Solar cell

Breakthrough solar cell captures CO2 and sunlight, produces burnable fuel

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Researchers at the University of Illinois at Chicago have engineered a potentially game-changing solar cell that cheaply and efficiently converts atmospheric carbon dioxide directly into usable hydrocarbon fuel, using only sunlight for energy.

The finding is reported in the July 29 issue of Science and was funded by the National Science Foundation and the U.S. Department of Energy. A provisional patent application has been filed.

Unlike conventional solar cells, which convert sunlight into electricity that must be stored in heavy batteries, the new device essentially does the work of plants, converting atmospheric carbon dioxide into fuel, solving two crucial problems at once. A solar farm of such “artificial leaves” could remove significant amounts of carbon from the atmosphere and produce energy-dense fuel efficiently.

“The new solar cell is not photovoltaic — it’s photosynthetic,” says Amin Salehi-Khojin, assistant professor of mechanical and industrial engineering at UIC and senior author on the study.

“Instead of producing energy in an unsustainable one-way route from fossil fuels to greenhouse gas, we can now reverse the process and recycle atmospheric carbon into fuel using sunlight,” he said.

While plants produce fuel in the form of sugar, the artificial leaf delivers syngas, or synthesis gas, a mixture of hydrogen gas and carbon monoxide. Syngas can be burned directly, or converted into diesel or other hydrocarbon fuels.

The ability to turn CO2 into fuel at a cost comparable to a gallon of gasoline would render fossil fuels obsolete.

Chemical reactions that convert CO2 into burnable forms of carbon are called reduction reactions, the opposite of oxidation or combustion. Engineers have been exploring different catalysts to drive CO2 reduction, but so far such reactions have been inefficient and rely on expensive precious metals such as silver, Salehi-Khojin said.

“What we needed was a new family of chemicals with extraordinary properties,” he said.

Amin Salehi-Khojin & Mohammad Asadi

Amin Salehi-Khojin (left), UIC assistant professor of mechanical and industrial engineering, and postdoctoral researcher Mohammad Asadi with their breakthrough solar cell that converts atmospheric carbon dioxide directly into syngas.

Salehi-Khojin and his coworkers focused on a family of nano-structured compounds called transition metal dichalcogenides — or TMDCs — as catalysts, pairing them with an unconventional ionic liquid as the electrolyte inside a two-compartment, three-electrode electrochemical cell.

The best of several catalysts they studied turned out to be nanoflake tungsten diselenide.

“The new catalyst is more active; more able to break carbon dioxide’s chemical bonds,” said UIC postdoctoral researcher Mohammad Asadi, first author on the Science paper.

In fact, he said, the new catalyst is 1,000 times faster than noble-metal catalysts — and about 20 times cheaper.

Other researchers have used TMDC catalysts to produce hydrogen by other means, but not by reduction of CO2. The catalyst couldn’t survive the reaction.

“The active sites of the catalyst get poisoned and oxidized,” Salehi-Khojin said. The breakthrough, he said, was to use an ionic fluid called ethyl-methyl-imidazolium tetrafluoroborate, mixed 50-50 with water.

“The combination of water and the ionic liquid makes a co-catalyst that preserves the catalyst’s active sites under the harsh reduction reaction conditions,” Salehi-Khojin said.

The UIC artificial leaf consists of two silicon triple-junction photovoltaic cells of 18 square centimeters to harvest light; the tungsten diselenide and ionic liquid co-catalyst system on the cathode side; and cobalt oxide in potassium phosphate electrolyte on the anode side.

When light of 100 watts per square meter – about the average intensity reaching the Earth’s surface – energizes the cell, hydrogen and carbon monoxide gas bubble up from the cathode, while free oxygen and hydrogen ions are produced at the anode.

“The hydrogen ions diffuse through a membrane to the cathode side, to participate in the carbon dioxide reduction reaction,” said Asadi.

The technology should be adaptable not only to large-scale use, like solar farms, but also to small-scale applications, Salehi-Khojin said. In the future, he said, it may prove useful on Mars, whose atmosphere is mostly carbon dioxide, if the planet is also found to have water.

“This work has benefitted from the significant history of NSF support for basic research that feeds directly into valuable technologies and engineering achievements,” said NSF program director Robert McCabe.

“The results nicely meld experimental and computational studies to obtain new insight into the unique electronic properties of transition metal dichalcogenides,” McCabe said. “The research team has combined this mechanistic insight with some clever electrochemical engineering to make significant progress in one of the grand-challenge areas of catalysis as related to energy conversion and the environment.”

“Nanostructured transition metal dichalcogenide electrocatalysts for CO2 reduction in ionic liquid” is online at Science.

Solar cell polymers with multiplied electrical output

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One challenge in improving the efficiency of solar cells is that some of the absorbed light energy is lost as heat. So scientists have been looking to design materials that can convert more of that energy into useful electricity. Now a team from the U.S. Department of Energy’s Brookhaven National Laboratory and Columbia University has paired up polymers that recover some of that lost energy by producing two electrical charge carriers per unit of light instead of the usual one.

Solar cell polymers with multiplied electrical output

“Critically, we show how this multiplication process can be made efficient on a single molecular polymer chain,” said physicist Matthew Sfeir, who led the research at Brookhaven Lab’s Center for Functional Nanomaterials, a DOE Office of Science User Facility. Having the two charges on the same molecule means the light-absorbing, energy-producing don’t have to be arrayed as perfect crystals to produce extra electrical charges. Instead, the self-contained materials work efficiently when dissolved in liquids, which opens the way for a wide range of industrial scale manufacturing processes, including “printing” solar-energy-producing material like ink.

The research is published as an Advance Online Publication in Nature Materials, January 12, 2015.

The concept of producing two charges from one unit of light is called “.” (Think of the fission that splits a single biological cell into two when cells multiply.) Devices based on this multiplication concept have the potential to break through the upper limit on the efficiency of so-called single junction , which is currently around 34 percent. The challenges go beyond doubling the electrical output of the solar cell materials, because these materials must be incorporated into actual current-producing devices. But the hope is that the more-efficient current-generating materials could be added on to existing solar cell materials and device structures, or spark new types of solar cell designs.

Most singlet fission materials explored so far result in twin charge carriers being produced on separate molecules. These only work well when the material is in a crystalline film with long-range order, where strong coupling results in an additional charge being produced on a neighboring molecule. Producing such high quality crystalline films and integrating them with solar cell manufacturing complicates the process.

Producing the twin charges on a single polymer molecule, in contrast, results in a material that’s compatible with a much wider variety of industrial processes.

The materials were designed and synthesized by a Columbia University team led by Professor Luis Campos, and analyzed at Brookhaven using specialized tools at the CFN and in the Chemistry Department. For Sfeir and Campos, the most fascinating part of the interdisciplinary project was exploring the electronic and chemical requirements that enable this multiplication process to occur efficiently.

“We expect a significant leap in the development of third-generation, hot-carrier solar cells,” said Campos. “This approach is especially promising because the materials’ design is modular and amenable to current synthetic strategies that are being explored in second-generation .”

Details of the materials’ analysis

At the CFN, Sfeir and Erik Busby (a postdoctoral fellow) used time-resolved optical spectroscopy to induce and quantify singlet fission in the various polymer compositions using a single laser photon. Xiaoyang Zhu of Columbia helped to understand the data and interpret results.

“We put light energy into a material with a laser pulse and watch what happens to that energy using a series of weaker light pulses – somewhat analogous to taking snapshots using a camera with a very fast shutter,” Sfeir said.

The team also studied the same process using “pulse radiolysis” in collaboration with John Miller, who runs the Laser-Electron Accelerator Facility.

“The differences observed between these two experiments allowed us to unambiguously identify singlet fission as the primary process responsible for the production of these twin charges,” Sfeir said.

With Qin Wu, the team also used a powerful computer cluster at the CFN to model these materials and understand the design requirements that were necessary for singlet fission to take place.

“The ideas for this project and supervision of the work were really shared between Brookhaven and Columbia,” Sfeir said. “It’s a great example of the kind of collaborative work that takes place at DOE user facilities like the CFN.”

The next steps for the CFN-Columbia team will be to test a large class of materials using the design framework they’ve identified, and then integrate some of these carbon-based polymer materials into functioning solar cells.

“Even though we have demonstrated the concept of multiplication in single molecules, the next challenge is to show we can harness the extra excitations in an operating device. This may be in conventional bulk type solar cells, or in third-generation concepts based on other inorganic (non-carbon) nanomaterials. The dream is to build hot-carrier solar cells that could be fully assembled using solution processing of our organic singlet fission materials.”

New Solar Battery Could Generate Cheaper Clean Energy

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A new kind of solar cell could store electrical energy without any help from traditional batteries, according to a new study.

Researchers at Ohio State University, in Columbus, have developed what they’re calling the world’s first solar battery — a hybrid device that combines the energy-capturing abilities of a solar cell with the energy-storing capabilities of a battery.

The new cell could lower the cost of harvesting renewable energy from the sun by as much as 25 percent, according to the researchers. [Top 10 Craziest Environmental Ideas]
The key to the device’s success is a mesh solar panel that allows both sunlight and air to enter the cell. This porous material represents a departure from the solid semiconductor materials typically used to make solar cells. Allowing both light and oxygen into the cell enables the chemical reactions that typically occur inside a battery to occur within the solar cell itself.

“The state of the art is to use a solar panel to capture the light, and then use a cheap battery to store the energy,” lead researcher Yiying Wu, a professor of chemistry at Ohio State, said in a statement. “We’ve integrated both functions into one device. Any time you can do that, you reduce cost.”

But this innovative device can do more than just lower the cost of renewable energy, Wu said. It can also help solve a problem that’s been plaguing scientists for years: how to store energy from the sun without losing a lot of that energyin the process.

A loss of electricity naturally occurs within any solar cell when the electrons released by the cell’s semiconductor materials travel outside the cell and into a battery. Only about 80 percent of the electrons produced by solar cells successfully complete this journey. But the new solar cell is designed to ensure that 100 percent of the electrons captured find their way into a battery, the researchers said.

This high efficiency is possible because the conversion of sunlight to electric current isn’t happening inside the solar cell before being transferred to the battery. Since the battery is located inside the cell, electrons are not able to escape, the researchers said.

The hybrid solar cell-battery is made up of three electrodes, or materials that conduct electricity. The first electrode is the mesh solar panel (which is really a collection of solar cells), the second electrode is made of a thin sheet of porous carbon and the third electrode is a sheet of lithium metal. Between these three electrodes is an electrolyte that can shuttle charges back and forth.

When the battery is in use — a phase known as “discharge” — the lithium metal and porous carbon electrodes are connected to an external circuit. Lithium ions can then travel to the carbon electrode and form lithium peroxide. This chemical process drives an external electrical current, Wu told Live Science in an email.

To recharge the solar battery, light hits the mesh panel and generates electron-hole pairs, which can carry an electrical charge. One of the most important features of the device is that it uses added molecules, known as redox shuttle additives, to transfer these charges from the mesh solar panel to the lithium electrode, where they cause the lithium peroxide to decompose into oxygen and lithium ions.

The oxygen is released out of the cell, but the lithium ions, as well as electrical charges, are stored inside the battery in the lithium electrode, Wu said.

“Basically, it’s a breathing battery,” he said. “It breathes in air when it discharges, and breathes out when it charges.”

The researchers are still experimenting with other ways to improve the design of their solar battery, a project that is funded by the U.S. Department of Energy.

Solar cell efficiency improved with new polymer .

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New light has been shed on solar power generation using devices made with polymers, thanks to collaboration between scientists in the University of Chicago’s chemistry department, the Institute for Molecular Engineering and Argonne National Laboratory.

Researchers identified a new polymer—a type of large molecule that forms plastics and other familiar materials—that improved the efficiency of solar cells. The group also determined the method by which the polymer improved the cells’ efficiency. The polymer allows electrical charges to move more easily throughout the cell, boosting the production of electricity—a mechanism never before demonstrated in such devices.

“Polymer solar cells have great potential to provide low-cost, lightweight and flexible electronic devices to harvest solar energy,” said Luyao Lu, graduate student in chemistry and lead author of a paper describing the result, published online last month in the journal Nature Photonics.

Solar cells made from polymers are a popular topic of research due to their appealing properties, but researchers are still struggling to efficiently generate electrical power with these materials.

“The field is rather immature—it’s in the infancy stage,” said Luping Yu, professor in chemistry and fellow in the Institute for Molecular Engineering, who led the UChicago group carrying out the research.

The active regions of such solar cells are composed of a mixture of polymers that give and receive electrons to generate electrical current when exposed to light. The new polymer developed by Yu’s group, called PID2, improves the efficiency of electrical power generation by 15 percent when added to a standard polymer-fullerene mixture.

“Fullerene, a small carbon molecule, is one of the standard materials used in polymer solar cells,” Lu said. “Basically, in polymer solar cells we have a polymer as electron donor and fullerene as electron acceptor to allow charge separation.” In their work, the UChicago-Argonne researchers added another polymer into the device, resulting in solar cells with two polymers and one fullerene.

8.2% efficiency

The group achieved an efficiency of 8.2% when an optimal amount of PID2 was added—the highest ever for solar cells made up of two types of polymers with fullerene—and the result implies that even higher efficiencies could be possible with further work. The group is now working to push efficiencies toward 10%, a benchmark necessary for polymer solar cells to be viable for commercial application.

7169063498_0c83762d93_z.jpg
Flickr/Intel Free Press, CC BY 2.0

The result was remarkable not only because of the advance in technical capabilities, Yu noted, but also because PID2 enhanced the efficiency via a new method. The standard mechanism for improving efficiency with a third polymer is by increasing the absorption of light in the device. But in addition to that effect, the team found that when PID2 was added, charges were transported more easily between polymers and throughout the cell.

In order for a current to be generated by the solar cell, electrons must be transferred from polymer to fullerene within the device. But the difference between electron energy levels for the standard polymer-fullerene is large enough that electron transfer between them is difficult. PID2 has energy levels in between the other two, and acts as an intermediary in the process.

“It’s like a step,” Yu said. “When it’s too high, it’s hard to climb up, but if you put in the middle another step then you can easily walk up.”

Thanks to collaboration with Argonne, Yu and his group were also able to study the changes in structure of the polymer blend when PID2 was added, and show that these changes likewise improved the ability of charges to move throughout the cell, further improving the efficiency. The addition of PID2 caused the polymer blend to form fibers, which improve the mobility of electrons throughout the material. The fibers serve as a pathway to allow electrons to travel to the electrodes on the sides of the solar cell.

“It’s like you’re generating a street and somebody that’s traveling along the street can find a way to go from this end to another,” Yu said.

To reveal this structure, Wei Chen of the Materials Science Division at Argonne National Laboratory and the Institute for Molecular Engineering performed X-ray scattering studies using the Advanced Photon Source at Argonne and the Advanced Light Source at Lawrence Berkeley National Laboratory.

“Without that it’s hard to get insight about the structure,” Yu said, calling the collaboration with Argonne “crucial” to the work. “That benefits us tremendously,” he said.

Chen noted that “Working together, these groups represent a confluence of the best materials and the best expertise and tools to study them, to achieve progress beyond what could be achieved with independent efforts.”

“This knowledge will serve as a foundation from which to develop high-efficiency organic photovoltaic devices to meet the nation’s future energy needs,” Chen said.

Japanese firm to supply solar energy from Moon to Earth.

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A Japanese firm has proposed an out-of-this-world solution to our planet’s power woes – building a solar panel array around the Moon’s equator and sending the electricity it collects back to Earth.

Moon energy

The project called LUNA RING is developed by construction firm Shimizu Corporation. According to the firm, such a system would be capable of sending 13,000 terawatts of power back to Earth and that construction could begin on the project as early as 2035, Phys.org reported.

To ensure continuous generation of power, an array of

solar cells will extend like a belt along the entire 11,000km

lunar equator.

This belt will be built in width from a few kilometres to 400km, the company said on its website.

Robots will play a vital role in construction on the lunar surface. They will be tele-operated 24 hours a day from the Earth.

The concrete would be covered with solar panels, which

would be connected via cables to microwave and laser

transmission stations.

The energy beams sent from the Moon would be directed at receiving stations on Earth, allowing for a round-the-clock source of energy as there are no clouds or other bad weather on the Moon.

The cables will transfer the electric power from the lunar solar cells to the transmission facilities.

High-energy-density laser will be beamed to the receiving facilities using 20km-diameter antennas. A guidance beacon (radio beacon) brought from the Earth will be used to ensure accurate transmission.

Materials needed for the construction and maintenance of the Solar Belt will be transported along this route. Electric power cables will be installed under the transportation route.

The plants will move automatically while producing solar cells from lunar resources and installing them.

Since the earthquake and tsunami that struck Japan in March 2011 – which led to closing the country’s nuclear power plants – scientists have been scrambling to find ways to create electricity for the country in other ways.

However, the project doesn’t address the costs and

considerable hurdles it would have to overcome – important

among them would be building such a massive structure from such a great distance.

 

Playing Pop and Rock Music Boosts Performance of Solar Cells.

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Playing pop and rock music improves the performance of solar cells, according to new research from scientists at Queen Mary University of London and Imperial College London.

The high frequencies and pitch found in pop and rock music cause vibrations that enhanced energy generation in solar cells containing a cluster of ‘nanorods’, leading to a 40 per cent increase in efficiency of the solar cells.

The study has implications for improving energy generation from sunlight, particularly for the development of new, lower cost, printed solar cells.

The researchers grew billions of tiny rods (nanorods) made from zinc oxide, then covered them with an active polymer to form a device that converts sunlight into electricity.

Using the special properties of the zinc oxide material, the team was able to show that sound levels as low as 75 decibels (equivalent to a typical roadside noise or a printer in an office) could significantly improve the solar cell performance.

“After investigating systems for converting vibrations into electricity this is a really exciting development that shows a similar set of physical properties can also enhance the performance of a photovoltaic,” said Dr Steve Dunn, Reader in Nanoscale Materials from Queen Mary’s School of Engineering and Materials Science and co-author of the paper.

Scientists had previously shown that applying pressure or strain to zinc oxide materials could result in voltage outputs, known as the piezoelectric effect. However, the effect of these piezoelectric voltages on solar cell efficiency had not received significant attention before.

“We thought the soundwaves, which produce random fluctuations, would cancel each other out and so didn’t expect to see any significant overall effect on the power output,” said James Durrant, Professor of Photochemistry at Imperial College London, who co-led the study.

“We tried playing music instead of dull flat sounds, as this helped us explore the effect of different pitches. The biggest difference we found was when we played pop music rather than classical, which we now realise is because our acoustic solar cells respond best to the higher pitched sounds present in pop music,” he concluded.

The discovery could be used to power devices that are exposed to acoustic vibrations, such as air conditioning units or within cars and other vehicles.

Co-author Dr Joe Briscoe also from Queen Mary’s School of Engineering and Materials Science, commented: “The whole device extremely simple and inexpensive to produce as the zinc oxide was grown using a simple, chemical solution technique and the polymer was also deposited from a solution.”

Dr Dunn added: “The work highlights the benefits of collaboration to develop new and interesting systems and scientific understanding.”

Big beats bolster solar cell efficiency.

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Playing pop and rock music improves the performance of solar cells, according to new research from scientists at Queen Mary University of London and Imperial College London.

The high frequencies and pitch found in pop and rock music cause vibrations that enhanced in  containing a cluster of ‘nanorods‘, leading to a 40 per cent increase in efficiency of the solar cells.

Big beats bolster solar cell efficiency

The study has implications for improving energy generation from sunlight, particularly for the development of new, lower cost, printed solar cells.

The researchers grew billions of tiny rods (nanorods) made from zinc oxide, then covered them with an active polymer to form a device that converts sunlight into electricity.

Using the special properties of the zinc oxide material, the team was able to show that sound levels as low as 75 decibels (equivalent to a typical roadside noise or a printer in an office) could significantly improve the solar cell performance.

“After investigating systems for converting vibrations into electricity this is a really exciting development that shows a similar set of physical properties can also enhance the performance of a photovoltaic,” said Dr Steve Dunn, Reader in Nanoscale Materials from Queen Mary’s School of Engineering and Materials Science.

Scientists had previously shown that applying pressure or strain to  materials could result in voltage outputs, known as the piezoelectric effect. However, the effect of these piezoelectric voltages on  had not received significant attention before.

“We thought the soundwaves, which produce random fluctuations, would cancel each other out and so didn’t expect to see any significant overall effect on the power output,” said James Durrant, Professor of Photochemistry at Imperial College London, who co-led the study.

“The key for us was that not only that the  from the sound didn’t cancel each other out, but also that some frequencies of sound seemed really to amplify the solar cell output – so that the increase in power was a remarkably big effect considering how little sound energy we put in.”

“We tried playing music instead of dull flat sounds, as this helped us explore the effect of different pitches. The biggest difference we found was when we played pop music rather than classical, which we now realise is because our acoustic solar cells respond best to the higher pitched sounds present in pop music,” he concluded.

The discovery could be used to power devices that are exposed to acoustic vibrations, such as air conditioning units or within cars and other vehicles.

Dr Dunn added: “The work highlights the benefits of collaboration to develop new and interesting systems and scientific understanding.”

Silicon Supercapacitor Powers Phones for Weeks on Single Charge.

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Charge

Material scientists at Vanderbilt University have developed a supercapacitor made out of silicon. Previously thought to be kind of a crazy idea, the silicon capacitor can be built into a chip — which could give cellphones weeks of life from one charge, or solar cells that produce energy with or without the sun. Pretty sweet deal.Published in Scientific Reports, the first-ever silicon supercap stores energy by gathering ions on the surface of the porous material. Different from batteries, which work on chemical reactions, the silicon supercaps can be charged in minutes and last way longer. Silicon had been considered unsuitable for supercaps because of the way it reacts with the electrolytes that make the energy-storing ions.

“If you ask experts about making a supercapacitor out of silicon, they will tell you it is a crazy idea,” said assistant professor Cary Pint, who headed the development team at Vanderbilt. “But we’ve found an easy way to do it.”

Pint’s team coated the silicon in carbon — well, technically a few nanometers of graphene — and it stabilized the surface of the silicon, making it perfect for storing energy.

“All the things that define us in a modern environment require electricity,” said Pint. “The more that we can integrate power storage into existing materials and devices, the more compact and efficient they will become.”

Geekosystem is a Mashable publishing partner that aims to unite all the tribes of geekdom under one common banner. This article is reprinted with the publisher’s permission.

New device stores electricity on silicon chips.

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Solar cells that produce electricity 24/7, not just when the sun is shining. Mobile phones with built-in power cells that recharge in seconds and work for weeks between charges.

These are just two of the possibilities raised by a novel supercapacitor design invented by material scientists at Vanderbilt University that is described in a paper published in the Oct. 22 issue of the journal Scientific Reports.

It is the first supercapacitor that is made out of silicon so it can be built into a silicon chip along with the microelectronic circuitry that it powers. In fact, it should be possible to construct these power cells out of the excess silicon that exists in the current generation of solar cells, sensors, mobile phones and a variety of other electromechanical devices, providing a considerable cost savings.

“If you ask experts about making a supercapacitor out of silicon, they will tell you it is a crazy idea,” said Cary Pint, the assistant professor of mechanical engineering who headed the development. “But we’ve found an easy way to do it.”

Instead of storing energy in chemical reactions the way batteries do, “supercaps” store electricity by assembling ions on the of a porous material. As a result, they tend to charge and discharge in minutes, instead of hours, and operate for a few million cycles, instead of a few thousand cycles like batteries.

These properties have allowed commercial , which are made out of activated carbon, to capture a few niche markets, such as storing energy captured by regenerative braking systems on buses and electric vehicles and to provide the bursts of power required to adjust of the blades of giant wind turbines to changing wind conditions. Supercapacitors still lag behind the electrical energy storage capability of lithium-ion batteries, so they are too bulky to power most consumer devices. However, they have been catching up rapidly.

https://i0.wp.com/cdn.physorg.com/newman/gfx/news/2013/2-newdevicesto.jpg

Research to improve the energy density of supercapacitors has focused on carbon-based nanomaterials like graphene and nanotubes. Because these devices store electrical charge on the surface of their electrodes, the way to increase their energy density is to increase the electrodes’ surface area, which means making surfaces filled with nanoscale ridges and pores.

“The big challenge for this approach is assembling the materials,” said Pint. “Constructing high-performance, functional devices out of nanoscale building blocks with any level of control has proven to be quite challenging, and when it is achieved it is difficult to repeat.”

So Pint and his research team – graduate students Landon Oakes, Andrew Westover and post-doctoral fellow Shahana Chatterjee – decided to take a radically different approach: using porous silicon, a material with a controllable and well-defined nanostructure made by electrochemically etching the surface of a silicon wafer.

This allowed them to create surfaces with optimal nanostructures for supercapacitor electrodes, but it left them with a major problem. Silicon is generally considered unsuitable for use in supercapacitors because it reacts readily with some of chemicals in the electrolytes that provide the ions that store the electrical charge.

With experience in growing carbon nanostructures, Pint’s group decided to try to coat the porous with carbon. “We had no idea what would happen,” said Pint. “Typically, researchers grow graphene from silicon-carbide materials at temperatures in excess of 1400 degrees Celsius. But at lower temperatures – 600 to 700 degrees Celsius – we certainly didn’t expect graphene-like material growth.”

When the researchers pulled the porous silicon out of the furnace, they found that it had turned from orange to purple or black. When they inspected it under a powerful scanning electron microscope they found that it looked nearly identical to the original material but it was coated by a layer of graphene a few nanometers thick.

When the researchers tested the coated material they found that it had chemically stabilized the silicon surface. When they used it to make supercapacitors, they found that the graphene coating improved energy densities by over two orders of magnitude compared to those made from uncoated and significantly better than commercial supercapacitors.

The graphene layer acts as an atomically thin protective coating. Pint and his group argue that this approach isn’t limited to graphene. “The ability to engineer surfaces with atomically thin layers of materials combined with the control achieved in designing porous materials opens opportunities for a number of different applications beyond energy storage,” he said.

“Despite the excellent device performance we achieved, our goal wasn’t to create devices with record performance,” said Pint. “It was to develop a road map for integrated energy storage. Silicon is an ideal material to focus on because it is the basis of so much of our modern technology and applications. In addition, most of the silicon in existing devices remains unused since it is very expensive and wasteful to produce thin wafers.”

Pint’s group is currently using this approach to develop that can be formed in the excess materials or on the unused back sides of and sensors. The supercapacitors would store excess the electricity that the generate at midday and release it when the demand peaks in the afternoon.

When the researchers tested the coated material they found that it had chemically stabilized the silicon surface. When they used it to make supercapacitors, they found that the graphene coating improved energy densities by over two orders of magnitude compared to those made from uncoated and significantly better than commercial supercapacitors.

The graphene layer acts as an atomically thin protective coating. Pint and his group argue that this approach isn’t limited to graphene. “The ability to engineer surfaces with atomically thin layers of materials combined with the control achieved in designing porous materials opens opportunities for a number of different applications beyond energy storage,” he said.

“Despite the excellent device performance we achieved, our goal wasn’t to create devices with record performance,” said Pint. “It was to develop a road map for integrated energy storage. Silicon is an ideal material to focus on because it is the basis of so much of our modern technology and applications. In addition, most of the silicon in existing devices remains unused since it is very expensive and wasteful to produce thin wafers.”

Pint’s group is currently using this approach to develop that can be formed in the excess materials or on the unused back sides of and sensors. The supercapacitors would store excess the electricity that the generate at midday and release it when the demand peaks in the afternoon.

When the researchers tested the coated material they found that it had chemically stabilized the silicon surface. When they used it to make supercapacitors, they found that the graphene coating improved energy densities by over two orders of magnitude compared to those made from uncoated and significantly better than commercial supercapacitors.

The graphene layer acts as an atomically thin protective coating. Pint and his group argue that this approach isn’t limited to graphene. “The ability to engineer surfaces with atomically thin layers of materials combined with the control achieved in designing porous materials opens opportunities for a number of different applications beyond energy storage,” he said.

“Despite the excellent device performance we achieved, our goal wasn’t to create devices with record performance,” said Pint. “It was to develop a road map for integrated energy storage. Silicon is an ideal material to focus on because it is the basis of so much of our modern technology and applications. In addition, most of the silicon in existing devices remains unused since it is very expensive and wasteful to produce thin wafers.”

Pint’s group is currently using this approach to develop that can be formed in the excess materials or on the unused back sides of and sensors. The supercapacitors would store excess the electricity that the generate at midday and release it when the demand peaks in the afternoon.

“All the things that define us in a modern environment require electricity,” said Pint. “The more that we can integrate power storage into existing and devices, the more compact and efficient they will become.”

Cheaper solar material explained.

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In the near future, solar panels will not only be more efficient but also a lot cheaper and affordable for everyone, thanks to research by Nanyang Technological University (NTU) scientists.

This next generation solar cell, made from organic-inorganic hybrid perovskite materials, is about five times cheaper than current thin-film solar cells, due to a simpler solution-based manufacturing process.

Perovskite is known to be a remarkable solar cell material as it can convert up to 15 per cent of sunlight to electricity, close to the efficiency of the current solar cells, but scientists did not know why or how, until now.

In a paper published in the world’s most prestigious academic journal, Science, NTU’s interdisciplinary research team was the first in the world to explain this phenomenon.

The team of eight researchers led by Assistant Professor Sum Tze Chien and Dr Nripan Mathews had worked closely with NTU Visiting Professor Michael Grätzel, who currently holds the record for perovskite solar cell efficiency of 15 per cent, and is a co-author of the paper. Prof Grätzel, who is based at the Swiss Federal Institute of Technology in Lausanne (EPFL), has won multiple awards for his invention of dye-sensitised solar cells.

The high sunlight-to-electricity efficiency of perovskite solar cells places it in direct competition with thin film solar cells which are already in the market and have efficiencies close to 20 per cent.

The new knowledge on how these solar cells work is now being applied by the Energy Research Institute @ NTU (ERI@N), which is developing a commercial prototype of the perovskite solar cell in collaboration with Australian clean-tech firm Dyesol Limited (ASX: DYE).

Asst Prof Sum said the discovery of why perovskite worked so well as a solar cell material was made possible only through the use of cutting-edge equipment and in close collaboration with NTU engineers.

“In our work, we utilise ultrafast lasers to study the perovskite materials. We tracked how fast these materials react to light in quadrillionths of a second (roughly 100 billion times faster than a camera flash),” said the Singaporean photophysics expert from NTU’s School of Physical and Mathematical Sciences.

“We discovered that in these perovskite materials, the electrons generated in the material by sunlight can travel quite far. This will allow us to make thicker solar cells which absorb more light and in turn generate more electricity.”

The NTU physicist added that this unique characteristic of perovskite is quite remarkable since it is made from a simple solution method that normally produces low quality materials.

His collaborator, Dr Nripan Mathews, a senior scientist at ERI@N, said that their discovery is a great example of how investment in fundamental research and an interdisciplinary effort, can lead to advances in knowledge and breakthroughs in applied science.

“Now that we know exactly how perovskite materials behave and work, we will be able to tweak the performance of the new solar cells and improve its efficiency, hopefully reaching or even exceeding the performance of today’s thin-film solar cells,” said Dr Mathews, who is also the Singapore R&D Director of the Singapore-Berkeley Research Initiative for Sustainable Energy (SinBeRISE) NRF CREATE programme.

“The excellent properties of these materials, allow us to make light weight, flexible solar cells on plastic using cheap processes without sacrificing the good sunlight conversion efficiency.”

Professor Subodh Mhaisalkar, the Executive Director of ERI@N said they are now looking into building prototype solar cell modules based on this exciting class of materials.

“Perovskite-based solar cells have the potential to reach 20 per cent solar cell efficiencies and another great benefit of these materials is their amenability to yield different translucent colours, such as red, yellow or brown. Having such colourful solar glass will create new opportunities for architectural design,” he added.

The NTU team, consisting of six scientists, one postgraduate and one undergraduate, took six months to complete this fundamental research project, which was funded by NTU and the National Research Foundation, Prime Minister’s Office, Singapore.