image: Michael Grätzel, winner of the BBVA Foundation Frontiers of Knowledge Award in Basic Sciences. view more
Credit: BBVA FOUNDATION
The BBVA Foundation Frontiers of Knowledge Award in the Basic Sciences category has gone in this thirteenth edition to Paul Alivisatos (University of California, Berkeley, United States) and Michael Grätzel (Ecole Polytechnique Fédérale de Lausanne, Switzerland) for their fundamental contributions to the development of new nanomaterials already in use for the production of renewable energies and in latest-generation electronics. "Grätzel's groundbreaking work includes the invention of a dye-sensitized solar cell named after him," reads the committee's citation, while "Alivisatos has made pioneering contributions in using semiconductor nanocrystals for energy and display applications."
Scientists have long been fascinated by the way in which light interacts with matter, and the quest to control this interaction in fine detail is at the basis of some of today's most powerful technologies. Alivisatos and Grätzel are leaders in controlling the play of light-matter through the use of nanomaterials that act upon the latter. The committee recognizes them as key figures in the fundamental science that led to "the development of nanostructured materials for energy-related applications."
Grätzel - nominated by Jean S. Hesthaven, dean of the School of Basic Sciences at the Ecole Polytechnique Fédérale de Lausanne (EPFL) - was the first to combine molecular systems with nanoparticles to create a new kind of solar cell that mimics photosynthesis, bringing closer the goal of converting sunlight into a clean, efficient and cheap source of electricity on a major scale.
Alivisatos created nanocrystals of barely a thousand atoms, known as "quantum dots," to emit light whose color can be minutely controlled. He has also used these nanocrystals to explore new renewable energy sources. At present, the most advanced application of his work is a new generation of screens that incorporate quantum dots to achieve high color quality, already on the market as QLED televisions, standing for Quantum Dot LED. Professor Alivisatos was nominated by Jennifer Doudna, Director of the Innovative Genomics Institute at the University of California, Berkeley, winner of the Frontiers Award in Biomedicine in 2017 and Nobel Chemistry Laureate in 2020; Mike Witherell, Director of the Lawrence Berkeley National Laboratory; and Milan Mrksich, Vice President for Research at Northwestern University.
In a sense, Alivisatos remarked in a video conference after hearing of the award, "Michael has looked more at how to get electricity from the light coming into the system, whereas I've probably done a bit more work where energy is extracted in terms of light coming back out of the system, and then making something that people can use."
Emulating photosynthesis
Photosynthesis, whereby the leaves of plants convert sunlight into organic matter - essentially just a means of storing energy - is the natural process that gave Grätzel his inspiration.
Plants use chlorophyll and other pigments to absorb as much as they can of visible light; the chlorophyll molecule is so structured that it emits electrons when excited by the sun's protons, triggering chemical reactions to build organic matter with water and carbon dioxide. Grätzel's solar cells also use a pigment that takes the role of chlorophyll, harvesting the sun's light and generating electrons which are then collected and transported by a semiconductor material such as titanium dioxide.
His masterstroke was to arrange the titanium dioxide in nanoparticles. Each titanium dioxide nanoparticle is coated in pigment, and the result is a liquid that holds the nanoparticles and serves to fabricate the solar cells.
"That was the first use of nanoparticles to build photovoltaic cells, something no one had thought of before," said Grätzel in a video conference following news of the award. "The first time we tried it was so exciting, we were genuinely astonished because the response we got [of light conversion into energy] was thousands of times greater than we had expected."
He and his team presented their new photovoltaic solar cell in a 1991 paper in Nature - "A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films" - since cited tens of thousands of times. This was the world's introduction to what would come to be the new DSSC or dye-sensitized solar cells, also known simply as Grätzel cells in honor of their inventor.
The discovery would lead to "thousands of patents," he himself remarks, and open up "a whole new field of research." For the Grätzel cells offer multiple advantages: abundant raw materials, a cheap manufacturing process, transparency - meaning they can be mounted on windows, flexibility and the capacity to obtain electricity from even ambient light of the kind you find in any room. In 2013, they were used to create a colorful glass façade for the convention center on the EPFL campus.
The cells' efficiency is approximately 15%, less than that of conventional silicon cells. But this drawback could soon be overcome with another type of cell following on from Grätzel's, known as perovskite cells. This material, which also starts from a liquid so is suitable for flexible surfaces, entered use in 2009 and in less than a decade had achieved efficiencies of 25%. Grätzel, who has also been a pivotal player in perovskite cell research, remarks that "the speed of perovskite cell efficiency gains is on a scale not seen in any other material." Indeed the figures coming in are already comparable to those of silicon.
Whatever degree of reach Grätzel's cells eventually achieve, the committee highlights the power of his work to launch new lines of research on use of nanomaterials in the renewable energies domain.
Nanocrystals for high-resolution screens
Alivisatos' nanocrystals, also known as quantum dots, are likewise at the core of multiple applications, from the search for new clean energy sources to consumer electronics by way of biomedical imaging techniques. The U.S. scientist is himself a leader in the development of nanocrystals, a new kind of macromolecule that can be studied, controlled and widely used - in a liquid medium, like Grätzel's nanoparticles.
Ultraprecise control of nanocrystal size brings with it control over the color of light it emits, as the new laureate explains: "An electron in a nanocrystal can emit light and the color of that light will depend on the nanocrystal's size. If it is a little bit smaller the energy of the light will be higher, so it will be bluer light. And in this way you can use nanocrystals to make materials that emit the full rainbow of colors; such a large rainbow that you can reconstruct with it every color you can see in nature."
Among its most successful applications are the displays developed in the mid-1990s that are now a part of QLED television sets. Alivisatos showed that it was possible to manufacture them in a way that combined high resolution with energy saving efficiency.
"In a color display," he elaborates, "there is always a red, a blue and a green color that can be excited. And those colors interact inside your eye - mixtures of them - to reproduce all the colors that we can see around us. When we put quantum dots into a television to produce the reds, greens and blues, the size of the particle can be used to precisely tune the color to match the best spot in energy, which matches the receptors in your eye. So that's an example which enables, for example, artists and photographers to achieve better color reproduction, but it also results in very, very high efficiency for those displays, which means that they consume less energy and they can be used in a variety of new applications."
In the biomedicine field, Alivisatos and his group have developed nanocrystals for the staining of biological samples - by adjusting the size of the nanocrystal, the liquid will tag one or other cell type. In fact, hundreds of quantum dot-based products are now commercially available for bioimaging purposes.
The environmental dividend of nanomaterials
The two laureates are convinced that, given the serious threat of climate change and the need to ramp up production of renewable energies, the new lines of research enabled by their work in nanomaterials could provide forefront solutions from the realm of science and technology.
"Climate change," says Grätzel, "is certainly a major challenge. We need to curtail our use of fossil fuels, while scaling up photovoltaic energy supply by a factor of 200 in the next few decades. That means new technologies, and, in this respect, the dye-sensitized cell has led onto the new perovskite cell, whose efficiency in pilot tests is already outperforming that of conventional silicon cells."
Alivisatos, meantime, is convinced that nanomaterials have yet to reveal their full potential, and that they have a part to play in tackling the key environmental issue of our time: "Climate change is one of the greatest challenges facing humanity, and part of that challenge is to learn how to make new materials that can harvest the energy of the sun and put it to beneficial use with as few losses as possible. But also, to do it on a vast scale. It turns out that nanomaterials can be made in extremely high quality but at relatively low cost. And they can be used to absorb light from the sun, and absorb it without losing it to thermal energy or heat, which allows more efficient conversion to electricity. Michael Grätzel has already shown some uses of nanomaterials in solar energy but there will be many more over the years to come."
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Laureate bio notes
Paul Alivisatos (Chicago, Illinois, United States, 1959) earned a BA in Chemistry from the University of Chicago (1981), then went on to complete a PhD in the same subject at the University of California, Berkeley (1986). After two years researching at AT&T Bell Labs, in 1988 he joined the faculty at UC Berkeley, where he is currently Executive Vice Chancellor and Provost, and Samsung Distinguished Professor of Nanoscience and Nanotechnology. Also at Berkeley, he is the Founding Director of the Kavli Energy Nanoscience Institute, and Director Emeritus of the Lawrence Berkeley National Laboratory (Berkeley Lab), which he headed from 2009 to 2016 and where he remains a senior faculty scientist. He also holds professorships in the university's departments of chemistry and materials science. Among his previous positions at the Berkeley Lab, he was Founding Director of the Molecular Foundry, a U.S. Department of Energy's Nanoscale Science Research Center, and Director of the Materials Science Division. Author of more than 400 publications, he is co-holder of 38 patents and founder of two companies, Nanosys and Quantum Dot Corporation (now part of Thermo Fisher). Alivisatos is also founding editor of Nano Letters, a publication of the American Chemical Society, and formerly served on the senior editorial board of Science magazine.
Michael Grätzel (Dorfchemnitz, Germany, 1944) completed a degree in chemistry at the Free University of Berlin (1968), then a doctorate in Physical Chemistry at TU Berlin (1971). He joined the faculty at the Ecole Polytechnique Fédérale de Lausanne (Switzerland) as an associate professor in 1977, and four years later was appointed Professor of Physical Chemistry. That same year he founded the Laboratory of Photonics and Interfaces at EPFL, which he has headed ever since. He has held visiting or research positions at centers including UC Berkeley (United States), the National University of Singapore, Delft University of Technology (Netherlands), the Hahn Meitner Institute Berlin (Germany) and the Ecole Normale Supérieure de Cachan (Paris, France). An External Scientific Member of the Max Planck Institute for Solid State Research (Germany), he chairs one of the panels of the ERC Advanced Grants program, and has served on the scientific advisory boards of the presidents of the Daegu Gyeongbuk Institute of Science and Technology (South Korea), KTH Stockholm (Sweden), the University of Helsinki (Finland) and the Weizmann Institute of Science (Israel). He is author of over 1,700 scientific papers and 2 books, holds more than 80 patents and has co-founded two start-ups.
Basic Sciences committee and evaluation support panel
The committee in this category was chaired by Theodor Hänsch, Director of the Division of Laser Spectroscopy at the Max Planck Institute of Quantum Optics (Germany), and the 2005 Nobel Laureate in Physics, with Ignacio Cirac, Director of the Theory Division at the Max Planck Institute of Quantum Optics (Germany) acting as secretary.
The evaluation support panel of the Spanish National Research Council (CSIC) was coordinated by M. Victoria Moreno, Deputy Vice President for Scientific and Technical Areas, and formed by: José Luis Fernández Barbon, scientific researcher at the Institute for Theoretical Physics (IFT); Carmen García García, Deputy Coordinator of the MATERIA Global Area and research professor at the Institute of Corpuscular Physics (IFIC); Berta Gómez-Lor Pérez, scientific researcher at the Institute of Materials Science of Madrid (ICMM); José Luis de Miguel Antón, tenured scientist at the Daza de Valdés Institute of Optics (IO); and Carlos Prieto de Castro, Coordinator of the MATERIA Global Area and research professor at the Institute of Materials Science of Madrid (ICMM).
About the BBVA Foundation Frontiers of Knowledge Awards
The BBVA Foundation centers its activity on the promotion of world-class scientific research and cultural creation, and the encouragement of talent.
The BBVA Foundation Frontiers of Knowledge Awards, funded with 400,000 euros in each of their eight categories, recognize and reward contributions of singular impact in science, technology, social sciences and the humanities, privileging those that significantly expand the frontiers of the known world, open up new fields, or emerge from the interaction of various disciplinary areas. The goal of the awards, established in 2008, is to celebrate and promote the value of knowledge as a public good without frontiers, the best instrument at our command to take on the great global challenges of our time for the benefit of all humanity. Their eight categories are congruent with the knowledge map of the 21st century, ranging from basic science to key challenges for the natural environment by way of domains characterized by the overlap of disciplines - Biology and Medicine; Economics, Finance and Management - or the supremely creative realms of music and the opera.
The BBVA Foundation has been aided in the evaluation of the 105 nominees for the Frontiers Award in Basic Sciences by the Spanish National Research Council (CSIC), the country's premier public research organization. CSIC appoints evaluation support panels made up of leading experts in the corresponding knowledge area, who are charged with undertaking an initial assessment of the candidates proposed by numerous institutions across the world, and drawing up a reasoned shortlist for the consideration of the award committees. CSIC is also responsible for designating each committee's chair and participates in the selection of its members, thus helping to ensure objectivity in the recognition of innovation and scientific excellence.