Harvard University and MIT Team Up: New blue-light emitting molecules for amazing displays resolution


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Harvard University researchers have designed more than 1,000 new blue-light emitting molecules for organic light-emitting diodes (OLEDs) that could dramatically improve displays for televisions, phones, tablets and more.

OLED screens use organic molecules that emit light when an electric current is applied. Unlike ubiquitous liquid crystal displays (LCDs), OLED screens don’t require a backlight, meaning the display can be as thin and flexible as a sheet of plastic. Individual pixels can be switched on or entirely off, dramatically improving the screen’s color contrast and energy consumption.

OLEDs are already replacing LCDs in high-end consumer devices but a lack of stable and efficient blue materials has made them less competitive in large displays such as televisions.

The interdisciplinary team of Harvard researchers, in collaboration with MIT and Samsung, developed a large-scale, computer-driven screening process, called the Molecular Space Shuttle, that incorporates theoretical and experimental chemistry, machine learning and cheminformatics to quickly identify new OLED molecules that perform as well as, or better than, industry standards.

“People once believed that this family of organic light-emitting molecules was restricted to a small region of molecular space,” said Alán Aspuru-Guzik, Professor of Chemistry and Chemical Biology, who led the research. “But by developing a sophisticated molecular builder, using state-of-the art machine learning, and drawing on the expertise of experimentalists, we discovered a large set of high-performing blue OLED materials.”

The research is described in the current issue of Nature Materials. The biggest challenge in manufacturing affordable OLEDs is emission of the color blue. Like LCDs, OLEDs rely on green, red and blue subpixels to produce every color on screen.  

But it has been difficult to find organic molecules that efficiently emit blue light. To improve efficiency, OLED producers have created organometallic molecules with expensive transition metals like iridium to enhance the molecule through phosphorescence. This solution is expensive and it has yet to achieve a stable blue color.

 Aspuru-Guzik and his team sought to replace these organometallic systems with entirely organic molecules.

 The team began by building libraries of more than 1.6 million candidate molecules. Then, to narrow the field, a team of researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS), led by Ryan Adams, Assistant Professor of Computer Science, developed new machine learning algorithms to predict which molecules were likely to have good outcomes, and prioritize those to be virtually tested. This effectively reduced the computational cost of the search by at least a factor of ten.

“This was a natural collaboration between chemistry and machine learning,” said David Duvenaud, a postdoctoral fellow in the Adams lab and coauthor of the paper. “Since the early stages of our chemical design process starts with millions of possible candidates, there’s no way for a human to evaluate and prioritize all of them. So, we used neural networks to quickly prioritize the candidates based on all the molecules already evaluated.”

“Machine learning tools are really coming of age and starting to see applications in a lot of scientific domains,” said Adams.  “This collaboration was a wonderful opportunity to push the state of the art in computer science, while also developing completely new materials with many practical applications. It was incredibly rewarding to see these designs go from machine learning predictions to devices that you can hold in your hand.”

“We were able to model these molecules in a way that was really predictive,” said Rafael Gómez-Bombarelli, a postdoctoral fellow in the Aspuru-Guzik lab and first author of the paper.  “We could predict the color and the brightness of the molecules from a simple quantum chemical calculation and about 12 hours of computing per molecule. We were charting chemical space and finding the frontier of what a molecule can do by running virtual experiments.”

“Molecules are like athletes,” Aspuru-Guzik said. “It’s easy to find a runner, it’s easy to find a swimmer, it’s easy to find a cyclist but it’s hard to find all three. Our molecules have to be triathletes. They have to be blue, stable and bright.”

But finding these super molecules takes more than computing power — it takes human intuition, said Tim Hirzel, a senior software engineer in the Department of Chemistry and Chemical Biology and coauthor of the paper.

To help bridge the gap between theoretical modeling and experimental practice, Hirzel and the team built a web application for collaborators to explore the results of more than half a million quantum chemistry simulations.

Every month, Gómez-Bombarelli and coauthor Jorge Aguilera-Iparraguirre, also a postdoctoral fellow in the Aspuru-Guzik lab, selected the most promising molecules and used their software to create “baseball cards,” profiles containing important information about each molecule. This process identified 2500 molecules worth a closer look.  The team’s experimental collaborators at Samsung and MIT then voted on which molecules were most promising for application. The team nicknamed the voting tool “molecular Tinder” after the popular online dating app.

 “We facilitated the social aspect of the science in a very deliberate way,” said Hirzel. “The computer models do a lot but the spark of genius is still coming from people,” said Gómez-Bombarelli. “The success of this effort stems from its multidisciplinary nature,” said Aspuru-Guzik. “Our collaborators at MIT and Samsung provided critical feedback regarding the requirements for the molecular structures.”

“The high throughput screening technique pioneered by the Harvard team significantly reduced the need for synthesis, experimental characterization, and optimization,” said Marc Baldo, Professor of Electrical Engineering and Computer Science at MIT and coauthor of the paper. “It shows the industry how to advance OLED technology faster and more efficiently.”

After this accelerated design cycle, the team was left with hundreds of molecules that perform as well as, if not better than, state-of-the-art metal-free OLEDs. Applications of this type of molecular screening also extend far beyond OLEDs.

“This research is an intermediate stop in a trajectory towards more and more advanced organic molecules that could be used in flow batteries, solar cells, organic lasers, and more,” said Aspuru-Guzik. “The future of accelerated molecular design is really, really exciting.”

In addition to the authors mentioned, the manuscript was coauthored by Dougal Maclaurin, Martin A. Blood-Forsythe, Hyun Sik Chae, Markus Einzinger, Dong-Gwang Ha, Tony Wu, Georgios Markopoulos, Soonok Jeon, Hosuk Kang, Hiroshi Miyazaki, Masaki Numata, Sunghan Kim, Wenliang Huang and Seong Ik Hong.

Reference:

Design of efficient molecular organic light-emitting diodes by a high-throughput virtual screening and experimental approach

Nature Material, Published Online: 8 August 2016, DOI: 10.1038/NMAT4717

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KAUST: Using Graphene Quantum Dots to Get More Energy from the Solar Spectrum


Graphene quantum dots can improve the efficiency of silicon solar cells.

 

A graphene quantum dot (white) on top of a solar cell formed by silicon (Si) insulating (ITO) and metal (Au) layers. 
Reproduced with permission from ref 1. © 2016 American Chemical Society

Small flakes of graphene could1 expand the usable spectral region of light in silicon solar cells to boost their efficiency, new research from KAUST shows1.

Solar cell materials have become significantly cheaper to produce in recent years, yet further cost savings are needed to make solar technologies commercially attractive. The prevalence of silicon in solar cells makes them a good target for efficiency enhancement.

“By improving the efficiency of silicon solar cells, we can provide a more cost-effective way for energy production,” said Jr-Hau He, KAUST associate professor of electrical engineering, who also led the research team.

Graphene quantum dots are small flakes of graphene that are useful because of their interaction with light. One of these interactions is optical downconversion, which is a process that transforms light of high energies into lower energy (for example, from the ultraviolet to the visible).

Downconversion can be used to boost solar cells. Silicon absorbs light very efficiently in the visible part of the spectrum, and therefore appears black. However, the absorption strength of silicon for ultraviolet light is much smaller, meaning that less of this light is absorbed, reducing the efficiency of solar cells in that part of the spectrum.
One way to circumvent this problem is the downconversion of ultraviolet light to energies where silicon is a more efficient absorber.

Graphene quantum dots are ideal candidates for this purpose. They are easy to manufacture using readily-available materials such as sugar and by then heating them with microwave radiation. While the dots are almost transparent to visible light, which is important to pass that light through to the solar cell, they are efficient in converting UV light to lower energies.

The researchers integrated the quantum dots on a silicon solar cell device. The efficiency of the solar cells increased in comparison to control samples. For a mature technology to show a clear improvement in efficiency is promising, because it can be produced using an easy manufacturing process.

The test sample solar cells measured so far have not yet been optimized to be closer to the record-breaking performances seen in silicon. The researchers therefore plan to combine some other enhancement technologies previously achieved in similar devices.
He noted. “We have been successfully utilized surface engineering treatments, including fabricating nanostructures and passivation layers, to improve the light harvesting and the electrical properties of solar cells. By integrating these techniques all together, we hope that in the next few years the world record can be broken at KAUST,” he said.

Reference
Tsai, M.-L., Tu, W.-C., Tang, L., Wei, T.-C., Wei, W.-R., Lau, S.P., Chen, L.-J. & He, J.-H. Efficiency enhancement of silicon heterojunction solar cells via photon management using graphene quantum dot as downconverters. Nano Letters 16, 309−313 (2016).| article

Read Genesis Nanotech Online: Latest Nano-News & Updates


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New ‘ukidama’ nanoparticle structure revealed

MIT: A Big Leap for an Artificial Leaf: Making Liquid Fuel from Sunlight, Water and CO2: Video

The Ups and Downs of Investing in Today’s Energy Tech Startups

Rice University Scientists Create single-molecule-Light Driven “Nano-Submarines” 

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Rice University: Graphene Quantum Dots: The Next Big “Small Thing”


graphenequan 033116A Rice University laboratory has found a way to turn common carbon fiber into graphene quantum dots, tiny specks of matter with properties expected to prove useful in electronic, optical and biomedical applications.

The Rice lab of materials scientist Pulickel Ajayan, in collaboration with colleagues in China, India, Japan and the Texas Medical Center, discovered a one-step chemical process that is markedly simpler than established techniques for making quantum dots. The results were published online this month in the American Chemical Society’s journal Nano Letters.

“There have been several attempts to make graphene-based quantum dots with specific electronic and luminescent properties using chemical breakdown or e-beam lithography of graphene layers,” said Ajayan, Rice’s Benjamin M. and Mary Greenwood Anderson Professor of Mechanical Engineering and Materials Science and of Chemistry. “We thought that as these nanodomains of graphitized carbons already exist in carbon fibers, which are cheap and plenty, why not use them as the precursor?”

Quantum dots, discovered in the 1980s, are semiconductors that contain a size- and shape-dependent . These have been promising structures for applications that range from computers, LEDs, and lasers to medical imaging devices. The sub-5 nanometer carbon-based quantum dots produced in bulk through the wet chemical process discovered at Rice are highly soluble, and their size can be controlled via the temperature at which they’re created.

Graphene quantum dots: The next big small thing
Green-fluorescing graphene quantum dots created at Rice University surround a blue-stained nucleus in a human breast cancer cell. Cells were placed in a solution with the quantum dots for four hours. The dots, each smaller than 5 …more

The Rice researchers were attempting another experiment when they came across the technique. “We tried to selectively oxidize carbon fiber, and we found that was really hard,” said Wei Gao, a Rice graduate student who worked on the project with lead author Juan Peng, a visiting student from Nanjing University who studied in Ajayan’s lab last year. “We ended up with a solution and decided to look at a few drops with a .”

The specks they saw were bits of graphene or, more precisely, oxidized nanodomains of graphene extracted via chemical treatment of carbon fiber. “That was a complete surprise,” Gao said. “We call them quantum dots, but they’re two-dimensional, so what we really have here are graphene quantum discs.” Gao said other techniques are expensive and take weeks to make small batches of graphene quantum dots. “Our starting material is cheap, commercially available . In a one-step treatment, we get a large amount of quantum dots. I think that’s the biggest advantage of our work,” she said.

Graphene quantum dots: The next big small thing
Dark spots on a transmission electron microscope grid are graphene quantum dots made through a wet chemical process at Rice University. The inset is a closeup of one dot. Graphene quantum dots may find use in electronic, optical and …more

Further experimentation revealed interesting bits of information: The size of the dots, and thus their photoluminescent properties, could be controlled through processing at relatively low temperatures, from 80 to 120 degrees Celsius. “At 120, 100 and 80 degrees, we got blue, green and yellow luminescing dots,” she said.

They also found the dots’ edges tended to prefer the form known as zigzag. The edge of a sheet of graphene — the single-atom-thick form of carbon — determines its electrical characteristics, and zigzags are semiconducting.

Their luminescent properties give graphene quantum dots potential for imaging, protein analysis, cell tracking and other , Gao said. Tests at Houston’s MD Anderson Cancer Center and Baylor College of Medicine on two human breast cancer lines showed the dots easily found their way into the cells’ cytoplasm and did not interfere with their proliferation.

“The green quantum dots yielded a very good image,” said co-author Rebeca Romero Aburto, a graduate student in the Ajayan Lab who also studies at MD Anderson. “The advantage of graphene dots over fluorophores is that their fluorescence is more stable and they don’t photobleach. They don’t lose their fluorescence as easily. They have a depth limit, so they may be good for in vitro and in vivo (small animal) studies, but perhaps not optimal for deep tissues in humans.

“But everything has to start in the lab, and these could be an interesting approach to further explore for bioimaging,” Romero Alburto said. “In the future, these graphene could have high impact because they can be conjugated with other entities for sensing applications, too.”

Explore further: Single Atom Quantum Dots Bring Real Devices Closer (Video)

More information: Nano Lett., Article ASAP DOI: 10.1021/nl2038979

Provided by:Rice University

 

Graphene Quantum Dot Based Invisible ink for secret data, product and document security


invisibleink

Ciphers and invisible ink – many of us experimented with these when we were children. A team of Chinese scientists has now developed a clever, high-tech version of “invisible ink”. As reported in the journal Angewandte Chemie, the ink is based on carbon nitride quantum dots. Information written with this ink is not visible under ambient or UV light; however, it can be seen with a fluorescence microplate reader. The writing can be further encrypted or decrypted by quenching or recovering the fluorescence with different reagents.

Fluorescing security inks are primarily used to ensure the authenticity of products or documents, such as certificates, stock certificates, transport documents, currency notes, or identity cards. Counterfeits may cost affected companies lost profits, and the poor quality of the false products may damage their reputations. In the case of sensitive products like pharmaceuticals and parts for airplanes and cars, human lives and health may be endangered. Counterfeiters have discovered how to imitate UV tags but it is significantly harder to copy security inks that are invisible under UV light.
Researchers working with Xinchen Wang and Liangqia Guo at Fuzhou University have now introduced an inexpensive “invisible” ink that increases the security of encoded data while also making it possible to encrypt and decrypt secure information.
The new ink is based on water-soluble quantum dots, nanoscopic “heaps” of a semiconducting material. Quantum dots have special optoelectronic properties that can be controlled by changing the size of the dots.

The scientists used quantum dots made from graphitic carbon nitride. This material consists of ring systems made of carbon and nitrogen atoms linked into two-dimensional molecular layers. The structure is similar to that of graphite (or graphene), one of the forms of pure carbon, but also has semiconductor properties.
Information written with this new ink is invisible under ambient and UV light because it is almost transparent in the visible light range and emits fluorescence with a peak in the UV range. The writing only becomes visible under a microplate reader like those used in biological fluorescence tests. In addition, the writing can be further encrypted and decrypted: treatment with oxalic acid renders it invisible to the microplate reader. Treatment with sodium bicarbonate reverses this process, making the writing visible to the reader once more.
Explore further: Luminescent ink from eggs
More information: Zhiping Song et al. Invisible Security Ink Based on Water-Soluble Graphitic Carbon Nitride Quantum Dots, Angewandte Chemie International Edition (2016). DOI: 10.1002/anie.201510945
Journal reference: Angewandte Chemie Angewandte Chemie International Edition
Provided by: Angewandte Chemie

Catching more of the sun with Quantum Dots and Organic Molecules 


Published online Mar 20, 2016

Combining quantum dots and organic molecules can enable solar cells to capture more of the sun’s light.

Organic molecules aid charge transfer from large lead sulfide quantum dots for improved solar-cell performance. Light from the sun is our most abundant source of renewable energy, and learning how best to harvest this radiation is key for the world’s future power needs.

Researchers at KAUST have discovered that the efficiency of solar cells can be boosted by combining inorganic semiconductor nanocrystals with organic molecules.

Quantum dots are crystals that only measure roughly 10 nanometers across. An electron trapped by the dot has quite different properties from those of an electron free to move through a larger material. “One of the greatest advantages of quantum dots for solar cell technologies is their optical properties’ tunability,” explained KAUST Assistant Professor of Chemical Science Omar Mohammed. “They can be controlled by varying the size of the quantum dot.”

Mohammed and his colleagues are developing lead sulfide quantum dots for optical energy harvesting; these tend to be larger than dots made from other materials.

Accordingly, lead sulfide quantum dots can absorb light over a wider range of frequencies. This means they can absorb a greater proportion of the light from the sun when compared to other smaller dots. To make a fully functioning solar cell, electrons must be able to move away from the quantum dot absorption region and flow toward an electrode. Ironically, the property of large lead sulfide quantum dots that makes them useful for broadband absorption—a smaller electron energy bandgap—also hinders this energy harvesting process.

Previously, efficient electron transfer had only been achieved for lead sulfide quantum dots smaller than 4.3 nanometers across, which caused a cut-off in the frequency of light converted. The innovation by Mohammed and the team was to mix lead sulfide quantum dots of various sizes with molecules from a family known as porphyrins. 

The researchers showed that by changing the porphyrin used, it is possible to control the charge transfer from large lead sulfide dots; while one molecule switched off charge transfer altogether, another one enabled transfer at a rate faster than 120 femtoseconds.

The team believe this improvement in energy harvesting ability is due to the interfacial electrostatic interactions between the negatively charged quantum dot surface and the positively charged porphyrin.
“With this approach, we can now extend the quantum dot size for efficient charge transfer to include most of the near-infrared spectral region, reaching beyond the previously reported cut-off,” stated Mohammed. “We hope next to implement this idea in solar-cells with different architectures to optimize efficiency.”
Reference
El-Ballouli, A. O., Alarousu, E., Kirmani, A. R., Amassian, A., Bakr, O. M. & Mohammed O. F. Overcoming the cut-off charge transfer bandgaps at the PbS quantum dot interface. Advanced Functional Materials 25, 7435–7441 (2015). | article

Nanotechnology: The Science of the Very .. Very Small: Video


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From macrosize to microsize to nanosize: great video for those learning about the potential (and awesomeness) of nanotechnology! (See an Example of ‘Nano-Crystals’ – Quantum Dots – Below). Watch the Video below:

Quantum Dots – An Example of New Nano-Materials

A quantum dot is a semiconductor nanostructure that confines the motion of conduction band electrons, valence band holes, or excitons (bound pairs of conduction band electrons and valence band holes) in all three spatial directions.

 

Small quantum dots, such as colloidal semiconductor nanocrystals, can be as small as 2 to 10 nanometers, corresponding to 10 to 50 atoms in diameter and a total of 100 to 100,000 atoms within the quantum dot volume.

Self-assembled quantum dots are typically between 10 and 50 nm in size.

Quantum dots defined by lithographically patterned gate electrodes, or by etching on two-dimensional electron gases in semiconductor heterostructures can have lateral dimensions exceeding 100 nm.

At 10 nm in diameter, nearly 3 million quantum dots could be lined up end to end and fit within the width of a human thumb.

Current and future applications of QDs impact a broad range of industrial markets. These include, for example:

Biology and biomedicine

Computing and memory

Electronics and displays

Optoelectronic devices such as LEDs, lighting and lasers

Optical components in telecommunications and image sensors

Security applications such as covert identification tagging or biowarfare detection sensors.

The global market for quantum dots (QDs) was estimated to generate $121 million in revenues in 2013. This market is expected to reach about $1.1 billion in 2016 and about $3.1 billion by 2018, at a compound annual growth rate (CAGR) of 90.8% for the five-year period, 2013 to 2018.

 

 

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Reinventing LEDs with nanotechnology


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Lighting is a vital aspect of our existence. Nanotechnology is accelerating the pace of technological advances, shaping our world and lighting.

Technology is evolving at an amazing speed. Every day there are new scientific discoveries, new equipment, new developments in engineering, computer science, medicine, biomedicine, and yes, lighting too.

Lighting is a vital aspect of our existence. However the world is fast running out of natural sources of energy including fossil fuels, meaning the need to find green and efficient lighting sources has become even more important.

Nanotechnology may be a new word to many of us but this technology has accelerated the pace of technological advances, shaping our world. It has also contributed greatly to our electrical industry and now promises to start a new era in lighting.

Nanowhat?

Invented in 1947 – just over 60 years ago – nanoscience or nanotechnology is the study and application of extraordinarily small things and can be used across all the other scientific spheres such as physics, engineering, biology and chemistry. Advances in this field have allowed a huge boost in the development of electronics, IT and telecommunications, and have created all the equipment that we use on a day-to-day basis:  plasma TVs, digital cameras, smartphones, GPS’s, DVD players and recorders, computers, laptops, tablets, and many other gadgets. 

The use of nanotechnology is defined as the ability to see and to manipulate individual molecules and atoms. On Earth everything is made up of atoms — the food we eat, the clothes we wear, the buildings we live and work in, and even our own bodies. So can you see the potential?

The essence of nanotechnology is the ability to create structures with new molecular organization. Today we can build transistors that function by manipulation of individual electrons. Lighting is no exception.

Green lighting will blind you

CFL (compact fluorescent light) and LEDor light emitting diode lights are just two of the most common examples of green lighting sources. Despite that, as new ground is covered in science and technology improves, the use of nanotechnology to increase the efficiency of LED lighting has started to look more of a realistic proposition.

Currently, LED is efficiently replacing lamps and conventional fixtures in external and internal areas. Why? Because LED lighting uses only a small percentage of energy as required by regular bulbs and they don’t contain any toxic metals ( e.g.. mercury) which are used in CFL bulbs. Consequently this makes LED lights more efficient, green, durable, and long lasting.

The standard bulb, for example, only has ten thousand hours of life span. This value was expanded in fluorescent lamps and LED but, on the other hand, these technologies generate a very artificial light, so white that it surpasses what the human eye is naturally prepared for.

That’s why, for example, the LED headlamp of a car can completely obscure the driver’s vision. But nanopower could be the answer.

Nanotech LED Lighting

New nanotechnology can change the rules of how we manipulate light. We can use this to make devices with unprecedented performance.

Passing electrons through nano-semiconductors, also known as ‘quantum dots,’ emits light which has many applications in fields including solar heating and lighting. Therefore there is a huge focus in researching the use of different nanotechnologies to develop more energy efficient LEDs. 

Companies like Nanosys are using semiconductors of remote phosphorous to develop LEDs that turn blue light into a warmer shade of white that is similar to the currently used traditional white of fluorescent bulbs. The phosphorous used in this experiment is created from ‘nano-materials.’

Since human eyes are hyper-sensitive to the colour green, the LEDs have an increased level of green that give us a false sense of brightness, without actually heightening the brightness level of the display.

This helps create an excellent picture quality, but uses only very little energy, making it the primary method to be employed in devices that have display panels.

This is encouraging news for those following the use of nanotechnology in various fields. With this endeavour, Nanosys believes they will be able to design LEDs in just about any colour, which will be a huge leap forward from the current LED displays (as well as in other electronic devices that emit stronger hues).

While the company has created many experimental LED bulbs, these LED quantum dots will firstly be used for notebook displays and TV to offer consumer a wider range of colours. However, a larger range of colours will lead to inferior battery life, especially in case of laptops etc. 

The day when nanocrystals (Quantum Dots) can be ‘painted’ on flat surfaces and create paper-thin displays is not too far from now. We’ll be able to use LED to paint our walls and use any colour of our choice, rather than actual paint. Yes, truly with use nanotech, life is only going to be more exciting and, dare we say it, vibrantly colourful!

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What Are Quantum Dots, and Why Do I Want Them in My TV?


Quantum dots glow a specific color when they are hit with any kind of light. Here, a vial of green quantum dots are activated by a blue LED backlight system.

Quantum dots glow a specific color when they are hit with any kind of light. Here, a vial of green quantum dots are activated by a blue LED backlight system.

If you look at the CES 2015 word cloud—a neon blob of buzz radiating from the Nevada desert, visible from space—much of it is a retweet of last year’s list. Wearables. 4K. The Internet of Things, still unbowed by its stupid name. Connected cars. HDR. Curved everything. It’s the same-old, same-old, huddled together for their annual #usie at the butt-end of a selfie stick.

But there at the margin, ready to photobomb the shot, is the new kid: quantum dot. It goes by other names, too, which is confusing, and we’ll get to that in a minute. Regardless of what you call it, QD was all over CES this year, rubbing shoulders with the 4K crowd. You may have heard people say it’s all hype. Those people can go pound sand. Quantum dot is gonna be the next big thing in TVs‎, bringing better image quality to cheaper sets.

A Quantum-Dot TV Is an LCD TV

The first thing to know is quantum-dot televisions are a new type of LED-backlit LCD TV. The image is created just like it is on an LCD screen, but quantum-dot technology enhances the color.

On an LCD TV, you have a backlight system, which is a bank of LEDs mounted at the edge of the screen or immediately behind it. That light is diffused, directed by a light-guide plate and beamed through a polarized filter. The photons then hit a layer of liquid crystals that either block the light or allow it to pass through a second polarized filter.

Where a Nanosys quantum-dot film sheet (QDEF) fits into an LCD display.

Before it gets to that second polarizer, light passes through a layer of red, blue, and green (and sometimes yellow) color filters. These are the subpixels. Electrical charges applied to the subpixels moderate the blend of colored light visible on the other side. This light cocktail creates the color value of each pixel on the screen.

With a quantum-dot set, there are no major changes to that process. The same pros and cons cited for LCD TVs also apply. You can have full-array backlit quantum-dot sets with local-dimming technology (Translation: good for image uniformity and deeper blacks). There can be edge-lit quantum-dot sets with no local dimming (Translation: thinner, but you may see light banding and grayer blacks). You can have 1080p quantum-dot sets, but you’re more likely to see only 4K quantum-dot sets because of the industry’s big push toward UltraHD/4K resolution.

But a Quantum-Dot TV Is Different

In a quantum-dot set, the changes start with the color of the backlight. The LEDs in most LCD TVs emit white light, but those in quantum-dot televisions emit blue light. Both types actually use blue LEDs, but they’re coated with yellow phosphor in normal LCD televisions and therefore emit white light.

Quantum dots can be arranged along the entire back of the display in a film insert or in a "quantum rail" alongside an edge-lit system. This is QD Vision's quantum rail insert alongside a TCL TV.

Here’s where the quantum dots come in. The blue LED light drives the blue hues of the picture, but red and green light is created by the quantum dots. The quantum dots are either arranged in a tube—a “quantum rail”—adjacent to the LEDs or in a sheet of film atop the light-guide plate.

Quantum dots have one job, and that is to emit one color. They excel at this. When a quantum dot is struck by light, it glows with a very specific color that can be finely tuned. When those blue LEDs shine on the quantum dots, the dots glow with the intensity of angry fireflies.

“Blue is an important part of the spectrum, and it’s the highest-energy portion—greater than red or green,” explains John Volkmann, chief marketing officer at QD Vision, which makes quantum dots for several TVs and monitors. “You start with high energy light and refract it to a lower energy state to create red or green… Starting with red or green would be pushing a rock uphill.”

Quantum dots are tiny, and their size determines their color. There are two sizes of dots in these TVs. The “big” ones glow red, and they have a diameter of about 50 atoms. The smaller ones, which glow green, have a diameter of about 30 atoms. There are billions of them in a quantum-dot TV.

This is a batch of red quantum dots being prepared in a 70-liter vat. It's lit with an ultraviolet flashlight, which is what makes the dots glow red.

If you observed quantum-dot light with a spectrometer, you would see a very sharp and narrow emission peak. Translation: Pure red and pure green light, which travels with the blue light through the polarizers, liquid crystals, and color filters.

Because that colored light is the good stuff, quantum dots have an advantage over traditional LCD TVs when it comes to vivid hues and color gamut. In a normal LCD, white light produced by the LEDs has a wider spectrum. It’s kind of dirty, with a lot of light falling in a color range unusable by the set’s color filters.

“A filter is a very lossy thing,” says Nanosys President and CEO Jason Hartlove. Nanosys makes film-based quantum-dot systems for several products. “When you purify the color using a color filter, then you will get practically no transmission through the filter. The purer the color you start with, the more relaxed the filter function can be. That translates directly to efficiency.”

So with a quantum-dot set, there is very little wasted light. You can get brighter, more-saturated, and more-accurate colors. The sets I saw in person at CES 2015 certainly looked punchier than your average LCD.

That Sounds Expensive

There’s no doubt that quantum-dot TVs will cost more than normal LCDs—especially because they’re likely to be 4K sets. But quantum-dot is getting a lot of buzz because its cheaper than OLED.

In most peoples’ eyes, OLED TVs are the best tech available. But they’re expensive to build and expensive to buy—you’re looking at $3,500 to as much as $20,000—and the manufacturing process differs in several key ways. That’s a big reason LG is the only company putting big money into building them.

Conversely, quantum-dot sets don’t require overhauling the LCD fabrication process, and they produce a much wider color gamut than traditional LCDs. They’re closer to OLED in color performance, and they also can get brighter. That’s important for HDR video.

“The attraction to the OEM is that this is a pure drop-in solution,” says Nanoco CEO Michael Edelman, whose company makes quantum-dot film in a licensing deal with Dow Chemical. “They remove a diffuser sheet in front of the light-guide plate and replace it with quantum-dot film. Nothing in the supply chain gets changed, nothing in the factory gets changed. They get, in some cases, better than OLED-type color at a fraction of the cost.”

As you’d expect, companies making film-based and tube-based solutions are touting each approach as superior. QD Vision claims its tube-based approach is easier and cheaper to implement, and it can boost the color performance of cheaper edge-lit LCD sets. According to QD Vision, the oxygen-barrier film needed for film-based dots is costly, which explains why Nanoco and Nanosys are partnering with Dow and 3M for that film.

Film-based suppliers say their method has the upper hand due to “light coupling,” or the ability to feed all that quantum-dot light directly into a light-guide plate. The film layer also purportedly works better with full-array backlight systems, which will be used in a lot of UHD and HDR TVs.

Super! So This Is OLED for Less Money?

Not entirely. Color gamut is important, but it’s only one aspect of picture quality. Because these are LCD sets, they won’t have the blackest blacks, super-wide viewing angles, and amazing contrast of OLED. And while the extra brightness and saturation makes onscreen colors really pop, all that luminance may create light bleeding.

Here's a sheet of quantum-dot film on top of a blue LED backlight system. The red and green quantum dots combine with blue light to produce a "pure" white that can be efficiently channeled by the set's color filters.

Some quantum dots also contain cadmium, which is toxic at high levels—think “factory emission” levels rather than “sealed tube or film in your TV” levels. Still, there are health and environmental concerns, especially if a bunch of quantum-dot TVs end up in landfills. The European Union restricts the use of cadmium in household appliances. Some quantum-dot producers are marketing their product as cadmium-free. QD Vision, which supplies quantum dots for TCL’s new flagship 4K TV, Sony’s well-reviewed 2013 Triluminos sets, and Philips and AOC monitors, still uses cadmium.

“There are only a couple of materials that deliver on the promise of quantum dots,” says QD Vision’s Volkmann. “The other is based on indium. Cadmium is superior with respect to delivering higher-quality color, meaning a broader color gamut. But also much more energy-efficient at converting blue light to other forms of light that allow you to fill out that spectrum. The folks making indium-based solutions like to paint cadmium as the bad guy… Cadmium is under observation by different regulatory agencies around the world, but it turns out indium is too.”

Nanosys, which produces both cadmium and cadmium-free quantum dots, agrees that cadmium-based dots are more efficient.

“Cadmium-based materials have a narrower spectral width,” says Nanosys’s Hartlove. “More pure color. And what that means is the other things the system has to do in order to keep that color pure, the burden on the rest of the system is reduced.”

Hartlove also says that cadmium may be a greener solution. The cad selenide crystal used in quantum dots isn’t as toxic as pure metallic cadmium, and the efficiency of their color-producing ways has benefits.

“The type of power we generate in the US from coal-based power plants throws cadmium into the atmosphere,” says Hartlove. “That’s one of the byproducts of burning coal. And you look at the net cadmium content over this whole lifecycle, and it turns out that cadmium sequestration is actually net better for the environment.”

Why Isn’t Everybody Calling It “Quantum Dot”?

Each manufacturer with a quantum-dot TV set seemingly has a different name for the technology. Samsung likes “nano-crystal semiconductors.” Sony has new Triluminos TVs that “incorporate the same benefits as quantum dots.” LG, TCL, Hisense, and Changhong are actually calling it quantum dot, which is nice.

“The term quantum dot is generic,” says Hartlove. “Each company kind of wants to grab this for their own and brand it their own way. That will probably lead to some consumer confusion… but I think most of the industry will converge on a way to describe this technology.”

There are slight differences between the technologies everyone’s using, but they’re variations on a theme. The differences center on whether the TVs are edge-lit or back-lit with quantum dots, and whether the systems use cadmium- or indium-based quantum dots.

Who Is Making Quantum Dots?

At this stage, three companies are the big players in the quantum-dot TV landscape.

QD Vision specializes in glass-tube “edge-lit” components, and its systems will be found in TCL TVs and monitors from Philips and AOC. It supplied the quantum-dot component for Sony’s 2013 Triluminos sets, but Sony recently ditched the company in favor of another.

Nanoco focuses on cadmium-free, film-based quantum dot systems. They have a licensing deal with Dow Chemical, and Dow is currently building a factory in South Korea to ramp up production of quantum-dot film. Nanoco’s cadmium-free technology will be found in LG’s quantum-dot TVs in 2015.

Nanosys is another film-based producer that has partnered with 3M on the film-sheet tech. It makes both cadmium-based and cadmium-free quantum dots. They are the company behind Amazon’s HDX 7 display and the Asus Zenbook NX500, and Samsung licenses the cadmium-free quantum-dot tech in its new SUHD 4K sets from Nanosys. Nanosys is also working with Panasonic, Hisense, TCL, Changhong, and Skyworth on future TVs.

When Can I Get One, and What Will It Cost?

The new TVs showcased at CES each year usually start hitting stores in the spring, but some higher-end models don’t arrive until the fall. That’s a little bit of a wait, but it’s probably for the best—there are UltraHD content-delivery complications to work out, anyway.

The TV we know the most about in terms of pricing is TCL’s 55-inch H9700, and we still don’t know much. It’s already available in China for around $2,000 U.S., and TCL representatives at CES hinted that it will be close to that mark when it hits the U.S.

Expect that to be at the low end of the quantum-dot price bracket; LG, Samsung, and Sony generally have pricy TVs, and similar 4K LCDs from last year—minus the quantum dots—went in the $2,000 to $3,000 range for a 55-incher. For this initial wave of quantum-dot TVs, most MSRPs will probably fall between $2,500 to $4,000 for a 55-inch 4K set.

NTU develops ultra-fast charging batteries that last 20 years


NTU 50294NTU develops ultra-fast charging batteries that last 20 years

Singapore | Posted on October 14th, 2014

The new generation batteries also have a long lifespan of over 20 years, more than 10 times compared to existing lithium-ion batteries.

This breakthrough has a wide-ranging impact on all industries, especially for electric vehicles, where consumers are put off by the long recharge times and its limited battery life.

With this new technology by NTU, drivers of electric vehicles could save tens of thousands on battery replacement costs and can recharge their cars in just a matter of minutes.

Commonly used in mobile phones, tablets, and in electric vehicles, rechargeable lithium-ion batteries usually last about 500 recharge cycles. This is equivalent to two to three years of typical use, with each cycle taking about two hours for the battery to be fully charged.

In the new NTU-developed battery, the traditional graphite used for the anode (negative pole) in lithium-ion batteries is replaced with a new gel material made from titanium dioxide.

Titanium dioxide is an abundant, cheap and safe material found in soil. It is commonly used as a food additive or in sunscreen lotions to absorb harmful ultraviolet rays.

Naturally found in spherical shape, the NTU team has found a way to transform the titanium dioxide into tiny nanotubes, which is a thousand times thinner than the diameter of a human hair. This speeds up the chemical reactions taking place in the new battery, allowing for superfast charging.

Invented by Associate Professor Chen Xiaodong from NTU’s School of Materials Science and Engineering, the science behind the formation of the new titanium dioxide gel was published in the latest issue of Advanced Materials, a leading international scientific journal in materials science.

Prof Chen and his team will be applying for a Proof-of-Concept grant to build a large-scale battery prototype. With the help of NTUitive, a wholly-owned subsidiary of NTU set up to support NTU start-ups, the patented technology has already attracted interest from the industry.

The technology is currently being licensed by a company for eventual production. Prof Chen expects that the new generation of fast-charging batteries will hit the market in the next two years. It also has the potential to be a key solution in overcoming longstanding power issues related to electro-mobility.

“Electric cars will be able to increase their range dramatically, with just five minutes of charging, which is on par with the time needed to pump petrol for current cars,” added Prof Chen.

“Equally important, we can now drastically cut down the toxic waste generated by disposed batteries, since our batteries last ten times longer than the current generation of lithium-ion batteries.”

The 10,000-cycle life of the new battery also mean that drivers of electric vehicles would save on the cost of battery replacements, which could cost over US$5,000 each.

Easy to manufacture

According to Frost & Sullivan, a leading growth-consulting firm, the global market of rechargeable lithium-ion batteries is projected to be worth US$23.4 billion in 2016.

Lithium-ion batteries usually use additives to bind the electrodes to the anode, which affects the speed in which electrons and ions can transfer in and out of the batteries.

However, Prof Chen’s new cross-linked titanium dioxide nanotube-based electrodes eliminates the need for these additives and can pack more energy into the same amount of space.

Manufacturing this new nanotube gel is very easy. Titanium dioxide and sodium hydroxide are mixed together and stirred under a certain temperature so battery manufacturers will find it easy to integrate the new gel into their current production processes.

Recognised as the next big thing by co-inventor of today’s lithium-ion batteries

NTU professor Rachid Yazami, the co-inventor of the lithium-graphite anode 30 years ago that is used in today’s lithium-ion batteries, said Prof Chen’s invention is the next big leap in battery technology.

“While the cost of lithium-ion batteries has been significantly reduced and its performance improved since Sony commercialised it in 1991, the market is fast expanding towards new applications in electric mobility and energy storage,” said Prof Yazami, who is not involved in Prof Chen’s research project.

Last year, Prof Yazami was awarded the prestigious Draper Prize by The National Academy of Engineering for his ground-breaking work in developing the lithium-ion battery with three other scientists.

“However, there is still room for improvement and one such key area is the power density – how much power can be stored in a certain amount of space – which directly relates to the fast charge ability. Ideally, the charge time for batteries in electric vehicles should be less than 15 minutes, which Prof Chen’s nanostructured anode has proven to do so.”

Prof Yazami is now developing new types of batteries for electric vehicle applications at the Energy Research Institute at NTU (ERI@N).

This battery research project took the team of four scientists three years to complete. It is funded by the National Research Foundation (NRF), Prime Minister’s Office, Singapore, under its Campus for Research Excellence and Technological Enterprise (CREATE) Programme of Nanomaterials for Energy and Water Management.

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About Nanyang Technological University
A research-intensive public university, Nanyang Technological University (NTU) has 33,500 undergraduate and postgraduate students in the colleges of Engineering, Business, Science and Humanities, Arts, & Social Sciences, It has a new medical school, the Lee Kong Chian School of Medicine, set up jointly with Imperial College London, and also an Interdisciplinary Graduate School.

NTU is home to world-class autonomous institutes – the National Institute of Education, S Rajaratnam School of International Studies, Earth Observatory of Singapore, and Singapore Centre on Environmental Life Sciences Engineering – and various leading research centres such as the Nanyang Environment & Water Research Institute (NEWRI), Energy Research Institute @ NTU (ERI@N) and the Institute on Asian Consumer Insight (ACI).

A fast-growing university with an international outlook, NTU is putting its global stamp on Five Peaks of Excellence: Sustainable Earth, Future Healthcare, New Media, New Silk Road, and Innovation Asia.

Besides the main Yunnan Garden campus, NTU also has a satellite campus in Singapore’s science and tech hub, one-north, and a third campus in Novena, Singapore’s medical district.