Tag Archives: King Abdullah University of Science and Technology

High speed fabrication of adhesive and flexible electronics

For a university that celebrated its opening in Sept. 2009 (mentioned in my Sept. 24, 2009 posting; scroll down about 40% of the way; look for a reference to the House of Wisdom), the King Abdullah University of Science and Technology (KAUST) has made some impressive announcements including this one in a Jan. 3, 2017 press release on EurekAlert,

The healthcare industry forecasts that our wellbeing in the future will be monitored by wearable wirelessly networked sensors. Manufacturing such devices could become much easier with decal electronics. A KAUST-developed process prints these high-performance silicon-based computers on to soft, sticker-like surfaces that can be attached anywhere1.

Fitting electronics on to the asymmetric contours of human bodies demands a re-think of traditional computer fabrications. One approach is to print circuit patterns on to materials such as polymers or cellulose using liquid ink made from conductive molecules. This technique enables high-speed roll-to-roll assembly of devices and packaging at low costs.

Flexible printed circuits, however, require conventional silicon components to handle applications such as digitizing analog signals. Such rigid modules can create uncomfortable hot spots on the body and increase device weight.

For the past four years, Muhammad Hussain and his team from the KAUST Computer, Electrical and Mathematical Science and Engineering Division have investigated ways to improve the flexibility of silicon materials while retaining their performance.

“We are trying to integrate all device components–sensors, data management electronics, battery, antenna–into a completely compliant system,” explained Hussain. “However, packaging these discrete modules on to soft substrates is extremely difficult.”

Searching for potential electronic skin applications, the researchers developed a sensor containing narrow strips of aluminum foil that changes conductivity at different bending states.

The devices, which could monitor a patient’s breathing patterns or activity levels, feature high-mobility zinc oxide nanotransistors on silicon wafers thinned down lithographically to microscale dimensions for maximum flexibility. Using three-dimensional (3-D) printing techniques, the team encapsulated the silicon chips and foils into a polymer film backed by an adhesive layer.

Hussain and his colleagues found a way to make the e-sticker sensors work in multiple applications. They used inkjet printing to write conductive wiring patterns on to different surfaces, such as paper or clothing. Custom-printed decals were then attached or re-adhered to each location.

“You can place a pressure-sensing decal on a tire to monitor it while driving and then peel it off and place it on your mattress to learn your sleeping patterns,” said Galo Torres Sevilla, first author of the findings and a KAUST Ph.D. graduate.

The robust performance and high-throughput manufacturing potential of decal electronics could launch a number of innovative sensor deployments, noted Hussain.

“I believe that electronics have to be democratized–simple to learn and easy to implement. Electronic decals are a right step in that direction,” Hussain said.

Here’s a link to and a citation for the paper,

Decal Electronics: Printable Packaged with 3D Printing High-Performance Flexible CMOS Electronic Systems by Galo A. Torres Sevilla, Marlon D. Cordero, Joanna M. Nassar, Amir N. Hanna, Arwa T. Kutbee, Arpys Arevalo, and Muhammad M. Hussain. Advanced Materials Technologies DOI: 10.1002/admt.201600175 Version of Record online: 13 OCT 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This paper is behind a paywall.

Putting a gold atom in a silver nanocluster changes things

Considering that the King Abdullah University of Science and Technology (KAUST) opened on Sept. 23, 2009 (mentioned in my Sept. 24, 2009 post; scroll down about 50% of the way), the university has done a remarkable job of establishing itself within the research community. Here’s some of the latest news from KAUST in a July 15, 2016 news item on Nanowerk,

The appearance of metals, such as their shiny surface or their electrical conductivity, is determined by the ensemble of atoms that comprise the metal. The situation differs on the molecular scale, and KAUST researchers have shown that replacing a single atom in a cluster of 25 silver atoms with one gold atom fundamentally changes its properties …

Composing a silver nanocrystal: the center silver atom (a) surrounded by a cage of 12 other silver atoms (b) embedded by further atoms (c) and stabilized by further ligands (d). Reproduced with permission from ref 1.© 2016 John Wiley and Sons.

Composing a silver nanocrystal: the center silver atom (a) surrounded by a cage of 12 other silver atoms (b) embedded by further atoms (c) and stabilized by further ligands (d). Reproduced with permission from ref 1.© 2016 John Wiley and Sons.

A July (??), 2016 KAUST news release, which originated the news item, provides more detail,

Metal atom nanoclusters are made from a core of a few metal atoms surrounded by a protective shell of stabilizing ligands. Nanoclusters come in different sizes, but each stable variation of nanoclusters has exactly the same number of metal atoms. This leads to very controllable properties, noted Osman Bakr, KAUST associate professor of material science and engineering and leader of the research team.

“Nanoclusters have unique arrangements of atoms and size-dependent absorption, fluorescence, electronic and catalytic properties,” he said.

A popular metal nanocluster is [Ag25(SR)18], which consists of of 25 silver atoms. This nanocluster is unique as it corresponds to a gold nanocluster that has exactly the same number of atoms. Both clusters have different properties due to the different metal used. To understand how exactly the atomic composition affects these properties, the researchers replaced a single silver atom with gold.

Replacing a single atom in a nanocluster is a difficult task. Direct chemical methods can be used, but these give little control over how many atoms are replaced, making it difficult to ascribe particular properties to the nanocluster structure.

Instead, the researchers used a galvanic replacement process that relies on difference in the electrochemical potential between the incoming and outgoing atoms to induce atomic replacements. To their surprise, the process produced a reliable and precise atomic exchange in which only the center silver atom is replaced by gold.

The replacement yielded dramatic changes in the nanocluster. A solution of the silver nanoclusters appears orange, whereas after the replacement of the central atom the color turns dark green.

This indicates more fundamental changes in properties, Bakr said. “The ambient stability and fluorescence of the nanocluster were enhanced by a factor of 25 as a result of this single atom replacement. Furthermore, we are now able to demonstrate the importance of a single atom impurity on nanoparticles and modulate the properties at the single atom level,” he noted.

The reliable replacement of only a single gold atom opens the door to a more systematic investigation of metal nanoclusters, which can help to uncover the mechanisms of the chemical and physical changes arising from the replacement.

Here’s a link to and a citation for the paper,

Templated Atom-Precise Galvanic Synthesis and Structure Elucidation of a [Ag24Au(SR)18] Nanocluster by Dr. Megalamane S. Bootharaju, Chakra P. Joshi, Dr. Manas R. Parida, Prof. Omar F. Mohammed and Prof. Osman M. Bakr. Angewandte Chemie International Edition DOI: 10.1002/anie.201509381 Version of Record online: 27 NOV 2015

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

They’ve certainly waited a while to tout this research. Ah well. This paper is behind a paywall.

King Abdullah University of Science and Technology (Saudi Arabia) develops sensors from household materials

Researchers at the King Adbullah University of Science and Technology (KAUST) are developing sensors made of household materials according to a Feb. 19, 2016 KAUST news release (also on EurekAlert but dated Feb. 21, 2016),

Everyday materials from the kitchen drawer, such as aluminum foil, sticky note paper, sponges and tape, have been used by a team of electrical engineers from KAUST to develop a low-cost sensor that can detect external stimuli, including touch, pressure, temperature, acidity and humidity.

The sensor, which is called Paper Skin, performs as well as other artificial skin applications currently being developed while integrating multiple functions using cost-effective materials1.

“This work has the potential to revolutionize the electronics industry and opens the door to commercializing affordable high-performance sensing devices,” stated Muhammad Mustafa Hussain from the University’s Integrated Nanotechnology Lab, where the research was conducted.

Wearable and flexible electronics show promise for a variety of applications, such as wireless monitoring of patient health and touch-free computer interfaces. Current research in this direction employs expensive and sophisticated materials and processes.

The team used sticky note paper to detect humidity, sponges and wipes to detect pressure and aluminum foil to detect motion. Coloring a sticky note with an HB pencil allowed the paper to detect acidity levels, and aluminum foil and conductive silver ink were used to detect temperature differences.

The materials were put together into a simple paper-based platform that was then connected to a device that detected changes in electrical conductivity according to external stimuli.

Increasing levels of humidity, for example, increased the platform’s ability to store an electrical charge, or its capacitance. Exposing the sensor to an acidic solution increased its resistance, while exposing it to an alkaline solution decreased it. Voltage changes were detected with temperature changes. Bringing a finger closer to the platform disturbed its electromagnetic field, decreasing its capacitance.

The team leveraged the various properties of the materials they used, including their porosity, adsorption, elasticity and dimensions to develop the low-cost sensory platform. They also demonstrated that a single integrated platform could simultaneously detect multiple stimuli in real time.

Several challenges must be overcome before a fully autonomous, flexible and multifunctional sensory platform becomes commercially achievable, explained Hussain. Wireless interaction with the paper skin needs to be developed. Reliability tests also need to be conducted to assess how long the sensor can last and how good its performance is under severe bending conditions.

“The next stage will be to optimize the sensor’s integration on this platform for applications in medical monitoring systems. The flexible and conformal sensory platform will enable simultaneous real-time monitoring of body vital signs, such as heart rate, blood pressure, breathing patterns and movement,” Hussain said.

Here’s a link to and a citation for the paper,

Paper Skin Multisensory Platform for Simultaneous Environmental Monitoring by Joanna M. Nassar, Marlon D. Cordero, Arwa T. Kutbee, Muhammad A. Karimi, Galo A. Torres Sevilla, Aftab M. Hussain, Atif Shamim, and Muhammad M. Hussain. Advanced Materials Technologies DOI: 10.1002/admt.201600004 Article first published online: 19 FEB 2016

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

This appears to be an open access paper.

Nano-alchemy: silver nanoparticles that look like and act like gold

This work on ‘nano-alchemy’ comes out of the King Abduhllah University of Science and Technology (KAUST) according to a Sept. 22, 2015 article by Lisa Zynga for phys.org (Note: A link has been removed),

In an act of “nano-alchemy,” scientists have synthesized a silver (Ag) nanocluster that is virtually identical to a gold (Au) nanocluster. On the outside, the silver nanocluster has a golden yellow color, and on the inside, its chemical structure and properties also closely mimic those of its gold counterpart. The work shows that it may be possible to create silver nanoparticles that look and behave like gold despite underlying differences between the two elements, and could lead to creating similar analogues between other pairs of elements.

“In some aspects, this is very similar to alchemy, but we call it ‘nano-alchemy,'” Bakr [Osman Bakr, Associate Professor of Materials Science and Engineering at King Abdullah University of Science and Technology (KAUST) in Saudi Arabia] told Phys.org. “When we first encountered the optical spectrum of the silver nanocluster, we thought that we may have inadvertently switched the chemical reagents for silver with gold, and ended up with gold nanoparticles instead. But repeated synthesis and measurements proved that the clusters were indeed silver and yet show properties akin to gold. It was really surprising to us as scientists to find not only similarities in the color and optical properties, but also the X-ray structure.”

In their study, the researchers performed tests demonstrating that the silver and gold nanoclusters have very similar optical properties. Typically, silver nanoclusters are brown or red in color, but this one looks just like gold because it emits light at almost the same wavelength (around 675 nm) as gold. The golden color can be explained by the fact that both nanoclusters have virtually identical crystal structures.

The question naturally arises: why are these silver and gold nanoclusters so similar, when individual atoms of silver and gold are very different, in terms of their optical and structural properties? As Bakr explained, the answer may have to do with the fact that, although larger in size, the nanoclusters behave like “superatoms” in the sense that their electrons orbit the entire nanocluster as if it were a single giant atom. These superatomic orbitals in the silver and gold nanoclusters are very similar, and, in general, an atom’s electron configuration contributes significantly to its properties.

Here’s one of the images used to illustrate Zynga’s article and the paper published by the American Chemical Society,

(Left) Optical properties of the silver and gold nanoclusters, with the inset showing photographs of the actual color of the synthesized nanoclusters. The graph shows the absorption (solid lines) and normalized emission (dotted lines) spectra. (Right) Various representations of the X-ray structure of the silver nanocluster. Credit: Joshi, et al. ©2015 American Chemical Society

(Left) Optical properties of the silver and gold nanoclusters, with the inset showing photographs of the actual color of the synthesized nanoclusters. The graph shows the absorption (solid lines) and normalized emission (dotted lines) spectra. (Right) Various representations of the X-ray structure of the silver nanocluster. Credit: Joshi, et al. ©2015 American Chemical Society

I encourage you to read Zynga’s article in its entirety. For the more technically inclined, here’s a link to and a citation for the researchers’ paper,

[Ag25(SR)18]: The “Golden” Silver Nanoparticle by Chakra P. Joshi, Megalamane S. Bootharaju, Mohammad J. Alhilaly, and Osman M. Bakr.J. Am. Chem. Soc., 2015, 137 (36), pp 11578–11581 DOI: 10.1021/jacs.5b07088 Publication Date (Web): August 31, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

Spray-on solar cells from the University of Toronto (Canada)

It’s been a while since there’s been a solar cell story from the University of Toronto (U of T) and I was starting to wonder if Ted (Edward) Sargent had moved to another educational institution. The drought has ended with the announcement of three research papers being published by researchers from Sargent’s U of T laboratory. From a Dec. 5, 2014 ScienceDaily news item,

Pretty soon, powering your tablet could be as simple as wrapping it in cling wrap.

That’s Illan Kramer’s … hope. Kramer and colleagues have just invented a new way to spray solar cells onto flexible surfaces using miniscule light-sensitive materials known as colloidal quantum dots (CQDs) — a major step toward making spray-on solar cells easy and cheap to manufacture.

A Dec. 4, 2014 University of Toronto news release (also on EurekAlert) by Marit Mitchell, which originated the news item, gives a bit more detail about the technology (Note: Links have been removed),

 Solar-sensitive CQDs printed onto a flexible film could be used to coat all kinds of weirdly-shaped surfaces, from patio furniture to an airplane’s wing. A surface the size of a car roof wrapped with CQD-coated film would produce enough energy to power three 100-watt light bulbs – or 24 compact fluorescents.

He calls his system sprayLD, a play on the manufacturing process called ALD, short for atomic layer deposition, in which materials are laid down on a surface one atom-thickness at a time.

Until now, it was only possible to incorporate light-sensitive CQDs onto surfaces through batch processing – an inefficient, slow and expensive assembly-line approach to chemical coating. SprayLD blasts a liquid containing CQDs directly onto flexible surfaces, such as film or plastic, like printing a newspaper by applying ink onto a roll of paper. This roll-to-roll coating method makes incorporating solar cells into existing manufacturing processes much simpler. In two recent papers in the journals Advanced Materials and Applied Physics Letters, Kramer showed that the sprayLD method can be used on flexible materials without any major loss in solar-cell efficiency.

Kramer built his sprayLD device using parts that are readily available and rather affordable – he sourced a spray nozzle used in steel mills to cool steel with a fine mist of water, and a few regular air brushes from an art store.

“This is something you can build in a Junkyard Wars fashion, which is basically how we did it,” says Kramer. “We think of this as a no-compromise solution for shifting from batch processing to roll-to-roll.”

“As quantum dot solar technology advances rapidly in performance, it’s important to determine how to scale them and make this new class of solar technologies manufacturable,” said Professor Ted Sargent, vice-dean, research in the Faculty of Applied Science & Engineering at University of Toronto and Kramer’s supervisor. “We were thrilled when this attractively-manufacturable spray-coating process also led to superior performance devices showing improved control and purity.”

In a third paper in the journal ACS Nano, Kramer and his colleagues used IBM’s BlueGeneQ supercomputer to model how and why the sprayed CQDs perform just as well as – and in some cases better than – their batch-processed counterparts. This work was supported by the IBM Canada Research and Development Centre, and by King Abdullah University of Science and Technology.

For those who would like to see the sprayLD device,

Here are links and citation for all three papers,

Efficient Spray-Coated Colloidal Quantum Dot Solar Cells by Illan J. Kramer, James C. Minor, Gabriel Moreno-Bautista, Lisa Rollny, Pongsakorn Kanjanaboos, Damir Kopilovic, Susanna M. Thon, Graham H. Carey, Kang Wei Chou, David Zhitomirsky, Aram Amassian, and Edward H. Sargent. Advanced Materials DOI: 10.1002/adma.201403281 Article first published online: 10 NOV 2014

© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Colloidal quantum dot solar cells on curved and flexible substrates by Illan J. Kramer, Gabriel Moreno-Bautista, James C. Minor, Damir Kopilovic, and Edward H. Sargent. Appl. Phys. Lett. 105, 163902 (2014); http://dx.doi.org/10.1063/1.4898635 Published online 21 October 2014

© 2014 AIP Publishing LLC

Electronically Active Impurities in Colloidal Quantum Dot Solids by Graham H. Carey, Illan J. Kramer, Pongsakorn Kanjanaboos, Gabriel Moreno-Bautista, Oleksandr Voznyy, Lisa Rollny, Joel A. Tang, Sjoerd Hoogland, and Edward H. Sargent. ACS Nano, 2014, 8 (11), pp 11763–11769 DOI: 10.1021/nn505343e Publication Date (Web): November 6, 2014

Copyright © 2014 American Chemical Society

All three papers are behind paywalls.

Given the publication dates for the papers, this looks like an attempt to get some previously announced research noticed by sending out a summary news release using a new ‘hook’ to get attention. I hope it works for them as it must be disheartening to have your research sink into obscurity because the announcements were issued during one or more busy news cycles.

One final note, if I understand the news release correctly, this work is still largely theoretical as there don’t seem to have been any field tests.

Inventions Nanotech Middle East conference in 2013

It’s a bit early to be talking about this conference since there isn’t much information, no speakers, no programme, etc. but there’s still time to pull that all together since the Inventions Nanotech Middle East Conference (aka, Inventions Nanotech ME) is scheduled for Nov. 3-5, 2013. From the Conference Overview page,

The Conference will host top notch industry experts from all over the world who will address the following crucial topics through live demonstrations and case studies:

Energy / Oil & Gas
Consumer Products

The event will be held at the Qatar National Convention Center.

There are two main sources of nanotech news items in that region. Iran or INIC  (Iran Nanotechnology Initiative Council [my Dec. 27, 2012 posting]), which continuously publicizes its nanotechnology research, and Saudi Arabia (KAUST or King Abdullah University of Science and Technology), which publicizes its work on solar energy (my July 30, 2012 posting), for the most part.

Good luck to the conference organizers.

Hands off the bubbles in my boiling water!

The discovery that boiling water bubbled was important to me. I’ve never really thought about it until now when researchers at Northwestern University have threatened to take my bubbles away, metaphorically speaking. From the Sept. 13, 2012 news item on ScienceDaily,

Every cook knows that boiling water bubbles, right? New research from Northwestern University turns that notion on its head.

“We manipulated what has been known for a long, long time by using the right kind of texture and chemistry to prevent bubbling during boiling,” said Neelesh A. Patankar, professor of mechanical engineering at Northwestern’s McCormick School of Engineering and Applied Science and co-author of the study.

This discovery could help reduce damage to surfaces, prevent bubbling explosions and may someday be used to enhance heat transfer equipment, reduce drag on ships and lead to anti-frost technologies.

The Sept. 13, 2012 news release from McCormick University (which originated the news item) provides details,

This phenomenon is based on the Leidenfrost effect. In 1756 the German scientist Johann Leidenfrost observed that water drops skittered on a sufficiently hot skillet, bouncing across the surface of the skillet on a vapor cushion or film of steam. The vapor film collapses as the surface falls below the Leidenfrost temperature. When the water droplet hits the surface of the skillet, at 100 degrees Celsius, boiling temperature, it bubbles.

To stabilize a Leidenfrost vapor film and prevent bubbling during boiling, Patankar collaborated with Ivan U. Vakarelski of King Abdullah University of Science and Technology, Saudi Arabia. Vakarelski led the experiments and Patankar provided the theory. The collaboration also included Derek Chan, professor of mathematics and statistics from the University of Melbourne in Australia.

In their experiments, the stabilization of the Leidenfrost vapor film was achieved by making the surface of tiny steel spheres very water-repellant. The spheres were sprayed with a commercially available hydrophobic coating — essentially self-assembled nanoparticles — combined with other water-hating chemicals to achieve the right amount of roughness and water repellency. At the correct length scale this coating created a surface texture full of tiny peaks and valleys.

When the steel spheres were heated to 400 degrees Celsius and dropped into room temperature water, water vapors formed in the valleys of the textured surface, creating a stable Leidenfrost vapor film that did not collapse once the spheres cooled to the temperature of boiling water. In the experiments, researchers completely avoided the bubbly phase of boiling.

To contrast, the team also coated tiny steel spheres with a water-loving coating, heated the objects to 700 degrees Celsius, dropped them into room temperature water and observed that the Leidenfrost vapor collapsed with a vigorous release of bubbles.

The scientists have provided a video illustrating their work,

This movie shows the cooling of 20 mm hydrophilic (left) and superhydrophobic (right) steel spheres in 100 C water. The spheres’ initial temperature is about 380 C. The bubbling phase of boiling is completely eliminated for steel spheres with superhydrophobic coating. (from Vimeo, http://vimeo.com/49391913)

I understand there are advantages to not having bubbles in hot water but it somehow seems wrong. I’ve given up a lot over the years: gravity, boundaries between living and non-living (that was a very big thing to give up), and other distinctions that I have made based on traditional science but, today, this is one step too far.

It may seem silly but that memory of my mother explaining that you identify boiling water by its bubbles is important to me. It was one of my first science lessons. I imagine I will recover from this moment but it does remind me of how challenging it can be when your notions of reality/normalcy are challenged by various scientific endeavours. The process can get quite exhausting as you keep recalibrating everything you ‘know’ all the time.

University of Toronto, KAUST, Pennsylvania State University and quantum colloidal dots

I’ve written about colloidal quantum dot solar cells and University of Toronto professor Ted Sargent’s work before (June 28, 2011). He and his team have been busy again. From the Sept. 18, 2011 news item on Nanowerk,

Researchers from the University of Toronto (U of T), King Abdullah University of Science & Technology (KAUST) and Pennsylvania State University (Penn State) have created the most efficient colloidal quantum dot (CQD) solar cell ever.

The discovery is reported in the latest issue of Nature Materials.

The first time (June 28)  I wrote about the colloidal quantum dot (CQD) solar cells, the team had made a breakthrough with the architecture of the solar cell by creating what they called a ‘graded recombination layer’ allowing infrared and visible light harvesters to be linked without compromising either layer. The next time I wrote about Sargent’s work  (July 11, 2011),  it concerned self-assembling quantum dots and DNA.

The very latest work is focussed on making the CQD solar cells more efficient by packing them closer together,

Until now, quantum dots have been capped with organic molecules that separate the nanoparticles by a nanometer. On the nanoscale, that is a long distance for electrons to travel.

To solve this problem, the researchers utilized inorganic ligands, sub-nanometer-sized atoms that bind to the surfaces of the quantum dots and take up less space. The combination of close packing and charge trap elimination enabled electrons to move rapidly and smoothly through the solar cells, thus providing record efficiency.

I gather this last breakthrough has made commercialization possible,

As a result of the potential of this research discovery, a technology licensing agreement has been signed by U of T and KAUST, brokered by MaRS Innovations (MI), which will enable the global commercialization of this new technology.

Here’s the competitive advantage that a CQD solar cell offers,

Quantum dots are nanoscale semiconductors that capture light and convert it into electrical energy. Because of their small scale, the dots can be sprayed onto flexible surfaces, including plastics. This enables the production of solar cells that are less expensive than the existing silicon-based version.


There are more details about this latest breakthrough both in the Nanowerk news item and in this University of Toronto Sept.19, 2011 news release credited to Liam Mitchell. For anyone who’s curious about MaRS, it’s located in Toronto, Ontario and seems to be some sort of technology company incubator or here’s how they describe themselves (from their How did MaRS get started page?),

A charitable organization could be created to better connect the worlds of science, business and government. A public-private partnership with a mission to remove the barriers between silos. Nurture a culture of innovation. And help create global enterprises that would contribute to Canada’s economic and social development.

University of Toronto research team’s efficient tandem solar cell with colloidal quantum dots (CQD)

Professor Ted Sargent, electrical and computer engineering professor at the University of Toronto, heads an engineering research team which recently published a paper about solar cells and colloidal quantum dots (CQD) in Nature Photonics. From Wayne MacPhail’s June 27, 2011 news release for the University of Toronto,

The researchers, led by Professor Ted Sargent of electrical and computer engineering, report the first efficient tandem solar cell based on colloidal quantum dots (CQD). “The U of T device is a stack of two light-absorbing layers – one tuned to capture the sun’s visible rays, the other engineered to harvest the half of the sun’s power that lies in the infrared,” said lead co-author Xihua Wang, a post-doctoral fellow.

“We needed a breakthrough in architecting the interface between the visible and infrared junction,” said Sargent, Canada Research Chair in Nanotechnology. “The team engineered a cascade – really a waterfall – of nanometers-thick materials to shuttle electrons between the visible and infrared layers.”

According to doctoral student Ghada Koleilat, lead co-author of the paper, “We needed a new strategy – which we call the graded recombination layer – so that our visible and infrared light harvesters could be linked together efficiently, without any compromise to either layer.” [emphasis mine]

The team pioneered solar cells made using CQDs, nanoscale materials that can readily be tuned to respond to specific wavelengths of the visible and invisible spectrum. By capturing such a broad range of light waves – wider than normal solar cells – tandem CQD solar cells can in principle reach up to 42 per cent efficiencies. The best single-junction solar cells are constrained to a maximum of 31 per cent efficiency. In reality, solar cells that are on the roofs of houses and in consumer products have 14 to 18 per cent efficiency. The work expands the Toronto team’s world-leading 5.6 per cent efficient colloidal quantum dot solar cells.

According to the University of Toronto news item and the June 28, 2011 news item by Cameron Chai on Azonano, Sargent believes that this ‘graded recombination layer’ will be found in building materials and mobile devices in five years.

It’s always informative to look at the funding agencies for these projects. The CQD project received its funding from King Abdullah University of Science and Technology (KAUST) [mentioned in my Sept. 24, 2009 posting—scroll down 1/2 way), by the Ontario Research Fund Research Excellence Program and by the Natural Sciences and Engineering Research Council (NSERC) of Canada.

ETA July 4, 2011: You can get another take on this work from Dexter Johnson, Nanoclast blog on the IEEE website in his June 28, 2011 posting, Harvesting Visible and Invisible Light in PVs with Colloidal Quantum Dots.