Solar-to-Fuel System Recycles CO2 to Make Ethanol and Ethylene: Berkeley National Lab



Schematic of a solar-powered electrolysis cell which converts carbon dioxide into hydrocarbon and oxygenate products with an efficiency far higher than natural photosynthesis. Power-matching electronics allow the system to operate over a range of sun conditions. (Credit: Clarissa Towle/Berkeley Lab)

Berkeley Lab advance is first demonstration of efficient, light-powered production of fuel via artificial photosynthesis

Scientists at the Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) have harnessed the power of photosynthesis to convert carbon dioxide into fuels and alcohols at efficiencies far greater than plants. The achievement marks a significant milestone in the effort to move toward sustainable sources of fuel.

Many systems have successfully reduced carbon dioxide to chemical and fuel precursors, such as carbon monoxide or a mix of carbon monoxide and hydrogen known as syngas. This new work, described in a study published in the journal Energy and Environmental Science, is the first to successfully demonstrate the approach of going from carbon dioxide directly to target products, namely ethanol and ethylene, at energy conversion efficiencies rivaling natural counterparts.

The researchers did this by optimizing each component of a photovoltaic-electrochemical system to reduce voltage loss, and creating new materials when existing ones did not suffice.

“This is an exciting development,” said study principal investigator Joel Ager, a Berkeley Lab scientist with joint appointments in the Materials Sciences and the Chemical Sciences divisions. “As rising atmospheric CO2 levels change Earth’s climate, the need to develop sustainable sources of power has become increasingly urgent. Our work here shows that we have a plausible path to making fuels directly from sunlight.”

That sun-to-fuel path is among the key goals of the Joint Center for Artificial Photosynthesis (JCAP), a DOE Energy Innovation Hub established in 2010 to advance solar fuel research. The study was conducted at JCAP’s Berkeley Lab campus.

The initial focus of JCAP research was tackling the efficient splitting of water in the photosynthesis process. Having largely achieved that task using several types of devices, JCAP scientists doing solar-driven carbon dioxide reduction began setting their sights on achieving efficiencies similar to those demonstrated for water splitting, considered by many to be the next big challenge in artificial photosynthesis.

Another research group at Berkeley Lab is tackling this challenge by focusing on a specific component in a photovoltaic-electrochemical system. In a study published today, they describe a new catalyst that can achieve carbon dioxide to multicarbon conversion using record-low inputs of energy.

Not just for noon


For this JCAP study, researchers engineered a complete system to work at different times of day, not just at a light energy level of 1-sun illumination, which is equivalent to the peak of brightness at high noon on a sunny day. They varied the brightness of the light source to show that the system remained efficient even in low light conditions.

When the researchers coupled the electrodes to silicon photovoltaic cells, they achieved solar conversion efficiencies of 3 to 4 percent for 0.35 to 1-sun illumination. Changing the configuration to a high-performance, tandem solar cell connected in tandem yielded a conversion efficiency to hydrocarbons and oxygenates exceeding 5 percent at 1-sun illumination.

Copper-Silver Cathode

At left is a surface view of a bimetallic copper-silver nanocoral cathode taken from a scanning electron micrograph. To the right is an energy-dispersive X-ray image of the cathode with the copper (in pink/red) and silver (in green) highlighted. (Credit: Gurudayal/Berkeley Lab)

“We did a little dance in the lab when we reached 5 percent,” said Ager, who also holds an appointment as an adjunct professor at UC Berkeley’s Materials Science and Engineering Department.

Among the new components developed by the researchers are a copper-silver nanocoral cathode, which reduces the carbon dioxide to hydrocarbons and oxygenates, and an iridium oxide nanotube anode, which oxidizes the water and creates oxygen.

“The nice feature of the nanocoral is that, like plants, it can make the target products over a wide range of conditions, and it is very stable,” said Ager.

The researchers characterized the materials at the National Center for Electron Microscopy at the Molecular Foundry, a DOE Office of Science User Facility at Berkeley Lab. The results helped them understand how the metals functioned in the bimetallic cathode. Specifically, they learned that silver aids in the reduction of carbon dioxide to carbon monoxide, while the copper picks up from there to reduce carbon monoxide further to hydrocarbons and alcohols.

Seeking better, low-energy breakups



Because carbon dioxide is a stubbornly stable molecule, breaking it up typically involves a significant input of energy.
“Reducing CO2 to a hydrocarbon end product like ethanol or ethylene can take up to 5 volts, start to finish,” said study lead author Gurudayal, postdoctoral fellow at Berkeley Lab. “Our system reduced that by half while maintaining the selectivity of products.”

Notably, the electrodes operated well in water, a neutral pH environment.

“Research groups working on anodes mostly do so using alkaline conditions since anodes typically require a high pH environment, which is not ideal for the solubility of CO2,” said Gurudayal. “It is very difficult to find an anode that works in neutral conditions.”

The researchers customized the anode by growing the iridium oxide nanotubes on a zinc oxide surface to create a more uniform surface area to better support chemical reactions.

“By working through each step so carefully, these researchers demonstrated a level of performance and efficiency that people did not think was possible at this point,” said Berkeley Lab chemist Frances Houle, JCAP deputy director for Science and Research Integration, who was not part of the study. “This is a big step forward in the design of devices for efficient CO2 reduction and testing of new materials, and it provides a clear framework for the future advancement of fully integrated solar-driven CO2-reduction devices.”

Other co-authors on the study include James Bullock, a Berkeley Lab postdoctoral researcher in materials sciences, who was instrumental in engineering the system’s photovoltaic and electrolysis cell pairing. Bullock works in the lab of study co-author Ali Javey, Berkeley Lab senior faculty scientist and a UC Berkeley professor of electrical engineering and computer sciences.

This work is supported by the DOE Office of Science.

Lawrence Berkeley National Laboratory addresses the world’s most urgent scientific challenges by advancing sustainable energy, protecting human health, creating new materials, and revealing the origin and fate of the universe. Founded in 1931, Berkeley Lab’s scientific expertise has been recognized with 13 Nobel Prizes. 
The University of California manages Berkeley Lab for the U.S. Department of Energy’s Office of Science. For more, visit http://www.lbl.gov.
DOE’s Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

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NREL, Swiss Scientists Power Past Solar Efficiency Records


NREL scientist Adele Tamboli, co-author of a recent article on silicon-based multijunction solar cells, stands in front of an array of solar panels. Credit: Dennis Schroeder

August 25, 2017




Second collaborative effort proves silicon-based multijunction cells that reach nearly 36% efficiency

Collaboration between researchers at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL), the Swiss Center for Electronics and Microtechnology (CSEM), and the École Polytechnique Fédérale de Lausanne (EPFL) shows the high potential of silicon-based multijunction solar cells.

The research groups created tandem solar cells with record efficiencies of converting sunlight into electricity under 1-sun illumination. The resulting paper, “Raising the One-Sun Conversion Efficiency of III–V/Si Solar Cells to 32.8% for Two Junctions and 35.9% for Three Junctions,” appears in the new issue of Nature Energy. Solar cells made solely from materials in Groups III and V of the Periodic Table have shown high efficiencies, but are more expensive.

Stephanie Essig, a former NREL post-doctoral researcher now working at EPFL in Switzerland, is lead author of the newly published research that details the steps taken to improve the efficiency of the multijunction cell. While at NREL, Essig co-authored “Realization of GaInP/Si Dual-Junction Solar Cells with 29.8% 1-Sun Efficiency,” which was published in the IEEE Journal of Photovoltaics a year ago.

In addition to Essig, authors of the new research paper are Timothy Remo, John F. Geisz, Myles A. Steiner, David L. Young, Kelsey Horowitz, Michael Woodhouse, and Adele Tamboli, all with NREL; and Christophe Allebe, Loris Barraud, Antoine Descoeudres, Matthieu Despeisse, and Christophe Ballif, all from CSEM.

“This achievement is significant because it shows, for the first time, that silicon-based tandem cells can provide efficiencies competing with more expensive multijunction cells consisting entirely of III-V materials,” Tamboli said. “It opens the door to develop entirely new multijunction solar cell materials and architectures.”

In testing silicon-based multijunction solar cells, the researchers found that the highest dual-junction efficiency (32.8%) came from a tandem cell that stacked a layer of gallium arsenide (GaAs) developed by NREL atop a film of crystalline silicon developed by CSEM. An efficiency of 32.5% was achieved using a gallium indium phosphide (GaInP) top cell, which is a similar structure to the previous record efficiency of 29.8% announced in January 2016. 

A third cell, consisting of a GaInP/GaAs tandem cell stacked on a silicon bottom cell, reached a triple-junction efficiency of 35.9%—just 2% below the overall triple-junction record.

The existing photovoltaics market is dominated by modules made of single-junction silicon solar cells, with efficiencies between 17% and 24%. 

The researchers noted in the report that making the transition from a silicon single-junction cell to a silicon-based dual-junction solar cell will enable manufacturers to push efficiencies past 30% while still benefiting from their expertise in making silicon solar cells.

The obstacle to the adoption of these multijunction silicon-based solar cells, at least in the near term, is the cost. Assuming 30% efficiency, the researchers estimated the GaInP-based cell would cost $4.85 per watt and the GaAs-based cell would cost $7.15 per watt. 

But as manufacturing ramps up and the efficiencies of these types of cells climbs to 35%, the researchers predict the cost per watt could fall to 66 cents for a GaInP-based cell and to 85 cents for the GaAs-based cell. 

The scientists noted that such a precipitous price drop is not unprecedented; for instance, the cost of Chinese-made photovoltaic modules fell from $4.50 per watt in 2006 to $1 per watt in 2011.

The cost of a solar module in the United States accounts for 20% to 40% of the price of a photovoltaic system. Increasing cell efficiency to 35%, the researchers estimated, could reduce the system cost by as much as 45 cents per watt for commercial installations. 

However, if the costs of a III-V cell cannot be reduced to the levels of the researchers’ long-term scenario, then the use of cheaper, high-efficiency materials for the top cell will be needed to make them cost-competitive in general power markets.

The funding for the research came from the Energy Department’s SunShot Initiative—which aims to make solar energy a low-cost electricity source for all Americans through research and development efforts in collaboration with public and private partners—and from the Swiss Confederation and the Nano-Tera.ch initiative.


NREL is the U.S. Department of Energy’s primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by The Alliance for Sustainable Energy, LLC.

Army COE Creates New Energy Efficient ‘Graphene Oxide’ Water Filter at Commercial Scale



The Army Corps of Engineers have successfully created a usable prototype of a new type of water filter.

The membranes are made of a mixture of chitosan, a material commonly found in shrimp shells, and a new synthetic chemical known as “graphene oxide”. Graphene oxide is a highly researched chemical worldwide.

  According to the Army Corps, one problem encountered by scientists working with graphene oxide is not being able to synthesize the material on a scale that can be put to use.

“One of the major breakthroughs that we’ve had here is that with our casting process, we’re not limited by size,” explains Luke Gurtowski, a research chemical engineer working on the membranes.


These filters have been found to effectively remove a number of different contaminants commonly found in water.

Dr. Christopher Griggs is the research scientist in charge of overseeing development of the new membranes.

Dr. Griggs told us, “Anybody who’s experienced water shortages or has been concerned about their water quality, or any type of contaminants in the water, this type of technology certainly works to address that.”

Another challenged faced by conventional water filtering methods is maintaining high energy efficiency.

“It requires a lot of energy for the net driving pressure to force the water through the membrane,” Dr. Griggs explains. “…we’re going to have to look to new materials to try to get those efficiency gains, and so graphene oxide is a very promising candidate for that.”

The Engineer Research and Development Center currently has two patents associated with the new filters and hopes to apply them for both civil and military purposes in the near future. 

Google’s Parent Company Will Soon Compete With Tesla for Energy Storage Solutions: Project Malta at ‘Alphabet X’



Maximizing Renewables



Given the dramatic impact human-made carbon emissions are having on our planet, cleaner energy sources have become increasingly popular alternatives to their fossil fuel counterparts. Currently, solar and wind are the most widely used renewable energy sources, but both are dependent on certain conditions.

The former can capture energy only during daylight hours, while the latter is more unpredictable, but often peaks at night.
As such, there’s a mismatch between when solar and wind energy are available and when energy is needed.

The world needs a way to maximize renewable energy usage, and that’s what Malta, a project currently brewing at Alphabet X, the “moonshot” factory by Google’s parent company, is hoping to provide.

The goal of Alphabet X is to develop technologies that could “someday make the world a radically better place.” The organization follows a three-part blueprint for their moonshot projects that starts with identifying a “huge problem” and then providing a “radical solution” that could be implemented using a “breakthrough technology.”

For Malta, the idea was to find a way to maximize the use of energy generated from renewables. Their radical solution is bridging the gap between renewable energy and grid-scale energy storage technologies using a breakthrough technology developed by Stanford physicist and Nobel laureate Robert Laughlin.

According to the project’s website, this technology is still theoretical and involves storing electricity as either heat within molten salt or cold within a liquid similar to the antifreeze used in cars. They claim this energy could remain stored for up to weeks at a time.

Storing Energy


Essentially, Malta is hoping to develop clean and cost-effective energy storage devices, which is similar to the concept behind Tesla’s Powerpack. The difference between the Malta project’s tech and the Powerpack is mostly what’s inside. While Tesla’s energy storage device uses 16 individual battery pods, Malta’s relies on molten salt or the antifreeze-like liquid.

Additionally, the tanks used to store the salt used by Malta’s system could potentially last for up to 40 years, which the project claims is three or more times longer than other current storage options. That extended lifespan would make Malta a cheaper alternative to other renewable energy storage devices.
alphabet x malta renewable energy.

Image credit: Malta/X

After two years of developing and designing their system, the Malta team is now gearing up to test the commercial viability of their technology. “The next step is to build a megawatt-scale prototype plant which would be large enough to prove the technology at commercial scale,” according to their website.
We now have multiple ways to generate energy from renewables, but if we ever hope to fully transition away from traditional energy solutions, we need better storage devices.

Though they are clearly better for the environment, renewables aren’t as consistent as fossil fuels, and that unreliability is a huge barrier to widespread adoption.

Storage systems like those proposed by Malta could collect the energy generated by renewables and ensure it is available to power grids whenever needed, putting us one step closer to a future completely free of fossil fuels.

Watch Our Video on a New Energy Storage Company for Nano-Enabled Batteries and Super Capacitors

Update: Super Capacitor Assisted Silicon Nanowire Batteries for EV and Small Form Factor Markets. A New Class of Battery /Energy Storage Materials is being developed to support the High Energy – High Capacity – High Performance High Cycle Battery Markets.

“Ultrathin Asymmetric Porous-Nickel Graphene-Based
Supercapacitor with High Energy Density and Silicon Nanowire,”

A New Generation Battery that is:

 Energy Dense
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 Low Manufacturing Cost
 Rapid Charge/ Re-Charge
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 Long Warranty Life
 Non-Toxic
 Highly Scalable

Key Markets & Commercial Applications

 EV, (18650 & 21700); Drone and Marine Batteries
 Wearable Electronics and The Internet of Things
 Estimated $240 Billion Market by 2025



Rice University (NEWT) / China team use phage-enhanced nanoparticles to kill bacteria that foul water treatment systems


Clusters of nanoparticles with phage viruses attached find and kill Escherichia coli bacteria in a lab test at Rice University. 

Abstract:
Magnetic nanoparticle clusters have the power to punch through biofilms to reach bacteria that can foul water treatment systems, according to scientists at Rice University and the University of Science and Technology of China.
Magnetized viruses attack harmful bacteria: Rice, China team uses phage-enhanced nanoparticles to kill bacteria that foul water treatment systems.

Researchers at Rice and the University of Science and Technology of China have developed a combination of antibacterial phages and magnetic nanoparticle clusters that infect and destroy bacteria that are usually protected by biofilms in water treatment systems. (Credit: Alvarez Group/Rice University)

The nanoclusters developed through Rice’s Nanotechnology-Enabled Water Treatment (NEWT) Engineering Research Center carry bacteriophages – viruses that infect and propagate in bacteria – and deliver them to targets that generally resist chemical disinfection.

Without the pull of a magnetic host, these “phages” disperse in solution, largely fail to penetrate biofilms and allow bacteria to grow in solution and even corrode metal, a costly problem for water distribution systems.

The Rice lab of environmental engineer Pedro Alvarez and colleagues in China developed and tested clusters that immobilize the phages. A weak magnetic field draws them into biofilms to their targets.

The research is detailed in the Royal Society of Chemistry’s Environmental Science: Nano.
“This novel approach, which arises from the convergence of nanotechnology and virology, has a great potential to treat difficult-to-eradicate biofilms in an effective manner that does not generate harmful disinfection byproducts,” Alvarez said.

Biofilms can be beneficial in some wastewater treatment or industrial fermentation reactors owing to their enhanced reaction rates and resistance to exogenous stresses, said Rice graduate student and co-lead author Pingfeng Yu. “However, biofilms can be very harmful in water distribution and storage systems since they can shelter pathogenic microorganisms that pose significant public health concerns and may also contribute to corrosion and associated economic losses,” he said.

The lab used phages that are polyvalent – able to attack more than one type of bacteria – to target lab-grown films that contained strains of Escherichia coli associated with infectious diseases and Pseudomonas aeruginosa, which is prone to antibiotic resistance.

The phages were combined with nanoclusters of carbon, sulfur and iron oxide that were further modified with amino groups. The amino coating prompted the phages to bond with the clusters head-first, which left their infectious tails exposed and able to infect bacteria.

The researchers used a relatively weak magnetic field to push the nanoclusters into the film and disrupt it. Images showed they effectively killed E. coli and P. aeruginosa over around 90 percent of the film in a test 96-well plate versus less than 40 percent in a plate with phages alone.

The researchers noted bacteria may still develop resistance to phages, but the ability to quickly disrupt biofilms would make that more difficult. Alvarez said the lab is working on phage “cocktails” that would combine multiple types of phages and/or antibiotics with the particles to inhibit resistance.

Graduate student Ling-Li Li of the University of Science and Technology of China, Hefei, is co-lead author of the paper. Co-authors are graduate student Sheng-Song Yu and Han-Qing Yu, a professor at the University of Science and Technology of China, and graduate student Xifan Wang and temporary research scientist Jacques Mathieu of Rice.


The National Science Foundation and its Rice-based NEWT Engineering Research Center supported the research.

Grid Batteries Are Poised to Become Cheaper Than Natural-Gas Plants in Minnesota



A 60-acre solar farm in Camp Ripley, a National Guard base in Minnesota.

A new report suggests the economics of large-scale batteries are reaching an important inflection point.

When it comes to renewable energy, Minnesota isn’t typically a headline-grabber: in 2016 it got about 18 percent of its energy from wind, good enough to rank in the top 10 states. 
But it’s just 28th in terms of installed solar capacity, and its relatively small size means projects within its borders rarely garner the attention that giants like California and Texas routinely get.

A new report on the future of energy in the state should turn some heads (PDF). According to the University of Minnesota’s Energy Transition Lab, starting in 2019 and for the foreseeable future, the overall cost of building grid-scale storage there will be less than that of building natural-gas plants to meet future energy demand.


Minnesota currently gets about 21 percent of its energy from renewables. That’s not bad, but current plans also call for bringing an additional 1,800 megawatts of gas-fired “peaker” plants online by 2028 to meet growing demand. As the moniker suggests, these plants are meant to spin up quickly to meet daily peaks in energy demand—something renewables tend to be bad at because the wind doesn’t always blow and the sun doesn’t always shine.

Storing energy from renewables could solve that problem, but it’s traditionally been thought of as too expensive compared with other forms of energy.

The new report suggests otherwise. According to the analysis, bringing lithium-ion batteries online for grid storage would be a good way to stockpile energy for when it’s needed, and it would prove less costly than building and operating new natural-gas plants.

The finding comes at an interesting time. For one thing, the price of lithium-ion batteries continues to plummet, something that certainly has the auto industry’s attention. And grid-scale batteries, while still relatively rare, are popping up more and more these days. The Minnesota report, then, suggests that such projects may become increasingly common—and could be a powerful way to lower emissions without sending our power bills skyrocketing in the process.
(Read more: Minnesota Public Radio, “Texas and California Have Too Much Renewable Energy,” 

“The One and Only Texas Wind Boom,” “By 2040, More Than Half of All New Cars Could Be Electric”)

Solar paint offers endless energy from water vapor: Breakthrough by RMIT Researchers


Credit: CC0 Public Domain


Researchers have developed a solar paint that can absorb water vapour and split it to generate hydrogen – the cleanest source of energy.

The paint contains a newly developed compound that acts like silica gel, which is used in sachets to absorb moisture and keep food, medicines and electronics fresh and dry.

But unlike silica gel, the new material, synthetic molybdenum-sulphide, also acts as a semi-conductor and catalyses the splitting of water atoms into hydrogen and oxygen.

Lead researcher Dr Torben Daeneke, from RMIT University in Melbourne, Australia, said: “We found that mixing the compound with titanium oxide particles leads to a sunlight-absorbing paint that produces hydrogen fuel from solar energy and moist air.

“Titanium oxide is the white pigment that is already commonly used in wall paint, meaning that the simple addition of the new material can convert a brick wall into energy harvesting and fuel production real estate.

“Our new development has a big range of advantages,” he said. “There’s no need for clean or filtered water to feed the system. Any place that has water vapour in the air, even remote areas far from water, can produce fuel.”

 

His colleague, Distinguished Professor Kourosh Kalantar-zadeh, said hydrogen was the cleanest source of energy and could be used in fuel cells as well as conventional combustion engines as an alternative to fossil fuels.

“This system can also be used in very dry but hot climates near oceans. The sea water is evaporated by the hot sunlight and the vapour can then be absorbed to produce fuel.

“This is an extraordinary concept – making fuel from the sun and water vapour in the air.”

 

More information: Torben Daeneke et al, Surface Water Dependent Properties of Sulfur-Rich Molybdenum Sulfides: 
Electrolyteless Gas Phase Water Splitting, ACS Nano (2017). DOI: 10.1021/acsnano.7b01632
Provided by: RMIT University

What Do You Think About Nanotechnology? Tell Us with Our Quick Survey – Pleeez!


slate-survey-160928_ft_nano-survey-jpg-crop-promo-xlarge2

Slate Nanotechnology Survey

Slate has recently published an online survey “Tell Us What You Think About Nanotechnology” (Follow the link above to take that survey).

Which … got us to thinking. “We” (Team GNT) should have our very own Survey on Nanotechnology with more focus on youOUR READERS!

entrepren-climbing-mtn-090116-aaeaaqaaaaaaaairaaaajdm5ode1yznlltu4njutngmzyy1hztm3ltgznmnimtvjzwfioaWith over 5 Years of publication, 132,000+ hits on any average reporting cycle, representing Followers in over 50 Countries, and 10,000 plus Followers across Social Media … we are guessing you just might have some very “illuminating” and valuable thoughts, visions and opinions to share with us!

 

So … we are asking you to share your comments with us by answering a few questions and also … leaving us any ‘Open Comments’ you would care to leave. We will gather your responses, share the most interesting ones and let you know what others are “thinking and saying” about Nanotechnology. 

fourth-ir-051416-aaeaaqaaaaaaaatfaaaajgezy2e0nwvilwu4ogitndzkzi1hymzilta1yty1nzczngqzna

Questions Like

1. What Area or Application of Nanotechnology do you find most interesting? (Examples: Bio-Med, Cancer Treatment-Diagnosis, Electronics, Energy – Energy Storage, Materials, Sensors, Quantum Computing, etc.) Don’t let our suggestions limit your responses!

2. Which Areas or Applications do you think are most promising right now? In the future? that will dramatically change the World we live in?

3. Are you worried about the ‘safety’ of nanomaterials? On a scale of 1 to 10, 10 being MOST WORRIED. Why?

4. Which Nanotechnology Application or Area of Research interests you the most?

We have provided a ‘Response/ Contact Form’ for you below OR … you can Leave Us a Comment in the Comments Section. We are really looking forward to hearing from ALL of you!

Thanks! We are expecting … “Great Things from Small Things”!

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Remember to ‘Follow Us on Twitter’ @Genesisnanotech

 

(Cadmium) Telluride Promising Alternative to Silicon: Crystalline fault lines provide pathway for solar cell current (w/video) [U Conn and Brookhaven NL]


telluride-id44636

** From Brookhaven National Laboratory & Nanowerk  

A team of scientists studying solar cells made from cadmium telluride, a promising alternative to silicon, has discovered that microscopic “fault lines” within and between crystals of the material act as conductive pathways that ease the flow of electric current. This research—conducted at the University of Connecticut and the U.S. Department of Energy’s Brookhaven National Laboratory, and described in the journal Nature Energy (“Charge transport in CdTe solar cells revealed by conductive tomographic atomic force microscopy”), may help explain how a common processing technique turns cadmium telluride into an excellent material for transforming sunlight into electricity, and suggests a strategy for engineering more efficient solar devices that surpass the performance of silicon.

“If you look at semiconductors like silicon, defects in the crystals are usually bad,” said co-author Eric Stach, a physicist at Brookhaven Lab’s Center for Functional Nanomaterials (CFN). As Stach explained, misplaced atoms or slight shifts in their alignment often act as traps for the particles that carry electric current—negatively charged electrons or the positively charged “holes” left behind when electrons are knocked loose by photons of sunlight, making them more mobile. The idea behind solar cells is to separate the positive and negative charges and run them through a circuit so the current can be used to power houses, satellites, or even cities. Defects interrupt this flow of charges and keep the solar cell from being as efficient as it could be.
But in the case of cadmium telluride, the scientists found that boundaries between individual crystals and “planar defects”—fault-like misalignments in the arrangement of atoms—create pathways for conductivity, not traps.
CTAFM Image
These CTAFM images show a cadmium telluride solar cell from the top (above) and side profile (bottom) with bright spots representing areas of higher electron conductivity. The images reveal that the conductive pathways coincide with crystal grain boundaries. (Image: University of Connecticut)
 

Members of Bryan Huey’s group at the Institute of Materials Science at the University of Connecticut were the first to notice the surprising connection. In an effort to understand the effects of a chloride solution treatment that greatly enhances cadmium telluride’s conductive properties, Justin Luria and Yasemin Kutes studied solar cells before and after treatment. But they did so in a unique way.

Several groups around the world had looked at the surfaces of such solar cells before, often with a tool known as a conducting atomic force microscope. The microscope has a fine probe many times sharper than the head of a pin that scans across the material’s surface to track the topographic features—the hills and valleys of the surface structure—while simultaneously measuring location-specific conductivity. Scientists use this technique to explore how the surface features relate to solar cell performance at the nanoscale.
But no one had devised a way to make measurements beneath the surface, the most important part of the solar cell. This is where the UConn team made an important breakthrough. They used an approach developed and perfected by Kutes and Luria over the last two years to acquire hundreds of sequential images, each time intentionally removing a nanoscale layer of the material, so they could scan through the entire thickness of the sample. They then used these layer-by-layer images to build up a three-dimensional, high-resolution ‘tomographic’ map of the solar cell—somewhat like a computed tomography (CT) brain scan.
Assembling the layer-by-layer CTAFM scans into a side-profile video file reveals the relationship between conductivity and planar defects throughout the entire thickness of the cadmium telluride crystal, including how the defects appear to line up to form continuous pathways of conductivity. (Video: University of Connecticut)

 

“Everyone using these microscopes basically takes pictures of the ‘ground,’ and interprets what is beneath,” Huey said. “It may look like there’s a cave, or a rock shelf, or a building foundation down there. But we can only really know once we carefully dig, like archeologists, keeping track of exactly what we find every step of the way—though, of course, at a much, much smaller scale.”
The resulting CT-AFM maps uniquely revealed current flowing most freely along the crystal boundaries and fault-like defects in the cadmium telluride solar cells. The samples that had been treated with the chloride solution had more defects overall, a higher density of these defects, and what appeared to be a high degree of connectivity among them, while the untreated samples had few defects, no evidence of connectivity, and much lower conductivity.
Huey’s team suspected that the defects were so-called planar defects, usually caused by shifts in atomic alignments or stacking arrangements within the crystals. But the CTAFM system is not designed to reveal such atomic-scale structural details. To get that information, the UConn team turned to Stach, head of the electron microscopy group at the CFN, a DOE Office of Science User Facility.
“Having previously shared ideas with Eric, it was a natural extension of our discovery to work with his group,” Huey said.
Said Stach, “This is the exact type of problem the CFN is set up to handle, providing expertise and equipment that university researchers may not have to help drive science from hypothesis to discovery.”
CFN staff physicist Lihua Zhang used a transmission electron microscope (TEM) and UConn’s results as a guide to meticulously study how atomic scale features of chloride-treated cadmium telluride related to the conductivity maps. The TEM images revealed the atomic structure of the defects, confirming that they were due to specific changes in the stacking sequence of atoms in the material. The images also showed clearly that these planar defects connected different grains in the crystal, leading to high-conductivity pathways for the movement of electrons and holes.
“When we looked at the regions with good conductivity, the planar defects linked from one crystal grain to another, forming continuous pathways of conductance through the entire thickness of the material,” said Zhang. “So the regions that had the best conductivity were the ones that had a high degree of connectivity among these defects.”
stacking pattern of individual atoms
These transmission electron microscopy images taken at Brookhaven’s CFN reveals how the stacking pattern of individual atoms (bright spots) shifts. The images confirmed that the bright spots of high conductivity observed with CTAFM imaging at UConn occurred at the interfaces between two different atomic alignments (left) and that these “planar defects” were continuous between individual crystals, creating pathways of conductivity (right). The labels WZ and ZB refer to the two atomic stacking sequences “wurtzite” and “zinc blende,” which are the two types of crystal structures cadmium telluride can form. (click on image to enlarge)
 

The authors say it’s possible that the chloride treatment helps to create the connectivity, not just more defects, but that more research is needed to definitively determine the most significant effects of the chloride solution treatment.

In any case, Stach says that combining the CTAFM technique and electron microscopy, yields a “clear winner” in the search for more efficient, cost-competitive alternatives to silicon solar cells, which have nearly reached their limit for efficiency.
“There is already a billion-dollar-a-year industry making cadmium telluride solar cells, and lots of work exploring other alternatives to silicon. But all of these alternatives, because of their crystal structure, have a higher tendency to form defects,” he said. “This work gives us a systematic method we can use to understand if the defects are good or bad in terms of conductivity. It can also be used to explore the effects of different processing methods or chemicals to control how defects form. In the case of cadmium telluride, we may want to find ways to make more of these defects, or look for other materials in which defects improve performance.”
Source: Brookhaven National Laboratory

 

From start-up to scale-up: what it takes to become a successful entrepreneur — World Economic Forum | Agenda


entrepren-climbing-mtn-090116-aaeaaqaaaaaaaairaaaajdm5ode1yznlltu4njutngmzyy1hztm3ltgznmnimtvjzwfioa

 

Ellen Olafsen of the World Bank on how to turn start-ups into successful firms.

via From start-up to scale-up: what it takes to become a successful entrepreneur — World Economic Forum | Agenda

What do you think of when you hear the term “entrepreneur”? What about “growth entrepreneur”? Do Elon Musk and Tesla come to mind? Travis Kalanick and Garrett Camp of Uber? Jack Ma of Alibaba?

Forget for a moment the immense scale that these few, highly successful tech giants have achieved. Such cases will always be outliers. Instead, imagine the potential collective impact of companies in developing countries growing from a $50,000 to a $1 million company, or from a $1 million to a $10 million company. Imagine how this could help generate dynamism in the local economy and ultimately increase competitiveness, incomes and jobs.

 

fourth-ir-051416-aaeaaqaaaaaaaatfaaaajgezy2e0nwvilwu4ogitndzkzi1hymzilta1yty1nzczngqznaAlso Read: Nanotechnology and the ‘Fourth Industrial Revolution’ ~ Solving the World’s Biggest Challenges with the ‘Smallest of Things’

 

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