Inexpensive hydrogen for automotive or jet fuel may be possible by mimicking photosynthesis, according to a Penn State materials chemist, but a number of problems need to be solved first.

“We are focused on the hardest way to make fuel,” said Thomas Mallouk, Evan Pugh Professor of Materials Chemistry and Physics. “We are creating an artificial system that mimics photosynthesis, but it will be practical only when it is as cheap as gasoline or jet fuel.”

Splitting water into hydrogen and oxygen can be done in a variety of ways, but most are heavily energy intensive. The resultant hydrogen, which can be used to fuel vehicles or converted into a variety of hydrocarbons, inevitably costs more than existing fossil-based fuels.

While some researchers have used solar cells to make electricity or use concentrated solar heat to split water, Mallouk’s process uses the energy in blue light directly. So far, it is much less efficient than other solar energy conversion technologies.

The key to direct conversion is electrons. Like the dyes that naturally occur in plants, inorganic dyes absorb sunlight and the energy kicks out an electron. Left on its own, the electron would recombine creating heat, but if the electrons can be channeled – molecule to molecule – far enough away from where they originate, the electrons can reach the catalyst and split the hydrogen from the oxygen in water.

“Currently, we are getting only 2 to 3 percent yield of hydrogen,” Mallouk told attendees on Feb. 19 at the annual meeting of the American Association for the Advancement of Science. “For systems like this to be useful, we will need to get closer to 100 percent,” he added.

But recombination of electrons is not the only problem with the process. The oxygen-evolving end of the system is a chemical wrecking ball and this means the lifetime of the system is currently limited to a few hours.

“The oxygen side of the cell is making a strong oxidizing agent and the molecules near can be oxidized,” said Mallouk. “Natural photosynthesis has the same problem, but it has a self-repair mechanism that periodically replaces the oxygen-evolving complex and the protein molecules around it.”

So far, the researchers do not have a fix for the oxidation, so their catalysts and other molecules used in the cell structure eventually degrade, limiting the life of the solar fuel cell.

Currently, the researchers are using only blue light, but would like to use the entire visible spectrum from the sun. They are also using expensive components – a titanium oxide electrode, a platinum dark electrode and iridium oxide catalyst. Substitutions for these are necessary, and other researchers are working on solutions. A Massachusetts Institute of Technology group is investigating cobalt and nickel catalysts, and at Yale University and Princeton University they are investigating manganese.

“Cobalt and nickel don’t work as well as iridium, but they aren’t bad,” said Mallouk. “The cobalt work is spreading to other institutions as well.”

While the designed structure of the fuel cell directs many of the electrons to the catalyst, most of them still recombine, giving over their energy to heat rather than chemical bond breaking. The manganese catalysts in photosystem II – the photosynthesis system by which plants, algae and photosynthetic bacteria evolve oxygen — are just as slow as ours, said Mallouk. Photosystem II works efficiently by using an electron mediator molecule to make sure there is always an electron available for the dye molecule once it passes its current electron to the next molecule in the chain.

“We could slow down major recombination in the artificial system in the same way,” said Mallouk. “Electron transfer from the mediator to the dye would effectively outrun the recombination reaction.”

Currently the system uses only one photon at a time, but a two-photon system, while more complicated, would be more effective in using the full spectrum of sunlight.

Mallouk’s main goal now is to track all the energy pathways in his cell to understand the kinetics. Once he knows this, he can model the cells and adjust portions to decrease energy loss and increase efficiency.

Penn State (2011, February 20). Mimicking photosynthesis path to solar-derived hydrogen fuel. ScienceDaily. Retrieved March 10, 2011, from http://www.sciencedaily.com­ /releases/2011/02/110219165217.htm

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The Original Post is Located Here: Mimicking Photosynthesis Path to Solar-Derived Hydrogen Fuel

We provide a number of resources such as photos, articles, videos and links that may be of interest if you want more detailed information on full-spectrum solar cells.

Solar cells are made from semiconductors whose ability to respond to light is determined by their band gaps (energy gaps). Different colors have different energies, and no single semiconductor has a band gap that can respond to sunlight’s full range, from low-energy infrared through visible light to high-energy ultraviolet.

Although full-spectrum solar cells have been made, none yet have been suitable for manufacture at a consumer-friendly price. Now Wladek Walukiewicz, who leads the Solar Energy Materials Research Group in the Materials Sciences Division (MSD) at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab), and his colleagues have demonstrated a solar cell that not only responds to virtually the entire solar spectrum, it can also readily be made using one of the semiconductor industry’s most common manufacturing techniques.

The new design promises highly efficient solar cells that are practical to produce. The results are reported in a recent issue of Physical Review Letters.

How to make a full-spectrum solar cell
“Since no one material is sensitive to all wavelengths, the underlying principle of a successful full-spectrum solar cell is to combine different semiconductors with different energy gaps,” says Walukiewicz.

A solar cell's ability to convert sunlight to electric current is limited by the band gaps of the semiconductors from which it is made. For example, semiconductors with wide band gaps respond to shorter wavelengths with higher energies (lower left). A semiconductor with an intermediate band has multiple band gaps and can respond to a range of energies (lower right). (Credit: Image courtesy of DOE/Lawrence Berkeley National Laboratory)

One way to combine different band gaps is to stack layers of different semiconductors and wire them in series. This is the principle of current high-efficiency solar cell technology that uses three different semiconductor alloys with different energy gaps. In 2002, Walukiewicz and Kin Man Yu of Berkeley Lab’s MSD found that by adjusting the amounts of indium and gallium in the same alloy, indium gallium nitride, each different mixture in effect became a different kind of semiconductor that responded to different wavelengths. By stacking several of the crystalline layers, all closely matched but with different indium content, they made a photovoltaic device that was sensitive to the full solar spectrum.

However, says Walukiewicz, “Even when the different layers are well matched, these structures are still complex — and so is the process of manufacturing them. Another way to make a full-spectrum cell is to make a single alloy with more than one band gap.”

In 2004 Walukiewicz and Yu made an alloy of highly mismatched semiconductors based on a common alloy, zinc (plus manganese) and tellurium. By doping this alloy with oxygen, they added a third distinct energy band between the existing two — thus creating three different band gaps that spanned the solar spectrum. Unfortunately, says Walukiewicz, “to manufacture this alloy is complex and time-consuming, and these solar cells are also expensive to produce in quantity.”

The new solar cell material from Walukiewicz and Yu and their colleagues in Berkeley Lab’s MSD and RoseStreet Labs Energy, working with Sumika Electronics Materials in Phoenix, Arizona, is another multiband semiconductor made from a highly mismatched alloy. In this case the alloy is gallium arsenide nitride, similar in composition to one of the most familiar semiconductors, gallium arsenide. By replacing some of the arsenic atoms with nitrogen, a third, intermediate energy band is created. The good news is that the alloy can be made by metalorganic chemical vapor deposition (MOCVD), one of the most common methods of fabricating compound semiconductors.

How band gaps work
Band gaps arise because semiconductors are insulators at a temperature of absolute zero but inch closer to conductivity as they warm up. To conduct electricity, some of the electrons normally bound to atoms (those in the valence band) must gain enough energy to flow freely — that is, move into the conduction band. The band gap is the energy needed to do this.

When an electron moves into the conduction band it leaves behind a “hole” in the valence band, which also carries charge, just as the electrons in the conduction band; holes are positive instead of negative.

A large band gap means high energy, and thus a wide-band-gap material responds only to the more energetic segments of the solar spectrum, such as ultraviolet light. By introducing a third band, intermediate between the valence band and the conduction band, the same basic semiconductor can respond to lower and middle-energy wavelengths as well.

This is because, in a multiband semiconductor, there is a narrow band gap that responds to low energies between the valence band and the intermediate band. Between the intermediate band and the conduction band is another relatively narrow band gap, one that responds to intermediate energies. And finally, the original wide band gap is still there to take care of high energies.

“The major issue in creating a full-spectrum solar cell is finding the right material,” says Kin Man Yu. “The challenge is to balance the proper composition with the proper doping.”

In solar cells made of some highly mismatched alloys, a third band of electronic states can be created inside the band gap of the host material by replacing atoms of one component with a small amount of oxygen or nitrogen. In so — called II-VI semiconductors (which combine elements from these two groups of Mendeleev’s original periodic table), replacing some group VI atoms with oxygen produces an intermediate band whose width and location can be controlled by varying the amount of oxygen. Walukiewicz and Yu’s original multiband solar cell was a II-VI compound that replaced group VI tellurium atoms with oxygen atoms. Their current solar cell material is a III-V alloy. The intermediate third band is made by replacing some of the group V component’s atoms — arsenic, in this case — with nitrogen atoms.

Finding the right combination of alloys, and determining the right doping levels to put an intermediate band right where it’s needed, is mostly based on theory, using the band anticrossing model developed at Berkeley Lab over the past 10 years.

“We knew that two-percent nitrogen ought to do the job,” says Yu. “We knew where the intermediate band ought to be and what to expect. The challenge was designing the actual device.”

Passing the test
Using their new multiband material as the core of a test cell, the researchers illuminated it with the full spectrum of sunlight to measure how much current was produced by different colors of light. The key to making a multiband cell work is to make sure the intermediate band is isolated from the contacts where current is collected.

“The intermediate band must absorb light, but it acts only as a stepping stone and must not be allowed to conduct charge, or else it basically shorts out the device,” Walukiewicz explains.

The test device had negatively doped semiconductor contacts on the substrate to collect electrons from the conduction band, and positively doped semiconductor contacts on the surface to collect holes from the valence band. Current from the intermediate band was blocked by additional layers on top and bottom.

For comparison purposes, the researchers built a cell that was almost identical but not blocked at the bottom, allowing current to flow directly from the intermediate band to the substrate.

The results of the test showed that light penetrating the blocked device efficiently yielded current from all three energy bands — valence to intermediate, intermediate to conduction, and valence to conduction — and responded strongly to all parts of the spectrum, from infrared with an energy of about 1.1 electron volts (1.1 eV), to over 3.2 eV, well into the ultraviolet.

By comparison, the unblocked device responded well only in the near infrared, declining sharply in the visible part of the spectrum and missing the highest-energy sunlight. Because it was unblocked, the intermediate band had essentially usurped the conduction band, intercepting low-energy electrons from the valence band and shuttling them directly to the contact layer.

Further support for the success of the multiband device and its method of operation came from tests “in reverse” — operating the device as a light emitting diode (LED). At low voltage, the device emitted four peaks in the infrared and visible light regions of the spectrum. Primarily intended as a solar cell material, this performance as an LED may suggest additional possibilities for gallium arsenide nitride, since it is a dilute nitride very similar to the dilute nitride, indium gallium arsenide nitride, used in commercial “vertical cavity surface-emitting lasers” (VCSELs), which have found wide use because of their many advantages over other semiconductor lasers.

With the new, multiband photovoltaic device based on gallium arsenide nitride, the research team has demonstrated a simple solar cell that responds to virtually the entire solar spectrum — and can readily be made using one of the semiconductor industry’s most common manufacturing techniques. The results promise highly efficient solar cells that are practical to produce.

DOE/Lawrence Berkeley National Laboratory (2011, January 25). Practical full-spectrum solar cell comes closer. ScienceDaily. Retrieved January 25, 2011, from http://www.sciencedaily.com­ /releases/2011/01/110125141810.htm

If you would like more articles like this, please take a few moments to give us your feedback. Though full-spectrum solar cells is often discussed, access to information about it can be hard to find. Please come back and visit us again, we will have more quality articles for your reading pleasure.

The Original Post is Located Here: Practical Full-Spectrum Solar Cell Comes Closer

In the smooth, white, bunny-suited clean-room world of silicon wafers and solar cells, it turns out that a little roughness may go a long way, perhaps all the way to making solar power an affordable energy source, say Stanford engineers.

Their research shows that light ricocheting around inside the polymer film of a solar cell behaves differently when the film is ultra thin. A film that’s nanoscale-thin and has been roughed up a bit can absorb more than 10 times the energy predicted by conventional theory.

This schematic diagram of a thin film organic solar cell shows the top layer, a patterned, roughened scattering layer, in green. The organic thin film layer, shown in red, is where light is trapped and electrical current is generated. The film is sandwiched between two layers that help keep light contained within the thin film. (Credit: Reproduced with permission from Proceedings of the National Academy of Sciences USA)

The key to overcoming the theoretical limit lies in keeping sunlight in the grip of the solar cell long enough to squeeze the maximum amount of energy from it, using a technique called “light trapping.” It’s the same as if you were using hamsters running on little wheels to generate your electricity — you’d want each hamster to log as many miles as possible before it jumped off and ran away.

“The longer a photon of light is in the solar cell, the better chance the photon can get absorbed,” said Shanhui Fan, associate professor of electrical engineering. The efficiency with which a given material absorbs sunlight is critically important in determining the overall efficiency of solar energy conversion. Fan is senior author of a paper describing the work published online by Proceedings of the National Academy of Sciences.

Light trapping has been used for several decades with silicon solar cells and is done by roughening the surface of the silicon to cause incoming light to bounce around inside the cell for a while after it penetrates, rather than reflecting right back out as it does off a mirror. But over the years, no matter how much researchers tinkered with the technique, they couldn’t boost the efficiency of typical “macroscale” silicon cells beyond a certain amount.

Eventually the scientists realized that there was a physical limit related to the speed at which light travels within a given material.

But light has a dual nature, sometimes behaving as a solid particle (a photon) and other times as a wave of energy, and Fan and postdoctoral researcher Zongfu Yu decided to explore whether the conventional limit on light trapping held true in a nanoscale setting. Yu is the lead author of the PNAS paper.

“We all used to think of light as going in a straight line,” Fan said. “For example, a ray of light hits a mirror, it bounces and you see another light ray. That is the typical way we think about light in the macroscopic world.

“But if you go down to the nanoscales that we are interested in, hundreds of millionths of a millimeter in scale, it turns out the wave characteristic really becomes important.”

Visible light has wavelengths around 400 to 700 nanometers (billionths of a meter), but even at that small scale, Fan said, many of the structures that Yu analyzed had a theoretical limit comparable to the conventional limit proven by experiment.

“One of the surprises with this work was discovering just how robust the conventional limit is,” Fan said.

It was only when Yu began investigating the behavior of light inside a material of deep subwavelength-scale — substantially smaller than the wavelength of the light — that it became evident to him that light could be confined for a longer time, increasing energy absorption beyond the conventional limit at the macroscale.

“The amount of benefit of nanoscale confinement we have shown here really is surprising,” said Yu. “Overcoming the conventional limit opens a new door to designing highly efficient solar cells.”

Yu determined through numerical simulations that the most effective structure for capitalizing on the benefits of nanoscale confinement was a combination of several different types of layers around an organic thin film.

He sandwiched the organic thin film between two layers of material — called “cladding” layers — that acted as confining layers once the light passed through the upper one into the thin film. Atop the upper cladding layer, he placed a patterned rough-surfaced layer designed to send the incoming light off in different directions as it entered the thin film.

By varying the parameters of the different layers, he was able to achieve a 12-fold increase in the absorption of light within the thin film, compared to the macroscale limit.

Nanoscale solar cells offer savings in material costs, as the organic polymer thin films and other materials used are less expensive than silicon and, being nanoscale, the quantities required for the cells are much smaller.

The organic materials also have the advantage of being manufactured in chemical reactions in solution, rather than needing high-temperature or vacuum processing, as is required for silicon manufacture.

“Most of the research these days is looking into many different kinds of materials for solar cells,” Fan said. “Where this will have a larger impact is in some of the emerging technologies; for example, in organic cells.”

“If you do it right, there is enormous potential associated with it,” Fan said.

Aaswath Raman, a graduate student in applied physics, also worked on the research and is a coauthor of the paper.

The project was supported by funding from the King Abdullah University of Science and Technology, which supports the Center for Advanced Molecular Photovoltaics at Stanford, and by the U.S. Department of Energy.

Stanford University (2010, September 28). Solar cells thinner than wavelengths of light hold huge power potential. ScienceDaily http://www.sciencedaily.com­ /releases/2010/09/100928092841.htm

The Original Post is Located Here: Solar Cells Thinner Than Wavelengths of Light Hold Huge Power Potential

Processes which lend materials new characteristics are generally complicated and therefore often rather difficult to reproduce. So surprise turns to astonishment when scientists report on new methods which not only produce outstanding results despite the fact that they use economically priced starting materials but also do not need expensive instrumentation.

Just a simple framework made of polystyrene

These are "sea urchins" made of tiny polystyrene balls, with zinc oxide nanowire "spines" are created using a simple electrochemical process. (Credit: Empa)

This is exactly what Jamil Elias and Laetitia Philippe of Empa’s Mechanics of Materials and Nanostructures Laboratory in Thun have succeeded in doing. They used polystyrene spheres as a sort of scaffolding to create three-dimensional nanostructures of semiconducting zinc oxide on various substrates. The two scientists are convinced that the (nanostructured) “rough” but regularly-structured surfaces they have produced this way can be exploited in a range of electronic and optoelectronic devices such as solar cells and also short wave lasers, light emitting diodes and field emission displays.

The scientific world reacted promptly. The paper in which the results were reported was published in January 2010 in the on line edition of Advanced Materials. In the same month it became the most frequently downloaded article, and in April it was selected to appear on the Inside Front Cover of the journal.

The principle behind the process is quite simple. Little spheres of polystyrene a few micrometers in diameter are placed on an electrically conducting surface where they orient themselves in regular patterns. Polystyrene is cheap and ubiquitous — it is widely used as a packaging material (for example for plastic yoghurt pots) or as insulating material in expanded form as a solidified foam.

Hollow bodies with prickles for photovoltaic applications

The tiny balls of polystyrene anchored in this way form the template on which the nanowires are desposited. Jamil Elias has succeeded in using an electrochemical method which himself has developed to vary the conductivity and electrolytic properties of the polystyrene balls in such way that the zinc oxide is deposited on the surface of the microspheres. Over time regular nanowires grow from this surface, and when this process is complete the polystyrene is removed, leaving behind hollow spherical structures with spines — little sea-urchins, as it were! Tightly packed on the underlying substrate, the sea-urchins lend it a three-dimensional structure, thereby increasing considerably its surface area.

This nanostructured surface is predestined for use in photovoltaic applications. The researchers expect that it will have excellent light scattering properties. This means the surface will be able to absorb significantly more sunlight and therefore be able to convert radiated energy into electricity more efficiently. In a project supported by the Swiss Federal Office of Energy (SFOE), Laetitia Philippe and her research team are developing extremely thin absorbers (ETAs) for solar cells, based these zinc oxide nanostructures.

Swiss Federal Laboratories for Materials Science and Technology (EMPA) ‘Sea urchin’-shaped nanostructures grown in the lab. ScienceDaily http://www.sciencedaily.com­ /releases/2010/07/100729074910.htm

The Original Post is Located Here: ‘Sea Urchin’-Shaped Nanostructures Grown in the Lab

No matter what your ethics are with regard to the source of the power you use, its price will be highly relevant to you and it is believed by many people that renewable energy is expensive and that by switching their provider to green power they will face higher monthly bills. Wrong! Examples of these sources are solar cells, tidal power, wind generators and even hydro-electricity, and these are certainly cheaper than nuclear power plants and can be less expensive than traditional fossil fuels such as oil or coal-powered electricity generators.

Nevertheless, surely you would surey think very carefully if you were offered the possibility of switching your electricity provider to a green company that offered the choice between 100% renewable energy or a mixture of the two, would you not? Of course you would – with certain provisos.

Most people and businesses are usually fairly happy with their current gas and electricity suppliers; otherwise they would already have made the change. It would have to be a very good offer to persuade them to move to another provider. If the alternative was a source of power that was greener and renewable, then that would certainly be an incentive, although the problem is that in many cases people have no interest in whether their energy source can be sustained or not. All they are interested in is price.

Motives such as reducing the consumption of fossil fuels and saving the planet come second to hard cash generation in the eyes of corporations and some individuals. As long as it does what it has to do then the least expensive will be most preferred, and there are few doubts that oil and coal provide inexpensive electricity reliably and easily. In fact, renewable energy sources can work out at around 30% cheaper than traditional fossil fuel sources, and shoiuld render them very attractive propositions to corporations, non-profit organizations and also to individual consumers.

In spite of the facts many are unaware of this, and the green industries have done a very poor job in educating people on the true cost situation. If consumers: businesses, charity organizations or individuals, could be offered a source of green electricity that saved them up to 30% on their monthly bills they would certainly switch over.

In fact, that is the situation right now! By changing your electricity supplier to a green power source it is possible to reduce your electricity bills – but only with the right sustainable power provider. Another thing to keep in mind is that one day in not too distant future there will be no fossil fuels left and then what will happen? Your grandchildren having to tolerate nuclear power plants growing up all over the countryside?

No, I am sure not. Look around for the best green power offers available, and you will find that changing your electricity supplier is free, your monthly bills will drop, and your grandchildren will thank you for it.

The Original Post is Located Here: Going Green: Changing Your Electricity Provider to Green Power

Advantages of Solar Power
Solar power is a renewable source generated from the sun, meaning that the solar energy source is never going to finish. So, we do not need to worry about we may jeopardy of the energy source if you over use it.

Solar power is environmental friendly energy source. Unlike oil, the use of solar energy will never causes green house effects or emits carcinogens into the air and causes the air pollution.

The sun is FREE. Unlike the traditional energy source which you need to pay more if you use more, there is not limit on how much you can use the energy generated from solar power, and you do not need to think of the electricity cost when you use a solar-powered energy generator, because the sun is FOC (Free of Charge).

Little maintenance cost on solar power system. Solar cells can last for a lifetime and because there are no moving parts, it needs very little maintenance. You do not really need to allocate significant budget for it maintenance cost.

Disadvantages of Solar Power
The key stopping factor that makes most of people who are interested to install solar power system is the total cost is expensive. A solar power system that provides enough energy to power an average sized home can cost anywhere from $6,000 to $20,000. Seeing the potential market demand on solar power system, the industries with continue research efforts are trying to reduce the material costs. Moreover, there are many simple-to-follow DIY instruction manuals had been made published to teach people how to build their own solar power system using cheap materials which can be found at local market.

The solar power can be generated without sunlight, which means the power cannot be created at night, during rain and winter season when sun is hiding behind the cloud. This had been one of key discouragement of using solar power as the alternative power solution.

If you build the solar panel at the roof of your home, it becomes part of the house. You may need to sell it together with your house if you decide to move to a new home. And you need to reinstall the solar power system at your new home.

Summary
You should clearly understand of both the advantages and the disadvantages of solar power system before you go ahead to convert your home to be solar-powered so that you can really benefited from the advantages of solar power while handling the disadvantages of solar power to minimize the impacts.

The Original Post is Located Here: Advantages of Solar Power Vs Disadvantages of Solar Power

Transparent solar cells offer a multitude of uses. (Credit: Image courtesy of Fraunhofer-Gesellschaft)

To translate the vision of see-through solar cells and transparent electronics into reality, two different transparent coatings would be required – one to conduct the electricity via electrons, the n-conductors, and one in which electron holes enable the electricity to flow, the p-conductors. To produce these coatings the engineers dope the base material with a few other atoms. Depending on which atoms they use, they obtain the differently conducting coatings. N-conducting transparent materials are state of the art, but the p-conductors are problematic. Their conductivity is too low and often their transparency is poor. Manufacturers need a transparent base material which is amenable to both n- and p-doping.

At present, indium tin oxide is mainly used for the n-conductors, but this is costly. Indium has become a rare commodity and its price has increased tenfold since 2002. The search for substitute materials is therefore in full swing. At the same time, various questions need to be answered, such as which materials would be best suitable, what they should be doped with to obtain good conductivity, and how good their transparency is. Research scientists at the Fraunhofer Institute for Mechanics of Materials IWM working in cooperation with other Fraunhofer colleagues have developed material physics models and methods which help in the search.

“If transparent p-conductors with adequate conductivity could be produced, it would be possible to realize completely transparent electronics,” says Dr. Wolfgang Körner, research scientist at the IWM. Using electron microscope images, the researchers initially determine the grain boundaries which most frequently occur in the material – i.e. irregularities in the ordered crystal structure. These defect structures are modeled atom by atom. Special simulation methods calculate how the electrons are distributed in the structures and thus in the solid body. From the data the researchers extract how conductive and transparent the material is. “We have found, for example, that phosphorus is suitable for p-doping zinc oxide, but that nitrogen is more promising,” says Körner.

Fraunhofer-Gesellschaft. “Transparent Solar Cells Made For Windows.” ScienceDaily

The Original Post is Located Here: Transparent Solar Cells Made For Windows

Now, a team of University of Florida chemists is the latest to report a new mechanism to transform light straight into motion – albeit at a very, very, very tiny scale.

In a paper expected to appear soon in the online edition of the journal Nano Letters, the UF team reports building a new type of “molecular nanomotor” driven only by photons, or particles of light. While it is not the first photon-driven nanomotor, the almost infinitesimal device is the first built entirely with a single molecule of DNA — giving it a simplicity that increases its potential for development, manufacture and real-world applications in areas ranging from medicine to manufacturing, the scientists say.

“It is easy to assemble, has fewer parts and theoretically should be more efficient,” said Huaizhi Kang, a doctoral student in chemistry at UF and the first author of the paper.

The scale of the nanomotor is almost vanishingly small.

In its clasped, or closed, form, the nanomotor measures 2 to 5 nanometers — 2 to 5 billionths of a meter. In its unclasped form, it extends as long as 10 to 12 nanometers. Although the scientists say their calculations show it uses considerably more of the energy in light than traditional solar cells, the amount of force it exerts is proportional to its small size.

But that won’t necessarily limit its potential.

In coming years, the nanomotor could become a component of microscopic devices that repair individual cells or fight viruses or bacteria. Although in the conceptual stage, those devices, like much larger ones, will require a power source to function. Because it is made of DNA, the nanomotor is biocompatible. Unlike traditional energy systems, the nanomotor also produces no waste when it converts light energy into motion.

“Preparation of DNA molecules is relatively easy and reproducible, and the material is very safe,” said Yan Chen, a UF chemistry doctoral student and one of the authors of the paper.

Applications in the larger world are more distant. Powering a vehicle, running an assembly line or otherwise replacing traditional electricity or fossil fuels would require untold trillions of nanomotors, all working together in tandem — a difficult challenge by any measure.

“The major difficulty lies ahead,” said Weihong Tan, a UF professor of chemistry and physiology, author of the paper and the leader of the research group reporting the findings. “That is how to collect the molecular level force into a coherent accumulated force that can do real work when the motor absorbs sunlight.”

Tan added that the group has already begun working on the problem.

“Some prototype DNA nanostructures incorporating single photo-switchable motors are in the making which will synchronize molecular motions to accumulate forces,” he said.

To make the nanomotor, the researchers combined a DNA molecule they created in the lab with azobenzene, a chemical compound that responds to light. A high-energy photon prompts one response; lower energy another.

To demonstrate the movement, the researchers attached a fluorophore, or light-emitter, to one end of the nanomotor and a quencher, which can quench the emitting light, to the other end. Their instruments recorded emitted light intensity that corresponded to the motor movement.

“Radiation does cause things to move from the spinning of radiometer wheels to the turning of sunflowers and other plants toward the sun,” said Richard Zare, distinguished professor and chairman of chemistry at Stanford University. “What Professor Tan and co-workers have done is to create a clever light-actuated nanomotor involving a single DNA molecule. I believe it is the first of its type.”

The National Institutes of Health and the National Science Foundation funded the research. The other coauthors of this paper are Haipeng Liu, Joseph A. Phillips, Zehui Cao, Youngmi Kim, Zunyi Yang and Jianwei Li.

University of Florida. “New, Light-driven Nanomotor Is Simpler, More Promising, Scientists Say” ScienceDaily

The Original Post is Located Here: New Light-Driven Nanomotor

Cell phones, computers, MP3 players, kitchen stoves, and irons all have one thing in common: They need electricity. And in the future, more and more cars will also be fuelled by electric power. If the latest forecast from the World Energy Council WEC can be believed, global electricity requirements will double in the next 40 years. At the same time, prices for the dwindling resources of petroleum and natural gas are climbing.

“Rising energy prices are making alternative energy sources increasingly cost-effective. Sometime in the coming years, renewable energy sources, such as solar energy, will be competitive, even without subsidization,” explains Dr. Arnold Gillner, head of the microtechnology department at the Fraunhofer Institute for Laser Technology in Aachen, Germany. “Experts predict that grid parity will be achieved in a few years. This means that the costs and opportunities in the grid will be equal for solar electricity and conventionally generated household electricity.” Together with his team at the Fraunhofer Institute for Laser Technology ILT in Aachen, this researcher is developing technologies now that will allow faster, better, and cheaper production of solar cells in the future. “Lasers work quickly, precisely, and without contact. In other words, they are an ideal tool for manufacturing fragile solar cells. In fact, lasers are already being used in production today, but there is still considerable room for process optimization.” In addition to gradually improving the manufacturing technology, the physicists and engineers in Aachen are working with solar cell developers – for example, at the Fraunhofer Institute for Solar Energy Systems ISE in Freiburg – on new engineering and design alternatives.

New production technologies allow new design alternatives
At “Laser 2009” in Munich, the researchers will be demonstrating how lasers can drill holes into silicon cells at breathtaking speed: The ILT laser system drills more than 3,000 holes within one second. Because it is not possible to move the laser source at this speed, the experts have developed optimized manufacturing systems which guide and focuses the light beam at the required points. “We are currently experimenting with various laser sources and optical systems,” Gillner explains. “Our goal is to increase the performance to 10,000 holes a second. This is the speed that must be reached in order to drill 10,000 to 20,000 holes into a wafer within the cycle time of the production machines.”

The tiny holes in the wafer – their diameter is only 50 micrometers – open up undreamt-of possibilities for the solar cell developers. “Previously, the electrical contacts were arranged on the top of the cells. The holes make it possible to move the contacts to the back, with the advantage that the electrodes, which currently act as a dark grid to absorb light, disappear. And so the energy yield increases. The goal is a degree of efficiency of 20 percent% in industrially-produced emitter wrap-through (EWT) cells, with a yield of one-third more than classic silicon cells,” Gillner explains. The design principle itself remains unchanged: In the semi-conductor layer, light particles, or photons, produce negative electrons and positive holes, each of which then wanders to the oppositely poled electrodes. The contacts for anodes and cathodes in the EWT cells are all on the back, there is no shading caused by the electrodes, and the degree of efficiency increases. With this technique, it may one day be possible to use unpurified “dirty” silicon to manufacture solar cells that have poorer electrical properties, but that are cheaper.

Drilling holes into silicon cells is only one of many laser applications in solar cell manufacturing. In the EU project Solasys – Next Generation Solar Cell and Module Laser Processing Systems – an international research team is currently developing new technologies that will allow production to be optimized in the future. ILT in Aachen is coordinating the six million euro project. “We are working on new methods that make the doping of semiconductors, the drilling and the surface structuring of silicon, the edge isolation of the cells, and the soldering of the modules more economical,” project coordinator Gillner explains. For example, “selective laser soldering” makes it possible to improve the rejection rates and quality of the contacting, and so reduce manufacturing costs. Until now, the electrodes were mechanically pressed onto the cells, and then heated in an oven. “But silicon cells often break during this process,” Gillner knows. “Breakage is a primary cost factor in production.” On the other hand, however, with “selective laser soldering” the contacts are pressed on to the cells with compressed air and then soldered with the laser. The mechanical stress approaches zero and the temperature can be precisely regulated. The result: Optimal contacts and almost no rejects.

Laser technology means more efficient thin film cells
Laser technology is also helping to optimize the manufacture of thin film solar cells. The extremely thin film packages made of semiconducting oxide, amorphous silicon, and metal that are deposited onto the glass panels still have a market share of only ten percent. But as Gillner knows, “This could be higher, because thin film solar cells can be used anywhere that non-transparent glass panels can be mounted, for example, on house facades or sound-insulating walls. But the degrees of efficiency are comparable low at five to eight percent, and the production costs are comparatively high.” The laser researchers are working to improve these costs. Until now, the manufacturers have used mechanical methods or solid-state lasers in the nanosecond range in order to structure the active layers on the glass panels. In order to produce electric connections between the semiconductor and the metal, grooves only a few micrometers wide must be created. At the Fraunhofer-Gesellschaft booth at “Laser 2009” the ILT researchers will be demonstrating a 400-watt ultrashort pulse laser that processes thin-film solar modules ten times faster than conventional diode-pumped solid-state lasers. “The ultrashort pulse laser is an ideal tool for ablating thin layers: It works very precisely, does not heat the material and, working with a pulse frequency of 80 MHz, can process a 2-by-3 meter glass panel in under two minutes,” Gillner reports. “The technology is still very new, and high-performance scanning systems and optical systems adapted to the process must be developed first. In the medium term, however, this technology will be able to reduce production costs.”

The rise of laser technology in solar technology is just taking off, and it still has a long way to go. “Lasers simplify and optimize the manufacture of classic silicon and thin-film cells, and they allow the development of new design alternatives,” Gillner continues. “And so laser technology is making an important contribution towards allowing renewable energy sources to penetrate further into the energy market.”

Fraunhofer-Gesellschaft. “Lasers Are Making Solar Cells Competitive” ScienceDaily

The Original Post is Located Here: Lasers Are Making Solar Cells Competitive

This system has been developed by Daniel Chemisana, member of the research group in Agrometeorology and Energy for Environment, leaded by UdL lecturers Manel Ibáñez and Joan Ignasi Rosell.

This thermal-photovoltaic modular system has a solar concentration of 10 suns, that is, it only needs a tenth part of a standard system’s active surface to produce the same energy, be it electricity, heat, or both simultaneously. Besides the reduction in the surface of used solar cells and the cost reduction this implies, this new technology can generate cold by connecting a heat pump to the system.

Rosell highlighted the architectural integration that these modules will allow either in roofs or in façades, which will reduce their visual impact. They can be directly installed in roofs, on the closure of concrete or brick blocks, forming a curtain wall in the façades or as a part of the railings in terraces, “as if they were a building’s second skin”. They can also be used in residential buildings, companies or farms.

The system, of which the international patent has already been requested, consists of a stationary lens and a linear absorber plate that concentrates sunlight to generate energy. This concentration system reduces the space that until now was needed with traditional plates, which move around in search of sunlight.

Rosell also underlined the global efficiency of energetic conversion in this module, which could rise above 60%. Researchers at UdL anticipate that the product could be commercialised in a year if companies opt for this technology. The prototype has financed by CIDEM and has the support of the UdL Technological Springboard.

ScienceDaily
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