Center for Excitonics
Seminar Series Announcement
The Center for Excitonics (
http://www.rle.mit.edu/excitonics) invites you
to join us at the next and final
seminar of the Spring 2009 series. Please forward this information on to
others who might be interested
in attending this seminar.
Title: Overcoming the Exciton Diffusion
Bottleneck in Organic Photovoltaic Cells
Presenter: Professor Russell J. Holmes
Organization: Department of Chemical Engineering and
Materials Science
Date: May 20, 2009
Time: 3:00 - 4:00pm
Place: W20-407
Refreshments: Yes
URL:
http://www.rle.mit.edu/excitonics/holmes-052009.html
abstract
Organic materials are attractive for application in photovoltaic cells due
to their compatibility with lightweight, flexible substrates, and high
throughput processing techniques. Optical absorption in these materials
leads to the creation of a bound electron-hole pair known as an exciton.
The exciton is mobile, and diffuses to a heterojunction where
electron-hole separation and photocurrent generation may take place. In
most organic materials, the exciton diffusion length is much shorter than
the optical absorption length. This “exciton bottleneck” limits the
active layer thickness and reduces cell absorption efficiency. Routes
around the bottleneck have centered on the use of mixed donor-acceptor
film morphologies to increase the area of the dissociating interface.
While promising, these architectures are difficult to optimize, and can
introduce resistance for the collection of photogenerated carriers.
This talk will examine two alternate techniques to overcome the exciton
bottleneck. First, the use of energy transfer to a long-lived
phosphorescent sensitizer will be described as a means to enhance the
exciton diffusion length in fluorescent, electron donating materials. A
second approach involving the use of donor-acceptor films with engineered
film composition and morphology will be discussed as a means to
simultaneously maximize the exciton diffusion and charge collection
efficiencies.
bio
Russell Holmes is an Assistant Professor in the Department of Chemical
Engineering and Materials Science at the University of Minnesota. He
completed his M.A. and Ph.D. in Electrical Engineering at Princeton
University, and holds a B.Sc. (Honours) in Physics from the University of
Manitoba, Canada. Prof. Holmes’ research is focused on the fundamental
optoelectronic properties of organic and hybrid materials, and their
application in organic light-emitting devices, photovoltaic cells, and
lasers.