Solar cells made from quantum dots could be low-cost, flexible, and easy to make. But the efficiency with which they convert light into electricity remains too low for practical use. Researchers at the Massachusetts Institute of Technology now show that incorporating nanowires into quantum dot solar cells increases the cells’ efficiency by 35%.
Quantum dots are semiconductor nanocrystals that absorb different wavelengths of light depending on their size. Solar cells made from different-sized crystals should absorb light over a much wider range of colors than silicon devices. What’s more, because quantum dots are made in solution, they could be easily printed or painted onto flexible surfaces. Scientists have calculated that quantum dots could be used to make thin-film solar cells that could convert light to electricity with 15% efficiency, the same as commercial silicon devices.
The best-performing quantum dot solar cells consist of a lead sulfide quantum dot layer butted up against a zinc oxide or titanium dioxide layer. The quantum dots absorb light, and electrons created in the process travel to the metal oxide layer to reach the electrical circuit. The problem is that the quantum dot layer has to be thick enough to absorb light efficiently, but thin enough for the electrons to quickly traverse it.
The MIT researchers, led by electrical engineering and computer science professor Vladimir Bulovic, overcame that tradeoff by replacing the flat ZnO layer with an array of vertical zinc oxide nanowires. The nanowires penetrate the quantum dot layer, providing conductive paths for the electrons to follow out to the electrical circuit, says Joel Jean, a graduate student in Bulovic’s group. The researchers published their results in the journal Advanced Materials.
The researchers start with glass substrates that are coated with indium tin oxide transparent electrodes. They deposit a ZnO layer on top and float the entire susbtrate upside down in an aqueous solution of zinc precursors. An array of aligned nanowires grows downwards from the ZnO layer. After about an hour, the researchers rinse the substrates. Finally, they deposit PbS quantum dots, which fill up the space between the nanowires, and top it off with a gold electrode.
The nanowires boost the output current of the devices by 50% and the efficiency by 35% over planar ZnO devices. The overall light-to-electricity conversion efficiency of the new devices is 4.9 percent, among the highest reported for ZnO-based quantum dot solar cells, Jean says.
The researchers believe the efficiency could be further enhanced by using thicker light-absorbing layers and longer nanowires, as well as by controlling the spacing between nanowires to better accommodate quantum dots.
The idea of using ZnO nanowires to increase efficiency in quantum dot solar cells is not new, but this is the first significant implementation of the concept, says Matthew Beard, a senior scientist at the National Renewable Energy Laboratory. “The observed efficiency boost is promising and significant,” he says. “The efficiencies for these types of solar cells are increasing rapidly and this work demonstrates that the improvements in efficiency will continue.”
A key advantage of the nanowire-quantum dot cells, says Jean, is that they could be made on large areas. “One of the main benefits of quantum dots is that they’re grown in and deposited from solution,” he says. “This translates to fabrication of large-area films, which is necessary for making solar panels. Zinc oxide nanowires are also grown in an aqueous solution process. Scalability should be one of the primary practical advantages of this type of solar cell.”
Glo AB, a company that provides high-quality light source solutions for displays, illumination, and automotive sectors using its proprietary nanowire-based LED technology (nLEDTM) was named today by the Cleantech Group (CTG) as one of Europe’s Cleantech Companies of the Decade.
“This is a great acknowledgement of the significance of our advanced technology and its potential to be a game-changer in the area of LED solutions for display as well as lighting applications,” said Lars Samuelson, Chief Scientific Officer of Glo AB and Professor at Lund University. GLO AB originates from the Nanoscience research at Lund University.
This one-off award was made in connection with the 10th anniversary of Cleantech Forum Europe, held in Stockholm this year. The award was made in Stockholm’s City Hall, the venue of the annual Nobel Prize ceremony. “To identify the best five European cleantech companies of the decade would be an impossible task. After all, how can you meaningfully compare, say, a profitable ESCO with a pre-revenue bio-materials developer?” said Sheeraz Haji, CEO, CTG. “Instead, we set out to select private companies that got started and have achieved impressive results in the timeframe since we first conceived of a Cleantech Forum Europe. We sought companies whose stories are illustrative of the collective journey we have all been on, and whose promise for 2014 and beyond is exciting and speaks to the sustainable innovation opportunities in front of us.”
“We selected Glo—a 2013 Global Cleantech 100 company—because it represents the energy efficiency opportunity, as well as the quality of Europe’s science base as a lever for more start-ups in the future,” explained Richard Youngman, Managing Director Europe & Asia, CTG. “All the indicators and information we are privy to suggest a very bright future for Glo.”
Can Organic Solar Cells Using Polymeric Materials and Fullerenes (Quantum Dots) be a Solution for Abundant & Cheap Solar Energy?
Abstract
Photovoltaic cells directly convert sun light into electricity and hence are key technological devices to meet one of the challenges that mankind has to face in this century: a sustainable and clean production of renewable energy. Organic solar cells, using polymeric materials to capture sun light, have particularly favorable properties. They are low-cost, light-weight and flexible, and their color can be adapted by varying the material composition. Such solar cells typically consist of nanostructured blends of conjugated polymers (long chains of carbon atoms), acting as light absorbers, and fullerenes (nanoscale carbon soccer balls), acting as electron acceptors.
The primary and most elementary step in the light-to-current conversion process, the light-induced transfer of an electron from the polymer to the fullerene, occurs at such a staggering speed that it has previously proven difficult to follow it directly.
Now, a team of German and Italian researchers from Oldenburg, Modena and Milano reported the first real time movies of the light-to-current conversion process in an organic solar cell. In a report published in the May 30 issue of Science Magazine, the researchers show that the quantum-mechanical, wavelike nature of electrons and their coupling to the nuclei is of fundamental importance for the charge transfer in an organic photovoltaic device.
“Our initial results were actually very surprising”, says Christoph Lienau, a physics professor from the University of Oldenburg who led the research team. “When we used extremely short, femtosecond (1 billionth of a millionth of a second, i.e. 0.000000000000001 seconds) light pulses to illuminate the polymer layer in an organic cell, we found that the light pulses induced oscillatory, vibrational motion of the polymer molecules. Unexpectedly, however, we saw that also the fullerene molecules all started to vibrate synchronously.
We could not understand this without assuming that the electronic wave packets excited by the light pulses would coherently oscillate back and forth between the polymer and the fullerene.” All colleagues with whom the scientists discussed these initial results, obtained by PhD student Sarah Falke from Oldenburg in close collaboration with the team of Giulio Cerullo from Politecnico di Milano, leading experts in ultrafast spectroscopy, were skeptical.
“In such organic blends, the interface morphology between polymer and fullerene is very complex and the two moieties are not covalently bound”, says Lienau, “therefore one might not expect that vibronic coherence persists even at room temperature. We therefore asked Elisa Molinari and Carlo A. Rozzi, of the Istituto Nanoscienze of CNR and the University of Modena and Reggio Emilia, for help.”
A series of sophisticated quantum dynamics simulations, performed by Rozzi and colleagues, provided impressive movies of the evolution of the electronic cloud and of the atomic nuclei in this system, which are responsible of the oscillations found in experiments. “Our calculations indicate”, says Molinari, “that the coupling between electrons and nuclei is of crucial importance for the charge transfer efficiency. Tailoring this coupling by varying the device morphology and composition hence may be important for optimizing device efficiency”.
Will the new results immediately lead to better solar cells?
“Such ultrafast spectroscopic studies, and in particular their comparison with advanced theoretical modelling, provide impressive and most direct insight in the fundamental phenomena that initiate the organic photovoltaic process. They turn out to be very similar to the strategies developed by Nature in photosynthesis.”, says Lienau. “Recent studies indicate that quantum coherence apparently plays an important role in that case. Our new result provide evidence for similar phenomena in functional artificial photovoltaic devices: a conceptual advancement which could be used to guide the design of future artificial light-harvesting systems in an attempt to match the yet unrivalled efficiency of natural ones . “
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Prof. Dr. Christoph Lienau
Carl von Ossietzky University Oldenburg
Institute of Physics
Ultrafast Nano-Optics
Prof. Dr. Elisa Molinari
Istituto Nanoscienze–Consiglio Nazionale delle Ricerche (CNR),
Naval Admiral William H. McRaven gave a commencement speech at his alma mater at the University of Texas at Austin worth reading, printing out and hanging on the inside of your front door.
No one has to be a Navy SEAL to get the most out of these 10 life lessons (life lesson listed first for ease of reading). Via Business Insider:
“If You Want to Change the World … “
#1. If you want to change the world, start off by making your bed.
“If you make your bed every morning you will have accomplished the first task of the day. It will give you a small sense of pride and it will encourage you to do another task and another and another. […]
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If you can’t do the little things right, you will never do the big things right.”
Naval Admiral William H. McRaven gave a commencement speech at his alma mater at the University of Texas at Austin worth reading, printing out and hanging on the inside of your front door.
No one has to be a Navy SEAL to get the most out of these 10 life lessons (life lesson listed first for ease of reading). Via Business Insider:
“If You Want to Change the World … “
#1. If you want to change the world, start off by making your bed.
“If you make your bed every morning you will have accomplished the first task of the day. It will give you a small sense of pride and it will encourage you to do another task and another and another. […]
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If you can’t do the little things right, you will never do the big things right.”
#2. If you want to change the world, find someone to help you paddle.
“For the boat to make it to its destination, everyone must paddle.
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You can’t change the world alone—you will need some help— and to truly get from your starting point to your destination takes friends, colleagues, the good will of strangers and a strong coxswain to guide them.”
#3. If you want to change the world, measure a person by the size of their heart, not the size of their flippers.
“The munchkin boat crew had one American Indian, one African American, one Polish American, one Greek American, one Italian American, and two tough kids from the mid-west.
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They out paddled, out-ran, and out swam all the other boat crews. […]
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But somehow these little guys, from every corner of the Nation and the world, always had the last laugh— swimming faster than everyone and reaching the shore long before the rest of us.
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SEAL training was a great equalizer. Nothing mattered but your will to succeed. Not your color, not your ethnic background, not your education and not your social status.”
#4. If you want to change the world get over being a sugar cookie and keep moving forward.
“For failing the uniform inspection, the student had to run, fully clothed into the surfzone and then, wet from head to toe, roll around on the beach until every part of your body was covered with sand.
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The effect was known as a ‘sugar cookie.’ You stayed in that uniform the rest of the day—cold, wet and sandy.
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There were many a student who just couldn’t accept the fact that all their effort was in vain. That no matter how hard they tried to get the uniform right—it was unappreciated.
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Those students didn’t make it through training. […]
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Sometimes no matter how well you prepare or how well you perform you still end up as a sugar cookie.
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It’s just the way life is sometimes.”
#5 But if you want to change the world, don’t be afraid of the circuses.
“A ‘circus’ was two hours of additional calisthenics—designed to wear you down, to break your spirit, to force you to quit.
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No one wanted a circus.
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A circus meant that for that day you didn’t measure up. A circus meant more fatigue—and more fatigue meant that the following day would be more difficult—and more circuses were likely.
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.Life is filled with circuses.
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You will fail. You will likely fail often. It will be painful. It will be discouraging. At times it will test you to your very core.”
#6. If you want to change the world sometimes you have to slide down the obstacle head first.
“But the most challenging obstacle was the slide for life. It had a three level 30 foot tower at one end and a one level tower at the other. In between was a 200-foot long rope.
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You had to climb the three tiered tower and once at the top, you grabbed the rope, swung underneath the rope and pulled yourself hand over hand until you got to the other end.
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The record seemed unbeatable, until one day, a student decided to go down the slide for life—head first.
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Instead of swinging his body underneath the rope and inching his way down, he bravely mounted the TOP of the rope and thrust himself forward.
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It was a dangerous move—seemingly foolish, and fraught with risk. Failure could mean injury and being dropped from the training.
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Without hesitation—the student slid down the rope—perilously fast, instead of several minutes, it only took him half that time and by the end of the course he had broken the record.”
#7. So, if you want to change the world, don’t back down from the sharks.
“During the land warfare phase of training, the students are flown out to San Clemente Island which lies off the coast of San Diego.
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The waters off San Clemente are a breeding ground for the great white sharks. To pass SEAL training there are a series of long swims that must be completed. One—is the night swim.
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Before the swim the instructors joyfully brief the trainees on all the species of sharks that inhabit the waters off San Clemente.
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They assure you, however, that no student has ever been eaten by a shark—at least not recently.
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But, you are also taught that if a shark begins to circle your position—stand your ground. Do not swim away. Do not act afraid.
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And if the shark, hungry for a midnight snack, darts towards you—then summons up all your strength and punch him in the snout and he will turn and swim away.
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There are a lot of sharks in the world. If you hope to complete the swim you will have to deal with them.”
#8. If you want to change the world, you must be your very best in the darkest moment.
“To be successful in your mission, you have to swim under the ship and find the keel—the center line and the deepest part of the ship.
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This is your objective. But the keel is also the darkest part of the ship—where you cannot see your hand in front of your face, where the noise from the ship’s machinery is deafening and where it is easy to get disoriented and fail.
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Every SEAL knows that under the keel, at the darkest moment of the mission—is the time when you must be calm, composed—when all your tactical skills, your physical power and all your inner strength must be brought to bear.”
#9. So, if you want to change the world, start singing when you’re up to your neck in mud.
“The mud consumed each man till there was nothing visible but our heads. The instructors told us we could leave the mud if only five men would quit—just five men and we could get out of the oppressive cold.
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Looking around the mud flat it was apparent that some students were about to give up. It was still over eight hours till the sun came up—eight more hours of bone chilling cold.
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The chattering teeth and shivering moans of the trainees were so loud it was hard to hear anything and then, one voice began to echo through the night—one voice raised in song.
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The song was terribly out of tune, but sung with great enthusiasm.
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One voice became two and two became three and before long everyone in the class was singing. […]
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The instructors threatened us with more time in the mud if we kept up the singing—but the singing persisted.
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And somehow—the mud seemed a little warmer, the wind a little tamer and the dawn not so far away.
If I have learned anything in my time traveling the world, it is the power of hope. The power of one person—Washington, Lincoln, King, Mandela and even a young girl from Pakistan—Malala—one person can change the world by giving people hope.”
#10. If you want to change the world don’t ever, ever ring the bell.
Finally, in SEAL training there is a bell. A brass bell that hangs in the center of the compound for all the students to see.
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All you have to do to quit—is ring the bell. Ring the bell and you no longer have to wake up at 5 o’clock. Ring the bell and you no longer have to do the freezing cold swims.
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Ring the bell and you no longer have to do the runs, the obstacle course, the PT—and you no longer have to endure the hardships of training.
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Just ring the bell.”
Of course, if you ring that bell, you can never accomplish your goal in life. When things seem hardest, that’s when you push hardest. That’s the only way you can stop being a “sugar cookie.”
Solution processing is a promising route for the realization of low-cost, large-area, flexible and lightweight photovoltaic devices with short energy payback time and high specific power.
However, solar cells based on solution-processed organic, inorganic and hybrid materials reported thus far generally suffer from poor air stability, require an inert-atmosphere processing environment or necessitate high-temperature processing1, all of which increase manufacturing complexities and costs.
Simultaneously fulfilling the goals of high efficiency, low-temperature fabrication conditions and good atmospheric stability remains a major technical challenge, which may be addressed, as we demonstrate here, with the development of room-temperature solution-processed ZnO/PbS quantum dot solar cells.
By engineering the band alignment of the quantum dot layers through the use of different ligand treatments, a certified efficiency of 8.55% has been reached.
Furthermore, the performance of unencapsulated devices remains unchanged for over 150 days of storage in air. This material system introduces a new approach towards the goal of high-performance air-stable solar cells compatible with simple solution processes and deposition on flexible substrates.
At a glance
a, Device architectures. b, Representative J–V characteristics of devices with Au anodes under simulated AM1.5G irradiation (100 mW cm−2). The PbS-TBAI device consists of 12 layers of PbS-TBAI and the PbS-TBAI/PbS-EDT device consists o…
a, Energy levels with respect to vacuum for pure PbS-TBAI, pure PbS-EDT and PbS-TBAI films covered with different thicknesses of PbS-EDT layers. The Fermi levels (EF, dashed line) and valence band edges (EV, blue lines) were determined
a, Open circuit voltage (VOC). b, Short-circuit current (JSC). c, Fill factor (FF). d, Power conversion efficiency (PCE). Measurements were performed in a nitrogen-filled glovebox. Day 0 denotes measurements performed after anode evapo…
a, Evolution of photovoltaic parameters of PbS-TBAI (black) and PbS-TBAI/PbS-EDT (red) devices. Open symbols represent the average values and solid symbols represent the values for the best-performing device. b, Device performance of a…
Schematic of a quantum dot-graphene nano-photonic device, as described in this research project.
Semiconductor quantum dots (QDs) are nanoscale semiconductors that exhibit size dependent physical properties. For example, the color (wavelength) of light that they absorb changes dramatically as the diameter decreases. Graphene is an atomically thick sheet of carbon atoms, arranged in a hexagonal lattice pattern. In this work, QDs have been combined with graphene to develop nanoscale photonic devices that can dramatically improve our ability to detect light.
Quantum dots can absorb light and transfer it to graphene, but the efficiency of the transfer depends on how far the QDs and the graphene are separated from each other. This study demonstrated that the thickness of the organic molecule layer that typically surrounds the QDs is crucial in attaining sufficiently high efficiency of this light/energy transfer into the graphene. In other works, the thinner the organic layer, the better.
This transfer can be further optimized by engineering the interface between the two nanomaterials, specifically optimizing the thickness of the organic capping molecules on the quantum dots. Based on this work, further improvement of the performance of these nano-photonic devices can be expected.
a) Schematic of a chloride-terminated CdSe quantum dot. b) A high resolution transmission electron microscopy image of such quantum dots.
Commercial cadmium selenide (CdSe) quantum dots have long insulating organic ligands that prevent their utilization in energy and charge transfer applications for which short distances between the QDs and other materials are critical. Short, chlorine ligands that passivated CdSe QDs are an intriguing alternative material to enhance the interaction with materials into which charge carriers, such as electrons, can easily conduct.
Graphene is such a material. The combination of CdSe quantum dots and graphene could hold the key to the development and implementation of nanoscale materials systems in flexible electronics and photodetectors.
Photoluminescence lifetime decay of isolated quantum dots on glass (blue) and graphene (red) demonstrate efficient energy transfer between the quantum dots and graphene.
What Are The Details?
— CFN Capabilities: The Advanced Optical Microscopy Facility measured the time-resolved photoluminescence from isolated CdSe quantum dots deposited on graphene.
— The team discovered that short, chloride-capped CdSe quantum dots, deposited on chemical-vapor-deposited, monolayer layer graphene, exhibited highly efficient energy transfer to the graphene with a 4x observed reduction in the excitonic lifetime. This demonstrated significant near-field coupling between quantum dots and the graphene.
More information: “Time-resolved energy transfer from single chloride-terminated nanocrystals to graphene.” O. A. Ajayi, et al. Appl. Phys. Lett. 104, 171101 (2014); dx.doi.org/10.1063/1.4874298
Early tests of the “nanodaisy” drug delivery technique show promise against a number of cancers.
Raleigh, NC | Posted on May 28th, 2014
Biomedical engineering researchers have developed daisy-shaped, nanoscale structures that are made predominantly of anti-cancer drugs and are capable of introducing a “cocktail” of multiple drugs into cancer cells. The researchers are all part the joint biomedical engineering program at North Carolina State University and the University of North Carolina at Chapel Hill.
“We found that this technique was much better than conventional drug-delivery techniques at inhibiting the growth of lung cancer tumors in mice,” says Dr. Zhen Gu, senior author of the paper and an assistant professor in the joint biomedical engineering program. “And based on in vitro tests in nine different cell lines, the technique is also promising for use against leukemia, breast, prostate, liver, ovarian and brain cancers.”
To make the “nanodaisies,” the researchers begin with a solution that contains a polymer called polyethylene glycol (PEG). The PEG forms long strands that have much shorter strands branching off to either side. Researchers directly link the anti-cancer drug camptothecin (CPT) onto the shorter strands and introduce the anti-cancer drug doxorubicin (Dox) into the solution.
PEG is hydrophilic, meaning it likes water. CPT and Dox are hydrophobic, meaning they don’t like water. As a result, the CPT and Dox cluster together in the solution, wrapping the PEG around themselves. This results in a daisy-shaped drug cocktail, only 50 nanometers in diameter, which can be injected into a cancer patient.
Once injected, the nanodaisies float through the bloodstream until they are absorbed by cancer cells. In fact, one of the reasons the researchers chose to use PEG is because it has chemical properties that prolong the life of the drugs in the bloodstream.
Once in a cancer cell, the drugs are released. “Both drugs attack the cell’s nucleus, but via different mechanisms,” says Dr. Wanyi Tai, lead author and a former postdoctoral researcher in Gu’s lab.
“Combined, the drugs are more effective than either drug is by itself,” Gu says. “We are very optimistic about this technique and are hoping to begin pre-clinical testing in the near future.”
Abstract:
“Folding Graft Copolymer with Pedant Drug Segment for Co-Delivery of Anticancer Drugs”
Authors: Wanyi Tai, Ran Mo, Yue Lu, Tianyue Jiang, and Zhen Gu, North Carolina State University and University of North Carolina at Chapel Hill
Published: May 27, 2014, Biomaterials
Abstract: A graft copolymer with pendant drug segment can fold into nanostructures in a “protein folding-like” manner. The graft copolymer is constructed by directly polymerizing γ-camptothecin-glutamate N-carboxyanhydride (Glu(CPT)-NCA) on multiple sites of poly(ethylene glycol) (PEG)-based main chain via the ring open polymerization. The “purely” conjugated anticancer agent camptothecin (CPT) is hydrophobic and serves as the principal driving force during the folding process.
When exposed to water, the obtained copolymer, together with doxorubicin (Dox), another anticancer agent, can fold into uniform nanocarriers for dual-drug delivery. Equipped with a PEG shell, the nanocarriers displayed good stability and can be internalized by a variety of cancer cell lines via the lipid raft and clathrin-mediated endocytotic pathway without premature leakage, which showed a high synergetic activity of CPT and Dox toward various cancer cells.In vivo study validated that the nanocarriers exhibited strong accumulation in tumor sites and showed a prominent anticancer activity against the lung cancer xenograft mice model compared with free drugs.
BASF increased spending on research and development to €1.8 billion (2012: €1.7 billion) in 2013. “In absolute terms, we lead the field in the chemical industry with our research and development expenditures,” said Dr. Andreas Kreimeyer, member of the Board of Executive Directors of BASF SE and Research Executive Director, at the Research Press Conference on the topic ”Nanotechnology: Small dimensions – great opportunities” in Ludwigshafen.
BASF has a workforce of around 10,650 employees working in international and interdisciplinary teams on around 3,000 research projects to find answers to the challenges of the future and secure sustainable profitable growth for the company.
The innovative strength of BASF is demonstrated once more by sales of new products introduced onto the market within the past five years: Last year these amounted to about €8 billion. In 2013 alone, the company launched more than 300 new products on the market. The patent portfolio also reflects the success of the company’s research activities. With 1,300 patents filed last year and about 151,000 registrations and intellectual property rights worldwide, BASF is at the top of the Patent Asset Index for the fifth time in succession.
New research laboratories in North America and Asia
In future, BASF is expecting strong impulses from the regions for its innovation pipeline. By 2020, 50% of its research activities are to be conducted outside Europe. In 2013, BASF came another step closer to this goal and increased the proportion of its research outside Europe to 28% (2012: 27%). To drive the globalization of research further forward, the company has, among other things, established six new laboratories at different locations in Asia and the United States. Moreover, for example in cooperation with highly innovative universities, BASF has founded the “California Research Alliance by BASF” (CARA) in California. Here, the main research focus is on the biosciences and new inorganic materials for the areas energy, electronics and renewable resources. In Asia, the company has, for example, joined forces with top-ranking universities from China, Japan and Korea to found the research initiative ”Network for Advanced Materials Open Research” (NAO). In this joint project, research is underway on materials for a wide range of applications, including products for the automotive, construction and water industries and for the wind energy sector.
BASF collaborates in a global network with more than 600 outstanding universities, research institutes and companies. “Interdisciplinary and international cooperations are a decisive element of BASF’s Know-how Verbund,” added Kreimeyer. Offering intelligent solutions for the challenges of the future based on new systems and functional materials requires not only interdisciplinary approaches but also the use of cross-sectional technologies like nanotechnology.
Nanotechnology – helping to develop solutions for the future
Nanotechnology is concerned with the development, manufacture and use of materials that have structures, particles, fibers or platelets smaller than 100 nanometers and so possess novel properties. Many innovations in areas such as automotive technology, energy, electronics or construction and medicine would not be possible without nanotechnology. BASF uses this technology to develop new solutions and improve existing products.
High-performance insulation materials
Nanopores provide the specific material characteristics in one of BASF’s new high-performance insulation material. Slentite™ is the first high-performance insulation panel based on polyurethane, which needs only half the space compared to traditional materials while offering the same insulation performance. Up to 90% of the volume of the organic aerogel consists of air-filled pores which have a diameter of only 50 to 100 nanometers. As a result, the air molecules’ freedom of movement is limited and the transfer of heat is reduced. The high-performance insulation material can be used, for example, in the construction sector for old and new buildings.
Microencapsulation
One BASF research field in which nanotechnology plays a key role focuses on the development of formulations of active components, especially on microencapsulation. Active substances are thereby enclosed with a wax, polymer or oil-based protective shell. This enables the actives to be used more specifically for the application concerned and function more effectively. The important factor here is the controlled release of the actives. Researchers at BASF have succeeded in designing the shell according to the application need, making it only a few nanometers thick or nanostructured. This allows control of the time and speed at which the active substances can be released at the desired target location.
A material that could contribute to the key technological progress of Organic Light Emitting Diodes (OLEDs), displays and even batteries and catalysts is graphene. It is closely related to graphite, which is used, for example, in pencil leads. Unlike graphite, graphene consists of only one layer of carbon atoms, making it less than one nanometer thin. This material is a very efficient electricity and heat conductor and is very stable but also elastic and flexible. Because it is so thin, the actually black material appears transparent. An international team of researchers is currently exploring the scientific basis and application potential of innovative carbon-based materials like graphene at the joint research and development platform of BASF and the Max Planck Institute for Polymer Research in Mainz, Germany.
Color filters
BASF’s new red color, Irgaphor® Red S 3621 CF, ensures an excellent image quality of liquid crystal displays (LCD). It is used in color filters for notebook, computer and television screens. The smaller the particles are, the more intense the brightness of screens becomes. BASF has succeeded in manufacturing its product with a particle size of less than 40 nanometers. The tiny particles enable considerably less scattering of light in the color filter. Compared to traditional color products, BASF’s new red doubles the contrast ratio of displays. This leads to a sharp, pure-colored, high-contrast and thus brilliant image.
Safely utilizing the potentials of nanotechnology
Accessing new technologies requires an objective assessment of both the opportunities and risks. In addition to the manufacture and development of nanomaterials, another research priority is the risk assessment of nanoparticles. For about ten years, BASF has therefore been pursuing safety research with nanomaterials. During this time the company has conducted more than 150 own toxicology and ecotoxicology studies and participated in approximately 30 different projects with external partners.
Open dialog for a common understanding
Innovation-friendly social and political conditions are decisive in allowing the potentials of nanotechnology to be utilized. “Public discussion is very important for us. We actively seek dialog, also with critical opinion leaders,” said Kreimeyer. For example, BASF has – as the first and so far only company in Germany – established a regularly held dialog forum focusing on nanotechnology. At these events, BASF employees conduct discussions with various representatives of environmental and consumer organizations, labor unions, scientific institutions and churches to improve understanding of current concerns, explain opportunities, answer questions and jointly identify constructive solutions.
About BASF
BASF is the world’s leading chemical company: The Chemical Company. Its portfolio ranges from chemicals, plastics, performance products and crop protection products to oil and gas. We combine economic success with environmental protection and social responsibility. Through science and innovation, we enable our customers in nearly every industry to meet the current and future needs of society. Our products and solutions contribute to conserving resources, ensuring nutrition and improving quality of life. We have summed up this contribution in our corporate purpose: We create chemistry for a sustainable future. BASF had sales of about €74 billion in 2013 and over 112,000 employees as of the end of the year. Further information on BASF is available on the Internet at http://www.basf.com.
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 journal Nature Materials (“Improved performance and stability in quantum dot solar cells through band alignment engineering”), by MIT professors Moungi Bawendi and Vladimir Bulović and graduate students Chia-Hao Chuang and Patrick Brown.
Researcher displays a sample of the record-setting new solar cell on the MIT campus. (Photo courtesy of Chia-Hao Chen)
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 (“Energy Level Modification in Lead Sulfide Quantum Dot Thin Films Through Ligand Exchange”), 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.”
Solar cells made from quantum dots could be low-cost, flexible, and easy to make. But the efficiency with which they convert light into electricity remains too low for practical use. Researchers at the Massachusetts Institute of Technology now show that incorporating nanowires into quantum dot solar cells increases the cells’ efficiency by 35%. 
Genesis Nanotechnologyo and l o 
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