10 Questions with Matt Sfeir
Interview with a CFN Scientist
January 19, 2016
Physicist Matthew Sfeir specializes in exploring and developing technologies that convert light into other forms of energy, such as electricity or fuel. The pursuit of such high-performing photovoltaic or fuel cell technologies is a high priority within the U.S. Department of Energy’s national labs, driven in part by pressure for clean and sustainable energy that addresses climate change. Sfeir, a staff scientist at Brookhaven Lab’s Center for Functional Nanomaterials (CFN), uses a suite of cutting-edge instruments to study next-generation materials with the potential to enhance light-based energy conversion processes
What interests you about exploring science that plays out across just billionths of a meter?
The nanoscale is a fascinating regime where the physics of molecules and the physics of crystals meet in this uncomfortable place. As a result, the properties of a nanomaterial become extremely dependent on its size and structure. This occurs because the amount of surface relative to the total volume becomes large, and the overall size becomes comparable to the characteristic length scales for light and the motion of electrons. So some really novel, but often messy and complex physics starts to occur.
This novel physics allows you to imagine really amazing applications in energy, catalysis, and other technologies. However, in nanoscience in particular, I think we often undersell the importance of the fundamental science questions that these materials allow us to explore. For example, nanomaterials allow us to study how discrete building blocks can be assembled into extended systems that produce new functionality. It is inevitable that this research will affect new technologies, though perhaps in unexpected ways.
What are the key tools and techniques involved in exploring materials that exhibit these phenomena?
My lab contains equipment that essentially acts like a camera that can follow the energy flow in a material or device. Using lasers with very short pulses, we can inject light energy into a material and then see how fast it dissipates through the generation of things like heat, electrical charge carriers, or even other types of light. The advantage of these optical methods is that we do not have to fabricate a full device or solar cell. We can often just study the active component (in which the energy conversion process occurs) and project how well it would perform in an optimized device.
How can you actually measure that fleeting, nanoscale energy conversion?
In general, the energy a material gets from light goes away very quickly. For example, in a typical material, the cycle of light absorption followed by full energy dissipation can occur a billion times a second. So, we need a very fast camera to follow the dynamics of energy conversion. The general rule is that if you want to make a measurement, you need another thing that is smaller (or shorter in this case) than the object you are measuring. Certain laser technologies, called ultrafast lasers, produce pulses that are shorter than the characteristic motion of atoms and electrons in materials (approximately 1 millionth of 1 billionth of a second). This allows us to understand how the atomic design of a material influences the manner and speed of energy conversion.
Why do this research at the CFN?
The CFN has amazing facilities for the optical characterization of materials. The large variety of techniques we can support in our lab is the kind of thing that makes working at a National Lab unique and special. Just as important for me is the shared sense of mission among the Brookhaven Lab staff and scientists. While we all have our own research programs, we are invested in one another’s success and have many goals and interests in common. Every day I get to work with these incredible professionals who are world experts in their fields.
Do you use any Brookhaven Lab facilities beyond CFN?
I was a user of the infrared synchrotron beamlines at the National Synchrotron Light Source (NSLS) and will hopefully be a User again when these capabilities come back to NSLS-II. The infrared spectral region is important for understanding the electronic structure of many nanomaterials. NSLS and NSLS-II offer world-class facilities for high-brightness infrared spectroscopy, providing a capability that is otherwise unavailable with laser or lamp-based light sources.
What’s one recent example of your work and what makes it interesting and impactful?
My group, in collaboration with Professor Luis Campos at Columbia University, recently made an important breakthrough in demonstrating multi-exciton generation in a new class of organic materials with potential applications in next-generation photovoltaic devices. This particular multiplication process is called singlet exciton fission, and utilizes molecules with a large singlet-triplet energy gap to generate two electron-hole pairs from one absorbed photon. Third generation photovoltaic devices utilizing a singlet fission sensitizing layer have the potential to exceed the thermodynamic efficiency limit (~ 33%) for a single junction solar cell.
Practical implementations of singlet fission devices have been hindered by the limited number of materials that undergo efficient singlet fission, which until recently have largely been restricted to molecular crystals of oligoacenes and related materials. Devices based on these crystals are hindered by the lack of high throughput and compatible processing strategies that makes device integration challenging. The CFN-Columbia collaboration has demonstrated that efficient multiple exciton generation via intramolecular singlet fission (iSF) can be achieved in isolated molecules (e.g., in solution). We have demonstrated this process in both conjugated polymers and small molecules, materials that offer distinct advantages relative to previously reported compounds. For example, their solution processability and highly tunable molecular and electronic structure allows us to envision and build new device concepts.
You can learn more in these recent publications:
- Nature Materials, “A design strategy for intramolecular singlet fission mediated by charge-transfer states in donor–acceptor organic materials”
- Journal of the America Chemical Society, “Quantitative Intramolecular Singlet Fission in Bipentacenes”
What excites you about the future of your research?
I am excited by our plan for the future of the Advanced Optical Facility at CFN and the way it will transform our research efforts. In the next few years, we plan to deploy new laser and detector technologies that have recently become available. This new equipment will enable us to make measurements under conditions that more closely resemble sunlight, which will let us better understand and optimize materials for light harvesting. Currently we have to use light pulses with high power in order to generate enough signal for measurements. These high powers sometimes lead to extrinsic effects that reduce the overall efficiency of energy conversion. Also, we will be able to overcome current sample limitations and finally be able to perform experiments on materials that are difficult to grow or fabricate over large areas or materials that are large but very inhomogeneous.
Postdoctoral fellow Erik Busby and Matt Sfeir with optical equipment they used to study charge carrier production in organic photovoltaic polymers at Brookhaven Lab's Center for Functional Nanomaterials.
What opportunities do you see for future collaborators to work with you?
The equipment and methods used to characterize the dynamics of energy conversion are very challenging and complex. In my facility, we have invested a lot of time and effort to increase the accessibility of these measurements to outside users who may not have any experience in optics. Sometimes these improvements come from equipment and software development, but I think the most important thing is the availability of our scientific research staff and our ability to provide training, mentoring, and expertise.
The benefit of a place like the CFN is that a scientist who makes a new material or device can then be directly involved in evaluating its potential for technological applications. It is often difficult for researchers to find collaborators who share a common interest and who can provide the necessary expertise to complete a study. Through our user program, the researchers themselves define the direction of the project and are able to directly leverage the resources of the CFN to accomplish tasks that would otherwise be out of their reach.
Why should other scientists (especially users) come to CFN to conduct research?
Other scientists should come to the CFN because we are great at what we do and it will make your project more successful. There is an open, enthusiastic, and vibrant community of staff and users here ready to support you. We have unbelievable equipment and a world-class research effort in nanomaterial synthesis and characterization. It is a really unique environment, especially for students and postdocs, where you get to work closely with senior research staff members who are real experts in their fields. And it’s all free!
Why did you become a scientist and what keeps you invested?
I really believe in the mission of the CFN and the Department of Energy. The research we do is incredibly important for our country and our future. I’m proud to work at Brookhaven and to be making even small contributions to fundamental questions about the natural world.
I don’t remember ever choosing to become a scientist. I remember that quantum mechanics blew my mind as an undergraduate, so I kept taking science classes. Then I got an opportunity to work in a research lab, with huge pieces of complex equipment that were the coolest things I had ever seen. I think I just figured I would keep doing these really fun, stimulating things until someone made me stop. It amazes me that I still get to do this every day.
To be a successful scientist, I think you need a really high tolerance for failure, since that is really the day-to-day norm. The most rewarding thing for me is that critical moment when a project really gets going, sometimes after months of fruitless effort. With persistence and a little luck, this singular magical event occurs when you start getting that piece of data that you know is going to make the project a success. Sometimes, that moment never comes and you have to move on. You really have to enjoy the process.
2016-6173 | INT/EXT | Newsroom
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