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ProgrammableWeb

Marketstack API Provides Lightweight, Cost-Effective Access to Stock Data

Marketstack first released its API-driven market data product in 2018. The original thought behind the Marketstack API was a cost-effective alternative to Yahoo Finance. Just a couple of years later, the Marketstack API is one of the most popular solutions for real-time, intraday, and historical stock data. It supports over 125,000 stock tickers from 72 stock exchanges across the globe.

The API supports millions of concurrent API requests each day. In addition to basic stock and rate information, the API provides metadata, company information, and exchange information. The API exists as part of the broader apilayer portfolio of products which include currencylayer, ipapi and scrapestack.

The API is RESTful. Requests use an HTTP GET structure and responses are delivered in JSON format. Features cover data associated with end of day data, intraday data, real-time updates, historical data, tickers, exchanges, currencies, and timezones. For more details, check out the API documentation.

End of day requests are free up to 1,000 monthly requests. Paid subscriptions are available for real-time and intraday data. Visit the Marketstack site to sign up for a free API key.

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ScienceDaily

New light shed on intelligent life existing across the galaxy

One of the biggest and longest-standing questions in the history of human thought is whether there are other intelligent life forms within our Universe. Obtaining good estimates of the number of possible extraterrestrial civilizations has however been very challenging.

A new study led by the University of Nottingham and published today in The Astrophysical Journal has taken a new approach to this problem. Using the assumption that intelligent life forms on other planets in a similar way as it does on Earth, researchers have obtained an estimate for the number of intelligent communicating civilizations within our own galaxy -the Milky Way. They calculate that there could be over 30 active communicating intelligent civilizations in our home Galaxy.

Professor of Astrophysics at the University of Nottingham, Christopher Conselice who led the research, explains: “There should be at least a few dozen active civilizations in our Galaxy under the assumption that it takes 5 billion years for intelligent life to form on other planets, as on Earth.” Conselice also explains that, “The idea is looking at evolution, but on a cosmic scale. We call this calculation the Astrobiological Copernican Limit.”

First author Tom Westby explains: “The classic method for estimating the number of intelligent civilizations relies on making guesses of values relating to life, whereby opinions about such matters vary quite substantially. Our new study simplifies these assumptions using new data, giving us a solid estimate of the number of civilizations in our Galaxy.

The two Astrobiological Copernican limits are that intelligent life forms in less than 5 billion years, or after about 5 billion years — similar to on Earth where a communicating civilization formed after 4.5 billion years. In the strong criteria, whereby a metal content equal to that of the Sun is needed (the Sun is relatively speaking quite metal rich), we calculate that there should be around 36 active civilizations in our Galaxy.”

The research shows that the number of civilizations depends strongly on how long they are actively sending out signals of their existence into space, such as radio transmissions from satellites, television, etc. If other technological civilizations last as long as ours which is currently 100 years old, then there will be about 36 ongoing intelligent technical civilizations throughout our Galaxy.

However, the average distance to these civilizations would be 17,000 light-years away, making detection and communication very difficult with our present technology. It is also possible that we are the only civilization within our Galaxy unless the survival times of civilizations like our own are long.

Professor Conselice continues: “Our new research suggests that searches for extraterrestrial intelligent civilizations not only reveals the existence of how life forms, but also gives us clues for how long our own civilization will last. If we find that intelligent life is common then this would reveal that our civilization could exist for much longer than a few hundred years, alternatively if we find that there are no active civilizations in our Galaxy it is a bad sign for our own long-term existence. By searching for extraterrestrial intelligent life — even if we find nothing — we are discovering our own future and fate.”

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Hackster.io

Representation Matters

Representation matters! But if you haven’t thought about it before, it can be hard to know how to help. If you live every day as a marginalized person, it can be hard to find resources to support you. So, here are a few places to start.

Whether you’re looking for speakers for your conference, a cofounder for your next robotics startup, or just cool and inspiring people to follow – check out these resources supporting Black scientists, engineers, and other STEM specialists.

// https://twitter.com/i/events/1266753444116860928
// https://twitter.com/iamcamilleeddy
// https://hanselminutes.com/607/removing-bias-from-ai-and-machine-learning-with-camille-eddy
// https://twitter.com/datanbotspod
// https://hanselminutes.com/669/exploring-algorithms-of-oppression-with-dr-safiya-noble
// https://twitter.com/safiyanoble
// https://backstagecapital.com/headliners/
// https://twitter.com/Backstage_Cap
// https://twitter.com/ArlanWasHere
// https://www.itsaboutdamntime.com/

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ScienceDaily

What’s Mars made of?

Earth-based experiments on iron-sulfur alloys thought to comprise the core of Mars reveal details about the planet’s seismic properties for the first time. This information will be compared to observations made by Martian space probes in the near future. Whether the results between experiment and observation coincide or not will either confirm existing theories about Mars’ composition or call into question the story of its origin.

Mars is one of our closest terrestrial neighbors, yet it’s still very far away — between about 55 million and 400 million kilometers depending on where Earth and Mars are relative to the sun. At the time of writing, Mars is around 200 million kilometers away, and in any case, it is extremely difficult, expensive and dangerous to get to. For these reasons, it is sometimes more sensible to investigate the red planet through simulations here on Earth than it is to send an expensive space probe or, perhaps one day, people.

Keisuke Nishida, an Assistant Professor from the University of Tokyo’s Department of Earth and Planetary Science at the time of the study, and his team are keen to investigate the inner workings of Mars. They look at seismic data and composition which tell researchers not just about the present state of the planet, but also about its past, including its origins.

“The exploration of the deep interiors of Earth, Mars and other planets is one of the great frontiers of science,” said Nishida. “It’s fascinating partly because of the daunting scales involved, but also because of how we investigate them safely from the surface of the Earth.”

For a long time it has been theorized that the core of Mars probably consists of an iron-sulfur alloy. But given how inaccessible the Earth’s core is to us, direct observations of Mars’ core will likely have to wait some time. This is why seismic details are so important, as seismic waves, akin to enormously powerful sound waves, can travel through a planet and offer a glimpse inside, albeit with some caveats.

“NASA’s Insight probe is already on Mars collecting seismic readings,” said Nishida. “However, even with the seismic data there was an important missing piece of information without which the data could not be interpreted. We needed to know the seismic properties of the iron-sulfur alloy thought to make up the core of Mars.”

Nishida and team have now measured the velocity for what is known as P-waves (one of two types of seismic wave, the other being S-waves) in molten iron-sulfur alloys.

“Due to technical hurdles, it took more than three years before we could collect the ultrasonic data we needed, so I am very pleased we now have it,” said Nishida. “The sample is extremely small, which might surprise some people given the huge scale of the planet we are effectively simulating. But microscale high-pressure experiments help exploration of macroscale structures and long time-scale evolutionary histories of planets.”

A molten iron-sulfur alloy just above its melting point of 1,500 degrees Celsius and subject to 13 gigapascals of pressure has a P-Wave velocity of 4,680 meters per second; this is over 13 times faster than the speed of sound in air, which is 343 meters per second. The researchers used a device called a Kawai-type multianvil press to compress the sample to such pressures. They used X-ray beams from two synchrotron facilities, KEK-PF and SPring-8, to help them image the samples in order to then calculate the P-wave values.

“Taking our results, researchers reading Martian seismic data will now be able to tell whether the core is primarily iron-sulfur alloy or not,” said Nishida. “If it isn’t, that will tell us something of Mars’ origins. For example, if Mars’ core includes silicon and oxygen, it suggests that, like the Earth, Mars suffered a huge impact event as it formed. So, what is Mars made of and how was it formed? I think we are about to find out.”

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ScienceDaily

New study examines which galaxies are best for intelligent life

Giant elliptical galaxies are not as likely as previously thought to be cradles of technological civilizations such as our own, according to a recent paper by a University of Arkansas astrophysicist.

The paper, published May 1 in the journal Monthly Notices of the Royal Astronomical Society, contradicts a 2015 study that theorized giant elliptical galaxies would be 10,000 times more likely than spiral disk galaxies such as the Milky Way to harbor planets that could nurture advanced, technological civilizations.

The increased likelihood, the authors of the 2015 study argued, would be because giant elliptical galaxies hold many more stars and have low rates of potentially lethal supernovae.

But Daniel Whitmire, a retired professor of astrophysics who is an instructor in the U of A mathematics department, believes that the 2015 study contradicts a statistical rule called the principle of mediocrity, also known as the Copernican Principle, which states that in the absence of evidence to the contrary, an object or some property of an object should be considered typical of its class rather than atypical.

Historically, the principle has been employed several times to predict new physical phenomena, such as when Sir Isaac Newton calculated the approximate distance to the star Sirius by assuming that the sun is a typical star and then comparing the relative brightness of the two.

“The 2015 paper had a serious problem with the principle of mediocrity,” said Whitmire. “In other words, why don’t we find ourselves living in a large elliptical galaxy? To me this raised a red flag. Any time you find yourself as an outlier, i.e. atypical, then that is a problem for the principle of mediocrity.”

He also had to show that most stars and therefore planets reside in large elliptical galaxies in order to nail down his argument that the earlier paper violated the principle of mediocrity.

According to the principle of mediocrity, Earth and its resident technological society should be typical, not atypical, of planets with technological civilizations elsewhere in the universe. That means that its location in a spiral-shaped disk galaxy should also be typical. But the 2015 paper suggests the opposite, that most habitable planets would not be located in galaxies similar to ours, but rather in large, spherical-shaped elliptical galaxies.

In his paper, Whitmire suggests a reason why large elliptical galaxies may not be cradles of life: They were awash in lethal radiation when they were younger and smaller, and they went through a series of quasar and star-burst supernovae events at that time.

“The evolution of elliptical galaxies is totally different than the Milky Way,” said Whitmire. “These galaxies went through an early phase in which there is so much radiation that it would just completely have nuked any habitable planets in the galaxy and subsequently the star formation rate, and thus any new planets, went to essentially zero. There are no new stars forming and all the old stars have been irradiated and sterilized.”

If habitable planets hosting intelligent life are unlikely in large elliptical galaxies, where most stars and planets reside, then by default galaxies such as the Milky Way will be the primary sites of these civilizations, as expected by the principle of mediocrity, Whitmire said.

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Exoplanet apparently disappears in latest Hubble observations

Now you see it, now you don’t.

What astronomers thought was a planet beyond our solar system has now seemingly vanished from sight. Though this happens in science fiction, such as Superman’s home planet Krypton exploding, astronomers are looking for a plausible explanation.

One interpretation is that, rather than being a full-sized planetary object, which was first photographed in 2004, it could instead be a vast, expanding cloud of dust produced in a collision between two large bodies orbiting the bright nearby star Fomalhaut. Potential follow-up observations might confirm this extraordinary conclusion.

“These collisions are exceedingly rare and so this is a big deal that we actually get to see one,” said András Gáspár of the University of Arizona, Tucson. “We believe that we were at the right place at the right time to have witnessed such an unlikely event with NASA’s Hubble Space Telescope.”

“The Fomalhaut system is the ultimate test lab for all of our ideas about how exoplanets and star systems evolve,” added George Rieke of the University of Arizona’s Steward Observatory. “We do have evidence of such collisions in other systems, but none of this magnitude has been observed in our solar system. This is a blueprint of how planets destroy each other.”

The object, called Fomalhaut b, was first announced in 2008, based on data taken in 2004 and 2006. It was clearly visible in several years of Hubble observations that revealed it was a moving dot. Until then, evidence for exoplanets had mostly been inferred through indirect detection methods, such as subtle back-and-forth stellar wobbles, and shadows from planets passing in front of their stars.

Unlike other directly imaged exoplanets, however, nagging puzzles arose with Fomalhaut b early on. The object was unusually bright in visible light, but did not have any detectable infrared heat signature. Astronomers conjectured that the added brightness came from a huge shell or ring of dust encircling the planet that may possibly have been collision-related. The orbit of Fomalhaut b also appeared unusual, possibly very eccentric.

“Our study, which analyzed all available archival Hubble data on Fomalhaut revealed several characteristics that together paint a picture that the planet-sized object may never have existed in the first place,” said Gáspár.

The team emphasizes that the final nail in the coffin came when their data analysis of Hubble images taken in 2014 showed the object had vanished, to their disbelief. Adding to the mystery, earlier images showed the object to continuously fade over time, they say. “Clearly, Fomalhaut b was doing things a bona fide planet should not be doing,” said Gáspár.

The interpretation is that Fomalhaut b is slowly expanding from the smashup that blasted a dissipating dust cloud into space. Taking into account all available data, Gáspár and Rieke think the collision occurred not too long prior to the first observations taken in 2004. By now the debris cloud, consisting of dust particles around 1 micron (1/50th the diameter of a human hair), is below Hubble’s detection limit. The dust cloud is estimated to have expanded by now to a size larger than the orbit of Earth around our Sun.

Equally confounding is that the team reports that the object is more likely on an escape path, rather than on an elliptical orbit, as expected for planets. This is based on the researchers adding later observations to the trajectory plots from earlier data. “A recently created massive dust cloud, experiencing considerable radiative forces from the central star Fomalhaut, would be placed on such a trajectory,” said Gáspár. “Our model is naturally able to explain all independent observable parameters of the system: its expansion rate, its fading, and its trajectory.”

Because Fomalhaut b is presently inside a vast ring of icy debris encircling the star, colliding bodies would likely be a mixture of ice and dust, like the comets that exist in the Kuiper belt on the outer fringe of our solar system. Gáspár and Rieke estimate that each of these comet-like bodies measured about 125 miles (200 kilometers) across (roughly half the size of the asteroid Vesta).

According to the authors, their model explains all the observed characteristics of Fomalhaut b. Sophisticated dust dynamical modeling done on a cluster of computers at the University of Arizona shows that such a model is able to fit quantitatively all the observations. According to the author’s calculations, the Fomalhaut system, located about 25 light-years from Earth, may experience one of these events only every 200,000 years.

Gáspár and Rieke — along with other members of an extended team — will also be observing the Fomalhaut system with NASA’s upcoming James Webb Space Telescope in its first year of science operations. The team will be directly imaging the inner warm regions of the system, spatially resolving for the first time the elusive asteroid-belt component of an extrasolar planetary system. The team will also search for bona fide planets orbiting Fomalhaut that might be gravitationally sculpting the outer disk. They will also analyze the chemical composition of the disk.

Their paper, “New HST [Hubble] data and modeling reveal a massive planetesimal collision around Fomalhaut” is being published on April 20, 2020, in the Proceedings of the National Academy of Sciences.

The Hubble Space Telescope is a project of international cooperation between NASA and ESA (European Space Agency). NASA’s Goddard Space Flight Center in Greenbelt, Maryland, manages the telescope. The Space Telescope Science Institute (STScI) in Baltimore, Maryland, conducts Hubble science operations. STScI is operated for NASA by the Association of Universities for Research in Astronomy in Washington, D.C.

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Looking for dark matter

Dark matter, which cannot be physically observed with ordinary instruments, is thought to account for well over half the matter in the Universe, but its properties are still mysterious. One commonly held theory states that it exists as ‘clumps’ of extremely light particles. When the earth passes through such a clump, the fundamental properties of matter are altered in ways that can be detected if instruments are sensitive enough. Physicists Rees McNally and Tanya Zelevinsky from Columbia University, New York, USA, have now published a paper in EPJ D proposing two new methods of looking for such perturbations and, thus, dark matter. This paper is part of a special issue of the journal on quantum technologies for gravitational physics.

Until now, searches for dark matter clumps have relied on the fact that tiny changes in the values of fundamental constants will alter the ‘tick rate’ of atomic clocks, some of which may be precise enough to pick up this difference. McNally and Zelevinsky’s work adds methods that involve measuring a small extra ‘push’ or acceleration on normal matter caused by the clump, using, firstly, gravity sensors and, secondly, gravitational wave detectors. Gravity sensors are already spread around the world in the IGETS network, which is used for geological research; and scientists at the LIGO observatories in the United States are already looking for gravitational waves. Thus, McNally and Zelevinsky can mine the data from these ongoing experiments for evidence of dark matter.

McNally explains that this work was inspired by two things: the benefits of re-purposing existing experiments, and science fiction. “I enjoy novels like A Fire Upon the Deep [by Vernor Vinge] and The Three-Body Problem [by Liu Cixin] that explore what might happen if fundamental constants change, and it’s fun to explore such things in the real world.” As for practical applications of this work, however, he advised taking things one step at a time. “First we need to find out what Dark Matter is, then maybe we can find out how to use it.”

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  1. Rees L. McNally, Tanya Zelevinsky. Constraining domain wall dark matter with a network of superconducting gravimeters and LIGO. The European Physical Journal D, 2020; 74 (4) DOI: 10.1140/epjd/e2020-100632-0

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Electrochemical method for extracting uranium, and potentially other metal ions, from solution

Fifty years ago, scientists hit upon what they thought could be the next rocket fuel. Carboranes — molecules composed of boron, carbon and hydrogen atoms clustered together in three-dimensional shapes — were seen as the possible basis for next-generation propellants due to their ability to release massive amounts of energy when burned.

It was technology that at the time had the potential to augment or even surpass traditional hydrocarbon rocket fuel, and was the subject of heavy investment in the 1950s and 60s.

But things didn’t pan out as expected.

“It turns out that when you burn these things you actually form a lot of sediment,” said Gabriel MĂ©nard, an assistant professor in UC Santa Barbara’s Department of Chemistry and Biochemistry. In addition to other problems found when burning this so-called “zip fuel,” its residue also gummed up the works in rocket engines, and so the project was scrapped.

“So they made these huge stockpiles of these compounds, but they actually never used them,” MĂ©nard said.

Fast forward to today, and these compounds have come back into vogue with a wide range of applications, from medicine to nanoscale engineering. For MĂ©nard and fellow UCSB chemistry professor Trevor Hayton, as well as Tel Aviv University chemistry professor Roman Dobrovetsky, carboranes could hold the key to more efficient uranium ion extraction. And that, in turn, could enable things like better nuclear waste reprocessing and uranium (and other metal) recovery from seawater.

Their research — the first example of applying electrochemical carborane processes to uranium extraction — is published in a paper (link) that appears in the journal Nature.

Key to this technology is the versatility of the cluster molecule. Depending on their compositions these structures can resemble closed cages, or more open nests, due to control of the compound’s redox activity — its readiness to donate or gain electrons. This allows for the controlled capture and release of metal ions, which in this study was applied to uranium ions.

“The big advancement here is this ‘catch and release’ strategy where you can switch between two states, where one state binds the metal and another state releases the metal,” Hayton said.

Conventional processes, such as the popular PUREX process that extracts plutonium and uranium, rely heavily on solvents, extractants and extensive processing.

“Basically, you could say it’s wasteful,” MĂ©nard said. “In our case, we can do this electrochemically — we can capture and release the uranium with the flip of a switch.

“What actually happens,” added MĂ©nard, “is that the cage opens up.” Specifically, the formerly closed ortho-carborane becomes an opened nido- (“nest”) carborane capable of capturing the positively-charged uranium ion.

Conventionally, the controlled release of extracted uranium ions, however, is not as straightforward and can be somewhat messy. According to the researchers, such methods are “less established and can be difficult, expensive and or destructive to the initial material.”

But here, the researchers have devised a way to reliably and efficiently flip back and forth between open and closed carboranes, using electricity. By applying an electrical potential using an electrode dipped in the organic portion of a biphasic system, the carboranes can receive and donate the electrons needed to open and close and capture and release uranium, respectively.

“Basically you can open it up, capture uranium, close it back up and then release uranium,” MĂ©nard said. The molecules can be used multiple times, he added.

This technology could be used for several applications that require the extraction of uranium and by extension, other metal ions. One area is nuclear reprocessing, in which uranium and other radioactive “trans-uranium” elements are extracted from spent nuclear material for storage and reuse (the PUREX process).

“The problem is that these trans-uranium elements are very radioactive and we need to be able to store these for a very long time because they’re basically very dangerous,” MĂ©nard said. This electrochemical method could allow for the separation of uranium from plutonium, similar to the PUREX process, he explained. The extracted uranium could then be enriched and put back into the reactor; the other high-level waste can be transmuted to reduce their radioactivity.

Additionally, the electrochemical process could also be applied to uranium extraction from seawater, which would ease pressure on the terrestrial mines where all uranium is currently sourced.

“There’s about a thousand times more dissolved uranium in the oceans than there are in all the land mines,” MĂ©nard said. Similarly, lithium — another valuable metal that exists in large reserves in seawater — could be extracted this way, and the researchers plan to take this research direction in the near future.

“This gives us another tool in the toolbox for manipulating metal ions and processing nuclear waste or doing metal capture out of oceans,” Hayton said. “It’s a new strategy and new method to achieve these types of transformations.”

Research in this study was conducted also by Megan Keener (lead author), Camden Hunt and Timothy G. Carroll at UCSB; and by Vladimir Kampel at Tel Aviv University.

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Views of giant planet in wild orbit would be unparalleled

Contrary to previous thought, a gigantic planet in wild orbit does not preclude the presence of an Earth-like planet in the same solar system — or life on that planet.

What’s more, the view from that Earth-like planet as its giant neighbor moves past would be unlike anything it is possible to view in our own night skies on Earth, according to new research led by Stephen Kane, associate professor of planetary astrophysics at UC Riverside.

The research was carried out on planets in a planetary system called HR 5183, which is about 103 light years away in the constellation of Virgo. It was there that an eccentric giant planet was discovered earlier this year.

Normally, planets orbit their stars on a trajectory that is more or less circular. Astronomers believe large planets in stable, circular orbits around our sun, like Jupiter, shield us from space objects that would otherwise slam into Earth.

Sometimes, planets pass too close to each other and knock one another off course. This can result in a planet with an elliptical or “eccentric” orbit. Conventional wisdom says that a giant planet in eccentric orbit is like a wrecking ball for its planetary neighbors, making them unstable, upsetting weather systems, and reducing or eliminating the likelihood of life existing on them.

Questioning this assumption, Kane and Caltech astronomer Sarah Blunt tested the stability of an Earth-like planet in the HR 5183 solar system. Their modeling work is documented in a paper newly published in the Astronomical Journal.

Kane and Blunt calculated the giant planet’s gravitational pull on an Earth analog as they both orbited their star. “In these simulations, the giant planet often had a catastrophic effect on the Earth twin, in many cases throwing it out of the solar system entirely,” Kane said.

“But in certain parts of the planetary system, the gravitational effect of the giant planet is remarkably small enough to allow the Earth-like planet to remain in a stable orbit.”

The team found that the smaller, terrestrial planet has the best chance of remaining stable within an area of the solar system called the habitable zone — which is the territory around a star that is warm enough to allow for liquid-water oceans on a planet.

These findings not only increase the number of places where life might exist in the solar system described in this study — they increase the number of places in the universe that could potentially host life as we know it.

This is also an exciting development for people who simply love stargazing. HR 5813b, the eccentric giant in Kane’s most recent study, takes nearly 75 years to orbit its star. But the moment this giant finally swings past its smaller neighbor would be a breathtaking, once-in-a-lifetime event.

“When the giant is at its closest approach to the Earth-like planet, it would be fifteen times brighter than Venus — one of the brightest objects visible with the naked eye,” said Kane. “It would dominate the night sky.”

Going forward, Kane and his colleagues will continue studying planetary systems like HR 5183. They’re currently using data from NASA’s Transiting Exoplanet Survey Satellite and the Keck Observatories in Hawaii to discover new planets, and examine the diversity of conditions under which potentially habitable planets could exist and thrive.

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Semiconducting material more affected by defects than previously thought

A promising semiconductor material could be improved if flaws previously thought irrelevant to performance are reduced, according to research published today in Nature Communications. A group of researchers at Rensselaer Polytechnic Institute and other universities has shown that a specific defect impacts the ability of halide perovskite to hold energy derived from light in the form of electrons.

“Defects could be good or bad in semiconductors,” said Jian Shi, associate professor of materials science engineering. “For some reason, people did not pay attention to dislocations in halide perovskite, but we have shown that this defect is a problem in halide perovskite.”

Research on halide perovskite has rapidly improved the efficiency of the material from about a 3% conversion of light to electrical energy to 25% — equivalent to state-of-the-art silicon solar cells — over the course of a decade. Researchers wrestled with silicon for decades to reach that material’s current level of efficiency.

Halide perovskite also has promising carrier dynamics, which are roughly defined as the length of time that light energy absorbed by the material is retained in the form of an excited electron. To make a good prospect for solar energy conversion, electrons in the material must retain their energy long enough to be harvested by an electrode attached to the material, thus completing the conversion of light to electrical energy.

The material had long been considered “defect tolerant,” meaning flaws like missing atoms, shoddy bonds across grains of the crystal, and a mismatch known as crystallographic dislocation were not believed to have much impact on efficiency. More recent research has questioned that assumption and found that some defects do affect aspects of the crystal’s performance.

Shi’s team tested whether the defect of crystallographic dislocation impacts carrier dynamics by growing the crystal on two different substrates. One substrate had a strong interaction with the halide perovskite as it was being deposited, producing a higher density of dislocations. The other had a weaker interaction and produced a lower density of dislocations.

The results show that dislocations negatively impact the carrier dynamics of halide perovskite. Reducing dislocation densities by more than one order of magnitude is found to lead to an increase of electron lifetime by four times.

“A conclusion is that halide perovskite has a similar dislocation effect as conventional semiconductors,” Shi said. “We need to be careful of dislocations in halide perovskite, which is a factor people have been ignoring as they work on this material.”

Shi’s last significant work on halide perovskite revealed the role of pressure on this semiconductor’s optical properties published in Science Advances in 2018.

At Rensselaer, Shi was joined by researchers in both the Department of Materials Science and Engineering and Department of Physics, Applied Physics and Astronomy. Researchers from the Kunming University of Science and Technology, Tsinghua University, University of Science and Technology Beijing, Forschungszentrum Julich, and Brown University also contributed to the research.

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