Improving a new breed of solar cells Quantum-dot photovoltaics set new record for efficiency in such devices, could unlock new uses.

Solar-cell technology has advanced rapidly, as hundreds of groups around the world pursue more than two dozen approaches using different materials, technologies, and approaches to improve efficiency and reduce costs. Now a team at MIT has set a new record for the most efficient quantum-dot cells — a type of solar cell that is seen as especially promising because of its inherently low cost, versatility, and light weight.

While the overall efficiency of this cell is still low compared to other types — about 9 percent of the energy of sunlight is converted to electricity — the rate of improvement of this technology is one of the most rapid seen for a solar technology. The development is described in a paper, published in the journalNature Materials, by MIT professors Moungi Bawendi and Vladimir Bulović and graduate students Chia-Hao Chuang and Patrick Brown.

The new process is an extension of work by Bawendi, the Lester Wolfe Professor of Chemistry, to produce quantum dots with precisely controllable characteristics — and as uniform thin coatings that can be applied to other materials. These minuscule particles are very effective at turning light into electricity, and vice versa. Since the first progress toward the use of quantum dots to make solar cells, Bawendi says, “The community, in the last few years, has started to understand better how these cells operate, and what the limitations are.”

The new work represents a significant leap in overcoming those limitations, increasing the current flow in the cells and thus boosting their overall efficiency in converting sunlight into electricity.

Many approaches to creating low-cost, large-area flexible and lightweight solar cells suffer from serious limitations — such as short operating lifetimes when exposed to air, or the need for high temperatures and vacuum chambers during production. By contrast, the new process does not require an inert atmosphere or high temperatures to grow the active device layers, and the resulting cells show no degradation after more than five months of storage in air.

Bulović, the Fariborz Maseeh Professor of Emerging Technology and associate dean for innovation in MIT’s School of Engineering, explains that thin coatings of quantum dots “allow them to do what they do as individuals — to absorb light very well — but also work as a group, to transport charges.” This allows those charges to be collected at the edge of the film, where they can be harnessed to provide an electric current.

The new work brings together developments from several fields to push the technology to unprecedented efficiency for a quantum-dot based system: The paper’s four co-authors come from MIT’s departments of physics, chemistry, materials science and engineering, and electrical engineering and computer science. The solar cell produced by the team has now been added to the National Renewable Energy Laboratories’ listing of record-high efficiencies for each kind of solar-cell technology.

The overall efficiency of the cell is still lower than for most other types of solar cells. But Bulović points out, “Silicon had six decades to get where it is today, and even silicon hasn’t reached the theoretical limit yet. You can’t hope to have an entirely new technology beat an incumbent in just four years of development.” And the new technology has important advantages, notably a manufacturing process that is far less energy-intensive than other types.

Chuang adds, “Every part of the cell, except the electrodes for now, can be deposited at room temperature, in air, out of solution. It’s really unprecedented.”

The system is so new that it also has potential as a tool for basic research. “There’s a lot to learn about why it is so stable. There’s a lot more to be done, to use it as a testbed for physics, to see why the results are sometimes better than we expect,” Bulović says.

A companion paper, written by three members of the same team along with MIT’s Jeffrey Grossman, the Carl Richard Soderberg Associate Professor of Power Engineering, and three others, appears this month in the journal ACS Nano, explaining in greater detail the science behind the strategy employed to reach this efficiency breakthrough.

The new work represents a turnaround for Bawendi, who had spent much of his career working with quantum dots. “I was somewhat of a skeptic four years ago,” he says. But his team’s research since then has clearly demonstrated quantum dots’ potential in solar cells, he adds.

Arthur Nozik, a research professor in chemistry at the University of Colorado who was not involved in this research, says, “This result represents a significant advance for the applications of quantum-dot films and the technology of low-temperature, solution-processed, quantum-dot photovoltaic cells. … There is still a long way to go before quantum-dot solar cells are commercially viable, but this latest development is a nice step toward this ultimate goal.”

The work was supported by the Samsung Advanced Institute of Technology, the Fannie and John Hertz Foundation, and the National Science Foundation.

source- OPLI

ENERGY BREAKTHROUGH USES SUN TO CREATE SOLAR ENERGY MATERIALS

In a recent advance in solar energy, researchers have discovered a way to tap the sun not only as a source of power, but also to directly produce the solar energy materials that make this possible.

This breakthrough by chemical engineers at Oregon State University could soon reduce the cost of solar energy, speed production processes, use environmentally benign materials, and make the sun almost a “one-stop shop” that produces both the materials for solar devices and the eternal energy to power them.

The findings were published in RSC Advances, a journal of the Royal Society of Chemistry, in work supported by the National Science Foundation.

“This approach should work and is very environmentally conscious,” said Chih-Hung Chang, a professor of chemical engineering at Oregon State University, and lead author on the study.

“Several aspects of this system should continue to reduce the cost of solar energy, and when widely used, our carbon footprint,” Chang said. “It could produce solar energy materials anywhere there’s an adequate solar resource, and in this chemical manufacturing process, there would be zero energy impact.”

The work is based on the use of a “continuous flow” microreactor to produce nanoparticle inks that make solar cells by printing. Existing approaches based mostly on batch operations are more time-consuming and costly.

In this process, simulated sunlight is focused on the solar microreactor to rapidly heat it, while allowing precise control of temperature to aid the quality of the finished product. The light in these experiments was produced artificially, but the process could be done with direct sunlight, and at a fraction of the cost of current approaches.

“Our system can synthesize solar energy materials in minutes compared to other processes that might take 30 minutes to two hours,” Chang said. “This gain in operation speed can lower cost.”

In these experiments, the solar materials were made with copper indium diselenide, but to lower material costs it might also be possible to use a compound such as copper zinc tin sulfide, Chang said. And to make the process something that could work 24 hours a day, sunlight might initially be used to create molten salts that could later be used as an energy source for the manufacturing. This could provide more precise control of the processing temperature needed to create the solar energy materials.

State-of-the-art chalcogenide-based, thin film solar cells have already reached a fairly high solar energy conversion efficiency of about 20 percent in the laboratory, researchers said, while costing less than silicon technology. Further improvements in efficiency should be possible, they said.

Another advantage of these thin-film approaches to solar energy is that the solar absorbing layers are, in fact, very thin- about 1 to 2 microns, instead of the 50 to 100 microns of more conventional silicon cells. This could ease the incorporation of solar energy into structures, by coating thin films onto windows, roof shingles or other possibilities.

Additional support for this work was provided by the Oregon Nanoscience and Microtechnologies Institute, or ONAMI, and the Oregon Built Environment and Sustainable Technologies Center, or Oregon BEST.

Source: Oregon State University

NOVEL STAPLED PEPTIDE NANOPARTICLE COMBINATION PREVENTS RSV INFECTION, STUDY FINDS

A combination of advanced technologies may lead to a therapy to prevent or treat respiratory syncytial virus, a potentially lethal respiratory infection affecting infants, young children and the elderly, new research suggests. Despite a wide range of anti-RSV efforts, there are no vaccines or drugs on the market to effectively prevent or treat the infection.

Despite a wide range of anti-RSV efforts, there are no vaccines or drugs on the market to effectively prevent or treat the infection.

Now researchers at the Dana-Farber/Boston Children's Cancer and Blood Disorders Center and Harvard Medical School in Boston, MA, and the James A. Haley VA Hospital and the University of South Florida (USF) in Tampa, FL, have developed novel double-stapled peptides that inhibit RSV in cells and in mice. The team also showed that this peptide's capacity to block infection was significantly boosted when delivered to the lungs by miniscule, biodegradable particles known as nanoparticles.

The team's findings are reported online today in The Journal of Clinical Investigation.

RSV employs a fusion protein with a helical structure to enable the virus to bind to and penetrate epithelial cells lining the nose and lungs.

The Dana-Farber/Boston Children's/Harvard laboratory led by co-senior author Loren Walensky, MD, PhD, used their chemical strategy known as hydrocarbon stapling to make "double-stapled" RSV peptides. Stapling helps the peptides retain their natural helical shape and resist degradation by the body's enzymes while disrupting the fusion process needed for RSV to infect host cells.

The VA/USF group led by co-senior author Shyam Mohapatra, PhD, tested these double-stapled peptides, alone and in combination with propriety nanoparticles, in mice to demonstrate significant inhibition of RSV infection.

"This is an exciting advance in the fight against respiratory syncytial virus infection," said Dr. Mohapatra, director of the USF Nanomedicine Research Center and the USF Health Morsani College of Medicine's Division of Translational Medicine, and a research career scientist at James A. Haley VA Hospital.

"We found that double-stapled peptide interference targeting the virus fusion protein can be administered in the form of a nasal drop or spray. The treatment suppressed viral entry and reproduction, including spread from nose to lungs, providing substantial protection from infection when administered several days before viral exposure."

"Designing therapeutic peptides based on a virus' very own fusion apparatus was previously exploited to block HIV-1 infection, but this class of drugs was severely limited by the pharmacologic liabilities of peptides in general, including loss of bioactive structure and rapid digestion in the body," said Dr. Walensky, associate professor of pediatrics at Harvard Medical School, pediatric hematologist/oncologist at Dana-Farber/Boston Children's and principal investigator in Dana-Farber's Linde Program in Cancer Chemical Biology.

"Peptide stapling restores the natural helical shape, which also inhibits proteolysis, providing a new opportunity to take advantage of a well-validated mechanism of action to thwart viruses like RSV that otherwise lack drugs for preventing or treating infection."

Dr. Mohapatra and his team developed nose drops containing the Walensky laboratory's double-stapled peptides after combining them with TransGenex's chitosan nanoparticles that stick to mucous-producing cells lining the lungs.

First, the researchers treated mice intranasally with stapled peptide nose drops, both before and during infection with RSV. The treated mice showed significantly lower levels of virus in the nose and lungs, and less airway inflammation, compared to untreated mice.

Then, double-stapled peptides encapsulated in nanoparticles were delivered to the lungs via the trachea to test whether the combination could further increase the effectiveness of this experimental therapy. The nanoparticle preparation markedly improved delivery of the peptides to the lungs, and the combination worked better and longer in preventing RSV pneumonia than the double-stapled peptide alone.

The researchers say to the best of their knowledge this preclinical study is the first to combine peptide stapling and nanoparticle technologies to maximize the delivery, persistence, and effectiveness of an antiviral therapy.

RSV is the most common virus causing lung and airway infections in infants and young children. Most have had this infection by age 2, and it can be especially serious, even deadly, in high-risk groups, such as babies born prematurely and those whose immune systems do not work well. The virus hospitalizes thousands of infants each year for pneumonia or brochiolitis and has been associated with a significantly greater risk of developing asthma later in life. The elderly are also at high risk of complications from RSV infection.

"This is a new way forward in the development of strategies to prevent RSV infection," said Terrence Dermody, MD, the Dorothy Overall Wells professor of pediatrics and director of the Division of Pediatric Infectious Diseases at Vanderbilt University School of Medicine, who was not involved with the research. "The authors are to be complimented on the clever design, interdisciplinary approach and extension from cell-culture experiments to animal studies. I am particularly excited about the possible application of this technology to other viruses."

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source- University of South Florida (USF Health)

FIRST SINGLE-MOLECULE LED

Light emitting diodes are components that emit light when an electric current passes through them and only let light through in one direction. LEDs play an important role in everyday life, as light indicators. They also have a promising future in the field of lighting, where they are progressively taking over the market. A major advantage of LEDs is that it is possible to make them very small, so point light sources can be obtained. With this in mind, one final miniaturization hurdle has recently been overcome by researchers at IPCMS in Strasbourg, in collaboration with a team from the Institut Parisien de Chimie Moléculaire (CNRS/UPMC): they have produced the first ever single-molecule LED.

To achieve this, they used a single polythiophene wire. This substance is a good electricity conductor. It is made of hydrogen, carbon and sulfur, and is used to make larger LEDs that are already on the market. The polythiophene wire was attached at one end to the tip of a scanning tunneling microscope, and at the other end to a gold surface. The scientists recorded the light emitted when a current passed through this nanowire. They observed that the thiophene wire acts as a light emitting diode: light was only emitted when electrons went from the tip of the microscope towards the gold surface.. When the polarity was reversed, light emission was negligible.

In collaboration with a theoretical team from the Service de Physique de l'Etat Condensé (CNRS-CEA/IRAMIS/SPEC), the researchers showed that this light was emitted when a negative charge (an electron) combined with a positive charge (a hole) in the nanowire and transmitted most of its energy to a photon. For every 100,000 electrons injected into the thiophene wire, a photon was emitted. Its wavelength was in the red range.

From a fundamental viewpoint, this device gives researchers a new tool to probe phenomena that are produced when an electrical conductor emits light and it does so at a scale where quantum physics takes precedence over classical physics. Scientists will also be able to optimize substances to produce more powerful light emissions. Finally, this work is a first step towards making molecule-sized components that combine electronic and optical properties. Similar components could form the basis of a molecular computer.

Source- CNRS