Printable solar cells just got a little closer

FEBRUARY 24,2017

Research removes a key barrier to large-scale manufacture of low-cost, printable perovskite solar cells

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The new perovskite solar cells have achieved an efficiency of 20.1 per cent and can be manufactured at low temperatures, which reduces the cost and expands the number of possible applications.

Credit: Kevin Soobrian
A U of T Engineering innovation could make printing solar cells as easy and inexpensive as printing a newspaper. Dr. Hairen Tan and his team have cleared a critical manufacturing hurdle in the development of a relatively new class of solar devices called perovskite solar cells. This alternative solar technology could lead to low-cost, printable solar panels capable of turning nearly any surface into a power generator.
“Economies of scale have greatly reduced the cost of silicon manufacturing,” said Professor Ted Sargent, an expert in emerging solar technologies and the Canada Research Chair in Nanotechnology. “Perovskite solar cells can enable us to use techniques already established in the printing industry to produce solar cells at very low cost. Potentially, perovskites and silicon cells can be married to improve efficiency further, but only with advances in low-temperature processes.”
Today, virtually all commercial solar cells are made from thin slices of crystalline silicon which must be processed to a very high purity. It’s an energy-intensive process, requiring temperatures higher than 1,000 degrees Celsius and large amounts of hazardous solvents.
In contrast, perovskite solar cells depend on a layer of tiny crystals — each about 1,000 times smaller than the width of a human hair — made of low-cost, light-sensitive materials. Because the perovskite raw materials can be mixed into a liquid to form a kind of ‘solar ink’, they could be printed onto glass, plastic or other materials using a simple inkjet printing process.
But, until now, there’s been a catch: in order to generate electricity, electrons excited by solar energy must be extracted from the crystals so they can flow through a circuit. That extraction happens in a special layer called the electron selective layer, or ESL. The difficulty of manufacturing a good ESL has been one of the key challenges holding back the development of perovskite solar cell devices.
“The most effective materials for making ESLs start as a powder and have to be baked at high temperatures, above 500 degrees Celsius,” said Tan. “You can’t put that on top of a sheet of flexible plastic or on a fully fabricated silicon cell — it will just melt.”
Tan and his colleagues developed a new chemical reaction than enables them to grow an ESL made of nanoparticles in solution, directly on top of the electrode. While heat is still required, the process always stays below 150 degrees C, much lower than the melting point of many plastics.
The new nanoparticles are coated with a layer of chlorine atoms, which helps them bind to the perovskite layer on top — this strong binding allows for efficient extraction of electrons. In a paper recently published in Science, Tan and his colleagues report the efficiency of solar cells made using the new method at 20.1 per cent.
“This is the best ever reported for low-temperature processing techniques,” said Tan. He adds that perovskite solar cells using the older, high-temperature method are only marginally better at 22.1 per cent, and even the best silicon solar cells can only reach 26.3 per cent.
Another advantage is stability. Many perovskite solar cells experience a severe drop in performance after only a few hours, but Tan’s cells retained more than 90 per cent of their efficiency even after 500 hours of use. “I think our new technique paves the way toward solving this problem,” said Tan, who undertook this work as part of a Rubicon Fellowship.
“The Toronto team’s computational studies beautifully explain the role of the newly developed electron-selective layer. The work illustrates the rapidly-advancing contribution that computational materials science is making towards rational, next-generation energy devices,” said Professor Alan Aspuru-Guzik, an expert on computational materials science in the Department of Chemistry and Chemical Biology at Harvard University, who was not involved in the work.
“To augment the best silicon solar cells, next-generation thin-film technologies need to be process-compatible with a finished cell. This entails modest processing temperatures such as those in the Toronto group’s advance reported in Science,” said Professor Luping Yu of the University of Chicago’s Department of Chemistry. Yu is an expert on solution-processed solar cells and was not involved in the work.
Keeping cool during the manufacturing process opens up a world of possibilities for applications of perovskite solar cells, from smartphone covers that provide charging capabilities to solar-active tinted windows that offset building energy use. In the nearer term, Tan’s technology could be used in tandem with conventional solar cells.
“With our low-temperature process, we could coat our perovskite cells directly on top of silicon without damaging the underlying material,” said Tan. “If a hybrid perovskite-silicon cell can push the efficiency up to 30 per cent or higher, it makes solar power a much better economic proposition.”

Source : Science Daily

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Triangulene molecule synthesised after six decades

FEBRUARY 23,2017

AFM images reveal peculiar biradical aromatic created by single atom manipulation

(An atomic force microscopy image of triangulene on a copper surface and a representation of its structure)

Sixty-four years after it was first hypothesised, researchers have succeeded in making triangulene, a peculiar biradical aromatic that has so far remained elusive because of its extreme reactivity, but could pave the way to quantum computing devices.
Triangulene is planar, cyclic and has 22 π electrons – properties of a fully aromatic molecule according to Hückel’s rule. However, any attempt at drawing its resonance structures results in two unpaired electrons: triangulene is a non-Kekulé aromatic and permanent biradical.
Chemists have been trying to make triangulene through traditional synthesis, but never managed to make unsubstituted triangulene as it has proven to be highly unstable and instantly polymerises or rearranges into more stable structures. Now, Niko Pavliček’s team from IBM Research in Zurich, Switzerland, and the University of Warwick, UK, made triangulene using single atom manipulation – an art IBM researchers have been perfecting since they arranged 35 xenon atoms to spell out ‘IBM’ in 1989.
Pavliček’s team placed a hydrogenated precursor on a copper surface and shocked it into losing two hydrogen atoms and creating triangulene by applying a small voltage with the tip of a combined scanning tunnelling/atomic force microscope. This allowed researchers for the first time to study the biradical’s structure and molecular orbitals in the hope that these types of compounds could one day be used for information storage.
References
N Pavliček et al, Nat. Nanotechnol., 2017, DOI: 10.1038/nnano.2016.305

Source : ChemistryWorld

Sulfur linkage takes click chemistry in a different direction

FEBRUARY 22,2017

Thionyl tetrafluoride-based ‘sleeping beauties’ enable click chemistry in a tetrahedral shape

Nobel laureate Barry Sharpless and his collaborators have smashed together two storybook-nicknamed scientific worlds, calling on ‘sleeping beauty’ chemical groups to break his famous click chemistry out of ‘flatland’.

The original click chemistry – clean, copper-catalysed triazole formation developed by Sharpless’ team at Scripps Research Institute in San Diego, US – has many uses today, including tagging biomolecules. However, the chemical groups it can be used with are largely limited to azides and alkynes, while the flat triazole molecule means attachments always form along a straight line.
But now, click chemistry’s repertoire has been expanded significantly. The new approach starts from thionyl tetrafluoride (O=SF4) gas, onto which the scientists click functional groups from the important amine class, and phenols, over three steps.
Thionyl tetrafluoride-based click chemistry can involve up to three steps

‘We demonstrate that three sequential reactions, each creating a unique connection, can be achieved with almost perfection,’ comments team member John Moses, from the University of Nottingham, UK. ‘These connections depart from a single sulfur hub into the 3D world, which is a first for a click connector.’

A primary amine can displace two of thionyl tetrafluoride’s four fluorine atoms to make a tetrahedral connective hub when a tertiary amine catalyst is present. Secondary amines, amino acids and protected phenols can displace a third fluorine atom, when an amine or related basic catalyst is present. The final fluorine from the product of reactions with protected phenols can be displaced by a secondary amine directly, or another protected phenol in the presence of a phosphazene base catalyst.
This temporary inertness, and subsequent controllable clean reaction, is exactly what constitutes click chemistry. According to Moses, the sulfur (VI) fluoride compounds’ stability until exposed to tertiary amines led Sharpless to dub them ‘sleeping beauties’.
‘This is a nice continuation of work from the Sharpless lab on extensions of click chemistry, creating more versatile methods with controllable three-dimensional control at the conjugating agent,’ comments Eric Anslyn at the University of Texas, Austin. He adds that it should help in fragment-based drug discovery, due to the simple assembly around a single core.
One limitation is that thionyl tetrafluoride is not currently commercially available, but the team is working with a Chinese company to develop a ton-scale process, Moses reveals. They are also biologically screening the sulfur-derived compounds they have produced and making new types of functional polymers. ‘This is a very exciting time for click chemistry,’ Moses says.
References
S Li et al, Angew. Chem. Int. Ed., 2017, DOI: 10.1002/anie.201611048

Source : ChemistryWorld

What are Supermolecules !

February 22, 2017

                                                                   Carboxylic Acid dimers
The term supermolecule (or supramolecule) was introduced by Karl Lothar Wolf et al. (Übermoleküle) in 1937 to describe hydrogen-bonded acetic acid dimers.The study of non-covalent association of complexes of molecules has since developed into the field of supramolecular chemistry. The term supermolecule is sometimes used to describe supramolecular assemblies, which are complexes of two or more molecules (often macromolecules) that are not covalently bonded.The term supermolecule is also used in biochemistry to describe complexes of biomolecules, such as peptides and oligonucleotides composed of multiple strands.

Supramolecular chemistry

Supramolecular chemistry is the domain of chemistry beyond that of molecules and focuses on the chemical systems made up of a discrete number of assembled molecular subunits or components. The forces responsible for the spatial organization may vary from weak (intermolecular forces, electrostatic or hydrogen bonding) to strong (covalent bonding), provided that the degree of electronic coupling between the molecular component remains small with respect to relevant energy parameters of the component.[8][9]While traditional chemistry focuses on the covalent bond, supramolecular chemistry examines the weaker and reversible noncovalent interactions between molecules. These forces include hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, pi-pi interactions and electrostatic effects. Important concepts that have been demonstrated by supramolecular chemistry include molecular self-assembly, folding, molecular recognition, host-guest chemistry, mechanically-interlocked molecular architectures, and dynamic covalent chemistry.[10] The study of non-covalent interactions is crucial to understanding many biological processes from cell structure to vision that rely on these forces for structure and function. Biological systems are often the inspiration for supramolecular research.

220px-supramolecular_assembly_lehn

An example of a supramolecular assembly

Supramolecular complex of a chloride ion, cucurbit[5]uril, and cucurbit[10]uril

Supramolecular complex of a chloride ion, cucurbit[5]uril, and cucurbit[10]uril

More on Supermolecular Chemistry

Source:Wikipedia

New hydronium-ion battery presents opportunity for more sustainable energy storage

February 21, 2017                                phys_308px

A new type of battery developed by scientists at Oregon State University shows promise for sustainable, high-power energy storage.

It’s the world’s first battery to use only hydronium ions as the charge carrier.

The new battery provides an additional option for researchers, particularly in the area of stationary storage.

Stationary storage refers to batteries in a permanent location that store grid power – including power generated from such as wind turbines or solar cells – for use on a standby or emergency basis.

Hydronium, also known as H3O+, is a positively charged ion produced when a proton is added to a water molecule. Researchers in the OSU College of Science have demonstrated that hydronium ions can be reversibly stored in an electrode material consisting of perylenetetracarboxylic dianhydridem, or PTCDA.

This material is an organic, crystalline, molecular solid. The battery, created in the Department of Chemistry at Oregon State, uses dilute sulfuric acid as the electrolyte.

Graduate student Xingfeng Wang was the first author on the study, which has been published in the journal Angewandte Chemie International Edition, a publication of the German Chemical Society.

“This may provide a paradigm-shifting opportunity for more sustainable batteries,” said Xiulei Ji, assistant professor of chemistry at OSU and the corresponding author on the research. “It doesn’t use lithium or sodium or potassium to carry the charge, and just uses acid as the electrolyte. There’s a huge natural abundance of acid so it’s highly renewable and sustainable.”

Ji points out that until now, cations – ions with a positive charge – that have been used in batteries have been alkali metal, alkaline earth metals or aluminum.

“No nonmetal cations were being considered seriously for batteries,” he said.

The study observed a big dilation of the PTCDA lattice structure during intercalation – the process of its receiving ions between the layers of its structure. That meant the electrode was being charged, and the PTCDA structure expanded, by hydronium ions, rather than extremely tiny protons, which are already used in some batteries.

“Organic solids are not typically contemplated as crystalline electrode materials, but many are very crystalline, arranged in a very ordered structure,” Ji said. “This PTCDA material has a lot of internal space between its molecule constituents so it provides an opportunity for storing big ions and good capacity.”

The hydronium also migrate through the electrode structure with comparatively low “friction,” which translates to high power.

“It’s not going to power electric cars,” Ji said. “But it does provide an opportunity for battery researchers to go in a new direction as they look for new alternatives for energy storage, particularly for stationary grid storage.”

 

Provided by: Oregon State University  website

Source : Phys.Org

How humans bond: The brain chemistry revealed

FEBRUARY 21,2107

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In new research published Monday in the journal Proceedings of the National Academy of Sciences, Northeastern University psychology professor Lisa Feldman Barrett found, for the first time, that the neurotransmitter dopamine is involved in human bonding, bringing the brain’s reward system into our understanding of how we form human attachments. The results, based on a study with 19 mother-infant pairs, have important implications for therapies addressing postpartum depression as well as disorders of the dopamine system such as Parkinson’s disease, addiction, and social dysfunction.
“The infant brain is very different from the mature adult brain — it is not fully formed,” says Barrett, University Distinguished Professor of Psychology and author of the forthcoming book How Emotions Are Made: The Secret Life of the Brain. “Infants are completely dependent on their caregivers. Whether they get enough to eat, the right kind of nutrients, whether they’re kept warm or cool enough, whether they’re hugged enough and get enough social attention, all these things are important to normal brain development. Our study shows clearly that a biological process in one person’s brain, the mother’s, is linked to behavior that gives the child the social input that will help wire his or her brain normally. That means parents’ ability to keep their infants cared for leads to optimal brain development, which over the years results in better adult health and greater productivity.”
To conduct the study, the researchers turned to a novel technology: a machine capable of performing two types of brain scans simultaneously — functional magnetic resonance imaging, or fMRI, and positron emission tomography, or PET.
fMRI looks at the brain in slices, front to back, like a loaf of bread, and tracks blood flow to its various parts. It is especially useful in revealing which neurons are firing frequently as well as how different brain regions connect in networks. PET uses a small amount of radioactive chemical plus dye (called a tracer) injected into the bloodstream along with a camera and a computer to produce multidimensional images to show the distribution of a specific neurotransmitter, such as dopamine or opioids.
Barrett’s team focused on the neurotransmitter dopamine, a chemical that acts in various brain systems to spark the motivation necessary to work for a reward. They tied the mothers’ level of dopamine to her degree of synchrony with her infant as well as to the strength of the connection within a brain network called the medial amygdala network that, within the social realm, supports social affiliation.
“We found that social affiliation is a potent stimulator of dopamine,” says Barrett. “This link implies that strong social relationships have the potential to improve your outcome if you have a disease, such as depression, where dopamine is compromised. We already know that people deal with illness better when they have a strong social network. What our study suggests is that caring for others, not just receiving caring, may have the ability to increase your dopamine levels.”
Before performing the scans, the researchers videotaped the mothers at home interacting with their babies and applied measurements to the behaviors of both to ascertain their degree of synchrony. They also videotaped the infants playing on their own.
Once in the brain scanner, each mother viewed footage of her own baby at solitary play as well as an unfamiliar baby at play while the researchers measured dopamine levels, with PET, and tracked the strength of the medial amygdala network, with fMRI.
The mothers who were more synchronous with their own infants showed both an increased dopamine response when viewing their child at play and stronger connectivity within the medial amygdala network. “Animal studies have shown the role of dopamine in bonding but this was the first scientific evidence that it is involved in human bonding,” says Barrett. “That suggests that other animal research in this area could be directly applied to humans as well.”
The findings, says Barrett, are “cautionary.” “They have the potential to reveal how the social environment impacts the developing brain,” she says. “People’s future health, mental and physical, is affected by the kind of care they receive when they are babies. If we want to invest wisely in the health of our country, we should concentrate on infants and children, eradicating the adverse conditions that interfere with brain development.”
Story Source: ScienceDaily

Materials provided by Northeastern University. Original written by Thea Singer. Note: Content may be edited for style and length.