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Nanoimprint lithography for the fabrication of efficient low band gap polymer solar cells

National Nanomanufacturing Network - November 13, 2014 - 7:55am
In recent years, polymer solar cells have drawn considerable research interest due to their attractive features including flexibility, semi-transparency, and manufacturability using cost-effective continuous printing processes (read more: "The state of nanoimprinted polymer organic solar cell technology (http://www.nanowerk.com/spotlight/spotid=28622.php)"). However, one challenge limiting their commercialization is the relatively low power conversion efficiency when compared to inorganic solar cells."One of the causes for polymer solar cells' low performance is the difficulty to simultaneously realize donor-acceptor phase separation within the short exciton diffusion length (∼10 nm) and high charge mobility, especially hole mobility, which are critical for charge separation and transport," Yi Yang, a senior engineer at Globalfoundries, tells Nanowerk. "So far it has been impossible to achieve such a morphology in the most widely used bulk heterojunction structure in which randomly distributed phases cause significant charge recombination." New work, led by Walter Hu (http://www.ee.utdallas.edu/people/facultypages/Hu.html), an Associate Professor of Electrical Engineering, and Anvar Zakhidov (http://nanotech.utdallas.edu/personnel/staff/zakhidov.html), a professor of physics, both at UT Dallas, shows that nanoimprint lithography (NIL) is an effective technique to solve these issues simultaneously. The results, recently published in ACS Applied Materials Interfaces ("Efficient Low Bandgap Polymer Solar Cell with Ordered Heterojunction Defined by Nanoimprint Lithography" (http://dx.doi.org/doi:10.1021/am505303a)), show that low bandgap polymer solar cells with high efficiency of 5.5% can be fabricated using NIL. "Taking into account the fact that low bandgap polymers are becoming the main stream for this type of solar cell, we believe this technique will increasingly find more applications," says Yang. In a previous study ("How nanostructure geometry affects polymer photovoltaic device efficiency (http://www.nanowerk.com/spotlight/spotid=36631.php)"), the researchers focused on nanoimprinted P3HT solar cells. After carefully optimizing the nanostructure geometry, they achieved an efficiency of 3-4%, which is not as high as the efficiency record (over 4%) other groups have achieved with this polymer. In the new study, they extended their technique to low bandgap polymer solar cells and realized a high efficiency up to 5.5%, which is among the best efficiencies for this polymer reported in the literature. This result indicates that nanoimprint fabrication works better for low bandgap polymer solar cells. In the new work, the team demonstrates the feasibility of using nanoimprint lithography to make efficient low bandgap polymer solar cells with well-ordered heterojunction. They fabricate high-quality low bandgap conjugated polymer (PCPDTBT) nanogratings using this technique for the first time. "We found that NIL makes PCPDTBT chains interact more strongly and form an improved structural ordering," says Yang. "Solar cells made with the highest aspect ratio PCPDTBT nanostructures show a high power conversion efficiency of 5.5%. They are the most efficient nanoimprinted polymer solar cells, as well as the best reported solar cells using the same material." Nanoimprint lithography has emerged as an effective fabrication technique to precisely define the nanomorphology in polymer solar cells. Controlled chain ordering as well as a bicontinuous and interdigitized heterojunction can be achieved by imprinting conjugated polymers, where a nanoimprint induced chain alignment is present, followed by infiltrating fullerene into patterned polymer nanostructures. However, as Yang notes, most studies so far have focused on nanoimprinted P3HT/fullerene solar cells. "This material combination is not ideal due to a mismatch between the absorption of P3HT and solar spectrum, which has a maximum photon flux at 1.6-1.8 eV while P3HT has a relatively large bandgap of 1.9-2.0 eV," he explains. "A bandgap of 1.3-1.5 eV is considered to be ideal for polymer-fullerene solar cells." In recent years, many low bandgap polymers have been synthesized with record-breaking efficiencies. However, as Yang points out, it has been proven that the donor and acceptor phase separation for these polymers cannot be realized by thermal or solvent vapor annealing, which is usually carried out on P3HT/fullerene solar cells. Although additives such as 1,8-octanedithiol are added into the solution to help separate donor and acceptor domains, this separation cannot be controlled precisely. Therefore, NIL would provide an effective solution if an ordered active layer morphology could be formed by it. However, so far no results have been published that show that NIL can be applied to a wide variety of materials in the polymer solar cell field. Now, the UT Dallas team has utilized NIL to pattern the low bandgap (1.4 eV) solar cell polymer PCPDTBT. For the first time, they have used NIL to fabricate high quality nanogratings for this polymer. "After carefully optimizing the nanograting geometry, we were able to achieve a high solar cell efficiency of 5.5%," notes Yang. Furthermore, this work demonstrates that NIL is not only limited to solar cells made of the most widely studied polymer P3HT, but also can be applied to a wide variety of materials used in the fabrication of polymer solar cells – low bandgap polymers can also be patterned by this technique to make efficient devices. Despite considerable effort, the highest reported power conversion efficiencies obtained from nanoimprinted P3HT solar cells have been in the 3-4% range. These values are lower than the highest values (∼4-5%) when the same polymer is used in a bulk heterojunction structure. "This indicates that NIL works better for low bandgap polymer solar cells," says Yang. "One possible explanation is that the method of using thermal or solvent vapor annealing to control the phase separation in P3HT based bulk heterojunction solar cells is very effective, as shown by a number of studies; while that of using additives in the low bandgap polymer solar cells is not, as described in literature." "This less effective approach leaves NIL more space to demonstrate its advantage in improving the solar cell performance when compared to the bulk heterojunction structure," he concludes. "This is our preliminary thinking and more studies are required to understand these different behaviors. Also as predicted in our recent study, a larger interface area between polymer and fullerene is preferable for efficient devices. A practical way to further increase it is needed as well. Our future work will focus on these aspects." Source: Nanowerk (http://www.nanowerk.com/spotlight/spotid=38076.php)

Call for Presentations for Int'l Conf. on Nanotechnology for Renewable Materials

National Nanomanufacturing Network - November 13, 2014 - 4:30am
(http://www.tappi.org/15Nano) What’s New for 2015 Two Tracks for Presentations: As the Nano Conference continues to grow, this year there will be two tracks to guide attendees in choosing sessions to attend. The Fundamental Research Track will focus on new technical advances in characterization, isolation, functionalities and other properties of renewable and sustainable nanomaterials. The Industry Applications Track will focus on manufacturing applications, new markets, and other end user issues. The conference organizers have extended the Call for Submissions (https://www.eiseverywhere.com/file_uploads/7a30b75854987d218fd0996b1a0895f6_Nano2015CallForPresentations-Extension.pdf) .Abstracts are due by 1 December 2014. New Technology and Product Showcase: Promote your new products or technologies at this special session. Sponsors and exhibitors will be given priority for available slots. See the Call for Submissions tab for more details. Research Perspectives and Business Acumen Seminar: Designed for academics, this workshop will show how researchers can gain industrial support for their projects. Led by corporate R D directors, this workshop will have limited seating. Check the website for additional details. Plan to AttendExplore a world of possibilities for opening the door to new markets by unlocking the potential of renewable biomaterials. TAPPI’s tenth International Conference on Nanotechnology for Renewable Materials is the only event that explores how nanotechnology can transform biomaterials into high-value products that expand and transcend traditional forest products portfolios. Bringing together leading researchers, industry experts, government representatives and other stakeholders from around the world, this year’s event promises a unique, multi-disciplinary look at the rewards of using nanotechnology – from the forest to marketed products. Whether your focus is new product development, academic study or supplier research, this year’s conference will provide the big picture for unlocking value from this tiny technology. Conference Co-Chairs:Sean Ireland, Verso Paper (USA)Yaman Boluk, University of Alberta (Canada)Alain Dufresne, Grenoble Institute of Technology (France)Celebrating 100 Years of TAPPI!To honor TAPPI's 100th anniversary in 2015, the 2015 Conference will be held in Atlanta, Georgia, USA. TAPPI headquarters are located in Peachtree Corners, a northern suburb of Atlanta.

Carbon nanotubes indiscriminately boost transistors

Nanotechweb - November 12, 2014 - 12:45pm
Carbon nanotube electrodes improve organic thin-film transistor performance regardless of the film morphology and structure, studies show.
Categories: Nanotechnology News

Open Materials Development Will Be Key for HP's Success in 3D Printing: HP can make a big splash in 3D printing, but it needs to shore up technology claims and avoid the temptation of the razor/razor blade business model in order to flourish

Nanotech-Now - November 12, 2014 - 7:45am
Hewlett-Packard (HP) recently released a white paper detailing its planned 3D printer. HP's "Multi Jet Fusion" system claims a tenfold increase in build speed, improved part quality with controllable...
Categories: Nanotechnology News

Dyesol (ASX:DYE) signs agreement with SPECIFIC - marking next steps to commercialisation in the UK

Nanotech-Now - November 12, 2014 - 7:45am
Today, Dyesol signed an important agreement with SPECIFIC which marks the next step in its plan to commercialise its technology in the U.K. The agreement plays a critical role in Dyesol's plans to est...
Categories: Nanotechnology News

Pseudospin-driven spin relaxation mechanism in graphene

Nanotech-Now - November 12, 2014 - 7:45am
Members of ICN2 Theoretical and Computational Nanoscience Group unveil an unprecedented spin relaxation mechanism unique to graphene, and related with entanglement of spin and pseudospin quantum degre...
Categories: Nanotechnology News

Drexel Engineers Improve Strength, Flexibility of Atom-Thick Films

Nanotech-Now - November 12, 2014 - 7:45am
Making a paper airplane in school used to mean trouble. Today it signals a promising discovery in materials science research that could help next-generation technology -like wearable energy storage de...
Categories: Nanotechnology News

Microtubes create cozy space for neurons to grow, and grow fast

Nanotech-Now - November 12, 2014 - 7:45am
Tiny, thin microtubes could provide a scaffold for neuron cultures to grow so that researchers can study neural networks, their growth and repair, yielding insights into treatment for degenerative neu...
Categories: Nanotechnology News

Graphene-Toughened Composites – A Milestone for Next Generation Aerospace Structures? Plasma functionalisation technology produces significant improvements in mechanical performance and damage tolerance in carbon fibre composites

Nanotech-Now - November 12, 2014 - 7:45am
The School of Engineering at Cardiff University and Haydale have announced new research demonstrating significant improvements in mechanical performance including impact resistance in carbon fibre com...
Categories: Nanotechnology News

Iranian Scientists Use Nanodrugs to Treat Cancer

Nanotech-Now - November 12, 2014 - 7:45am
Iranian researchers from Tehran University of Medical Sciences studied the possibility of application of nanotechnology in targeted drug delivery systems to treat cancer.
Categories: Nanotechnology News

Harris & Harris Group Reports Financial Statements as of September 30, 2014

Nanotech-Now - November 12, 2014 - 7:45am
Harris & Harris Group, Inc. (Nasdaq:TINY), an investor in transformative companies enabled by disruptive science, reported today that, as of September 30, 2014, its net asset value and net asset value...
Categories: Nanotechnology News

Heat Transfer Sets the Noise Floor for Ultrasensitive Electronics

Nanotech-Now - November 12, 2014 - 7:45am
A team of engineers and scientists has identified a source of electronic noise that could affect the functioning of instruments operating at very low temperatures, such as devices used in radio telesc...
Categories: Nanotechnology News

NanoThinking unveils NanoTechValley, the reference platform for collaboration in nanotechnology

Nanotech-Now - November 12, 2014 - 7:45am
Following a conception period in close connection with innovation and nanotechnology professionals, NanoThinking now offers NanoTechValley : a collaborative platform dedicated to providers and users o...
Categories: Nanotechnology News

Implementation of DNA Chains in Designing Nanospin Pieces

Nanotech-Now - November 10, 2014 - 7:45am
Researchers from Iran University of Science and Technology studied the possibility of using DNA chains in designing spin pieces.
Categories: Nanotechnology News

Neural Canals Produced in Iran for Recovery of Sciatica Nerve

Nanotech-Now - November 10, 2014 - 7:45am
Neural canals were produced in a joint research carried out by Iranian researchers from Tarbiat Modarres University and National Cell Bank of Pasteur Institute of Iran to recover the damaged periphera...
Categories: Nanotechnology News

NEI Development Update on NANOMYTE® TC-5001, a Protective Coating for Zinc-Plated and Galvanized Steel

Nanotech-Now - November 10, 2014 - 7:45am
NEI Corporation has issued a product update, following the successful introduction of NANOMYTE® TC‐5001 - a nanotechnology-enabled, anti-corrosion coating for zinc‐plated and hot‐dip...
Categories: Nanotechnology News

SEMATECH Names Ronald Goldblatt Permanent Chief Executive Officer

Nanotech-Now - November 10, 2014 - 7:45am
SEMATECH, the global consortium of semiconductor manufacturers, today announced that Dr. Ronald Goldblatt has been named President and Chief Executive Officer by the company's Board of Directors, effe...
Categories: Nanotechnology News

How to make mobile batteries last longer by controlling energy flows at nano-level

Nanotech-Now - November 10, 2014 - 7:45am
Electronic devices waste a lot of energy by producing useless heat. This is one of the main reasons our mobiles use up battery power so quickly. Researchers at University of Luxembourg have made a lea...
Categories: Nanotechnology News

Production of Biodegradable Nanocomposites of Wheat Gluten in Iran

Nanotech-Now - November 10, 2014 - 7:45am
Iranian researchers from Isfahan University of Technology used wheat proteins to produce a new generation of biodegradable nanocomposites with applications in different industries, specially packaging...
Categories: Nanotechnology News

Iranian Scientists Investigate Effective Parameters on Structure of Graphene Sheets

Nanotech-Now - November 10, 2014 - 7:45am
Iranian researchers from Mashhad Branch of Islamic Azad University studied different parameters effective on the mechanical properties of graphene sheets under load.
Categories: Nanotechnology News