One useful property that so far has not been observed in perovskites is called “carrier multiplication”, an effect that makes materials much more efficient in converting light into electricity. Perovskites form a group of crystals that have many promising properties for applications in nano-technology. New research performed in collaboration between the University of Amsterdam (UA) and Osaka University (OU) and led by professor Tom Gregorkiewicz (UA, OU) and professor Yasufumi Fujiwara (OU), has now shown that certain perovskites in fact do have this desirable property.

Crystals are configurations of atoms, molecules or ions, that are ordered in a structure that repeats itself in all directions. Everyone has encountered some crystals in everyday life: ordinary salt, diamond and even snowflakes are examples. What is perhaps less well-known is that certain crystals show very interesting properties when their size is not familiar to our everyday life but that of nanometers, a few billionths of a meter. There, we enter the world of nanocrystals, structures that have shown to be extremely useful in constructing technological applications at tiny scales.

Dr. Leyre Gomez (right) and Dr. Chris de Weerd (left) with a sample of the studied material.  Image Credit: the University of Amsterdam. Click image for the largest view.

Perovskites, named after 19th century Russian mineralogist Lev Perovski, form a particular family of nanocrystals that all share the same crystal structure. At the nanoscale, these perovskites have many desirable electronic properties, making them useful for constructing for example LEDs, TV-screens, solar cells and lasers. For this reason over the past years, perovskite nanocrystals have been studied extensively by physicists.

A property which so-far had not been shown to exist in perovskites is carrier multiplication. When nanocrystals for example in solar cells, convert the energy of light into electricity, this is usually done one particle at a time: a single infalling photon results in a single excited electron (and the corresponding “hole” where the electron used to be) that can carry an electrical current. However, in certain materials, if the infalling light is energetic enough, further electron-hole pairs can be excited as a result; it is this process that is known as carrier multiplication.

When carrier multiplication occurs, the conversion from light into electricity can become much more efficient. For example, in ordinary solar cells there is a theoretical limit (known as the Shockley-Queisser limit) on the amount of energy that can be converted in this way, topping out a bit over 30% of the solar power gets turned into electrical power. In materials that display the carrier multiplication effect, however, an efficiency of up to 44% has already been obtained.

This makes it very interesting to search for the carrier multiplication effect in perovskites as well. Which is precisely what Dr. Chris de Weerd and Dr. Leyre Gomez from the Optoelectronic Materials group led by professor Tom Gregorkiewicz, in collaboration with the group of professor Yasufumi Fujiwara, and with support of their colleagues from the National AIST Institute in Tsukuba and Technical University Delft have now done.

Using spectroscopy methods, studying the frequencies of the radiation that comes from a material after very briefly illuminating it with a flash of light, the researchers showed that a perovskite nanocrystals made out of cesium, lead and iodine, do indeed display carrier multiplication. Moreover, they argue that the efficiency of this effect is higher than reported thus far for any other materials. Therefore with this finding the extraordinary properties of perovskite receive a new boost.

De Weerd, who successfully defended her PhD thesis based on this and other research last week, said,` “Until now, carrier multiplication had not been reported for perovskites. That we have now found it is of great fundamental impact on this upcoming material. For example, this shows that perovskites can be used to construct very efficient photodetectors, and in the future perhaps solar cells.”

The team’s research paper has been published in the journal Nature Communications.

This looks to be quite a breakthrough for the perovskite researcher community. There is little to add to an excellent and quite complete press release. Good work by everyone.

Daegu Gyeongbuk Institute of Science and Technology (DGIST) researchers led by DGIST Professor Jong-Sung Yu’s team at the Department of Energy Science and Engineering have developed new photocatalyst synthesis method using Magnesium hydride (MgH2) and Titanium dioxide (TiO2). The result is expected to contribute to hydrogen mass production through the development of photocatalyst that reacts to solar light.

This diagram illustrates the surface reactions and characteristics of reduced titanium based photocatalysts developed at DGIST. Image Credit: DGIST. Click image for the largest view.

Intense research is being conducted globally on how to produce hydrogen using solar light and photocatalysts for decomposing water. To overcome the limitations of photocatalysts that only reacts to light in ultraviolet rays, researchers have doped dual atom such as Nitrogen (N), Sulfur (S), and Phosphorus (P) on photocatalyst or synthesized new photocatalysts, developing a photocatalyst that reacts efficiently to visible light.

The team detailed their work in a paper published in the journal Applied Catalysis B: Environmental.

With Professor Samuel Mao’s team at UC Berkeley in the U.S., Professor Yu’s research team developed a new H-doped photocatalyst by removing oxygen from the photocatalyst surface made of titanium dioxide and filling hydrogen into it through the decomposition of MgH2. Energy of long wavelength including visible light could not be used for the existing white Titanium dioxide because it has a wide band gap energy. However, the development of MgH2 reduction could overcome this through oxygen flaw induction and H-doping while enabling the use of solar light with 570nm-wavelength.

MgH2 reduction can synthesize new materials by applying to Titanium oxide used in this research as well as the oxides composed of other atoms such as Zr, Zn, and Fe. This method is applicable to various other fields such as photocatalyst and secondary battery. The photocatalyst synthesized in this research has four times higher photoactivity than the existing white titanium dioxide and is not difficult to manufacture, thus being very advantageous for hydrogen mass production.

Another characteristic of the photocatalyst developed by the research team is that it reduces band gap more than the existing Titanium dioxide photocatalyst used for hydrogen generation and can maintain four times higher activity with stability for over 70 days.

The new method can also react to visible light unlike existing photosynthesis, overcoming the limitation of hydrogen production. With the new photocatalyst development, the efficiency and stability of hydrogen production can both dramatically improved, which will help popularize hydrogen energy in the near future.

Professor Yu said, “The photocatalyst developed this time is a synthesis method with much better performance than the existing photocatalyst method used to produce hydrogen. It is a very simple method that will greatly help commercialize hydrogen energy. With a follow-up research on improving the efficiency and economic feasibility of photocatalyst, we will take the lead in creating an environment stable hydrogen energy production that can replace fossil energy.”

The hydrogen fuel photocatalysts are popping up quite often lately. Its seems that one or more could have real potential. This one seems to use low cost materials and lasts a fairly long while, two important attributes.

There is still quite a way to go for roof top hydrogen production. Any and all of what we’ve been seeing have to be proven up, packaging developed for outdoor exposure and a long list of the things about getting to market. Then the real bugaboos get underway.

That’s, storage, safety and something to use the fuel. We’re not seeing those products offered at mass scale at all so far.

Ulsan National Institute of Science and Technology (UNIST) has announced that an international team of researchers has introduced a simple technique to fabricate full-color perovskite LEDs.

Perovskite nanoparticles are regarded as next-generation of optical materials that can achieve vivid colors even on very large screens. Due to their high color purity and low cost advantages, perovskite LEDs have also gained much interest in industry. A recent study, affiliated with UNIST, published in the journal Joule, has introduced a simple technique to extract the three primary colors (red, blue, green) from this material.

This breakthrough was led by Professor Jin Young Kim in the School of Energy and Chemical Engineering at UNIST. In the study, the research team introduced a simple technique that freely controls light emitting spectrums by adjusting the anion halides in perovskite materials. The key is to adjust the anion halides by simply dissolving them in solvents to achieve red, blue, and green lights. Application of this technique to LEDs can result in crystal-clear picture quality.

Perovskite is a semiconductor material with a special structure, containing metal and halogen elements. The solar cell adopting this material is considered to be the next-generation solar cell candidate because it has high photoelectric efficiency that converts sun light into electricity. This material is also attracting attention as a light emitting device because of its high luminous efficiency which turns electricity into light.

Perovskite nanoparticles are microscopic perovskite materials at nanometer (nm, 1 nm / 1 billionths of a meter) level, which emit different colors depending on the internal halogen element. It is a formula that emits red when it is rich in iodine, green when it is rich in bromine, and blue when it is rich in chlorine.

However, perovskite is highly sensitive, making it difficult to change elements stably. In search for an answer, Professor Kim has developed a simple technique to replace certain elements by a solution process. This is a method of inducing element substitution, using nonpolar solvent and chemical additives.

Yung Jin Yoon in the Combined M.S./Ph.D Program of Energy Engineering, the first author of the study said, “In the study, we added a nonpolar solvent, containing iodine (I), bromine (Br) and chlorine (Cl) to a solution of perovskite nanoparticles. Once the reaction takes place, the elements mixed within the nonpolar solvent switches its place with elements in original perovskite, which causes changes in luminescence.”

The added chemical additive serve to separate the halogen element present in the nonpolar solvent. As a result, the amount of halogen element in the solution increases, and over time, it is replaced with a halogen element in the conventional perovskite. The emission color is determined by the number of elements in the perovskite. The researchers also succeeded in making LEDs with red, blue, and green colors using perovskite nanoparticles made with this technology.

Kim Ki-Hwan, a research professor in the Department of Energy and Chemical Engineering, said, “It is stable compared to the existing technology to change the element in the solid perovskite. It can be applied variously to change the element composition in the perovskite material, I hope it will be possible. ”

“With our simple method, we obtained luminescence covering the entire visible spectrum from 400 to 700 nm,” said Professor Kim. “Furthermore, saturated and vivid RGB LED devices were successfully fabricated using the anion-exchanged nanocrystals.”

The vagaries of language translation. One was thinking this new technology was ready for testing at scale and working out the production processes. Maybe that’s what Professor Kim means that he hopes is possible.

Televisions and monitors have come a very long way over the past decade. 8K is coming. Its likely this team has made a contribution, and at the pace this industry moves, we’ll know soon.

A Massachusetts Institute of Technology class project developed a new design suggesting a solution to a longstanding problem how to get rid of excess heat generated in next-generation fusion power plants.


The ARC conceptual design for a compact, high magnetic field fusion power plant. The design now incorporates innovations from the newly published research to handle heat exhaust from the plasma. Image Credit for the ARC rendering: Alexander Creely, MIT. Click image for the largest view.

A class exercise at MIT, aided by industry researchers, offers a new solution made possible by an innovative approach to compact fusion reactors, using high-temperature superconducting magnets. This method formed the basis for a massive new research program launched this year at MIT and the creation of an independent startup company to develop the concept. The new design, unlike that of typical fusion plants, would make it possible to open the device’s internal chamber and replace critical components; this capability is essential for the newly proposed heat-draining mechanism.

The new approach is detailed in a paper in the journal Fusion Engineering and Design, authored by Adam Kuang, a graduate student from that class, along with 14 other MIT students, engineers from Mitsubishi Electric Research Laboratories and Commonwealth Fusion Systems, and Professor Dennis Whyte, director of MIT’s Plasma Science and Fusion Center, who taught the class.

In essence, Whyte explained, the shedding of heat from inside a fusion plant can be compared to the exhaust system in a car. In the new design, the “exhaust pipe” is much longer and wider than is possible in any of today’s fusion designs, making it much more effective at shedding the unwanted heat. But the engineering needed to make that possible required a great deal of complex analysis and the evaluation of many dozens of possible design alternatives.

Fusion harnesses the reaction that powers the sun itself, holding the promise of eventually producing clean, abundant electricity using a fuel derived from seawater – deuterium, a heavy form of hydrogen, and lithium – so the fuel supply is essentially limitless. But decades of research toward such power-producing plants have still not led to a device that produces as much power as it consumes, much less one that actually produces a net energy output.

But earlier this year MIT’s proposal for a new kind of fusion plant – along with several other innovative designs being explored by others – finally made the goal of practical fusion power seem within reach. However, several design challenges remain to be solved, including an effective way of shedding the internal heat from the super-hot, electrically charged material, called plasma, confined inside the device.

Most of the energy produced inside a fusion reactor is emitted in the form of neutrons, which heat a material surrounding the fusing plasma, called a blanket. In a power-producing plant, that heated blanket would in turn be used to drive a generating turbine. But about 20 percent of the energy is produced in the form of heat in the plasma itself, which somehow must be dissipated to prevent it from melting the materials that form the chamber.

No material is strong enough to withstand the heat of the plasma inside a fusion device, which reaches temperatures of millions of degrees, so the plasma is held in place by powerful magnets that prevent it from ever coming into direct contact with the interior walls of the donut-shaped fusion chamber. In typical fusion designs, a separate set of magnets is used to create a sort of side chamber to drain off excess heat, but these so-called divertors are insufficient for the high heat in the new, compact plant.

One of the desirable features of the ARC (for advanced, robust, and compact) design is that it would produce power in a much smaller device than would be required from a conventional reactor of the same output. But that means more power confined in a smaller space, and thus more heat to get rid of.

Kuang, who is the lead author of the paper, described the challenge the team addressed – and ultimately solved said, “If we didn’t do anything about the heat exhaust, the mechanism would tear itself apart.”

In conventional fusion reactor designs, the secondary magnetic coils that create the divertor lie outside the primary ones, because there is simply no way to put these coils inside the solid primary coils. That means the secondary coils need to be large and powerful, to make their fields penetrate the chamber, and as a result they are not very precise in how they control the plasma shape.

But the new MIT-originated design, known as ARC, features magnets built in sections so they can be removed for service. This makes it possible to access the entire interior and place the secondary magnets inside the main coils instead of outside. With this new arrangement, “just by moving them closer [to the plasma] they can be significantly reduced in size,” said Kuang.

In the one-semester graduate class 22.63 (Principles of Fusion Engineering), students were divided into teams to address different aspects of the heat rejection challenge. Each team began by doing a thorough literature search to see what concepts had already been tried, then they brainstormed to come up with multiple concepts and gradually eliminated those that didn’t pan out. Those that had promise were subjected to detailed calculations and simulations, based, in part, on data from decades of research on research fusion devices such as MIT’s Alcator C-Mod, which was retired two years ago. C-Mod scientist Brian LaBombard also shared insights on new kinds of diverters, and two engineers from Mitsubishi worked with the team as well. Several of the students continued working on the project after the class ended, ultimately leading to the solution described in this new paper. The simulations demonstrated the effectiveness of the new design they settled on.

“It was really exciting, what we discovered,” Whyte said. The result is divertors that are longer and larger, and that keep the plasma more precisely controlled. As a result, they can handle the expected intense heat loads.

“You want to make the ‘exhaust pipe’ as large as possible,” Whyte said, explaining that the placement of the secondary magnets inside the primary ones makes that possible. “It’s really a revolution for a power plant design,” he said. Not only do the high-temperature superconductors used in the ARC design’s magnets enable a compact, high-powered power plant, “but they also provide a lot of options” for optimizing the design in different ways – including, it turns out, this new divertor design.

Going forward, now that the basic concept has been developed, there is plenty of room for further development and optimization, including the exact shape and placement of these secondary magnets, the team said. The researchers are working on further developing the details of the design.

“This is opening up new paths in thinking about divertors and heat management in a fusion device,” Whyte said.

Ah, the Tokamak, the idea that never gives up. Still, maybe this MIT class, its professors and industry engineers have finally gotten the Tokamak in a configuration that might work. It might even be small enough to be practical. We’re still a very long way off from even imagining how long such a device might cost or even last.

Some folks think Tokamak research will go on even after one or more of the other technologies goes net power. But lets not make the mistake thinking all this is useless, real lessons are being learned and will make contributions to other fields.

Rice University scientists have demonstrated a new catalyst for making clean-burning hydrogen from ammonia. They describe a plasmonic effect that lowers chemical activation barriers, improves efficiency and could be of general use in other catalysts.

Scientists with Rice’s Laboratory for Nanophotonics have shown how a light-driven plasmonic effect allows catalysts of copper and ruthenium to more efficiently break apart ammonia molecules, which each contain one nitrogen and three hydrogen atoms. When the catalyst is exposed to light (right), resonant plasmonic effects produce high-energy “hot carrier” electrons that become localized at ruthenium reaction sites and speed up desorption of nitrogen compared with reactions conducted in the dark with heat (left). Image Credit: LANP/Rice University. Click image for the largest view.

The study from Rice’s Laboratory for Nanophotonics (LANP) has been published in Science describing the new catalytic nanoparticles, which are made mostly of copper with trace amounts of ruthenium metal. Tests showed the catalyst benefited from a light-induced electronic process that significantly lowered the “activation barrier,” or minimum energy needed, for the ruthenium to break apart ammonia molecules.

The research comes as governments and industry are investing billions of dollars to develop infrastructure and markets for carbon-free liquid ammonia fuel that will not contribute to greenhouse warming. But the researchers say the plasmonic effect could have implications beyond the “ammonia economy.”

LANP Director Naomi Halas, a chemist and engineer who’s spent more than 25 years pioneering the use of light-activated nanomaterials said, “A generalized approach for reducing catalytic activation barriers has implications for many sectors of the economy because catalysts are used in the manufacture of most commercially produced chemicals. If other catalytic metals can be substituted for ruthenium in our synthesis, these plasmonic benefits could be applied to other chemical conversions, making them both more sustainable and less expensive.”

Catalysts are materials that speed up chemical reactions without reacting themselves. An everyday example is the automotive catalytic converter that reduces harmful emissions from a vehicle’s exhaust. Chemical producers spend billions of dollars on catalysts each year, but most industrial catalysts work best at high temperature and high pressure. The decomposition of ammonia is a good example. Each molecule of ammonia contains one nitrogen and three hydrogen atoms. Ruthenium catalysts are widely used to break apart ammonia and produce hydrogen gas (H2), a fuel whose only byproduct is water, and nitrogen gas (N2), which makes up about 78 percent of Earth’s atmosphere.

The process begins with the ammonia sticking, or adsorbing, to the ruthenium, and proceeds through a series of steps as the bonds in ammonia are broken one by one. The hydrogen and nitrogen atoms left behind grab a partner then leave, or desorb, from the ruthenium surface. This final step turns out to be the most critical, because the nitrogen has a strong affinity for the ruthenium and likes to stick around, which blocks the surface from attracting other ammonia molecules. To drive it away, more energy must be added to the system.

Graduate student Linan Zhou, the lead author of the Science study, said the efficiency of LANP’s copper-ruthenium catalyst derives from a light-induced electronic process that produces localized energy at ruthenium reaction sites, which aids desorption.

The process, known as “hot carrier-driven photocatalysis,” has its origins in the sea of electrons that constantly swirl through the copper nanoparticles. Some wavelengths of incoming light resonate with the sea of electrons and set up rhythmic oscillations called localized surface plasmon resonances. LANP has pioneered a growing list of technologies that make use of plasmonic resonances for applications as diverse as color-changing glass, molecular sensing, cancer diagnosis and treatment and solar energy collection.

In 2011, LANP’s Peter Nordlander, one of the world’s leading theoretical experts on nanoparticle plasmonics, Halas and colleagues showed that plasmons could be used to boost the amount of short-lived, high-energy electrons called “hot carriers” that are created when light strikes metal. In 2016, a LANP team that included Dayne Swearer, who’s also a co-author of this week’s study, showed that plasmonic nanoparticles could be married with catalysts in an “antenna-reactor” design where the plasmonic nanoparticle acted as antenna to capture light energy and transfer it to a nearby catalytic reactor via a near-field optical effect.

Zhou said of the antenna-reactor, “That was the first generation and the main catalytic effect came from the near-field induced by the antenna when it absorbs light. This near-field drives oscillations in the adjacent reactor, which then generate hot carriers. But if we can have hot carriers that can directly reach the reactor and drive the reaction, it would be much more efficient.”

Zhou, a chemist, spent months refining the synthesis of the copper-ruthenium nanoparticles, which are much smaller than a red blood cell. Each nanoparticle contains tens of thousands of copper atoms but just a few thousand ruthenium atoms, which take the place of some copper atoms on the particle’s surface.

Swearer explained, “Basically, there are ruthenium atoms scattered in a sea of copper atoms, and it’s the copper atoms that are absorbing the light, and their electrons are shaking back and forth collectively. Once a few of those electrons gain enough energy through a quantum process called nonradiative plasmon decay, they can localize themselves within the ruthenium sites and enhance catalytic reactions.”

Taking the explanation further Swearer said, “Room temperature is about 300 Kelvin and plasmon resonances can raise the energy of these hot electrons up to 10,000 Kelvin, so when they localize on the ruthenium, that energy can be used to break the bonds in molecules, assist in adsorption and more importantly in desorption,”

Just as a metal picnic table heats up on a sunny afternoon, the white laser light – a stand-in for sunlight in Zhou’s experiments – also caused the copper-ruthenium catalyst to heat. Because there is no way to directly measure how many hot carriers were created in the particles, Zhou used a heat-sensing camera and spent months taking painstaking measurements to tease apart the thermal-induced catalytic effects from those induced by hot carriers.

“About 20 percent of the light energy was captured for ammonia decomposition,” Zhou said. “This is good, and we think we can refine to improve this and make more efficient catalysts.”

Zhou and Halas said the team is already working on follow-up experiments to see if other catalytic metals can be substituted for ruthenium, and the initial results are promising.

“Now that we have insight about the specific role of hot carriers in plasmon-mediated photochemistry, it sets the stage for designing energy-efficient plasmonic photocatalysts for specific applications,” Halas said.

The other people on this team include co-authors Chao Zhang, Hossein Robatjazi, Hangqi Zhao, Luke Henderson and Liangliang Dong, all of Rice; Phillip Christopher of the University of California, Santa Barbara; and Emily Carter of Princeton University.

Halas is Rice’s Stanley C. Moore Professor of Electrical and Computer Engineering and professor of chemistry, bioengineering, physics and astronomy, and materials science and nanoengineering. Nordlander is the Wiess Chair and Professor of Physics and Astronomy, and professor of electrical and computer engineering, and materials science and nanoengineering.

This is fantastically interesting work. This also represents real progress in deepening the catalyst field.

As far as making hydrogen fuel, there are some issues. Making ammonia isn’t free and so far its a natural gas intensive product. That is not to say this isn’t great work. The cost of this level of catalyst sophistication is unknown, but its potential is just being explored.

Its just that ammonia might not be the greatest source for hydrogen, today. But that could change, and probably will. It is after all, a very effective way to store hydrogen for a very long time.