MIT: New ‘Solar Skin’ Solar panels get a face-lift with custom Display Capabilities

Startup aims for wider U.S. solar adoption with photovoltaic panels that can display any image.

Founded at the MIT Sloan School of Management, Sistine Solar creates custom solar panels designed to mimic home facades and other environments, as well as display custom designs, with aims of enticing more homeowners to install photovoltaic systems. Courtesy of Sistine Solar

Residential solar power is on a sharp rise in the United States as photovoltaic systems become cheaper and more powerful for homeowners. A 2012 study by the U.S. Department of Energy (DOE) predicts that solar could reach 1 million to 3.8 million homes by 2020, a big leap from just 30,000 homes in 2006.

But that adoption rate could still use a boost, according to MIT spinout Sistine Solar. “If you look at the landscape today, less than 1 percent of U.S. households have gone solar, so it’s nowhere near mass adoption,” says co-founder Senthil Balasubramanian MBA ’13.

Founded at the MIT Sloan School of Management, Sistine creates custom solar panels designed to mimic home facades and other environments, with aims of enticing more homeowners to install photovoltaic systems.

Sistine’s novel technology, SolarSkin, is a layer that can be imprinted with any image and embedded into a solar panel without interfering with the panel’s efficacy. Homeowners can match their rooftop or a grassy lawn. Panels can also be fitted with business logos, advertisements, or even a country’s flag. SolarSkin systems cost about 10 percent more than traditional panel installations. But over the life of the system, a homeowner can still expect to save more than $30,000, according to the startup.

A winner of a 2013 MIT Clean Energy Prize, Sistine has recently garnered significant media attention as a rising “aesthetic solar” startup. Last summer, one of its pilot projects was featured on the Lifetime television series “Designing Spaces,” where the panels blended in with the shingle roof of a log cabin in Hubbardston, Massachusetts.

In December, the startup installed its first residential SolarSkin panels, in a 10-kilowatt system that matches a cedar pattern on a house in Norwell, Massachusetts. Now, the Cambridge-based startup says it has 200 homes seeking installations, primarily in Massachusetts and California, where solar is in high demand.

“We think SolarSkin is going to catch on like wildfire,” Balasubramanian says. “There is a tremendous desire by homeowners to cut utility bills, and solar is finding reception with them — and homeowners care a lot about aesthetics.”

 

 

 

 

Captivating people with solar – Who Said Solar Can’t Be Beautiful?

SolarSkin is the product of the co-founders’ unique vision, combined with MIT talent that helped make the product a reality.

Balasubramanian came to MIT Sloan in 2011, after several years in the solar-power industry, with hopes of starting his own solar-power startup — a passion shared by classmate and Sistine co-founder Ido Salama MBA ’13.

One day, the two were brainstorming at the Muddy Charles Pub, when a surprisingly overlooked issue popped up: Homeowners, they heard, don’t really like the look of solar panels. That began a nebulous business mission to “captivate people’s imaginations and connect people on an emotional level with solar,” Balasubramanian says.

Recruiting Jonathan Mailoa, then a PhD student in MIT’s Photovoltaic Research Laboratory, and Samantha Holmes, a mosaic artist trained in Italy who is still with the startup, the four designed solar panels that could be embedded on massive sculptures and other 3-D objects. They took the idea to 15.366 (Energy Ventures), where “it was drilled into our heads that you have to do a lot of market testing before you build a product,” Balasubramanian says.

That was a good thing, too, he adds, because they realized their product wasn’t scalable. “We didn’t want to make a few installations that people talk about. … We [wanted to] make solar so prevalent that within our lifetime we can see the entire world convert to 100 percent clean energy,” Balasubramanian says.

The team’s focus then shifted to manufacturing solar panels that could match building facades or street fixtures such as bus shelters and information kiosks. In 2013, the idea earned the team — then officially Sistine Solar — a modest DOE grant and a $20,000 prize from the MIT Clean Energy Prize competition, “which was a game-changer for us,” Balasubramanian says.

But, while trying to construct custom-designed panels, another idea struck: Why not just make a layer to embed into existing solar panels? Recruiting MIT mechanical engineering student Jody Fu, Sistine created the first SolarSkin prototype in 2015, leading to pilot projects for Microsoft, Starwood Hotels, and other companies in the region.

That summer, after earning another DOE grant for $1 million, Sistine recruited Anthony Occidentale, an MIT mechanical engineering student who has since helped further advance SolarSkin. “We benefited from the incredible talent at MIT,” Balasubramanian says. “Anthony is a shining example of someone who resonates with our vision and has all the tools to make this a reality.”

Imagination is the limit

SolarSkin is a layer that employs selective light filtration to display an image while still transmitting light to the underlying solar cells. The ad wraps displayed on bus windows offer a good analogy: The wraps reflect some light to display an image, while allowing the remaining light through so passengers inside the bus can see out. SolarSkin achieves a similar effect — “but the innovation lies in using a minute amount of light to reflect an image [and preserve] a high-efficiency solar module,” Balasubramanian says.

To achieve this, Occidentale and others at Sistine have developed undisclosed innovations in color science and human visual perception. “We’ve come up with a process where we color-correct the minimal information we have of the image on the panels to make that image appear, to the human eye, to be similar to the surrounding backdrop of roof shingles,” Occidentale says.

As for designs, Sistine has amassed a database of common rooftop patterns in the United States, such as asphalt shingles, clay tiles, and slate, in a wide variety of colors. “So if a homeowner says, for instance, ‘We have manufactured shingles in a barkwood pattern,’ we have a matching design for that,” he says. Custom designs aren’t as popular, but test projects include commercial prints for major companies, and even Occidentale’s face on a panel.

Currently, Sistine is testing SolarSkin for efficiency, durability, and longevity at the U.S. National Renewable Energy Laboratory under a DOE grant.

The field of aesthetic solar is still nascent, but it’s growing, with major companies such as Tesla designing entire solar-panel roofs. But, as far as Balasubramanian knows, Sistine is the only company that’s made a layer that can be integrated into any solar panel, and that can display any color as well as intricate patterns and actual images.

Companies could thus use SolarSkin solar panels to double as business signs. Municipalities could install light-powering solar panels on highways that blend in with the surrounding nature. Panels with changeable advertisements could be placed on bus shelters to charge cell phones, information kiosks, and other devices. “You can start putting solar in places you typically didn’t think of before,” Balasubramanian says. “Imagination is really the only limit with this technology.”

A BIG Boost for Nano Enabled Solar Cells

Using nanotech to boost solar output: A Kyoto University and Osaka Gas silicon device could double the energy conversion rate of solar cells. Each vertical rod measures about 500 nm in height. Credit: Kyoto University/Noda Lab

Solar cells convert light into electricity. While the sun is one source of light, the burning of natural resources like oil and natural gas can also be harnessed.

However, solar cells do not convert all light to power equally, which has inspired a joint industry-academia effort to develop a potentially game-changing solution.

“Current solar cells are not good at converting visible light to electrical power. The best efficiency is only around 20%,” explains Kyoto University’s Takashi Asano, who uses optical technologies to improve energy production.

Higher temperatures emit light at shorter wavelengths, which is why the flame of a gas burner will shift from red to blue as the heat increases. The higher heat offers more energy, making short wavelengths an important target in the design of solar cells.

“The problem,” continues Asano, “is that heat dissipates light of all wavelengths, but a solar cell will only work in a narrow range.

“To solve this, we built a new nano-sized semiconductor that narrows the wavelength bandwidth to concentrate the energy.”

Previously, Asano and colleagues of the Susumu Noda lab had taken a different approach. “Our first device worked at high wavelengths, but to narrow output for visible light required a new strategy, which is why we shifted to intrinsic silicon in this current collaboration with Osaka Gas,” says Asano.

To emit visible wavelengths, a temperature of 1000˚C was needed, but conveniently silicon has a melting temperature of over 1400˚C. The scientists etched silicon plates to have a large number of identical and equidistantly-spaced rods, the height, radii, and spacing of which was optimized for the target bandwidth.

According to Asano, “the cylinders determined the emissivity,” describing the wavelengths emitted by the heated device.

Using this material, the team has shown in Science Advances that their nanoscale semiconductor raises the energy conversion rate of solar cells to at least 40%.

“Our technology has two important benefits,” adds lab head Noda. “First is energy efficiency: we can convert heat into electricity much more efficiently than before. Secondly is design. We can now create much smaller and more robust transducers, which will be beneficial in a wide range of applications.”

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Story Source:

Materials provided by Kyoto University. Note: Content may be edited for style and length.

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Journal Reference:

1. Takashi Asano, Masahiro Suemitsu, Kohei Hashimoto, Menaka De Zoysa, Tatsuya Shibahara, Tatsunori Tsutsumi, Susumu Noda. Near-infrared–to–visible highly selective thermal emitters based on an intrinsic semiconductor. Science Advances, 2016; 2 (12): e1600499 DOI: 10.1126/sciadv.1600499

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Toronto’s QD (Quantum Dot) Solar sole Canadian among five winners of solar technology challenge

Five North American solar start-up companies have been selected to receive further support in developing their technology and moving them closer to market under the SunRISE TechBridge Challenge, which had 56 team entries.

Of the five winners, one is Canadian colloidal quantum dot cell developerQD Solar, which will gain support from Greentown Launch acceleration and DSM Partnership/Investment, as well as desk and lab space at Greentown Labs in Somerville, MA, and networking and coaching to accelerate their business and networking in the cleantech community in the Greater Boston area.

QD Solar uses low-cost, nano-engineered particles to produce solar cells that can capture wasted infrared light, resulting in a 20% increase in efficiency over conventional solar panels, based on research conducted at the Nanomaterials for Energy Laboratory in the University of Toronto’s Department of Electrical and Computer Engineering.

The SunRISE TechBridge Challenge challenged companies to present innovative solutions and new materials that will lower the levelized cost of energy (LCOE) for photovoltaic (PV) systems, including novel materials for existing and emerging high performance PV modules, technologies enabling non-traditional solar deployment, and business models that integrate solar PV with energy storage.

QD Solar started life at the University of Toronto and MaRS Innovation, and in March received $2.55 million from Sustainable Development Technology Canada (SDTC).

Conventional solar panels waste a large portion of available sun energy because their silicon solar cells can’t capture infrared light energy, a problem that QD Solar set out to solve with their proprietary quantum dot-based solar cells using nano-engineered, low-cost materials that can absorb infrared light.

QD Solar CEO Dan Shea is a former executive with Celestica and Blackberry.

In 2009, co-founder Edward Sargent and his team at the University of Toronto received a grant from King Abdullah University of Science and Technology (KAUST) in Saudi Arabia to advance their research into colloidal quantum dots for solar power applications.

The SunRISE TechBridge Challenge was organized by Fraunhofer TechBridge and the SunRISE Partners, which include Royal DSM and Greentown Labs.

The Fraunhofer TechBridge Challenge is an offering of the Fraunhofer Center for Sustainable Energy Systems (CSE), which organizes several industry-sponsored annual challenges to accelerate promising technologies through targeted industry-driven validation projects, including the SunRISE Challenge, Advanced Industrial Surfaces, the Microgrid Challenge, and the Innovation Ecosystem Program.

Fraunhofer Gesellschaft is a German applied R&D organization which has 66 institutes and independent research units throughout Germany and 80 institutes and centers around the world.

Nicola Bettio, a member of QD Solar’s Board of Directors, manages the KAUST Innovation Fund and anticipates the establishment of the company’s presence in a significant development facility in KAUST’s Research & Technology Park in the near future.

New ‘Hybrid’ Nano-Glass now has smart potential

A graphic representation of nanoparticles embedded in glass. Credit: University of Adelaide

Australian researchers at the University of Adelaide have developed a method for embedding light-emitting nanoparticles into glass without losing any of their unique properties – a major step towards ‘smart glass’ applications such as 3D display screens or remote radiation sensors.

This new “hybrid glass” successfully combines the properties of these special luminescent (or light-emitting) nanoparticles with the well-known aspects of glass, such as transparency and the ability to be processed into various shapes including very fine optical fibres.

The research, in collaboration with Macquarie University and University of Melbourne, has been published online in the journal Advanced Optical Materials.

“These novel luminescent nanoparticles, called upconversion nanoparticles, have become promising candidates for a whole variety of ultra-high tech applications such as biological sensing, biomedical imaging and 3D volumetric displays,” says lead author Dr Tim Zhao, from the University of Adelaide’s School of Physical Sciences and Institute for Photonics and Advanced Sensing (IPAS).

“Integrating these nanoparticles into glass, which is usually inert, opens up exciting possibilities for new hybrid materials and devices that can take advantage of the properties of nanoparticles in ways we haven’t been able to do before. For example, neuroscientists currently use dye injected into the brain and lasers to be able to guide a glass pipette to the site they are interested in. If fluorescent nanoparticles were embedded in the glass pipettes, the unique luminescence of the hybrid glass could act like a torch to guide the pipette directly to the individual neurons of interest.”

Although this method was developed with upconversion nanoparticles, the researchers believe their new ‘direct-doping’ approach can be generalised to other nanoparticles with interesting photonic, electronic and magnetic properties. There will be many applications – depending on the properties of the nanoparticle.

“If we infuse glass with a nanoparticle that is sensitive to radiation and then draw that hybrid glass into a fibre, we could have a remote sensor suitable for nuclear facilities,” says Dr Zhao.

To date, the method used to integrate upconversion nanoparticles into glass has relied on the in-situ growth of the nanoparticles within the glass.

“We’ve seen remarkable progress in this area but the control over the nanoparticles and the glass compositions has been limited, restricting the development of many proposed applications,” says project leader Professor Heike Ebendorff-Heideprem, Deputy Director of IPAS.

“With our new direct doping method, which involves synthesizing the nanoparticles and glass separately and then combining them using the right conditions, we’ve been able to keep the nanoparticles intact and well dispersed throughout the glass. The nanoparticles remain functional and the glass transparency is still very close to its original quality. We are heading towards a whole new world of hybrid glass and devices for light-based technologies.”

Explore further: Ancient Roman glass inspires modern science

More information: Jiangbo Zhao et al. Upconversion Nanocrystal-Doped Glass: A New Paradigm for Photonic Materials, Advanced Optical Materials (2016). DOI: 10.1002/adom.201600296

Journal reference: Advanced Optical Materials

Provided by: University of Adelaide

 

Update: MIT; UC San Diego; Harvard Universities: Energy-carrying particles called ‘topological plexcitons’ could make possible the design of ‘next generation’ solar cells and miniaturized optical circuitry

Plexcitons travel for 20,000 nanometers, a length which is on the order of the width of human hair. Credit: Joel Yuen-Zhou

Scientists at UC San Diego, MIT and Harvard University have engineered “topological plexcitons,” energy-carrying particles that could help make possible the design of new kinds of solar cells and miniaturized optical circuitry.

The researchers report their advance in an article published in the current issue of Nature Communications.

Within the Lilliputian world of solid state physics, light and matter interact in strange ways, exchanging energy back and forth between them.

“When light and matter interact, they exchange energy,” explained Joel Yuen-Zhou, an assistant professor of chemistry and biochemistry at UC San Diego and the first author of the paper. “Energy can flow back and forth between light in a metal (so called plasmon) and light in a molecule (so called exciton). When this exchange is much faster than their respective decay rates, their individual identities are lost, and it is more accurate to think about them as hybrid particles; excitons and plasmons marry to form plexcitons.” 

Materials scientists have been looking for ways to enhance a process known as exciton energy transfer, or EET, to create better solar cells as well as miniaturized photonic circuits which are dozens of times smaller than their silicon counterparts.

“Understanding the fundamental mechanisms of EET enhancement would alter the way we think about designing solar cells or the ways in which energy can be transported in nanoscale materials,” said Yuen-Zhou.

The drawback with EET, however, is that this form of energy transfer is extremely short-ranged, on the scale of only 10 nanometers, and quickly dissipates as the excitons interact with different molecules.

One solution to avoid those shortcomings is to hybridize excitons in a molecular crystal with the collective excitations within metals to produce plexcitons, which travel for 20,000 nanometers, a length which is on the order of the width of human hair.

Plexcitons are expected to become an integral part of the next generation of nanophotonic circuitry, light-harvesting solar energy architectures and chemical catalysis devices. But the main problem with plexcitons, said Yuen-Zhou, is that their movement along all directions, which makes it hard to properly harness in a material or device.

He and a team of physicists and engineers at MIT and Harvard found a solution to that problem by engineering particles called “topological plexcitons,” based on the concepts in which solid state physicists have been able to develop materials called “topological insulators.”

“Topological insulators are materials that are perfect electrical insulators in the bulk but at their edges behave as perfect one-dimensional metallic cables,” Yuen-Zhou said. “The exciting feature of topological insulators is that even when the material is imperfect and has impurities, there is a large threshold of operation where electrons that start travelling along one direction cannot bounce back, making electron transport robust. In other words, one may think about the electrons being blind to impurities.”

Plexcitons, as opposed to electrons, do not have an electrical charge. Yet, as Yuen-Zhou and his colleagues discovered, they still inherit these robust directional properties. Adding this “topological” feature to plexcitons gives rise to directionality of EET, a feature researchers had not previously conceived. This should eventually enable engineers to create plexcitonic switches to distribute energy selectively across different components of a new kind of solar cell or light-harvesting device.

Explore further: Topological insulators could exist in six new types not seen before, theorists predict

More information: Nature Communications, DOI: 10.1038/NCOMMS11783

Journal reference:Nature Communications

Provided by:University of California – San Diego

 

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Quantum Dots: Enhancing Light-to-Current Conversion: Better Semiconductors, Solar Cells and Photdetectors

Single nanocrystal spectroscopy identifies the interaction between zero-dimensional CdSe/ZnS nano crystals (quantum dots) and two-dimensional layered tin disulfide as a non-radiative energy transfer, whose strength increases with increasing …more

Harnessing the power of the sun and creating light-harvesting or light-sensing devices requires a material that both absorbs light efficiently and converts the energy to highly mobile electrical current. Finding the ideal mix of properties in a single material is a challenge, so scientists have been experimenting with ways to combine different materials to create “hybrids” with enhanced features.

In two just-published papers, scientists from the U.S. Department of Energy’s Brookhaven National Laboratory, Stony Brook University, and the University of Nebraska describe one such approach that combines the excellent light-harvesting properties of quantum dots with the tunable electrical conductivity of a layered tin disulfide semiconductor.

The hybrid material exhibited enhanced light-harvesting properties through the absorption of light by the quantum dots and their energy transfer to tin disulfide, both in laboratory tests and when incorporated into electronic devices. The research paves the way for using these materials in optoelectronic applications such as energy-harvesting photovoltaics, light sensors, and light emitting diodes (LEDs).

According to Mircea Cotlet, the physical chemist who led this work at Brookhaven Lab’s Center for Functional Nanomaterials (CFN), a DOE Office of Science User Facility, “Two-dimensional metal dichalcogenides like tin disulfide have some promising properties for solar energy conversion and photodetector applications, including a high surface-to-volume aspect ratio. But no semiconducting material has it all. These materials are very thin and they are poor light absorbers. So we were trying to mix them with other nanomaterials like light-absorbing quantum dots to improve their performance through energy transfer.”

One paper, just published in the journal ACS Nano, describes a fundamental study of the hybrid quantum dot/tin disulfide material by itself. The work analyzes how light excites the quantum dots (made of a cadmium selenide core surrounded by a zinc sulfide shell), which then transfer the absorbed energy to layers of nearby tin disulfide.

“We have come up with an interesting approach to discriminate energy transfer from charge transfer, two common types of interactions promoted by light in such hybrids,” said Prahlad Routh, a graduate student from Stony Brook University working with Cotlet and co-first author of the ACS Nano paper. “We do this using single nanocrystal spectroscopy to look at how individual quantum dots blink when interacting with sheet-like tin disulfide. This straightforward method can assess whether components in such semiconducting hybrids interact either by energy or by charge transfer.”

The researchers found that the rate for non-radiative energy transfer from individual quantum dots to tin disulfide increases with an increasing number of tin disulfide layers. But performance in laboratory tests isn’t enough to prove the merits of potential new materials. So the scientists incorporated the hybrid material into an electronic device, a photo-field-effect-transistor, a type of photon detector commonly used for light sensing applications.

As described in a paper published online March 24 in Applied Physics Letters, the hybrid material dramatically enhanced the performance of the photo-field-effect transistors-resulting in a photocurrent response (conversion of light to electric current) that was 500 percent better than transistors made with the tin disulfide material alone.

“This kind of energy transfer is a key process that enables photosynthesis in nature,” said Chang-Yong Nam, a materials scientist at Center for Functional Nanomaterials and co-corresponding author of the APL paper. “Researchers have been trying to emulate this principle in light-harvesting electrical devices, but it has been difficult particularly for new material systems such as the tin disulfide we studied. Our device demonstrates the performance benefits realized by using both energy transfer processes and new low-dimensional materials.”

Cotlet concludes, “The idea of ‘doping’ two-dimensional layered materials with quantum dots to enhance their light absorbing properties shows promise for designing better solar cells and photodetectors.”

Explore further: Small size enhances charge transfer in quantum dots

More information: Yuan Huang et al. Hybrid quantum dot-tin disulfide field-effect transistors with improved photocurrent and spectral responsivity, Applied Physics Letters (2016). DOI: 10.1063/1.4944781

Huidong Zang et al. Nonradiative Energy Transfer from Individual CdSe/ZnS Quantum Dots to Single-Layer and Few-Layer Tin Disulfide, ACS Nano (2016). DOI: 10.1021/acsnano.6b01538

Journal reference: ACS Nano Applied Physics Letters

Making Solar Cells more Efficient: Nanocrystals Expand the Range of Solar Cell Light Energy to Ultraviolet and Infrared Regions

Common solar cells made of crystalline silicon can only access roughly half of the total sunlight spectrum for conversion of light energy into electricity. Searching for more effective materials, Chinese scientists have now combined three semiconducting sulfide crystals to a ternary nanostructured photovoltaic system that absorbs irradiation from ultraviolet to near infrared regions.

 

As they report in the journal Angewandte Chemie, the nanorods effectively convert the full-spectrum light energy into electric current. This discovery marks a new level in the development of more efficient solar cells.

 

 
The photovoltaic material that is most commonly used today is crystalline silicon, but it absorbs sunlight effectively only in the visible region. Other semiconducting materials cover slightly different regions of the solar spectrum, but the most efficient photovoltaic materials would be clearly those that include every region from the ultraviolet to the infrared. Shu-Hong Yu and Jun Jiang and their collaborators at the University of Science and Technology of China in Hefei have now introduced a nanostructured system made of three sulfide crystals.

The ternary hybrid material of zinc, cadmium, and copper sulfides effectively absorbs the ultraviolet, visible, and near infrared light, and the segmented node-sheath structure of the tiny rods provides the ideal energy band alignment for an effective accumulation of charge carriers.

The basis of this photocollecting system is nanosized rods of zinc sulfide on which crystalline sheaths of cadmium sulfide are deposited like an arrangement of pearls. The zinc sulfide basis provides the UV absorption, while the cadmium sulfide covers the visible light region. As a third component for IR absorption, the scientists chose copper sulfide nanocrystals with copper deficiencies, as this material is known to feature a special type of absorption in the near-infrared region called surface plasmon resonance. “These heteronanorods absorb across nearly the full spectrum of solar energy,” the scientists report.

To test the functionality of the nanorods, the scientists measured their performance in a photoelectrochemical water-splitting cell. Upon full-spectrum illumination, the photocurrent response was pronounced, which was a first experimental evidence for the successful design of their photovoltaic material.

 

One of the crucial achievements of this work, however, was the correct adjusting of the sensitive heterojunctions that connect the different semiconducting structures to align the energy gaps of the semiconducting materials. “Such a staggered alignment enables the separation of the photogenerated electrons and holes in the ternary hybrid nanostructure,” say the authors. Although further experiments have to be performed, this ternary semiconducting system can be regarded as an important step toward a new generation of efficient solar cells covering the rainbow colors and beyond.

Explore further: Reshaping the solar spectrum to turn light to electricity

More information: Tao-Tao Zhuang et al. Integration of Semiconducting Sulfides for Full-Spectrum Solar Energy Absorption and Efficient Charge Separation, Angewandte Chemie International Edition (2016). DOI: 10.1002/anie.201601865

Journal reference: Angewandte Chemie Angewandte Chemie International Edition

 

Case Western University: Using Solar Cells (Energy) to Charge a lithium-ion Batteries for Electric Vehicles

Consumers aren’t embracing electric cars and trucks, partly due to the dearth of charging stations required to keep them moving. Even the conservation-minded are hesitant to go electric in some states because, studies show, if fossil fuels generate the electricity, the car is no greener than one powered with an efficient gasoline.

Charging cars by solar cell would appear to be the answer. But most cells fail to meet the power requirements needed to directly charge lithium-ion batteries used in today’s all-electric and plug-in hybrid electric vehicles.

Researchers at Case Western Reserve University, however, have wired four perovskite solar cells in series to enhance the voltage and directly photo-charged lithium batteries with 7.8 percent efficiency–the most efficient reported to date, the researchers believe.

The research, published in the Aug. 27 issue of Nature Communications, holds promise for cleaner transportation, home power sources and more.

“We found the right match between the solar cell and battery,” said Liming Dai, the Kent Hale Smith Professor of macromolecular science and engineering and leader of the research. “Others have used polymer solar cells to charge lithium batteries, but not with this efficiency.”

In fact, the researchers say their overall photoelectric conversion and storage outperformed all other reported couplings of a photo-charging component with lithium-ion batteries, flow batteries or super-capacitors.

Perovskite solar cells have active materials with a crystalline structure identical to the mineral perovskite and are considered a promising new design for capturing solar energy. Compared to silicon-based cells, they convert a broader spectrum of sunlight into electricity.

In short order, they have matched the energy conversion of silicon cells, and researchers around the world are pursuing further advances.

Dai’s lab made multilayer solar cells, which increases their energy density, performance and stability. Testing showed that, as desired, the three layers convert into a single perovskite film.

By wiring four lab-sized cells, about 0.1 centimeter square each, in series, the researchers further increased the open circuit voltage. The solar-to-electric power conversion efficiency was 12.65 percent.

To charge button-sized lithium-ion batteries, they used a lithium-ion-phosphate cathode and a lithium-titanium-oxide anode. The photoelectric conversion and storage efficiency was 7.8 percent. Through 10 photo-charge/galvanostatic (steady current) discharge cycles lasting nearly 18 hours, the technology maintained almost identical discharge/charge curves over all cycles, showing high cycling stability and compatibility of the components.

“We envision, in the not too distant future, this is a system that you could have at home to refuel your car and, eventually, because perovskite solar cells can be made as a flexible film, they would be on the car itself,” said Jiantie Xu, who, with Yonghua Chen, is an equally contributing first author of the study. Both are macromolecular science and engineering research associates in Case School of Engineering.

The researchers are developing small-scale prototypes and working to further improve the perovskite cell’s stability and optimize the system.

 

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Story Source:

The above post is reprinted from materials provided by Case Western Reserve University. Note: Materials may be edited for content and length.

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Journal Reference:

1. Jiantie Xu, Yonghua Chen, Liming Dai. Efficiently photo-charging lithium-ion battery by perovskite solar cell. Nature Communications, 2015; 6: 8103 DOI: 10.1038/ncomms9103

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St. Mary’s College Maryland: New research puts us closer to DIY Spray-on Solar Cell Technology

A new study out of St. Mary’s College of Maryland puts us closer to do-it-yourself spray-on solar cell technology — promising third-generation solar cells utilizing a nanocrystal ink deposition that could make traditional expensive silicon-based solar panels a thing of the past.

In a 2014 study, published in the journal Physical Chemistry Chemical Physics, St. Mary’s College of Maryland energy expert Professor Troy Townsend introduced the first fully solution-processed all-inorganic photovoltaic technology.

While progress on organic thin-film photovoltaics is rapidly growing, inorganic devices still hold the record for highest efficiencies which is in part due to their broad spectral absorption and excellent electronic properties. Considering the recorded higher efficiencies and lower cost per watt compared to organic devices, combined with the enhanced thermal and photo stability of bulk-scale inorganic materials, Townsend, in his 2014 study, focused on an all-inorganic based structure for fabrication of a top to bottom fully solution-based solar cell.

A major disadvantage compared to organics, however, is that inorganic materials are difficult to deposit from solution. To overcome this, Townsend synthesized materials on the nanoscale. Inorganic nanocrystals encased in an organic ligand shell are soluble in organic solvents and can be deposited from solution (i.e., spin-, dip-, spray-coat) whereas traditional inorganic materials require a high temperature vacuum chamber. The solar devices are fabricated from nanoscale particle inks of the light absorbing layers, cadmium telluride/cadmium selenide, and metallic inks above and below. This way, the entire electronic device can be built on non-conductive glass substrates using equipment you can find in your kitchen.

The outstanding challenge facing the (3-5 nm) inorganic nanocrystals is that they must be annealed or heated to form larger ‘bulk scale’ grains (100 nm to 1 μm) in order to produce working devices. Townsend recently teamed with Navy researchers to explore this process.

A spray-on nanocrystal solar cell array.

Credit: Image courtesy of St. Mary’s College of Maryland

“When you spray on these nanocrystals, you have to heat them to make them work,” explained Townsend, “but you can’t just heat the crystals by themselves, you have to add a sintering agent and that, for the last 40 years, has been cadmium chloride, a toxic salt used in commercial thin-film devices. No one has tested non-toxic alternatives for nanoscale ink devices, and we wanted to explore the mechanism of the sintering process to be able to implement safer salts.”

In his latest study, published this year in the Journal of Materials Chemistry A, Townsend, along with Navy researchers, found that ammonium chloride is a non-toxic, inexpensive viable alternative to cadmium chloride for nanocrystal solar cells. This discovery came after testing several different salts. Devices made using ammonium chloride (which is commonly used in bread making) had comparable device characteristics to those made with cadmium chloride, and the move away from cadmium salt treatments alleviates concerns about the environmental health and safety of current processing methods.

The team also discovered that the role of the salt treatment involves crucial ligand removal reactions. This is unique to inorganic nanocrystals and is not observed for bulk-scale vacuum deposition methods. “A lot of exciting work has been done on nanocrystal ligand exchange, but, for the first time, we elucidated the dual role of the salt as a ligand exchange agent and a simultaneous sintering agent. This is an important distinction for these devices, because nanocrystals are typically synthesized with a native organic ligand shell. This shell needs to be removed before heating in order to improve the electronic properties of the film,” said Townsend about the discovery. Because nanomaterials are at the forefront of emerging new properties compared to their bulk counterpart, the study is important to the future of electronic device fabrication.

The research comes in the wake of the Obama Administration’s announcement in July to put more solar panels on low-income housing and expand access to solar power for renters, and recent pledge to get 20 percent of the U.S. total electricity from renewable sources by the year 2030.

“Right now, solar technology is somewhat unattainable for the average person,” said Townsend. “The dream is to make the assembly and installation process so cheap and simple that you can go to your local home improvement store and buy a kit and then spray it on your own roof. That is why we we’re working on spray-on solar cells.” Townsend plans for further research to increase the efficiency of the all-inorganic nanocrystal solar cells (currently reaching five percent), while building them with completely non-toxic components.

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Story Source:

The above post is reprinted from materials provided by St. Mary’s College of Maryland. Note: Materials may be edited for content and length.

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Journal References:

1. Troy K. Townsend, William B. Heuer, Edward E. Foos, Eric Kowalski, Woojun Yoon, Joseph G. Tischler. Safer salts for CdTe nanocrystal solution processed solar cells: the dual roles of ligand exchange and grain growth. J. Mater. Chem. A, 2015; 3 (24): 13057 DOI: 10.1039/C5TA02488A
2. Troy K. Townsend, Edward E. Foos. Fully solution processed all inorganic nanocrystal solar cells. Physical Chemistry Chemical Physics, 2014; 16 (31): 16458 DOI: 10.1039/C4CP02403F

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