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Magnetic Nanoparticles Boost Polymer Solar Cells

Just about every manner of nanoparticle and nanomaterial has been applied to polymer solar cells.  Despite all of this work, conversion efficiencies for single p-n junction polymer solar cells are mired at around 9 percent, while cells with more than one p-n junction have mustered efficiencies only as high as 10.6 percent.

All those frustrated efforts made it reasonable to wonder whether nanoparticles would ever provide much of a boost to polymer solar cells.

Now, an X-ray study performed at the Deutsches Elektronen-Synchrotron (DESY) by a team from the Technical University of Munich (TUM) using DESY’s synchrotron radiation source, PETRA III, has demonstrated that magnetic nanoparticles can improve the performance of polymer solar cells—if the mix is right.

In research published in the journal Advanced Energy Materials, the German-based researchers demonstrated that by making sure the solar cell material contains just about one percent of magnetic nanoparticles by weight, they were able to boost the solar cell’s efficiency.

“The X-ray investigation shows that if you mix a large number of nanoparticles into the material used to make the solar cell, you change its structure”, explains coauthor Stephan Roth, who runs DESY’s microfocus small- and wide-angle x-ray scattering beamline at PETRA III, in a press release. “The solar cells we looked at will tolerate magnetic nanoparticle doping levels of up to one percent by mass without changing their structure.”

How to exploit the nanoparticles is where the Germany-based researchers departed from recent research. Solar cell material doped with gold nanoparticles had already been demonstrated to absorb additional sunlight—which, in turn, produced additional electrical charge carriers when the energy was released again by the gold particles.

“The light creates pairs of charge carriers in the solar cell, consisting of a negatively charged electron and a positively charged hole, which is a site where an electron is missing,” explained the main author of the current study, Daniel Moseguí González, in a press release. “The art of making an organic solar cell is to separate this electron-hole pair before they can recombine. If they did, the charge produced would be lost. We were looking for ways of extending the life of the electron-hole pair, which would allow us to separate more of them and direct them to opposite electrodes.”

To extend the life of the electron-hole pair, the researchers exploited the spin of the electrons. The positively charged hole also has a spin. If the two spins are in the same direction, they can add up to a value of one, or cancel each other out, for a value of zero, if they are oriented in opposite directions. Pairs that have an overall spin value of one last longer than those that have an overall spin of zero.

The key was finding a material capable of converting an electron-hole pair’s overall spin state from zero to one. To accomplish this, the researchers needed nanoparticles made from heavy elements, because they can flip the spin of the electron or the hole so that spins are aligned in the same direction.

The material they hit upon was iron oxide magnetite. By adding just the right amount of the magnetite (doping the substrate with 0.6 percent nanoparticles by weight) they were able to increase the energy conversion efficiency by 11 percent, from 3.05 to 3.37 percent.

“The combination of high-performance polymers with nanoparticles holds the promise of further increases in the efficiency of organic solar cells in the future,” said Peter Müller-Buschbaum of TUM in the release. “However, without a detailed examination, such as that using the X-rays emitted by a synchrotron, it would be impossible to gain a fundamental understanding of the underlying processes involved.”

Optical Nanosensor Production Only Needs CDs, Tape, and Aluminum

Researchers at the Universidad Politécnica de Madrid (UPM) in Spain have developed a way to produce optical nanosensors that can stick to uneven surfaces as well as biological surfaces such as human skin.

The researchers believe that this technique will expand the use of wearable devices for monitoring body temperature, respiration, blood pressure, and other vital signs.

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Magnetic Nanoparticles Promise to Prevent Strokes and Heart Attacks

Magnetic nanoparticles have served as the foundation for a number of medical technologies, including drug delivery, medical imaging contrast agents and cancer diagnosis and treatment

Now researchers at Houston Methodist are loading up magnetic nanoparticles with drugs and camouflaging them from the immune systems so that they can  destroy blood clots at a rate about 100 to 1000 times faster than a commonly used clot-busting technique.

The researchers believe that if the technique proves successful in human trials that it could help prevent strokes, heart attacks and pulmonary embolisms.

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Silicon Nanofibers Boost Li-ion Batteries for EVs

Last summer, Mihri and Cengiz Ozkan, both professors at the University of California Riverside, put a small twist on all the attempts to use nanostructured silicon on the anodes of lithium-ion (Li-ion) batteries. They dispersed silicon particles onto nanostructures rather than making nanostructures on silicon.

Now the Ozkans are at it again. This time they and their colleagues at UC Riverside have created a paper-like nanofiber material that can be applied to the anodes of Li-ion batteries, boosting by several times a battery’s specific energy—the amount of energy that can be delivered per unit weight.

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Crumpling Graphene Could Expand Its Applications

Last October, researchers at MIT showed that graphene could be crumpled and then flattened again and still remain effective for use in the electrodes of supercapacitors that could be used to power flexible electronics.

Now a team at the University of Illinois at Urbana-Champaign are showing that if you keep the graphene crumpled, you increase its surface area. This 3D surfaced graphene could open new application areas for the material in electronics and biomaterials. 

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Nanowire Brushes Usher in New Generation of Smoke Detectors

Zinc oxide's' ability to absorb and emit ultraviolet light has long been the operational foundation of photoelectric smoke detectors.

While this technology has proved effective in detecting larger smoke particles found in dense smoke, it’s not quite as sensitive in detecting the small smoke particles produced by fast burning fires.

Now researchers at the University of Surrey’s Advanced Technology Institute have dramatically increased the effective surface area of zinc oxide by fashioning the material into what amounts to nanowire "brushes," making the smoke detectors they’re used in 10,000 times more sensitive to UV light than a traditional zinc-oxide detector.

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DNA Data Storage Just Got a Bit More Practical

For two years now, researchers have been storing digital information in the form of DNA, but there has remained some question as to whether it’s a practical solution for digital storage.

Now researchers at the Swiss Federal Institute of Technology in Zurich (ETHZ) have addressed a number of the problems associated with using DNA as data storage—enough so that they believe it can be used for error-free storage of information.  If their solution proves successful, it could open the door for data storage that lasts for a million years.

Researchers around the world have been investigating a variety of new methods for storing digital information because we’ll be lucky if the solutions we have now, like hard drives and servers, can keep faithful records for fifty years. DNA has been among those potential alternatives. But errors during data retrieval have been the method’s bugaboo. Gaps and false information in the encoded data result from chemical degradation and mistakes in DNA sequencing.

In research published in the journal Angewandte Chemie, the Swiss team was able to overcome the problem of chemical degradation of the DNA by encapsulating the genetic material in silica (glass) spheres with diameters of around 150 nanometers.

In order to test the quality of their encapsulation, the researchers simulated a long period of time by storing the information-encoded DNA at temperatures between 60 and 70 degrees Celsius for up to a month. This simulated, within a few weeks, the degradation that would occur over hundreds of years under normal conditions.

After finding that the silica capsules outperformed several other materieals they tested, the researchers then moved on to ensuring that the DNA remained error free.

While advances in DNA sequencing make it possible to read stored data on DNA affordably, affordability and exactitude don’t always go hand in hand. To overcome this problem, the researchers have developed a way to correct any errors based on the Reed-Solomon Codes, error-correcting codes normally used to ensure accurate data recovery after long-distance data transmission.

The scheme adds just a bit more data to ensure that what’s encoded is error free. “In order to define a parabola, you basically need only three points,” said Reinhard Heckel from ETH Zurich’s Communication Technology Laboratory in a press release. “We added a further two in case one gets lost or is shifted.”

Mollusks Show the Way to Better Li-ion Batteries

Biomimicry has served as the foundation for a significant portion of nanotech research. Nature has had a few billion years to work out the most effective way to get things done on the nanoscale so it makes sense to do a fair amount of cribbing from it solutions.

Now researchers at the University of Maryland, Baltimore County (UMBC) have borrowed a process from mollusks to develop a method for improving the properties of lithium-ion (Li-ion) batteries.

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New Manufacturing Method Promises Scalable Graphene Electronics Production

When you hear people sing the praises of graphene, they are usually referring to the single-crystal graphene that has many attractive properties like high electron mobility. Unfortunately, producing that pure single-crystal graphene requires a decidedly unscalable method known as the “Scotch Tape” method; graphene is pulled off in single-layer flakes directly from bulk graphite.

Chemical Vapor Deposition (CVD) has been seen as a bridge between scalability and purity in graphene production. With that technique, graphene is grown on a metal substrate like copper or nickel. But because the graphene eventually has to be peeled off of the metal substrate, the graphene can either be completely ruined or contaminated.

Now researchers at the University of Groningen in the Netherlands have devised a production method based on CVD that eliminates the potential for ruin or contamination while still remaining scalable. It is based on something they discovered when analyzing CVD-grown graphene three years ago.

“When we analyzed a sample of graphene on copper, we made some strange observations,” said Meike Stöhr, one of the researchers, in a press release.

What the researchers observed was that some copper oxide was present next to the copper. In fact, the graphene formed a kind of film on top of the copper oxide. Because oxidized metals are often used in passivation of electronics—a process in which a light coat of a protective oxide is used to create a shell against corrosion—the researchers suspected that the copper oxide layer could leave the graphene’s properties untouched.

In research published in the journal Nano Letters, the Groningen researchers took their initial observations and demonstrated the ability to grow graphene on copper oxide. Most importantly, the process of decoupling the graphene and copper oxide preserves the graphene’s attractive electronic properties.

While Stöhr concedes that their work will need to be duplicated by other research groups, their findings could have a long-reaching impact on the future of graphene devices. If this process enables the growth of large single-domain crystals of graphene, it would be possible to then use common lithographic techniques to etch a host of electronic devices in a way analogous to silicon.

Thermoelectric Nanowires Promise Energy Harvesting From Car Exhaust

Researchers at Sandia National Labs have developed a manufacturing process capable of controlling the crystal orientation, crystal size, and alloy uniformity of nanowires so that they could be used in a range of thermoelectric applications. 

Because thermoelectric materials are capable of generating an electrical current as a result of a difference in temperature between one side of the material and the other, the Sandia team believes the new nanowires could make it possible for carmakers to harvest power from the heat wasted by exhaust systems or lead to more efficient devices for cooling computer chips.

Nanowires have been suggested for a range of applications, but in thermoelectric applications, the quality of the nanowires has heretofore been inadequate. The trick for any thermoelectric material is to combine high electrical conductivity and relatively low thermal conductivity—a property known as thermoelectric efficiency.

Researchers have been investigating a number of nanomaterials for thermoelectric applications; traditional materials possess a relatively poor thermoelectric conversion efficiency or they are prohibitively expensive for commercial uses.

The Sandia researchers turned to nanowires despite their previous poor performance, believing that if they could better control the manufacturing process, they could improve the nanowires’ quality enough to make them a useful thermoelectric material.

In research published in the Cambridge Journal of Materials Research, the Sandia team employed a method known as room-temperature electroforming, which is widely used in commercial electroplating. In electroforming, material is deposited at a constant rate, which results in the nanowires growing uniformly.

This uniformity of composition held for the entire length of each nanowire and even across an array of them. The crystals that made up the nanowires were all oriented in one direction, making it easier for electrons to travel along the conduits.

“There are little nuances in the technique that I do to allow the orientation, the crystal growth, and the composition to be maintained within a fairly tight range,” said Graham Yelton of Sandia in a press release. “It’s turning the knobs of the process to get these things to behave.”

The next step in the research will be to make an electrical contact with the nanowire-based material and to measure the resulting thermoelectric behavior.

One hurdle the team has to overcome: “Thermoelectric materials readily form oxides or intermetallics, leading to poor contact connections or higher electrical contact resistance. That reduces the gains achieved in developing the materials,” Yelton said.

So far the team has had some success in getting good contact at the bottom of an array, but making a connection at the top has proved difficult.

At the moment, the researchers are seeking additional funding to solve the problem of making contacts, and then they plan to characterize the thermal electric properties of the arrays.

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Nanoclast

IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.

 
Editor
Dexter Johnson
Madrid, Spain
 
Contributor
Rachel Courtland
Associate Editor, IEEE Spectrum
New York, NY
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