Third-Generation Solar Cells using Metalorganic Perovskites Challenges silicon based Solar Cells


nanotubefilmAn illustration of a perovskite solar cell. Credit: Photo by Aalto University / University of Uppsala / EPFL

Five years ago, the world started to talk about third-generation solar cells that challenged the traditional silicon cells with a cheaper and simpler manufacturing process that used less energy.

Methylammonium lead iodide is a metal-organic material in the perovskite crystal structure that captures light efficiently and conducts electricity well—both important qualities in . However, the lifetime of solar cells made of metalorganic perovskites has proven to be very short compared to cells made of .

Now researchers from Aalto University, Uppsala University and École polytechnique fédérale de Lausanne (EPFL) in Switzerland have managed to improve the long term stability of solar cells made of perovskite using “random network” nanotube films developed under the leadership of Professor Esko Kauppinen at Aalto University. Random network nanotube films are films composed of single-walled carbon nanotubes that in an electron microscope image look like spaghetti on a plate.

‘In a traditional perovskite solar cell, the hole conductor layer consists of organic material and, on top of it, a thin layer of gold that easily starts to disintegrate and diffuse through the whole solar cell structure. We replaced the gold and also part of the organic material with films made of carbon nanotubes and achieved good cell stability in 60 degrees and full one sun illumination conditions‘, explains Kerttu Aitola, who defended her doctoral dissertation at Aalto University and now works as a researcher at Uppsala University

In the study, thick black films with conductivity as high as possible were used in the back contact of the solar cell where light does not need to get through. According to Aitola, nanotube films can also be made transparent and thin, which would make it possible to use them as the front contact of the cell, in other words as the contact that lets light through.

‘The solar cells were prepared in Uppsala and the long-term stability measurement was carried out at EPFL. The leader of the solar cell group at EPFL is Professor Michael Grätzel, who was awarded the Millennium Prize 2010 for dye-sensitised solar cells, on which the are also partly based on’, says Aitola.

Nanotube film may resolve longevity problem of challenger solar cells
Cross-section of the solar cell in an electron microscope image. The fluff seen in the front of the image is composed of bundles of nanotubes that have become half-loose when the samples have been prepared for imaging. Credit: Photo by Aalto University / University of Uppsala / EPFL

 

The lifetime of solar cells made of silicon is 20-30 years and their industrial production is very efficient. Still, alternatives are needed as reducing the silicon dioxide in sand to silicon consumes a huge amount of energy. It is estimated that a needs two or three years to produce the energy that was used to manufacture it, whereas a perovskite solar cell would only need two or three months to do it.

‘In addition, the silicon used in solar cells must be extremely pure’, says Aitola.

‘Perovskite solar cell is also interesting because its efficiency, in other words how efficiently it converts sunlight energy into electrical energy, has very quickly reached the level of silicon solar cells. That is why so much research is conducted on perovskite solar cells globally.’

The alternative solar cells are even more interesting because of their various application areas. Flexible solar cells have until now been manufactured on conductive plastic. Compared with the conductive layer of plastic, the flexibility of nanotube films is superior and the raw materials are cheaper. Thanks to their flexibility, solar cells could be produced using the roll-to-roll processing method known from the paper industry.

‘Light and would be easy to integrate in buildings and you could also hang them in windows by yourself’, says Aitola.

Explore further: New way to make low-cost solar cell technology

More information: Kerttu Aitola et al, High Temperature-Stable Perovskite Solar Cell Based on Low-Cost Carbon Nanotube Hole Contact, Advanced Materials (2017). DOI: 10.1002/adma.201606398

McMaster University: Researchers resolve problem holding back a Technology Revolution – Smaller, Nimbler Semiconductors that are expected to Replace Silicon – Carbon Nanotubes


 

mcmasterrese carbon nanotubes 081916Artistic rendition of a metallic carbon nanotube being pulled into solution, in analogy to the work described by the Adronov group. Credit: Alex Adronov, McMaster University

Imagine an electronic newspaper that you could roll up and spill your coffee on, even as it updated itself before your eyes.

It’s an example of the that has been waiting to happen, except for one major problem that, until now, scientists have not been able to resolve.

Researchers at McMaster University have cleared that obstacle by developing a new way to purify nanotubes – the smaller, nimbler semiconductors that are expected to replace silicon within computer chips and a wide array of electronics.

“Once we have a reliable source of pure nanotubes that are not very expensive, a lot can happen very quickly,” says Alex Adronov, a professor of Chemistry at McMaster whose research team has developed a new and potentially cost-efficient way to purify carbon nanotubes.

Carbon nanotubes – hair-like structures that are one billionth of a metre in diameter but thousands of times longer – are tiny, flexible conductive nano-scale materials, expected to revolutionize computers and electronics by replacing much larger silicon-based chips.

A major problem standing in the way of the new technology, however, has been untangling metallic and semiconducting carbon nanotubes, since both are created simultaneously in the process of producing the microscopic structures, which typically involves heating carbon-based gases to a point where mixed clusters of nanotubes form spontaneously as black soot.

Only pure semiconducting or metallic carbon nanotubes are effective in device applications, but efficiently isolating them has proven to be a challenging problem to overcome. Even when the nanotube soot is ground down, semiconducting and metallic nanotubes are knotted together within each grain of powder. Both components are valuable, but only when separated.

Researchers around the world have spent years trying to find effective and efficient ways to isolate carbon nanotubes and unleash their value.

While previous researchers had created polymers that could allow semiconducting carbon nanotubes to be dissolved and washed away, leaving metallic nanotubes behind, there was no such process for doing the opposite: dispersing the metallic nanotubes and leaving behind the semiconducting structures.Nanotubes images

Now, Adronov’s research group has managed to reverse the electronic characteristics of a polymer known to disperse semiconducting nanotubes – while leaving the rest of the polymer’s structure intact. By so doing, they have reversed the process, leaving the nanotubes behind while making it possible to disperse the metallic nanotubes.

The researchers worked closely with experts and equipment from McMaster’s Faculty of Engineering and the Canada Centre for Electron Microscopy, located on the university’s campus.

“There aren’t many places in the world where you can to this type of interdisciplinary work,” Adronov says.

The next step, he explains, is for his team or other researchers to exploit the discovery by finding a way to develop even more efficient polymers and scale up the process for commercial production.

The research is described in the cover story of Chemistry – A European Journal.

Explore further: Carbon nanotube ‘ink’ may lead to thinner, lighter transistors and solar cells

 

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Berkeley Lab Researchers: 5 Nanoscience Research Projects That Could Deliver Big Results


south-africa-ii-nanotechnology-india-brazil_261.jpgFrom energy efficiency to carbon capture, Berkeley Lab scientists are on it.

Berkeley Lab researchers are using the science of the very small to help solve big challenges. That’s because, at the nanoscale—the scale of molecules and proteins—new and exciting properties emerge that can possibly be put to use.

Here are five projects, now underway and recently highlighted in the News Center, which promise big results from the smallest of building blocks:

1. A DIY paint-on coating for energy efficient windows

This “cool” DIY retrofit tech could improve the energy efficiency of windows and save money. Researchers are developing a polymer-based heat-reflective coating that makes use of the unusual molecular architecture of a polymer.

It has the potential to be painted on windows at one-tenth the cost of current retrofit approaches. Window films on the market today reflect infrared solar energy back to the sky while allowing visible light to pass through, but a professional contractor is needed to install them. A low-cost option could significantly expand adoption and result in potential annual energy savings equivalent to taking 5 million cars off the road.

 

2. Nanowires that move data at light speed

Researchers have found a new way to produce nanoscale wires that can serve as tiny, tunable lasers. The excellent performance of these tiny lasers is promising for the field of optoelectronics, which is focused on combining electronics and light to transmit data, among other applications. Miniaturizing lasers to the nanoscale could further revolutionize computing, bringing light-speed data transmission to desktop, and ultimately, handheld computing devices.

 

3. Nano sponges that fight climate change

MOF

Scientists are developing nano sponges that could capture carbon from power plants before it enters the atmosphere. Initial tests show the hybrid membrane, composed of nano-sized cages (called metal-organic frameworks) and a polymer, is eight times more carbon dioxide permeable than membranes composed only of the polymer.

Boosting carbon dioxide permeability is a big goal in efforts to develop carbon capture materials that are energy efficient and cost competitive. Watch this video for more on this technology.

 

 

4. Custom-made chemical factories

4-JACS-Press-release_ca

Scientists have recently reengineered a building block of a nanocompartment that occurs naturally in bacteria, greatly expanding the potential of nanocompartments to serve as custom-made chemical factories. Researchers hope to tailor this new use to produce high-value chemical products, such as medicines, on demand.

The sturdy nanocompartments are formed by hundreds of copies of just three different types of proteins. Their natural counterparts, known as bacterial microcompartments, encase a wide variety of enzymes that carry out highly specialized chemistry in bacteria.

 

5. Nanotubes that assemble themselves

5-peptoid-nanotube-cropped

Researchers have discovered a family of nature-inspired polymers that, when placed in water, spontaneously assemble into hollow crystalline nanotubes. What’s more, the nanotubes can be tuned to all have the same diameter of between five and ten nanometers. Controlling the diameter of nanotubes, and the chemical groups exposed in their interior, enables scientists to control what goes through. Nanotubes have the potential to be incredibly useful, from delivering cancer-fighting drugs inside cells to desalinating seawater.

 

The Science of Small Revealed Using a Penny

Just how small can nanoscience get? Here’s a great example using an American penny from the Molecular Foundry.

In this video, the letters that spell Molecular Foundry were written with a beam of electrons fired at the surface. The smallest feature is 20 nanometers, or roughly 100 atoms. As the video zooms out, you lose sight of Molecular Foundry and see the Berkeley Lab logo, which was written with a beam of charged gallium atoms. As you continue to zoom out, you see an 18 hour timelapse of Abraham Lincoln’s face, again written with gallium atoms. Finally, all of this is done within the Lincoln Memorial side of the penny as it is removed from the focused ion beam.

Photolithography, which literally means writing with light, is the foundation for most top-down fabrication of things like microprocessors. However, because of something called the diffraction limit, photolithography is limited to devices that have features no smaller than the wavelength of the light used, often in the 100s of nanometers. As a result, things smaller than light like atoms and electrons must be used.

 

Updated:

Nanotechnology and the ‘Fourth Industrial Revolution’: Solving Our Biggest Challenges with the Smallest of Things


Fourth IR 051416 AAEAAQAAAAAAAATfAAAAJGEzY2E0NWViLWU4OGItNDZkZi1hYmZiLTA1YTY1NzczNGQzNAThe Fourth Industrial Revolution: The 7 Technologies Changing Our world: When Will the Future “Arrive”?

From intelligent robots and self-driving cars to gene editing and 3D printing, dramatic technological change is happening at lightning speed all around us.

The Fourth Industrial Revolution is being driven by a staggering range of new technologies that are blurring the boundaries between people, the internet and the physical world. It’s a convergence of the digital, physical and biological spheres.

It’s a transformation in the way we live, work and relate to one another in the coming years, affecting entire industries and economies, and even challenging our notion of what it means to be human.

So what exactly are these technologies, and what do they mean for us?

Read the Full Article Here: The Fourth Industrial Revolution: The 7 Technologies Changing Our world: When Will the Future “Arrive”?

Four Ways 051416 AAEAAQAAAAAAAAS7AAAAJDgyY2FlNGQ1LWUzY2EtNDQzNS04ODkwLTRmM2MxNWI4YmI1MAFour Ways Innovation Will Drive Change and Business – “The Fourth Industrial Revolution”

Innovation. In today’s business environment, there’s no word more powerful and all-encompassing. Finance, education, healthcare, retail and transportation: No sector is immune. Every day, new companies are introducing technologies that have the potential to reshape entire industries and how people conduct their day-to-day transactions.

All you need to do is look at the success of companies like Uber to realize the scale and scope of the transformation enveloping our world.

The World Economic Forum calls this era of innovation the Fourth Industrial Revolution. In January government and business leaders met in Davos, Switzerland to discuss how to navigate these unprecedented changes. It is a monumental discussion, because the reality is that these regular and system-wide innovations will continue to crack the foundations of traditional industries for years to come. Businesses need to recognize this and make sure that they will be nimble enough to succeed wherever change takes them.

Read the Full Article Here: Four Ways Innovation Will Drive Change and Business – “The Fourth Industrial Revolution”

Fourth Why All 051416 AAEAAQAAAAAAAAg8AAAAJDZiYTBjM2JlLTBlZGMtNDdmYy1hNjdkLTk0NzUyZDFjMGM0MgWhy Everyone Must Get Ready For The 4th Industrial Revolution

First came steam and water power; then electricity and assembly lines; then computerization… So what comes next?

Some call it the fourth industrial revolution, or industry 4.0, but whatever you call it, it represents the combination of cyber-physical systems, the Internet of Things, and the Internet of Systems.

In short, it is the idea of smart factories in which machines are augmented with web connectivity and connected to a system that can visualize the entire production chain and make decisions on its own.

And it’s well on its way and will change most of our jobs.

Professor Klaus Schwab, Founder and Executive Chairman of the World Economic Forum, has published a book entitled The Fourth Industrial Revolution in which he describes how this fourth revolution is fundamentally different from the previous three, which were characterized mainly by advances in technology.

In this fourth revolution, we are facing a range of new technologies that combine the physical, digital and biological worlds. These new technologies will impact all disciplines, economies and industries, and even challenge our ideas about what it means to be human.

These technologies have great potential to continue to connect billions more people to the web, drastically improve the efficiency of businessand organizations and help regenerate the natural environment through ….

Read the Full Article Here: Why Everyone Must Get Ready For The 4th Industrial Revolution

 

Nanoparticle 2 051316 coated-nanoparticlePreparing For and Embracing the Future

At Genesis Nanotechnology, Inc. it’s been a busy few years! But really … we have only ‘scratched the surface’ of the tidal wave of discoveries being made everyday at leading Nano-Universities around the World! And as exciting as the new technologies and discoveries are … as anyone who has been working in “Nano” recognizes and acknowledges, new Financing Structures, Synergistic Collaborations, Private Industry and Government Partnerships have had to be created to “bring the promise of the new technologies” into our everyday world. And that … that is why we at GNT™ are so excited about our relationships with our Partners, our Technologies and our Approach to sustaining developing “game changing” technologies to Commercial Viability. 

Genesis Nanotechnology shares the vision of those who believe that “nanotechnology” will change the way we innovate everything!

Dr. Richard Smalley, (Nobel Laureate, Smalley Institute – Rice University) asserted over 30 years ago, quote:

“… Most of the BIG problems we now face and will face in the future [Energy, Water, Food Supply and Health] will be solved by the application of “nanotechnology … Expecting Big Things from Small Things.”

We (GNT) also believe, as Dr. Smalley did and as Geoffrey Moore asserted in his book “Crossing the Chasm”

“… that we are now 30+ years into a developing technology (maturation) representing a paradigm shift in technology.” The “Innovators” and the “Early Adopters” are already in the marketplace, engaging new technologies into existing market sectors and industries.”

Fourth Industrial 041516 GWvqS6TuZDSUwlO6uZ8RUNjHjFxtgz0o3MSaRlhp5_oWe believe we are now transitioning from the cycle of The Early Adopters to the cycle of the Early Majority. We believe the explosion of technological capabilities represents an enormous “once in a lifetime” opportunity to be part of the fundamental and revolutionary changes that will redefine and reshape the physical and financial world we live in. Truly then …. “A Fourth Industrial Revolution”.

 

 

cropped-9-disruptive-technologies.jpgHow We Do What We Do

Genesis Nanotechnology actively seeks and evaluates emerging nanotechnology opportunities for Joint Venture Partners and Strategic Alliances that will create ‘enterprise value’ by identifying, developing, integrating and commercializing, nanotechnologies that demonstrate significant new disruptive capabilities, enhance new or existing product performance and/or beneficially impact input cost reductions and efficiency and therefore will achieve a sustainable and competitive advantage in their chosen market sector.

Market and Industry Applications Much like the changes plastics and polymers brought to our world, (making things stronger, cheaper, better) applied Nanomaterials are being integrated into existing markets and are also facilitating emerging products and technologies that are being developed by a very deep field of mature and financially capable companies: Examples: Sony, Sharp, Samsung, Tokyo Electron, IKEA, Merck, GlaxoSmithKline. Literally Nanomaterials will change the way we innovate everything. They will touch almost every aspect in our everyday lives from Nano-Medicine and Consumer Electronics to Energy Solutions and Advanced Fabrics.

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How nanoparticles flow through the environment


Nanoparticel 1 051316 nanoparticles.jpg

Carbon nanotubes remain attached to materials for years while titanium dioxide and nanozinc are rapidly washed out of cosmetics and accumulate in the ground. Researchers from the National Research Programme “Opportunities and Risks of Nanomaterials” (NRP 64) have developed a new model to track the flow of the most important nanomaterials in the environment.

How many human-made nanoparticles make their way into the air, earth or water? In order to assess these amounts, a group of researchers led by Bernd Nowack from Empa in St. Gallen has developed a computer model as part of the National Research Programme “Opportunities and Risks of Nanomaterials” (NRP 64). “Our estimates offer the best available data at present about the environmental accumulation of nanosilver, nanozinc, nano-tinanium dioxide and carbon nanotubes,” says Nowack.

Cosmetics and tennis racquets

In contrast to the static calculations hitherto in use, their new, dynamic model does not just take into account the significant growth in the production and use of nanomaterials, but also makes provision for the fact that different nanomaterials are used in different applications. For example, nanozinc and nano-titanium dioxide are found primarily in cosmetics. Roughly half of these nanoparticles find their way into our waste water within the space of a year, and from there they enter into sewage sludge. Carbon nanotubes, however, are integrated into composite materials and are bound in products such as which are immobilized and are thus found for example in tennis racquets and bicycle frames. It can take over ten years before they are released, when these products end up in waste incineration or are recycled.

Nanoparticle 2 051316 coated-nanoparticle39,000 metric tons of nanoparticles

The researchers involved in this study come from Empa, ETH and the University of Zurich. They use an estimated annual production of nano-titanium dioxide across Europe of 39,000 metric tons — considerably more than the total for all other nanomaterials. Their model calculates how much of this enters the atmosphere, surface waters, sediments and Earth, and accumulates there. In the EU, the use of sewage sludge as fertiliser (a practice forbidden in Switzerland) means that nano-titanium dioxide today reaches an average concentration of 61 micrograms per kilo in the affected ground.

Knowing the degree of accumulation in the environment is only the first step in the risk assessment of nanomaterials, however. Now this data has to be compared with ecotoxicological test results and the statutory thresholds, says Nowack. A risk assessment has not been carried out with his new model until now. Earlier work with data from a static model showed, however, that the concentrations determined for all four nanomaterials investigated is not expected to have any impact on the environment.

But in the case of nanozinc at least, its concentration in the environment is approaching the critical level. This is why this particular nanomaterial has to be given priority in future ecotoxicological studies — even though nanozinc is produced in smaller quantities than nano-titanium dioxide. Furthermore, ecotoxicological tests have until now been carried out primarily with freshwater organisms. The researchers conclude that complementary investigations using soil-dwelling organisms is a priority.


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The above post is reprinted from materials provided by Swiss National Science Foundation (SNSF). Note: Materials may be edited for content and length.

NREL Study finds Carbon Nanotube Semiconductors Well-Suited for PV Systems


NREL C nanotubes 042616 studyfindsna

 

Researchers at the Energy Department’s National Renewable Energy Laboratory (NREL) discovered single-walled carbon nanotube semiconductors could be favorable for photovoltaic systems because they can potentially convert sunlight to electricity or fuels without losing much energy.

The research builds on the Nobel Prize-winning work of Rudolph Marcus, who developed a fundamental tenet of physical chemistry that explains the rate at which an electron can move from one chemical to another. The Marcus formulation, however, has rarely been used to study photoinduced electron transfer for emerging organic semiconductors such as (SWCNT) that can be used in organic PV devices.

In organic PV devices, after a photon is absorbed, charges (electrons and holes) generally need to be separated across an interface so that they can live long enough to be collected as electrical current. The electron transfer event that produces these separated charges comes with a potential loss as the molecules involved have to structurally reorganize their bonds. This loss is called reorganization energy, but NREL researchers found little energy was lost when pairing SWCNT semiconductors with fullerene molecules.

“What we find in our study is this particular system—nanotubes with fullerenes—have an exceptionally low reorganization energy and the nanotubes themselves probably have very, very low reorganization energy,” said Jeffrey Blackburn, a senior scientist at NREL and co-author of the paper “Tuning the driving force for exciton dissociation in single-walled carbon nanotube heterojunctions.”

The paper appears in the new issue of the journal Nature Chemistry. Its other co-authors are Rachelle Ihly, Kevin Mistry, Andrew Ferguson, Obadiah Reid, and Garry Rumbles from NREL, and Olga Boltalina, Tyler Clikeman, Bryon Larson, and Steven Strauss from Colorado State University.

Organic PV devices involve an interface between a donor and an acceptor. In this case, the SWCNT served as the donor, as it donated an electron to the acceptor (here, the fullerene). The NREL researchers strategically partnered with colleagues at Colorado State University to take advantage of expertise at each institution in producing donors and acceptors with well-defined and highly tunable energy levels: semiconducting SWCNT donors at NREL and fullerene acceptors at CSU. This partnership enabled NREL’s scientists to determine that the event didn’t come with a large energy loss associated with reorganization, meaning solar energy can be harvested more efficiently. For this reason, SWCNT semiconductors could be favorable for PV applications.

Explore further: Researchers achieve record 8.4 percent conversion efficiency in fullerene-free organic solar cells

More information: Rachelle Ihly et al, Tuning the driving force for exciton dissociation in single-walled carbon nanotube heterojunctions, Nature Chemistry (2016). DOI: 10.1038/nchem.2496

Journal reference:Nature Chemistrysearch and more infowebsite

Provided by: National Renewable Energy Laboratory

 

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Nanotubes “Line-Up” to Form Films for Flexible Electonics: Video


Rice logo_rice3 Rice University researchers discover way to make highly aligned, wafer-scale films 

A simple filtration process helped Rice University researchers create flexible, wafer-scale films of highly aligned and closely packed carbon nanotubes.

Scientists at Rice, with support from Los Alamos National Laboratory, have made inch-wide films of densely packed, chirality-enriched single-walled carbon nanotubes through a process revealed today in Nature Nanotechnology.

In the right solution of nanotubes and under the right conditions, the tubes assemble themselves by the millions into long rows that are aligned better than once thought possible, the researchers reported.

The thin films offer possibilities for making flexible electronic and photonic (light-manipulating) devices, said Rice physicist Junichiro Kono, whose lab led the study. Think of a bendable computer chip, rather than a brittle silicon one, and the potential becomes clear, he said.

“Once we have centimeter-sized crystals consisting of single-chirality nanotubes, that’s it,” Kono said. “That’s the holy grail for this field. For the last 20 years, people have been looking for this.”Rice scanning 040616 0215.WAFERS-5-rn-26x5r2v

A scanning electron microscope image shows highly aligned and closely packed carbon nanotubes gathered into a film by researchers at Rice. Courtesy of the Kono Lab

 

The Rice lab is closing in, he said, but the films reported in the current paper are “chirality-enriched” rather than single-chirality. A carbon nanotube is a cylinder of graphene, with its atoms arranged in hexagons. How the hexagons are turned sets the tube’s chirality, and that determines its electronic properties. Some are semiconducting like silicon, and others are metallic conductors.

A film of perfectly aligned, single-chirality nanotubes would have specific electronic properties. Controlling the chirality would allow for tunable films, Kono said, but nanotubes grow in batches of random types.

For now, the Rice researchers use a simple process developed at the National Institute of Standards and Technology to separate nanotubes by chirality. While not perfect, it was good enough to let the researchers make enriched films with nanotubes of different types and diameters and then make terahertz polarizers and electronic transistors.

Rice CNT Inventors 040616 0215.WAFERS-1-rn-168jkgm

Rice graduate students Xiaowei He, left, and Weilu Gao, center, and Professor Junichiro Kono show a film of highly aligned carbon nanotubes made in Kono’s lab. Photo by Jeff Fitlow

The Rice lab discovered the filtration technique in late 2013 when graduate students and lead authors Xiaowei He and Weilu Gao inadvertently added a bit too much water to a nanotube-surfactant suspension before feeding it through a filter assisted by vacuum. (Surfactants keep nanotubes in a solution from clumping.)

The film that formed on the paper filter bore further investigation. “Weilu checked the film with a scanning electron microscope and saw something strange,” He said. Rather than drop randomly onto the paper like pickup sticks, the nanotubes – millions of them – had come together in tight, aligned rows.

“That first picture gave us a clue we might have something totally different,” He said. A year and more than 100 films later, the students and their colleagues had refined their technique to make nanotube wafers up to an inch wide (limited only by the size of their equipment) and of any thickness, from a few to hundreds of nanometers.

Further experiments revealed that each element mattered: the type of filter paper, the vacuum pressure and the concentration of nanotubes and surfactant. Nanotubes of any chirality and diameter worked, but each required adjustments to the other elements to optimize the alignment.

The films can be separated from the paper and washed and dried for use, the researchers said.

They suspect multiwalled carbon nanotubes and non-carbon nanotubes like boron nitride would work as well.

Co-author Wade Adams, a senior faculty fellow at Rice who specializes in polymer science, said the discovery is a step forward in a long quest for aligned structures.

“They formed what is called a monodomain in liquid crystal technology, in which all the rigid molecules line up in the same direction,” Adams said. “It’s astonishing. (The late Rice Nobel laureate) Rick Smalley and I worked very hard for years to make a single crystal of nanotubes, but these students have actually done it in a way neither of us ever imagined.”

Why do the nanotubes line up? Kono said the team is still investigating the mechanics of nucleation — that is, how the first few nanotubes on the paper come together. “We think the nanotubes fall randomly at first, but they can still slide around on the paper,” he said. “Van der Waals force brings them together, and they naturally seek their lowest-energy state, which is in alignment.” Because the nanotubes vary in length, the researchers suspect the overhangs force other tubes to line up as they join the array.

The researchers found their completed films could be patterned with standard lithography techniques. That’s yet another plus for manufacturers, said Kono, who started hearing buzz about the discovery months before the paper’s release.

“I gave an invited talk about our work at a carbon nanotube conference, and many people are already trying to reproduce our results,” he said. “I got so much enthusiastic response right after my talk. Everybody asked for the recipe.”

Co-authors are Rice graduate students Qi Zhang, Sidong Lei and John Robinson and postdoctoral researcher Bo Li; Lijuan Xie of Zhejiang University, who has a complimentary appointment at Rice.

Rice alumnus Erik Haroz and Stephen Doorn of Los Alamos National Laboratory; Robert Vajtai, a faculty research fellow at Rice; Pulickel Ajayan, chair of Rice’s Department of Materials Science and NanoEngineering, the Benjamin M. and Mary Greenwood Anderson Professor in Engineering and a professor of chemistry; and the late Robert Hauge, distinguished faculty fellow in chemistry and in materials science and nanoengineering at Rice.

Adams is a senior faculty fellow in materials science and nanoengineering. Kono is a Rice professor of electrical and computer engineering, of physics and astronomy and of materials science and nanoengineering.

The Department of Energy and the Robert A. Welch Foundation supported the research.

 

U of Texas – Arlington – Researchers Devise more Efficient Materials for Solar Fuel Cells


Solar Fuel Cell U of T energy_cycle

University of Texas at Arlington chemists have developed new high-performing materials for cells that harness sunlight to split carbon dioxide and water into usable fuels like methanol and hydrogen gas. These “green fuels” can be used to power cars, home appliances or even to store energy in batteries.

“Technologies that simultaneously permit us to remove greenhouse gases like carbon dioxide while harnessing and storing the energy of sunlight as fuel are at the forefront of current research,” said Krishnan Rajeshwar, UTA distinguished professor of chemistry and biochemistry and co-founder of the University’s Center of Renewable Energy, Science and Technology.

“Our new material could improve the safety, efficiency and cost-effectiveness of solar fuel generation, which is not yet economically viable,” he added.

The new hybrid platform uses ultra-long carbon nanotube networks with a homogeneous coating of copper oxide nanocrystals. It demonstrates both the high electrical conductivity of carbon nanotubes and the photocathode qualities of copper oxide, efficiently converting light into the photocurrents needed for the photoelectrochemical reduction process.

Morteza Khaledi, dean of the UTA College of Science, said Rajeshwar’s work is representative of the University’s commitment to addressing critical issues with global environmental impact under the Strategic Plan 2020.

“Dr. Rajeshwar’s ongoing, global leadership in research focused on solar fuel generation forms part of UTA’s increasing focus on renewable and sustainable energy,” Khaledi said. “Creating inexpensive ways to generate fuel from an unwanted gas like carbon dioxide would be an enormous step forward for us all.”

For the solar fuel cells project, Rajeshwar worked with Csaba Janáky, an assistant chemistry professor at the University of Szeged in Hungary and Janáky’s master’s student Egon Kecsenovity. Janaky served as a UTA Marie Curie Fellow from 2011 to 2013.

The findings are the subject of a Feb. 15 minireview, “Electrodeposition of Inorganic Oxide/Nanocarbon Composites: Opportunities and Challenges,” published in ChemElectroChem Europe and a companion article in the Journal of Materials Chemistry A on “Decoration of ultra long carbon nanotubes with Cu2O nanocrystals: a hybrid platform for photoelectrochemical CO2 reduction.”

“The performance of our hybrid has proved far superior to the properties of the individual materials,” Rajeshwar said. “These new hybrid films demonstrate five-fold higher electrical conductivity compared to their copper oxide counterparts, and generate a three-fold increase in the photocurrents needed for the reduction process.”

The new material also demonstrates much greater stability during long-term photoelectrolysis than pure copper oxide, which corrodes over time, forming metallic copper.

The research involved developing a multi-step electrodeposition process to ensure that a homogeneous coating of copper oxide nanoparticles were deposited on the carbon nanotube networks. By varying the thickness of the carbon nanotube film and the amount of electrodeposited copper oxide, the researchers were able to optimize the efficiency of this new hybrid material.

Rajeshwar also is working with Brian Dennis, a UTA associate professor of mechanical and aerospace engineering, and Norma Tacconi, a research associate professor of chemistry and biochemistry, on a project with NASA to develop improved methods for oxygen recovery and reuse aboard human spacecraft.

The team is designing, building and demonstrating a “microfluidic electrochemical reactor” to recover oxygen from carbon dioxide extracted from cabin air. The prototype will be built over the next months at the Center for Renewable Energy Science and Technology at UTA.

Rajeshwar joined the College of Science in 1983, is a charter member of the UTA Academy of Distinguished Scholars and senior vice president of The Electrochemical Society, an organization representing the nation’s premier researchers who are dedicated the advancing solid state, electrochemical science and technology.

He is an expert in photoelectrochemistry, nanocomposites, electrochemistry and conducting polymers, and has received numerous awards, including the Wilfred T. Doherty Award from the American Chemical Society and the Energy Technology Division Research Award of the Electrochemical Society.

Rajeshwar earned his Ph.D. in chemistry from the Indian Institute of Science in Bangalore, India, and completed his post-doctoral training in Colorado State University.


Story Source:

The above post is reprinted from materials provided byUniversity of Texas at Arlington. Note: Materials may be edited for content and length.


Journal Reference:

  1. E. Kecsenovity, B. Endrődi, Zs. Pápa, K. Hernádi, K. Rajeshwar, C. Janáky. Decoration of ultra-long carbon nanotubes with Cu2O nanocrystals: a hybrid platform for enhanced photoelectrochemical CO2reduction. J. Mater. Chem. A, 2016; 4 (8): 3139 DOI:10.1039/C5TA10457B

Quantum Dots of Iron Arranged on Boron Nitride Nanotubes (BNNTs) for Better Wearable Tech Without Semiconductors: “Iron Stepping Stones” with Video


Nanotube Iron QDs image131438-horiz

Iron-dotted boron nitride nanotubes, made in Yoke Khin Yaps’ lab at Michigan Tech, could make for better wearable tech because of their flexibility and electronic behaviors.

February 5, 2016—

The road to more versatile wearable technology is dotted with iron. Specifically, quantum dots of iron arranged on boron nitride nanotubes (BNNTs). The new material is the subject of a studypublished in Scientific Reports in February, led by Yoke Khin Yap, a professor of physics at Michigan Technological University.

Yap says the iron-studded BNNTs are pushing the boundaries of electronics hardware. The transistors modulating electron flow need an upgrade.

“Look beyond semiconductors,” he says, explaining that materials like silicon semiconductors tend to overheat, can only get so small and leak electric current. The key to revamping the fundamental base of transistors is creating a series of stepping-stones.

Quantum Dots

The nanotubes are the mainframe of this new material. BNNTs are great insulators and terrible at conducting electricity. While at first that seems like an odd choice for electronics, the insulating effect of BNNTs is crucial to prevent current leakage and overheating. Additionally, electron flow will only occur across the metal dots on the BNNTs.

In past research, Yap and his team used gold for quantum dots, placed along a BNNT in a tidy line. With enough energy potential, the electrons are repelled by the insulating BNNT and hopscotch from gold dot to gold dot. This electron movement is called quantum tunneling.

“Imagine this as a river, and there’s no bridge; it’s too big to hop over,” Yap says. “Now, picture having stepping stones across the river—you can cross over, but only when you have enough energy to do so.”

Nanotech for Wearable Electronics

Unlike with semiconductors, there is no classical resistance with quantum tunneling. No resistance means no heat. Plus, these materials are very small; the nanomaterials enable the transistors to shrink as well. An added bonus is that BNNTs are also quite flexible, a boon for wearable electronics.

“Here’s where the challenge comes in,” Yap says, holding up a pen to demonstrate. He gestures along the length of the pen, which mimics a straight BNNT, tapping out a line of quantum dots. “We have an array here to do quantum tunneling, but what if we want to bend the array to be flexible like a piece of wearable electronics?”

Yap sets down the pen and curls up his index finger: “And if I bend the dots, the distance between them changes—in doing so, we change the electronic behavior.”

Changing the behavior means that the quantum tunneling may not work. The solution is to get out of line: Yap and his team arranged a grid of quantum dots around the outside of the BNNT.

“This time we used iron instead of gold,” Yap adds, explaining that gold’s melting temperature was low for the process his team used. “And when we tested the material, the electrons distributed uniformly across the whole surface of the nanotubes.”

That means that instead of having a line of stepping stones, there are many different paths across the river, and an electron will jump to the nearest one. For future use in wearable electronics, the multiplicity of paths ensures electricity is moving from one riverbank to the next, one way or another. Using scanning tunneling microscopy inside a transmission electron microscope (STM-TEM), the team successfully bent the iron dot-coated BNNT while monitoring the electron flows. The electronic behaviors remain the same even when the BNNT was bent all the way up to 75 degrees.

Next Steps

Yap says that this experiment is a proof of concept. While the iron BNNT material shows promise, it’s not a full transistor yet, capable of modulating electron movement. Right now, it’s called a flexible tunneling channel.

“Next, we’ll put the BNNT and iron onto a bendable plastic substrate,” Yap says. “Then we’ll bend this substrate and watch where the electrons go.”

This experimental work is complemented by computer simulations by John Jaszczak, professor of physics, and Paul Bergstrom, professor of electrical and computer engineering.

Which route the electricity takes is hard to track, which will be the main challenge for the next experiment. But one direction is certain, Yap’s research is headed down a path to change the basic level of electronics and make wearable tech more adaptable.

Michigan Technological University (www.mtu.edu) is a leading public research university developing new technologies and preparing students to create the future for a prosperous and sustainable world. Michigan Tech offers more than 120 undergraduate and graduate degree programs in engineering; forest resources; computing; technology; business; economics; natural, physical and environmental sciences; arts; humanities; and social sciences.

DARPA & Georgia Institute of Technology: Optical “Rectenna” Converts Light to DC Current: A New Way to Efficiently Capture Solar Energy


Rectenna Naval Optical 150928122542_1_540x360Using nanometer-scale components, researchers have demonstrated the first optical rectenna, a device that combines the functions of an antenna and a rectifier diode to convert light directly into DC current.

Based on multiwall carbon nanotubes and tiny rectifiers fabricated onto them, the optical rectennas could provide a new technology for photodetectors that would operate without the need for cooling, energy harvesters that would convert waste heat to electricity — and ultimately for a new way to efficiently capture solar energy.

In the new devices, developed by engineers at the Georgia Institute of Technology, the carbon nanotubes act as antennas to capture light from the sun or other sources. As the waves of light hit the nanotube antennas, they create an oscillating charge that moves through rectifier devices attached to them. The rectifiers switch on and off at record high petahertz speeds, creating a small direct current.

Billions of rectennas in an array can produce significant current, though the efficiency of the devices demonstrated so far remains below one percent. The researchers hope to boost that output through optimization techniques, and believe that a rectenna with commercial potential may be available within a year.

“We could ultimately make solar cells that are twice as efficient at a cost that is ten times lower, and that is to me an opportunity to change the world in a very big way” said Baratunde Cola, an associate professor in the George W. Woodruff School of Mechanical Engineering at Georgia Tech. “As a robust, high-temperature detector, these rectennas could be a completely disruptive technology if we can get to one percent efficiency. If we can get to higher efficiencies, we could apply it to energy conversion technologies and solar energy capture.”

The research, supported by the Defense Advanced Research Projects Agency (DARPA), the Space and Naval Warfare (SPAWAR) Systems Center and the Army Research Office (ARO), is scheduled to be reported September 28 in the journal Nature Nanotechnology.

Rectenna Naval Optical 150928122542_1_540x360

Optical rectenna schematic. This schematic shows the components of the optical rectenna developed at the Georgia Institute of Technology.
Credit: Thomas Bougher, Georgia Tech

Developed in the 1960s and 1970s, rectennas have operated at wavelengths as short as ten microns, but for more than 40 years researchers have been attempting to make devices at optical wavelengths. There were many challenges: making the antennas small enough to couple optical wavelengths, and fabricating a matching rectifier diode small enough and able to operate fast enough to capture the electromagnetic wave oscillations. But the potential of high efficiency and low cost kept scientists working on the technology.

“The physics and the scientific concepts have been out there,” said Cola. “Now was the perfect time to try some new things and make a device work, thanks to advances in fabrication technology.”

Using metallic multiwall carbon nanotubes and nanoscale fabrication techniques, Cola and collaborators Asha Sharma, Virendra Singh and Thomas Bougher constructed devices that utilize the wave nature of light rather than its particle nature. They also used a long series of tests — and more than a thousand devices — to verify measurements of both current and voltage to confirm the existence of rectenna functions that had been predicted theoretically. The devices operated at a range of temperatures from 5 to 77 degrees Celsius.

Fabricating the rectennas begins with growing forests of vertically-aligned carbon nanotubes on a conductive substrate. Using atomic layer chemical vapor deposition, the nanotubes are coated with an aluminum oxide material to insulate them. Finally, physical vapor deposition is used to deposit optically-transparent thin layers of calcium then aluminum metals atop the nanotube forest. The difference of work functions between the nanotubes and the calcium provides a potential of about two electron volts, enough to drive electrons out of the carbon nanotube antennas when they are excited by light.

In operation, oscillating waves of light pass through the transparent calcium-aluminum electrode and interact with the nanotubes. The metal-insulator-metal junctions at the nanotube tips serve as rectifiers switching on and off at femtosecond intervals, allowing electrons generated by the antenna to flow one way into the top electrode. Ultra-low capacitance, on the order of a few attofarads, enables the 10-nanometer diameter diode to operate at these exceptional frequencies.

“A rectenna is basically an antenna coupled to a diode, but when you move into the optical spectrum, that usually means a nanoscale antenna coupled to a metal-insulator-metal diode,” Cola explained. “The closer you can get the antenna to the diode, the more efficient it is. So the ideal structure uses the antenna as one of the metals in the diode — which is the structure we made.”

The rectennas fabricated by Cola’s group are grown on rigid substrates, but the goal is to grow them on a foil or other material that would produce flexible solar cells or photodetectors.

Cola sees the rectennas built so far as simple proof of principle. He has ideas for how to improve the efficiency by changing the materials, opening the carbon nanotubes to allow multiple conduction channels, and reducing resistance in the structures.

“We think we can reduce the resistance by several orders of magnitude just by improving the fabrication of our device structures,” he said. “Based on what others have done and what the theory is showing us, I believe that these devices could get to greater than 40 percent efficiency.”


Story Source:

The above post is reprinted from materials provided by Georgia Institute of Technology. Note: Materials may be edited for content and length.


Journal Reference:

  1. Asha Sharma, Virendra Singh, Thomas L. Bougher, Baratunde A. Cola. A carbon nanotube optical rectenna. Nature Nanotechnology, 2015; DOI: 10.1038/nnano.2015.220