efficiency we achieved in the paper.”

The caveat, or caffeat if you so prefer, is that this approach likely won’t work with other types of solar cells. It only works here because it can tie into the unique molecular structure of perovskite precursors. However, it may be enough to give this type of solar cell variety an edge on the market.

Currently, perovskite solar cells are the cheaper and more flexible option available on the market. They’re also easier to manufacture, as they can be fabricated from liquid precursors — their silicon counterparts are cast from solid crystal ingots. Wang believes that caffeine might make them even easier to fabricate on a large scale, in addition to making them more efficient.

“Caffeine can help the perovskite achieve high crystallinity, low defects, and good stability,” he says. “This means it can potentially play a role in the scalable production of perovskite solar cells.”

The team plans to continue their efforts by investigating the chemical structure of the caffeine-infused perovskite crystals and identify what materials would best serve as a protective layer for the solar cells.

The paper “Caffeine Improves the Performance and Thermal Stability of Perovskite Solar Cells” has been published in the journal Joule.

1 cm2 monolithic perovskite-silicon tandem solar cell. This image was used for illustrative purposes, and the pictured solar cell was not involved in the present research. Credit: Rongrong Cheacharoen/Stanford University

Charge nano-map could help scientists turn perovskite into THE solar cell material

A crystal known to science for more than a century was only recently recognized for its use in harvesting solar power. Since the first successful usage of perovskite in solar cells in 2009, the advances in the field have grown exponentially over time, making it a potential candidate for revamping the solar industry in favor of silicon.  Despite solar cells made with perovskite recently crossed the 20 percent efficiency mark, researchers say there’s still room to improve if only they knew how charge flows at the nanometer scale. They just had to ask, and the  Department of Energy’s Oak Ridge National Laboratory delivered.

Why you should care about perovskite

1 cm2 monolithic perovskite-silicon tandem solar cell. This image was used for illustrative purposes, and the pictured solar cell was not involved in the present research. Credit: Rongrong Cheacharoen/Stanford University

1 cm2 monolithic perovskite-silicon tandem solar cell. This image was used for illustrative purposes, and the pictured solar cell was not involved in the present research. Credit: Rongrong Cheacharoen/Stanford University

The perovskite mineral was originally found in the Ural Mountains in 1839, but it was only a few years ago that its ability to transport solar energy and convert it into electricity was discovered. Just a couple of years later, rated efficiency in the lab has soared from 3.8% to 19.3%, a pace of improvement unmatched by any other solar technology. Currently, the leading commercial solar tech employs crystalline silicon solar cells, which convert roughly 25% of incoming photon energy into electricity, but have decades worth of research backing them.

What makes this mineral so exciting  is its uncanny ability  to diffuse photons a long distance through the cell when prepared in a liquid solution. Typically, solar cells convert energy to electricity by exploiting the hole-pair phenomenon. The photon hits the semiconducting material, then if its energy falls into the semiconductor bandcamp, an electron is offset, leaving a gap in the atom or hole. The electron travels from atom to atom within the material, occupying holes and offsetting at the same time until it eventually reaches an electrode and has its charge transferred to a circuit. Last step: profit and generate electricity.

The key is to have electron moving for as long as possible, and thanks to its diffusing capabilities, perovskite can theoretically generate more electricity. Perovskite is also dirt cheap which is highly important if we’re ever to cover a significant portion of the planet’s surface with solar cells for a 100% sustainable energy future.

Zooming in on charges

(Top) A phasor plot of the transient absorption data shows the presence of free charges and excitons; a false colored image shows their contributions at different spatial positions. Credit: ORNL

(Top) A phasor plot of the transient absorption data shows the presence of free charges and excitons; a false colored image shows their contributions at different spatial positions. Credit: ORNL

An experimental setup combined microscopy and ultra-short laser pulses that fire every 50 millionths of a billionth of a second. These pulses mimicked the sun’s rays by providing photons that got absorbed by a perovskite solar cell. A second laser measured minute changes in light absorption in the material. Eventually, the researchers drew a pixel-by-pixel map of the material.

“The ability to identify what will be created after the solar cell absorbs a photon, either a pair of free charges or their bound form called an exciton, is crucial from both fundamental and applied perspectives,” said co-author Yingzhong Ma, who led the research team. “We found that both free charges and excitons are present, and the strength of our approach lies in not only identifying where they are but also determining what their relative contributions are when they are both present at a given spatial location.”

“With conventional approaches of studying photovoltaic materials, we are unable to accurately map out electronic processes and how electrons are getting lost,” said  said Benjamin Doughty, one of the authors and a member of ORNL’s Chemical Sciences Division. “Those processes can translate into losses in efficiency.”

Now, it only remains to identify what causes this spatial difference, Ma says. If and when this happens, they might also learn what causes the degradation issues due to moisture many have reported.

Reference: “Separation of Distinct Photoexcitation Species in Femtosecond Transient Absorption Microscopy,http://pubs.acs.org/doi/abs/10.1021/acsphotonics.5b00638.

 

Test sample of a monolithic perovskite-silicon multijunction solar cell produced by the MIT-Stanford University team. Image: Felice Frankel

The two-in-one solar cell might harness energy cheaply and efficiently

A team at Stanford and MIT has devised a novel configuration that combines silicon – the leading solar cell semiconductor – and perovskite – a cheap mineral, only recently exploited for converting solar energy – to form two different layers of sunlight-absorbing material in order to harness energy across a wider spectrum. While performance at this stage is not impressive (it’s equally as good or bad as conventional single-layer silicon cells), researchers believe they have methods at their disposal that could double efficiency. If that were to happen, than these could be the cheap, but efficient solar cells we’ve all been waiting for.

Test sample of a monolithic perovskite-silicon multijunction solar cell produced by the MIT-Stanford University team.  Image: Felice Frankel

Test sample of a monolithic perovskite-silicon multijunction solar cell produced by the MIT-Stanford University team.
Image: Felice Frankel

Perovskite is a calcium titanium oxide mineral composed of calcium titanate (CaTiO3). The mineral has received much attention in recent years as artificial perovskite crystals have increasingly been used in solar cells. Perovskite tech has seen 400 percent growth in solar conversion efficiency in less than five years. If initially we heard about clumsy perovskite cells with a rated efficiency of only 3.8%, there are now reports of conversions closed to 19%. Definitely one to watch for, this perovskite.

This is what the researchers thought as well. They added a semi-transparent perovskite layer on top of a silicon one. Since different materials absorb different light frequencies, combining the two theoretically helps you harvest more electricity. The team first did this last year, but in a tandem configuration in which the two layers were stacked, but each had its own separate electrical connection. Now, the configuration connects the two together under the same circuit.

It’s much simpler to install and make this way, but there are some important challenges to keep in mind. The two layers were initially wired separately  for good reason: the current produced is limited by the capacity of the lesser of the two layers. MIT associate professor of mechanical engineering Tonio Buonassisi offers an analogy. Imagine a flow of water through two non-identical pipes. At one point, the volume of water that may pass through the stacked pipes is limited by the narrowest one. A chain is only as strong as its weakest link, in other words.

This is why the only currently report a modest efficiency of 13.7 percent, but Buonassisi claims his team has identified low-cost methods to up this to 30 percent.  This would involve matching the two output currents as closely as possible, according to the paper published in the journal Applied Physics Letters. Since it’s the first time perovskite and silicon have been combined in this configuration, there’s reason to believe there’s much room for improvement.

Scientists create better, cheaper perovskite crystals

Researchers at Brown University have found a cheaper and easier way to create hybrid perovskites, enabling engineers to develop more affordable and efficient solar cells.

 

Credit: Padture Lab / Brown University.

Perovskite is a calcium titanium oxide mineral composed of calcium titanate (CaTiO3). The mineral has received much attention in recent years as artificial perovskite crystals have increasingly been used in solar cells. Perovskite films in solar cells are excellent light absorbers, but they until now, they were more expensive to fabric and only created small crystals.

“People have made good [perovskite] films over relatively small areas – a fraction of a centimeter or so square,” says researcher Nitin Padture, a professor of engineering.

However, the research team developed a new technique, which only requires a room-temperature solvent bath to create perovskite crystals, rather than the blast of heat used in current crystallization methods.

The high temperature process involved temperatures of 100-150 degrees Celsius (212-302 Fahrenheit) and this also limited the kinds of substrates films can be deposited on. For example, plastics would make an excellent substrate, but you can’t really place these hot films on plastic because they’d just melt the plastic. The heat also created a tendency for crystals to form unevenly with tiny pinholes throughout the resulting film, which can reduce the efficiency of solar cells.

Yuanyuan Zhou, a graduate student in Padture’s lab, wanted to see if he could create perovskite crystals without having to use high temperatures and he came up with a solvent-solvent extraction method (SSE). He basically took the materials needed to create the crystals and dissolved them in a solvent called N-Methyl-2-pyrrolidone (NMP). Then, instead of heating, the substrate is bathed in a second solvent, diethyl ether (DEE). DEE selectively grabs the NMP and washes it away, and leaves behind a smooth film of perovskite crystals – exactly what researchers wanted to see. The entire process takes less than two minutes, it’s really cheap, and the crystals can be applied to any substrate. The SSE approach also ensures a very high quality and eliminates unwanted holes in the material.

“Using the other methods, when the thickness gets below 100 nanometers you can hardly make full coverage of film,” Zhou said. “You can make a film, but you get lots of pinholes. In our process, you can form the film evenly down to 20 nanometers because the crystallization at room temperature is much more balanced and occurs immediately over the whole film upon bathing.”

To make things even better, the new films are transparent, so we could be having transparent windows generating energy pretty soon. Zhou has also been able to make cells in different colors, to be used for decorative purposes. What I personally like a lot about this study is that unlike most solar cell developments which are strictly lab innovations and can take years to develop into something useful, this actually has the potential of becoming big soon.

“We think this could be a significant step toward a variety of commercially available perovskite cell products,” Padture said.

Journal Reference: Journal of Materials Chemistry A.

perovskite_battery

One single scrap car battery could be turned into solar cells that power 30 homes

perovskite_battery

One single lead-iron battery could be used to build enough solar panels to power 30 homes. Image: MIT

Lead-acid car batteries used to be the norm, but luckily we’re seeing a massive shift towards more efficient and environmentally friendly alternatives like lithium-ion. Still, there are fleets of hundreds of millions of cars that still employ these archaic and toxic batteries. Typically, manufacturers try to have car owners bring their old lead-acid batteries, which are then converted into more environmentally friendly new batteries. The vast majority of them go into landfills, tough. Researchers at MIT present a remarkable alternative: using old car batteries to power a new generation of dirt cheap and efficient solar cells, based on perovskite. One single used battery could be employed as a prime material for solar cells that could power up to 30 homes.

A new found purpose

“Perovskite” is a general term used to describe a group of materials that have a distinctive crystal structure of cuboid and diamond shapes. In the past few years, researchers have demonstrated that solar cells that use this wonder mineral can reach a solar energy conversion efficiency of up to 19%, comparable to silicon tech that’s somewhere between 21% and 25%. There are some significant differences; perovskite efficiency has only recently crossed the single-digit efficiency margin (they’ve only been investigated for their solar energy potential, seriously at least, only in the last decade, while silicon has been around for more than 30 years), and there’s good reason to think this can be increased. Secondly, manufacturing perovskite solar cells is a whole lot easier energy-wise than the silicon-based variety, not requiring nearly the same temperatures and pressure.

A new research by engineers at MIT suggests that perovskite solar cells can be manufactured efficiently using recycled lead, giving old car batteries as an example of a prime feedstock. So, instead of adding more lead to the environment, potentially poisoning the soil and plants, the material could be recycled from one solar cell to another in much the same way that car batteries continue to use it from generation to generation.

Because the solar cells are very thin, only a small fraction of the lead that comprises of an old car battery would be used. In fact, one such battery could funnel enough lead to make solar panel that power 30 homes.

“This isn’t perfect,” said W.M. Keck Professor of Energy at MIT Angela Belcher said. “It’s very exciting, and lots of people are really pushing the edge of the technology, but it’s also new. Silicon has been around for a long time, and it’s known to work. But we’re excited about this, because we think it could be a competitor that’s easy to process, has rapidly increasing efficiency, and can be made in an environmentally friendly way.”

The findings appeared in the journal Energy and Environmental Science. The video below details the MIT process.

perovskite_led

Brighter and cheaper LEDs could be made from perovskite

perovskite_led

LEDs made from perovskite (credit: Zhi-Kuang Tan)

We’ve covered quite a bit the recent developments involving perovskite as an extremely promising light-to-energy conversion semiconductor. Now, researchers at University of Cambridge, University of Oxford, and Ludwig-Maximilians-Universität are performing research on perovskite-based devices that work the other way around by emitting light. Their research has turned out promising results that suggest high-brightness LEDs, manufactured at low cost and more easily, can be harnessed using perovskite.

High power LEDs of the future

“Perovskite” is a general term used to describe a group of materials that have a distinctive crystal structure of cuboid and diamond shapes. Their efficiency at converting light into electrical energy has opened up a wide range of potential applications. The perovskites that were used to make the LEDs are known as organometal halide perovskites, and contain a mixture of lead, carbon-based ions, and halogen ions known as halides. These materials dissolve well in common solvents, and assemble to form perovskite crystals when dried, making them cheap and simple to make.

“These organometal halide perovskites are remarkable semiconductors,” said Zhi-Kuang Tan, a PhD student at the University of Cambridge’s Cavendish Laboratory and the paper’s lead author. “We have designed the diode structure to confine electrical charges into a very thin layer of the perovskite, which sets up conditions for the electron-hole capture process to produce light emission.”

The team reports an infrared radiance of 13.2 W sr−1 m−2 at a current density of 363 mA cm−2, with highest external and internal quantum efficiencies of 0.76% and 3.4%, respectively. The LEDs were made a simple manufacturing process, where the perovskite solution is prepared and spin-coated onto a substrate. Unlike current LED manufacturing, the process doesn’t involve high temperature, vacuum or complex purification procedures, because the perovskite assembles readily into crystals. The team is now looking to increase the efficiency of the LEDs and to use them for diode lasers, which are used in a range of scientific, medical and industrial applications, such as materials processing and medical equipment.

Findings appeared in the journal Nature Communications.

An artist's impression of spray-coating glass with the polymer to create a solar cell. Image: Energy and Environmental Science

Spray-coated solar cells bring solar power to every corner

Solar cells don’t necessarily come in bulky, sandwich panels you see hang up most roofs. There are a myriad of solutions at your disposal: thin or ultrathin cells, organic cells, flexible cells, you name it. Perhaps the most versatile option, in theory at least, is a spray-on solar cell. Image having a solar cell active solution in a can. You can then turn virtually any surface fitted with electrodes into a solar power source. It’s really amazing, but what it makes in ingenuity, it lacks in efficiency. Researchers at University of Sheffield  aim to change all this, after they report they’ve for the first time developed perovskite solar cells using a spray-on process. The resulting cells are efficient and affordable.

Solar power in a can

An artist's impression of spray-coating glass with the polymer to create a solar cell. Image: Energy and Environmental Science

An artist’s impression of spray-coating glass with the polymer to create a solar cell. Image: Energy and Environmental Science

A while ago, I wrote a bit about how perovskite might significantly boost the solar power market. Discovered for its solar power conversion capabilities just a couple of years ago, research into perovskite solar cells have so far rendered fantastic results. In just a couple of years, rated efficiency has jumped from 3.8% to over 19%.  Cheap, readily available and easy to make, perovskite is regarded as a viable candidate for complementing or replacing silicon at the helm of solar cell materials, because it takes less energy to make. Currently silicon solar cells, the mainstream type, have a rated efficiency of over 25%.

Paint-on or spray-on solar cells aren’t exactly new. Either using quantum dots or some other kind of solutions, spray-on solar cells have been very interesting to watch, but not that interesting to use. Expensive and with a low efficiency, they showed little practical use apart from show and tell. Experts at University of Sheffield have now developed  spray-painting method to produce solar cells using perovskite.

Lead researcher Professor David Lidzey said: “There is a lot of excitement around perovskite based photovoltaics.”
“Remarkably, this class of material offers the potential to combine the high performance of mature solar cell technologies with the low embedded energy costs of production of organic photovoltaics.”

Previously, the researchers demonstrated a spray-on manufacturing process for organic semiconductors. Adapting the process, the researchers created devices with a perovskite absorber instead of an organic absorber, and reached much higher efficiency – around 11%. This is huge, considering no spray-on method has led to cells topping two figures in efficiency.

Professor Lidzey said: “This study advances existing work where the perovskite layer has been deposited from solution using laboratory scale techniques. It’s a significant step towards efficient, low-cost solar cell devices made using high volume roll-to-roll processing methods.”
Solar power is becoming an incr

Findings appeared in the journal Energy & Environmental Science.

perovskite

Perovskite solar cells might help the solar market grow to new heights

NREL Senior Scientist Kai Zhu prepares a perovskite solar cell in his lab. Photo: NREL

NREL Senior Scientist Kai Zhu prepares a perovskite solar cell in his lab. Photo: NREL

A crystal known to science for more than a century has only in recent years become recognized for its use in harvesting solar power. Since the first successful usage of perovskite in solar cells in 2009, the advances in the field have grown exponentially over time, making it a potential candidate for revamping the solar industry. Indeed, the crystal might just be what mainstream solar power has been waiting for: an easy to grow/manufacture solar harvesting platform that can be scaled.

The perovskite mineral was originally found in the Ural Mountains in 1839, but it was only a few years ago that its ability to transport solar energy and convert it into electricity was discovered. Just a couple of years later, rated efficiency in the lab has soared from 3.8% to 19.3%, a pace of improvement unmatched by any other solar technology. Currently, the leading commercial solar tech employs crystalline silicon solar cells, which convert roughly 25% of incoming photon energy into electricity, but have decades worth of research backing them.

[RELATED] This material can be turned into a solar cell by day and light source by night

A promise, not a guarantee

What makes perovskite so interesting is its uncanny ability  to diffuse photons a long distance through the cell when prepared in a liquid solution. Typically, solar cells convert energy to electricity by exploiting the hole-pair phenomenon. The photon hits the semiconducting material, then if its energy falls into the semiconductor bandcamp, an electron is offset, leaving a gap in the atom or hole. The electron travels from atom to atom within the material, occupying holes and offsetting at the same time until it eventually reaches an electrode and has its charge transferred to a circuit. Last step: profit and generate electricity.

The key is to have electron moving for as long as possible, and thanks to its diffusing capabilities, perovskite can theoretically generate more electricity.  So far, however, what’s impressive about perovskite is how its been growing, not actual performance. Perovskite tech has seen 400 percent growth in solar conversion efficiency in less than five years. By contrast, traditional solar cells only increased their performance by 50 percent in their first five years.

It’s important to note that the upper end efficiencies come at a serious drawback – the complex crystalline structures are designed with lead. The resulting crystals readily dissolve in water or even humid air, which means people could be surprise to find dissolved lead is dripping from their rooftops. Not that great of a prospect, really. There’s a solution to this, however: replacing lead with tin, an element that sits right next to its toxic cousin in the periodic table and thus shares a similar electronic configuration.

perovskite

Comparing the rate of increase in perovskite solar cell efficiencies (purple lines and markers) with leading third-generation (i.e., relatively new) solar cells and with amorphous Si (a-Si), green; dye sensitized, blue; organic, gray. The first two perovskite cells (2009 and 2011) refer to liquid junction cells, which were not stable but were important in initiating the subsequent solid-state cells. PHOTO FROM ADAM SMIGIELSKI/ISTOCKPHOTO

Henry Snaith, a physicist at the University of Oxford in the United Kingdom, and colleagues report making tin perovskite solar cells that achieve a maximum efficiency of 6.4% – a very noticeable drop in efficiency, but there’s not reason to think this couldn’t be improved to match lead-based perovskite performance.

“There is no reason this new material can’t reach an efficiency better than 15 percent,” said Mecouri Kanatzidis, one of the researchers who published in Nature Photonics. “Tin and lead are in the same group in the periodic table, so we expect similar results.”

Tin perovskite is also easier to produce and integrate in current manufacturing processes. Also,  the material can also be fine tuned to access different parts of the solar spectrum, so instead of using multiple semiconductors as is the case of >40% high-efficient multi-junction solar cells, you can use various tweaked layers made from the same crystal.

“It doesn’t require high-temperature processing. You can just dip glass into two chemicals and get the material to form on it,” said Joey Luther, a senior scientist at the Energy Department’s National Renewable Energy Laboratory (NREL).

According to N.R.E.L. senior scientist Joey Luther, the theoretical maximum efficiency of a perovskite-based solar cell would be around 31 percent.

“The goal shouldn’t be to stop at 20% efficiency,” Mr. Luther said. “The goal should be to try to get to 28% or higher. In the lab, the best cells need to be almost perfect at small scale. Then the commercial people can stop at whatever efficiency is economical for them to deploy.”

Clearly, perovskite momentum will definitely drop (a 400% growth in efficiency in the next five years is technically impossible), but it will remain to be seen just how far it can be integrated in commercial applications.  Findings appeared in the journal Nature.

 

Earth’s most abundant mineral finally gets a name

What’s the most common mineral on Earth? Is it quartz, limestone? Maybe olivine? Well, if you take into consideration the entire planet, the most common mineral would be something known as silicate-perovskite – but now, that mineral finally has a name.

A sample of the 4.5 billion-year-old Tenham meteorite that contains submicrometer-sized crystals of bridgmanite. Yes, it’s that really small thing.

On June 2, bridgmanite was approved as the formal name for silicate-perovskite – possibly of the Earth’s most plentiful yet elusive mineral known to exist in the Earth’s lower mantle, between 670 and 2,900 kilometers (416 and1,802 miles). . The name was given in honor of 1946 Nobel Prize winning physicist Percy Bridgman, honoring his researches concerning the effects of high pressures on materials and their thermodynamic behaviour.

You won’t find any bridgmanite on the surface, as the mineral naturally exists only in the lower part of the mantle (which is made 93% from it). Scientists have known (or had very strong theories regarding its existence) for decades, but were unable to find a surface sample, until this year.

“This [find] fills a vexing gap in the taxonomy of minerals,” Oliver Tschauner, an associate research professor at the University of Nevada-Las Vegas who characterized the mineral, said in an email.

Tschauner worked with his colleague, Chi Ma, a senior scientist and mineralogist at the California Institute of Technology in Pasadena, Calif., to characterize the structure of silicate-perovskite since 2009. However, this year they made a big breakthrough, after analyzing a meteorite which fell in Australia in 1879. The meteorite formed 4.5 billion years ago, and was “highly shocked”.

“Shocked meteorites are the only accessible source of natural specimens of minerals that we know to be rock-forming in the transition zone of the Earth,” said Tschauner.

After throughly analyzing it with every available technique, they were finally able to find the bridgmanite veins in the meteorite. Thus, confirming decades of research, they were also able to submit an official name for the mineral, which they did in March 2014.

“We are glad no one used [Bridgman] for other minerals,” said Ma, “this one is so important.”

NTU's new Perovskite solar cell can also emit light when electrical current is passed through the material. Photo: Nanyang Technological University (NTU)

This material can be turned into a solar cell by day and light source by night

NTU's new Perovskite solar cell can also emit light when electrical current is passed through the material. Photo: Nanyang Technological University (NTU)

NTU’s new Perovskite solar cell can also emit light when electrical current is passed through the material. Photo: Nanyang Technological University (NTU)

Scientists have made great efforts to discover a material that can be used to both absorb and emit light. A fluke may have suffice, since researchers at Nanyang Technological University (NTU) in Singapore discovered by accident a material that can be used to work as a solar panel, harnessing energy from the sun during the day, as well as a light panel during the night, emitting light with electricity is passed through it.

The implications could be major if the material can be integrated with existing technology. For instance, the smartphones of the future could charge just like a solar panel during the day by placing the display facing the sun, while still being able to display information. Other more immediate applications include advertising billboards that are less demanding and dynamic than consumer electronics (no need for touchscreen or complicated software). The mall’s of the future could have windows layered with this material, since it can be fashioned to be trans-lucid. The possible applications are numerous.

Solar cell at day, light panel by night

This solar cell is developed from Perovskite, a promising material that could hold the key to creating high-efficiency, inexpensive solar cells. The researchers discovered it dual use by chance after NTU physicist Sum Tze Chien asked one of his postdoctoral researchers to shine a laser on the Perovskite material. Since most solar cell materials are good at absorbing, not producing light, the research team was surprised when the Perovskite glowed brightly.

This is a significant finding as most solar cell materials are good at absorbing light but are generally not expected to generate light. In fact, this highly luminescent new Perovskite material is also very suitable for the making of lasers. Not only this, by tuning the composition of the material, when an electrical current is passed through the Perovskite material you can make it emit a wide range of colours, which also makes it suitable as a light emitting device, such as flat screen displays.

“The fact that it can also emit light makes it useful as light decorations or displays for the facades of shopping malls and offices,” said Dr Nripan Mathews, who is also the Singapore R&D Director of the Singapore-Berkeley Research Initiative for Sustainable Energy (SinBeRISE) NRF CREATE program.
“Such a versatile yet low-cost material would be a boon for green buildings. Since we are already working on the scaling up of these materials for large-scale solar cells, it is pretty straightforward to modify the procedures to fabricate light emitting devices as well. More significantly, the ability of this material to lase, has implications for on-chip electronic devices that source, detect and control light,” he added.

The discovery is important not only because of the material’s interesting properties, but also because its incredibly durable and can be up to five times cheaper than silicon to manufacture. Silicon is the de facto material of choice when solar cells are considered.

The findings were reported in the journal Science.

The mysterious case of the missing Xenon

Xenon is a noble gas, the second heaviest of the chemically inert noble gases. The only problem with is that… it’s gone missing! Xenon is almost entirely missing from our atmosphere, somethign which researchers were unable to answer – until now, that is. German researchers believe they managed to find out where the gas is hiding.

In the air or in the ground?

The missing xenon case was something many researchers tried, but ultimately failed, to explain. Since it’s not in the atmosphere, that most likely means it’s either in the glaciers, in the litosphere, or even in the Earth’s core.

“Scientists always said the xenon is not really missing. It’s not in the atmosphere, but it’s hiding somewhere,” says professor Hans Keppler, a geophysicist at the University of Bayreuth in Germany. He and his colleague Svyatoslav Shcheka are the latest geoscientists to tackle the case, in a report published today in Nature.

As you could expect from geophysicists, they searched for the answer in minerals. A magnesium silicate, called perovskite, is a major component of the Earth’s lower mantle. For some reason, they had a hunch the xenon might be hiding in this perkovite, so they went searching.

“I was quite sure that it must be possible to stuff noble gases into perovskite,” says Keppler. “I suspected xenon may be in there.”

Researchers tried replicating the conditions in the lower mantle, and so they dissolved xenon and argon in perovskite at temperatures exceeding 1,600 ºC and pressures about 250 times those at sea level. Under these conditions, the mineral dramatically absorbed argon, but had little room left for xenon. This result seemed pretty disappointing, but in fact, it gave geophysicists a rather strange idea: What if the xenon isn’t hiding at all?

Elementary, my dear Watson

Some 4 billion years ago, the Earth was truly a hellish place. It was still a molten mass, lacking an atmosphere and constantly bombarded by meteorites. Keppler and Shcheka suggest that argon and other noble gases hid in the perovskite, which was on the surface then, and xenon, unable to dissolve, simply went into outer space.

“This is completely different from what everybody else is saying. They are saying the xenon is here but it’s hiding somewhere. We are saying it is not here because very early in Earth’s history it had no place to hide,” says Keppler.

When the Earth started cooling and the atmosphere started forming, a big part of the noble gases were released in the atmosphere, but by that time, xenon was already gone. As a significant, but not fully conclusive evidence, researchers also point out that the relative ratios of three noble gases — xenon, krypton and argon — pretty much correspond to their relative sollubilities in erovskite.

But not all agree with this creative theory:

“I don’t think this discovery accounts for the missing xenon.”, says Chrystele Sanloup, a geoscientist at Pierre and Marie Curie University in Paris. She notes that the theory does not totally explain all of the excess heavy xenon in the atmosphere, nor for additional xenon made from the radioactive decay of uranium and plutonium in rocks.

Besides, every explanation that works on Earth should also work on Mars too, right? Keppler and Shcheka suggest that here, too, the ancient xenon escaped into space: the planet’s puny gravitational field prevented it from holding onto the gas. As a result, all the xenon found on the red planet is what little could dissolve into the early perovskite. But some don’t believe Mars had all that perovskite to begin with. That being said, we’re going to have to solve this mystery on Mars too, if the theory works.

Source

Results were published in Nature: Shcheka, S. S. & Keppler, H. Nature http://dx.doi.org/10.1038/nature11506 (2012).