Imagine hearing aids powered by see-through solar cells coating your eyeglasses, tiny switches operated efficiently by squeezable molecules, and television displays as colorful as nature operating at a fraction of today’s energy consumption. These are just some of the visions being brought to life in the laboratory of MIT Professor Vladimir Bulović. “Basic science discoveries lead us to devices that can exceed the state-of-the-art performances,” says Bulović, the Fariborz Maseeh Chair in Emerging Technology at MIT's School of Engineering.
An entrepreneur with multiple startups, holder of more than 75 patents, and award-winning educator, Bulović is at heart an applied scientist. His Organic and Nanostructured Electronics Lab (ONE Lab) has 18 students and postdoctoral associates but is used collaboratively by over 70 individuals. "Every student participates as a team member in the operation of the lab," he says.
One key motivation for Bulović's work is increasing energy efficiency. "Today, more than 2 percent of the world's electricity is used on TVs and display monitors. We think we can reduce that by a factor of two, which would be a significant energy impact. Even more, today, 20 percent of electricity is used on powering light bulbs. We think we can reduce that number by a factor of two, as well. Increasing energy efficiency is one key driver of our research," Bulović explains.
Principles and applications
"All of the pursuits start with the understanding of the basic physical principles which are then applied to the operation of practical devices," says Bulović. The group combines expertise in electricity and magnetism and knowledge of quantum mechanics together with uses of nanomaterials to make devices as diverse as solar cells, LEDs, lasers, chemosensors, and mechanical actuators. "We use our devices as test beds of physics, and try to ascertain what physical mechanisms dominate the nanoscale proceses within them. If the devices do not perform as well as we expected, they serve as a platform through which we learn physical behavior that we have missed previously, and then from that we apply the new refined physical principle to design a better structure," he says.
Development of renewable energy technologies that could be manufactured at scale is another driver of the group's research. In May of last year, Bulović and collaborators set a new record, 8.55 percent efficiency, for quantum-dot solar cells. This collaboration with MIT chemistry Professor Moungi Bawendi and graduate students Chia-Hao Chuang and Patrick Brown demonstrated a fabrication process that does not require an inert atmosphere or high temperatures for its active layers, with the exception of electrodes. In these solar structures, quantum dots, fine-tuned for their optical response and charge transport, absorb the incident light, which promotes an electron from its ground to its excited state, and from there charges can move through the quantum dot film yielding an electric current.
In another recent development, Bulović and Richard Lunt, who was a postdoc at the time and is now a professor at Michigan State University, demonstrated a new solar technology that uses molecular films, which do not absorb visible light, enabling these solar cells to appear uniquely optically transparent, practically invisible. These transparent solar cells can power devices such as an electronic book reader or provide electricity to future office buildings by coating their windows. Bulović also envisions coatings for eyeglasses that power Bluetooth radios or hearing aids from available light. "These invisible coatings absorb infrared light, which we can not see, to generate electricity, and could be as simple to place on your glasses as it is to paint a surface," he says.
Working in ONE Lab, MIT graduate student Farnaz Niroui and colleagues demonstrated electromechanical switches that use nanoscale deformations of thin films of molecules to control current passage through such switches. Niroui's latest work builds on her earlier work showing a design for a squeezable switch — or "squitch" — which fills the narrow gap between metal contacts with an organic molecular film that can be compressed tightly enough to allow current to tunnel, or flow, from one electrode to another without any physical contact between the electrodes (the "on" position). When compressing pressure is released, the molecules spring back to open the gap between the electrodes wide enough that current cannot flow (the "off" position). The goal is to develop a fast-acting, low-power switch that can complement or replace switches in transistor-based systems.
"We are just as excited to discover a new physical operation within our structures as we are to make an operating device that exceeds the state of the art," Bulović explains. "And it's that interplay between the basic physical principles, demonstration of them in a device, sometimes not meeting the full potential in a device, and hence going back to the demonstration of why the physics has not quite worked the way you expected it. That refinement of ideas, the feedback, is what leads us to the next and next and next advancement."
"What today's researchers are exploring is just the beginning of a vast opportunity in the nano sciences and technology," he adds. For example, Polina Anikeeva and Will Tisdale, former members of the Bulović lab and now both MIT faculty members in their own right, have followed opportunities in biological and optical measurement applications of nanotechnology. "They exemplify the breadth of opportunity that is ahead of us," Bulović says. The planned MIT.nano facility, whose construction Bulović is supervising, will help move forward the new era of nanotechnology, he says.
"The hardest decision for our group is to decide what not to work on because there are so many exciting research areas one could engage in. I am often delighted to see a field that we might have been among the first to be in, grow and blossom, allowing us to step out of it and allowing us to think about the next challenge we should engage," Bulović says.
Breakthrough technologies like transparent solar cells come from looking at old problems in a new way. "When our group talks about the next solar cell, we are not considering conventional ones. We are looking at ways of changing the paradigm of what matters for solar technology adoption," Bulović explains. "Often, solar cell efficiencies are cited as the one metric that you need to push forward to advance the technology, and that is true, as efficiency is a very important metric. However, it is also important to notice that there are other solar technology properties one can advance to deliver impact."
"In the example of optically transparent devices," Bulović adds, "their nearly invisible format enables integration of solar technology on any surface, hence advancing a new paradigm for solar deployment. As another example, in our lab we consider how much does the solar cell weigh? If one can provide a lightweight cell, it would be easier to install it, reducing one of the dominant costs of solar deployment. A lightweight solar cell will also be easier to deliver to a remote village, which might have no access to grid electricity and possibly no paved roads. When carrying a solar cell on one's back to bring it to a remote village, the question of 'What is the solar cell efficiency?' is less important than knowing how many trips you will have to make, which is the same as asking how much power can you generate per kilogram of the solar cell. In this case it could be desirable to have a less efficient cell if it is significantly lighter. By changing the weight, we can change modality of use."
So a solar cell can change its form from a panel that you install on your roof, to a flexible device that you can have on any surface, including clothes, bags, sheets, or whatever else one can imagine. Indeed, a 2011 collaboration between Professor Karen Gleason's and Bulović's groups generated extremely light solar cells grown on a sheet of paper. In December 2014, Joel Jean and Annie Wang from the Bulović group further reduced the solar cell substrate thickness to only a few microns, making these solar devices light enough to float on a soap bubble.
Translation of technologies from Bulović's lab to marketplace is often done by startup ventures initiated by graduating students. Such was the case with the transparent solar cell technology, which was licensed by Ubiquitous Energy, an MIT startup that opened its research facility just a few months ago, with the aim of changing the paradigm of what solar technology can be. Prior to that, in 2005 Bulović co-founded with MIT students QD Vision, which uses quantum dots for display technology that can presently be found in over 2 million televisions. In addition, QD Vision's quantum dot lighting technology was shown to enhance the color quality of the most efficient lightbulbs, reproducing the glow spectrum of a typical incandescent light bulb, but consuming only one-sixth the power. In 2008, Professor Martin Schmidt and Bulović, with their students, spun out Kateeva, which is commercializing printing technology for large-scale electronics, including the toolsets enabling reliable fabrication of organic light emitting diodes (OLEDs) over 2-meter wide substrates.
Bulović also heads MIT.nano, a $350 million construction project to build a state-of-the-art nanotechnology research facility in the heart of the MIT campus. "The goal of MIT.nano is to provide a transformational 21st-century workshop. In our building designs we are imagining what kind of toolbox will the campus need for the next three decades, 'til 2050. We need to build a flexible research space and a community-oriented space so that people feel empowered to go to it, use it, and then redefine it as the years progress, adapting it to the needs of the next generation of researchers," he says.
Bulović also is co-chair of the MIT Innovation Initiative, which aims to combine education, research, outreach, and the study of innovation science and policy to positively affect the world by accelerating the impact of multitudes of ideas generated on campus.
A preliminary report in December 2014 made specific recommendations for improving innovation impact, including the creation of a Laboratory for Innovation Science and Policy. The new lab is envisioned to study the social and market context of taking ideas from lab demonstration to practical, large-scale application in the world. It would conduct research on venture formation, scale-up, and understanding the marketplace, as well as social need and response to it.
Also envisioned as part of the Innovation Initiative are new programs in entrepreneurship for postdocs, graduate students, and a minor for undergraduates with a certificate in innovation and entrepreneurship.
Third-, fourth-, and fifth-grade math
Despite his intensive workload, Bulović finds time to teach math to elementary-school students — third-graders this year and fourth- and fifth-graders in years past. "Inspired by the curiosity of our four children, my wife and I have been developing and delivering materials for a number of years that aim to expose early learners to the wonders of math applied to the real world," he says. "Once a week we have the privilege to join a group of students who engage with us in discovery of how a lever works, help us determine the height of a tree from its shadow, estimate the number of books in a library, practice sorting algorithms, determine angles between hands of a clock. ... With cartoons of smiling penguins, mischievous cows, or other unexpected characters on our math worksheets, the math problems are presented as stories of quests and adventures. It has been a remarkably enjoyable experience for all of us, now in its eighth year."