Energy-collecting Windows Dream One-Step Closer


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Silicon-based luminescent solar concentrator. While most of the light concentrated to the edge of the silicon-based luminescent solar concentrator is actually invisible, we can better see the concentration effect by the naked eye when the slab is illuminated by a “black light” which is composed of mostly ultraviolet wavelengths. (image: Uwe Kortshagen, University of Minnesota)

February 20, 2017

Researchers at the University of Minnesota and University of Milano-Bicocca are bringing the dream of windows that can efficiently collect solar energy one step closer to reality thanks to high tech silicon nanoparticles.

The researchers developed technology to embed the silicon nanoparticles into what they call efficient luminescent solar concentrators (LSCs). These LSCs are the key element of windows that can efficiently collect solar energy. When light shines through the surface, the useful frequencies of light are trapped inside and concentrated to the edges where small solar cells can be put in place to capture the energy.

The research is published today in Nature Photonics (“Highly efficient luminescent solar concentrators based on Earth-abundant indirect-bandgap silicon quantum dots”).

Windows that can collect solar energy, called photovoltaic windows, are the next frontier in renewable energy technologies, as they have the potential to largely increase the surface of buildings suitable for energy generation without impacting their aesthetics—a crucial aspect, especially in metropolitan areas. LSC-based photovoltaic windows do not require any bulky structure to be applied onto their surface and since the photovoltaic cells are hidden in the window frame, they blend invisibly into the built environment.

The idea of solar concentrators and solar cells integrated into building design has been around for decades, but this study included one key difference—silicon nanoparticles. Until recently, the best results had been achieved using relatively complex nanostructures based either on potentially toxic elements, such as cadmium or lead, or on rare substances like indium, which is already massively utilized for other technologies. Silicon is abundant in the environment and non-toxic. It also works more efficiently by absorbing light at different wavelengths than it emits. However, silicon in its conventional bulk form, does not emit light or luminesce.

“In our lab, we ‘trick’ nature by shrinking the dimension of silicon crystals to a few nanometers, that is about one ten-thousandths of the diameter of human hair,” said University of Minnesota mechanical engineering professor Uwe Kortshagen, inventor of the process for creating silicon nanoparticles and one of the senior authors of the study. “At this size, silicon’s properties change and it becomes an efficient light emitter, with the important property not to re-absorb its own luminescence. This is the key feature that makes silicon nanoparticles ideally suited for LSC applications.”

Using the silicon nanoparticles opened up many new possibilities for the research team.

“Over the last few years, the LSC technology has experienced rapid acceleration, thanks also to pioneering studies conducted in Italy, but finding suitable materials for harvesting and concentrating solar light was still an open challenge,” said Sergio Brovelli, physics professor at the University of Milano-Bicocca, co-author of the study, and co-founder of the spin-off company Glass to Power that is industrializing LSCs for photovoltaic windows “Now, it is possible to replace these elements with silicon nanoparticles.”

Researchers say the optical features of silicon nanoparticles and their nearly perfect compatibility with the industrial process for producing the polymer LSCs create a clear path to creating efficient photovoltaic windows that can capture more than 5 percent of the sun’s energy at unprecedented low costs.

“This will make LSC-based photovoltaic windows a real technology for the building-integrated photovoltaic market without the potential limitations of other classes of nanoparticles based on relatively rare materials,” said Francesco Meinardi, physics professor at the University of Milano-Bicocca and one of the first authors of the paper.

The silicon nanoparticles are produced in a high-tech process using a plasma reactor and formed into a powder.

“Each particle is made up of less than two thousand silicon atoms,” said Samantha Ehrenberg, a University of Minnesota mechanical Ph.D. student and another first author of the study. “The powder is turned into an ink-like solution and then embedded into a polymer, either forming a sheet of flexible plastic material or coating a surface with a thin film.”

The University of Minnesota invented the process for creating silicon nanoparticles about a dozen years ago and holds a number of patents on this technology. In 2015, Kortshagen met Brovelli, who is an expert in LSC fabrication and had already demonstrated various successful approaches to efficient LSCs based on other nanoparticle systems. The potential of silicon nanoparticles for this technology was immediately clear and the partnership was born. The University of Minnesota produced the particles and researchers in Italy fabricated the LSCs by embedding them in polymers through an industrial based method, and it worked.

“This was truly a partnership where we gathered the best researchers in their fields to make an old idea truly successful,” Kortshagen said. “We had the expertise in making the silicon nanoparticles and our partners in Milano had expertise in fabricating the luminescent concentrators. When it all came together, we knew we had something special.”

Source: University of Minnesota

 

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Scientists purify copper nanowires – Woot – Woot! Why this Discovery will Matter to YOU – Apple and Others


An illustration of the separation process from a mixture of various copper nanocrystal shapes (two tubes to the left) to pure nanowires and nanoparticles (two tubes to the right). Credit: Lawrence Livermore National Laboratory



Cell phones and Apple watches could last a little longer due to a new method to create copper nanowires.

A team of Lawrence Livermore National Laboratory (LLNL) scientists have created a new method to purify copper nanowires with a near-100 percent yield. These nanowires are often used in nanoelectronic applications.




The research, which appears in the online edition of Chemical Communications and on the cover of the hardcopy issue, shows how the method can yield large quantities of long, uniform, high-purity copper nanowires. 
High-purity copper nanowires meet the requirements of nanoelectronic applications as well as provide an avenue for purifying industrial-scale synthesis of copper nanowires, a key step for commercialization and application.

Metal nanowires (NWs) hold promise for commercial applications such as flexible displays, solar cells, catalysts and heat dissipators.

The most common approach to create nanowires not only yield nanowires but also other low-aspect ratio shapes such as nanoparticles (NPs) and nanorods. These undesired byproducts are almost always produced due to difficulties in controlling the non-instantaneous nucleation of the seed particles as well as seed types, which causes the particles to grow in multiple pathways.

“We created the purest form of copper nanowires with no byproducts that would affect the shape and purity of the nanowires,” said LLNL’s Fang Qian, lead author of the paper.
The team demonstrated that copper nanowires, synthesized at a liter-scale, can be purified to near 100 percent yield from their nanoparticle side-products with a few simple steps.

Functional nanomaterials are notoriously difficult to produce in large volumes with highly controlled composition, shapes and sizes. This difficulty has limited adoption of nanomaterials in many manufacturing technologies.




“This work is important because it enables production of large quantities of copper nanomaterials with a very facile and elegant approach to rapidly separate nanowires from nanoparticles with extremely high efficiency,” said Eric Duoss, a principal investigator on the project. “We envision employing these purified nanomaterials for a wide variety of novel fabrication approaches, including additive manufacturing.”

The key to success is the use of a hydrophobic surfactant in aqueous solution, together with an immiscible water organic solvent system to create a hydrophobic-distinct interface, allowing nanowires to crossover spontaneously due to their different crystal structure and total surface area from those of nanoparticles.

“The principles developed from this particular case of copper nanowires may be applied to a variety of nanowire applications,” Qian said. “This purification method will open up new possibilities in producing high quality nanomaterials with low cost and in large quantities.”
Other Livermore researchers include: Pui Ching Lan, Tammy Olson, Cheng Zhu and Christopher Spadaccini.

“We also are developing high surface area foams as well as printable inks for additive manufacturing processes, such as direct-ink writing using the NWs,” said LLNL’s Yong Han, a corresponding author of the paper.

 Explore further: A novel method of making high-quality vertical nanowires

More information: Fang Qian et al. Multiphase separation of copper nanowires, Chem. Commun. (2016). DOI: 10.1039/C6CC06228H 

Journal reference: Chemical Communications  

Provided by: Lawrence Livermore National Laboratory

Nano-Crystal (Quantum Dots) Boosted System Shows Doubled Light-Harvesting Ability


1-ACS Solar Band Gap nl-2014-03322a_0005Publication Date (Web): October 16, 2014

Conventional solar cells exhibit limited efficiencies in part due to their inability to absorb the entire solar spectrum. Sub-band-gap photons are typically lost but could be captured if a material that performs up-conversion, which shifts photon energies higher, is coupled to the device.

Recently, molecular chromophores that undergo triplet–triplet annihilation (TTA) have shown promise for efficient up-conversion at low irradiance, suitable for some types of solar cells. However, the molecular systems that have shown the highest up-conversion efficiency to date are ill suited to broadband light harvesting, reducing their applicability.

1-ACS Solar Band Gap nl-2014-03322a_0005

Here we overcome this limitation by combining an organic TTA system with highly fluorescent CdSe semiconductor nanocrystals. Because of their broadband absorption and spectrally narrow, size-tunable fluorescence, the nanocrystals absorb the radiation lost by the TTA chromophores, returning this energy to the up-converter. The resulting nanocrystal-boosted system shows a doubled light-harvesting ability, which allows a green-to-blue conversion efficiency of ∼12.5% under 0.5 suns of incoherent excitation. This record efficiency at subsolar irradiance demonstrates that boosting the TTA by light-emitting nanocrystals can potentially provide a general route for up-conversion for different photovoltaic and photocatalytic applications.

Dipartimento di Scienza dei Materiali, Università degli Studi di Milano Bicocca, 20125 Milano, Italy
Optical Materials Engineering Laboratory, ETH Zurich, 8092 Zurich, Switzerland
Nano Lett., Article ASAP
DOI: 10.1021/nl503322a
Publication Date (Web): October 16, 2014
Copyright © 2014 American Chemical Society

Stanford’s GCEP awards $10.5 million for Research on Renewable Energy


 

Nano fuel cells c2cs35307e-f1The Global Climate and Energy Project (GCEP) at Stanford University has awarded $10.5 million for seven research projects designed to advance a broad range of renewable energy technologies. The funding will be shared by six Stanford research teams and an international group from the United States and Europe.

“The seven projects funded by GCEP could spark discoveries that lead to dramatic improvements in energy storage, solar cells and renewable biofuels,” said GCEP Director Sally Benson, a professor of energy resources engineering at Stanford. “I’m delighted to add that many of the scientists who received funding for these innovative projects will be featured speakers at our 2014 GCEP Research Symposium in October.”

The seven awards bring the total number of GCEP-supported research programs to 117 since the project’s launch in 2002. In total, GCEP has awarded approximately $161 million to researchers at Stanford and 40 other institutions worldwide.

“These awards demonstrate GCEP’s continued commitment to advancing cutting- edge research in energy,” said GCEP management committee member Steven Freilich, director of materials science at DuPont Central Research & Development. “As a science company, DuPont believes that collaboration enhances our power to innovate. Programs like GCEP help build the great working relationships between scientists and engineers at universities, companies and government institutions that are required to develop innovative solutions for people everywhere.”

The following Stanford faculty members received funding for advanced research on photovoltaics, battery technologies and new catalysts for sustainable fuels:

Self-healing polymers for high energy density lithium-ion batteries. The goal is to develop high-energy, durable lithium-ion batteries for electric vehicles by improving the cycle life of the battery electrodes. Researchers will design self-healing polymers that can stretch to accommodate large volume changes in the battery during charge and discharge. Investigators: Zhenan Bao, Chemical Engineering; Yi Cui, Materials Science and Engineering.Battery Secret untitled

Photo-electrochemically rechargeable zinc-air batteries. The zinc-air battery is a promising technology that has high energy density but limited power density. The research team will develop a photo-electrochemical battery with a stable zinc electrode capable of generating electricity using sunlight and air. Investigator: Hongjie Dai, Chemistry.

Novel inorganic-organic perovskites for photovoltaics. The mineral perovskite is a promising, low-cost material for enhancing the efficiency of silicon solar cells. The goal of this project is to develop a hybrid perovskite-silicon solar cell that significantly improves the light-to-energy conversion efficiency of conventional cells. Investigators: Michael McGehee, Materials Science and Engineering; Hemamala Karunadasa, Chemistry.

ElectrodeBarrierLight trapping in high‐efficiency, low‐cost silicon solar cells. This work aims to develop a new technique for trapping sunlight in thin-film silicon solar cells. Silicon and other materials will be engineered into nanosize spheres, domes and wires that promote light absorption and improve the overall efficiency of the solar cell. Investigator: Mark Brongersma, Materials Science and Engineering.

Maximizing solar-to-fuel conversion efficiency in photo-electrochemical cells. The goal is to create an efficient, stable photo-electrochemical cell capable of converting sunlight into hydrogen and other renewable fuels at elevated temperatures of 500°C to 700°C. Investigators: William Chueh and Nick Melosh, Materials Science and Engineering.

Electrochemical conversion of carbon gases to sustainable fuels and chemicals. Researchers will use computational analysis and experimental techniques to develop new catalysts that convert carbon dioxide and carbon monoxide into renewable fuels and chemicals. Investigators: Thomas Jaramillo, Chemical Engineering; Jens Nørskov, Chemical Engineering and SLAC National Accelerator Laboratory; Anders Nilsson, SLAC.

A team of scientists from the United States, Belgium and Scotland also received support for research that could lead to the large-scale conversion of cellulosic plants to biofuels:

Optimizing yield and composition in lignin‐modified plants. The inability to process lignin, a cement-like component of plant cell walls, has been a major hurdle in the production of biofuels from switchgrass and other cellulosic plants. In a previous GCEP study, the research team genetically engineered plants with reduced lignin that were smaller than normal. This project seeks to develop larger lignin-modified plants that can be cultivated for biofuels at scale. Investigators: Clint Chapple, Purdue University; Wout Boerjan, VIB and University of Ghent (Belgium); John Ralph, University of Wisconsin-Madison; Xu Li, North Carolina State University; Claire Halpin and Gordon Simpson, University of Dundee (Scotland).

GCEP is an industry partnership that supports innovative research on energy technologies that address the challenge of global climate change by reducing greenhouse gas emissions. Based at Stanford, the project includes five corporate sponsors – ExxonMobil, GE, Schlumberger, DuPont and Bank of America.

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For more information visit http://gcep.stanford.edu.

This article was written by Mark Shwartz, Precourt Institute for Energy, Stanford University.

New “gold nanocluster” Technology Revolutionizes Solar Power


QDOT images 6Scientists at Western University have discovered that a small molecule created with just 144 atoms of gold can increase solar cell performance by more than 10 per cent.

 

 

 

These findings, published recently by the high-impact journal Nanoscale, represent a game-changing innovation that holds the potential to take solar power mainstream and dramatically decrease the world’s dependence on traditional, resource-based sources of energy, says Giovanni Fanchini from Western’s Faculty of Science.

Fanchini, the Canada Research Chair in Carbon-based Nanomaterials and Nano-optoelectronics, says the new technology could easily be fast-tracked and integrated into prototypes of solar panels in one to two years and solar-powered phones in as little as five years.

“Every time you recharge your cell phone, you have to plug it in,” says Fanchini, an assistant professor in Western’s Department of Physics and Astronomy. “What if you could charge mobile devices like phones, tablets or laptops on the go? Not only would it be convenient, but the potential energy savings would be significant.”

The Western researchers have already started working with manufacturers of solar components to integrate their findings into existing and are excited about the potential.

“The Canadian business industry already has tremendous know-how in solar manufacturing,” says Fanchini. “Our invention is modular, an add-on to the existing production process, so we anticipate a working prototype very quickly.”

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Making nanoplasmonic enhancements, Fanchini and his team use “gold nanoclusters” as building blocks to create a flexible network of antennae on more traditional to attract an increase of light. While nanotechnology is the science of creating functional systems at the molecular level, nanoplasmonics investigates the interaction of light with and within these systems.

“Picture an extremely delicate fishnet of gold,” explains Fanchini explains, noting that the antennae are so miniscule they are unseen even with a conventional optical microscope. “The fishnet catches the light emitted by the sun and draws it into the active region of the solar cell.”

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According to Fanchini, the spectrum of light reflected by gold is centered on the yellow colour and matches the light spectrum of the sun making it superior for such antennae as it greatly amplifies the amount of sunlight going directly into the device.

“Gold is very robust, resilient to oxidization and not easily damaged, making it the perfect material for long-term use,” says Fanchini. “And gold can also be recycled.”

It has been known for some time that larger gold nanoparticles enhance solar cell performance, but the Western team is getting results with “a ridiculously small amount” – approximately 10,000 times less than previous studies, which is 10,000 times less expensive too.

Explore further: Using solar energy to turn raw materials into ingredients for everyday life

Provided by University of Western Ontario