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Organic PV cells modeled on plant chemistry, "antennas" composed of carbon nano-tubes

Solar Server Interview with MIT Professor Michael S. Strano on new solar photovoltaic devices
Solar Server Interview with MIT Professor Michael S. Strano on new solar photovoltaic devices

Professor Michael S. Strano is currently the Charles and Hilda Roddey Associate Professor in the Chemical Engineering Department at the Massachusetts Institute of Technology (MIT). His research is in the area of nano-materials and nano-particle surface chemistry, with an interest in how molecules adsorb and chemically react with low dimensional materials where geometric constraints or patterning provide quantum confinement of electrons. Such materials include carbon nanotubes, semi-conductor nanocrystals and graphene nano-ribbons as examples.

MIT research on more productive and long-lasting solar photovoltaic devices

In September, 2010, teams of researchers led by Michael Strano published two exciting discoveries, each of which has the potential to lead to new, more productive and long-lasting solar photovoltaic (PV) devices. The first was the creation of a self-repairing organic PV cell modeled on plant chemistry, and the second was an "antenna" device composed of bundles of carbon nano-tubes which capture and concentrate light. These discoveries were first announced in the journals "Nature Chemistry" and "Nature Materials" on September 5, 2010 and September 12, 2010, respectively. Professor Strano was joined in these research projects by Dr. Moon Ho Ham, Dr. Jae Hee Han, and Geraldine Paulus.


Solar Server: How did you get started on research for photovoltaic applications?

Professor Strano: Our team has always been interested in quantum confined systems such as carbon nano-tube and graphene, and in studying both fundamental properties as well as applications. One of the intriguing properties of single walled carbon nanotubes is the diversity in bandgaps some of them exhibit. In solar applications, the bandgap of a solar device is the key to determining the wavelength of light it absorbs and the efficiency of the device. So from that standpoint, it seems only natural to consider them for solar applications.

Carbon nano-tube antenna emitting photons. Courtesy: MIT
Carbon nano-tube antenna emitting photons. Courtesy: MIT


In addition to variations in bandgaps, nanotubes are also notorious for self-assembly presence of amphillic molecules and water. Though all the pieces of the puzzle are there, they all came together when our group discovered the ability to extend this self-assembly dynamics to a light-harvesting protein to produce a dynamic solar cell. Since that initial step toward the photovoltaic field, our group has continued to expand in that direction.


Solar Server: We have reported on two discoveries that you have worked on - the first being self-replicating solar cells based on plant chemistry, and the second being carbon nano-tube antennas. Which of these started first? Did they influence each other? How so?

Professor Strano: Both these projects, the regenerating solar cell and the nanotube antennas, we had been working on for quite some time. Both projects share the same, overall goal: mimicking nature's way of producing energy. For example, the regenerative solar cells mimic the self-repair process in plants whereas the optical antennas mimic the solar antennas plants use to concentrate energy and increase efficiency. So in that sense, these two projects are complementary, deriving from different aspects of photosynthesis.


Solar Server: The self-replicating solar cells are a remarkable discovery. What steps need to be taken before this technology is ready for commercialization?

MIT Researchers Assistant Professor Michael Strano, postdoctoral researcher Moon-Ho Ham and graduate student Ardemis Boghossian
MIT Researchers Assistant Professor Michael Strano, postdoctoral researcher Moon-Ho Ham and graduate student Ardemis Boghossian

Professor Strano: Though the regenerative systems introduce a new approach to the development of dynamic solar cells, they are only a modest first step in the direction of creating truly biomimetic systems.

One aspect that needs to be considered is efficiency. To increase it we have to dramatically increase the density of complexes per volume compare do what we have now. This means moving to a gel like phase or other dense structure, and maintaining the fluidity necessary to enable regeneration will be critical.


Solar Server: As far as the carbon nano-tubes, when do you see a prototype model being developed? What are some of the technical challenges that carbon nano-tube antenna design faces?

Professor Strano: Like the regenerative solar cell, we still have some technical challenges that we need to overcome before commercializing the optical antennas. Namely, we are currently in the process of tuning these solar funnels so that we can concentrate power over the range of energy emitted by the sun. That way, we can optimize our antennas to boost our device efficiencies under conditions that more closely resemble those demonstrated by typical solar cells.

Solar Server: Are you currently working on any other research for photovoltaic applications, and do you have any plans to do so in the future?

Professor Strano: Our group is currently working on several photovoltaic applications. We have expanded upon our regeneration and antenna work, and are also interested in other solid state devices. In one of our most recent developments, we fabricate a planar nano-hetero-junction polymer/CNT array that teaches us how to extract energy more efficiently from nanotube based photovoltaic materials. This is an exciting and emerging application from which I hope that we will learn a lot.



Biography background

Michael S. Strano is the recipient of numerous awards for his work, including a 2005 Presidential Early Career Award for Scientists and Engineers, a 2006 Beckman Young Investigator Award, the 2006 Coblentz Award for Molecular Spectroscopy, the Unilever Award from the American Chemical Society in 2007 for excellence in colloidal science, the 2008 Young Investigator Award from the Materials Research Society,  the 2008 Allen P. Colburn award from the American Institute of Chemical Engineers, and a 2009 Brilliant 10, award from "Popular Science Magazine". More information on Professor Strano and his group can be found at: http://web.mit.edu/stranogroup


This interview was conducted by Solar Server International Correspondent Christian Roselund.