Center for Excitonics
Seminar Series Announcement
The Center for Excitonics invites you to join us at the next seminar of
the
2009 series. Please forward this information on to others who might be
interested in attending this and other center seminars.
Title: Hierarchical Pattern Control in
Semiconducting Polymers
Presenter: Prof. Rachel A. Segalman
Organization: Chemical Engineering Department
University of California, Berkeley and
Lawrence Berkeley National Laboratories
Date: October 15, 2009
Time: 3:00 - 4:00pm
Place: 34-401A
Refreshments: Yes
Center URL:
http://www.rle.mit.edu/excitonics
Seminar URL:
http://www.rle.mit.edu/excitonics/segalman-101509.html
Abstract
While polymers hold significant potential as low cost, mechanically
flexible, light weight large area photovoltaics and light emitting devices
(OLEDs), their performance relies crucially on understanding and
controlling the morphology on the nanometer scale. Two important materials
constraints are responsible for the morphology challenges faced in these
fields. The 10nm lengthscale of exciton diffusion sets the patterning
lengthscale necessary to affect charge separation in photovoltaics. The
imbalance of electrons and holes mobilities in most organic materials
necessitates the use of multiple components in many device architectures.
Both light emitting and photovoltaic devices rely crucially on
crystal/grain structure for improved charge transport. These
requirements for hierarchical patterning in large area, solution processed
devices suggest that block copolymer strategies, previously employed for
more classical, insulating polymer systems, may be very useful in organic
electronics. The thermodynamics of these materials, however, is distinct
from classical block copolymers due to the conformational asymmetry of a
rigid, conjugated polymer chain. We have studied both the fundamental
self-assembly of molecules of unusual shapes as well as applied these
principles to bipolar molecules for photovoltaic and light emitting
devices. We can use these molecular handles to control the orientation
of the internal interfaces within the active layer of a device. In
addition to our work on the internal interfaces of a device, I will also
discuss efforts to understand the electrode interface where the discrete
density of states of the molecule interact with the continuous states of
the electrode. In particular, we have found that single molecule
conductivity and thermopower measurements lend significant insight and
suggest that organics may find new applications as thermoelectric energy
generating devices.
Bio
Dr. Segalman is an Associate Professor of Chemical Engineering at UC
Berkeley and Faculty Scientist of Lawrence Berkeley National Laboratories.
She graduated from the University of Texas at Austin with a B.S. with
Highest Honors in Chemical Engineering. While pursuing a Ph.D. with Ed
Kramer at UC Santa Barbara, she developed a graphoepitaxial strategy for
aligning arrays of block copolyme r spheres over distances previously
unobserved. Further quantitative microscopic analysis of this nanometer
scale patterning then led to fundamental discoveries as to the nature of
ordering and melting on in two dimensions. Dr. Segalman then received a
Chateaubriand fellowship to pursue research in Strasbourg, France in the
group of Georges Hadziioannou studying the synthesis of conducting block
copolymers. Her current research is focused on understanding the
connection between morphology and properties in functional polymers. She
has won numerous awards including: Alfred P. Sloan Fellow (2009);
Presidential Early Career Award in Science and Engineering (PECASE, 2008),
Lawrence Berkeley National Lab, Materials Science Division’s Young
Scientist of the Year Award (2008); Mohr-Davidow Ventures Innovators Award
(2007), Technology Review’s Top 35 Innovators under 35 years old
(TR35-2007), 3M Untenured Faculty Award (2006-2008), Hellman Family Young
Faculty Award (2007); National Science Foundation CAREER Award (2005);
Intel Young Faculty Award (2004). She is also an Associate Editor of the
Annual Reviews of Chemical Engineering and on the editorial advisory board
for Macromolecules.