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News from the Department of Physics.

older | 1 | .... | 6 | 7 | (Page 8)

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    An international team of researchers led by the University of Cambridge found that the addition of potassium iodide ‘healed’ the defects and immobilised ion movement, which to date have limited the efficiency of cheap perovskite solar cells. These next-generation solar cells could be used as an efficiency-boosting layer on top of existing silicon-based solar cells, or be made into stand-alone solar cells or coloured LEDs. The results are reported in the journal Nature.

    The solar cells in the study are based on metal halide perovskites – a promising group of ionic semiconductor materials that in just a few short years of development now rival commercial thin film photovoltaic technologies in terms of their efficiency in converting sunlight into electricity. Perovskites are cheap and easy to produce at low temperatures, which makes them attractive for next-generation solar cells and lighting.

    Despite the potential of perovskites, some limitations have hampered their efficiency and consistency. Tiny defects in the crystalline structure of perovskites, called traps, can cause electrons to get ‘stuck’ before their energy can be harnessed. The easier that electrons can move around in a solar cell material, the more efficient that material will be at converting photons, particles of light, into electricity. Another issue is that ions can move around in the solar cell when illuminated, which can cause a change in the bandgap – the colour of light the material absorbs.  

    “So far, we haven’t been able to make these materials stable with the bandgap we need, so we’ve been trying to immobilise the ion movement by tweaking the chemical composition of the perovskite layers,” said Dr Sam Stranks from Cambridge’s Cavendish Laboratory, who led the research. “This would enable perovskites to be used as versatile solar cells or as coloured LEDs, which are essentially solar cells run in reverse.”

    In the study, the researchers altered the chemical composition of the perovskite layers by adding potassium iodide to perovskite inks, which then self-assemble into thin films. The technique is compatible with roll-to-roll processes, which means it is scalable and inexpensive. The potassium iodide formed a ‘decorative’ layer on top of the perovskite which had the effect of ‘healing’ the traps so that the electrons could move more freely, as well as immobilising the ion movement, which makes the material more stable at the desired bandgap.

    The researchers demonstrated promising performance with the perovskite bandgaps ideal for layering on top of a silicon solar cell or with another perovskite layer – so-called tandem solar cells. Silicon tandem solar cells are the most likely first widespread application of perovskites. By adding a perovskite layer, light can be more efficiently harvested from a wider range of the solar spectrum.

    “Potassium stabilises the perovskite bandgaps we want for tandem solar cells and makes them more luminescent, which means more efficient solar cells,” said Stranks, whose research is funded by the European Union and the European Research Council’s Horizon 2020 Programme. “It almost entirely manages the ions and defects in perovskites.”

    “We’ve found that perovskites are very tolerant to additives – you can add new components and they’ll perform better,” said first author Mojtaba Abdi-Jalebi, a PhD candidate at the Cavendish Laboratory who is funded by Nava Technology Limited. “Unlike other photovoltaic technologies, we don’t need to add an additional layer to improve performance, the additive is simply mixed in with the perovskite ink.”

    The perovskite and potassium devices showed good stability in tests, and were 21.5% efficient at converting light into electricity, which is similar to the best perovskite-based solar cells and not far below the practical efficiency limit of silicon-based solar cells, which is (29%). Tandem cells made of two perovskite layers with ideal bandgaps have a theoretical efficiency limit of 45% and a practical limit of 35% - both of which are higher than the current practical efficiency limits for silicon. “You get more power for your money,” said Stranks.

    The research has also been supported in part by the Royal Society and the Engineering and Physical Sciences Research Council. The international team included researchers from Cambridge, Sheffield University, Uppsala University in Sweden and Delft University of Technology in the Netherlands.

    Reference:
    Mojtaba Abdi-Jalebi et al. ‘Maximising and Stabilising Luminescence from Halide Perovskites with Potassium Passivation.’ Nature (2018). DOI: 10.1038/nature25989

    A simple potassium solution could boost the efficiency of next-generation solar cells, by enabling them to convert more sunlight into electricity. 

    Perovskites are very tolerant to additives – you can add new components and they’ll perform better.
    Mojtaba Abdi-Jalebi
    Atomic scale view of perovskite crystal formation

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    Joanna Waldie

    My research focuses on developing devices that can manipulate electrons one at a time. I also happen to have long gaps on my CV that take some creativity to explain in job interviews. This is because I’ve had mental health problems since I was a teenager.  During treatment for this, I’ve been privileged to meet some wonderful people with a variety of mental health conditions and to gain a little insight into their struggles.

    Mental health conditions are often invisible. If I have a broken leg or a sore throat then it doesn’t take much for my colleagues to understand that I need time off work. If my mental health is bad then the onus is on me to explain to other people why I need time off work.

    I worry that people will think I am silly, or oversensitive, or lazy, or skiving. However, the first person you need to convince that it’s OK to have time off is yourself. It feels like a great step forward when you do.

    There are a lot of misconceptions about mental illnesses, not least because their invisibility makes awareness of their prevalence remain low. If I tell someone what mental health conditions I have, I have no idea what this will mean to them, and whether it will match the reality of how I feel. This is particularly the case in the multicultural research environment, where different cultures may have very different understandings of mental health.

    As researchers we have succeeded in our University studies and got our PhDs. We are used to solving problems, achieving highly and getting stuff done.

    When faced with a mental health condition, we feel desperately that we need to understand and solve the problem, and soon. But even after many years I do not fully understand my mental health problems. I cannot fix them or solve them as I would a problem in the lab.

    It has taken me years to learn to spot triggers and recognise warning signs when things are getting bad, and to learn some things that sometimes help. I have learned a huge amount, but there is still much I don’t understand about this illness.

    I have told few colleagues about my health problems, but those I have told have been supportive. I’ve benefited from some fantastic services at the University including the staff counselling and occupational health services. That support – at work and from family and friends – makes a huge difference.

    There are still challenges – my ongoing mental health problems are classed as a disability, and that meant I had to tick a box labelling me as a “disabled person” when I started this job in order to qualify for reasonable adjustments. Not everyone would feel OK about that. These labels can create barriers to people coming forward to seek help.

    Researchers often have to move around a lot to advance their careers, doing a series of short-term contracts in several places. If someone with a mental health condition comes to the UK for an 18-month postdoc job, it might take them a while to understand how to access treatment in the UK. They might wait for months to be seen by a specialist. And treatment in the UK might be very different to what they have known in in their home country.

    I’ve been very lucky in this respect. When I was a PhD student, my College provided me with free accommodation near to the hospital where I was being treated so I didn’t have to move back to live with my parents and start all over again on a waiting list.

    My fellowship is normally only open to people who are moving to Cambridge. But the selection panel took into account that I wanted to stay in Cambridge to continue to access treatment and support at the same clinic.

    The sector needs to do more to help researchers who have moved for a job, uprooting themselves from their support networks.

    Research is challenging. In trying to do things no one has ever done before there are always setbacks. For someone with a mental health condition, you can go from one setback in the lab to deep despair in the time it takes to say ‘Supercalifragilisticexpialidocious’.

    Sometimes I wish having someone beside me to give moral support during difficult experiments counted as a ‘reasonable adjustment’. But I am lucky to have colleagues and a boss who do support me.

    As a researcher you need to believe in your research ideas and your ability to carry them out. You need to be able to sell your research. You need to be excited by your research and be able to convince other people to get excited about it, to publish it, to fund it. This is hard to do if you are feeling depressed, and you don’t even feel like life is worth living. It’s really hard.

    But friends and colleague can make a real difference in helping people with mental health problems to flourish in their research.

    A greater openness about mental health in the research community will surely benefit us all.

    Herchel Smith postdoctoral research fellow in Physics Dr Joanna Waldie shares her personal story to support Mental Health Awareness Week

    When I need time off, I worry that people will think I am silly, or oversensitive, or lazy, or skiving - the first person you need to convince that it’s OK is yourself
    Joanna Waldie

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    The researchers, whose work appears in the journal Science, say their findings could be a “game changer” by allowing the energy from sunlight absorbed in these materials to be captured and used more efficiently. 

    Lightweight semiconducting plastics are now widely used in mass market electronic displays such as those found in phones, tablets and flat-screen televisions.  However, using these materials to convert sunlight into electricity to make solar cells is far more complex. 

    The photo-excited states – when photons of light are absorbed by the semiconducting material – need to move so that they can be “harvested” before they lose their energy.  These excitations typically only travel about 10 nanometres in plastic (or polymeric) semiconductors, so researchers need to build tiny structures patterned at the nanoscale to maximise the “harvest”.

    Dr Xu-Hui Jin and colleagues at the University of Bristol developed a new way to make highly ordered crystalline semiconducting structures using polymers.

    Dr Michael Price of Cambridge's Cavendish Laboratory measured the distance that the photo-exited states travelled, which reached distances of 200 nanometres – 20 times further than was previously possible.

    200 nanometres is especially significant because it is greater than the thickness of material needed to completely absorb ambient light, making these polymers more suitable as “light harvesters” for solar cells and photodetectors.

    “The gain in efficiency would actually be for two reasons: first, because the energetic particles travel further, they are easier to “harvest”, and second, we could now incorporate layers around 100 nanometres thick, which is the minimum thickness needed to absorb all the energy from light – the so-called optical absorption depth,” said co-author Dr George Whittell from the University of Bristol. “Previously, in layers this thick, the particles were unable to travel far enough to reach the surfaces.”

    “The distance that energy can be moved in these materials comes as a big surprise and points to the role of unexpected quantum coherent transport processes,” said co-author Professor Sir Richard Friend from Cambridge's Cavendish Laboratory, and a Fellow of St John's College. 

    The research team now plans to prepare structures thicker than those in the current study and greater than the optical absorption depth, with a view to building prototype solar cells based on this technology.

    They are also preparing other structures capable of using light to perform chemical reactions, such as the splitting of water into hydrogen and oxygen.

    Reference:
    Xu-Hui Jin et al.Long-range exciton transport in conjugated polymer nanofibers prepared by seeded growth.’ Science (2018). DOI: 10.1126/science.aar8104 

    Adapted from a University of Bristol press release. 

    Scientists from the Universities of Cambridge and Bristol have found a way to create plastic semiconductor nanostructures that absorb light and transport its energy 20 times further than has been previously observed, paving the way for more flexible and more efficient solar cells and photodetectors. 

    The distance that energy can be moved in these materials comes as a big surprise.
    Richard Friend
    Image showing light emission from the polymeric nanostructures and schematic of a single nanostructure

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    Researchers at the University of Cambridge and the University of Illinois at Urbana-Champaign say their lipid-scrambling DNA enzyme is the first to outperform naturally occurring enzymes – and does so by three orders of magnitude. Their findings are published in the journal Nature Communications.

    “Cell membranes are lined with a different set of molecules on the inside and outside, and cells devote a lot of resources to maintaining this,” said study leader Aleksei Aksimentiev, a professor of physics at Illinois. “But at some points in a cell’s life, the asymmetry has to be dismantled. Then the markers that were inside become outside, which sends signals for certain processes, such as cell death. There are enzymes in nature that do that called scramblases. However, in some other diseases where scramblases are deficient, this doesn’t happen correctly. Our synthetic scramblase could be an avenue for therapeutics.”

    Aksimentiev’s group came upon DNA’s scramblase activity when looking at DNA structures that form pores and channels in cell membranes. They used the Blue Waters supercomputer at the National Center for Supercomputing Applications at Illinois to model the systems at the atomic level. They saw that when certain DNA structures insert into the membrane – in this case, a bundle of eight strands of DNA with cholesterol at the ends of two of the strands – lipids in the membrane around the DNA begin to shuffle between the inner and outer membrane layers.

    To verify the scramblase activity predicted by the computer models, Aksimentiev’s group at Illinois partnered with Professor Ulrich Keyser’s group at Cambridge. The Cambridge group synthesised the DNA enzyme and tested it in model membrane bubbles, called vesicles, and then in human breast cancer cells.

    “The results show very conclusively that our DNA nanostructure facilitates rapid lipid scrambling,” said co-first author Alexander Ohmann, a PhD student in Keyser’s group in Cambridge’s Cavendish Laboratory. “Most interestingly, the high flipping rate indicated by the molecular dynamics simulations seems to be of the same order of magnitude in experiments: up to a thousand-fold faster than what has previously been shown for natural scramblases.”

    On its own, the DNA scramblase produces cell death indiscriminately, said Aksimentiev. The next step is to couple it with targeting systems that specifically seek out certain cell types, a number of which have already been developed for other DNA agents.

    “We are also working to make these scramblase structures activated by light or some other stimulus, so they can be activated only on demand and can be turned off,” said Aksimentiev.

    “Although we have still a long way to go, this work highlights the enormous potential of synthetic DNA nanostructures with possible applications for personalised drugs and therapeutics for a variety of health conditions in the future,” said Ohmann, who has also written a blog post on their new paper.

    The US National Science Foundation and the National Institutes of Health supported this work.  

    Reference:
    Alexander Ohmann et al. ‘A synthetic enzyme built from DNA flips 107 lipids per second in biological membranes.’ Nature Communications (2018). DOI: 10.1038/s41467-018-04821-5

    ​Adapted from a University of Illinois at Urbana-Champaign press release.

    A new synthetic enzyme, crafted from DNA rather than protein, ‘flips’ lipid molecules within the cell membrane, triggering a signal pathway that could be harnessed to induce cell death in cancer cells.

    This work highlights the enormous potential of synthetic DNA nanostructures for personalised drugs and therapeutics for a variety of health conditions.
    Alexander Ohmann
    DNA scramblase

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  • 07/13/18--02:08: Homeward Bound
  • Earlier this year a team of 78 women from around the world took part in a three-week expedition to Antarctica, a trip that marked the culmination of the year-long Homeward Bound leadership programme for women in Science, Technology, Engineering, Mathematics and Medicine (STEMM). Read more about their adventure here

    Homeward bound expedition

    Creative Commons License
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    The researchers, from the University of Cambridge and the Medical Research Council Laboratory of Molecular Biology (MRC LMB), found that the chances for life to develop on the surface of a rocky planet like Earth are connected to the type and strength of light given off by its host star.

    Their study, published in the journal Science Advances, proposes that stars which give off sufficient ultraviolet (UV) light could kick-start life on their orbiting planets in the same way it likely developed on Earth, where the UV light powers a series of chemical reactions that produce the building blocks of life.

    The researchers have identified a range of planets where the UV light from their host star is sufficient to allow these chemical reactions to take place, and that lie within the habitable range where liquid water can exist on the planet’s surface.

    “This work allows us to narrow down the best places to search for life,” said Dr Paul Rimmer, a postdoctoral researcher with a joint affiliation at Cambridge’s Cavendish Laboratory and the MRC LMB, and the paper’s first author. “It brings us just a little bit closer to addressing the question of whether we are alone in the universe.”

    The new paper is the result of an ongoing collaboration between the Cavendish Laboratory and the MRC LMB, bringing together organic chemistry and exoplanet research. It builds on the work of Professor John Sutherland, a co-author on the current paper, who studies the chemical origin of life on Earth.

    In a paper published in 2015, Professor Sutherland’s group at the MRC LMB proposed that cyanide, although a deadly poison, was in fact a key ingredient in the primordial soup from which all life on Earth originated.

    In this hypothesis, carbon from meteorites that slammed into the young Earth interacted with nitrogen in the atmosphere to form hydrogen cyanide. The hydrogen cyanide rained to the surface, where it interacted with other elements in various ways, powered by the UV light from the sun. The chemicals produced from these interactions generated the building blocks of RNA, the close relative of DNA which most biologists believe was the first molecule of life to carry information.

    In the laboratory, Sutherland’s group recreated these chemical reactions under UV lamps, and generated the precursors to lipids, amino acids and nucleotides, all of which are essential components of living cells.

    “I came across these earlier experiments, and as an astronomer, my first question is always what kind of light are you using, which as chemists they hadn’t really thought about,” said Rimmer. “I started out measuring the number of photons emitted by their lamps, and then realised that comparing this light to the light of different stars was a straightforward next step.”

    The two groups performed a series of laboratory experiments to measure how quickly the building blocks of life can be formed from hydrogen cyanide and hydrogen sulphite ions in water when exposed to UV light. They then performed the same experiment in the absence of light.

    “There is chemistry that happens in the dark: it’s slower than the chemistry that happens in the light, but it’s there,” said senior author Professor Didier Queloz, also from the Cavendish Laboratory. “We wanted to see how much light it would take for the light chemistry to win out over the dark chemistry.”

    The same experiment run in the dark with the hydrogen cyanide and the hydrogen sulphite resulted in an inert compound which could not be used to form the building blocks of life, while the experiment performed under the lights did result in the necessary building blocks.

    The researchers then compared the light chemistry to the dark chemistry against the UV light of different stars. They plotted the amount of UV light available to planets in orbit around these stars to determine where the chemistry could be activated.

    They found that stars around the same temperature as our sun emitted enough light for the building blocks of life to have formed on the surfaces of their planets. Cool stars, on the other hand, do not produce enough light for these building blocks to be formed, except if they have frequent powerful solar flares to jolt the chemistry forward step by step. Planets that both receive enough light to activate the chemistry and could have liquid water on their surfaces reside in what the researchers have called the abiogenesis zone.

    Among the known exoplanets which reside in the abiogenesis zone are several planets detected by the Kepler telescope, including Kepler 452b, a planet that has been nicknamed Earth’s ‘cousin’, although it is too far away to probe with current technology. Next-generation telescopes, such as NASA’s TESS and James Webb Telescopes, will hopefully be able to identify and potentially characterise many more planets that lie within the abiogenesis zone.

    Of course, it is also possible that if there is life on other planets, that it has or will develop in a totally different way than it did on Earth.

    “I’m not sure how contingent life is, but given that we only have one example so far, it makes sense to look for places that are most like us,” said Rimmer. “There’s an important distinction between what is necessary and what is sufficient. The building blocks are necessary, but they may not be sufficient: it’s possible you could mix them for billions of years and nothing happens. But you want to at least look at the places where the necessary things exist.”

    According to recent estimates, there are as many as 700 million trillion terrestrial planets in the observable universe. “Getting some idea of what fraction have been, or might be, primed for life fascinates me,” said Sutherland. “Of course, being primed for life is not everything and we still don’t know how likely the origin of life is, even given favourable circumstances - if it’s really unlikely then we might be alone, but if not, we may have company.”

    The research was funded by the Kavli Foundation and the Simons Foundation.

    Reference:
    Paul B. Rimmer et al. ‘The Origin of RNA Precursors on Exoplanets.’ Science Advances (2018). DOI: 10.1126/sciadv.aar3302

    Inset image: Diagram of confirmed exoplanets within the liquid water habitable zone (as well as Earth). Credit: Paul Rimmer

    Scientists have identified a group of planets outside our solar system where the same chemical conditions that may have led to life on Earth exist. 

    This work brings us just a little bit closer to addressing the question of whether we are alone in the universe.
    Paul Rimmer
    Artist's concept depicting one possible appearance of the planet Kepler-452b

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    The Quantum Flagship, which is being officially launched today in Vienna, is one of the most ambitious long-term research and innovation initiatives of the European Commission. It is funded under the Horizon 2020 programme, and will have a budget of €1 billion over the next ten years.                   

    The Quantum Flagship is the third large-scale research and innovation initiative of this kind funded by the European Commission, after the Graphene Flagship – of which the University of Cambridge is a founding partner – and the Human Brain Project. The Quantum Flagship work in Cambridge is being coordinated by Professor Mete Atature of the Cavendish Laboratory and Professor Andrea Ferrari, Director of the Cambridge Graphene Centre.

    Quantum technologies take advantage of the ability of particles to exist in more than one quantum state at a time. A quantum computer could enable us to make calculations that are well out of reach of even the most powerful supercomputers, while quantum secure communication could power ‘unhackable’ networks made safe by the laws of physics.

    The long-term research goal is the so-called quantum web, where quantum computers, simulators and sensors are interconnected via quantum networks, distributing information and quantum resources such as coherence and entanglement.

    The potential performance increase resulting from quantum technologies may yield unprecedented computing power, guarantee data privacy and communication security, and provide ultra-high precision synchronisation and measurements for a range of applications available to everyone, locally and in the cloud.

    The new Quantum Flagship will bring together academic and industrial partners, with over 500 researchers working on solving these problems, and help turn the results into technological opportunities that can be taken up by industry.

    In close partnership with UK, Italian, Spanish, Swedish universities and companies, Cambridge will develop layered quantum materials and devices for scalable integrated photonic circuits, for applications in quantum communication and networks.

    Cambridge is investigating and refining layered semiconductors just a few atoms thick, based on materials known as transition metal dichalcogenides (TMDs). Certain TMDs contain quantum light sources that can emit single photons of light, which could be used in quantum computing and sensing applications.

    These quantum light emitters occur randomly in layered materials, as is the case for most other material platforms. Over the past three years, the Cambridge researchers have developed a technique to obtain large-scale arrays of these quantum emitters in different TMDs and on a variety of substrates, establishing a route to build quantum networks on compact chips. The Cambridge team has also shown how to electrically control emission from these devices.

    Additionally, the researchers have found that TMDs can support complex quasi-particles, called quintons. Quintons could be a source of entangled photons - particles of light which are intrinsically linked, no matter how far apart they are - if they can be trapped in quantum emitters.

    These findings are the basis of the work being done in the Quantum Flagship, aimed at the development of scalable on-chip devices for quantum integrated photonic circuits, to enable secure quantum communications and quantum sensing applications.

    “Our goal is to bring some of the amazing properties of the layered materials platform into the quantum technologies realm for a number of applications,” said Atature. “Achieving compact integrated quantum photonic circuits is a challenge pursued globally and our patented layered materials technology offers solutions to this challenge. This is a great project that combines quantum physics, optoelectronics and materials science to produce technology for the future.”

    “Quantum technology is a key investment area for Europe, and layered materials show great promise for the generation and manipulation of quantum light for future technological advances,” said Ferrari. “The Graphene Flagship led the way for these large European Initiatives, and we are pleased to be part of the new Quantum Flagship. The Flagships are the largest and most transformative investments in research of the European Union, and will cement the EU leadership in future and emerging technologies.” 

    Andrus Ansip, Commission Vice-President for the Digital Single Market, said: “Europe is determined to lead the development of quantum technologies worldwide. The Quantum Technologies Flagship project is part of our ambition to consolidate and expand Europe's scientific excellence. If we want to unlock the full potential of quantum technologies, we need to develop a solid industrial base making full use of our research.”

    Inset images: Mete Atature and Andrea Ferrari; Artist’s impression of on-chip quantum photonics architecture with single photon sources and nonlinear switches on optical waveguides, credit Matteo Barbone.

    The University of Cambridge is a partner in the €1 billion Quantum Flagship, an EU-funded initiative to develop quantum technologies across Europe. 

    The Flagships are the largest and most transformative investments in research of the European Union, and will cement the EU leadership in future and emerging technologies
    Andrea Ferrari

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    Compared to OLEDs, which are widely used in high-end consumer electronics, the perovskite-based LEDs, developed by researchers at the University of Cambridge, can be made at much lower costs, and can be tuned to emit light across the visible and near-infrared spectra with high colour purity.

    The researchers have engineered the perovskite layer in the LEDs to show close to 100% internal luminescence efficiency, opening up future applications in display, lighting and communications, as well as next-generation solar cells.

    These perovskite materials are of the same type as those found to make highly efficient solar cells that could one day replace commercial silicon solar cells. While perovskite-based LEDs have already been developed, they have not been nearly as efficient as conventional OLEDs at converting electricity into light.

    Earlier hybrid perovskite LEDs, first developed by Professor Sir Richard Friend’s group at the University’s Cavendish Laboratory four years ago, were promising, but losses from the perovskite layer, caused by tiny defects in the crystal structure, limited their light-emission efficiency.

    Now, Cambridge researchers from the same group and their collaborators have shown that by forming a composite layer of the perovskites together with a polymer, it is possible to achieve much higher light-emission efficiencies, close to the theoretical efficiency limit of thin-film OLEDs. Their results are reported in the journal Nature Photonics.

    “This perovskite-polymer structure effectively eliminates non-emissive losses, the first time this has been achieved in a perovskite-based device,” said Dr Dawei Di from Cambridge’s Cavendish Laboratory, one of the corresponding authors of the paper. “By blending the two, we can basically prevent the electrons and positive charges from recombining via the defects in the perovskite structure.”

    The perovskite-polymer blend used in the LED devices, known as a bulk heterostructure, is made of two-dimensional and three-dimensional perovskite components and an insulating polymer. When an ultra-fast laser is shone on the structures, pairs of electric charges that carry energy move from the 2D regions to the 3D regions in a trillionth of a second: much faster than earlier layered perovskite structures used in LEDs. Separated charges in the 3D regions then recombine and emit light extremely efficiently.

    “Since the energy migration from 2D regions to 3D regions happens so quickly, and the charges in the 3D regions are isolated from the defects by the polymer, these mechanisms prevent the defects from getting involved, thereby preventing energy loss,” said Di.

    “The best external quantum efficiencies of these devices are higher than 20% at current densities relevant to display applications, setting a new record for perovskite LEDs, which is a similar efficiency value to the best OLEDs on the market today,” said Baodan Zhao, the paper’s first author.

    While perovskite-based LEDs are beginning to rival OLEDs in terms of efficiency, they still need better stability if they are to be adopted in consumer electronics. When perovskite-based LEDs were first developed, they had a lifetime of just a few seconds. The LEDs developed in the current research have a half-life close to 50 hours, which is a huge improvement in just four years, but still nowhere near the lifetimes required for commercial applications, which will require an extensive industrial development programme. “Understanding the degradation mechanisms of the LEDs is a key to future improvements,” said Di.

    The research was funded by the Engineering and Physical Sciences Research Council (EPSRC) and the European Research Council (ERC).

    Reference:
    Baodan Zhao et al. ‘High-efficiency perovskite-polymer bulk heterostructure light-emitting diodes.’ Nature Photonics (2018). DOI: 10.1038/s41566-018-0283-4

    Researchers have set a new efficiency record for LEDs based on perovskite semiconductors, rivalling that of the best organic LEDs (OLEDs). 

    Artistic impression of the perovskite-polymer heterostructure used in LEDs

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