Simplificarea celulelor solare cu un amestec nou de materiale(Simplifying solar cells with a new mix of materials)

O echipă internațională de cercetare a simplificat pașii de creare a celulelor solare de înaltă eficiență prin aplicarea unui nou amestec de materiale într-un design standard. Structurile de celule solare sunt utilizate în panouri solare pentru a transforma lumina solară în energie electrică.
Amestecul special de materiale – care ar putea fi de asemenea util în componentele semiconductoare – elimină necesitatea unui proces cunoscut sub numele de dopaj care să conducă proprietățile dispozitivului prin introducerea de atomi străini în contactele sale electrice. Acest proces de dopaj adaugă complexitate dispozitivului și îi poate degrada performanțele

Posted: Jan 27, 2016

Simplifying solar cells with a new mix of materials

(Nanowerk News) An international research team has simplified the steps to create highly efficient silicon solar cells by applying a new mix of materials to a standard design. Arrays of solar cells are used in solar panels to convert sunlight to electricity.
The special blend of materials–which could also prove useful in semiconductor components–eliminates the need for a process known as doping that steers the device’s properties by introducing foreign atoms to its electrical contacts. This doping process adds complexity to the device and can degrade its performance.
„The solar cell industry is driven by the need to reduce costs and increase performance,” said James Bullock, the lead author of the study, published this week in Nature Energy („Efficient silicon solar cells with dopant-free asymmetric heterocontacts”). Bullock participated in the study as a visiting researcher at the U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) and UC Berkeley.
The Making of a Solar Cell
In this illustration, the top images show a cross-section of a solar cell design, called DASH, that uses a combination of moly oxide and lithium fluoride. This combination of materials allows the device to achieve high efficiency in converting sunlight to energy without the need for a process known as doping. The bottom images shows the dimensions of the DASH solar cell components. (© Nature Publishing Group)
„If you look at the architecture of the solar cell we made, it is very simple,” said Bullock, of Australian National University (ANU). „That simplicity can translate to reduced cost.”
Other scientists from Berkeley Lab, UC Berkeley, ANU and The Swiss Federal Institute of Technology of Lausanne (EPFL) also participated in the study.
Bullock added, „Conventional silicon solar cells use a process called impurity doping, which does bring about a number of limitations that are making further progress increasingly difficult.”
Most of today’s solar cells use crystalline silicon wafers. The wafer itself, and sometimes the layers deposited on the wafer, are doped with atoms that either have electrons to spare when they bond with silicon atoms, or alternatively generate electron deficiencies, or „holes.” In both cases, this doping enhances electrical conductivity.
In these devices, two types of dopant atoms are required at the solar cell’s electrical contacts to regulate how the electrons and holes travel in a solar cell so that sunlight is efficiently converted to electrical current that flows out of the cell.
Crystalline silicon-based solar cells with doped contacts can exceed 20 percent efficiency–meaning more than 20 percent of the sun’s energy is converted to electricity. A dopant-free silicon cell had not previously exceeded 14 percent efficiency.
The new study, though, demonstrated a dopant-free silicon cell, referred to as a DASH cell (dopant free asymmetric heterocontact), with an average efficiency above 19 percent. This increased efficiency is a product of the new materials and a simple coating process for layers on the top and bottom of the device. Researchers showed it’s possible to create their solar cell in just seven steps.
In this study, the research team used a crystalline silicon core (or wafer) and applied layers of dopant-free type of silicon called amorphous silicon.
Then, they applied ultrathin coatings of a material called molybdenum oxide, also known as moly oxide, at the sun-facing side of the solar cell, and lithium fluoride at the bottom surface. The two layers, having thicknesses of tens of nanometers, act as dopant-free contacts for holes and electrons, respectively.
„Moly oxide and lithium fluoride have properties that make them ideal for dopant-free electrical contacts,” said Ali Javey, program leader of Electronic Materials at Berkeley Lab and a professor of Electrical Engineering and Computer Sciences at UC Berkeley.
Both materials are transparent, and they have complementary electronic structures that are well-suited for solar cells.
„They were previously explored for other types of devices, but they were not carefully explored by the crystalline silicon solar cell community,” said Javey, the lead senior author of the study.
Javey noted that his group had discovered the utility of moly oxide as an efficient hole contact for crystalline silicon solar cells a couple of years ago. „It has a lot of defects, and these defects are critical and important for the arising properties. These are good defects,” he said.
Stefaan de Wolf, another author who is team leader for crystalline silicon research at EPFL in Neuchâtel, Switzerland, said, „We have adapted the technology in our solar cell manufacturing platform at EPFL and found out that these moly oxide layers work extremely well when optimized and used in combination with thin amorphous layer of silicon on crystalline wafers. They allow amazing variations of our standard approach.”
In the study, the team identified lithium fluoride as a good candidate for electron contacts to crystalline silicon coated with a thin amorphous layer. That layer complements the moly oxide layer for hole contacts.
The team used a room-temperature technique called thermal evaporation to deposit the layers of lithium fluoride and moly oxide for the new solar cell. There are many other materials that the research teams hopes to test to see if they can improve the cell’s efficiency.
Javey said there is also promise for adapting the material mix used in the solar cell study to improve the performance of semiconductor transistors. „There’s a critical need to reduce the contact resistance in transistors so we’re trying to see if this can help.”
Source: Lawrence Berkeley National Laboratory

Lăsați-i să vă vadă transpirația: Ce senzori noi pot dezvălui din transpirație(Let them see you sweat:What new wearable sensors can reveal from perspiration)

este un sistem flexibil de senzori care poate măsura metaboliții și electroliții în transpirație, poate calibra datele pe baza temperaturii pielii și poate sincroniza rezultatele în timp real cu un smartphone

76 sept

Noi nanomateriale fluorescente se inspiră din sistemele de antenă ale instalațiilor(New fluorescent nanomaterials take inspiration from plant antenna systems)

a proiectat un set de nanomateriale fluorescente care s-au inspirat din sistemele de antenă ale plantelor.
Aceste noi materiale multifuncționale urmăresc să imite organismele fotosintetice ale plantelor. Aceste microorganisme constau din mii de molecule de clorofilă încorporate într-o matrice de proteine, care le furnizează o orientare / aranjament specific și o distanță eculară. Una dintre caracteristicile principale ale acestor sisteme este funcția antenei, care le permite să recolteze energia solară într-o gamă spectrală largă și să o transporte prin multiple procese eficiente de transfer de energie către un centru de reacție specific, energie.

Posted: Jan 26, 2016

New fluorescent nanomaterials take inspiration from plant antenna systems

(Nanowerk News) One of the biggest temptations facing a scientist is to try and reproduce natural phenomena which are so fascinating given their effectiveness and perfection. This is the aim being pursued by the UPV/EHU’s Molecular Spectroscopy Group which, coinciding with the International Year of Light, has designed a set of fluorescent nanomaterials which have taken their inspiration from the antenna systems of plants.
These new multifunctional materials aim to imitate the photosynthetic organisms of plants. These microorganisms consist of thousands of chlorophyll molecules embedded in a protein matrix, which provides them with a specific orientation/arrangement and intermolecular distance. One of the main characteristics of these systems is their antenna function, which enables them to harvest solar energy in a broad spectral range and transport it by means of multiple, efficient energy transfer processes to a specific reaction centre, where it is finally turned into chemical energy.
Jorge Bañuelos, Iñigo López Arbeloa, and Leire Gartzia
Jorge Bañuelos, Iñigo López Arbeloa, and Leire Gartzia.
It is a well-known fact that solar radiation is made up of many colours (blue, green, yellow, red, etc.), as borne out by the broad range of colours present in the rainbow. The aim of artificial antenna systems is to capture the greatest light range possible so that it can then be efficiently turned into electrical energy (activating of photovoltaic cells)or the emitting of red light, so useful in photonic applications, such as those of biomedical interest. In this respect, and with the aim of coming up with artificial antenna systems, the Molecular Spectroscopy Group has been developing new dyes and photoactive nanomaterials capable of absorbing a broad interval of chromatic radiation which can then be transformed into a red-only emission.
Energy donor and acceptor molecules coexist in these photoactive dyes and nanomaterials developed by the Molecular Spectroscopy Group. The former are highly photostable fluorescent molecules and are responsible for absorbing the light which they then transfer to the acceptor species, which will emit light. This strategy allows the limitations inherent in the red dyes to be reduced; these red dyes are characterised by their reduced light absorption and their low photostability and offer a great advantage in photonic and biophotonic applications as they allow the photostability of the system and detection sensitivity to be improved.
Three different alternatives have been chosen to develop these antenna systems: two of them are based on the encapsulation of fluorescent dyes in either inorganic or organic hosts, and the other one in the assembly of different dyes into a single molecular structure. “We have replaced the protein matrix of the natural systems by synthetic hosts of nanometric dimensions which protect the dyes and provide a significant arrangement that will help to make the energy transfer processes viable and efficient.
Furthermore, with respect to the photoactive part, which is responsible for interacting with the light, the chlorophyll molecules have been replaced by fluorescent molecules many of which have been tuned à la carte,” explained Leire Gartzia, author of the thesis the most salient results of which have been included in the paper published in International Reviews in Physical Chemistry(„Excitation energy transfer in artificial antennas: from photoactive materials to molecular assemblies”).
In the first of the alternatives, the solid matrix chosen to encapsulate the fluorescent dyes is of crystalline aluminosilicate known as Zeolite L., characterised by the fact that it has unidimensional channels and a suitable pore size (7Å) in which the molecules fit like a glove. “This produces a highly ordered nanomaterial that allows the light emission to be modulated to produce a red or white light depending on the control we exert on the efficiency of the energy transfer process,” added the researcher. This chameleon-like property turns them into materials capable of generating new light emitting diodes (LEDs), featuring white-light emitting diodes (WLED), which are so useful in lighting technologies such as liquid crystal displays (LCD).
The other matrix chosen to host dyes consists of polymer nanoparticles capable of hosting inside them extremely high dye concentrations without it becoming aggregated. “Confining the dyes reduces the photodegradation processes, considerably increases their useful service life and encourages the transfer of energy, which has enabled us not only to obtain an antenna system but also tunable red laser radiation that is efficient and long-lasting in stable aqueous suspensions,” pointed out Leire Gartzia.
Finally, they have developed antenna systems made up solely of organic molecules in which the energy donor and acceptor species are linked by a spacer ensuring short intermolecular distances, thus achieving efficiencies in the energy transfer processes of practically 100%. This has meant a great improvement in the harvesting of light across the visible spectrum, leading to exclusively stable bright red which means they are highly recommended as active hosts for tunable lasers in the zone close to the infrared. The main interest in this wavelength is its great tissue penetration capacity, a key in photodynamic therapy with uses in ophthalmology and dermatology and in cancer treatment, for example.
Source: University of the Basque Country

Sinteza microundelor „înscrie” grafenul spre perfecțiune(Microwave synthesis ‘zaps’ graphene to perfection)

Surprinzator, cercetatorii au descoperit ca lichidul lor ionic oligomeric ar putea dizolva suficiente foi exfoliate pentru a se transforma intr-un gel fizic – primul pentru grafenul curat. Acest material tridimensional are o structură intrinsecă, dependentă de câmpul magnetic, care poate duce la aplicații ale dispozitivelor.

Posted: Jan 22, 2016

Microwave synthesis ‘zaps’ graphene to perfection

(Nanowerk News) By employing microwave radiation and a special ionic liquid solvent, RIKEN researchers have developed a quick, efficient and potentially scalable way to produce large quantities of single-layer graphene (Nature Chemistry, „Ultrahigh-throughput exfoliation of graphite into pristine ‘single-layer’ graphene using microwaves and molecularly engineered ionic liquids”).
Graphene can move electrons at extraordinary speeds because of its unique, ultrathin arrangement of carbon atoms. But isolating this two-dimensional material has proved challenging. While early experiments famously used adhesive tape to separate graphite crystals into single-layer graphene, recent efforts have focused on techniques involving liquid-phase exfoliation that mechanically agitate graphite particles dispersed in a solvent. However, this kind of physical shaking makes it difficult to produce structurally intact graphene sheets in high yields.
graphene
A quick and efficient way to produce single-layer graphene using microwaves and ionic liquids has been found by RIKEN researchers.
Takuzo Aida from the RIKEN Center for Emergent Matter Science and colleagues from across Japan theorized that using everyday microwave ovens might improve graphene synthesis. “We envisioned that a perturbation that activates graphite without mechanical force would give highly efficient exfoliation,” explains Michio Matsumoto, a co-author of the study. “We chose to irradiate graphite with microwaves because graphite is a good absorber of microwaves and releases heat after irradiation.”
Successful exfoliation requires a way to keep the freshly peeled materials separated; otherwise, the graphene layers will recoalesce into larger particles. Ionic liquids—salts that remain in a liquefied state—are promising for this role because their charged nature generates strong attractions to graphitic surfaces. Previously, the RIKEN team used ionic liquids based on imidazolium, a positively charged, nitrogen-bearing ring, to exfoliate carbon nanotubes. But, preliminary studies revealed the need for a different chemical approach.
“The face-to-face stacking that binds graphene layers in graphite was too strong for conventional imidazolium compounds to prevent aggregation of graphite,” explains Matsumoto. “To overcome that stacking force, we designed new ionic liquids inspired by the biological concept of multivalent interactions.”
To make ionic ligands that can stick to multiple sites on a graphene layer, the researchers polymerized imidazolium and ethylene oxide atoms into short chains known as oligomers. When they mixed the oligomeric ionic liquid with graphite powder and heated the solution for 30 minutes in a microwave oven, the results were impressive—exfoliation occurred with a yield of 93 per cent and practically all of the graphene produced was in the form of single layers.
“This work brings large-scale synthesis of high-quality graphene one step closer,” says Matsumoto.
Surprisingly, the researchers found their oligomeric ionic liquid could dissolve enough of the exfoliated sheets to turn into a physical gel—a first for pristine graphene. This three-dimensional material has an intriguing, magnetic-field-dependent structure that may lead to device applications.
Source: RIKEN

Betonul de dezghețare ar putea îmbunătăți siguranța pe carosabil, ar putea proteja împotriva spionajului corporativ(De-icing concrete could improve roadway safety , guard against corporate espionage)

Am o terasă în curtea mea, care este făcută din beton conductiv;Echipa de cercetare a lui Tuan demonstrează performanța de dezghețare a betonului la aviația federală în timpul unei faze de testare

77 sept

Producția de nanotehnologii ar putea beneficia de o tehnică nouă de creștere nanosheet(

echivalentul microscopic al unei singure coli de hârtie, o foaie de date 2D este un material care este limitat la doar câteva straturi atomice într-o direcție. Nanomaterialele – materiale care sunt constrânse în cel puțin o dimensiune la maximum un număr de straturi atomice – au proprietăți fizice unice care modifică proprietățile lor electronice și chimice în raport cu materialele lor identice compozite dar convenționale și mai mari. „Ce este frumos cu un nanomaterial 2D este faptul că pentru că este o foaie, este mult mai ușor pentru noi să manipulăm în comparație cu alte tipuri de nanomateriale

Posted: Jan 21, 2016

Nanotechnology manufacturing could benefit from novel nanosheet growth technique

(Nanowerk News) After six years of painstaking effort, a group of University of Wisconsin-Madison materials scientists believe their breakthrough in growing tiny sheets of zinc oxide could have huge implications for the future of nanomaterial manufacturing—and in turn, on a host of electronic and biomedical devices.
The group, led by Xudong Wang, an associate professor of materials science and engineering at UW-Madison, and postdoctoral researcher Fei Wang, has developed a novel technique for synthesizing two-dimensional nanosheets from compounds that do not naturally form the atomic-layer-thick materials. It is the first time such a technique has been successful, and the researchers described their findings 20, January, 2016, in the journal Nature Communications(„Nanometre-thick single-crystalline nanosheets grown at the water–air interface”).
Schematic illustration of the formation of ZnO nanosheets directed by surfactant monolayer
Schematic illustration of the formation of ZnO nanosheets directed by surfactant monolayer.
Essentially the microscopic equivalent of a single sheet of paper, a 2D nanosheet is a material that is constrained to up to only a few atomic layers in one direction. Nanomaterials—materials that are constrained in at least one dimension to a maximum of a handful of atomic layers—have unique physical properties that alter their electronic and chemical properties in relation to their compositionally identical but conventional, and larger, material counterparts. “What’s nice with a 2D nanomaterial is that because it’s a sheet, it’s much easier for us to manipulate compared to other types of nanomaterials,” says Xudong Wang.
Until now, materials scientists were limited to working with naturally occurring 2D nanosheets. These natural 2D structures include graphene, a single layer of graphite, and a limited number of other compounds. Developing a reliable method to synthesize and manufacture 2D nanosheets from other materials has been a goal of materials researchers and the nanotechnology industry for years.
In their technique, the UW-Madison team applied a specially formulated surfactant—a detergent-like substance—onto the surface of a liquid containing zinc ions. Due to its chemical properties, the surfactant assembles itself into a single layer at the surface of liquid, with negatively charged sulfate ions pointed in the direction of the liquid. Those sulfate ions draw the positively charged zinc ions from within the liquid to the surface, and within a couple hours enough zinc ions are drawn up to form continuous zinc oxide nanosheets only a few atomic layers thick.
Xudong Wang first had the idea for using a surfactant to grow nanosheets during a lecture he was giving in a course on nanotechnology in 2009.
“The course includes a lecture about self-assembly of monolayers,” says Xudong Wang. “Under the correct conditions, a surfactant will self-assemble to form a monolayer. This is a well-known process that I teach in class. So while teaching this I wondered why we wouldn’t be able to reverse this method and use the surfactant monolayer first to grow the crystalline face.”
After five years of trial and error with different surfactant solutions, the idea finally paid off about a year ago.
“We are very excited about this,” says Xudong Wang. “This is definitely a new way to fabricate 2D nanosheets, and it has great potential for different materials and for many different applications.”
Already the researchers have has found that the 2D zinc oxide nanosheets they’ve grown are able to function as p-type semiconductor transistors, which is the opposite electronic behavior of naturally occurring zinc oxide. Researchers have for some time attempted to produce zinc oxide with reliable p-type semiconductor properties.
Zinc oxide is a very useful component of electronic materials, and the new nanosheets have potential for use in sensors, transducers and opto-electronics.
But the zinc oxide nanosheets are only the first of what could be a revolution in 2D nanomaterials. Already, the UW-Madison team is applying its surfactant method to growing 2D nanosheets of gold and palladium, and the technique holds promise for growing nanosheets from all sorts of metals that wouldn’t form them naturally.
“It brings a lot of new functional material to this 2D material category,” Xudong Wang says.
Source: University of Wisconsin-Madison

 

Primul material care urmează să fie țesut la nano nivel(First material to be woven at nano level)

Țesutul este un mod bine-cunoscut de fabricare a țesăturii, dar până acum nu a fost niciodată folosit la nivel molecular. Oamenii de știință au reușit acum să tese firele organice într-un material tridimensional, folosind cuprul ca șablon. Noul material este un cadru organic COF, covalent, și se numește COF-505. Ionii de cupru pot fi îndepărtați și adăugați fără a schimba structura de bază și, în același timp, elasticitatea poate fi schimbată în mod reversibil.

Posted: Jan 21, 2016

First material to be woven at nano level

(Nanowerk News) For the first time, scientists have been able to weave a material at molecular level. The research is led by University of California Berkeley, in cooperation with Stockholm University. The new material is presented in the scientific journal Science („Weaving of organic threads into a crystalline covalent organic framework”).
Weaving is a well-known way of making fabric, but has until now never been used at the molecular level. Scientists have now been able to weave organic threads into a three-dimensional material, using copper as a template. The new material is a COF, covalent organic framework, and is named COF-505. The copper ions can be removed and added without changing the underlying structure, and at the same time the elasticity can be reversibly changed.
„It almost looks like a molecular version of the Vikings chain-armour. The material is very flexible,” says Peter Oleynikov, researcher at the Department of Materials and Environmental Chemistry at Stockholm University.
COF’s are like MOF’s porous three-dimensional crystals with a very large internal surface that can adsorb and store enormous quantities of molecules. A potential application is capture and storage of carbon dioxide, or using COF’s as a catalyst to make useful molecules from carbon dioxide.
The research is led by Professor Omar Yaghi at University of California Berkeley. At Stockholm University Professor Osamu Terasaki, PhD Student Yanhang Ma and Researcher Peter Oleynikov have contributed to determine the structure of COF-505 at atomic level from a nano-crystal, using electron crystallography methods.
„It is a difficult, complicated structure and it was very demanding to resolve. We’ve spent lot of time and efforts on the structure solution. Now we know exactly where the copper is and we can also replace the metal. This opens up many possibilities to make other materials,” says Yanhang Ma, PhD Student at the Department of Materials and Environmental Chemistry at Stockholm University.
Source: Stockholm University

Un simplu material artificial poate influența proprietățile luminii vizibile(A simple artificial material can influence the properties of visible light)

Materiale fabricate artificial, numite metamateriale, pot fi utilizate pentru manipularea luminii pentru o serie de aplicații, dar necesită deseori structuri tridimensionale complicate cu caracteristici de câteva zeci de nanometri. Acum, cercetătorii A * STAR au construit o „metasurface” mai simplă, bidimensională, pentru manipularea luminii de transmisie de ultimă generație ( metaforele dielectrice de înaltă transmisie cu 2 controlul fazei la lungimi de undă vizibile „).Principalul dezavantaj al abordărilor anterioare la astfel de componente optice a fost fracțiunea redusă a luminii transmise. Structura creată de echipă a atins o transmisie de vârf de aproape 90%. „Cele mai multe abordări anterioare se bazează pe nanoparticule plasmonice, care au pierderi puternice în spectrul vizibil și de obicei au doar un răspuns rezonant electric”, explică Yu. „Particulele de siliciu pe care le folosim pot avea rezonante atât electrice, cât și magnetice.” Cercetătorii au eliminat aproape atât pierderile, cât și reflexia optică din metastru.

Posted: Jan 20, 2016

A simple artificial material can influence the properties of visible light

(Nanowerk News) Artificially engineered materials called metamaterials can be used to manipulate light for a range of applications, but often require complicated three-dimensional structures with features as small as a few tens of nanometers. Now, A*STAR researchers have constructed a simpler, two-dimensional ‘metasurface’ for state-of-the-art high-transmission light manipulation („High-transmission dielectric metasurface with 2 phase control at visible wavelengths”).
Visualization of the metasurface — a square array of silicon cylinders — manipulating the phase of visible light
Visualization of the metasurface — a square array of silicon cylinders — manipulating the phase of visible light. (Image: A*STAR Data Storage Institute)
A metamaterial is a periodic array of subwavelength-sized elements that interact with an electromagnetic wave’s electric or magnetic component, or both. Each element can be engineered to create a material with optical properties beyond those found in naturally occurring substances. Metasurfaces harness the same idea but are only two-dimensional, and so easier to create.
Yefeng Yu and his co-workers from A*STAR’s Data Storage Institute have created a metasurface that can alter a property of light known as phase (see image). Light can be thought of as a wave with successive peaks and troughs. Moving this wave, to delay or hasten the peaks and troughs, is known as a phase shift. The metasurface designed and created by Yu and the team is capable of complete control over the phase of visible light. By creating certain phase shift distributions it is possible to focus light or even create on-demand holographic images.
The team’s metasurface comprised a square array of silicon disks. Each was 130 nanometers tall with a center-to-center separation of 360 nanometers. Light striking the surface of the structure passed through to the other side, but was deflected by approximately ten degrees. The phase change imparted to the transmitted light by the metasurface was dependent on the radius of the silicon disks. The team showed that varying the radii between 120 and 155 nanometers could produce any desired phase shift.
The main drawback of previous approaches to such optical components has been the low fraction of light transmitted. The structure created by the team reached a peak transmission of almost 90 per cent. “Most previous approaches are based on plasmonic nanoparticles, which have strong losses in the visible spectrum and typically have only an electric resonant response,” explains Yu. “The silicon particles we use can have both electric and magnetic resonances.” The researchers have nearly eliminated both losses and optical reflection from their metasurface.
“To make metasurfaces interesting for practical applications it is important to tune them and dynamically control the phase of incoming light,” says Yu. “This is something our group is now working on.”
Source: A*STAR