Monthly Archives: January 2013
World record for battery storage set with nanoparticles
30 January 2013 (created 30 January 2013)
Lithium-ion batteries work by moving lithium ions back and forth between two electrodes, the cathode and anode. Charging the battery forces the ions and electrons into the anode, creating an electrical potential that can power a wide range of devices. Discharging the battery – using it to do work – moves the ions and electrons to the cathode. Today’s lithium-ion batteries typically retain about 80 percent of their initial capacity after 500 charge/discharge cycles.
Cui’s innovation is a cathode made of nanoparticles, each a tiny sulfur nugget surrounded by a hard shell of porous titanium dioxide, like an egg yolk in an eggshell. Between the yolk and shell, where the egg white would be, is an empty space into which the sulfur can expand. During discharging, lithium ions pass through the shell and bind to the sulfur, which expands to fill the void but not so much as to break the shell. The shell, meanwhile, protects the sulfur-lithium intermediate compound from electrolyte solvent that would dissolve it.
Over the past seven years, Cui’s group has demonstrated a succession of increasingly capable anodes that use silicon rather than carbon because it can store up to 10 times more charge per weight. Their most recent anode also has a yolk-shell design that retains its energy-storage capacity over 1,000 charge/discharge cycles.
The group’s next step is to combine the yolk-shell sulfur cathode with a yolk-shell silicon anode to see if together they produce a high-energy, long-lasting battery. Source: From Egg-cellent World-record Battery Performance by Mike Ross. This work is detailed in the paper “Sulphur–TiO2 yolk–shell nanoarchitecture with internal void space for long-cycle lithium–sulphur batteries” by Zhi Wei Seh, Weiyang Li, Judy J. Cha, Guangyuan Zheng, Yuan Yang, Matthew T. McDowell, Po-Chun Hsu & Yi Cui.
Researchers can deliver RNA, proteins and nanoparticles for many applications
How to squeeze large molecules into cells
January 28, 2013
As cells squeeze through a narrow channel, tiny holes open in their membranes, allowing large molecules such as RNA to pass through (credit: Armon Sharei and Emily Jackson)
Living cells are surrounded by a membrane that tightly regulates what gets in and out of the cell. This barrier is necessary for cells to control their internal environment, but it makes it more difficult for scientists to deliver large molecules such as nanoparticles for imaging, or proteins that can reprogram them into pluripotent stem cells.
Researchers from MIT have now found a safe and efficient way to get large molecules through the cell membrane, by squeezing the cells through a narrow constriction that opens up tiny, temporary holes in the membrane. Any large molecules floating outside the cell — such as RNA, proteins or nanoparticles — can slide through the membrane during this disruption.
Using this technique, the researchers were able to deliver reprogramming proteins and generate induced pluripotent stem cells with a success rate 10 to 100 times better than any existing method. They also used it to deliver nanoparticles, including carbon nanotubes and quantum dots, which can be used to image cells and monitor what’s happening inside them.
“It’s very useful to be able to get large molecules into cells. We thought it might be interesting if you could have a relatively simple system that could deliver many different compounds,” says Klavs Jensen, the Warren K. Lewis Professor of Chemical Engineering, professor of materials science and engineering, and a senior author of a paper describing the new device in the Proceedings of the National Academy of Sciences.
Robert Langer, the David H. Koch Institute Professor at MIT, is also a senior author of the paper. Lead authors are chemical engineering graduate student Armon Sharei, Koch Institute research scientist Janet Zoldan, and chemical engineering research associate Andrea Adamo.
The new MIT system appears to work for many cell types — so far, the researchers have successfully tested it with more than a dozen types, including both human and mouse cells. It also works in cells taken directly from human patients, which are usually much more difficult to manipulate than human cell lines grown specifically for lab research.
The new device builds on previous work by Jensen and Langer’s labs, in which they used microinjection to force large molecules into cells as they flowed through a microfluidic device. This wasn’t as fast as the researchers would have liked, but during these studies, they discovered that when a cell is squeezed through a narrow tube, small holes open in the cell membrane, allowing nearby molecules to diffuse into the cell.
To take advantage of that, the researchers built rectangular microfluidic chips, about the size of a quarter, with 40 to 70 parallel channels. Cells are suspended in a solution with the material to be delivered and flowed through the channel at high speed — about one meter per second. Halfway through the channel, the cells pass through a constriction about 30 to 80 percent smaller than the cells’ diameter. The cells don’t suffer any irreparable damage, and they maintain their normal functions after the treatment.
The research team is now further pursuing stem cell manipulation, which holds promise for treating a wide range of diseases. They have already shown that they can transform human fibroblast cells into pluripotent stem cells, and now plan to start working on delivering the proteins needed to differentiate stem cells into specialized tissues.
Another promising application is delivering quantum dots — nanoparticles made of semiconducting metals that fluoresce. These dots hold promise for labeling individual proteins or other molecules inside cells, but scientists have had trouble getting them through the cell membrane without getting trapped in endosomes.
In a paper published in November, working with MIT graduate student Jungmin Lee and chemistry professor Moungi Bawendi, the researchers showed that they could get quantum dots inside human cells grown in the lab, without the particles becoming confined in endosomes or clumping together. They are now working on getting the dots to tag specific proteins inside the cells.
The researchers are also exploring the possibility of using the new system for vaccination. In theory, scientists could remove immune cells from a patient, run them through the microfluidic device and expose them to a viral protein, and then put them back in the patient. Once inside, the cells could provoke an immune response that would confer immunity against the target viral protein.
The research was funded by the National Institutes of Health and the National Cancer Institute.
New 2-D Material for Next Generation High-Speed Electronics
Jan. 21, 2013 — Scientists at CSIRO and RMIT University have produced a new two-dimensional material that could revolutionise the electronics market, making “nano” more than just a marketing term.
The material — made up of layers of crystal known as molybdenum oxides — has unique properties that encourage the free flow of electrons at ultra-high speeds.
In a paper published in the January issue of materials science journal Advanced Materials, the researchers explain how they adapted a revolutionary material known as graphene to create a new conductive nano-material.
Graphene was created in 2004 by scientists in the UK and won its inventors a Nobel Prize in 2010. While graphene supports high speed electrons, its physical properties prevent it from being used for high-speed electronics.
The CSIRO’s Dr Serge Zhuiykov said the new nano-material was made up of layered sheets — similar to graphite layers that make up a pencil’s core.
“Within these layers, electrons are able to zip through at high speeds with minimal scattering,” Dr Zhuiykov said.
“The importance of our breakthrough is how quickly and fluently electrons — which conduct electricity — are able to flow through the new material.”
RMIT’s Professor Kourosh Kalantar-zadeh said the researchers were able to remove “road blocks” that could obstruct the electrons, an essential step for the development of high-speed electronics.
“Instead of scattering when they hit road blocks, as they would in conventional materials, they can simply pass through this new material and get through the structure faster,” Professor Kalantar-zadeh said.
“Quite simply, if electrons can pass through a structure quicker, we can build devices that are smaller and transfer data at much higher speeds.
“While more work needs to be done before we can develop actual gadgets using this new 2D nano-material, this breakthrough lays the foundation for a new electronics revolution and we look forward to exploring its potential.”
In the paper titled ‘Enhanced Charge Carrier Mobility in Two-Dimensional High Dielectric Molybdenum Oxide,’ the researchers describe how they used a process known as “exfoliation” to create layers of the material ~11 nm thick.
The material was manipulated to convert it into a semiconductor and nanoscale transistors were then created using molybdenum oxide.
The result was electron mobility values of >1,100 cm2/Vs — exceeding the current industry standard for low dimensional silicon.
The work, with RMIT doctoral researcher Sivacarendran Balendhran as the lead author, was supported by the CSIRO Sensors and Sensor Networks Transformational Capability Platform and the CSIRO Materials Science and Engineering Division.
It was also a result of collaboration between researchers from Monash University, University of California — Los Angeles (UCLA), CSIRO, Massachusetts Institute of Technology (MIT) and RMIT.
Major Breakthroughs in Solar Technology for 2013
Despite a tough market leading to widespread cost reductions and negative returns for many operators in the photovoltaic sector in 2012, solar technology nonetheless took major strides and achieved a number of landmark breakthroughs in key research areas.
In materials research, the North Carolina State University (NCSU) in Raleigh, North Carolina used cutting-edge nanotechnology to develop slimmer and more affordable solar cells.
The cells are comprised of sandwiched nanostructures which not only cut down on material usage and expenditures but also improve solar absorption and raise conversion efficiency.
As an added bonus, the manufacturing processes for the new technology are compatible with techniques currently employed throughout the industry for the production of thin-film solar cells.
In terms of government-funded initiatives, the National Renewable Energy Laboratory (NREL), a research arm of the US Department of Energy, teamed up with Natcore Technology to create the most absorbent solar cell ever devised, capable of capturing some 99.7 per cent of available sunlight.
In the field of flexible thin-film cells, a joint undertaking between scientists from Canada and Saudi Arabia smashed the world record for solar efficiency, surpassing the ousted place holder by a staggering 37 per cent. The colloidal quantum dot (CQD) thin-film solar cell, developed by scientists from Canada’s University of Toronto and the King Abdullah University of Science & Technology in Saudi Arabia, achieved a world-record efficiency level of seven per cent via the application of a “hybrid passivation scheme.”
The new technology could potentially be applied to the cheap, mass manufacture of thin-film solar cells by using flexible substrates to “print” the devices in a process akin to that traditionally employed for the production of newspapers.
Dow Chemical and NANOCO Enter Into Agreement for Quantum Dots
Dow to sell, market and manufacture cadmium-free quantum dots for LCD displays
Philadelphia, PA and Manchester, UK,January 23, 2013 – Dow Electronic Materials, a business unit of The Dow Chemical Company (NYSE: DOW) and Nanoco Group plc (AIM: NANO) today announced they have entered into a global licensing agreement for Nanoco’s cadmium-free quantum dot technology. Under the terms of the agreement, Dow Electronic Materials will have exclusive worldwide rights for the sale, marketing and manufacture of Nanoco’s cadmium-free quantum dots for use in electronic displays.
The agreement brings together Nanoco’s world-leading technology with Dow’s large-scale manufacturing capability and well-established sales, marketing and distribution network. Dow Electronic Materials is already a major supplier of critical electronic materials to the global display industry.
The financial details of the agreement are not being disclosed though Nanoco will receive royalty payments related to Dow’s sales of cadmium-free quantum dots. Nanoco will continue to provide any technology advances to its cadmium-free quantum dot technology throughout the lifetime of the agreement and participate with Dow in the marketing and technical support of these materials.
Dow intends to build production capacity in Asia where it has extensive manufacturing capabilities to supply high-performance materials to its customers in the display and semiconductor-related segments. Full commercial production is expected to begin in the first half of 2014.
“We believe that Nanoco’s cadmium-free quantum dots will become a new standard in the display industry owing to their ability to significantly improve the color performance of LCD displays both cost-effectively and by avoiding the use of heavy metals,” said C.G. Park, Global Business Director, Dow Electronic Materials. “When coupled with Nanoco’s technology, Dow’s deep technical, engineering and industry knowledge in films, LCD, LED, and OLED display segments brings our customers an unmatched portfolio of materials solutions.”
Michael Edelman, Nanoco’s Chief Executive Officer, commented: “We are delighted to sign this agreement with Dow Electronic Materials. This agreement is transformational for the quantum dot industry and a significant endorsement of Nanoco’s cadmium-free quantum dot technology. With Dow’s production expertise and deep customer relationships, display makers can begin to plan their quantum dot production requirements with further confidence.”
Graphene quantum dots: The next big small thing
Rice University-led team creates tiny materials in bulk from carbon fiber
This transmission electron microscope image shows a graphene quantum dot with zigzag edges. The quantum dots can be created in bulk from carbon fiber through a chemical process discovered at Rice University.
A 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 graphene 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 band gap. These have been promising structures for applications that range from computers, LEDs, solar cells 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.
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
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 nanometers, easily passed through the cell membranes, showing their potential value for bio-imaging.
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 transmission electron microscope.”
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 carbon fiber. 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.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 biomedical applications, 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 cytoplasm and did not interfere with the cells’ 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.
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 close-up of one dot. Graphene quantum dots may find use in electronic, optical and biomedical applications.
“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 quantum dots could have high impact because they can be conjugated with other entities for sensing applications, too.”
Co-authors include Angel Martí, a professor of chemistry and bioengineering, postdoctoral research associates Zheng Liu and Liehui Ge, senior research scientist Lawrence Alemany and graduate student Xiaobo Zhan, all of Rice; Rice alumnus Li Song of Shinshu University, Japan; Bipin Kumar Gupta of the National Physical Laboratory, New Delhi, who worked at the Ajayan lab on an Indo-US Science and Technology Forum fellowship; Guanhui Gao of the Ocean University of China; Sajna Antony Vithayathil, a research technician, and Benny Abraham Kaipparettu, a postdoctoral researcher, both at Baylor College of Medicine; Takuya Hayashi, an associate professor of engineering at Shinshu University, Japan; and Jun-Jie Zhu, a professor of chemistry at Nanjing University.
The research was supported by Nanoholdings, the Office of Naval Research MURI program on graphene, the Natural Science Foundation of China, the National Basic Research Program of China, the Indo-US Science and Technology Forum and the Welch Foundation.
Adoption by TV makers Expands Market for light-emitting nanocrystals. (Quantum Dot’s)
Sony has announced that it will embed quantum dots in its latest flat-screen televisions.
Live from your living room, in supersaturated colour: it’s the quantum-dot TV! Researchers working with nanoscale fluorescent particles called quantum dots have long predicted groundbreaking achievements, such as ultra-efficient light-emitting diodes (LEDs) and solar cells, but the technology has found mainly niche applications. That could change with the announcement last week that QD Vision, based in Lexington, Massachusetts, would supply Sony Corporation of Tokyo with quantum dots for flat-screen televisions that will transmit more richly coloured images than other TVs on the market.
Demand for quantum-dot displays, say industry watchers, could benefit quantum-dot companies, bring down the price of these nanomaterials and boost other applications that have stalled. “Displays are a potential market that could help quantum-dot companies find traction,” says Jonathan Melnick, an analyst at Lux Research in Boston, Massachusetts.
Quantum dots are crystals about 10 nanometres in diameter, made from a semiconductor material, commonly cadmium selenide. They are so tiny that their shape and size affect the quantum properties of their electrons, in particular their energy gap — the energy needed to kick electrons into a higher-energy band — which determines the colour of light that the material can emit. Whereas a bulk semiconductor is limited to emitting a single colour of light, researchers can tune the precise colour a quantum dot will absorb and re-emit by tailoring its size.
- Connect the quantum dots for a full-colour image
- Quantum dots go large
- Lighting technology: Time to change the bulb
Discovered in 1981, quantum dots did not find applications until 2002. That was when the Quantum Dot Corporation of Hayward, California, began selling them to cell biologists, who prize them as fluorescent imaging labels for proteins and other biological molecules. As recently as 2010, the biomedical sector was responsible for US$48 million of $67 million in total quantum-dot revenues, according to BCC Research of Wellesley, Massachusetts.
Quantum dots have shown promise for electronics, too — for example in solar cells, in which a mix of quantum dots tuned to absorb different wavelengths of light could capture more of the energy in the solar spectrum. But one hurdle to their exploitation was their temperature sensitivity. Near the backlight of a liquid-crystal display (LCD), for example, temperatures can be around 100 °C. At this temperature, the dots lose efficiency and up to half of their brightness, says QD Vision co-founder and chief technology officer Seth Coe-Sullivan. He says that the company spent a long time tuning the chemistry of its quantum dots to make them stable at higher temperatures.
Moungi Bawendi, a chemist at the Massachusetts Institute of Technology in Cambridge and a co-founder of QD Vision, admits that the company also made some business miscalculations. For its first product, in 2009, it provided Nexxus Lighting of Charlotte, North Carolina, with quantum-dot coatings to convert the harsh glare of LEDs into a warmer glow, to make them more appealing as long-life, low-energy light bulbs. But Bawendi says that LED designs and technology for the light-bulb market evolved too fast for the quantum-dot coatings to keep up. “You design something, and six months later it doesn’t work,” Bawendi says. “Television technology is more stable.”
His optimism will be tested this spring with the company’s quantum-dot debut in Sony LCD televisions, to be sold under the Triluminos brand name. The contrast with today’s flat screens begins with the light source. Conventional LCDs use a high-intensity blue LED backlight whose glow is converted by a phosphor coating to create a broadband, white light used to make the moving TV images. The new Triluminos televisions instead pair an uncoated blue LED with a thin glass tube filled with quantum dots. Two kinds of quantum dots in the tube absorb some of the blue light from the backlight and re-emit it as pure red andgreen light. The resulting white light is more intense at the wavelengths of these three specific colours than the white light made by a phosphor-coated LED, so that more colour comes through in the images.
Another quantum-dot company, Nanosys of Palo Alto, California, is providing 3M of St Paul, Minnesota, with material for a similar product. 3M will make a polymer film seeded with quantum dots that does the same jobas QD Vision’s glass tube. The film is layered between the LCD’s stack of light filters, diffusers and polarizers, and similarly converts raw blue light into white light made up of pure colours. Nanosys and 3M announced their partnership in June 2012, but have not yet named any customers.
BCC predicts that, by 2015, optoelectronics, including display components, will make up $310 million of a total $666 million in quantum-dot revenues. Melnick says that these numbers might be overly optimistic, because quantum dots remain expensive. “Even on the low end, they still cost in the hundreds of dollars per gram, and range up to $10,000 per gram,” he says. But demand from 3M and Sony could help to bring prices down. Although neither QD Vision nor Nanosys would comment on the volume of material they expect to make this year, or their selling price, both say that they are scaling up their manufacturing volume.
Bawendi is not surprised that it took quantum dots so long to find their footing. “You could argue that 30 years is about the right amount of time from fundamental discovery to applications,” he says.
New qubit control bodes well for future of quantum computing
Quantum computers would be exponentially faster than the most powerful computers of today.
“Our experiment is a dress rehearsal for a type of process essential for quantum computing,” said Michel Devoret, the Frederick William Beinecke Professor of Applied Physics & Physics at Yale and principal investigator of research published Jan. 11 in the journal Science. “What this experiment really allows is an active understanding of quantum mechanics. It’s one thing to stare at a theoretical formula and it’s another thing to be able to control a real quantum object.”
In quantum systems, microscopic units called qubits represent information. Qubits can assume either of two states — “0” or “1” — or both simultaneously. Correctly recognizing, interpreting, and tracking their state is necessary for quantum computing. However, the act of monitoring them usually damages their information content.
The Yale physicists successfully devised a new, non-destructive measurement system for observing, tracking and documenting all changes in a qubit’s state, thus preserving the qubit’s informational value. In principle, the scientists said, this should allow them to monitor the qubit’s state in order to correct for random errors.
“As long as you know what error process has occurred, you can correct,” Devoret said. “And then everything’s fine. You can basically undo the errors.”
An innovation by Yale University physicists offers scientists greater control in the volatile realm of quantum mechanics and greatly improves the prospects of quantum computing. Quantum computers would be exponentially faster than the most powerful computers oftoday.
“That’s the key,” said Michael Hatridge, a postdoctoral associate in physics at Yale and lead author of the Science paper, “the ability to talk to the qubit and hear what it’s telling you.”
He continued: “A major problem with quantum computing is the finite lifetime of information stored in the qubits, which steadily decays and which must be corrected. We now know that it is possible to do this correction by feedback involving a continuous measurement. Our work advances the prospects of large-scale quantum computers by opening the door to continuous measurement-based quantum feedback.”
The Yale physicists successfully measured one qubit. The challenge ahead is to measure and control many at once, and the team is developing ultra-fast digital electronics for this purpose.
“We are on the threshold between the ability to measure and control one or two qubits, and many,” Hatridge said.
Other authors of the paper are S. Shankar, M. Mirrahimi, F. Schackert, K. Geerlings, T. Brecht, K.M. Sliwa, B. Abdo, L. Frunzio, S.M. Girvin, and R.J. Schoelkopf.
Support for the research was provided by the National Science Foundation, the United States Army Research Office, the Intelligence Advanced Research Projects Activity, the Agence National de Recherche, and the College de France.
NRL Designs Multi-Junction Solar Cell to Break Efficiency Barrier
U.S. Naval Research Laboratory scientists in the Electronics Technology and Science Division, in collaboration with the Imperial College London and MicroLink Devices, Inc., Niles, Ill., have proposed a novel triple-junction solar cell with the potential to break the 50 percent conversion efficiency barrier, which is the current goal in multi-junction photovoltaic development.
Schematic diagram of a multi-junction (MJ) solar cell formed from materials lattice-matched to InP and achieving the bandgaps for maximum efficiency. (Photo: U.S. Naval Research Laboratory)
“This research has produced a novel, realistically achievable, lattice-matched, multi-junction solar cell design with the potential to break the 50 percent power conversion efficiency mark under concentrated illumination,” said Robert Walters, Ph.D., NRL research physicist. “At present, the world record triple-junction solar cell efficiency is 44 percent under concentration and it is generally accepted that a major technology breakthrough will be required for the efficiency of these cells to increase much further.”
In multi-junction (MJ) solar cells, each junction is ‘tuned’ to different wavelength bands in the solar spectrum to increase efficiency. High bandgap semiconductor material is used to absorb the short wavelength radiation with longer wavelength parts transmitted to subsequent semiconductors. In theory, an infinite-junction cell could obtain a maximum power conversion percentage of nearly 87 percent. The challenge is to develop a semiconductor material system that can attain a wide range of bandgaps and be grown with high crystalline quality.
By exploring novel semiconductor materials and applying band structure engineering, via strain-balanced quantum wells, the NRL research team has produced a design for a MJ solar cell that can achieve direct band gaps from 0.7 to 1.8 electron volts (eV) with materials that are all lattice-matched to an indium phosphide (InP) substrate.
“Having all lattice-matched materials with this wide range of band gaps is the key to breaking the current world record” adds Walters. “It is well known that materials lattice-matched to InP can achieve band gaps of about 1.4 eV and below, but no ternary alloy semiconductors exist with a higher direct band-gap.”
The primary innovation enabling this new path to high efficiency is the identification of InAlAsSb quaternary alloys as a high band gap material layer that can be grown lattice-matched to InP. Drawing from their experience with Sb-based compounds for detector and laser applications, NRL scientists modeled the band structure of InAlAsSb and showed that this material could potentially achieve a direct band-gap as high as 1.8eV. With this result, and using a model that includes both radiative and non-radiative recombination, the NRL scientists created a solar cell design that is a potential route to over 50 percent power conversion efficiency under concentrated solar illumination.
Recently awarded a U.S. Department of Energy (DoE), Advanced Research Projects Agency-Energy (ARPA-E) project, NRL scientists, working with MicroLink and Rochester Institute of Technology, Rochester, N.Y., will execute a three year materials and device development program to realize this new solar cell technology.
Through a highly competitive, peer-reviewed proposal process, ARPA-E seeks out transformational, breakthrough technologies that show fundamental technical promise but are too early for private-sector investment. These projects have the potential to produce game-changing breakthroughs in energy technology, form the foundation for entirely new industries, and to have large commercial impacts.
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