University of Toronto: New light-converting materials point to cheaper, more efficient solar power

Sargent 2-crystallightUniversity of Toronto engineers study first single crystal perovskites for new applicationsEngineers have shone new light on an emerging family of solar-absorbing materials that could clear the way for cheaper and more efficient solar panels and LEDs.

The materials, called , are particularly good at absorbing , but had never been thoroughly studied in their purest form: as perfect single crystals.Using a new technique, researchers grew large, pure perovskite crystals and studied how move through the material as light is converted to electricity.

Crystal light: New light-converting materials point to cheaper, more efficient solar power

Researchers Valerio Adinolfi (left) and Riccardo Comin examine a perovskite crystal. Perovskites are attracting growing interest in the context of thin-film solar technologies, but had never been studied in their purest form: as perfect single crystals. Credit: U of T Engineering

Led by Professor Ted Sargent of The Edward S. Rogers Sr. Department of Electrical & Computer Engineering at the University of Toronto and Professor Osman Bakr of the King Abdullah University of Science and Technology (KAUST), the team used a combination of laser-based techniques to measure selected properties of the perovskite crystals. By tracking down the rapid motion of electrons in the material, they have been able to determine the diffusion length—how far electrons can travel without getting trapped by imperfections in the material—as well as mobility—how fast the electrons can move through the material. Their work was published this week in the journal Science.

“Our work identifies the bar for the ultimate solar energy-harvesting potential of perovskites,” says Riccardo Comin, a post-doctoral fellow with the Sargent Group. “With these materials it’s been a race to try to get record efficiencies, and our results indicate that progress is slated to continue without slowing down..”

An artist’s rendering of the atomic model of organolead trihalide perovskite crystals. Researchers have succeeded in growing high-quality single crystals of these perovskites at room temperature. The grown crystals efficiently convert light …more

In recent years, perovskite efficiency has soared to certified efficiencies of just over 20 per cent, beginning to approach the present-day performance of commercial-grade silicon-based mounted in Spanish deserts and on Californian roofs.

“In their efficiency, perovskites are closely approaching conventional materials that have already been commercialized,” says Valerio Adinolfi, a PhD candidate in the Sargent Group and co-first author on the paper. “They have the potential to offer further progress on reducing the cost of in light of their convenient manufacturability from a liquid chemical precursor.”

The study has obvious implications for green energy, but may also enable innovations in lighting. Think of a solar panel made of perovskite crystals as a fancy slab of glass: light hits the crystal surface and gets absorbed, exciting electrons in the material. Those electrons travel easily through the crystal to electrical contacts on its underside, where they are collected in the form of electric current. Now imagine the sequence in reverse—power the slab with electricity, inject electrons, and release energy as light. A more efficient electricity-to-light conversion means perovskites could open new frontiers for energy-efficient LEDs.

Parallel work in the Sargent Group focuses on improving nano-engineered solar-absorbing particles called colloidal quantum dots. “Perovskites are great visible-light harvesters, and quantum dots are great for infrared,” says Professor Sargent. “The materials are highly complementary in solar energy harvesting in view of the sun’s broad visible and infrared power spectrum.”

“In future, we will explore the opportunities for stacking together complementary absorbent materials,” says Dr. Comin. “There are very promising prospects for combining perovskite work and quantum dot work for further boosting the efficiency.”

Explore further: Team develops new technique for growing high-efficiency perovskite solar cells

More information: Low trap-state density and long carrier diffusion in organolead trihalide perovskite single crystals, Science 30 January 2015: Vol. 347 no. 6221 pp. 519-522. DOI: 10.1126/science.aaa2725

A Quantum Leap In Display Quality From Quantum Dots: 3 Players Set to Dominate Emerging Markets

Q Dot Displays 1415226538155Quantum dots are improving screens worldwide, but their cadmium content worries some

Long the object of ivory tower fascination, quantum dots are entering the commercial realm. Factories that manufacture the nanomaterials are opening, and popular consumer products that use them are hitting the market.

Behind the gee-whiz technology are three companies with three different approaches to producing and delivering quantum dots. The firms—Nanosys, QD Vision, and Dow Chemical (Nanoco) — are racing to capture a share of the emerging market, but there may not be a place for everyone at the finish line.

Developed at Bell Labs in the 1980s, quantum dots are semiconducting inorganic particles small enough to force the quantum confinement of electrons. Ranging in size from 2 to 6 nm, the dots emit light after electrons are excited and return to the ground state. Larger ones emit red light, medium-sized ones emit green, and smaller ones emit blue.

Quantum dots have been proposed for all sorts of applications, including lighting and medical diagnostics, but the market that is taking off now is enhancing liquid-crystal displays (LCDs).

According to Yoosung Chung, an analyst who follows the quantum dot business for the consulting firm NPD DisplaySearch, last year saw the introduction of the first commercial display products to incorporate quantum dots: Bravia brand televisions from Sony and the Kindle Fire HDX tablet from Amazon. This year, the Chinese company TCL introduced a quantum-dot-containing TV and Taiwan’s Asus shipped a quantum dot laptop.

What quantum dots bring to displays is more vibrant colors generated with less energy. The liquid crystals in conventional LCD screens create colors by selectively filtering white light emitted by a light-emitting diode (LED) backlight, which typically runs along one edge of the screen. But that white light is broad spectrum and not optimal for producing the highly saturated reds, greens, and blues needed for lifelike images.

Jeff Yurek, a marketing manager at Nanosys, says the color performance of LCDs is only 70% of what is provided by more expensive organic light-emitting diode (OLED) displays.

Q Dot Displays 1415226538155

Quantum-dot-enabled displays incorporate a backlight that gives off blue light, some of which the dots convert into pure red and green. The three colors combine into an improved white light that the LCDs draw on to create pictures that are almost as vivid as those achieved with OLEDs.

Moreover, because no light is wasted, energy costs are lowered. That’s important, according to Yurek, because the display accounts for half of the power consumed in a mobile device. By incorporating Nanosys’s quantum dots in its new HDX tablet, Amazon was able to cut display power consumption by 20%, he claims.

“Going from the HD to the HDX, they made a thinner, lighter, higher resolution, more colorful display with longer battery life,” Yurek says.

On the strength of demand from companies such as Amazon, Nanosys has been investing in its quantum dot plant in Milpitas, Calif. According to Yurek, the company is now completing an expansion that will more than double its output. Soon, he says, the firm will have the capacity to supply dots for 250 million 10-inch tablet devices a year.

Also expanding is QD Vision, a Lexington, Mass.-based firm founded on chemistry developed at Massachusetts Institute of Technology. Its dots can be found in Sony’s Bravia line and are set to appear in TVs made by TCL, which is the third-largest TV maker after Samsung and LG.

Seth Coe-Sullivan, QD Vision’s chief technology officer and cofounder, explains that his firm and Nanosys use the same basic manufacturing technique: They decompose organocadmium and other compounds at high heat in the presence of surfactants and solvents. The resulting monomers nucleate and form nanocrystals. Size can be controlled stoichiometrically or by thermally quenching the growing crystals.

Where the two firms differ is the way in which they embed quantum dots in a consumer product. Nanosys works with companies such as 3M to create quantum-dot-containing films that are placed between the LED backlight and the LCDs in tablets and other displays. For example, the Asus quantum-dot-containing laptop, known as the NX500 Notebook PC, incorporates the 3M/Nanosys film.

QD Vision, in contrast, encapsulates its quantum dots in a polymer matrix inside a glass tube that is placed directly against the LED backlight. It’s a hot environment but one that the dots can withstand, Coe-Sullivan says, because of how they are synthesized and packaged.

QD Vision manufactures its dots in Lexington and ships them to a contractor in Asia to be packaged in the tubes. The contractor is in the process of quadrupling capacity to 4 million tubes per month, which is enough, Coe-Sullivan says, to supply a quarter of the world’s TV industry.

The display in Amazon’s Kindle Fire HDX tablet is enhanced with quantum dots.
Credit: Amazon


He argues that his firm’s tube approach is suited to TVs and other large displays, whereas a film works better with smaller tablets and laptops. So far, marketplace adoption bears this contention out. “I honestly don’t feel our products compete with each other,” Coe-Sullivan says.

Dow, however, is throwing down the gauntlet against both approaches. Using technology licensed from the British firm Nanoco, Dow is developing cadmium-free quantum dots. It is betting that the display industry is uneasy with the cadmium content of dots from Nanosys and QD Vision and that it will flock to a cadmium-free alternative.

In September, Dow announced that it will use the Nanoco technology to build the world’s first large-scale, cadmium-free quantum dot plant at its site in Cheonan, South Korea. When the plant opens in the first half of 2015, Dow says, it will enable the manufacture of millions of quantum dot TVs and other display devices.

Dow and Nanoco haven’t disclosed the active material in their quantum dots and declined an interview with C&EN. They acknowledge that the dots contain indium but insist that they aren’t indium phosphide, as their competitors claim.

The use of one heavy metal versus another might not seem to make a big difference environmentally. But in the European Union, cadmium is one of six substances regulated by the Restriction of Hazardous Substances, or RoHS, directive. Cadmium cannot be present in electronics at levels above 100 ppm without an exemption.

Larger amounts of cadmium are allowed in LED-containing displays under an exemption that expired on July 1. Late last year, in a consultation process moderated by Oeko-Institut (Institute for Applied Ecology), a German nonprofit, the major quantum dot players made their cases for why the expiring exemption should or shouldn’t be extended.

Nanosys, QD Vision, 3M, and others lobbied for extension to at least 2019, arguing that the benefits of cadmium-based quantum dots outweigh any potential harm. One big reason is that they lower energy consumption by devices, meaning less use of coal in power plants and fewer of the cadmium emissions that can come from burning coal.

In April, Oeko recommended to the EU that the exemption be extended—but only to July 1, 2017, in light of emerging technology that could reduce or eliminate the need for cadmium quantum dots. Industry executives expect the EU to adopt the recommendation by the end of the year.

In their submissions to the consultation process, Dow and Nanoco argued that no extension is necessary because cadmium-free dots are already here. In fact, the Korea Times recently reported that LG and Samsung plan to launch cadmium-free TVs in 2015 with quantum dots from Dow.

Coe-Sullivan says he’ll believe it when he sees it. “The idea that the product is just around the corner has been around for a long time,” he observes. Cadmium-free displays from LG and Samsung were expected to appear at the recent IFA electronics trade show in Berlin, he says, but ended up being a no-show.

The reason, according to cadmium dot proponents, is that indium-based dots have about half the energy efficiency and a narrower color range. “Cad-free today does not have the same performance as cadmium-containing quantum dots,” Coe-Sullivan says. QD Vision and Nanosys also contend that indium-containing quantum dots aren’t environmentally superior, pointing to indium phosphide’s presence on a list of substances being considered for inclusion in RoHS.

Meanwhile, Coe-Sullivan notes, QD Vision has moved away from the metal-alkyl precursors and phosphorus-containing solvents that can make quantum dot manufacturing hazardous. It now uses metal-carboxylate precursors and more benign alkane solvents. Last month, the shift won it one of the Environmental Protection Agency’s Presidential Green Chemistry Challenge Awards.

Chung, the DisplaySearch analyst, is watching the jousting between the cadmium and cadmium-free camps with interest, although he isn’t ready to predict a winner yet. Display makers are concerned about cadmium, he notes, yet they also have qualms about the lower efficiency of cadmium-free quantum dots.

Chung may not know which technology will prevail, but he is sure about one thing. “Now is the time for quantum dots to penetrate the market,” he says.  

Chemical & Engineering News
ISSN 0009-2347
Copyright © 2015 American Chemical Society

Printing Quantum Dot Displays: Electronics: A new printer uses electric fields to print quantum dots at high resolution for light-emitting diodes

Quantum Glow LED Print 1422381761226Researchers report a high-resolution method for printing quantum dots to make light-emitting diodes (Nano Lett. 2015, DOI: 10.1021/nl503779e). With further development, the technique could be used to print pixels for richly colored, low-power displays in cell phones and other electronic devices.

Quantum dots are appealing materials for displays because engineers can finely tune the light the semiconducting nanocrystals emit by controlling their dimensions.

Electronics makers already use quantum dots in some backlit displays on the market, in which red and green quantum dots convert blue light from a light-emitting diode (LED) into white light. Quantum dots also emit light in response to voltage changes, so researchers are looking into using them in red, green, and blue pixels in displays that wouldn’t need a backlight.

Quantum Glow LED Print 1422381761226


With a new printing method, researchers created high-resolution patterns (left) and shapes (right) of red and green quantum dots, shown in these fluorescence images.
Credit: Nano Letters

Quantum dot LED displays should provide richer colors and use less power than the liquid-crystal displays (LCDs) used in many flat screens, which require filters and polarizers that reduce efficiency and limit color quality. But it’s not yet clear how quantum dot LED displays would be made commercially, says John A. Rogers, a materials scientist at the University of Illinois, Urbana-Champaign.

In 2011, researchers at Samsung made the first full-color quantum dot LED display by using a rubber stamp to pick up and transfer quantum dot inks (Nat. Photonics, DOI: 10.1038/nphoton.2011.12). As a manufacturing strategy, printing from ink nozzles would offer more flexibility to change designs on the fly, without the need for making new transfer stamps. Jet printing also would require less material, Rogers says.

Unfortunately, the resolution of conventional ink-jet printers, which use a heating element to force vapor droplets out of a nozzle, is limited. “It’s hard to get droplets smaller than about 25 µm,” Rogers says, because the smaller the nozzle diameter, the more pressure required to get the droplet out.

So for the past seven years, Rogers has been developing another method called electrohydrodynamic jet printing. This kind of printer works by pulling ink droplets out of the nozzle rather than pushing them, allowing for smaller droplets. An electric field at the nozzle opening causes ions to form on the meniscus of the ink droplet. The electric field pulls the ions forward, deforming the droplet into a conical shape. Then a tiny droplet shears off and lands on the printing surface. A computer program controls the printer by directing the movement of the substrate and varying the voltage at the nozzle to print a given pattern.

The Illinois researchers used this new method, including specialized quantum dot inks, to print lines on average about 500 nm wide. This allowed them to fabricate red and green quantum dot LEDs. They also showed they could carefully control the thickness of the printed film, which is difficult to do with stamp transfer and ink-jet printing methods.

The ultimate resolution possible with these kinds of printers is very high, says David J. Norris, a materials engineer at the Swiss Federal Institute of Technology (ETH), Zurich. Last year, Norris used a similar printing method to print spots containing as few as 10 quantum dots (Nano Lett. 2014, DOI: 10.1021/nl5026997). He says it’s even possible to place single quantum dots using electrohydrodynamic nozzles, albeit with less control and repeatability. Single-particle printing isn’t needed for making pixels for displays, but it is useful for studying other kinds of optical effects in quantum dots, he says.

Chemical & Engineering News
ISSN 0009-2347
Copyright © 2015 American Chemical Society

Demystifying Nanocrystal Solar Cells: Engineering the Solar Cells of the Future

Great Things from Small Things .. Nanotechnology Innovation

QD Solar Cell demystifyingETH researchers have developed a comprehensive model to explain how electrons flow inside new types of solar cells made of tiny crystals. The model allows for a better understanding of such cells and may help to increase their efficiency.

Scientists are focusing on nanometre-sized crystals for the next generation of solar cells. These nanocrystals have excellent optical properties. Compared with silicon in today’s solar cells, nanocrystals can be designed to absorb a larger fraction of the solar light spectrum.

However, the development of nanocrystal-based solar cells is challenging: “These solar cells contain layers of many individual nano-sized crystals, bound together by a molecular glue. Within this nanocrystal composite, the electrons do not flow as well as needed for commercial applications,” explains Vanessa Wood, Professor of Materials and Device Engineering at ETH Zurich. Until now, the physics of electron transport in this complex material system was not understood so it…

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Quantum Dots Combined with Antibodies: Studying Cells in their Native Environment

Great Things from Small Things .. Nanotechnology Innovation

QD Native Cells54c7fd4e425c2To understand cell function, we need to be able to study them in their native environment, in vivo. While there are many techniques for studying cells in vitro, or in the laboratory setting, in vivo studies are much more difficult. A new study by a team of researchers at the Massachusetts Institute of Technology and Harvard Medical School used a unique quantum dot-antibody conjugate to facilitate in vivo studies of bone marrow stem cells in mice. This study was reported in the Proceedings of the National Academy of Science.

Typically, to study a cell in vivo involves making invasive modifications to the cell or the organism that disrupt the cell’s native environment. Additionally, many in vivo studies involve studying groups of cells, rather than tracking a single cell. Prior techniques involved manipulating the cells by immunohistochemistry, genetic engineering, or irradiation of the organism. All of these techniques either create…

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High-Resolution Patterns of Quantum Dots with E-jet printing: Application for High-Def QD Enabled Displays

Great Things from Small Things .. Nanotechnology Innovation

Q Dot E-Jet Printing highresolutiA team of 17 materials science and engineering researchers from the University of Illinois at Urbana−Champaign and Erciyes University in Turkey have authored “High-Resolution Patterns of Quantum Dots are Formed by Electrohydrodynamic Jet Printing for Light-Emitting Diodes.” Their paper was published in Nano Letters, an ACS journal. They demonstrated the materials and operating conditions that allow for high-resolution printing of layers of quantum dots with precise control over thickness and submicron lateral resolution and capabilities, for use as active layers of QD light-emitting diodes.

They wrote, “Patterning QDs with precise control of their thicknesses and nanoscale lateral dimensions represent two critical capabilities for advanced applications. The thickness can be controlled through a combination of printing parameters including the size of the nozzle, the stage speed, ink composition, and voltage bias.”

Their work on high-resolution patterns of quantum dots is of interest as it shows that advanced techniques in “e-jet

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Will “Super – Capacitors” Make Batteries as We Know them Today Obsolete? (Video)

Great Things from Small Things .. Nanotechnology Innovation

Super Capacitors ( TeK-THinK) Batteries , batteries everywhere. From your cell phone and music player to your car or motorcycle. Not to mention your remote controls. Batteries are the weak point of our electronic society. Once a battery is no longer usable it becomes an environmental nightmare to be disposed of properly.

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Crumpled Graphene Oxide Nanocomposites for Advanced Water Treatment

Great Things from Small Things .. Nanotechnology Innovation

Graphene Desal shutterstock_233104066-660x487A scientist from the American Washington University, by the name of John D. Fortner (PhD), received the prestigious Faculty Early Career Development Award (CAREER) from the National Science Foundation (NSF). The five-year, $500,000 award is for his project titled “Development and Application of Crumpled Graphene Oxide-Based Nanocomposites as a Platform Material for Advanced Water Treatment.”

Fortner will aim to develop 3D nanoscale composites made of crumpled graphene oxide as multifunctional platform materials for advanced water treatment technologies. Along with material synthesis and characterization, he plans to develop a range of membrane assemblies for advanced water treatment, including crumpled graphene oxide nanocomposites, which are highly water-permeable, photoreactive and antimicrobial. There is a patent pending for this platform technology.saltwater

Fortner’s research focuses on the environmental implications and applications of advanced materials. He has extensively studied the environmental fate, reactivity and impacts of engineered carbon nanomaterials in aqueous systems. Fortner also is developing nanoscale metal…

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Global Renewable Energy Trends From NREL

Great Things from Small Things .. Nanotechnology Innovation

NREL 20140609_buildings_26954_hpJanuary 26th, 2015  Silvio Marcacci

Accurately assessing renewable energy growth, especially compared to fossil fuels, is one of the biggest challenges facing our clean energy transition. After all, how can you measure progress without adequate benchmarks?

Industry tallies and analyst updates provide the quickest summaries, but they’re either piecemeal or criticized for being slanted. Government data is more reputable and comprehensive, but often lags behind – case in point the National Renewable Energy Laboratory’s (NREL) 2013 Renewable Energy Data Book.

Most of the trends highlighted in NREL’s data are already known, but still this is among the most comprehensive resources available and many of the charts within are incredible reference points. The full report is definitely worth reading, but since most people don’t have time to read through 135 pages, I’ve pulled a few of the most impressive statistics and charts for you.

US renewable electricity generation

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Canada Leads in the Race to Create “Quantum Valley”

Great Things from Small Things .. Nanotechnology Innovation

RThe Institute of Quantum Computing at the University of Waterloo. (PETER POWER/THE GLOBE AND MAIL)AYMOND LAFLAMME ~ Special to the Globe and Mail

My grandfather was born in 1906. It was the year that Romanian inventor Traian Vuia flew a heavier-than-air monoplane with unassisted takeoff for the first time at Montesson in France.

As a child, I remember how my grandfather would sometimes look up at the sky, spotting a plane in flight, and tell me about times that people would flock into the streets to marvel at the first passenger flights.

I would roll my eyes. Quebec City’s airport had been ferrying passengers in and out well before I was born in that city. Planes were, and still are, just part of my world. Something I take for granted.

I’d be willing to bet that Traian Vuia and other aviation pioneers never – even in their wildest dreams – imagined that air travel would become so normal. In far less than…

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