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High efficiency solar collectors grown from microscopic seeds

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2D Perovskite Thin Film Seeds


Rice University chemistry graduate student Siraj Sidhik holds a container of two-dimensional perovskite “seeds” (left) and a smaller vial containing a solution of dissolved seeds that can be used to make thin films for use in high-performance optoelectronic devices such as high-performance solar panels. … Credit: Photo by Jeff Fitlow / Rice University.

Engineers create seeds to grow near-perfect 2D perovskite crystals.

Rice University engineers have created microscopic seeds to grow remarkably uniform two-dimensional perovskite crystals that are both stable and highly efficient at harvesting electricity from sunlight.

Halide Perovskites are organic materials made from abundant, inexpensive ingredients, and the Rice seed growing method solves both operational and production issues that have held back the photovoltaic halide perovskite technology.

In a study published online at Advanced materials, chemical engineers at the Brown Rice School of Engineering describe how to produce seeds and use them to grow uniform thin films, highly sought after materials made up of uniformly thick layers. In laboratory tests, photovoltaic devices made from films have proven to be effective and reliable, which was previously a problematic combination for devices made from 3D or 2D perovskites.

2D perovskite thin film grown from seed

A thin film of two-dimensional crystals of halide perovskite of uniform thickness. Rice’s engineers discovered a self-assembly method to produce films from “seeds,” submicroscopic pieces of two-dimensional crystals that serve as templates. Credit: Photo by Jeff Fitlow / Rice University.

“We came up with a method where you can actually adapt the properties of macroscopic films by first adapting what you add to the solution,” said study co-author Aditya Mohite, assistant professor of chemical and biomolecular engineering and materials science. and nanoengineering at Rice. “You can get something very uniform in size and properties, resulting in higher efficiency. We got an almost ultra-modern efficiency of the device in the case of 2D at 17%, and this is without optimization. We think we can improve this in several ways. “

Mohit said that making uniform films from 2D perovskites has been a huge challenge for the halide perovskite photovoltaic processing community, which has grown significantly over the past decade.

“Homogeneous films are expected to provide optoelectronic devices with both high efficiency and technological stability,” he said.

Mohammad Samani and Siraj Sidhik

Rice University engineering graduate students Mohammad Samani (left) and Siraj Sidhik discovered a seeded growing method to create thin 2D films of halide perovskite with layers of uniform thickness. Uniform 2D perovskite films are in high demand and are expected to lead to solar panels and other highly efficient and stable optoelectronic devices. Credit: Photo by Jeff Fitlow / Rice University.

High-efficiency photovoltaic films grown from rice seeds have proven to be fairly stable, retaining more than 97% of their peak efficiency after 800 hours of illumination without any temperature control. In previous studies, 3D halide perovskite photovoltaic devices were highly efficient but prone to rapid degradation, while 2D devices were not efficient but very stable.

Rice’s study also details the seed growth process – a method available to many laboratories, said study co-author Amanda Marcel, chairman of the board of trustees of William Marsh Rice and assistant professor of chemical and biomolecular engineering at Rice.

“I think people will take this newspaper and say, ‘Oh. I’m going to start doing it, ”said Marcel. “It’s a really good paper for paperwork that allows you to go deeper into details that haven’t been done before.”

Aditya Mohite

Aditya Mohite is an Assistant Professor in the Department of Chemical and Biomolecular Engineering, Materials Science and Nanoengineering at Rice University. Credit: Jeff Fitlow / Rice University.

The name perovskite refers both to a specific mineral discovered in Russia in 1839 and to any compound with the crystal structure of this mineral. For example, halide perovskites can be prepared by mixing lead, tin, and other metals with bromide or iodide salts. Research interest in halide perovskites has skyrocketed since their potential for high-performance photovoltaics was demonstrated in 2012.

Mohit, who joined Rice in 2018, has spent more than five years researching photovoltaic cells based on halide perovskites, especially 2D perovskites – flat, almost atomically thin forms of material that are more stable than their thicker counterparts because of their inherent moisture resistance.

Amanda Marcel

Amanda Marcel. Credit: Photo by Jean Lasch.

Mohait named the study by co-lead author Siraj Sidhik, Ph.D. student in his laboratory, with the idea of ​​pursuing seed growth.

“The idea that memory or history — the genetic kind of seed — can determine the properties of a material is a powerful concept in materials science,” Mohite said. “Many templates work like this. If you want to grow, for example, a single crystal of diamond or silicon, you will need a single crystal seed that can serve as a template. “

While seed growth has often been demonstrated for inorganic crystals and other processes, Mohite said this is the first time it has manifested itself in organic 2D perovskites.

The process for growing 2D perovskite films from seeds is in many respects identical to the classical process for growing such films. In the traditional method, precursor chemicals are measured like the ingredients in the kitchen – X parts of ingredient A, Y parts of ingredient B, and so on – and they dissolve in a liquid solvent. The resulting solution is applied to a flat surface using centrifugal coating, a widely used technique that relies on centrifugal force to distribute liquid evenly over a rapidly rotating disc. As the solvent dissolves, the mixed ingredients crystallize into a thin film.

Mohita’s group has over the years created 2D perovskite films in this way, and although the films appear perfectly flat to the naked eye, they are uneven at the nanometer scale. In some places the film can be as thick as a single crystal, and in other places it can be as thick as several crystals.

“You end up with something completely polydisperse, and as size changes, so does the energy landscape,” Mohite said. “For a photovoltaic device, this means inefficiency because you waste energy to dissipate when charges hit the barrier before they reach electrical contact.”

In the seed growing method, seeds are produced by slowly growing a uniform 2D crystal and grinding it into a powder that dissolves in a solvent instead of individual precursors. The seeds contain the same ratio of ingredients as in the classic recipe, and the resulting solution is centrifuged onto discs in the same way as in the original method. The evaporation and crystallization stages are also identical. But the seed solution produces films with a uniform, uniform surface, very similar to the material from which the seeds were crushed.

When Sidhik initially succeeded in this approach, it was not immediately clear why he made the best films. Fortunately, Mohite’s lab is adjacent to Marciel’s lab, and while she and her student, co-lead author Mohammad Samani, hadn’t worked with perovskites before, they did have the perfect tool to find and study any pieces of undissolved seeds that could serve as a sample. for homogeneous films. …

“In my group, we were able to track nucleation and growth using light scattering techniques that we typically use to measure the size of polymers in solution,” said Marcel. “This is how cooperation arose. We’re lab neighbors, and we talked about it, and I’m like, “Hey, I have this equipment. Let’s see how big these seeds are and if we can track them over time using the same tools we use in polymer science. ”

The tool was dynamic light scattering, the main technique in the Marciel group. The solutions have been found to reach equilibrium under certain conditions, allowing some of the seeds to remain undissolved in the solution.

The study showed that these seed particles retained a “memory” of the perfectly uniform slow-growing crystal from which they were crushed, and Samani and Marcel found they could track the nucleation process that would eventually allow the seeds to form uniform, thin films.

Mohite said the collaboration resulted in something that is often done and rarely achieved in nanomaterial research – a method of self-assembly to create macroscopic materials that live up to the promises of the individual nanoparticles that make them up.

“This is truly the curse of nanomaterial technology,” Mohite said. “At the level of an individual element, you have wonderful properties that are orders of magnitude better than anything else, but when you try to combine them into something macroscopic and useful, such as film, these properties simply disappear, because you cannot make something consistent with only the properties you need.

“We haven’t experimented with other systems yet, but the success with perovskites raises questions about whether this type of seeded approach might work in other systems as well,” he said.

Reference: “Memory Seeds Provide High Structural Phase Purity in 2D Perovskite Films for High Performance Devices” Siraj Sidhik, Wenbin Lee, Mohammad H.K. Samani, Hao Zhang, Yafei Wang, Justin Hoffman, Austin C. Fer, Michael C. Wong, Claudine Catan, Jackie Even, Amanda B. Marcel, Mercury G. Kanatzidis, Jean-Christophe Blancon, Aditya D. Mohite, June 6, 2021 g., Advanced materials
DOI: 10.1002 / adma.202007176

The study was supported by the Office of Energy Efficiency and Renewable Energy of the Department of Energy (DOE), the Academic Institute of France and the Office of Naval Research (N00014-20-1-2725) and using DOE facilities at the Argonne National Laboratory. and Brookhaven National Laboratory.





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Farming robots are the future – we must prepare now to avoid dystopia

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Dystopian Farm Robots


This illustration shows the scenario of a utopian farming robot. Credit: Natalis Lorenz.

This is no longer science fiction, farm robots are already here – and they have created two possible extremes for the future of agriculture and its impact on the environment, says agricultural economist Thomas Daum in an article published July 13, 2021 in Science & Society. Journal Trends in ecology and evolution… One of them is a utopia, in which entire parks of small intelligent robots work in harmony with nature to produce a variety of organic crops. Another is a dystopia in which large, tractor-like robots conquer the landscape with heavy machinery and artificial chemicals.

He describes the utopian scenario as a mosaic of rich green fields, streams, wild flora and fauna, where fleets of small robots powered by sustained energy flutter around the fields, their buzzing mingling with the chirping of insects and the song of birds. “It’s like a Garden of Eden,” says Daum (@ThomDaum), a research associate at the University of Hohenheim in Germany who studies agricultural development strategies. “Small robots can help conserve biodiversity and combat climate change in ways that have never been possible before.”

He suggests that a utopian scenario that is too laborious for conventional farming, but possible with robots working around the clock, 7 days a week, is likely to benefit the environment in many ways. Plants would be more varied and the soil richer in nutrients. Thanks to micro-spraying of biopesticides and laser weed removal, nearby water, insect populations and soil bacteria will also become healthier. Organic crop yields, which are now often lower than traditional crop yields, will be higher and the impact of agriculture on the environment will be greatly reduced.

Dystopian farm robots

This illustration shows the scenario of a dystopian farming robot. Credit: Natalis Lorenz.

However, he believes that a parallel future with negative environmental consequences is quite possible. In this scenario, he says, large but technologically crude robots will bulldoze the natural landscape, and multiple monocultural cultures will dominate the landscape. Large fences would isolate people, farms and wildlife from each other. Once people are removed from farms, agrochemicals and pesticides can be used more widely. The ultimate goals will be structure and control: qualities that these simpler robots excel at, but which are likely to have detrimental effects on the environment.

While he notes that it’s unlikely the future will be limited to pure utopia or pure dystopia, by creating these two scenarios, Daum hopes to spark a conversation in what he sees as a crossroads in time. “Both utopia and dystopia are possible from a technological point of view. But without the right policy barriers, we could end up in a dystopia without even wanting to, if we don’t discuss it now, ”says Daum.

But this impact is not just limited to the environment – it affects normal people as well. “Robotic farming can also specifically impact you as a consumer,” he says. “In utopia, we don’t just grow crops – we have a lot of fruits and vegetables, the relative prices of which will fall, so a healthier diet will become more affordable.”

The small robots described in Daum’s utopian scenario would also be more suitable for small farmers who would find it easier to afford or share them through services like Uber. On the contrary, he argues that a family farm is less likely to survive in a dystopian scenario: only large producers, he says, will be able to manage huge tracts of land and high costs for large machinery.

In parts of Europe, Asia and Africa, where there are currently many small farms, deliberate efforts to implement a utopian scenario offer clear advantages. The situation is more difficult in countries such as the United States, Russia or Brazil, which have historically been dominated by large farms producing large volumes of low-value grains and oilseeds. There, small robots that are less efficient at performing energy-intensive tasks like threshing corn may not always be the most cost-effective option.

“While it is true that the preconditions for small robots are more complex in these areas,” he says, “even with large robots – or a mixture of small and large ones – we can take steps towards utopia with practices like interbreeding, having hedges. agroforestry and the shift from large farms to smaller plots of land owned by large farmers. Some of these methods may even pay off to farmers when robots can do their job as previously unprofitable methods become profitable. ”

To do this, Daum said, you need to act now. While some aspects of the utopian scenario, such as laser weeding, are already developed and ready for widespread adoption, funding must go to other aspects of machine learning and artificial intelligence in order to develop robots intelligent enough to adapt to complex unstructured farming systems. Policy changes are also needed and can take the form of subsidies, regulations, or taxes. “In the European Union, for example, farmers receive money when they perform certain landscape services, such as growing many trees or rivers on their farms,” he says.

While it may seem like a dystopian scenario is more likely, it is not the only way forward. “I think utopia is achievable,” says Daum. “It won’t be as easy as a dystopia, but it’s quite possible.”

Link: “Farming robots: ecological utopia or dystopia?” Thomas Daum, July 13, 2021 Trends in ecology and evolution
DOI: 10.1016 / j.tree.2021.06.002

This work was supported by the “Companion Research Program for Agricultural Innovation”, which is funded by the German Federal Ministry for Economic Cooperation and Development (BMZ).





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Dynamic control of THz wavefronts due to rotation of layers of cascade metasurfaces

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Metadevice for Dynamically Controlling THz Wavefronts


Meta-device for dynamic control of THz wavefronts by rotating layers of cascade metasurfaces. Credit: Shanghai University.

Cascading metasurfaces for dynamic control of THz wave fronts

Electromagnetic (EM) waves in terahertz (THz) mode are used for critical applications in communications, security imaging, and bio and chemical sensing. This widespread applicability has led to significant technological progress. However, due to the weak interaction between natural materials and THz waves, conventional THz devices are usually cumbersome and ineffective. Although ultra-compact active devices in the THz range do exist, modern electronic and photonic approaches to dynamic control are ineffective.

Recently, the rapid development of metasurfaces has opened up new opportunities for creating highly efficient ultra-compact devices in the THz range for dynamic wavefront control. Ultra-thin metamaterials formed by subwavelength planar microstructures (i.e., metaatoms), metasurfaces allow tuning optical responses to control the fronts of electromagnetic waves. By creating metasurfaces that have certain predefined phase profiles for transmitted or reflected waves, scientists have demonstrated exciting wave manipulation effects such as abnormal light deflection, polarization manipulation, photon spin hall and holograms.

Dynamic beam steering metaservice

Demonstration of the dynamic beam steering meta-device: (a) Schematic of the meta-device, which consists of two layers of transmissive metasurfaces aligned with a motorized turntable. (b) top view (left) and (c) bottom view (right) of a SEM image of the fabricated meta-device. (d) Diagram of the experimental setup shown to characterize the meta-device. (e) Experimental and (f) simulated far-field scattering power distribution with a meta device illuminated with 0.7 THz LCP light and evolving along path I at different times. (g) Evolution of the directions of the transmitted waves on the sphere of direction k when the meta device moves along Path I and Path II, with the solid line (asterisks) denoting the results of the simulation (experiment). Here, the blue area denotes the solid angle for beam steering coverage. Credit: X. Cai et al., Doi 10.1117 / 1.AP.3.3.036003.

Moreover, the integration of active elements with individual meta-atoms within passive metasurfaces allows the creation of “active” meta-devices that can dynamically manipulate the fronts of electromagnetic waves. While active elements in deep subwavelengths are easy to find in microwave mode (e.g. PIN diodes and varactors) and successfully contribute to active meta-devices for beam steering, programmable holograms, and dynamic imaging, they are difficult to create at frequencies above THz. … This difficulty stems from size limitations and significant ohmic losses in electronic circuits. Although terahertz frequencies can drive terahertz beams uniformly, they usually cannot dynamically manipulate terahertz wave fronts. Ultimately this is due to the lack of local tuning capabilities at subwavelength depth scales in this frequency domain. Therefore, developing new approaches to avoid local customization is a priority.

As reported in Advanced PhotonicsResearchers from Shanghai University and Fudan University have developed a general structure and meta-devices to achieve dynamic control of THz wave fronts. Instead of locally controlling individual meta-atoms in the THz metasurface (for example, via a PIN diode, varactor, etc.), They change the polarization of the light beam using rotating multilayer cascade metasurfaces. They demonstrate that rotating different layers (each exhibiting a specific phase profile) in a cascade meta-device at different speeds can dynamically change the effective Jones matrix property of the entire device, achieving unusual manipulations with the wavefront and polarization characteristics of terahertz rays. Two meta-devices are demonstrated: the first meta-device can effectively redirect a normally incident THz beam for scanning in a wide range of solid angles, and the second can dynamically manipulate both the wavefront and polarization of the THz beam.

This paper proposes an attractive alternative way to achieve inexpensive dynamic control of THz waves. The researchers hope this work will inspire future applications of terahertz radars as well as bio and chemical sensing and imaging.

Reference: “Dynamic control of terahertz wavefronts with cascading metasurfaces” Xiaodong Tsai, Rong Tang, Haoyang Zhou, Qiushi Li, Shaoji Ma, Dongyi Wang, Tong Liu, Xiaohui Lin, Wei Tang, Qiong He, Shii Xiao, and Lei Zhou, June 26 … 2021, Advanced Photonics
DOI: 10.1117 / 1.AP.3.3.036003





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Take part in ESA Space Camp 2021

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Take part in ESA Space Camp 2021


Space App Camp 2021. Credit: ESA.

ESA invites up to 25 dedicated mobile app developers and AI and machine learning specialists related to Earth observation from space to join this year’s Space App Camp, which will be a virtual event for eight weeks, from July 20 to September 20. …

The Space App Camp aims to make Earth observation data and services available to a wide range of citizens using their smartphones or personal devices. Numerous Earth observation satellites, including Copernicus Sentinel missions, collect a huge amount of data. This big data from space uncovers information about the atmosphere, land and water of our planet and offers countless possibilities for creating compelling, even transformative applications when combined with mobile applications.

Space App Camp attendees will experience Copernicus data and learn how big data from space can enrich mobile apps with a dedicated Earth observation data API. The 2021 virtual edition revolves around an expanded collaboration with ESA’s F-Lab, whose mission is to accelerate future Earth observation through new transformational ideas, and to select, develop, test and develop the most promising concepts.

2020 space camp winner

Quifer (aQuifer sUrveillance by sentInel InterFERometry) won the top prize in Space App Camp 2020. It uses terrain data from the Copernicus Sentinel-1 mission, combined with big data and artificial intelligence to monitor water use. Credit: ESA.

Although this is the tenth Space app campThis is the first time the camp has offered an expanded mentoring program that includes an end-to-end training and mobile software development scheme lasting eight weeks, supported by experts in Earth observation, artificial intelligence, intellectual property protection and business. development.

Winners will be awarded cash prizes of up to € 2,500 and a unique Earth observation support package that will allow them to continue working on their winning app idea. They will also be invited to participate in ESA exhibitions. Φ-week and Living Planet Symposium, with all expenses covered.

There is also a unique prize in the form of an Earth Observation Support Package worth around € 3,500. This includes technical advice on Earth observation data, eight hours of software development services, access to a global network of Earth observation experts in application and technical fields, and support from professional ESA business developers.

Carlos Garcia, member of the 2020 winning team, says: “The ESA Space App Camp is a great opportunity to build an app from scratch with guidance from tier 1 professionals. Although everything was virtual in my year, it was a fantastic learning experience – blocking the week and dedicating myself to building a meaningful app. “

The deadline for applications is July 8, 2021. Interested students, entrepreneurs, researchers, developers, and economists can register online individually or in a team (up to four people). This year’s edition is specifically targeted at contributors with profiles in mobile app development, Earth observation app development, machine learning, artificial intelligence, and business development.

To participate in the 8-week mentoring program from July 20 to September 20, 2021, up to 25 participants will be selected, within which special training and development sessions will be held every two weeks.

Since Space App Camp was created 10 years ago, about 480 developers from 30 countries have applied to participate and more than 60 applications have been developed. Some of them have already found use in commercially viable applications.





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