Researchers Unveil New Solar Cell: Carbon Nanotubes that Convert Sunlight into MORE Power


CNT Solar 1-researchersuA team of researchers with members from several research facilities in the U.S. has unveiled a new type of solar cell based on single walled carbon nanotubes (SWCNTs). In their paper published in the journal Nano Letters, the team claims they have overcome limitations with such technology resulting in a solar cell that is two times as good at converting sunlight into power as other SWCNT based cells.

Scientists would like to use carbon nanotubes in solar cells because it would mean lighter panels, lower costs and easier to make products. They’ve been hampered, however, by the limited amount of power that such cells are able to generate. In this new effort the research team claims they’ve overcome the limitations of prior generations of SWCNTs by adding more chiralities to the nanotubes. Chiralities describe the way atoms are arranged in their hexagonal patterns—different patterns allow for absorbing different portions of the . Most prior efforts have used just one. This new team has added what they call polychiral SWCNTs to their cells which allows for capturing much more of the solar spectrum—most notably, in the near infrared, which other don’t make use of at all.

CNT Solar 1-researchersu

The researchers also added an ability to control the interface between the underlying hole-transport layer and the active photovoltaic layer, allowing the electron and hole pair (excitons) to recombine more efficiently. Taken together the two improvements serve to allow for both higher current and voltage, resulting in record high power conversion efficiency. They report that The National Renewable Energy Laboratory has already certified (by verifying) the performance claimed by the team. But the team isn’t done just yet. They want to improve the even more and may do so by testing new materials not used in any other cell.

Scientists would like to use carbon nanotubes in solar cells because it would mean lighter panels, lower costs and easier to make products. They’ve been hampered, however, by the limited amount of power that such cells are able to generate. In this new effort the research team claims they’ve overcome the limitations of prior generations of SWCNTs by adding more chiralities to the nanotubes. Chiralities describe the way atoms are arranged in their hexagonal patterns—different patterns allow for absorbing different portions of the . Most prior efforts have used just one. This new team has added what they call polychiral SWCNTs to their cells which allows for capturing much more of the solar spectrum—most notably, in the near infrared, which other don’t make use of at all.

The researchers also added an ability to control the interface between the underlying hole-transport layer and the active photovoltaic layer, allowing the electron and hole pair (excitons) to recombine more efficiently. Taken together the two improvements serve to allow for both higher current and voltage, resulting in record high power conversion efficiency. They report that The National Renewable Energy Laboratory has already certified (by verifying) the performance claimed by the team. But the team isn’t done just yet. They want to improve the even more and may do so by testing new materials not used in any other cell.

While it could be awhile before a product is made for sale based on what the team has wrought, their research might cause others in the field to take notice, which could conceivably result in a resurgence of interest in carbon based in general—interest has lagged in recent years as researchers began to doubt they could make them both useful and profitable. Hopefully so, because it would mean less expensive (and lighter) that produce as much power as conventional panels or even more—leading perhaps to a major move from greenhouse gas emitting coal fired to something much cleaner.

Explore further: Inexpensive flexible fiber perovskite solar cells

More information: Polychiral Semiconducting Carbon Nanotube–Fullerene Solar Cells, Nano Lett., Article ASAP, DOI: 10.1021/nl5027452

Abstract
Single-walled carbon nanotubes (SWCNTs) have highly desirable attributes for solution-processable thin-film photovoltaics (TFPVs), such as broadband absorption, high carrier mobility, and environmental stability. However, previous TFPVs incorporating photoactive SWCNTs have utilized architectures that have limited current, voltage, and ultimately power conversion efficiency (PCE). Here, we report a solar cell geometry that maximizes photocurrent using polychiral SWCNTs while retaining high photovoltage, leading to record-high efficiency SWCNT–fullerene solar cells with average NREL certified and champion PCEs of 2.5% and 3.1%, respectively. Moreover, these cells show significant absorption in the near-infrared portion of the solar spectrum that is currently inaccessible by many leading TFPV technologies.

 

 

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Eco-Friendly ‘pre-fab nanoparticles’ Could Revolutionize Nano Manufacturing


 

Eco-Friendly Nano 49975

Eco-friendly ‘pre-fab nanoparticles’ could revolutionize nano manufacturing: UMass Amherst team invents a way to create versatile, water-soluble nano-modules

Amherst. MA | Posted on August 13th, 2014

 

A team of materials chemists, polymer scientists, device physicists and others at the University of Massachusetts Amherst today report a breakthrough technique for controlling molecular assembly of nanoparticles over multiple length scales that should allow faster, cheaper, more ecologically friendly manufacture of organic photovoltaics and other electronic devices. Details are in the current issue of Nano Letters.

Lead investigator, chemist Dhandapani Venkataraman, points out that the new techniques successfully address two major goals for device manufacture: controlling molecular assembly and avoiding toxic solvents like chlorobenzene. “Now we have a rational way of controlling this assembly in a water-based system,” he says. “It’s a completely new way to look at problems. With this technique we can force it into the exact structure that you want.”

Materials chemist Paul Lahti, co-director with Thomas Russell of UMass Amherst’s Energy Frontiers Research Center (EFRC) supported by the U.S. Department of Energy, says, “One of the big implications of this work is that it goes well beyond organic photovoltaics or solar cells, where this advance is being applied right now. Looking at the bigger picture, this technique offers a very promising, flexible and ecologically friendly new approach to assembling materials to make device structures.”

Eco-Friendly Nano 49975

 

Lahti likens the UMass Amherst team’s advance in materials science to the kind of benefits the construction industry saw with prefabricated building units. “This strategy is right along that general philosophical line,” he says. “Our group discovered a way to use sphere packing to get all sorts of materials to behave themselves in a water solution before they are sprayed onto surfaces in thin layers and assembled into a module. We are pre-assembling some basic building blocks with a few predictable characteristics, which are then available to build your complex device.”

“Somebody still has to hook it up and fit it out the way they want,” Lahti adds. “It’s not finished, but many parts are pre-assembled. And you can order characteristics that you need, for example, a certain electron flow direction or strength. All the modules can be tuned to have the ability to provide electron availability in a certain way. The availability can be adjusted, and we’ve shown that it works.”

The new method should reduce the time nano manufacturing firms spend in trial-and-error searches for materials to make electronic devices such as solar cells, organic transistors and organic light-emitting diodes. “The old way can take years,” Lahti says.

“Another of our main objectives is to make something that can be scaled up from nano- to mesoscale, and our method does that. It is also much more ecologically friendly because we use water instead of dangerous solvents in the process,” he adds.

For photovoltaics, Venkataraman points out, “The next thing is to make devices with other polymers coming along, to increase power conversion efficiency and to make them on flexible substrates. In this paper we worked on glass, but we want to translate to flexible materials and produce roll-to-roll manufactured materials with water. We expect to actually get much greater efficiency.” He suggests that reaching 5 percent power conversion efficiency would justify the investment for making small, flexible solar panels to power devices such as smart phones.

If the average smart phone uses 5 watts of power and all 307 million United States users switched from batteries to flexible solar, it could save more than 1500 megawatts per year. “That’s nearly the output of a nuclear power station,” Venkataraman says, “and it’s more dramatic when you consider that coal-fired power plants generate 1 megawatt and release 2,250 lbs. of carbon dioxide. So if a fraction of the 6.6 billion mobile phone users globally changed to solar, it would reduce our carbon footprint a lot.”

Doctoral student and first author Tim Gehan says that organic solar cells made in this way can be semi-transparent, as well, “so you could replace tinted windows in a skyscraper and have them all producing electricity during the day when it’s needed. And processing is much cheaper and cleaner with our cells than in traditional methods.”

Venkataraman credits organic materials chemist Gehan, with postdoctoral fellow and device physicist Monojit Bag, with making “crucial observations” and using “persistent detective work” to get past various roadblocks in the experiments. “These two were outstanding in helping this story move ahead,” he notes. For their part, Gehan and Bag say they got critical help from the Amherst Fire Department, which loaned them an infrared camera to pinpoint some problem hot spots on a device.

It was Bag who put similar sized and charged nanoparticles together to form a building block, then used an artist’s airbrush to spray layers of electrical circuits atop each other to create a solar-powered device. He says, “Here we pre-formed structures at nanoscale so they will form a known structure assembled at the meso scale, from which you can make a device. Before, you just hoped your two components in solution would form the right mesostructure, but with this technique we can direct it to that end.”

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This work at the Polymer-Based Materials for Harvesting Solar Energy is part of an EFRC supported by the U.S. DOE’s Office of Basic Energy Science.

 

Copyright © University of Massachusetts at Amherst

 

Researchers Intoduce an Electric Field to Enhance Solar Cell Performance


 

Electrical Field pic1Researchers at the Kavli Energy Nanosciences Institute, the University of California at Berkeley and the Lawrence Berkeley National Lab, have succeeded in boosting the performance of a new type of solar cell by simply applying an electric field to it. The device (made of low cost zinc phosphide and graphene) is novel in its design in that it lacks a junction between the two p- and n-type semiconductors that make it up – which is a first. The cell might be ideal for use in areas where the intensity of sunlight changes a lot over the course of the year.

The device and experimental results

“Our solar cell does not need to be doped, nor does it require high-quality heterojunctions, which are challenging and expensive to fabricate,” says team member Oscar Vazquez-Mena. “Our work is a novel and promising approach for making photovoltaics with low-cost and abundant materials such as certain phosphides and sulphides that are easy to synthesize and which are environmentally friendly.”

Beside expensive light absorbers like silicon, there are semiconductors like zinc phosphide, copper zinc tin sulphide, cuprous oxide and iron sulphide that are much cheaper. However, for these materials to efficiently convert sunlight into energy, they need to be doped to form homojunctions, or require complementary emitter materials to form high-quality p-n heterojunctions.

A team led by Alex Zettl, Harry Atwater, Ali Javey and Michael Crommie has now overcome this problem by making a simple junction with graphene rather than a semiconductor. A voltage applied to a gate over the junction can tune the energy barrier between the graphene and an adjoining layer of zinc phosphide to boost how efficiently solar cells made from these materials convert light into energy.

The devices are relatively simple to fabricate, says Vazquez-Mena. “Jeff Bosco from Harry Atwater’s team at Caltech makes high-quality zinc phosphide films and in our lab at UC Berkeley, we are experts at growing graphene on copper substrates. Basically, we transfer the graphene from the copper onto the zinc phosphide film to form a graphene- zinc phosphide junction. We then add an insulator layer on top of the graphene, prepared by our colleagues in Ali Javey’s team, also at UC Berkeley. Finally we add a thin top gate to the structure.”

Barrier is like a dam

Conventional solar cells normally contain two bulk semiconductors, with their electrons at different energy levels. These semiconductors are brought into contact to form an electric barrier between them that separates the electrons from each side. “This barrier can be likened to the dam in a hydroelectric power plant that separates two reservoirs of water at different heights,” explains Vazquez-Mena. “In a solar cell, the electric charges are the water in the dam and we use energy from the Sun to make the charges jump over the barrier.”

In the new device, the researchers used a layer of graphene in place of one of the semiconductors and added a top gate to it. “Why? Because it is easy to control the energy level of electrons in graphene by doing this,” Vazquez-Mena tells nanotechweb.org. “Such a thing is difficult to do in a bulk semiconductor.”

The top gate can regulate the barrier between graphene and the zinc phosphide, needed for the solar cell to work, he adds. “This is critical for the performance of the device and allows us to optimize the energy extracted from it. Going back to the dam analogy, it is as if we would be controlling the height of the dam.”

The fact that we can manipulate the barrier height in this way means that, in principle, we could make graphene junctions with many other materials, he says.

Modifying the barrier

In bulk semiconductor solar cells, the barrier height depends on the intrinsic properties of the materials making up the barrier. So, once you put the materials together, there is not much you can do to change the barrier, explains Vazquez-Mena.

“Our device is very different in that we can modify this barrier by simply applying an electric field to the top gate and adjusting the strength of the field applied for different materials and light conditions to optimize energy conversion. Our device, which is just a basic graphene-zinc phosphide solar cell, normally has an efficiency of 1% without any applied gate voltage, but we have doubled this to 2% by increasing the gate voltage to 2V. We have thus been able to boost its performance beyond the intrinsic properties of the material it is made up of.”

This type of solar cell might be ideal in climes where the sunlight varies a lot, he says – thanks to the fact that we can adjust the barrier to optimize energy conversion.

The California researchers say that they are looking to improve the efficiency of their devices and improving the quality of the graphene-zinc phosphide junction so that it produces a higher photocurrent. “We also want to apply our technology to other low-cost and readily available materials,” says Vazquez-Mena. “For example, the device we have made can be improved by using graphene itself or a transparent conductor like indium-tin oxide as the top gate.”

The team, reporting its work in Nano Letters, says that it will also test copper zinc tin sulphide, cuprous oxides and copper sulphide. “These materials are less harmful to the environment compared with commonly used solar cell materials like cadmium telluride and are cheaper than pure silicon. We definitely have many ideas to try but we also hope that other research groups will be inspired by our experiments and develop similar strategies to keep improving the efficiencies of alternative photovoltaic materials.”

Perovskite: New Wonder Material to make Cheaper & Easier to Manufacture LED’s


 

 

ledsmadefromColourful LEDs made from a material known as perovskite could lead to LED displays which are both cheaper and easier to manufacture in future. 

A hybrid form of perovskite – the same type of material which has recently been found to make highly efficient solar cells that could one day replace silicon – has been used to make low-cost, easily manufactured LEDs, potentially opening up a wide range of in future, such as flexible colour displays.

This particular class of semiconducting perovskites have generated excitement in the solar cell field over the past several years, after Professor Henry Snaith’s group at Oxford University found them to be remarkably efficient at converting light to electricity. In just two short years, perovskite-based solar cells have reached efficiencies of nearly 20%, a level which took conventional silicon-based 20 years to reach.

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Now, researchers from the University of Cambridge, University of Oxford and the Ludwig-Maximilians-Universität in Munich have demonstrated a new application for perovskite , using them to make high-brightness LEDs. The results are published in the journal Nature Nanotechnology.

Perovskite is a general term used to describe a group of materials that have a distinctive crystal structure of cuboid and diamond shapes. They have long been of interest for their superconducting and ferroelectric properties. But in the past several years, their at converting light into electrical energy has opened up a wide range of potential applications.

The perovskites that were used to make the LEDs are known as organometal halide perovskites, and contain a mixture of lead, carbon-based ions and halogen ions known as halides. These materials dissolve well in common solvents, and assemble to form perovskite crystals when dried, making them cheap and simple to make.

“These organometal halide perovskites are remarkable semiconductors,” said Zhi-Kuang Tan, a PhD student at the University of Cambridge’s Cavendish Laboratory and the paper’s lead author. “We have designed the diode structure to confine electrical charges into a very thin layer of the perovskite, which sets up conditions for the electron-hole capture process to produce light emission.”

The perovskite LEDs are made using a simple and scalable process in which a perovskite solution is prepared and spin-coated onto the substrate. This process does not require high temperature heating steps or a high vacuum, and is therefore cheap to manufacture in a large scale. In contrast, conventional methods for manufacturing LEDs make the cost prohibitive for many large-area display applications.

“The big surprise to the semiconductor community is to find that such simple process methods still produce very clean semiconductor properties, without the need for the complex purification procedures required for traditional semiconductors such as silicon,” said Professor Sir Richard Friend of the Cavendish Laboratory, who has led this programme in Cambridge.

“It’s remarkable that this material can be easily tuned to emit light in a variety of colours, which makes it extremely useful for colour displays, lighting and optical communication applications,” said Tan. “This technology could provide a lot of value to the ever growing flat-panel display industry.”

The team is now looking to increase the efficiency of the LEDs and to use them for diode lasers, which are used in a range of scientific, medical and industrial applications, such as materials processing and medical equipment. The first commercially-available LED based on perovskite could be available within five years.

Explore further: Scientists develop pioneering new spray-on solar cells

More information: Nature Nanotechnology, www.nature.com/nnano/journal/v… /nnano.2014.149.html

Read more at: http://phys.org/news/2014-08-material-perovskite.html#jCp

Efficient Triple-Junction Polymer Solar Cell Design Sets New Record


Triple Junc SC id36745_1. Copyright © Nanowerk

Organic solar cells are conventionally made from two materials: a donor and an acceptor, which facilitates an efficient charge separation. For the acceptor, the most commonly used molecule is one of the blue absorbing fullerenes. This leaves the absorption spectrum of the donor material responsible to cover as much as possible of the solar spectrum. But most organic semiconductors only have a small optical bandwidth.

Consequently, solar cells based on such materials only catch a small part of the solar spectrum. This problem can be overcome with a properly designed stacked or tandem configuration, in which several organic materials are tuned so that each absorbs a separate part of the spectrum, thereby increasing the efficiency of the overall device. High bandgap semiconductor materials are used to absorb the short wavelength radiation, with longer wavelength parts transmitted to subsequent semiconductors.

In this context, researchers have set great hopes in the development of multi-junction solar cells, hoping to substantially exceed the performance of single-junction organic photovoltaics. In theory, a solar cell with an infinite number of junctions could obtain a maximum power conversion efficiency (PCE) of nearly 87% under highly concentrated sun light.

The challenge is to develop a semiconductor material system that can attain a wide range of bandgaps and be grown with high crystalline quality. New research coming out of the Yang Yang lab at the University of California, Los Angeles (UCLA), one of the leading labs for organic tandem solar cell research, presents an efficient design for a triple-junction organic tandem solar cell featuring a configuration of bandgap energies designed to maximize the tandem photocurrent output.

The key innovation in this study, reported in the July 14, 2014 online edition of Advanced Materials (“An Efficient Triple-Junction Polymer Solar Cell Having a Power Conversion Efficiency Exceeding 11%”), is the demonstration of organic materials being able to mimic the record-setting efficiency of triple-junction structures in III-V solar cells. III-V based solar cells constructed with the industry-standard GaInP/GaInAs/Ge technology have achieved the highest energy conversion efficiencies of all solar cells, with the current record exceeding 40%.

“In III–V multijunction solar cells, the optimal arrangement for a high-current-output triple-junction tandem cell features one wide-bandgap absorber (2.0–1.85 eV), one medium-bandgap absorber (1.4–1.2 eV), and one low-bandgap absorber (1.0–0.7 eV)”, Chun-Chao Chen, a graduate student in Yang’s lab and first author of the paper, explains to Nanowerk. “This optimal design rule cannot be applied directly to organic solar cells, however, because of the lack of efficient donor materials having bandgaps as low as 1 eV. Therefore, we set out to determine a practical combination of bandgap energies for triple junctions to develop an efficient organic tandem solar cell structure.”

 

 

Layer stacks of a triple-junction tandem solar cell

Schematic representation of the complete device structure: Layer stacks of the triple-junction tandem solar cell in the inverted architecture. (Reprinted with permission by Wiley-VCH Verlag)

For their design, the team used three materials with different energy bandgaps (1.9, 1.58, and 1.4 eV) as electron donors, blended with fullerene derivatives. With this arrangement of bandgap energies, they fabricated a highly efficient triple-junction tandem solar cell having a PCE of 11% – exceeding the record efficiency of a double-junction tandem solar cell, previously demonstrated by Yang’s group as well.

Energy levels of various materials for solar cells

 

Energy levels of the materials investigated in this study. Values for ITO, ZnO, and WO3 were measured using ultraviolet photoelectron spectroscopy (UPS); other values were taken from the literature. (Reprinted with permission by Wiley-VCH Verlag)

 

The specific problem in triple-junction solar cells is the complicated optical interference effect between each subcell included in the tandem. “When there are two junctions in tandem, the optical effect is easy to resolve,” say the UCLA researchers. “However, when it comes to triple junctions, you can not use trial and error to find out the optimal layer thickness for absorption for each subcell.”

To solve this issue, and in order to understand how each subcell works and how much current it can deliver, the team carried out in-depth and detailed optical simulations for each subcell. Benefiting from this tool, they came up with a simple and effective structure for connecting the subcells in tandem solar cells. This interconnecting structure, made of WO3/PEDOT:PSS/ZnO, is completely solution processed, thus keeping the orthogonal processing advantage of organic solar cells unchanged – regardless of how many junctions are added.

According to the UCLA team, “this design significantly strengthens our faith in tandem structure for organic solar cell.” They also points out that one of the outcomes of this study is the message that innovations in device architecture can potentially push the efficiencies of organic solar cell technology into the realm of inorganic photovoltaics.

The team is confident that their experience and knowledge gained from designing tandem solar cells can be transferred to other photovoltaic technologies – e.g. hybrid solar cells; perovskite solar cell; CIGS solar cells. Last year, for instance, they have shown that tandem structures can be combined with existing semitransparent solar cell design can result in a doubling of efficiency (read more: “Transparent film could coat windows, smartphone screens with energy-harvesting material“).

Read more: Efficient triple-junction polymer solar cell design sets new record http://www.nanowerk.com/spotlight/spotid=36745.php#ixzz39Ya0Onsn

Translating Science into Business: The Business of Organic Semiconductors


 

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“There are many things which can go wrong when starting a company; but the worst thing that can go wrong is to not do it,” said Prof. Karl Leo, Director of KAUST’s Solar & Photovoltaics Engineering Research Center, when speaking at an Entrepreneurship Center speaker series event this past spring. Wearing the dual hats of scientist and entrepreneur, Prof. Leo is the author of 440 publications, holds more than 50 patents, and has co-created 8 companies which have generated over 300 jobs.

A physicist by training, Prof. Leo highlighted the point that he is primarily a scientist who stumbled onto business by chance. “For me it’s always started with and been about the science,” he says. All his spin-off companies came about as a result of basic research he and his group conducted on organic semiconductors. Speaking specifically to the young KAUST researchers hoping to emulate his success as academics and entrepreneurs, Prof. Leo said: “The message I want to pass along is if you really want to do things, just be curious. Don’t say I want to do research to make a company. Do very basic research and the spin-off ideas will come along.”

The Growing Influence of Organic Semiconductors

Prof. Karl Leo started doing research on organic semiconductors about 20 years ago. He has since been passionate about this field’s developments and future potential. Despite his early skepticism resulting from the ephemeral lifetime of organic semiconductors in the ’90s, the performance levels of LED devices for instance have gone from just a few minutes of useful life then to virtually not aging today. “In the long-term, as in 20 to 30 years from now, almost everything will be organics,” he believes. “Silicon has dominated electronics for a long time but organic is something new.” Organic products have evolved into a variety of applications such as: small OLED displays, OLED televisions, OLED lighting, OPV and organic electronics.

Organics, as opposed to traditional silicon-based semiconductors, are by nature essentially lousy semiconductors. Mobility, or the speed at which electrons move on these materials, is a really important property. However, when looking at the electronic properties of semiconductors, carbon offers interesting developments for the performance of organics. For instance, graphene, which is a carbon-based organic material, has even higher mobility than silicon.

Organic Semi untitled

One of the companies Prof. Karl Leo co-founded and began operating out of Dresden, Germany in 2003, Novaled, became a leader in in organic light-emitting diode (OLED) field. OLEDs are made up of multiple thin layers of organic materials, known as OLED stacks. They essentially emit light when electricity is applied to them. Novaled became a pioneer in developing highly efficient and long-lifetime OLED structures; and it currently holds the world record in power efficiency. They key to Novaled’s success, as Prof. Leo explains, is “the simple discovery that you can dope organics.” This was a major breakthrough achieved simply adding a very little amount of another molecule.

This organic conductivity doping technology, used to enhance the performance of OLED devices, was the main factor leading to the company being purchased by Samsung in 2013.

Organic Photovoltaics: Technology of the Future

Following the successful commercial penetration of OLED displays in the consumer electronics market, Prof. Karl Leo has since turned his focus on organic photovoltaics. “I think organic PV is something that can change the world,” said Leo. Among the many advantages of organic photovoltaics are that they are thin organic layers which can be applied on flexible plastic substrates. They consume little energy, can be made transparent, and are compatible with low-cost large-area production technologies. Because they are transparent, they can be made into windows for instance, and also be manufactured in virtually any color. All these characteristics make organic PV ideal for consumer products.

Again based on basic research conducted by his group, Prof. Leo also started a company, Heliatek, which is now a world-leader in the production of organic solar film. Heliatek has developed the current world record in the efficiency of transparent solar cells. The company also holds the record for efficiency of opaque cells at 12 percent. Leo believes that it’s possible to achieve up to 20 percent efficiency in the near future, which will be necessary to compete with silicon and become commercially viable.

Don’t Believe Business Plans

Prof. Leo explained that the experience he and his team gained from launching a successful company like Novaled helped them to both define the objectives and obtain funding from investors for his solar cell company, Heliatek. “Once you create a successful company, things get much easier,” he said. But Leo also cautioned the budding entrepreneurs in the audience to be willing to adapt as they present and implement their ideas.

“If you have a good idea and you are convinced you have a good idea, never give up,” he said. But being able to adapt to market needs is also crucial. For instance, Leo’s original business plan for Novaled focused on manufacturing displays. But the realities of the market, and the prohibitive cost of manufacturing displays, convinced his team that the smarter way to go was to supply materials. At the end of the day, what really succeeded in getting a venture capital firm’s attention, after haven been told no 49 times, was his team’s ability to demonstrate the value of the technology.

“Business plans are useful but they must not be overestimated,” said Prof. Leo. Business plans are a good indicator of how entrepreneurs are able to structure their thoughts, identify markets and create a roadmap, but “nobody is able to predict the future in a business plan; it’s not possible.”

 

Definition of Organic Semi-Conductors: Background

An organic semiconductor is an organic material with semiconductor properties, that is, with an electrical conductivity between that of insulators and that of metals. Single molecules, oligomers, and organic polymers can be semiconductive. Semiconducting small molecules (aromatic hydrocarbons) include the polycyclic aromatic compounds pentacene, anthracene, and rubrene. Polymeric organic semiconductors include poly(3-hexylthiophene), poly(p-phenylene vinylene), as well as polyacetylene and its derivatives.

There are two major overlapping classes of organic semiconductors. These are organic charge-transfer complexes and various linear-backbone conductive polymers derived from polyacetylene. Linear backbone organic semiconductors include polyacetylene itself and its derivatives polypyrrole, and polyaniline.

At least locally, charge-transfer complexes often exhibit similar conduction mechanisms to inorganic semiconductors. Such mechanisms arise from the presence of hole and electron conduction layers separated by a band gap.

Although such classic mechanisms are important locally, as with inorganic amorphous semiconductors, tunnelling, localized states, mobility gaps, and phonon-assisted hopping also significantly contribute to conduction, particularly in polyacetylenes. Like inorganic semiconductors, organic semiconductors can be doped. Organic semiconductors susceptible to doping such as polyaniline (Ormecon) and PEDOT:PSS are also known as organic metals

 

Further Information

Graphene (Oxide) for New Solar Cells: Stronger, Cheaper .. Better?


Graphene Solar Cells 9138062484_ca590547c3_kThere remains a lot to learn on the frontiers of solar power research, particularly when it comes to new advanced materials which could change how we harness energy.

Under the guidance of Canada Research Chair in Materials Science with Synchrotron Radiation, Dr. Alexander Moewes, University of Saskatchewan researcher Adrian Hunt spent his PhD investigating graphene , a cutting-edge material that he hopes will shape the future of technology.

To understand graphene oxide, it is best to start with pure graphene, which is a single-layer sheet of carbon atoms in a honeycomb lattice that was first made in 2004 by Andre Geim and Kostya Novoselov at the University of Manchester – a discovery that earned the two physicists a Nobel Prize in 2010.

“It is incredibly thin, therefore it is incredibly transparent. It also has extremely high conductivity, it’s much better than copper, and it’s extremely strong, its tensile strength is even stronger than steel,” Hunt said.

“Air doesn’t damage it. It can’t corrode, it can’t degrade. It’s really stable.”

All of this makes graphene a great candidate for . In particular, its transparency and conductivity mean that it solves two problems of solar cells: first, light needs a good conductor in order to get converted into usable energy; secondly, the cell also has to be transparent for light to get through.CNT multiprv1_jpg71ec6d8c-a1e2-4de6-acb6-f1f1b0a66d46Larger

Most solar cells on the market use with a non-conductive glass protective layer to meet their needs.

“Indium is extremely rare, so it is becoming more expensive all the time. It’s the factor that will keep solar cells expensive in the future, whereas graphene could be very cheap. Carbon is abundant,” said Hunt.

Although graphene is a great conductor, it is not very good at collecting the electrical current produced inside the solar cell, which is why researchers like Hunt are investigating ways to modify graphene to make it more useful.

Graphene oxide, the focus of Hunt’s PhD work, has oxygen forced into the carbon lattice, which makes it much less conductive but more transparent and a better charge collector. Whether or not it will solve the solar panel problem is yet to be seen, and researchers in the field are building up their understanding of how the new material works.

Using X-ray scattering techniques at the REIXS and SGM beamlines at the Canadian Light Source, as well as a Beamline 8.0.1 at the Advanced Light Source, Hunt set out to learn more about how oxide groups attached to the graphene lattice changed it, and how in particular they interacted with charge-carrying graphene atoms.

“Graphene oxide is fairly chaotic. You don’t get a nice simple structure that you can model really easily, but I wanted to model graphene oxide and understand the interplay of these parts.”

Previous models had seemed simplistic to Hunt, and he wanted a model that would reflect graphene oxide’s true complexity.

Each different part of the graphene oxide has a unique electronic signature. Using the synchrotron, Hunt could measure where electrons were on the graphene, and how the different oxide groups modified that.

He showed that previous models were incorrect, which he hopes will help improve understanding of the effects of small shifts in oxidization.

Moreover, he studied how graphene oxide decays. Some of the oxide groups are not stable, and can group together to tear the lattice; others can react to make water. If graphene oxide device has water in it, and it is heated up, the water can actually burn the and produce carbon dioxide. It’s a pitfall that could be important to understand in the development of long-lasting solar cells, where sun could provide risky heat into the equation.

More research like this will be the key to harnessing graphene for solar power, as Hunt explains.

“There’s this complicated chain of interreactions that can happen over time, and each one of those steps needs to be addressed and categorized before we can make real progress.”

Explore further: Super-stretchable yarn is made of grapheme

Read more at: http://phys.org/news/2014-08-stronger-solar-cells-graphene-cusp.html#jCp

Scientists Develop Pioneering New Spray-On Solar Cells


 

 

solarmediumDiscovery could help cut the cost of solar electricity

Perovskite is a promising new material for solar cells, combing high efficiency with low materials costs

Spray-painting method could be used in high volume manufacturing

 

A team of scientists at the University of Sheffield is the first to fabricate perovskite solar cells using a spray-painting process – a discovery that could help cut the cost of solar electricity.QDOT images 6

Experts from the University’s Department of Physics and Astronomy and Department of Chemical and Biological Engineering have previously used the spray-painting method to produce solar cells using organic semiconductors – but using perovskite is a major step forward.

Efficient organometal halide perovskite based photovoltaics were first demonstrated in 2012. They are now a very promising new material for solar cells as they combine high efficiency with low materials costs.

The spray-painting process wastes very little of the perovskite material and can be scaled to high volume manufacturing – similar to applying paint to cars and graphic printing.

Lead researcher Professor David Lidzey said: “There is a lot of excitement around perovskite based photovoltaics.

“Remarkably, this class of material offers the potential to combine the high performance of mature solar cell technologies with the low embedded energy costs of production of organic photovoltaics.”

Spraying device

The two spray heads. Picture by Alex Barrows.

While most solar cells are manufactured using energy intensive materials like silicon, perovskites, by comparison, requires much less energy to make. By spray-painting the perovskite layer in air the team hope the overall energy used to make a solar cell can be reduced further.

Professor Lidzey said: “The best certified efficiencies from organic solar cells are around 10 per cent.

“Perovskite cells now have efficiencies of up to 19 per cent. This is not so far behind that of silicon at 25 per cent – the material that dominates the world-wide solar market.”

He added: “The perovskite devices we have created still use similar structures to organic cells. What we have done is replace the key light absorbing layer – the organic layer – with a spray-painted perovskite.

“Using a perovskite absorber instead of an organic absorber gives a significant boost in terms of efficiency.”

The Sheffield team found that by spray-painting the perovskite they could make prototype solar cells with efficiency of up to 11 per cent.

Professor Lidzey said: “This study advances existing work where the perovskite layer has been deposited from solution using laboratory scale techniques. It’s a significant step towards efficient, low-cost solar cell devices made using high volume roll-to-roll processing methods.”

Solar power is becoming an increasingly important component of the world-wide renewables energy market and continues to grow at a remarkable rate despite the difficult economic environment.

Professor Lidzey said: “I believe that new thin-film photovoltaic technologies are going to have an important role to play in driving the uptake of solar-energy, and that perovskite based cells are emerging as likely thin-film candidates. “

Additional information

The University of Sheffield

With almost 25,000 of the brightest students from around 120 countries, learning alongside over 1,200 of the best academics from across the globe, the University of Sheffield is one of the world’s leading universities.

A member of the UK’s prestigious Russell Group of leading research-led institutions, Sheffield offers world-class teaching and research excellence across a wide range of disciplines.

Unified by the power of discovery and understanding, staff and students at the university are committed to finding new ways to transform the world we live in.

In 2011 it was named University of the Year in the Times Higher Education Awards and in the last decade has won four Queen’s Anniversary Prizes in recognition of the outstanding contribution to the United Kingdom’s intellectual, economic, cultural and social life.

Sheffield has five Nobel Prize winners among former staff and students and its alumni go on to hold positions of great responsibility and influence all over the world, making significant contributions in their chosen fields.

Genesis Nanotech Headlines Are Out!


Organ on a chip organx250Genesis Nanotech Headlines Are Out! Read All About It!

https://paper.li/GenesisNanoTech/1354215819#!headlines

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SUBCOMMITTE EXAMINES BREAKTHROUGH NANOTECHNOLOGY OPPORTUNITIES FOR AMERICA

Chairman Terry: “Nanotech is a true science race between the nations, and we should be encouraging the transition from research breakthroughs to commercial development.”

WASHINGTON, DCThe Subcommittee on Commerce, Manufacturing, and Trade, chaired by Rep. Lee Terry (R-NE), today held a hearing on:

“Nanotechnology: Understanding How Small Solutions Drive Big Innovation.”

 

 

electron-tomography

“Great Things from Small Things!” … We Couldn’t Agree More!

 

Quantum Dots may turn House Windows into Solar Panels


 

New-QD-Solar-Cell-id35756-150x150A house window that doubles as a solar panel could be on the horizon, thanks to recent quantum-dot work by researchers at Los Alamos National Laboratory in the US in collaboration with scientists from University of Milano-Bicocca (UNIMIB) in Italy.

Their work, published earlier this year in Nature Photonics, demonstrates that superior light-emitting properties of quantum dots can be applied in solar energy by helping more efficiently harvest sunlight.

“The key accomplishment is the demonstration of large-area luminescent solar concentrators that use a new generation of specially engineered quantum dots,” said lead researcher Victor Klimov of the Center for Advanced Solar Photophysics at Los Alamos. Quantum dots are ultra-small bits of semiconductor matter that can be synthesized with nearly atomic precision via modern methods of colloidal chemistry.

A luminescent solar concentrator (LSC) is a photon-management device, representing a slab of transparent material that contains highly efficient emitters such as dye molecules or quantum dots. Sunlight absorbed in the slab is re-radiated at longer wavelengths and guided toward the slab edge equipped with a solar cell.

Quantum dots are embedded in the plastic matrix and capture sunlight to improve solar-panel efficiency.
Courtesy Los Alamos Lab.
 
LUMINESCENT SOLAR CONCENTRATOR AS LIGHT HARVESTER

Sergio Brovelli, a faculty member at UNIMIB and a co-author of the paper, explained, “The LSC serves as a light-harvesting antenna which concentrates solar radiation collected from a large area onto a much smaller solar cell, and this increases its power output. LSCs are especially attractive because in addition to gains in efficiency, they can enable new interesting concepts such as photovoltaic windows that can transform house facades into large-area energy-generation units.”

Because of highly efficient, color-tunable emission and solution processability, quantum dots are attractive materials for use in inexpensive, large-area LSCs. To overcome a nagging problem of light reabsorption, the Los Alamos and UNIMIB researchers developed LSCs based on quantum dots with artificially induced large separation between emission and absorption bands, known as a large Stokes shift.

These “Stokes-shift-engineered” quantum dots represent cadmium selenide/cadmium sulfide (CdSe/CdS) structures in which light absorption is dominated by an ultra-thick outer shell of CdS, while emission occurs from the inner core of a narrower-gap CdSe.

Los Alamos researchers created a series of thick-shell (so-called “giant”) CdSe/CdS quantum dots, which were incorporated by their Italian partners into large slabs (sized in tens of centimeters across) of polymethylmethacrylate. While being large by quantum dot standards, the active particles are still tiny, only about hundred angstroms across.

QUANTUM DOTS USED FOR NEW DISPLAYS

Quantum dots are ultra-small bits of semiconductor matter that can be synthesized with nearly atomic precision via modern methods of colloidal chemistry.

Their emission color can be tuned by simply varying their dimensions. Color tunability is combined with high emission efficiencies approaching 100%.3D Printing dots-2

These properties have recently become the basis of a new technology — quantum-dot displays — employed, for example, in the newest generation of the Kindle Fire e-reader.

In a new SPIE.TV video, Lawrence Berkeley National Lab director Paul Alivisatos demonstrates the Kindle Fire quantum-dot display.

 

DOI: 10.1117/2.4201407.10

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