New technique could lead to cheaper, more efficient solar power and LEDs

Researchers Valerio Adinolfi (left) and Riccardo Comin examine a perovskite crystal. Perovskites are attracting growing interest in the context of thin-film solar technologies, but had never been studied in their purest form: as perfect single crystals. Credit; Toronto

U of T experts are shining new light on an emerging family of solar-absorbing materials that could lead to cheaper and more efficient solar panels and LEDs.

The materials, called perovskites, are particularly good at absorbing visible light, but had never been studied in their purest form: as perfect single crystals.

Using a new technique, researchers grew large, pure perovskite crystals and studied how electrons move through the material as light is converted to electricity.

Led by Professor Ted Sargent of The Edward S. Rogers Sr. Department of Electrical & Computer Engineering at the University of Toronto in collaboration with Professor Osman Bakr of the King Abdullah University of Science and Technology (KAUST), the team used a combination of laser-based techniques to measure selected properties of the perovskite crystals.

By tracking down the ultrafast motion of electrons in the material, they have been able to measure the diffusion length – how far electrons can travel without getting trapped by imperfections in the material – as well as mobility – how fast the electrons can move through the material. Their work was published this week in the journal Science.

“Our work sets the bar for the ultimate solar energy-harvesting performance of perovskites,” says Riccardo Comin, a post-doctoral fellow with the Sargent Group. “With these materials it’s been a race to try to get record efficiencies, and there are no signs of stopping or slowing down.”

In recent years, perovskite efficiency has soared to over 20 per cent, very close to the current best performance of commercial-grade silicon-based solar panels you see mounted in Spanish deserts and on Californian roofs.

“In terms of efficiency, perovskites are perfectly comparable or better than materials that have already been commercialized,” says Valerio Adinolfi, a PhD candidate in the Sargent Group and co-first author on the paper. “The challenge is to make solar attractive from the business side. It’s not just matter of making it efficient – the point is to make it efficient and cheap.”

The study has obvious implications for green energy, but may also enable innovations in lighting.

Think of a solar panel made of perovskite crystals as a fancy slab of glass: light hits the crystal surface and gets absorbed, exciting electrons in the material. Those electrons travel easily through the crystal to electrical contacts on its underside, where they are collected in the form of electric current.

Now imagine the sequence in reverse – power the slab with electricity, inject electrons and release energy as light. A more efficient electricity-to-light conversion means perovskites could open new frontiers for energy-efficient LEDs.

Parallel work in the Sargent Group focuses on improving nano-engineered solar-absorbing particles called colloidal quantum dots. “Perovskites are great visible-light harvesters, and quantum dots are great for infrared,” said Sargent.

“In future, we will explore the opportunities for stacking together complementary absorbent materials,” says Dr. Comin. “There are very promising prospects for combining perovskite work and quantum dot work for further boosting the efficiency.”

Source: U of T

Blazing car murder of 1930 investigated

Slide with Blazing Car victim's sample on it. Sample taken by Sir Bernard Spilsbury.
Credit: University of Leicester

University of Leicester leads collaboration with Northumbria University, Northamptonshire Police and The Royal London Hospital Museum, in investigation of the Blazing Car Murder of 1930

A forensic team from the University of Leicester and Northumbria University has spearheaded an investigation which has shed new light on a murder case from 1930.

A team from the University of Leicester, led by Dr John Bond OBE from the Department of Chemistry and Dr Lisa Smith from the Department of Criminology worked with colleagues from Northumbria University, Northamptonshire Police and The Royal London Hospital Museum to tackle the riddle of the 'Blazing Car Murder' from over 80 years ago.

The case involved the murder of a male in a car fire in Hardingstone, Northamptonshire, on 6 November 1930. Alfred Rouse was convicted, and later hanged, at Bedford Gaol in March 1931, for murdering his victim who to this day, has not been identified.

At the time, a post mortem examination was carried out in the garage of the local public house by the Home Office-appointed pathologist Sir Bernard Spilsbury, working alongside another local pathologist.

Sir Spilsbury reported that lavender coloured material and light brown hair were found at the scene. It was further documented that the victim's jawbone was removed to assist with possible identification and tissue samples taken for microscopical examination.

Two of these tissue samples are still in existence and archived in The Royal London Hospital Museum: one from the prostate to confirm the sex of the victim, and another from the lung to determine whether or not the victim was already dead before the fire was started.

In recent months, attention has turned to the fact that a man named William Briggs left his family home in London to attend a doctor's appointment at around the same time the crime was committed -- and was never seen or heard of again.

As part of their family ancestry research, the relatives of William Briggs wanted to verify earlier generations' belief that their ancestor may have been Rouse's car murder victim.

Last year, a number of William Briggs's relatives approached Northamptonshire Police in an attempt to put the 83-year-old mystery to rest and finally reveal the identity of the victim.

They met with the Force's curator and archivist Richard Cowley, discussed the story of the murder and were shown artefacts relating to the crime which, at the time received worldwide attention.

With the help of Northamptonshire Police, the family contacted University of Leicester academic Dr John Bond OBE. He and Dr Lisa Smith negotiated with The Royal London Hospital museum to allow one of the remaining tissue samples to be examined.

The slide was released with the approval of Professor Richard Trembath, at Queen Mary College University of London. The slide originates from the old Department of Forensic Medicine which formed part of The London Hospital Medical College. The College was merged with Queen Mary College in 1995.

The University of Leicester team considered whether there might just be enough mitochondrial DNA (mtDNA) left on the slide to get a profile to compare with mtDNA from the family.

Mitochondrial DNA is wholly inherited from the maternal line so it is essential to have an unbroken maternal line of descendants to test.

University of Leicester worked with the Northumbria University Centre for Forensic Science and Dr Eleanor Graham, a former member of staff at the University of Leicester, and Victoria Barlow to carry out DNA analysis on the samples to see if there was a match from the sample and the relatives.

Fortunately, the scientists obtained a full single male mtDNA profile from the slide to compare to the family.

Dr John Bond, from the University of Leicester said: "It's been very interesting and rewarding working on such a famous, local murder case. It was quite a unique investigation to be involved in, as the perpetrator had been identified long ago and brought to justice while the victim's identity remained unknown.

"It was a great example of how the scientific and criminological expertise at the University of Leicester and Northumbria University, working together with the police, could provide answers to this family after 83 years."

Detective Chief Superintendent Paul Phillips from Northamptonshire Police said: "From our perspective this is a closed case, the offender Alfred Rouse was convicted of murder and hanged, but this has been a long-standing mystery in Northamptonshire as the identity of the victim has never been established.

"Our work at Northamptonshire Police is victim focused so I was delighted to learn of new opportunities to establish the identity of the victim through the development of forensic science."

Dr Eleanor Graham from Northumbria University stated: "Projects such as this highlight the fact that forensic DNA analysis is not confined to 'catching criminals'. DNA analysis also has a critical role to play in the identification of those who have been killed during criminal acts, accidents or natural disasters, which have occurred recently, or many years ago."

The result is due to be revealed to the family on the BBC's The One Show on a date to be fixed.

Blazing Car Murder background:

Alfred Rouse sustained a head wound in the First World War, which left him with a personality disorder, to the point that he was described as 'a promiscuous rake with an enormous sexual appetite'.

Rouse was a commercial traveller who went all around the country and his promiscuous lifestyle resulted in him facing severe financial problems.

As a consequence, Rouse devised a plan to murder a homeless tramp who would not be missed by anyone which would enable him to stage his own death in a car accident and then disappear to start a new life free from financial restriction.

To that end, Rouse rendered his victim unconscious, placed him in the driver's seat of his car and set the car alight.

Rouse was making his way from the scene but bumped into two local youths keen to see what was going on and take part in some late Bonfire Night celebrations.

This initial contact eventually led to Rouse's arrest. He was convicted at Northampton Assizes and hanged in Bedford on 10 March 1931.

The local Herald newspaper suggested that the identity of Rouse's victim 'would likely remain a mystery forever.' But will it………..?

Source: University of Leicester

New biometric watches use light to non-invasively monitor glucose, dehydration, pulse

This schematic diagram shows how the new system can be used to measure a person's glucose levels noninvasively. Credit: Biomedical Optics Express

Monitoring a patient's vital signs and other physiological parameters is a standard part of medical care, but, increasingly, health and fitness-minded individuals are looking for ways to easily keep their own tabs on these measurements. Enter the biometric watch.

In a pair of papers published in The Optical Society's (OSA) open-access journal Biomedical Optics Express, groups of researchers from the Netherlands and Israel describe two new wearable devices that use changing patterns of scattered light to monitor biometrics: one tracks glucose concentration and dehydration levels, and the other monitors pulse.

The glucose sensor is the first wearable device that can measure glucose concentration directly but noninvasively, the authors say.
And while other wearable devices have been made to monitor pulse, the authors claim their new design would be less sensitive to errors when the wearer is in motion, for example while walking or playing sports

Both of the watches described in the two papers make use of the so-called "speckle" effect, the grainy interference patterns that are produced on images when laser light reflects from an uneven surface or scatters from an opaque material. When the material that is scattering the light is moving -- say, in the case of blood flowing through the circulatory system -- "the speckle pattern changes with changes in the flow," explained biomedical engineer Mahsa Nemati, a graduate student in the Optics Research Group at the Delft University of Technology in the Netherlands and the lead author of the Biomedical Optics Express paper on monitoring pulse. Those light variations are a valuable source of information, she says.

The 'Holy Grail' of Diagnostics

In the first paper, bioengineer Zeev Zalevsky of Israel's Bar-Ilan University and his colleagues describe a new wearable biometric system that uses the speckle effect to directly monitor the glucose concentration in the bloodstream, as well as the wearer's relative hydration level.

"Glucose is the holy grail of the world of biomedical diagnostics, and dehydration is a very useful parameter in the field of wellness, which is one of our main commercial aims," Zalevsky said.

The watch-like device consists of a laser to generate a wavefront of light that illuminates a patch of skin on the wrist near an artery, and a camera that measures changes over time in the light that is backscattered off the skin. Unlike other chemicals present in the blood, glucose exhibits a so-called Faraday effect. This means that in the presence of an external magnetic field (generated by a magnet attached to the device) the glucose molecule alters the polarization of the wavefront and thus influences the resulting speckle patterns. 
Analyzing these changing patterns provides a direct measurement of the glucose concentration. Because one of the main signs of mild to moderate dehydration is muscle weakness, which will alter the strength of the signals, the same device can also be used to indicate the relative dehydration level of the user as it changes over time.

Zalevsky and his colleagues are now working to reduce the margin of error in the device's readings. "Around 96 percent of our in vivo measurements were within a range of 15 percent deviation from the readout of a medical reference glucometer device," Zalevsky noted. "The main factor for errors now is the stability of our device on the wrist of the user. We are currently investing efforts in deriving proper calibration and motion cancellation procedures that will allow us to reduce this sensitivity."

Zalevsky says this is the first step toward non-invasive, continuous in vivo measurement of glucose that is based on sensing an effect that is directly related to glucose concentration. The team expects a commercial version of the device to reach the market within two to three years.

Pulse Tracker

In the second Biomedical Optics Express paper, Nemati and her colleagues at Delft and at Phillips Research developed a method that could be used to monitor pulse non-invasively with a sensor that isn't thrown off by the wearer's movement.

Using simulated heart beats generated in milk and measurements performed on the finger of a volunteer, they found that speckle changes can be used to accurately measure flow pulsations -- that is, the heart rate -- even when the light source used to create the speckle pattern is also moving, as would be the case with a wearable biometric sensor. The researchers found that just a couple of pixels from the image were sufficient to extract the pulse rate.

"This paper shows for the first time that a speckle pattern generated from a flowing liquid can give us the pulsation properties of the flow in spite of motion-induced artifacts," Nemati said. "Sophisticated optics is not necessary to implement this, so the costs for devices can be kept low. Another advantage is that the devices can be non-contact or far from the sample," she added.

The team is currently working with companies to integrate their motion-friendly pulse-monitoring technique into existing sensors, for potential use clinically as well as in sports, Nemati said.

Source: The Optical Society

Smart window that tints and powers itself invented

NTU Prof Sun Xiaowei holding his smart window invention that can self-tint and also functions as a battery. Credit: Image courtesy of Nanyang Technological University

Nanyang Technological University (NTU) scientists have developed a smart window which can darken or brighten without the need for an external power source.

This unique self-tinting window requires zero electricity to operate and is also a rechargeable battery. The window's stored energy can be used for other purposes, such as to light up low-powered electronics like a light emitting diode (LED).

Currently, the window solutions in the market are either using permanent tinting which cannot brighten at night or are windows that can change its light transmission properties only with an external power source.

The NTU smart window however can be turned into a cool blue tint in bright daylight, cutting light penetration by about half, and then reverts back to clear glass at night or as required.

This breakthrough research led by NTU Professor Sun Xiaowei, was published recently in Nature Communications.

How it works

The trick to making the self-powered smart window is a new technology developed by Prof Sun's team from NTU's School of Electrical and Electronic Engineering.

"Our new smart electrochromic window is bi-functional; it is also a transparent battery," Prof Sun explained. "It charges up and turns blue when there is oxygen present in the electrolyte -- in other words, it breathes."

The NTU smart window contains liquid electrolyte placed in between two glass sheets coated with indium tin oxide (ITO), commonly used as transparent conductive coatings for television displays. One sheet is coated with an additional layer of a pigment known as Prussian Blue and the other one is attached to a thin strip of aluminium foil. The Prussian Blue gives the glass a blue tint when it is fully charged.

The two glass sheets are connected by typical electrical cables. When the electrical circuit between them is broken, a chemical reaction starts between Prussian Blue and the dissolved oxygen in the electrolyte, turning the glass blue. To turn off the blue tint, the electrical circuit is closed to discharge the battery, turning the Prussian Blue into a colourless Prussian White.

Such an innovative technology can adjust the amount of sunlight coming into buildings in the day, which promises significant savings on cooling and lighting costs.

"Our technology is very attractive as a zero-sum consumption smart window. Buildings owners and even common households can reap energy savings right from the outset and over the long term. Developers who are looking at constructing environmentally-friendly green buildings will find our technology attractive for their building plans," said Prof Sun.

Prof Sun is an electrical engineering expert whose other innovations include various solar technologies, glass-free 3D technologies, next-generation lightings and displays.

The NTU team, consisting of five researchers, is now enhancing their invention and is looking forward to collaborating with industry partners to commercialise their technology.

Source: Nanyang Technological University

Instant-start computers possible with new breakthrough

Power button (stock image)

To encode data, today's computer memory technology uses electric currents -- a major limiting factor for reliability and shrinkability, and the source of significant power consumption. If data could instead be encoded without current -- for example, by an electric field applied across an insulator -- it would require much less energy, and make things like low-power, instant-on computing a ubiquitous reality.

A team at Cornell University led by postdoctoral associate John Heron, who works jointly with Darrell Schlom, professor of Industrial Chemistry in the Department of Materials Science and Engineering, and Dan Ralph, professor of Physics in the College of Arts and Sciences, has made a breakthrough in that direction with a room-temperature magnetoelectric memory device. Equivalent to one computer bit, it exhibits the holy grail of next-generation nonvolatile memory: magnetic switchability, in two steps, with nothing but an electric field. Their results were published online Dec. 17 in Nature, along with an associated "News and Views" article.

"The advantage here is low energy consumption," Heron said. "It requires a low voltage, without current, to switch it. Devices that use currents consume more energy and dissipate a significant amount of that energy in the form of heat. That is what's heating up your computer and draining your batteries."

The researchers made their device out of a compound called bismuth ferrite, a favorite among materials mavens for a spectacularly rare trait: It's both magnetic -- like a fridge magnet, it has its own, permanent local magnetic field -- and also ferroelectric, meaning it's always electrically polarized, and that polarization can be switched by applying an electric field. Such so-called ferroic materials are typically one or the other, rarely both, as the mechanisms that drive the two phenomena usually fight each other.

This combination makes it a "multiferroic" material, a class of compounds that has enjoyed a buzz over the last decade or so. Paper co-author Ramamoorthy Ramesh, Heron's Ph.D. adviser at University of California, Berkeley, first showed in 2003 that bismuth ferrite can be grown as extremely thin films and can exhibit enhanced properties compared to bulk counterparts, igniting its relevance for next-generation electronics.

Because it's multiferroic, bismuth ferrite can be used for nonvolatile memory devices with relatively simple geometries. The best part is it works at room temperature; other scientists, including Schlom's group, have demonstrated similar results with competing materials, but at unimaginably cold temperatures, like 4 Kelvin (-452 Fahrenheit) -- not exactly primed for industry. "The physics has been exciting, but the practicality has been absent," Schlom said.

A key breakthrough by this team was theorizing, and experimentally realizing, the kinetics of the switching in the bismuth ferrite device. They found that the switching happens in two distinct steps. One-step switching wouldn't have worked, and for that reason theorists had previously thought what they have achieved was impossible, Schlom said. But since the switching occurs in two steps, bismuth ferrite is technologically relevant.

The multiferroic device also seems to require an order of magnitude lower energy than its chief competitor, a phenomenon called spin transfer torque, which Ralph also studies, and that harnesses different physics for magnetic switching. Spin transfer torque is already used commercially but in only limited applications. They have some work to do; for one thing they made just a single device, and computer memory involves billions of arrays of such devices. They need to ramp up its durability, too. But for now, proving the concept is a major leap in the right direction.

"Ever since multiferroics came back to life around 2000, achieving electrical control of magnetism at room temperature has been the goal," Schlom said.

Source: Cornell University