Researchers improve efficiency of lowcost solar cells


first_img The researchers, Qijie Guo, Grayson M. Ford, Wei-Chang Yang, Bryce C. Walker, Eric A. Stach, Hugh W. Hillhouse, and Rakesh Agrawal, have published their study on the improved solar cells in a recent issue of the Journal of the American Chemical Society. They fabricated the solar cells from copper-zinc-tin-chalcogenide (CZTSSe), which is an Earth-abundant material, using a solution-based thin-film deposition method. Previous research has shown that these methods can provide high yields at lower manufacturing costs compared to other methods.The solar cell design is based on the researchers’ earlier study in which they demonstrated that solar cells fabricated using CZTS nanocrystals are potentially viable, although they had efficiencies of less than 1%. Here, the researchers made significant improvements to the design by tuning the composition of the nanocrystals as well as developing a more robust thin-film coating method.After synthesizing the nanocrystals and applying them on a substrate for a total film thickness of 1 micrometer, the researchers observed that the nanocrystal film featured large, densely packed grains, which leads to improved solar cell efficiency. In testing, the solar cells could achieve a total area efficiency of 7.2%. As coauthor Hugh Hillhouse explained, the total area efficiency refers to the entire cell, rather than just the “active area.””It is the total area efficiency that matters most,” he told PhysOrg.com. “Some people report an ‘active area’ efficiency, which only includes areas that the light reaches. However, all thin film solar cells are made with metal contacts that block the light from reaching some areas. When you include this loss, we use the term ‘total area’ efficiency. It is the most fair and important efficiency.”The 7.2% efficiency was reached after “light soaking” for 15 minutes under one-sun illumination; when the light was turned off, the efficiency dropped to 6.89%. “Light soaking simply means that we shine normal intensity simulated sunlight on the cell for a period of time before we make the measurement,” Hillhouse said. “Most likely, the light soaking allows photogenerated carriers to fill traps, shift the quasi-Fermi levels, and/or screen barriers created by band offsets. It doesn’t present a problem since real solar cells are naturally light soaked – they sit in the sun.”Although currently there are no CZTS or CZTSSe solar cells on the market for comparison, the solar cells in this study are very competitive with other fabrication methods.“The best cells formed by vacuum processes have only reached 6.7%,” Hillhouse said. “Typically, solar cells produced by vacuum-based processes have been more efficient, but also more expensive. For the case of CZTS, the solution phase approach (our nanocrystal route and IBM’s hydrazine route) is more efficient.”One potential area for improvement for these solar cells lies in improving their low quantum efficiency for light of longer wavelengths (i.e., the near-infrared range). The researchers attempted to improve this efficiency by increasing the thickness of the absorber, although their initial experiments showed that thicker absorber layers also had increased resistance. In the future, they plan to optimize the fabrication for thicker films, which could further increase the overall efficiency.“There is a lot of compositional freedom in the CZTSSe system, and it is likely that the optimum compositions, device structure, and processing conditions have not yet been found – but we are working on it,” Hillhouse said. Copyright 2010 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com. Structure of plastic solar cells impedes their efficiency, researchers find Citation: Researchers improve efficiency of low-cost solar cells (2010, December 7) retrieved 18 August 2019 from https://phys.org/news/2010-12-efficiency-low-cost-solar-cells.html (PhysOrg.com) — As part of the recent progress in improving solar cells for widespread use, researchers from Purdue University have designed solar cells made of low-cost, abundant materials that are easily scalable and very stable. The researchers have increased the solar cells’ total area efficiency to 7.2% and plan to make further improvements in the future. More information: Qijie Guo, et al. “Fabrication of 7.2% Efficient CZTSSe Solar Cells Using CZTS Nanocrystals.” J. Am. Chem. Soc. ASAP. DOI: 10.1021/ja108427b Explore further This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. This image shows a cross-section of a CZTSSe thin film solar cell. The film exhibits densely packed grains, which leads to a high efficiency. Image credit: Qijie Guo, et al. ©2010 American Chemical Society.last_img read more

Researchers theorize cold compression of graphite results in new superhard carbon allotropes


first_img © 2012 PhysOrg.com Crystal structure of H-carbon(a), initial AB stacking graphite supercell for H-carbon (b) and side view containing five and seven carbon rings of H-carbon (c). Crystal structure of S-carbon (d), initial AB stacking graphite supercell for Scarbon (e) and side view containing five and seven carbon rings of S-carbon (f). Image from arXiv:1203.5509v1 (PhysOrg.com) — Researchers in China have used math calculations to predict that under cold compression, two new carbon allotropes may be formed. In their paper pre-published on arXiv, the team describes how the two new allotropes would have a hardness factor somewhere between graphite and diamond. New carbon allotrope could have a variety of applications This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. More information: New Superhard Carbon Phases Between Graphite and Diamond, arXiv:1203.5509v1 [cond-mat.mtrl-sci] arxiv.org/abs/1203.5509AbstractTwo new carbon allotropes (H-carbon and S-carbon) are proposed, as possible candidates for the intermediate superhard phases between graphite and diamond obtained in the process of cold compressing graphite, based on the results of first-principles calculations.Both H-carbon and S-carbon are more stable than previously proposed M-carbon and W-carbon and their bulk modulus are comparable to that of diamond. H-carbon is an indirect-band-gap semiconductor with a gap of 4.459 eV and S-carbon is a direct-band-gap semiconductor with a gap of 4.343 eV. S-carbon is even more stable than the Z-carbon which is the most table carbon phase proposed recently. The transition pressure from cold compressing graphite is 10.08 GPa and 5.93 Gpa for H-carbon and S-carbon,respectively, which is in consistent with the recent experimental report.via Arxiv Blog Explore further An allotrope is a substance that is essentially the same as another, with just minor differences in structure. Thus, both graphite and diamonds are allotropes of carbon. In their paper, the research team shows, via mathematical calculations, that subjecting a graphite allotrope to varying degrees of both cold and high pressure, would result in small changes to the structure, resulting in two new carbon allotropes.Prior to this work, other researchers have theorized that applying pressure at room temperature (more than 10 GigaPascals) to graphite would also result in structural changes, creating new allotropes (M10-carbon, monoclinic M-carbon, orthorhombic W-carbon or cubic body center C4 carbon) though thus far it isn’t clear if those changes would remain in effect after the pressure is removed.The new allotropes that theoretically would be produced by exerting pressure under cold conditions, which the team have called H-carbon and S-carbon, would also apparently be more stable than the allotropes produced without the cold, and even more stable, they say, than graphite under pressure, which means they would be more likely to survive in their compressed state after being returned to normal conditions.By using mathematical models to predict the creation of new carbon allotropes, researchers pave the way for real world experiments to find out if the new materials would truly exist, and if so, to what purpose they might be used. New carbon allotropes would have different optical properties, such as their degree of transparency, for example or how well they reflect light, than already well understood allotropes that are already being used in real world applications,. Such properties in new allotropes, if they can be caused to persist under reasonable conditions, might lead to new and better products.But before researchers begin trying to produce these new allotropes, more theoretical work will need to be done to see if there are others out there still waiting to be discovered. Citation: Researchers theorize cold compression of graphite results in new superhard carbon allotropes (2012, March 30) retrieved 18 August 2019 from https://phys.org/news/2012-03-theorize-cold-compression-graphite-results.htmllast_img read more

Psychologists say Facebook Twitter harden gender walls


first_img This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Citation: Psychologists say Facebook, Twitter harden gender walls (2012, June 25) retrieved 18 August 2019 from https://phys.org/news/2012-06-psychologists-facebook-twitter-harden-gender.html Explore further Adding to a cynic’s file of Hardly-Shocking research is a new study out from the University of Bath that reports women are more attracted to social-networking sites than are men, who learn more toward Internet sites that carry games and gambling. Where the study does merit interest, however, is that it is a ten-year follow-up study that explores what if any changes have occurred since its first examination of gender differences in Internet usage in 2002. © 2012 Phys.Org Journal information: Cyberpsychology, Behavior, and Social Networking The paper, “Gender, Internet experience, Internet identification and Internet anxiety: a ten year follow-up,” appears in Cyberpsychology, Behavior and Social Networking. Dr. Richard Joiner is the lead author.”In our previous research we had found no gender differences in the use of the Internet for communication, whereas in the current study we have found that females use the Internet for communication than males and were using social network sites more than males.”As the study authors point out, the Internet has changed considerably since their 2002 look, with the introduction of Facebook, Twitter and deluge of smartphones. Interestingly, some theorists claimed early on that technology advancements would lessen gender differences and that the Internet would be an equalizer, but these authors have found otherwise.Women were more attracted to social networking sites such as Facebook and Twitter and were significantly more likely to use email and telephone over the web than males; males were more likely than females to use newsgroups, gaming and gambling sites.The University of Bath study examined results from 501 first-year psychology undergraduate students from six UK universities. There were 389 females and 100 males. Twelve participants did not specify their gender. The sample was chosen to match as closely as possible the 2002 study sample.Product vendors and marketing agencies, among others, are most likely to pay attention to Internet gender-usage studies. The takeaway of the University of Bath Department of Psychology study is that its authors say the gap has grown wider between the way in which men and women use the Internet.“Our findings indicate that rather than transcending or overcoming gender differences in wider society, Internet use by males and females seems to reflect, and in some instances even exacerbate, these broader trends.”They also express support of the view that gender differences in the use of the Internet reflect gender differences in wider society and are thus “more resistant to change than some people have suggested.” More information: opus.bath.ac.uk/30228/ Examining gender disparities in injury mortality; men at exceptional risklast_img read more

Researchers find blocking Internet pirating sites is not effective


first_img Citation: Researchers find blocking Internet pirating sites is not effective (2013, January 10) retrieved 18 August 2019 from https://phys.org/news/2013-01-blocking-internet-pirating-sites-effective.html Credit: Tobias Lauinger et al. Researchers find most BitTorrent users being monitored Explore further This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. There has been a lot of press coverage of pirating on the Internet and corporate efforts to stop it, yet to date, the researchers note, very little if any research has been conducted to determine if the methods used are effective. To find out for themselves, the team began monitoring the availably of thousands of files spread across the Internet via popular file-hosting sites. They noted that as sites were blocked, availability of certain files dropped, but only for a short time – soon other sites picked up the slack and the files formerly found on the blocked site soon became available on other hosting sites, making the blocking action moot.As part of their research, the team also noted that the shutdown of the wildly popular Megaupload site did little to curb the spread of content that users had previously found there. They suggest that if anything, shutting down arguably the most popular file sharing site on the Internet led to a more fractured landscape, with many more small sites sharing files, making stopping piracy even more difficult. The researchers also counted the number of file-sharing sites that are believed to currently host pirated content and found over 10,000 domain names covering more than 5,000 IP addresses.After analyzing their data, the research team concluded that blocking file-hosting sites is ineffective and the practice has done little to lessen the number of illegally shared files available for download from such sites. They suggest that taking away the ability to process payments from such services would likely be much more effective, though they also note the difficulty content providers might find in separating legitimate file-hosting sites from those that share pirated material. Another approach they suggest is that a more reasonable alternative be created that reduces demand, similar to the model that has been created for downloadable music. © 2013 Phys.org More information: Clickonomics: Determining the Effect of Anti-Piracy Measures for One-Click Hosting (paper PDF) (Phys.org)—Researchers at Boston’s Northeastern University have conducted a study on the effectiveness of anti-piracy measures taken by content providers to deter the illegal sharing of files on the Internet. Their research shows that tactics such as blocking sites by seizing domains names does little to curb the sharing of protected files. They suggest that providers instead focus on blocking the income stream such sites generate.last_img read more

Closer look reveals mechanism behind curling of ancient scrolls


first_img Journal information: Physical Review Letters Citation: Closer look reveals mechanism behind curling of ancient scrolls (2014, January 29) retrieved 18 August 2019 from https://phys.org/news/2014-01-closer-reveals-mechanism-ancient-scrolls.html People whose job it is to protect ancient art face a variety of destructive elements, from moisture and chemicals in the air to microbes that eat away at fabrics and paints. With scrolls, there is another problem—curling that results when fabric or paper is rolled up for storage. In addition to being unsightly, curling tends to damage the art that is being stored. For that reason, conservationists have been searching for thousands of years for ways to prevent it from happening. In this new effort, the researchers appear to have made progress in that direction by revealing what happens when material is rolled up and why it curls as a result.To find out what really happens when flat material is rolled up, the researchers subjected a variety of materials (plastics and paper) to rolling, watching very closely to see what changes came about. They also created computer models meant to replicate what occurred as rolling was applied. The one element they found that was common to all the test subjects was that the backing material underwent more stress than other parts and as a result was pulled slightly apart. When the material was unrolled (for viewing, for example) the material “tried” to shrink back to its original shape causing an expansion along its width—the end result being the familiar and undesired curling.The findings by the team suggests that a way to reduce curling is to add a backing to the underside of scrolls with material that has fibers that align with the long edges. Another approach would be to create tiny perforations in the backing to reduce stress and thus stretching—a technique that has been used on Japanese artwork for generations—they use a stiff brush.Interestingly, the work by the team in China may have a modern application—reducing curling on flexible electronic displays—a problem that consumers have recently been noting in newly developed bendable phone screens. © 2014 Phys.org Explore further More information: Curling Edges: A Problem that Has Plagued Scrolls for Millennia, Phys. Rev. Lett. 112, 034302 (2014) prl.aps.org/abstract/PRL/v112/i3/e034302AbstractQi-Wa refers to the up curl on the lengths of hand scrolls and hanging scrolls, which has troubled Chinese artisans and emperors for as long as the art of painting and calligraphy has existed. This warp is unwelcome not only for aesthetic reasons, but its potential damage to the fiber and ink. Although it is generally treated as a part of the cockling and curling due to moisture, consistency of paste, and defects from the mounting procedures, we demonstrate that the spontaneous extrinsic curvature incurred from the storage is in fact more essential to understanding and curing Qi-Wa. In contrast to the former factors whose effects are less predictable, the plastic deformation and strain distribution on a membrane are a well-defined mechanical problem. We study this phenomenon by experiments, theoretical models, and molecular dynamics simulation, and obtain consistent scaling relations for the Qi-Wa height. This knowledge enables us to propose modifications on the traditional mounting techniques that are tested on real mounted paper to be effective at mitigating Qi-Wa. By experimenting on polymer-based films, we demonstrate the possible relevance of our study to the modern development of flexible electronic paper.center_img Credit: Sun-Hsin Hung/National Palace Museum, Taipei Horsetail spores found able to ‘walk’ and ‘jump’ (w/ Video) (Phys.org) —A team of researchers in China has uncovered the reason for long side curling of scrolled artwork. In their paper published in Physical Review Letters, the researchers describe how experiments they conducted with various materials showed that curling results from stretching of backing material. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

Researchers build single molecule microphone that can detect proton size displacements


first_img(Phys.org) —A trio of researchers in the Netherlands has built a “microphone” out of just a single molecule that is capable of detecting displacements as small as a single proton. In their paper published in Physical Review Letters, Yuxi Tian, Pedro Navarro, and Michel Orrit describe how they embedded a single molecule in a crystal lattice along with a vibrating mechanism to create a new type of device capable of detecting vibrations at the nanoscale. (a) Sample mounting: an anthracene crystal doped with DBT was attached to the quartz crystal tuning fork. (b) The ZPL of a single DBT molecule is shifted upon deformation of its surrounding host crystal, as shown in (c) and (d). The real deformations are three-dimensional and much more complicated, as molecules can also rotate and be distorted. Credit: Phys. Rev. Lett. 113, 135505 – Published 26 September 2014 More information: Single Molecule as a Local Acoustic Detector for Mechanical Oscillators, Phys. Rev. Lett. 113, 135505 – Published 26 September 2014. journals.aps.org/prl/abstract/ … ysRevLett.113.135505ABSTRACTA single molecule can serve as a nanometer-sized detector of acoustic strain. Such a nanomicrophone has the great advantage that it can be placed very close to acoustic signal sources and high sensitivities can be achieved. We demonstrate this scheme by monitoring the fluorescence intensity of a single dibenzoterrylene molecule in an anthracene crystal attached to an oscillating tuning fork. The characterization of the vibration amplitude and of the detection sensitivity is a first step towards detection and control of nanomechanical oscillators through optical detection and feedback. Vibrational motion of a single molecule measured in real time Explore further Citation: Researchers build single molecule ‘microphone’ that can detect proton size displacements (2014, October 3) retrieved 18 August 2019 from https://phys.org/news/2014-10-molecule-microphone-proton-size-displacements.htmlcenter_img The researchers describe their device as a nanomicrophone, though it might best be shortened to just nanophone, as it picks up, or detects vibrations at the nanoscale. In either case, the effort was based on work conducted by a team in France recently who found that the electronic state of a molecule designated as a guest in a host matrix of another type of molecule, could be influenced by the matrix in such a way as to reveal vibrational properties of the matrix—finely enough to allow its use as a type of extremely miniature microphone.To build their micronanaphone, the researchers embedded individual dibenzoterrylene (DBT) molecules in a anthracene crystal lattice (with a low enough concentration to prevent the DBT molecules from touching). The crystal was then glued to a bit of quartz to act as a tuning fork. When the quartz was made to vibrate via an electric current it caused vibrations in the lattice which impacted the DBT molecule. In response the molecule changed how much it fluoresced (when excited by a laser), offering a way to measure how much vibration was occurring by degree of fluorescence. The team found they could focus on just one of the DBT molecules at a time because of imperfections in the crystal, which meant the final microphone was actually just one molecule in size.To test their device, the researchers stimulated the quartz in such a way as to fine tune the vibrations, measuring what they observed with just one molecule, photon by photon, over a full second and found that the device was able to accurately describe the amount of distortion occurring in the lattice. The researchers believe their micronanophone could be used for measuring either chemical or nano sized systems and because it’s so sensitive it could even be used to measure quantum effects in various structures such as extremely tiny cantilevers. One limitation is that the device only works at very low temperatures. © 2014 Phys.org This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Journal information: Physical Review Letterslast_img read more

Fossils from ancient extinct giant flightless goose suggests it was a fighter


first_img This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Reconstruction of Garganornis ballmanni Meijer, 2014 based on the newly described fossil remains. This reconstruction is based on a generic Western Palaearctic Goose with short and robust tarsometatarsus, short toes and very short wings according to the known elements of Garganornis ballmanni. Illustration made by Stefano Maugeri. Credit: Royal Society Open Science (2017). DOI: 10.1098/rsos.160722 (Phys.org)—A small team of researchers from Italy, Norway and Austria has found evidence of an ancient extinct goose relative that once lived in what is now central Italy. In their paper published in Royal Society Open Science, the team describes the fossils they found, what they suggest the bird once looked like and possibly how it behaved. Giant prehistoric bird fossils found in Antarctica Explore further Citation: Fossils from ancient extinct giant flightless goose suggests it was a fighter (2017, January 13) retrieved 18 August 2019 from https://phys.org/news/2017-01-fossils-ancient-extinct-giant-flightless.htmlcenter_img Journal information: Royal Society Open Science The fossils were found in the Gargano region near the town of Scontrone in central Italy, a place that prior research has shown was an island in the Mediterranean during the time that the bird was alive—approximately 6 to 9 million years ago. Its bones suggest it weighed approximately 22 kilograms and stood approximately one and a half meters tall. But its wings were perhaps too small to allow the bird to fly. The researchers suggest this is common in evolution, especially on islands where birds no longer rely on flight to escape predators. The large size, the researchers note, also suggests it was not an aquatic bird and perhaps lived in a forested area where it clearly had no problems finding enough food for itself and its offspring. Its wings also had carpal knobs (hard and rounded skin) on the carpometacarpus bone (the one on the end akin to the hand in humans)—they are used by modern birds to fight with one another. For that reason, the researchers suggest the ancient bird was likely a fighter, as well. They have dubbed it Garganornis ballmanni.Modern birds with carpal knobs also include some ducks and geese that commonly fight one another over territorial rights. There was also another bird, the Rodrigues solitaire, now extinct, which was known to fight so ferociously that pairs of them would break each other’s bones. The researchers suggest that G. ballmanni likely fended off any attackers by virtue of its large size, but it would likely also have had to fight with others for another precious resource: fresh water. That would mean that it was likely aggressive as well, a trait not uncommon in modern geese.The fossils also represent the first bird remains to be found at the dig site at Scontrone. More information: Marco Pavia et al. The extreme insular adaptation ofMeijer, 2014: a giant Anseriformes of the Neogene of the Mediterranean Basin, Royal Society Open Science (2017). DOI: 10.1098/rsos.160722AbstractNew skeletal elements of the recently described endemic giant anseriform Garganornis ballmanni Meijer, 2014 are presented, coming from the type-area of the Gargano and from Scontrone, southern and central Italy, respectively. The new remains represent the first bird remains found at Scontrone so far, and another shared element between these two localities, both part of the Apulia-Abruzzi Palaeobioprovince. The presence of a very reduced carpometacarpus confirms its flightlessness, only previously supposed on the basis of the very large size, while the morphologies of tarsometatarsus and posterior phalanges clearly indicate the adaptation of G. ballmanni to a terrestrial, non-aquatic, lifestyle. Its very large body size is similar to that observed in different, heavily modified, insular waterfowl and has been normally interpreted as the response to the absence of terrestrial predators and a protection from the aerial ones. The presence of a carpal knob in the proximal carpometacarpus also indicates a fighting behaviour for this large terrestrial bird species. © 2017 Phys.orglast_img read more

Efficient and stable emission of warm white light from leadfree halide double


first_img White light emission from a single emitter layer is of interest in lighting applications due to its simplicity compared to multiple emitters. Typically, broadband and white light emissions originate from self-trapped excitons (STEs) existing in semiconductors with localized carriers and a soft lattice. The authors focused on the double perovskite Cs2AgInCl6 as a promising material that emits warm white light due to its broad spectrum and all-inorganic, lead-free nature. The study optimized the alloy to form Cs2(Ag0.6Na0.4)InCl6 with a small percentage of bismuth doping to emit warm white light with increased quantum efficiency for more than 1000 hours. Materials for lighting applications can be defined as those emitting a “warm” white light for indoor applications and “cold” white light that approximates the visible region of the solar spectrum. In the study, Luo et al first sought to understand the origins of broadband emissions in Cs2AgInCl6 using mathematical modeling and computational studies to relax the lattice and represent self-trapped excitons (STEs) to investigate exciton-phonon coupling. Such systems will be fundamental to engineer the next generation of energy-efficient and cost-effective lighting and display technologies. A self-trapped exciton (STE) is defined as a bound electron-hole pair carrier that can dramatically enhance luminescence, energy transport and lattice defect formation in the crystal. The researchers found that STEs in the double perovskite Cs2AgInCl6, arose from strong Jahn-Teller distortion of the integral AgCl6 octahedron complex. The trapped excitons had a similar orbital character to the free exciton, indicating parity-forbidden transition (arising due to disruption of the centre of symmetry). The theoretical analysis showed an extremely low photoluminescence quantum yield (PLQY) for pure Cs2AgInCl6. To enhance the PLQY for practical applications as broadband materials, the system had to be modified, specifically by breaking parity-forbidden transition to manipulate the symmetry of the STE wavefunction. Explore further Lighting it up: A new non-toxic, cheap, and stable blue photoluminescent material Computational studies of self-trapped excitons (STEs) in Cs2AgInCl6. a) GW band structure of the double perovskite crystal (Cs2AgInCl6). The orbital characters and the free-exciton wavefunction are plotted as a fat-band structure. The green, blue, cyan and red colors denote the Cl 3p, Ag 4d, In 5s and Ag 5s orbitals. The magenta circles represent the lowest free-exciton amplitude. b) STE in Cs2AgInCl6, Cs atoms are omitted for clarity. The cyan and magenta isosurfaces represent the electron and hole orbital densities respectively. The electron state (red dashed circle) is extended and the hole state (black dashed circle) is compact, consistent with the small effective mass of the conduction band seen in (a). The inset shows the Jahn-Teller distortion of the AgCl6 octahedron. The hole isosurface is obvious and electron isosurface invisible due to its small density. c) Configuration coordinate diagram for the STE formation; Est, Ed and EPL are self-trapping, lattice-deformation and emission energies. d) The calculated photoluminescence spectrum compared with the experimental result. The calculated curve was shifted to align its maximum with that of the experimentally measured curve for better comparison. Credit: Nature, doi: https://doi.org/10.1038/s41586-018-0691-0 White light emission from Cs2Ag1−xNaxInCl6. a) Luminosity function (dashed line) and photoluminescence spectra (solid lines) of Cs2Ag0.6Na0.4InCl6 measured at different temperatures from 233 K to 343 K. b) Photoluminescence stability of Cs2Ag0.60Na0.40InCl6 against continuous heating on a hotplate, measured after cooling to room temperature. c) Operational stability of Cs2Ag0.6Na0.4InCl6 down-conversion devices measured in air without any encapsulation. The boxplot showed the results for the different samples measured separately with the box edges representing quartiles and band in the box representing the mean and maximum data. d) XRD patterns of a Cs2Ag0.6Na0.4InCl6 film (black line) and powder (red line). The inset shows a 300 nm thick quartz substrate and 500 nm thick Cs2Ag0.6Na0.4InCl6 films under 254 nm UV illumination. Credit: Nature, doi: https://doi.org/10.1038/s41586-018-0691-0. Since lattice mismatch between the two perovskites (Cs2AgInCl6 andCs2NaInCl6) was very low (0.3 percent) the scientists anticipated Na+ incorporation would occur without detrimental defects or phase separation. For the synthesis, CsCl, NaCl, AgCl and InCl3 precursors were mixed into an HCl solution in a hydrothermal autoclave. The mixture was heated for a defined period of time and cooled down to result in a final white precipitate product (90 percent yield). The pure double perovskite phase was confirmed using X-ray diffraction patterns (XRD) of a series of product compositions. The results agreed with plasma optical emission spectrometry (ICP-OES). The results were also in agreement with similar alloying experiments that were previously conducted with lithium (Li). The study thus suggested a general trend for alkali-metal-induced photoluminescent enhancement in double perovskites. Photoluminescence spectra were recorded for a series of product powders by varying the temperature of the measurements. The authors optimized the Na content alongside bismuth (Bi3+) doping to improve the crystal quality and slow cooling to obtain the highest PLQY (85 ± 5 percent) recorded thus far for white-light-emitting materials to form the optimally alloyed Cs2Ag0.6Na0.4InCl6 in the study. More information: Jiajun Luo et al. Efficient and stable emission of warm-white light from lead-free halide double perovskites, Nature (2018). DOI: 10.1038/s41586-018-0691-0 Yiru Sun et al. Management of singlet and triplet excitons for efficient white organic light-emitting devices, Nature (2006). DOI: 10.1038/nature04645 Zewen Xiao et al. Searching for promising new perovskite-based photovoltaic absorbers: the importance of electronic dimensionality, Materials Horizons (2016). DOI: 10.1039/C6MH00519E Citation: Efficient and stable emission of warm white light from lead-free halide double perovskites (2018, November 19) retrieved 18 August 2019 from https://phys.org/news/2018-11-efficient-stable-emission-white-lead-free.html Characterization of Cs2AgxNa1−xInCl6 with different Na content. All samples were doped using a small amount of (0.04 percent) Bi and the composition determined using ICP-OES. a) XRD patterns of Cs2AgxNa1−xInCl6 powders with different Na content were obtained. The Asterix marks the (III) diffraction peak, θ diffraction angle and au – arbitrary units. b) Optical absorption (solid lines) and photoluminescence (dashed lines) spectra of pure Cs2AgInCl6 and Cs2Ag0.6Na0.4InCl6. c) Activation energy and PLQY of Cs2AgxNa1−xInCl6 powder vs. Na content. The dashed lines guide the eye. d) Excitation spectra of photoluminescence measured at different wavelengths. e) Emission intensity vs. excitation power for Cs2Ag0.6Na0.4InCl6. f) Transient absorption spectra for Cs2Ag0.6Na0.4InCl6 (laser pulse of 325 nm), ∆ A/A is optical density. The irregular peaks located at ~650 nm is from frequency doubling of the pumping light. Credit: Nature, doi: https://doi.org/10.1038/s41586-018-0691-0. A practical approach to achieve this was via partial substitution of Ag with an element that could sustain the double perovskite structure. The substitute required a distinctively different electronic configuration to Ag, such as a group-IA element or alkali metal. The scientists therefore explored alloying Na into Cs2AgInCl6 to form pure Cs2NaInCl6, which demonstrated broadband emission on substitution but with very low efficiency due to strong phonon emission, requiring optimization of the Na content in the complex. Photoluminescence excitation (PLE) spectra confirmed STE origin of the white emission to experimentally confirm the calculated time-scale of exciton self-trapping. The Na perovskite (Cs2Ag0.6Na0.4InCl6) exhibited linear dependence on the photoexcitation power. Additional theoretical tests were done to understand how PLQY varied as a function of the Na content. As the Na content increased, the transition dipole moment increased and then decreased to support the composition-dependent PLQY observed in the study. The electron wavefunction of the STEs was also compared before and after alloying with Na. Incorporating Na broke the inversion symmetry of the Cs2AgInCl6lattice, changing the electron wavefunction at the Ag site from symmetric to asymmetric. Two factors contributed to the decrease in PLQY on further increase of the Na content. The first was orbital overlap between electrons and holes of the STEs upon increased Na content. The second reason for the observed decrease in PLQY with increased Na was due to increased non-radiative loss in the Na-rich alloy. The scientists then developed a white light emitting diode (LED) by directly pressing the Na perovskite powders on to a commercial ultraviolet LED chip, without epoxy or silica encapsulation for protection. With the contribution from the blue light of the UV LED chip the device demonstrated a color temperature of 4,054 K to fulfill requirements for indoor lighting. When the white LED was operated for more than 1000 hour in air, negligible degradation was observed. The outstanding photometric performance combined with easy manufacture indicated promise for white-phosphor lighting applications. In this way, the scientists presented a new strategy to produce broadband emission associated with the STEs for single-material based white-light electroluminescence, allowing prototype double-perovskite based electroluminescence device formation. To increase electroluminescence performance in the future, further research should focus on optimizing the emitting-layer quality of the Cs2Ag0.6Na0.4InCl6 films. The study showed that alloying Na into Cs2AgIn Cl6 broke parity-forbidden transition as anticipated to reduce its electronic dimensionality and enable efficient white light emission via STEs.The white light emitting material also demonstrated low cost manufacture and exceptional stability as a promising solid-state lighting platform. The authors believe that such halide double perovskites hold great possibility for applications in display and lighting after further study to realize their full potential. The results will stimulate research on single-emitter-based white-light-emitting phosphors and diodes to generate the next-generation of lighting and display technologies. One-fifth of global electricity consumption is based on lighting; efficient and stable white-light emission with single materials is ideal for applications. Photon emission that covers the entire visible spectrum is, however, difficult to attain with a single material. Metal halide perovskites, for instance, have outstanding emission properties but contain lead, and therefore yield unsatisfactory stability. A new report published by Jiajun Luo and co-workers details a lead-free double perovskite that exhibited stable and efficient white light emission. In its mechanism of action, the material produced self-trapped excitons (STEs) due to Jahn-Teller distortion of the AgCl6 octahedron in the excited state of the complex, observed when investigating exciton-phonon coupling in the crystal lattice. The results are now published in Nature. A key challenge for lighting applications is the parameter of emission stability. The Cs2Ag0.6Na0.4InCl6perovskite showed stable emission in the study with little emission degradation. When the powder was annealed to a hotplate, only minimal photoluminescence decay of the white emission was observed, the authors proposed that the observations may be due to strongly bound excitons and a nearly defect-free lattice that prevented photoluminescence quenching while resisting thermal stress. Schematically visualizing the phonon band structure of Cs2AgInCl6 and the zone-center Jahn-Teller phonon mode (inset). The Jahn-Teller phonon mode coupled to the photoexcited excitons were responsible in the formation of self-trapped excitons in the Cs2AgInCl6 complex. Credit: Nature, doi: https://doi.org/10.1038/s41586-018-0691-0 Journal information: Nature © 2018 Science X Network Mechanistic investigation of PLQY in Cs2Ag1−xNaxInCl6. a) Transition dipole moment (µ) in Cs2Ag1−xNaxInCl6 as a function of Na content in the system. b) Parity change of the electron wavefunction of the STE before and after Na incorporation (pure and alloy). The cyan and magenta isosurfaces indicate electrons and holes c) Configurations showing strengthened STE confinement by the surrounding NaCl6 octahedra. d) STEs in Na-rich Cs2Ag1−xNaxInCl6. The STE is located in two neighboring octahedra. e) Configuration coordinate diagram of the STE formation in Cs2NaInCl6 (inset). Credit: Nature, doi: https://doi.org/10.1038/s41586-018-0691-0. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. 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Want to better facilities for tourists Krishnendu Narayan Choudhury


first_imgWith a new dynamic tourism minister at the helm of affairs, West Bengal tourism is planning a big leap forward. The new tourism minister, Krishnendu Narayan Choudhury, on Thursday launched a major campaign in Delhi setting a tone that he means serious business. In an exclusive interview with the Millennium Post, he has described many of his new plans for the future. Read on…It is commonly perceived that West Bengal is lagging behind in promoting tourism? Also Read – ‘Playing Jojo was emotionally exhausting’It is a fact that our state earlier had not given enough importance to tourism but after the new government took over under the leadership of Mamata Banerjee, we have given a very special focus to tourism. We have the Sunderbans, Darjeeling, Deegha but enough initiative was not taken to promote such destinations. After I took over, I am focusing on improving the existing infrastructure so that we can offer better facilities to the tourists.   We are trying to do tie-ups with the industries as a whole like travel-agents, tour operators, other state governments, foreign governments and private players. Our budget allocation for tourism has also increased to Rs. 120 crores which is a big leap. We are also tied-up with Pawan Hans Helicopters Ltd to provide helicopter service facilities to different parts of Bengal particularly with tourist destinations like Sunderbans, the hills and Deegha. We are also trying to create new infrastructure for some tourist destinations like Gajaldoba which is near Bagdogra Airport and Jharkhali in Sunderban. Also Read – Leslie doing new comedy special with NetflixWhat other infrastructure developments are you planning?Through public-private partnership, we are planning to create road-side facilities for the travellers like restrooms, canteens etc. With our existing 27 tourist lodges (out of which 11 have been leased out to private companies), we are planning to improve the quality and services by professionalized management and training. Our motto is to treat every tourist as an important guest of the state. We are focusing on both, high-end as well as the budget travellers. How about foreign travelers? At present, an average of 3000 foreign travellers  come to West Bengal and our position is 6th in all India basis but we are planning to increase it to 10,000 within next three years. A lot of big hotel chains are showing interest to set up more hotels in our state for which our government is going to extend all assistance.But what about the disturbances in the hills, Darjeeling area due to agitation?After our government took over, highest number of tourists arrived in the hills after a long gap and our CM is doing everything for the development of the hills. The livelihood of the local people is totally linked with tourism and we are hopeful that peace will remain there and more tourists will visit the hills.last_img read more

A mix of music


first_imgA four-day musical event Raag Rang is being organised in the Capital that kick starts on 28 August at Central Park, Rajiv Chowk. Brought by the Department of Art and Culture, Delhi Government in association with Sahitya Kala Parishad, the festival will be a fine mix of classical, cultural and rock shows. Veteran singers and performers? like Malini Awasthi, Ahmed Hussain, Mohd. Hussain and the band Astitva will be enthralling the audience with their live renditions. Also Read – ‘Playing Jojo was emotionally exhausting’The opening day of the festival (28 August) will feature Anupriya Deotale, Ahmed Hussain and Mohd. Hussain. Ahmed and Mohammed Hussain, the two brothers, are classic ghazal singers from Jaipur. They started their singing career in 1958 as classical and thumri artistes. Their first album Guldasta was released in 1980 and since then they have released about 50 albums. Their recent release was Khwab Basera.The second day of the event (29 August)will see performances by well known sufi singer Indira Naik and the multi genre Hindi band Astitva. The band five member band was formed in 2007. They blend jazz, rock and Hindustani classic with their soulful lyrics written in Hindi and Urdu. Also Read – Leslie doing new comedy special with NetflixMalini Awasthi and Devand Jha will be taking the stage on the third day (30 August) of the event. Awasthi is the face of folk music in India and is credited in bringing back these traditional forms of music to the national stage. She is acclaimed for her gaayiki and her powerful varsatile performances. Singing the various forms of folk music from Benaras and Awadh like the Dadra, Sohar, Banna, Jhoola, Kajri, Holi, Chaiti, Vivaah, Dhobiya, Nirgun, etc. she showcased these different forms of folk music in her own way. She is one of the leading thumri singers of the Benaras Gharana. The closing day (31 August) will feature Teejan Bai and Sadhna Bhatia. Teejan Bai  is an exponent of Pandavani, a traditional performing art form, from Chhattisgarh, in which she enacts tales from the Mahabharata, with musical accompaniments. She travelled all over the world as a cultural ambassador, to countries like – England, France, Switzerland and Germany.When: 28- 31 AugustWhere: Central Park, Rajiv ChowkTiming: 6.30 pm onwardslast_img read more