The New OLEDs by Philips

See here an interesting video of the OLED (Organic Light-Emitting Diode) technology from Philips. This new technology is about to enter into our lifes providing a revolution in the concept of televisions, screens and interior lighting.

For more information you can visit the Philips OLED technology Luminable.

ITO Free Electrodes for OLEDS

ITO is the abbreviation of indium tin oxide, the standard transparent conductor for most of commercial optoelectronic devices. There are not many materials being transparent and electrically conductive at the same time, for this reason and for its limited supply, its cost and demand is increasing and it is becoming crucial to find a cost effective substitute.

Researchers from the Ames Laboratory at Iowa State University (USA) have recently published in the Advanced Materials Journal a possible alternative to ITO, based on PEDOT:PSS (poly (3,4-ethylene dioxythiophene):poly(styrene sulfonate)). This conductive polymer has been around for about 15 years, but until recently it was not conductive and transparent enough to be consider as an alternative to ITO. Using a multi-layering technique and special treatments, Joe Shinar and co-workers have been able to fabricate ITO-free OLEDs with enormously improved properties. They report a 44% higher efficiency compared with a standard ITO device.

Another important advantage of PEDOT:PSS versus ITO is that it is more suitable for flexible substrates, which is one of the main benefit of OLEDs versus LEDs. ITO is a ceramic, so more brittle in nature that a polymer. This achievement can lead to more affordable and cost-effective manufacturing of screen and lighting technologies, which are going to be part of our lives in a very near future.

has been around for about 15 years. Until recently, the material wasn't sufficiently conductive or transparent enough to be a viable ITO substitute, Shinar said. But by using a multi-layering technique and special treatments, Cai and his fellow scientists were able to fabricate PEDOT:PSS OLEDs with vastly improved properties.

Read more at: http://phys.org/news/2012-12-scientists-indium-free-light-emitting-diodes.html#jCp

has been around for about 15 years. Until recently, the material wasn't sufficiently conductive or transparent enough to be a viable ITO substitute, Shinar said. But by using a multi-layering technique and special treatments, Cai and his fellow scientists were able to fabricate PEDOT:PSS OLEDs with vastly improved properties.

Read more at: http://phys.org/news/2012-12-scientists-indium-free-light-emitting-diodes.html#jCp

has been around for about 15 years. Until recently, the material wasn't sufficiently conductive or transparent enough to be a viable ITO substitute, Shinar said. But by using a multi-layering technique and special treatments, Cai and his fellow scientists were able to fabricate PEDOT:PSS OLEDs with vastly improved properties.

Read more at: http://phys.org/news/2012-12-scientists-indium-free-light-emitting-diodes.html#jCp

has been around for about 15 years. Until recently, the material wasn't sufficiently conductive or transparent enough to be a viable ITO substitute, Shinar said. But by using a multi-layering technique and special treatments, Cai and his fellow scientists were able to fabricate PEDOT:PSS OLEDs with vastly improved properties.

Read more at: http://phys.org/news/2012-12-scientists-indium-free-light-emitting-diodes.html#jCp

New Solid State Dye Sensitised Solar Cells in Oxford

All-solid state dye-sensitised solar cells (DSCs) have experienced an impressive growth this year. In these cells the liquid electrolyte is replaced by a solid semiconductor, which can be processed from solution and then penetrate easily the nanoporous matrix of the TiO2. These novel semiconductors belong to the perovskites family and they can even act as the light absorber and the hole or electron conductor.

Apart from the Nature paper from Mercouri Kanatzidis' Group, where they show a cell with CsSnI2.95F0.05 exceeding 10% efficiency, Henry Snaith and his collaborators have reported a 10.9 % efficiency DSC based on the CH3NH3PbI2Cl perovskite. Surprisingly this result has been achieved without using TiO2. A nanostructured insulating Al2O3 film serving as a "scaffold" suffices to obtain this outstanding achievement. The perovskite itself conducts electrons more quickly than the TiO2. These results has been recently published in Science and Dr. Henry Snaith has set up a spin-out company from Oxford University to develop and commercialise this novel technology and all the intellectual property created by his group during their intense research. Oxford Photovoltaics is the name of this company that focus its efforts in building integrated photovoltaics.

However, despite the success of these novel devices, the scientific community have expressed concerns about the reproducibility and stability of some of the reported devices. We will probably have to wait some time to see that other groups are able to reproduce these results and they can be produced on a large scale. This final task is now under development at Oxford Photovoltaics. 

First All-Carbon Solar Cell

Few weeks ago, the first solar cell with all its components made of carbon-based materials has been published in ACS Nano journal. The work has been developed by researchers in Standford University (USA), University of Rochester (USA) and Nankai University (China). Previously a solar cell with their active layer made using carbon materials was reported, but Zhenan Bao and her colleagues have fabricated this new cell with even their electrodes based on carbon as well. They replaced the silver and ITO (Indium tin oxide) used in conventional electrodes with graphene and single-walled carbon nanotubes exhibiting extraordinary electrical conductivity and light-absorption properties. For the active layer, the scientists used carbon nanotubes and C60 derivatives. 

 

The all-carbon cell absorbs near-infrared wavelengths of light, leading to a laboratory efficiency of less than 1 percent (0.0041 %). However, as the inventors says, there is still plenty of room for improvement that could lead in the future to reach >1 % efficiencies. The main contribution of this new cell is its potential as an alternative to the expensive materials used in photovoltaic devices today, since the thin film prototype is made of carbon materials that can be coated from solution, are low-cost and Earth-abundant. 

Impedance Spectroscopy for Energy Conversion Devices

Impedance Spectroscopy (IS) has become a major tool for the analysis and understanding of energy conversion devices. Since the appearance of nanostructured and nanoporous materials as well as organic and molecular conductors, new models have been developed in the framework of this powerful technique to understand properly the new features observed in these novel materials. The main advantage of the technique is the possibility in most of the cases of separating all the physical processes that take place in the device or material, being able to provide in a single measurement most of the physical parameters needed to characterise the system. However, in order to properly extract the physical information from this technique an in depth knowledge and skilled interpretation is required, what makes it hard to apply to many scientists.


The Photovoltaic and Optoelectronic Devices (POD) group at Universitat Jaume I in Spain are the pioneers in the development of this knowledge and expertise and have successfully applied IS analysis to a wide range of energy conversion devices, such as Dye-Sensitised Solar Cells, Organic Solar Cells, Quantum Dots Solar Cells and more recently Photoelectrochemical Water Splitting devices. Prof. Juan Bisquert, the POD group leader, has shared in his blog a very interesting presentation covering the use of IS in all these devices mentioned. It can be accessed directly above or by clicking here.

2012 Physics Nobel Prize

Few days ago, the new Nobel Prize in Physics was announced by the Royal Swedish Academy of Science. This year Serge Haroche (left in the picture) of the College of France in Paris, and David Wineland (right in the picture) of the National Institute of Standards and Technology in Boulder, Colorado, have been awarded for the ground-breaking experimental methods that enable measuring and manipulation of individual quantum systems.

They have independently invented and developed methods for measuring and manipulating individual particles while preserving their quantum-mechanical nature, in ways that were previously thought unattainable. Haroche uses atoms as a sensitive probe of light particles trapped in a cavity, whereas Wineland takes the opposite approach, using light to measure the quantum states of atoms. Their ground-breaking methods have enabled to take the very first steps towards building a new type of super fast computer based on quantum physics. Perhaps the quantum computer will change our everyday lives in this century in the same radical way as the classical computer did in the last century. The research has also led to the construction of extremely precise clocks that could become the future basis for a new standard of time, with more than hundred-fold greater precision than present-day caesium clocks.

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Progress with Graphene

Since its discovery, graphene has been the most promising material under development nowadays. Its supreme properties make it suitable for a wide range of applications that could revolutionise many current technologies. However, switching to a new technology is usually a lengthy and expensive process that could present many inconveniences. Novoselov, the Nobel laureate, et al. analyse this fact and review the current progress in grapehene in a recently published article in Nature.

 Some of these promising applications are:

• Flexible electronics: Graphene (highly doped samples) shows sheet resistance of 30 ohm per square and excellent transmittance of 97.7% per layer. Graphene also has outstanding mechanical flexibility and strength, what makes it suitable for rollable devices.

• Photodetectors: Graphene can be used for a wide spectral range from ultraviolet to infrared, with a high operating bandwidth, which makes it suitable for high-speed data communications.

• Paints: Graphene-based paints can be used for conductive ink, antistatic, electromagnetic-interference shielding, and gas barrier applications. In addition, over the next few years chemical derivatives of graphene will be developed to control the conductivity and optical opacity of the products.

• Supercapacitors: Graphene offers high intrinsic electrical conductivity, an accessible and defined pore structure, good resistance to oxidative processes and high temperature stability

Although, a lot of applications exists, it will take some few years till new graphene products impact the market. It is likely that printable and flexible electronics, flexible solar cells and supercapacitors will be the first ones to appear.

Challenges for a Sustainable Energy Future

Nobody discusses that one of the main problems that the society has to face in the future is the problem to achieve sustainable energy sources that will not damage our planet. Few days ago, an excellent article has been published in Nature about this topic. There is a sentence on it that specially stood out to me:

"The world needs another industrial revolution in which our sources of energy are affordable, accessible and sustainable."

 This sentence is given after the introduction of the beginning of the industrial revolution in the mid-eighteenth century, when we started to develop our ability to exploit fossil fuel energy sources. The carbon emissions that result from this capability have created significant climate-change risks nowadays.

We tend to think that intense research efforts are needed to improve efficiencies of renewable energy devices and systems, but this is a significant step out of some others. To achieve the full economic benefit of these variable sources of energy, they need to be integrated with the current sources into transmission and distribution, load response and storage. A transformation of the electricity system on the basis of technology advances and new operating procedures, business models and regulatory approaches is extremely important.

The last part of the articlee remarks that due to the fact that we have improved the technologies in finding and extracting fossil fuels, the cost of these forms of energy could remain competitive with carbon-free sources for decades. This does not favour the urgent need to use renewable sources, what makes essential the contribution or government policies to stimulate the invention, innovation, and align the market forces.

There is increasing evidence that the increment in the number of extreme weather events (extreme temperatures, floods, wildfires, droughts and storms) over the past 30 years are linked with climate change. It is our responsibility to act now and it is not only a task for scientist, it requires the engament of scientific, financial, and public-policy communities, as well as the general public.

Transparent Polymer Solar Cell

Some people might be surprised and sceptical when reading the title of this post, since they might presume that a material absorbing light cannot be transparent. However this could be possible since the sunlight spectrum is not only formed by UV-Visible light but it also has a large percentage (~50 %) of IR light. If we can make a cell only absorbing UV and/or IR, we can have a transparent device, which is the novel polymer solar cell presented by Yang Yang and collaborators from the University of California, Los Angeles (UCLA).

These cells open the possibility of energy harvesting in a new wide range of applications such as windows and portable electronics, where you could be able to charge your mobile from the energy collected by the screen. This novel device relies on two achievements. First, a polymeric material sensitive to near-IR light but highly transparent to visible light. Secondly, high performance Ag nanowire-based composite works as the transparent conductive material in the cathode, role usually adopted by different metals that are opaque. The device reaches almost 70% transparency at 550 nm with an overall 4% efficiency.

[Article link]

Nanohub: A very useful nanoscience website

I have recently discovered a really useful and interesting website dedicated to nanoscience and nanotechnology: nanohub. It pays attention to many aspects of nanotechnology: simulation tools, dissemination, teaching, collaboration, publishing, etc. It really covers nanoscience as a whole, including all disciplines (chemistry, physics, engineering, etc.) and it is well organised, clear and with the most recent web technology. It offers a large amount of resources from courses, workshops, lectures and seminars, all recorded, up to a huge amount of simulations for structures, transport coefficients, key parameters, etc.

I found this website when I was looking for some background regarding the microscopic view of thermoelectricity, which is really difficult to find in the web and textbooks, may be due to the fact that the physics of thermoelectrics, at least bulk materials, is known since some decades ago. On this respect I found very useful the lectures from the course Near-Equilibrium Transport: Fundamentals and Applications by Mark Lundstrom. You can learn the basics of thermoelectricity transport coefficients from them.

There are lots of more information available I have not explored in detail, but I will do it for sure. Do not hesitate to have a look to it either if you are student, researcher or professor, it is helpful for everyone and all disciplines.

The OLED TVs About to Enter the Market

I remember in the early 2000s when attending to a conference I came across for the first time the Organic Light Emitting Diodes (OLED) technology. It was really impressive to see images of really thin TVs made out of plastic that could be rolled up and placed in your bag or your pocket. I thought that it would take a long time to develop this technology and to see the first TVs available. However it seems that this is about to become true this year, since Panasonic, Sony and LG have announced that the first OLED TVs will be released in 2012 and mass fabrication will be carried out in 2013.

OLEDs provide more efficient devices, brighter images, they are thinner and their contrast is much better than current LCD and plasma technologies. On the other hand OLEDs will be also soon present in lighting. These days the British company Lomox has announced the development of light emitting wallpaper that can be used in the interior of buildings and with time will substitute the classic bulbs. The OLED lighting is much more efficient that current technologies what will introduce significant savings in CO2 emission related with lighting energy consumption.

A High-performance Thermoelectric "Solar Cell"

Last year researchers from the Massachusetts Institute of Technology (USA) showed that thermoelectrics are an attractive alternative for converting solar energy into electricity. They designed a device that relies on the transformation of light into heat, which is stored in a solar absorber material, and then transformed into electricity by means of a single thermoelectric unicouple of nanostructured Bi2Te3. Unlike solar cells, this device is not based on exciting electron-hole pairs but the sunlight is stored as heat in the solar absorber, providing a very high temperature at the top side of the thermoelements. On the contrary the bottom side is contacted at a Cu heat sink. The whole system is encapsulated in a tube which is evacuated, reducing significantly heat losses and achieving a large temperature difference that is converted into electricity.

The novel Solar Thermoelectric Generator (STEG) shows a peak efficiency of 4.6% (7–8 times higher than previous flat-panel STEG). This new approach has the potential to achieve cost-effective conversion of solar energy into electricity. The video below from the program Science for the Public provides really interesting information about this novel development directly from Prof. Gang Chen, its inventor.

[Article link]

Dye Sensitized Solar Cells in the iPad

DSCs have become these days a commercial product in the mainstream market in a keyboard developed by Logitech and G24i, the leading company in flexible DSC fabrication in Wales (UK). In the Logitec website it can be seen this innovative Solar Keyboard Folio that integrates in the back side two DSC small modules.

This new product takes advantage of the ability of the DSCs to capture more efficiently the energy from indoor lighting with respect to other photovoltaic technologies. As stated in the product description "The built-in Bluetooth® keyboard is powered by light—low light and lamp light, indoors and out. Fully powered, you can type on it for two years—even in complete darkness".

 After 21 years of intense research since the publication of the nature paper by Grätzel and O'Regan reporting the first DSC, this technology has now arrived successfully to the market. Congratulations to the G24i team for this achievement and all the efforts dedicated to this technology.

High Efficiency All-solid-state Dye-sensitized Solar Cell

Researchers from Northwestern University in Illinois (USA) have published in Nature a novel solid state Dye-sensitized solar cell (DSC) that shows an outstanding efficiency higher than 10 %, very close to the best DSC value of around 11 % from their liquid counterpart. The cell has the classic structure for the photoanode (FTO/TiO2/dye) and the electrolyte is substituted by a solution processable p-type semiconductor (CsSnI3 doped with SnF).

Up to now, the best solid-state DSCs were made of hole transport materials such as spiro-OMeTAD or bis-EDOT, providing efficiencies around 6 %, whose main problem are related to the poor filling of the nanoporous TiO2 layer. This novel cell proposed by Mercouri Kanatzidis and co-workers fills easily the nanoporous matrix since the hole conductor, dissolved in a volatile organic solvent, is injected directly onto the sensitized photoelectrode. This facile and inexpensive process in addition to the use of abundant elements in the fabrication of the device make this new cell a breakthrough in the solar cell area and a feasible solution to the leaking problems of liquid DSCs.

[Article link]