Plenary Session Featuring the Fred Kavli Distinguished Lectureship in Materials Science

Moungi G. Bawendi, Massachusetts Institute of Technology

Quantum Dots: A Journey of Nano Exploration

Written by Vineeth Venugopal

Quantum Dots: A Journey of Nano Exploration

At the Materials Research Society’s (MRS) Fall Meeting, Moungi G. Bawendi, a 2023 Nobel Laureate in Chemistry, delivered a captivating Fred Kavli Distinguished Lecture. Titled Quantum Dots: A Journey of Nano Exploration, Bawendi delved into the fascinating evolution of quantum dots (QDs), from their conceptual beginnings to their transformative applications in science and technology.

 

The Origin Story of Quantum Dots

In the 1980s, the study of quantum dots (QDs) was a purely curiosity-driven endeavor. Bawendi underscored the importance of fundamental science, noting that the practical applications of QDs were far from apparent at the time. Early explorations hinted at their potential in lasers, but it would take decades for their transformative capabilities to materialize.

Quantum dots are nanometer-sized semiconductor crystals with unique quantum mechanical properties. As Bawendi illustrated with the analogy of wind instruments like the flute and tuba, electrons confined in these “nanoboxes” exhibit wave-like properties, with their behavior dependent on size.

The foundational work on QDs began with Alexey Ekimov and Louis Brus, co-recipients of the Nobel Prize alongside Bawendi. Ekimov, intrigued by the vibrant colors in stained glass, discovered that these hues resulted from the size-dependent quantum effects of embedded nanoparticles. His groundbreaking 1981 study, later translated into English, laid the groundwork for understanding quantum size effects. Around the same time, Brus investigated electron transfer kinetics in small particles, noting similar size-dependent color phenomena.

 

From Discovery to Synthesis

Bawendi, who worked as a postdoctoral researcher with Brus, revolutionized the field with his contributions to QD synthesis. Trained as a polymer physicist, Bawendi joined Bell Labs, where he delved into organometallic chemistry. Upon transitioning to MIT, he and his students developed the hot-injection method, a simple yet elegant process involving the nucleation and growth of QDs from metal-organic precursors at high temperatures. This work culminated in a landmark 1993 publication detailing the synthesis of monodisperse cadmium selenide (CdSe) QDs.

Advancements in synthesis have since achieved quantum yields of nearly 100%, enabling exquisite control over size and properties. The result has been a deeper understanding of quantum mechanics and band structure evolution, as demonstrated by PhD students like Chris Murray and Manoj Nirmal in their studies of particle size and theoretical frameworks.

Breakthrough Applications

The first major application of QDs emerged in biology. Due to their small size, comparable to large proteins, and sensitivity to environmental changes, QDs became invaluable in imaging and sensing. Early innovations enabled the visualization of single molecules and local field dynamics. In 1998, Bawendi co-founded Quantum Dot Corporation, now part of Thermo Fisher, to commercialize biocompatible QDs. These particles, more stable than traditional dyes, revolutionized cellular imaging and tumor tracking, offering extended observation periods.

A particularly striking application has been in short-wave infrared (SWIR) intravital microscopy, where QDs provide unparalleled insights into tumor microenvironments. SWIR-QD composites allow high-frame-rate imaging, revealing differences in blood flow between healthy and cancerous tissues. Such breakthroughs offer critical insights into drug delivery challenges in tumors.

QDs have also made their mark in consumer technology. Companies like Samsung have incorporated them into advanced display technologies such as QLED and QD-OLED TVs. By inkjet-printing QDs onto pixels, these displays achieve vibrant, precise colors. Other applications include luminescent solar concentrators and US-VIS imaging, showcasing the versatility of these nanostructures.

 

Toward the Future: Building Blocks of Nanotechnology

Bawendi’s lecture also touched on the future of QDs as building blocks for nanostructures. Magnetic QDs, for instance, can self-assemble into intricate arrangements, opening doors to novel applications in medicine and materials science. Iron oxide QDs are emerging as superior contrast agents in imaging, particularly for conditions like nephrogenic systemic fibrosis, outperforming traditional gadolinium-based compounds.

The lecture concluded with a nod to the serendipity of discovery. “Applications often come decades later,” Bawendi remarked, emphasizing the role of private companies in accelerating innovation beyond the scope of standard government funding. With their myriad applications in biology, medicine, energy, and consumer electronics, quantum dots continue to exemplify the profound impact of curiosity-driven research.

 

A Legacy of Exploration

Bawendi’s journey from fundamental discovery to practical innovation reflects the transformative power of interdisciplinary science. The story of quantum dots, spanning vibrant stained glass to cutting-edge medical imaging and high-definition displays, is a testament to the unexpected pathways that fundamental science can take. As he fielded questions from an inspired audience, Bawendi left a resonant message: the future of quantum dots—and science itself—rests on the unyielding spirit of exploration.

Keynote: Enhancing Materials Science through Research Collaborations between African and Non-African Institutions

Malik Maaza, University of South Africa 

Nanosciences & Nanotechnologies Towards SDGs & Science with Social Impact 

Written by Judy Meiksin and Matthew Hauwiller

The Enhancing Materials Science through Research Collaborations between African and Non-African Institutions session held at the 2024 MRS Spring Meeting & Exhibit in Seattle continued during the Virtual experience on May 8, with keynote speaker Malik Maaza of the University of South Africa. “Materials science is pivotal within the African landscape,” he said.

Maaza shared several research projects that integrated African indigenous knowledge with nanomaterials characterization and synthesis to innovate new solutions in medicine, sustainability, and optical materials, all tied to addressing some of the UN sustainable development goals (SDGs). In assembling the research teams, Maaza intentionally drew members, including graduate students and postdoctoral researchers, from countries throughout Africa and the global south while prioritizing having at least 50% women.

With the world population expected to reach ~2.5 billion in urban areas by 2050, with ~90% of this increase in Asia and Africa, green air-conditioning rises as one of the major technologies that needs to be achieved. According to Maaza, vanadium-based thermochromic nanocoatings are ideal for smart window applications regulating solar heat radiation with zero energy-input. Furthering the studies of vanadium, Maaza and colleagues worked with multilayered V₂O₅/V/V₂O₅ stacks deposited onto borosilicate glass substrates. The researchers varied the intermediate V layer within the range of 3–12 nm, which is within the coalescence threshold of vanadium. By controlling the nanoscale thickness of the intermediate V layer, Maaza’s group achieved net control and tunability of the optical transmission modulation in the NIR-IR region.

Maaza talked about his work with nanofluids as a new generation of superior coolants in waste heat recovery as well as for drug delivery. He reported his findings based on his study of Ag-H₂O and Ag-C₂H₆O₂ nanofluids; stable Ag-decorated 2D graphene nanocomposites; and gold nanoparticles-decorated graphene nanosheets.

“Zero hunger” is listed as the second SDG. Along with issues of transportation, Maaza said, “This shortage of food [especially] in Africa is related to the fertilizer market.” African countries rely on the import of fertilizer, which—particularly during times of war outside of Africa—can push food prices inexorably high. By hosting research fellows from various countries in Africa, Maaza was able to assemble a research team to study nanoparticles for developing a nanofertilizer prototype.

In the area of medicine, Maaza described research for protection against skin cancer and bacterial infection. His group relied on indigenous knowledge from communities in certain regions in southern Africa that was absent of these health problems. Maaza also covered research for water decontamination—referring to the problem of water scarcity as number six in the SDGs.

Maaza emphasized throughout his talk the value of international and intercontinental collaborations in the development of the materials research field in African countries toward global community benefits.

Next-Generation Solar Energy

Henry Snaith joins MRS TV to discuss his plenary lecture on metal halide perovskites and their role in the future of solar power.

 

 

Plenary Session Featuring the Fred Kavli Distinguished Lectureship in Materials Science

Henry Snaith, University of Oxford

Metal Halide Perovskites—From a Scientific Curiosity Toward an Industrialized Photovoltaic Technology 

Written by Rahul Rao

Solar photovoltaic cells are cheaper than ever; at current trends, photovoltaics could even meet the majority of the world’s energy needs by the middle of this century. But that doesn’t mean solar cell technology has reached its end. Researchers want photovoltaics more efficient than today’s predominant silicon- and cadmium-telluride-based cells, which reach a barrier at around 26% efficiency.

One of the best-known pathways around that barrier is paved with lead-and-halide-containing perovskites. At Tuesday’s plenary session, titled “Metal Halide Perovskites—From a Scientific Curiosity Toward an Industrialized Photovoltaic Technology,” Henry Snaith of Oxford University briefly discussed both the history of perovskite-based solar cells and the obstacles that remain on the pathway to deploying them on the mass market.

Although perovskites were explored for semiconductor-device applications since the 1990s, the history of metal halide perovskite photovoltaics only began in 2009. That year, a group at Toin University of Yokohama created the first effective metal halide perovskite solar cell by layering perovskites upon a substrate of porous titanium dioxide. Their creation had an efficiency of 3.8%: eye-catching for a new material, but very far from the market.

Snaith credited the Toin University researchers for teaching his own group how to create metal halide perovskites. By 2012, Snaith’s group had swapped out the porous titanium dioxide for insulating aluminum oxide, which allowed the team to push their efficiency up to 10.8%—far from commercialization, but a remarkable number for the time.

As Snaith and his colleagues steadily learned what made metal halide perovskites tick, they pushed for higher and higher efficiencies. They designed a multi-junction cell containing a perovskite layer atop silicon; the perovskite can capture higher-energy, shorter-wavelength light, while the silicon can do the same with lower-energy, longer-wavelength light. In 2017, Snaith’s group calculated that, in theory, a perovskite-on-silicon could reach efficiencies of more than 33 percent. As of 2024, other researchers have surpassed that target.

Still, there are some areas for improvement. Creating a wider-bandgap perovskite requires mixing iodide and bromide ions into the material, but under light, these ions tend to segregate themselves, creating lower-bandgap regions that come at the cost of voltage. Snaith spoke about how his colleagues and he are researching this phenomenon, called halide segregation, and other effects that cause voltage losses during recombination.

Beyond that, Snaith talked about creating all-perovskite multi-junction cells that do not feature silicon. Perovskite double junctions—a layer of a narrow-bandgap perovskite atop another layer of a different, wider-bandgap perovskite, for example—have reached efficiencies of about 29 percent. Additionally, Snaith revealed that recent work from his group has pushed the efficiency of perovskite triple junctions up to 27 percent.

Actually getting perovskites into mass real-world use will require effort, Snaith said, but he gave several reasons to be optimistic. Metal halide perovskites and silicon-perovskite multijunctions mostly use elements that are easily produced today. Although these cells do use lead, encapsulation prevents lead from leaching out; even if the lead from one cell did leach into the ground, environmental impact studies have shown that it would leach less lead than already exists in European soil. Snaith then closed by mentioning that several companies are working on perovskites, including his own Oxford PV, which has a production-ready cell of over 28% efficiency.

The Kavli Foundation is dedicated to advancing science for the benefit of humanity, promoting public understanding of scientific research and supporting scientists and their work.

The Future of Materials is Self-Driving with Alán Aspuru-Guzik

 

Alán Aspuru-Guzik's lab was a pioneer in early research in quantum computing. Today, his work reaches further to include both chemistry and machine learning. Sitting down with MRS TV, Dr. Aspuru-Guzik shares highlights from his 2023 Plenary Session, along with his hopes and expectations for the future in science and tech.

Plenary Session Featuring the Fred Kavli Distinguished Lectureship in Materials Science

Alán Aspuru-Guzik, University of Toronto

The Future of Materials Is Self-Driving

Written by Alison Hatt

In Monday’s plenary session, Alán Aspuru-Guzik gave an overview of his work on self-driving laboratories, in which he uses machine learning and robotics to accelerate materials discovery. He noted that 10 years ago at the MRS meeting, he and other researchers were focused on high-throughput virtual screening of materials. In a study from that time, Aspuru-Guzik used high-throughput screening to identify new materials for organic light-emitting diodes. His research team started with millions of candidates and gradually narrowed the list down to 1000 or so using machine learning and high-throughput calculations, but ultimately found that only 30 of them could be synthesized.

“It didn’t really move the needle,” said Aspuru-Guzik of the study. “We needed to actually accelerate discovery by not only calculating the materials but testing them.”

These efforts led to his vision for a self-driving lab. Instead of going serially through materials discovery process, he imagined a cycle of identifying candidate materials, synthesizing batches of them, and feeding the results back into the dataset continuously, so the machine learning tool can focus on synthesizable areas of parameter space.

 

But how to identify the candidate compounds? Using modern computational chemistry, we can determine the function of a material based on its structure, but a challenge for this century, according to Aspuru-Guzik, is to go the other way and determine the structure of a material to achieve a particular function.

In work published in 2018, Aspuru-Guzik and collaborators developed a tool for solving inverse design problems, using neural networks to encode a chemical structure, compress it into a bi-directional latent space, and then decompress it. In the latent space, the composition can be optimized by following gradients or doing sampling methods and, once a maximum is found, the material can be decoded to reveal the optimized structure. Many researchers are now using this generative model approach with various machine learning models, like genetic algorithms, generative adversarial networks, and, of course, large language models.

Demonstrating the power of the generative model approach, Aspuru-Guzik discussed a study in which he and collaborators developed a promising new drug candidate using artificial intelligence and generative models, going from ideation to testing in animals in just 45 days, usually a one-year process. He also shared examples from his work using a similar approach to design injectable materials for drug delivery and materials for carbon capture.

However, generative models can also dream up materials that are not synthesizable. With self-driving labs, Aspuru-Guzik hopes to better focus explorations on synthesizable materials space. As an example, he discussed efforts to discover new molecules for organic lasers, for which the screening criteria are a list of desired optical properties. Working with collaborators in British Columbia, Urbana Champaign, and Glasgow, his Toronto-based team took a modular approach, developing a library of molecular blocks and iteratively coupling them in varying configurations. The four collaborating teams all have self-driving labs, all of them slightly different, that can do synthesis, identification, and optical characterization of organic compounds. As a “hello world” experiment, the team produced 40 new organic laser compounds in just one weekend, several of them better than the molecule they started from.

More recently, the team demonstrated running the four geographically dispersed labs in parallel on a single discovery effort, sharing data and shipping materials between them. To achieve this, the researchers developed an asynchronous Bayesian optimization tool. They calculated 190,000 molecules with DFT, creating a model which they then calibrated experimentally by synthesizing and characterizing a hypercube sample of 500 compounds. Then, using their Bayesian optimization tool, the labs closed in on the most promising areas of materials space and ultimately identified 21 new compounds, now the brightest organic molecules in the world.

Looking forward, Aspuru-Guzik asked, what will the laboratory of the future look like? Anticipating a laboratory operated by independent robots, his group is training robotic arms to recognize transparent objects, which are particularly hard for robots to do but is an essential skill for working in a messy chemistry lab. They are also developing a computer program named Organa that integrates ChatGPT-4 technology and can plan and execute chemistry experiments given minimal input in natural language.

Aspuru-Guzik closed with a vision that computers can be agents of understanding, not just computational workhorses, a once-fantastical future that now seems almost within reach.

The Kavli Foundation is dedicated to advancing science for the benefit of humanity, promoting public understanding of scientific research and supporting scientists and their work.

Plenary Session Thoughts

We start day 2 with the plenary session titled “The Future of Materials is Self-Driving” by Alan Aspuru-Guzik.

Upon entering the ballroom on the 2^nd floor of the Sheraton, we were greeted with a beautiful blue backdrop accompanied by the sparkling crystal illuminated by a gentle lighting on the ceiling. The attendance amazing with full attendance.

Having an interview Saabir Petker, a 1^st Year PhD student working on using computational methods to simulate and predict barocaloric properties in polymers, I gained some insight into how people from different backgrounds benefitted from the talk. “It was very interesting and inspired me to work hard in my research, especially thinking about how I can adapt the sampling methods for relevant materials to my work. It gave me a lot to think about in terms of human input incorporated with AI”, he said.

Robots Making Cocktails in Chemistry Labs?

It was great listening to Prof. Alán Aspuru-Guzik at the first plenary talk today, where he talked about how the field of chemistry could be automated using robots. One of the things Prof. Aspuru-Guzik talked about towards the end is about how one can "talk" an experiment to the AI robot in his lab, where the current capabilities expand to making margaritas!!! Since making Cocktails is quite similar for a robotic arm to identify, pick and mix solutions from different beakers, it is quite possible for the automated robotics to also prepare margaritas on command. Imagine a group social where your friendly neighborhood robot chemist is making margaritas for everyone! 

Connect with Professor Alán Aspuru-Guzik from University of Toronto at MRS Fall 2023 to see if the self-driving chemistry robots could make your favorite cocktails! 

Plenary Session Featuring The Fred Kavli Distinguished Lectureship in Materials Science

Sir Konstantin ‘Kostya’ Novoselov, National University of Singapore & The University of Manchester

Materials for the Future

Written by Cullen Walsh

In his keynote talk, “Materials for the Future,” Konstantin Novoselov from the National University of Singapore and the University of Manchester explored what materials of the future will look like and how we will go about producing them. He started his talk by discussing graphene, which he successfully isolated in 2004, resulting in the 2010 Nobel Prize in physics. Since then, graphene has become commonplace in commercial applications, being used in Ford cars for noise cancelation and in Huawei phones for device cooling. To facilitate these new technologies, numerous advances have occurred in the production of graphene. For instance, we can now produce high-quality graphene at production scale using techniques like chemical vapor deposition, in which gas particles are condensed into a solid, and liquid phase exfoliation.

After reviewing these advances in graphene production, the remainder of Novoselov’s talk focused on the potential of other two-dimensional (2D) materials beyond graphene. There are now dozens of these 2D crystals that range from semiconductors to insulators to superconductors. By stacking these 2D materials, we can create customizable structures with unique properties which we call van der Waals heterostructures (due to the van der Waals forces holding the layers together). We can then further customize these heterostructures by changing the relative orientation of the stacked layers, resulting in dramatic changes in the physics and chemistry of the structure. For instance, if we rotate the topmost layer of bilayer hexagonal boron nitride (hBN) by 180 degrees, we get a ferroelectric material due to a change in the dipole moment between the stacked boron and nitrogen atoms.

Now that we can create these layered materials systems on demand and control their properties, what’s next? To answer this question, Novoselov proposed a new paradigm for creating these materials systems that involves “bottom-up functionality at the material level.” Current technologies are typically top-down, meaning the components are not functional until they are assembled into a system. As a result, complexity typically comes from the top-level. This is in stark contrast to biological systems, where functionality is spread across all scales, from proteins to cells to organs. What Novoselov and his group are now researching is whether we can produce materials similarly so that we can create technologies in which the composite materials provide the functionality.

Architecting this complexity is difficult and “I don’t have the solution,” said Novoselov. However, he outlined some principles of materials design to help achieve this goal. These included creating systems with a degenerate energy landscape, similar to that of proteins, that can allow for easy conformational or property changes. To explore these complex energy landscapes, Novoselov and his collaborators have begun using custom robotic systems and artificial intelligence to predict the non-equilibrium dynamics of novel materials systems. For instance, he highlighted predictive studies being performed on smart nanocontainers that open and close based on the pH of the environment.

Overall, Novoselov emphasized the need to think about how to design functional and intelligent materials out of equilibrium for new applications. This will allow us to take materials of different dimensionalities (from 0D to 3D) and assemble them into systems that can demonstrate new properties. Using this bottom-up design approach, we could one day revolutionize two-dimensional materials technologies.

The Kavli Foundation is dedicated to advancing science for the benefit of humanity, promoting public understanding of scientific research and supporting scientists and their work.

Plenary Session Featuring The Fred Kavli Distinguished Lectureship in Materials Science

Jenny Nelson, Imperial College London

Optimizing Solar Energy Conversion in Molecular Electronic Materials

Written by Rahul Rao

Today, the solar energy world is ruled by crystalline silicon. But recent advances in materials have spawned a host of alternative materials seeking to challenge silicon’s dominance. One class of challengers are molecular electronic materials: carbon-based organic semiconductors that can be excited by visible light.

At Monday’s Plenary Session, Jenny Nelson spoke about the titular materials, how they’ve rapidly developed, and how her group’s work has contributed to bring these organic materials closer to viable solar cells.

Just several decades ago, these materials barely registered on solar researchers’ radars. Most of them had been fashioned from fullerenes, limiting their variety. Additionally, such materials tend to be disordered and suffer from a poor dielectric constant, hurting their prowess as semiconductors.

But by the 1990s, researchers had learned how to circumvent those restrictions by interfacing two different disordered materials—one to donate electrons, another to accept them. Since then, the materials themselves have diversified from fullerenes into a wide range of other materials that researchers could easily process and readily customize. As a bonus, researchers have found that their coupled molecular electronic materials’ properties are easy to computationally predict.

The result: solar cells made from molecular electronic materials have blossomed in efficiency, from less than 2.5% in 2002 to 11% in 2016 to over 19% in 2022.

Still, any organic solar cells have a long way to go before they can match their crystalline silicon counterparts, many of which now clear the 30% mark. Nelson said that researchers need to quantify and understand the loss in materials.

One way of doing that is to take a solar cell and run it in reverse, like an LED—pushing electrons in and watching the light that comes out. Because a physical relationship exists between that emitted light and the light absorbed when the device is operating as designed, researchers can study how close their device’s efficiency is to its ideal limit.

Through this method, by 2015, Nelson’s group had helped demonstrate that organic solar cells shed much of their energy through non-radiative loss—something that researchers could address by improving their materials. Recent efforts to do just that have helped drive much of the rapid efficiency jumps these solar cells experienced from the late 2010s.

Their efficiency could rise even farther if researchers can understand which molecular properties lead to which changes in a solar cell’s performance. Nelson’s group probed this computationally, outfitting a model of a solar cell device with a molecular model. They found that varying just four molecular parameters controlled a device’s voltage, current density, and fill factor.

And molecular electronic materials may not need separate donor and acceptor components forever. A smattering of recent research has suggested that single-molecule materials—for instance, polymers built with donor and acceptor subunits—have already reached at least 11% efficiency. Rearranging and reshaping polymers might boost that even further.

Finally, Nelson mentioned that optimal solar cell materials already exist in nature: in the photosystems of photosynthesizing plants. If materials scientists studied them, she said, their findings could light possible paths into a bright future of bountiful organic solar cells.

The Kavli Foundation is dedicated to advancing science for the benefit of humanity, promoting public understanding of scientific research and supporting scientists and their work.