The Design of Future Nano-Electronic  Circuits – Free Flowing Electrons in Graphene 



Electrons flowing like liquid in graphene start a new wave of physics – University of Manchester 

A new understanding of the physics of conductive materials has been uncovered by scientists observing the unusual movement of electrons in graphene.

Graphene is many times more conductive than copper thanks, in part, to its two-dimensional structure. In most metals, conductivity is limited by crystal imperfections which cause electrons to frequently scatter like billiard balls when they move through the material.


Now, observations in experiments at the National Graphene Institute have provided essential understanding as to the peculiar behaviour of electron flows in graphene, which need to be considered in the design of future nanoelectronic circuits.

In some high-quality materials, like graphene, electrons can travel micron distances without scattering, improving the conductivity by orders of magnitude. This so-called ballistic regime, imposes the maximum possible conductance for any normal metal, which is defined by the Landauer-Buttiker formalism.

Appearing today in Nature Physics (“Superballistic flow of viscous electron fluid through graphene constrictions”), researchers at The University of Manchester, in collaboration with theoretical physicists led by Professor Marco Polini and Professor Leonid Levitov, show that Landauer’s fundamental limit can be breached in graphene. Even more fascinating is the mechanism responsible for this.

Last year, a new field in solid-state physics termed ‘electron hydrodynamics’ generated huge scientific interest. Three different experiments, including one performed by The University of Manchester, demonstrated that at certain temperatures, electrons collide with each other so frequently they start to flow collectively like a viscous fluid.

The new research demonstrates that this viscous fluid is even more conductive than ballistic electrons. 

The result is rather counter-intuitive, since typically scattering events act to lower the conductivity of a material, because they inhibit movement within the crystal. However, when electrons collide with each other, they start working together and ease current flow.

This happens because some electrons remain near the crystal edges, where momentum dissipation is highest, and move rather slowly. At the same time, they protect neighbouring electrons from colliding with those regions. Consequently, some electrons become super-ballistic as they are guided through the channel by their friends.

Sir Andre Geim said: “We know from school that additional disorder always creates extra electrical resistance. In our case, disorder induced by electron scattering actually reduces rather than increase resistance. This is unique and quite counterintuitive: Electrons when make up a liquid start propagating faster than if they were free, like in vacuum”.

The researchers measured the resistance of graphene constrictions, and found it decreases upon increasing temperature, in contrast to the usual metallic behaviour expected for doped graphene.

By studying how the resistance across the constrictions changes with temperature, the scientists revealed a new physical quantity which they called the viscous conductance. The measurements allowed them to determine electron viscosity to such a high precision that the extracted values showed remarkable quantitative agreement with theory.


Source: University of Manchester

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. 

Super Capacitors Could Make the Tesla ‘Battery Model for an EV World’ Obsolete: Videos



Tesla’s growth has been built on its pioneering battery technology but they’re slow to charge, have limited lifetimes and are heavy. The latest research on supercapacitors does away with all of that and may mean ‘Tesla Battery Model for an EV World’ is a losing bet (Watch Videos Below)

Introduction

Transportation is the largest consumer of oil and the globally, it’s the biggest source of pollution, greenhouse gases, soot and fine particulates; gasoline and diesel have fuelled global transport and been the lifeblood of the international oil majors and national oil companies.

That, however, may be changing. Oil’s power density and affordable price has made alternatives non-starters, pushed many mass transit systems to bankruptcy, and made auto, tyre, road construction, and insurance companies rich.

Fuel energy density including supercapacitors

The Tesla effect

Then came Tesla, for the first time offering a slick, high-performance car with reasonable range.

Currently too expensive for the mass market, Tesla has nevertheless challenged the internal combustion engine (ICE) industry and forced virtually all car markers to get into electric vehicles.

With a $5 billion gigafactory just completed in July 2016 near Reno, Nevada. Tesla is promising to move mainstream, offering more affordable cars with decent range. Tesla-Gigafactory-Nevada

That is all wonderful. But Tesla and all other electric and hybrid cars still suffer from lack of charging infrastructure, and even when that is in place, drivers will have to take long breaks on long drives to recharge their batteries. 
Depending on the details, 90 minutes or more are typically needed to more-or-less recharge an empty car battery, an annoying wait compared to a five-minute fillup at the corner gas station.

 

Tesla’s growth has been built on its pioneering battery technology but they’re slow to charge, have limited lifetimes and are heavy. The latest research on supercapacitors does away with all of that and may mean ‘Tesla Battery Model for an EV World’ is a losing bet


Battery Woes

Tesla Battery Pack 2014-08-19-19.10.42-1280Moreover, even with Tesla’s slick design, the batteries are heavy and can only be charged/discharged so many times, after which their performance drops. Trucks and heavy-duty vehicles pose even more difficult challenges if they are not recharged frequently – not always convenient or practical. Batteries, in other words, are not a perfect substitute for cheap petrol which is available nearly everywhere you go.

What would be ideal is a light, inexpensive battery that can pack large amounts of energy in a small space, can be charged more or less instantly, and discharged more or less indefinitely without loss of performance. 

That would be the holy grail of storage, not only challenging the ICEs but also making Tesla’s gigafactory virtually obsolete before it starts mass production.


Super Potential for Supercapacitors

A new generation of supercapacitors made from cheap and plentiful material – now in laboratories – is expected to become commercial in three to five years. According to UCLA Professor Richard Kaner, the company he is affiliated with, Nanotech Energy, is using graphene as the basic medium for storing energy. (Also See Video for ‘Tenka Energy’ below)

As the technology moves out of the laboratory, he expects it to initially find a role in high-value applications such as mobile phones and computers, followed by other applications such as electric vehicles.

Supercapacitors Recharge Rate

The ability to fast-charge a supercapacitor in, say, two minutes or so, will solve the range anxiety associated with current EVs. 
Imagine pulling into an electric charging station and getting more or less fully recharged in the amount of time it takes to fill up your tank with gas. Who needs clunky, noisy, polluting cars, or even Tesla batteries?

The same fast-charging supercapacitors can power mass transit buses in cities around the world. If the bus’ supercapacitor can be charged in two minutes or less, then every bus stop can be a charging station, allowing the bus to travel long distances without ever running out of juice. That would be a game changer.

Tesla, which is facing many daunting deadlines and competition from multiple directions, may find that its gigafactory is a losing bet if supercapacitors come to deliver as their proponents claim.

Now THAT … That would be yet another game changer!

From ‘The Energy Analyst’

 

Watch: Video Presentation of New ‘Tenka Power Max SuperCap’

Printed Organic Photovoltaics: OPVIUS


Printed Organic PHVLTCS 53

By developing self-adhesive OPV-films, OPVIUS together with S+L Selbstklebeprodukte GmbH are broadening the horizons for OPV products and OPV integration.
Imbedding OPVIUS modules in transparent carrier materials, for example glass or foil membranes, has been possible for some time.
Their integration into laminated polycarbonate sheets was recently presented as part of an installation at the Climate-Pavilion at the State Horticultural Show in Thüringen.

The integration techniques developed up until now are mainly aimed at integration, that is to say embedding the module in the carrier material by way of a lamination procedure. This is generally limited to transparent materials and predominantly serves the market for original equipment manufacturers.
OPVs can be integrated directly into construction materials whilst they are manufactured, and are therefore installed together with these materials.

By developing self-adhesive OPVIUS products, an additional solution can now be provided that will be of interest when retrofitting existing surfaces, as well as for use on non-transparent carrier materials.
S+L Selbstklebeprodukte GmbH’s many years of experience working with stickers for public transport as well as the manufacturing of classic car decals is of central interest to OPVIUS GmbH.

POPVTCS 2 download

Their expertise in various applications, processing procedures, and working with new technologies in the field of foils, all build the foundations of a joint collaboration.
Combined with OPVIUS’ production technology and the resulting freedom in terms of colour and form, this expertise will enable users to obtain customised products that are easy to install. This will significantly expand the range of applications of printed organic photovoltaics.
“By developing self-adhesive OPV foils, we can bring our products further into the market, and make them available to an additional user-group. OPVIUS stickers provide many new solutions, particularly for already existing surfaces” says Hermann Issa, Senior Director, Business Development and Sales, OPVIUS.
“The need for high quality in order to ensure a good and lasting adhesive bond is frequently underestimated. In this regard, in terms of cooperation, S+L Selbstklebeprodukte GmbH was our first choice for implementation.
It has paid off.”   Christian Lins, Business Director of S+L Selbstklebeprodukte GmbH added: “A good adhesion needs to work both visually and flawlessly in terms of function, and needs to last in both indoor and outdoor settings.

In addition, we had to look at the properties of the OPVs, and adjust our stickers to the OPVIUS products. Here, our great wealth of experience of adhesion to a large range of substrates, for example trains and buses, paid off, as they also need to be long-lasting and visually perfect under conditions of constant exposure.”
Source and top image: OPVIUS Learn more at the next leading event on the topic:

Energy Independent Electric Vehicles 2017 on 27 – 28 Sep 2017 in TU Delft, Delft, Netherlands hosted by IDTechEx.

 

Read more at:

http://www.electricvehiclesresearch.com/articles/11478/printed-organic-photovoltaics

Flexible Batteries Power the Future of Wearable Technology: U of Manchester


flexiblebattCredit: University of Manchester

The rapid development of wearable technology has received another boost from a new development using graphene for printed electronic devices.

New research from The University of Manchester has demonstrated flexible battery-like devices printed directly on to textiles using a simple screen-printing technique.

The current hurdle with wearable technology is how to power devices without the need for cumbersome battery packs. Devices known as supercapacitors are one way to achieve this. A  acts similarly to a battery but allows for rapid charging which can fully charge devices in seconds.

Now a solid-state flexible supercapacitor device has been demonstrated by using conductive -oxide ink to print onto cotton fabric. As reported in the journal 2-D Materials the printed electrodes exhibited excellent mechanical stability due to the strong interaction between the ink and textile substrate. Graphene-Ribbon-Developing-Flexible-Li-Ion-Battery

Further development of graphene-oxide printed supercapacitors could turn the vast potential of  into the norm. High-performance sportswear that monitors performance, embedded health-monitoring devices, lightweight military gear, new classes of  and even wearable computers are just some of the applications that could become available following further research and development.

To power these new wearable devices, the energy storage system must have reasonable mechanical flexibility in addition to high energy and power density, good operational safety, long cycling life and be low cost.

 Credit: University of Manchester

Dr Nazmul Karim, Knowledge Exchange Fellow, the National Graphene Institute and co-author of the paper said: “The development of graphene-based flexible textile supercapacitor using a simple and scalable printing technique is a significant step towards realising multifunctional next generation wearable e-textiles.”

“It will open up possibilities of making an environmental friendly and cost-effective smart e-textile that can store energy and monitor human activity and physiological condition at the same time”.

Graphene-oxide is a form of graphene which can be produced relatively cheaply in an ink-like solution. This solution can be applied to textiles to create supercapacitors which become part of the fabric itself.

Kaust wearablebattery1Dr Amor Abdelkader, also co-author of the paper said: “Textiles are some of the most flexible substrates, and for the first time, we printed a stable device that can store energy and be as flexible as cotton.

“The  is also washable, which makes it practically possible to use it for the future smart clothes. We believe this work will open the door for printing other types of devices on  using 2-D-materials inks.”

The University of Manchester is currently completing the construction of its second major graphene facility to complement the National Graphene Institute (NGI). Set to be completed 2018, the £60m Graphene Engineering Innovation Centre (GEIC) will be an international research and technology facility.

The GEIC will offer the UK the unique opportunity to establish a leading role in graphene and related two-dimensional materials. The GEIC will be primarily industry-led and focus on pilot production and characterisation.

 Explore further: Researchers develop simple way to fabricate micro-supercapacitors with high energy density

 

 

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
 High Specific Power
 Simple Manfacturing Process
 Low Manufacturing Cost
 Rapid Charge/ Re-Charge
 Flexible Form Factor
 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



Novel Bendable Batteries Powered by Cellular Fluids


This is an artistic rendering of fiber-shaped implantable batteries using biocompatible electrolytes. Credit: Guo et al.



The next generation of safer batteries could be powered by an unconventional source.

Researchers in China designed alternatives to lithium-ion batteries that are more flexible than their traditional counterparts and can run on body inspired liquids like normal IV saline solutions and cell-culture mediums.

The idea for these prototypes occurred when the researchers focused on the mechanical-stress demands of wearable electronics, like smartwatches, and the safety requirements of implantable electronics.

One challenge regarding lithium-ion batteries is that they need strong structural reinforcement to ensure hazardous chemical don’t leak out from the container. This requires an abundance of protective materials, which make them bulky and unbendable.

First, the team resolved the leakage issue by replacing the flammable liquids found in these batteries for inexpensive, environmentally conscious sodium-ion solutions like the IV solutions and cell-culture mediums. Both liquids are safe, since the IV solution is the same one used to help patients in the hospital while the cell-culture medium is infused with amino acids, sugars, vitamins, and other elements that mimic the fluid surrounding human cells.

To avoid hazards linked to possible leakage, the scientists then created two batteries.

One was a 1D fiber-shaped battery embedded with nanoparticles of electrode material encompassing a carbon nanotube backbone. The other one was a 2D “belt” shaped-battery, which the engineers adhered thin electrode films to a net of steel strands.

Experiments indicated both batteries were able to outperform most of the wearable lithium ion batteries on factors like charge holding capacity and power output. The performance held up even when the study authors folded and bent the batteries to simulate the impact of wrapping a sensor, watch, or similar device around an arm.

“We can implant these fiber-shaped electrodes into the human body to consume essential oxygen, especially for areas that are difficult for injectable drugs to reach,” said co-senior author Yonggan Wang, a chemistry professor at Fudan University and the Collaborative Innovation Center of Chemistry for Energy Materials, in a statement.

Some defects did emerge during the experiments. The carbon nanotubes that comprise the skeleton of the 1D battery can also accelerate the transformation of dissolved oxygen into hydroxide ions, which would initiate a process that hampers battery performance if left uncontrolled.

However, this process could yield therapeutic potential for cancer and bacterial infections.

“Deoxygenation might even wipe out cancerous cells or pathogenic bacteria since they are very sensitive to changes in living environment pH. Of course, this is hypothetical right now, but we hope to investigate further with biologists and medical scientists,” continued Wang.

The study was published in the journal Cell Press.

Metal-free nanoparticle could expand MRI use, tumor detection



What might sound like the set-up to a joke actually has a clinical answer: Both groups can face health risks when injected with metal-containing agents sometimes needed to enhance the color contrast — and diagnostic value — of MRIs.

But a new metal-free nanoparticle developed by the University of Nebraska-Lincoln and MIT could help circumvent these health- and age-related barriers to the powerful diagnostic tool, which physicians use to investigate or confirm a broad range of medical issues.

The team’s nanoparticle contains a non-metallic molecule that enhances MRI contrast to help distinguish among bodily tissue, a task typically performed by contrast agents containing gadolinium or other metals (ACS Central Science, “Nitroxide-Based Macromolecular Contrast Agents with Unprecedented Transverse Relaxivity and Stability for Magnetic Resonance Imaging of Tumors”).

It also survived long enough to congregate around tumors in mice, suggesting the nanoparticle could help detect cancers as well as its metallic counterparts while eliminating concerns about the long-term accumulation of metal in the body.


MRIs of a mouse before (first and third rows) and 20 hours after being injected with a low dose (second row) and high dose (fourth row) of a new metal-free contrast agent developed by Nebraska and MIT. The yellow arrow indicates the location of a tumor. (click on image to enlarge)

Contrast in styles

The molecules residing in the team’s nanoparticle belong to a family known as the nitroxides, which are among the most promising alternatives to the metallic agents often injected into patients prior to undergoing MRIs.

But antioxidants in the body typically begin breaking down nitroxides within minutes, limiting how long they can enhance the contrast of an MRI. And the team’s molecule of interest — a so-called organic radical — has just a single electron, a fact that normally inhibits how much contrast it can produce.

Gadolinium and other metals possess multiple electrons that help them influence how the magnetic waves produced by an MRI interact with water molecules in tissue. This magnetic influence, or relaxivity, ultimately dictates the strength of contrast signals that get converted into the familiar multicolored MRIs.

So Nebraska chemist Andrzej Rajca began collaborating with colleagues at MIT to design a metal-free nanoparticle that would exhibit stability and relaxivity comparable to gadolinium’s. Rajca previously designed a nitroxide that, when embedded within relatively small nanoparticles, displayed a relaxivity several times greater than its predecessors.

This time around, MIT researchers incorporated Rajca’s nitroxide into a large nanoparticle known as a brush-arm star polymer. The process involved assembling polymers into a spherical structure with a water-attracting core and water-repelling shell, then squeezing multitudes of nitroxide molecules between that core and shell.

The team found that packing so many nitroxides into such tight quarters effectively multiplied their individual relaxivity values, resulting in a nanoparticle with a relaxivity about 40 times higher than a typical nitroxide.

“You don’t need much of the (new) contrast agent to see a good image,” said Rajca, Charles Bessey Professor of chemistry.

The nanoparticle’s polymer shell also helped slow the advance of the disruptive antioxidants enough to prolong the nitroxides’ lifespan from roughly two hours to 20. By injecting mice with their agent, the researchers showed that the nanoparticle’s longevity and large size allow it to reach tumors and differentiate them from normal tissue. Even in doses larger than those typically needed for MRIs, the team’s contrast agent showed no signs of toxicity in human cells or mice.

Source: University of Nebraska-Lincoln

Harnessing the Functionality and ‘Power’ of Perovskites for Better Solar and LED’s



Originally a mineral, the perovskite used in today’s technology is quite different from the rock found in the Earth mantle. 

A “perovskite structure” uses a different combination of atoms but keep the general 3-dimensional structure originally observed in the mineral, which possesses superb optoelectronic properties such as strong light absorption and facilitated charge transport. These advantages qualify the perovskite structure as particularly suited for the design of electronic devices, from solar cells to lights.

The accelerating progress in perovskite technology over the past few years suggest new perovskite-based devices will soon outperform current technology in the energy sector. 

The Energy Materials and Surface Sciences Unit at OIST led by Prof. Yabing Qi is at the forefront of this development, with now two new scientific publications focusing on the improvement of perovskite solar cells and a cheaper and smarter way to produce emerging perovskite-based LED lights.

An extra layer in a solar cell “sandwich”

Perovskite-based solar cells is a rising technology forecast to replace the classic photovoltaic cells currently dominating the industry. 




In just seven years of development, the efficiency of perovskite solar cells increased to almost rival – and is expected to soon overtake – commercial photovoltaic cells, but the perovskite structure still plagued by a short lifespan due to stability issues. 


OIST
scientists have made constant baby steps in improving the cells stability, identifying the degradations factors and providing solutions towards better solar cell architecture.

The new finding, reported in the Journal of Physical Chemistry B (“Engineering Interface Structure to Improve Efficiency and Stability of Organometal Halide Perovskite Solar Cells”), suggests interactions between components of the solar cell itself are responsible for the rapid degradation of the device. 

More precisely, the titanium oxide layer extracting electrons made available through solar energy – effectively creating an electric current – causes unwanted deterioration of the neighboring perovskite layer. 

Imagine the solar cell as a multi-layered club sandwich: if not properly assembled, fresh and juicy vegetables in contact with the bread slices will make the bread very soggy in a matter of hours. 

But if you add a layer of ham or turkey between the vegetables and the bread, then your sandwich stays crisp all day in the lunchroom refrigerator.


A perovskite-based layer includes many layers, including for example the electrodes on both sides, and the perovskite in the middle. The addition of a polystyrene layer in-between prevents the titanium oxide layer to deteriorate the perovskite, but does not affect the overall power conversion efficiency. (© American Chemical Society)

This is exactly what the OIST researchers achieved: they inserted in the solar cell an additional layer made from a polymer to prevent direct contact between the titanium oxide and the perovskite layers. 
This polymer layer is insulating but very thin, which means it lets the electron current tunnel through yet does not diminish the overall efficiency of the solar cell, while efficiently protecting the perovskite structure.

“We added a very thin sheet, only a few nanometers wide, of polystyrene between the perovskite layer and the titanium oxide layer,” explained Dr. Longbin Qiu. 

“Electrons can still tunnel cross this new layer and it does not affect the light absorption of the cell. This way, we were able to extend the lifetime of the cell four-fold without loss in energy conversion efficiency”.

The lifespan of the new perovskite device was extended to over 250 hours – still not enough to compete with commercial photovoltaic cells regarding stability, but an important step forward toward fully functional perovskite solar cells.

Manufacturing LED lights from gasses

The bipolar electronic properties of the perovskite structure not only confer them the ability to generate electricity from solar energy but also can convert electricity into vivid light. Light-Emitting Diode – LED – technology, omnipresent in our daily life from laptop and smartphone screens to car lights and ceiling tubes, currently relies on semi-conductors that are difficult and expensive to manufacture. Perovskite LEDs are envisaged to become the new industry standard in the near future due to the lower cost and their efficiency to convert power into light. Moreover, by changing the atomic composition in the perovskite structure, perovskite LED can be easily tuned to emit specific colors.

The manufacturing of these perovskite LEDs is currently based on dipping or covering the targeted surface with liquid chemicals, a process which is difficult to setup, limited to small areas and with low consistency between samples. To overcome this issue, OIST researchers reported in the Journal of Physical Chemistry Letters (“Methylammonium Lead Bromide Perovskite Light-Emitting Diodes by Chemical Vapor Deposition”) the first perovskite LED assembled with gasses, a process called chemical vapor deposition or CVD.

“Chemical vapor deposition is already compatible with the industry, so in principle it would be easy to use this technology to produce LEDs,” commented Prof. Yabing Qi. “The second advantage in using CVD is a much lower variation from batch to batch compared to liquid-based techniques. Finally, the last point is scalability: CVD can achieve a uniform surface over very large areas”.

Like the solar cell, the perovskite LED also comprises many layers working in synergy. First, an indium tin oxide glass sheet and a polymer layer allow electrons into the LED. The chemicals required for the perovskite layer – lead bromide and methylammonium bromide – are then successively bound to the sample using CVD, in which the sample is exposed to gasses in order to convert to perovskite instead of typically solution-coating processes with liquid. In this process, the perovskite layer is composed of nanometer-small grains, whose sizes play a critical role in the efficiency of the device. Finally, the last step involves the deposition of two additional layers and a gold electrode, forming a complete LED structure. The LED can even form specific patterns using lithography during the manufacturing process.

Perovskite LED fabrication


Top: the perovskite LED sits in a furnace, where the Methylammonium Bromide (MABr) in gaseous form will be introduced into the system and deposit on the LED surface. Bottom left: a glass-based LED, glowing green when electricity is applied. Bottom right: size and shapes of the perovskite grains on the surface of the LED. (© American Chemical Society)

“With large grains, the surface of the LED is rough and less efficient in emitting light. The smaller the grain size, the higher the efficiency and the brighter the light,” explained Dr. Lingqiang Meng. “By changing the assembly temperature, we can now control the growth process and the size of the grains for the best efficiency”.

Controlling the grain size is not the only challenge for this first-of-its-kind assembling technique of LED lights.

“Perovskite is great, but the choice in the adjacent layers is really important too,” added Dr. Luis K. Ono. “To achieve high electricity-to-light conversion rates, every layer should be working in harmony with the others.”

The result is a flexible, thick film-like LED with a customizable pattern. The luminance, or brightness, currently reaches 560 cd/m2, while a typical computer screen emits 100 to 1000 cd/m2 and a ceiling fluorescent tube around 12,000 cd/m2.

Perovskite-LED


This large perovskite-LED was produced using chemical vapor deposition and connect to a 5V current, illuminating through an OIST pattern etched on the surface. (© American Chemical Society)

“Our next step is to improve the luminance a thousand-fold or more,” concluded Dr. Meng. “In addition, we have achieved a CVD-based LED emitting green light but we are now trying to repeat the process with different combinations of perovskite to obtain a vivid blue or red light”.

Source: By Wilko Duprez, Okinawa Institute of Technology

MIT team creates flexible, transparent solar cells with graphene electrodes



Researchers at the Massachusetts Institute of Technology (MIT) have developed flexible and transparent graphene-based solar cells, which can be mounted on various surfaces ranging from glass to plastic to paper and tape. The graphene devices exhibited optical transmittance of 61% across the whole visible regime and up to 69% at 550 nanometers. The power conversion efficiency of the graphene solar cells ranged from 2.8% to 4.1%.

MIT team’s flexible, transparent solar cell with graphene electrodes image

A common challenge in making transparent solar cells with graphene is getting the two electrodes to stick together and to the substrate, as well as ensuring that electrons only flow out of one of the graphene layers. Using heat or glue can damage the material and reduce its conductivity, so the MIT team developed a new technique to tackle this issue. Rather than applying an adhesive between the graphene and the substrate, they sprayed a thin layer of ethylene-vinyl acetate (EVA) over the top, sticking them together like tape instead of glue.

The MIT team compared their graphene electrode solar cells against others made from standard materials like aluminum and indium tin oxide (ITO), built on rigid glass and flexible substrates. The power conversion efficiency (PCE) of the graphene solar cells was far lower than regular solar panels, but much better than previous transparent solar cells. This is a positive advancement, obviously.
Samples of solar cells using electrodes of different materials for testing image


Efficiency is often a trade-off from the graphene solar cells being flexible and transparent. In that regard the cells performed well, transmitting almost 70% of the light in the middle of the human range of vision. Hopefully the numbers will continue to improve. According to the researchers’ calculations, the efficiency of these graphene solar cells could be pushed as high as 10% without losing any transparency, and doing just that is the next step in the project. The researchers are also working on ways to scale up the system to cover windows and walls.
Source:  newatlas