A Chemical Switch-Flip Helps Perovskite Solar Cells Beat the Heat

 

Thin films of crystalline materials called perovskites provide a promising new way of making inexpensive and efficient solar cells. Now, an international team of researchers has shown a way of flipping a chemical switch that converts one type of perovskite into another — a type that has better thermal stability and is a better light absorber.

The study, by researchers from Brown University, the National Renewable Energy Laboratory (NREL) and the Chinese Academy of Sciences’ Qingdao Institute of Bioenergy and Bioprocess Technology published in the Journal of the American Chemical Society, could be one more step toward bringing perovskite solar cells to the mass market.

“We’ve demonstrated a new procedure for making solar cells that can be more stable at moderate temperatures than the perovskite solar cells that most people are making currently,” said Nitin Padture, professor in Brown’s School of Engineering, director of Brown’s Institute for Molecular and Nanoscale Innovation, and the senior co-author of the new paper. “The technique is simple and has the potential to be scaled up, which overcomes a real bottleneck in perovskite research at the moment.”

Perovskites have emerged in recent years as a hot topic in the solar energy world. The efficiency with which they convert sunlight into electricity rivals that of traditional silicon solar cells, but perovskites are potentially much cheaper to produce. These new solar cells can also be made partially transparent for use in windows and skylights that can produce electricity, or to boost the efficiency of silicon solar cells by using the two in tandem.

Despite the promise, perovskite technology has several hurdles to clear — one of which deals with thermal stability. Most of the perovskite solar cells produced today are made with of a type of perovskite called methylammonium lead triiodide (MAPbI3). The problem is that MAPbI3 tends to degrade at moderate temperatures.

“Solar cells need to operate at temperatures up to 85 degrees Celsius,” said Yuanyuan Zhou, a graduate student at Brown who led the new research. “MAPbI3 degrades quite easily at those temperatures.”

That’s not ideal for solar panels that must last for many years. As a result, there’s a growing interest in solar cells that use a type of perovskite called formamidinium lead triiodide (FAPbI3) instead. Research suggests that solar cells based on FAPbI3 can be more efficient and more thermally stable than MAPbI3. However, thin films of FAPbI3 perovskites are harder to make than MAPbI3 even at laboratory scale, Padture says, let alone making them large enough for commercial applications.

(Right) Thin films of crystalline materials called perovskites provide a promising new way of making inexpensive and efficient solar cells. Now, an international team of researchers has shown a way of flipping a chemical switch that converts one type of perovskite into another — a type that has better thermal stability and is a better light absorber. Credit: Padture Lab / Brown University

Part of the problem is that formamidinium has a different molecular shape than methylammonium. So as FAPbI3 crystals grow, they often lose the perovskite structure that is critical to absorbing light efficiently.

This latest research shows a simple way around that problem. The team started by making high-quality MAPbI3 thin films using techniques they had developed previously. They then exposed those MAPbI3 thin films to formamidine gas at 150 degrees Celsius. The material instantly converted from MAPbI3 to FAPbI3 while preserving the all-important microstructure and morphology of the original thin film.

“It’s like flipping a switch,” Padture said. “The gas pulls out the methylammonium from the crystal structure and stuffs in the formamidinium, and it does so without changing the morphology. We’re taking advantage of a lot of experience in making excellent quality MAPbI3 thin films and simply converting them to FAPbI3 thin films while maintaining that excellent quality.”

This latest research builds on the work this international team of researchers has been doing over the past year using gas-based techniques to make perovskites. The gas-based methods have the potential of improving the quality of the solar cells when scaled up to commercial proportions. The ability to switch from MAPbI3 to FAPbI3 marks another potentially useful step toward commercialization, the researchers say.

“The simplicity and the potential scalability of this method was inspired by our previous work on gas-based processing of MAPbI3 thin films, and now we can make high-efficiency FAPbI3-based perovskite solar cells that can be thermally more stable,” Zhou said. “That’s important for bringing perovskite solar cells to the market.”

Laboratory scale perovskite solar cells made using this new method showed efficiency of around 18 percent — not far off the 20 to 25 percent achieved by silicon solar cells.

“We plan to continue to work with the method in order to further improve the efficiency of the cells,” said Kai Zhu, senior scientist at NREL and co-author of the new paper. “But this initial work demonstrates a promising new fabrication route.”

Advance could aid development of nanoscale biosensors

Imagine a hand-held environmental sensor that can instantly test water for lead, E. coli, and pesticides all at the same time, or a biosensor that can perform a complete blood workup from just a single drop. That’s the promise of nanoscale plasmonic interferometry, a technique that combines nanotechnology with plasmonics—the interaction between electrons in a metal and light.

Now researchers from Brown University’s School of Engineering have made an important fundamental advance that could make such devices more practical. The research team has developed a technique that eliminates the need for highly specialized external light sources that deliver coherent light, which the technique normally requires. The advance could enable more versatile and more compact devices.

“It has always been assumed that coherent light was necessary for plasmonic interferometry,” said Domenico Pacifici, a professor of engineering who oversaw the work with his postdoctoral researcher Dongfang Li, and graduate student Jing Feng. “But we were able to disprove that assumption.”

The research is described in Nature Scientific Reports.

Plasmonic interferometers make use of the interaction between light and surface plasmon polaritons, density waves created when light energy rattles free electrons in a metal. One type of interferometer looks like a bull’s-eye structure etched into a thin layer of metal. In the center is a hole poked through the metal layer with a diameter of about 300 nanometers—about 1,000 times smaller than the diameter of a human hair. The hole is encircled by a series of etched grooves, with diameters of a few micrometers. Thousands of these bulls-eyes can be placed on a chip the size of a fingernail.

When light from an external source is shown onto the surface of an interferometer, some of the photons go through the central hole, while others are scattered by the grooves. Those scattered photons generate surface plasmons that propagate through the metal inward toward the hole, where they interact with photons passing through the hole. That creates an interference pattern in the light emitted from the hole, which can be recorded by a detector beneath the metal surface.

When a liquid is deposited on top of an interferometer, the light and the surface plasmons propagate through that liquid before they interfere with each other. That alters the interference patterns picked up by the detector depending on the chemical makeup of the liquid or compounds present in it. By using different sizes of groove rings around the hole, the interferometers can be tuned to detect the signature of specific compounds or molecules. With the ability to put many differently tuned interferometers on one chip, engineers can hypothetically make a versatile detector.

Up to now, all plasmonic interferometers have required the use of highly specialized external light sources that can deliver coherent light—beams in which light waves are parallel, have the same wavelength, and travel in-phase (meaning the peaks and valleys of the waves are aligned). Without coherent light sources, the interferometers cannot produce usable interference patterns. Those kinds of light sources, however, tend to be bulky, expensive, and require careful alignment and periodic recalibration to obtain a reliable optical response.

But Pacifici and his group have come up with a way to eliminate the need for external coherent light. In the new method, fluorescent light-emitting atoms are integrated directly within the tiny hole in the center of the interferometer. An external light source is still necessary to excite the internal emitters, but it need not be a specialized coherent source.

“This is a whole new concept for optical interferometry,” Pacifici said, “an entirely new device.”

In this new device, incoherent light shown on the interferometer causes the fluorescent atoms inside the center hole to generate surface plasmons. Those plasmons propagate outward from the hole, bounce off the groove rings, and propagate back toward the hole after. Once a plasmon propagates back, it interacts with the atom that released it, causing an interference with the directly transmitted photon. Because the emission of a photon and the generation of a plasmon are indistinguishable, alternative paths originating from the same emitter, the process is naturally coherent and interference can therefore occur even though the emitters are excited incoherently.

“The important thing here is that this is a self-interference process,” Pacifici said. “It doesn’t matter that you’re using incoherent light to excite the emitters, you still get a coherent process.”

In addition to eliminating the need for specialized external light sources, the approach has several advantages, Pacifici said. Because the surface plasmons travel out from the hole and back again, they probe the sample on top of the interferometer surface twice. That makes the device more sensitive.

But that’s not the only advantage. In the new device, external light can be projected from underneath the metal surface containing the interferometers instead of from above. That eliminates the need for complex illumination architectures on top of the sensing surface, which could make for easier integration into compact devices.

The embedded light emitters also eliminate the need to control the amount of sample liquid deposited on the interferometer’s surface. Large droplets of liquid can cause lensing effects, a bending of light that can scramble the results from the interferometer. Most plasmonic sensors make use of tiny microfluidic channels to deliver a thin film of liquid to avoid lensing problems. But with internal light emitters excited from the bottom surface, the external light never comes in contact with the sample, so lensing effects are negated, as is the need for microfluidics.

Finally, the internal emitters produce a low intensity light. That’s good for probing delicate samples, such as proteins, than can be damaged by high-intensity light.

More work is required to get the system out of the lab and into devices, and Pacifici and his team plan to continue to refine the idea. The next step will be to try eliminating the external light source altogether. It might be possible, the researchers say, to eventually excite the internal emitters using tiny fiber optic lines, or perhaps electric current.

Still, this initial proof-of-concept is promising, Pacifici said.

“From a fundamental standpoint, we think this new device represents a significant step forward,” he said, “a first demonstration of plasmonic interferometry with incoherent light”.

Explore further: Periodic structures in organic light-emitters can efficiently enhance, replenish surface plasmon waves

Journal reference: Scientific Reports

Provided by: Brown University

Brown University: Researchers Make New Silicon-Based Nanomaterials: Electronics Applications

Chemists from Brown University have found a way to make new 2D, graphene-like semiconducting nanomaterials using an old standby of the semiconductor world: silicon.

In a paper published in the journal Nanoletters, the researchers describe methods for making nanoribbons and nanoplates from a compound called silicon telluride. The materials are pure, p-type semiconductors (positive charge carriers) that could be used in a variety of electronic and optical devices. Their layered structure can take up lithium and magnesium, meaning it could also be used to make electrodes in those types of batteries.

“Silicon-based compounds are the backbone of modern electronics processing,” said Kristie Koski, assistant professor of chemistry at Brown, who led the work.

“Silicon telluride is in that family of compounds, and we’ve shown a totally new method for using it to make layered, two-dimensional nanomaterials.”

Koski and her team synthesised the new materials through vapour deposition in a tube furnace. When heated in the tube, silicon and tellurium vaporise and react to make a precursor compound that is deposited on a substrate by an argon carrier gas. The silicon telluride then grows from the precursor compound.

Different structures can be made by varying the furnace temperature and using different treatments of the substrate. By tweaking the process, the researchers made nanoribbons that are about 50 to 1000 nm in width and about 10 microns long. They also made nanoplates flat on the substrate and standing upright.

“We see the standing plates a lot,” Koski said. “They’re half hexagons sitting upright on the substrate. They look a little like a graveyard.”

Each of the different shapes has a different orientation of the material’s crystalline structure. As a result, they all have different properties and could be used in different applications. The researchers also showed that the material can be ‘doped’ through the use of different substrates. Doping is a process through which tiny impurities are introduced to change a material’s electrical properties. In this case, the researchers showed that silicon telluride can be doped with aluminium when grown on a sapphire substrate. That process could be used, for example, to change the material from a p-type semiconductor (one with positive charge carriers) to an n-type (one with negative charge carriers).

The materials are not particularly stable out in the environment, Koski said, but that’s easily remedied. “What we can do is oxidise the silicon telluride and then bake off the tellurium, leaving a coating of silicon oxide,” she said. “That coating protects it and it stays pretty stable.”

From here, Koski and her team plan to continue testing the material’s electronic and optical properties. They’re encouraged by what they’ve seen so far. “We think this is a good candidate for bringing the properties of 2D materials into the realm of electronics,” Koski said.

Koski’s co-authors on the paper were postdoctoral researcher Sean Keuleyan, graduate student Mengjing Wang and undergraduates Frank Chung and Jeffrey Commons.

A new method for making perovskite solar cells

Research led by a Brown University Ph.D. student has revealed a new way to make light-absorbing perovskite films for use in solar cells.

The new method involves a room-temperature solvent bath to create perovskite crystals, rather than the blast of heat used in current crystallization methods. A study published in the Royal Society of Chemistry’s Journal of Materials Chemistry A (“Room-Temperature Crystallization of Hybrid-Perovskite Thin Films via Solvent-Solvent Extraction for High-Performance Solar Cells”) shows that the technique produces high-quality crystalline films with precise control over thickness across large areas, and could point the way toward mass production methods for perovskite cells.

Researchers have come up with a new way to make perovskite films for solar cells. The technique is especially well suited to making ultra-thin films that are semi-transparent, which could be useful for window photovoltaics. The cells can also be made in different colors. (Image: Padture lab/Brown University)

Perovskites, a class of crystalline materials, have caused quite a stir in the clean energy world. Perovskite films are excellent light absorbers and are much cheaper to make than the silicon wafers used in standard solar cells. The efficiency of perovskite cells — the percentage of sunlight converted to electricity — has increased at a staggering pace in just a few years. The first perovskite cells introduced in 2009 managed an efficiency of only about 4 percent, a far cry from the 25-percent efficiency boasted by standard silicon cells. But by last year, perovskite cells had been certified as having more than 20-percent efficiency. That rapid improvement in performance is promising, and researchers are racing to start using perovskite cells in commercial products.

There are a number of different ways to make the films, but nearly all of them require heat. Perovskite precursor chemicals are dissolved into a solution, which is then coated onto a substrate. Heat is applied to remove the solvent, leaving the perovskite crystals to form in a film across the substrate.

“People have made good films over relatively small areas — a fraction of a centimeter or so square. But they’ve had to go to temperatures from 100 to 150 degrees Celsius, and that heating process causes a number of problems,” said Nitin Padture, professor of engineering and director of the Institute for Molecular and Nanoscale Innovation.

For example, the crystals often form unevenly when heat-treated, leaving tiny pinholes in the film. In a solar cell, those pinholes can reduce efficiency. Heat also limits the substrates on which films can be deposited. Flexible plastic substrates, for example, cannot be used because they are damaged by high temperatures.

Yuanyuan Zhou, a graduate student in Padture’s lab, wanted to see if there was a way to make perovskite crystal thin films without having to apply heat. He came up with what is known as a solvent-solvent extraction (SSE) approach.

In his method, perovskite precursors are dissolved in a solvent called NMP and coated onto a substrate. Then, instead of heating, the substrate is bathed in diethyl ether (DEE), a second solvent that selectively grabs the NMP solvent and whisks it away. What’s left is an ultra-smooth film of perovskite crystals.

Because there is no heating involved, the crystals can be formed on virtually any substrate — even heat-sensitive polymer substrates used in flexible photovoltaics. Another advantage is that the entire SSE crystallization process takes less than two minutes, compared to an hour or more for heat-treating. That makes the process more amenable to mass production because it can be done in an assembly line kind of process.

The SSE approach also enables films to be made very thin while maintaining high quality. Standard perovskite films are generally on the order of 300 nanometers thick. But Zhou has been able to make high quality films as thin as 20 nanometers. The SSE films could also be made larger — several centimeters square — without generating pinholes.

“Using the other methods, when the thickness gets below 100 nanometers you can hardly make full coverage of film,” Zhou said. “You can make a film, but you get lots of pinholes. In our process, you can form the film evenly down to 20 nanometers because the crystallization at room temperature is much more balanced and occurs immediately over the whole film upon bathing.”

Those ultra-thin films are partially transparent (films of standard thickness are black and opaque), so they could be used to make photovoltaic windows, the researchers say. And by tweaking the perovskite precursor solution composition, Zhou has been able to make cells in different colors.

“These could potentially be used for decorative, building-integrated windows that can make power,” Padture said.

The group plans to do more work to refine the process, but they are encouraged by the early results. Working with scientists at the National Renewable Energy Laboratory in Colorado, initial testing of cells made with SSE films showed conversion efficiency of over 15 percent. Solar cells based on semitransparent 80-nanometer films made using the process were shown to have higher efficiency than any other ultra-thin film.

“We think this could be a significant step toward a variety of commercially available perovskite cell products,” Padture said.

Source: Brown University

Read more: A new method for making perovskite solar cells

Researchers discover boron “buckyball”: Borosphrene is Born!

 

The discovery of buckyballs—soccer-ball-shaped molecules of carbon—helped usher in the nanotechnology era. Now, Lai-Sheng Wang’s research group and colleagues from China have shown that boron, carbon’s neighbor on the periodic table, can form a cage-like molecule similar to the buckyball. Until now, such a boron structure had only been a theoretical speculation. The researchers dubbed their newfound nanostructure “borospherene.”

The discovery 30 years ago of soccer-ball-shaped carbon molecules called buckyballs helped to spur an explosion of nanotechnology research. Now, there appears to be a new ball on the pitch.

Researchers from Brown University, Shanxi University and Tsinghua University in China have shown that a cluster of 40 boron atoms forms a hollow molecular cage similar to a carbon buckyball. It’s the first experimental evidence that a boron cage structure—previously only a matter of speculation—does indeed exist.

“This is the first time that a boron cage has been observed experimentally,” said Lai-Sheng Wang, a professor of chemistry at Brown who led the team that made the discovery. “As a chemist, finding new molecules and structures is always exciting. The fact that boron has the capacity to form this kind of structure is very interesting.”

Wang and his colleagues describe the molecule, which they’ve dubbed borospherene, in the journal Nature Chemistry.

Carbon buckyballs are made of 60 carbon atoms arranged in pentagons and hexagons to form a sphere—like a soccer ball. Their discovery in 1985 was soon followed by discoveries of other hollow carbon structures including carbon nanotubes. Another famous carbon nanomaterial—a one-atom-thick sheet called graphene—followed shortly after.

After buckyballs, scientists wondered if other elements might form these odd hollow structures. One candidate was boron, carbon’s neighbor on the periodic table. But because boron has one less electron than carbon, it can’t form the same 60-atom structure found in the buckyball. The missing electrons would cause the cluster to collapse on itself. If a boron cage existed, it would have to have a different number of atoms.

Wang and his research group have been studying boron chemistry for years. In a paper published earlier this year, Wang and his colleagues showed that clusters of 36 boron atoms form one-atom-thick disks, which might be stitched together to form an analog to graphene, dubbed borophene. Wang’s preliminary work suggested that there was also something special about boron clusters with 40 atoms. They seemed to be abnormally stable compared to other boron clusters.

Figuring out what that 40-atom cluster actually looks like required a combination of experimental work and modeling using high-powered supercomputers.

On the computer, Wang’s colleagues modeled over 10,000 possible arrangements of 40 boron atoms bonded to each other. The computer simulations estimate not only the shapes of the structures, but also estimate the electron binding energy for each structure—a measure of how tightly a molecule holds its electrons. The spectrum of binding energies serves as a unique fingerprint of each potential structure.

The carbon buckyball has a boron cousin. A cluster for 40 boron atoms forms a hollow cage-like molecule.The next step is to test the actual binding energies of boron clusters in the lab to see if they match any of the theoretical structures generated by the computer. To do that, Wang and his colleagues used a technique called photoelectron spectroscopy.

Chunks of bulk boron are zapped with a laser to create vapor of boron atoms. A jet of helium then freezes the vapor into tiny clusters of atoms. The clusters of 40 atoms were isolated by weight then zapped with a second laser, which knocks an electron out of the cluster. The ejected electron flies down a long tube Wang calls his “electron racetrack.” The speed at which the electrons fly down the racetrack is used to determine the cluster’s electron binding energy spectrum—its structural fingerprint.

The experiments showed that 40-atom-clusters form two structures with distinct binding spectra. Those spectra turned out to be a dead-on match with the spectra for two structures generated by the computer models. One was a semi-flat molecule and the other was the buckyball-like spherical cage.

“The experimental sighting of a binding spectrum that matched our models was of paramount importance,” Wang said. “The experiment gives us these very specific signatures, and those signatures fit our models.”

The borospherene molecule isn’t quite as spherical as its carbon cousin. Rather than a series of five- and six-membered rings formed by carbon, borospherene consists of 48 triangles, four seven-sided rings and two six-membered rings. Several atoms stick out a bit from the others, making the surface of borospherene somewhat less smooth than a buckyball.

As for possible uses for borospherene, it’s a little too early to tell, Wang says. One possibility, he points out, could be hydrogen storage. Because of the electron deficiency of boron, borospherene would likely bond well with hydrogen. So tiny boron cages could serve as safe houses for hydrogen molecules.

But for now, Wang is enjoying the discovery.

“For us, just to be the first to have observed this, that’s a pretty big deal,” Wang said. “Of course if it turns out to be useful that would be great, but we don’t know yet. Hopefully this initial finding will stimulate further interest in boron clusters and new ideas to synthesize them in bulk quantities.”

The theoretical modeling was done with a group led by Prof. Si-Dian Li from Shanxi University and a group led by Prof. Jun Li from Tsinghua University. The work was supported by the U.S. National Science Foundation (CHE-1263745) and the National Natural Science Foundation of China.

Source: Brown Univ.

Researchers Develop Novel Technique for Separating Target Molecules from Mixed Solutions Using Magnetic Nanoparticles

Published on September 18, 2013 at 7:04 AM

Separating target molecules in biological samples is a critical part of diagnosing and detecting diseases. Usually the target and probe molecules are mixed and then separated in batch processes that require multiple pipetting, tube washing and extraction steps that can affect accuracy.

 

This is an illustration showing a simple new technique that is capable of separating tiny amounts of the target molecules from mixed solutions. Credit: J.Wang/Brown

 

Now a team of researchers at Brown University has developed a simple new technique that is capable of separating tiny amounts of the target molecules from mixed solutions by single motion of magnet under a microchannel. Their technique may make pipettes and test tubes a thing of the past in some diagnostic applications and increase the accuracy and sensitivity of disease detection.

The new platform developed by Anubhav Tripathi and his team at Brown doesn’t rely on external pumps to mix samples or flow target molecules. Instead, their system is static and handy for researchers to use, according to Ms. Jingjing Wang, a graduate student pursuing her PhD. Bead-like magnetic particles are specifically modified by attaching short pieces of DNA to them that can capture target DNA molecules with specific sequences matching. Those are then separated for detection simply by pulling the magnetic beads along the channel. The process is simple, fast and specific.

This process has great applicability particularly for point-of-care platforms that are used to detect bacterial, viral infections and prion diseases by DNA, RNA or protein identification. Specific disease applications include testing for HIV and influenza, explained Wang.

“It can also be used to evaluate the expression of certain protein markers, such as troponin (an indicator of damage to the heart muscle) or any detection that requires binding and separation of known target biomolecules,” she added.

Optimizing the system and characterizing the chip for biological assays was the biggest challenge for the research team as it required that both engineering as well as biological factors be considered, however the team is already developing assays using this new platform. A new microchip based Simple Method of Amplifying RNA Targets (SMART) assay developed to detect influenza from patient samples is already showing high agreement with Polymerase Chain Reaction (PCR), which is considered the “gold standard” for influenza diagnosis. The team’s next challenge is developing assays using this technique to detect wild type and drug-resistant HIV in areas with limited resources such as Kenya and South Africa.

Source: http://www.aip.org

Researchers to Study Quantum Metamaterials

Published on October 4, 2012 at 4:34 AM

Through a new Multidisciplinary University Research Initiative (MURI) awarded by the Air Force Office of Scientific Research, researchers from Brown University will lead an effort to study new optical materials and their interactions with light quantum scale. The initiative, titled Quantum Metaphotonics and Quantum Metamaterials, will receive $4.5 million over three years, with a possible two-year extension.

“The field of metamaterials has already expanded the range of optical materials and phenomenon available at larger, classical scales,” said Rashid Zia, Manning assistant professor of engineering and the lead investigator of the initiative. “What we’re doing now is asking what happens when we bring these metamaterials down to the scale of quantum emitters.”

Harnessing the power of light at the quantum scale could clear the way for super-fast optical microprocessors, high-capacity optical memory, securely encrypted communication, and untold other technologies. But before any of these potential applications sees the light of day, there are substantial obstacles to overcome. Not the least of which is the fact that the wavelength of light is larger than quantum-scale objects, limiting the range of possible light-matter interactions.

“The optical wavelength is approximately 100 times larger than a quantum emitter,” Zia said. “So we need to find ways of overcoming this size mismatch to increase interactions at the quantum scale, for example by shrinking the optical wavelength in highly confined metamaterial cavities. And hopefully we can learn something fundamental about the nature of light that opens up news ways of manipulating it to increase these interactions.”

The Quantum Metaphotonics and Metamaterials MURI team includes:

Harry Atwater, California Institute of Technology

Seth Bank, University of Texas at Austin

Mark Brongersma, Stanford University

Nader Engheta, University of Pennsylvania

Shanhui Fan, Stanford University

Nicholas Fang, Massachusetts Institute of Technology

Arto Nurmikko, Brown University

Jelena Vuckovic, Stanford University

Xiang Zhang, University of California, Berkeley

Rashid Zia, Brown University

“It’s really an exciting project,” Zia said. “Over the next five years, this program will bring together 10 groups and 40-plus researchers with complementary expertise to help answer questions that we couldn’t have imagined a short time ago. We are very optimistic about where this will lead.”

Source: http://www.brown.edu/about