March 9, 2017
Perovskite edges can be tuned for optoelectronic performance
Scientists are creating innovative 2D layered hybrid perovskites that allow greater freedom in designing and fabricating efficient optoelectronic devices.
Scientists at Los Alamos National Laboratory and their research partners are creating innovative 2D layered hybrid perovskites that allow greater freedom in designing and fabricating efficient optoelectronic devices.
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Credit: ACS
An organic-inorganic hybrid material may be the future for more efficient technologies that can generate electricity from either light or heat or devices that emit light from electricity.
Florida State University College of Engineering Assistant Professor Shangchao Lin has published a new paper in the journal ACS Nano that predicts how an organic-inorganic hybrid material called organometal halide perovskites could be more mechanically flexible than existing silicon and other inorganic materials used for solar cells, thermoelectric devices and light-emitting diodes.
In a separate study, Lin found that they might be more energy efficient as well.
“We’re addressing this from a theoretical perspective,” Lin said. “Nobody has really looked at the mechanical and thermal properties of this new material and how it could be used.”
Through mathematical simulations, Lin found that organic-inorganic hybrid perovskites should be extremely malleable and flexible. Although plenty of researchers have looked at perovskites for energy technologies, they did not think they were viable for certain devices because of their crystal structure. Scientists thought they would shatter if used for something like a solar panel.
However, Lin found that hybrid perovskites are predicted to fracture slowly through a crystalline-to-amorphous transition, which would make them very damage-tolerant.
Before mechanical failure, they might absorb twice as much elastic energy from external loading than currently used materials in electronic devices, such as silicon and gallium arsenide.
In a previous paper published in the journal Advanced Functional Materials, Lin and his team predicted that hybrid perovskites possess very low thermal conductivity due to the organic component. This could make them ideal materials for high efficiency thermoelectric energy conversion.
Specifically, his work suggested that hybrid perovskites are twice as efficient as the current state-of-art thermoelectric material, bismuth telluride, which is very expensive and composed of rare-earth elements.
“The amazing energy conversion efficiency found in hybrid perovskites has put it at the frontier of material discovery,” Lin said. “Even more exciting, hybrid perovskites-based solar cells are four times as efficient, in terms of quantum yield, than polymer-based ones. They are also as efficient as the current, mainstream silicon-based solar cells but are much more flexible and cheaper to make from a solution phase through a procedure very similar to inkjet printing.”
Read More About: Will New Method of Making Perovskites Solar Cells Make Solar Energy More Efficient – Less Costly?
Lin hopes to follow these two studies by teaming with experimental chemists, material scientists and device engineers who could put his theoretical framework to the test.
“Computational materials-by-design will be a powerful predicting tool for researchers at FSU and at other universities and industry to use as they move forward in this field,” he said.
Explore further: Discovery of new crystal structure holds promise for optoelectronic devices
More information: Mingchao Wang et al. Anisotropic and Ultralow Phonon Thermal Transport in Organic-Inorganic Hybrid Perovskites: Atomistic Insights into Solar Cell Thermal Management and Thermoelectric Energy Conversion Efficiency, Advanced Functional Materials (2016). DOI: 10.1002/adfm.201600284
Jingui Yu et al. Probing the Soft and Nanoductile Mechanical Nature of Single and Polycrystalline Organic–Inorganic Hybrid Perovskites for Flexible Functional Devices, ACS Nano (2016). DOI: 10.1021/acsnano.6b05913
Tubes filled with quantum dots produced in the Lehigh University lab. Credit: Christa Neu/Lehigh University Communications + Public Affairs
Quantum dots (QDs) are semiconducting nanocrystals prized for their optical and electronic properties. The brilliant, pure colors produced by QDs when stimulated with ultraviolet light are ideal for use in flat screen displays, medical imaging devices, solar panels and LEDs. One obstacle to mass production and widespread use of these wonder particles is the difficulty and expense associated with current chemical manufacturing methods that often requiring heat, high pressure and toxic solvents.
But now three Lehigh University engineers have successfully demonstrated the first precisely controlled, biological way to manufacture quantum dots using a single-enzyme, paving the way for a significantly quicker, cheaper and greener production method.
The Lehigh team— Bryan Berger, Class of 1961 Associate Professor, Chemical and Biomolecular Engineering; Chris Kiely, Harold B. Chambers Senior Professor, Materials Science and Engineering and Steven McIntosh, Class of 1961 Associate Professor, Chemical and Biomolecular Engineering, along with Ph.D. candidate Li Lu and undergraduate Robert Dunleavy—have detailed their findings in an article called “Single Enzyme Biomineralization of Cadmium Sulfide Nanocrystals with Controlled Optical Properties” published in theProceedings of the National Academy of Sciences.
“The beauty of a biological approach is that it cuts down on the production needs, environmental burden and production time quite a lot,” says Berger.
In July of last year, the team’s work was featured on the cover of Green Chemistry describing their use of “directed evolution” to alter a bacterial strain called Stenotophomonas maltophilia to selectively produce cadmium sulphide QDs. Because they discovered that a single enzyme produced by the bacteria is responsible for QD generation, the cell-based production route was scrapped entirely. The cadmium sulphide QDs, as they have now shown in the PNAS article, can be generated with the same enzyme synthesized from other easily engineered bacteria such as E. coli.
“We have evolved the enzyme beyond what nature intended,” says Berger, engineering it to not only make the crystal structure of the QDs, but control their size. The result is the ability to uniformly produce quantum dots that emit any particular color they choose—the very characteristic that makes this material attractive for many applications.
Industrial processes take many hours to grow the nanocrystals, which then need to undergo additional processing and purifying steps. Biosynthesis, on the other hand, takes minutes to a few hours maximum to make the full range of quantum dot sizes (about 2 to 3 nanometers) in a continuous, environmentally friendly process at ambient conditions in water that needs no post-processing steps to harvest the final, water-soluble product.
Perfecting the methodology to structurally analyze individual nanoparticles required a highly sophisticated Scanning Transmission Electron Microscope (STEM). Lehigh’s Electron Microscopy and Nanofabrication Facility was able to provide a $4.5 million state-of-the-art instrument that allowed the researchers to examine the structure and composition of each QD, which is only composed of tens to hundreds of atoms.
“Even with this new microscope, we’re pushing the limits of what can be done,” says Kiely.
The instrument scans an ultra-fine electron beam across a field of QDs. The atoms scatter the electrons in the beam, producing a kind of shadow image on a fluorescent screen, akin to the way an object blocking light produces a shadow on the wall. A digital camera records the highly magnified atomic resolution image of the nanocrystal for analysis.
The team is poised to scale-up its laboratory success into a manufacturing enterprise making inexpensive QDs in an eco-friendly manner. Conventional chemical manufacturing costs $1,000 to $10,000 per gram. A biomanufacturing technique could potentially slash the price by at least a factor of 10, and the team estimates yields on the order of grams per liter from each batch culture, says McIntosh.
Taking a long view, the three colleagues hope that their method will lead to a plethora of future QD applications, such as greener manufacturing of methanol, an eco-friendly fuel that could be used for cars, heating appliances and electricity generation. Water purification and metal recycling are two other possible uses for this technology.
“We want to create many different types of functional materials and make large-scale functional materials as well as individual quantum dots,” says McIntosh.
He imagines developing a process by which individual quantum dots arrange themselves into macrostructures, the way nature grows a mollusk shell out of individual inorganic nanoparticles or humans grow artificial tissue in a lab.
“If we’re able to make more of the material and control how it’s structured while maintaining its core functionality, we could potentially get a solar cell to assemble itself with quantum dots.”
Explore further: Robust approach for preparing polymer-coated quantum dots
More information: Robert Dunleavy et al, Single-enzyme biomineralization of cadmium sulfide nanocrystals with controlled optical properties, Proceedings of the National Academy of Sciences (2016).DOI: 10.1073/pnas.1523633113
Tubes filled with quantum dots, which emit many different crisp, dramatic colors under LED lights making them desirable for use in flat-screen displays and medical imaging devices
MAY 5, 2016
*** Re-Post from NY Times
CHRISTA NEU / LEHIGH UNIVERSITY
Over the past few years, screen manufacturers have become obsessed with the potential of tiny crystals known as quantum dots.
The idea is that a quantum dot television or cellphone may offer sharper and brighter images for less money. There was talk that Apple would release an iMac with a quantum dot screen last year.
But then the company switched course, declaring that the existing process for making these little crystals was too toxic to the environment. Samsung offers its SUHD TV with environmentally friendlier quantum dot technology, but it’s not cheap.
In a study published in Proceedings of the National Academy of Sciences last week, five chemical engineers at Lehigh University outline a simpler and more environmentally friendly way to create the dots: Feed some metal to a single enzyme extracted from bacteria. The colorful vials, pictured above, are filled with the little dots grown in a lab at Lehigh through this cost-effective method.
Under LED lights, the little crystals, which can generate both electricity and colored light, glow like plastic pegs on a Lite-Brite screen.
Bryan Berger, a co-author of the study, stumbled across this alternative for creating the little dots through an unintended sequence of events. It began when an alarmed hospital staff in Pennsylvania discovered a superbug growing on metal surfaces in 2011.
Doctors and nurses were worried: Stenotrophomonas maltophila, or steno, as the bacteria is called, can potentially cause bad infections in immune-compromised patients, and few antibiotics can kill it.
So they asked Dr. Berger, a chemical engineer at nearby Lehigh, to find out why the bacteria seemed to thrive on metal.
What Dr. Berger found surprised him. The microbe appeared to be taking in electrical charges, presumably from the metal surfaces, and spitting out clusters of tiny, metallic particles.
Dr. Berger did not know how to halt the superbug, but what he saw sparked his imagination. Could this same bacteria that was spitting out metal be re-engineered as a mini-crystal-generating machine?
Inside glassware under ultraviolet light, quantum dots glow in every spectrum of the rainbow. A new way of creating them may make televisions and cellphones better and cheaper.
The answer was yes.
“As an engineer, it’s extremely exciting, but as a medical scientist, it’s extremely scary,” Dr. Berger said.
He and his colleagues found that within a few minutes of feeding the metal cadmium to the steno bacteria — bam — they had created quantum dots.
They published those findings last year. The problem was that they were using a potentially infectious bug to create the dots. What’s significant about the new study is that Dr. Berger and his colleagues Steve McIntosh and Chris Kiely discovered that they didn’t need the bacteria after all; they could make the dots with a single enzyme inside it.
Quantum dot screens are still a long way from becoming as commonplace as LED screens because they have been expensive and messy to make.
Existing methods can require temperatures as high as 300 degrees Celsius, or 572 degrees Fahrenheit; oily organic solvents that can cause pollution; and costly facilities to make it all happen.
Dr. Berger and his colleagues created their multisize nanocrystals with one enzyme, in water at room temperature. It’s safer, more environmentally friendly and much cheaper than previous approaches, they say. It’s also possible to control the size of the crystals, which determines the color of their light, as you can see above.
Does this mean that sometime soon quantum dot TVs will become much more affordable?
Warren Chan, a biomedical engineer at the University of Toronto who has been synthesizing quantum dots for decades and was not involved in the study, said that’s unlikely with these particular dots.
While he agreed that safer and cheaper production is ideal, these easy-to-make dots aren’t going to be as crisp or as bright as the ones made with previous processes, he said. That means that while they may address Apple’s concerns about toxicity, they won’t meet its other needs — just yet.
But they could be helpful in other ways. Quantum dots are already being developed in medical imaging to tag tumors and identify diseases, and are being closely watched by manufacturers of green energy, for their potential to boost the efficiency of solar cells.
These new dots, if they can be engineered to be even brighter, may have applications there. But that’s a big if.
So what happened at the hospital? Dr. Berger is still trying to figure out how to prevent the superbug’s ability to colonize metal surfaces.
Single nanocrystal spectroscopy identifies the interaction between zero-dimensional CdSe/ZnS nano crystals (quantum dots) and two-dimensional layered tin disulfide as a non-radiative energy transfer, whose strength increases with increasing …more
Harnessing the power of the sun and creating light-harvesting or light-sensing devices requires a material that both absorbs light efficiently and converts the energy to highly mobile electrical current. Finding the ideal mix of properties in a single material is a challenge, so scientists have been experimenting with ways to combine different materials to create “hybrids” with enhanced features.
In two just-published papers, scientists from the U.S. Department of Energy’s Brookhaven National Laboratory, Stony Brook University, and the University of Nebraska describe one such approach that combines the excellent light-harvesting properties of quantum dots with the tunable electrical conductivity of a layered tin disulfide semiconductor.
The hybrid material exhibited enhanced light-harvesting properties through the absorption of light by the quantum dots and their energy transfer to tin disulfide, both in laboratory tests and when incorporated into electronic devices. The research paves the way for using these materials in optoelectronic applications such as energy-harvesting photovoltaics, light sensors, and light emitting diodes (LEDs).
According to Mircea Cotlet, the physical chemist who led this work at Brookhaven Lab’s Center for Functional Nanomaterials (CFN), a DOE Office of Science User Facility, “Two-dimensional metal dichalcogenides like tin disulfide have some promising properties for solar energy conversion and photodetector applications, including a high surface-to-volume aspect ratio. But no semiconducting material has it all. These materials are very thin and they are poor light absorbers. So we were trying to mix them with other nanomaterials like light-absorbing quantum dots to improve their performance through energy transfer.”
One paper, just published in the journal ACS Nano, describes a fundamental study of the hybrid quantum dot/tin disulfide material by itself. The work analyzes how light excites the quantum dots (made of a cadmium selenide core surrounded by a zinc sulfide shell), which then transfer the absorbed energy to layers of nearby tin disulfide.
“We have come up with an interesting approach to discriminate energy transfer from charge transfer, two common types of interactions promoted by light in such hybrids,” said Prahlad Routh, a graduate student from Stony Brook University working with Cotlet and co-first author of the ACS Nano paper. “We do this using single nanocrystal spectroscopy to look at how individual quantum dots blink when interacting with sheet-like tin disulfide. This straightforward method can assess whether components in such semiconducting hybrids interact either by energy or by charge transfer.”
The researchers found that the rate for non-radiative energy transfer from individual quantum dots to tin disulfide increases with an increasing number of tin disulfide layers. But performance in laboratory tests isn’t enough to prove the merits of potential new materials. So the scientists incorporated the hybrid material into an electronic device, a photo-field-effect-transistor, a type of photon detector commonly used for light sensing applications.
As described in a paper published online March 24 in Applied Physics Letters, the hybrid material dramatically enhanced the performance of the photo-field-effect transistors-resulting in a photocurrent response (conversion of light to electric current) that was 500 percent better than transistors made with the tin disulfide material alone.
“This kind of energy transfer is a key process that enables photosynthesis in nature,” said Chang-Yong Nam, a materials scientist at Center for Functional Nanomaterials and co-corresponding author of the APL paper. “Researchers have been trying to emulate this principle in light-harvesting electrical devices, but it has been difficult particularly for new material systems such as the tin disulfide we studied. Our device demonstrates the performance benefits realized by using both energy transfer processes and new low-dimensional materials.”
Cotlet concludes, “The idea of ‘doping’ two-dimensional layered materials with quantum dots to enhance their light absorbing properties shows promise for designing better solar cells and photodetectors.”
Explore further: Small size enhances charge transfer in quantum dots
More information: Yuan Huang et al. Hybrid quantum dot-tin disulfide field-effect transistors with improved photocurrent and spectral responsivity, Applied Physics Letters (2016). DOI: 10.1063/1.4944781
Huidong Zang et al. Nonradiative Energy Transfer from Individual CdSe/ZnS Quantum Dots to Single-Layer and Few-Layer Tin Disulfide, ACS Nano (2016). DOI: 10.1021/acsnano.6b01538
Large-area integration of quantum dots, photonic crystals produce brighter and more efficient light.
Recently, quantum dots (QDs)–nano-sized semiconductor particles that produce bright, sharp, color light–have moved from the research lab into commercial products like high-end TVs, e-readers, laptops, and even some LED lighting. However, QDs are expensive to make so there’s a push to improve their performance and efficiency, while lowering their fabrication costs.
Researchers from the University of Illinois at Urbana-Champaign have produced some promising results toward that goal, developing a new method to extract more efficient and polarized light from quantum dots (QDs) over a large-scale area. Their method, which combines QD and photonic crystal technology, could lead to brighter and more efficient mobile phone, tablet, and computer displays, as well as enhanced LED lighting.
With funding from the Dow Chemical Company, the research team, led by Electrical & Computer Engineering (ECE) Professor Brian Cunningham, Chemistry Professor Ralph Nuzzo, and Mechanical Science & Engineering Professor Andrew Alleyne, embedded QDs in novel polymer materials that retain strong quantum efficiency. They then used electrohydrodynamic jet (e-jet) printing technology to precisely print the QD-embedded polymers onto photonic crystal structures. This precision eliminates wasted QDs, which are expensive to make.
These photonic crystals limit the direction that the QD-generated light is emitted, meaning they produce polarized light, which is more intense than normal QD light output.
According to Gloria See, an ECE graduate student and lead author of the research reported in Applied Physics Letters, their replica molded photonic crystals could someday lead to brighter, less expensive, and more efficient displays. “Since screens consume large amounts of energy in devices like laptops, phones, and tablets, our approach could have a huge impact on energy consumption and battery life,” she noted.
“If you start with polarized light, then you double your optical efficiency,” See explained. “If you put the photonic-crystal-enhanced quantum dot into a device like a phone or computer, then the battery will last much longer because the display would only draw half as much power as conventional displays.”
To demonstrate the technology, See fabricated a novel 1mm device (aka Robot Man) made of yellow photonic-crystal-enhanced QDs. The device is made of thousands of quantum dots, each measuring about six nanometers.
“We made a tiny device, but the process can easily be scaled up to large flexible plastic sheets,” See said. “We make one expensive ‘master’ molding template that must be designed very precisely, but we can use the template to produce thousands of replicas very quickly and cheaply.”
Story Source:
The above post is reprinted from materials provided by University of Illinois College of Engineering. The original item was written by Laura Schmitt. Note: Materials may be edited for content and length.
Journal Reference:
The first graphene quantum dot light-emitting diodes (GQD-LEDs), fabricated by using high-quantum-yield graphene quantum dots through graphite intercalation compounds, exhibit luminance in excess of 1,000 cd/m2.
Graphene is a 2D carbon nanomaterial with many fascinating properties that can enable to creation of next-generation electronics. However, it is known that graphene is not applicable to optical devices due to its lack of an electronic band gap. On the other hand, graphene quantum dots (GQDs), which are merely a few nanometers large in the lateral dimension, are shown to emit light upon excitation in the visible spectral range. The GQDs have attracted a great deal of attention as a next-generation luminescent material for their outstanding properties: tunable luminescence, superior photostability, low toxicity, and chemical resistance.
Recently, Prof. Seokwoo Jeon (Material Science and Engineering), Prof. Yong-Hoon Cho (Physics), and Prof. Seunghyup Yoo (Electrical Engineering) have succeeded in developing LEDs based on graphene quantum dots. Highly pure GQDs were synthesized by an environmentally-friendly method designed by Prof. Jeon’s group, their light-emitting mechanisms were carefully studied by Prof. Cho’s group with their transient spectroscopic technique, and finally Prof. Yoo’s group brought their OLED expertise to create GQD-based LEDs.
Electroluminescent images of GQD-LEDs (left) and luminescence efficiency of GQD-LEDs (right). Credit: KAIST
The GQDs with high luminance tunability and efficiency were synthesized by a route based on graphite intercalation compounds (GICs). The proposed method is cost-effective, eco-friendly, and scalable, as it allows direct fabrication of GQDs using water without surfactant or chemical solvent.
GQDs were then used as emitters in organic light-emitting diodes (OLEDs) in order to identify the GQD’s key optical properties. After carefully designing the layer configuration so that electron and hole injection could be balanced, the constructed GQD LEDs exhibited luminance of 1,000 cd/m2, which is well over the typical brightness levels of the portable displays used in smartphones. Considering how thin GQDs are, a foldable paper-like display could soon become a reality.
The present work, for the first time, demonstrated that GQDs can be applied to optical devices by fabricating GQD-based LEDs with meaningful brightness. Although, the efficiency of GQD-based LEDs is currently less than those of conventional LEDs, they are expected to improve in the near future with an optimized material process and device structure.
This research was published as a cover article in Advanced Optical Materials (Vol.2, 1016-1023 (2014)), a premier journal that features significant advances in optical materials and devices based upon them.
Explore further: Cheap hybrid outperforms rare metal as fuel-cell catalyst
Bringing better pixels to UHD with Quantum Dots
The next wave of market push for TVs is Ultra-High Definition. The increase in resolution from HD to 4K is perhaps the most well known benefit of UHD but there is much more to this new broadcast specification. High dynamic range (HDR) and wide color gamut bring more perceptible benefits to users in terms of an improved viewing experience than improved resolution alone. The ultra-high color gamut standard Rec. 2020 was originally defined for laser-based projectors where the color primaries are on the color locus of the CIE diagram. Because of the deeply saturated color coordinates, Rec. 2020 is beyond the capabilities of OLEDs. Is the Rec. 2020 color standard reachable for consumer displays or is it only for high-end laser-based projection systems? This presentation explores the capability of using quantum dots in LCDs to reach the ultra-high color gamut of Rec. 2020.
For more information on Nanosys, visit: http://www.nanosysinc.com
For more information on the Quantum Dot Forum visit: http://www.quantumdotsforum.com
SAN MARCOS, Texas, Feb. 5, 2015 /PRNewswire/ — Rapidly growing North American quantum dot manufacturer Quantum Materials Corp (OTCQB:QTMM) today announced it has begun shipping Cadmium-free red and green quantum dots in evaluation and production quantities to select leading consumer electronics manufacturers.
The company has increased the uniformity and enhanced stability of its Cadmium-free nanomaterials as a result of bringing previously-reported automated capital equipment, facility and personnel investments online. Quantum Materials is at the forefront of Cadmium-free quantum dot development and recently announced increasing production capacity to 2000Kg of quantum dots and nanoparticles per annum in Q2 2015.
Meetings with manufacturers at the 2015 Consumer Electronics Show (CES) spurred requests for Cadmium-free red and green quantum dots with application-specific functionality. Quantum Materials has accelerated Cadmium-free quantum dot development because electronics manufacturers’ are seeking to stay ahead of environmental regulations governing dangerous materials in consumer electronic devices. Quantum dots are easily integrated into the industry-standard thin-film roll-to-roll inkjet and surface deposition technologies currently used in existing LCD display production lines, as illustrated in an informative video* detailing Cadmium-free quantum dot uses and benefits.
“We were very encouraged with the results of our meetings at CES,” said Quantum Materials Corp CEO Stephen Squires. “I personally am even more pleased with the dedication, hard work and creativity of our team. Their discoveries have enabled us to meet the stringent demands and tight delivery deadlines necessary to rapidly integrate our materials into commercial products.”
The U.S. leads the world in nanotechnology innovation with over $30 billion invested in research to date. Quantum Materials is working with manufacturers toward integrating its advanced materials into commercial products that will create jobs, generate profits, and strengthen our economy and balance of payments. The limited industrial availability of a reliable supply of Cadmium-free quantum dots has attracted the interest of the world’s largest display and solid-state lighting manufacturers in evaluating Quantum Materials mass-production capability.
Quantum Materials’ products are the foundation for technologically superior, energy efficient and environmentally sound LCD UHD displays, the next generation of solid-state lighting, solar photovoltaic power applications, advanced battery and energy storage solutions, biotech imaging, and biomedical theranostics.
*High Definition Video available for download by broadcast outlets at http://bit.ly/1KhSS9i for use with attribution.
About Quantum Materials Corp
Quantum Materials Corp develops and manufactures Quantum Dots and nanomaterials for use in medical, display, solar energy and lighting applications through its patent-pending volume production process. QMC’s volume manufacturing methods enable consistent quality and scalable cost reductions to drive innovative discovery to commercial success. Wholly-owned subsidiary Solterra Renewable Technologies develops sustainable quantum dot solar technology.
Safe Harbor statement under the Private Securities Litigation Reform Act of 1995
This press release contains forward-looking statements that involve risks and uncertainties concerning business, products, and financial results. Actual results may differ materially from the results predicted. More information about potential risk factors that could affect our business, products, and financial results are included in our annual report and in reports subsequently filed with the Securities and Exchange Commission (“SEC”). All documents are available through the SEC’s EDGAR System at http://www.sec.gov/ or www.QMCdots.com. We hereby disclaim any obligation to publicly update the information provided above, including forward-looking statements, to reflect subsequent events or circumstances.
Published in the scientific journal Nature Materials, University of Manchester and University of Sheffield researchers show that new 2D ‘designer materials’ can be produced to create flexible, see-through and more efficient electronic devices.
The team, led by Nobel Laureate Sir Kostya Novoselov, made the breakthrough by creating LEDs which were engineered on an atomic level.
The new research shows that graphene and related 2D materials could be utilised to create light emitting devices for the next-generation of mobile phones, tablets and televisions to make them incredibly thin, flexible, durable and even semi-transparent.
The LED device was constructed by combining different 2D crystals and emits light from across its whole surface. Being so thin, at only 10-40 atoms thick, these new components can form the basis for the first generation of semi-transparent smart devices.
One-atom thick graphene was first isolated and explored in 2004 at The University of Manchester. Its potential uses are vast but one of the first areas in which products are likely to be seen is in electronics. Other 2D materials, such as boron nitiride and molybdenum disulphide, have since been discovered opening up vast new areas of research and applications possibilities.
By building heterostructures – stacked layers of various 2D materials – to create bespoke functionality and introducing quantum wells to control the movement of electrons, new possibilities for graphene based optoelectronics have now been realised.
Freddie Withers, Royal Academy of Engineering Research Fellow at The University of Manchester, who led the production of the devices, said: “As our new type of LED’s only consist of a few atomic layers of 2D materials they are flexible and transparent. We envisage a new generation of optoelectronic devices to stem from this work, from simple transparent lighting and lasers and to more complex applications.”
Explaining the creation of the LED device Sir Kostya Novoselov said: “By preparing the heterostructures on elastic and transparent substrates, we show that they can provide the basis for flexible and semi-transparent electronics.
“The range of functionalities for the demonstrated heterostructures is expected to grow further on increasing the number of available 2D crystals and improving their electronic quality.”
Prof Alexander Tartakovskii, from The University of Sheffield added: “The novel LED structures are robust and show no significant change in performance over many weeks of measurements.
“Despite the early days in the raw materials manufacture, the quantum efficiency (photons emitted per electron injected) is already comparable to organic LEDs.”
Explore further: Beyond graphene: Controlling properties of 2D materials
More information: Light-emitting diodes by band-structure engineering in van der Waals heterostructures, DOI: 10.1038/nmat4205
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