Center for Excitonics
Seminar Series Announcement
The Center for Excitonics is an Energy Frontier Research Center funded by
the
U.S. Department of Energy, Office of Science and Office of Basic Energy
Sciences
The Center for Excitonics invites you to join us at the next seminar of
the
Spring 2010 series. Please forward this information on to others who
might be
interested in attending this and other center seminars.
Title: Hot Electron Transfer from Semiconductor
Nanocrystals
Presenter: William Tisdale
Organization: Department of Chemical Engineering and Materials Science
University of Minnesota
Date: March 30, 2010
Time: 3:00 - 4:00pm
Place: Haus Room 36-428
Center URL:
www.rle.mit.edu/excitonics
Seminar URL:
www.rle.mit.edu/excitonics/tisdale-033010.html
Abstract
In conventional semiconductor solar cells, absorption of photons with
energies greater than the semiconductor band gap generate “hot” charge
carriers that quickly “cool” before all of their energy can be captured –
a process that limits device efficiency. Semiconductor nanocrystals (or
quantum dots) have been touted as promising materials for photovoltaics
because discretization of their electronic energy levels can slow down
this cooling process, which might enable the extraction of photogenerated
charge carriers before their excess energy is converted to heat.
In this talk, I will demonstrate sub-50 fs electron transfer from hot
energy levels of PbSe nanocrystals to delocalized conduction band sates of
TiO2. In order to make these measurements, we developed the use of optical
second harmonic generation for femtosecond time-resolved studies of
interfacial charge separation. I will discuss the information we obtain
from this technique as well as the effect of temperature, nanocrystal
size, and surface chemistry. Additionally, I will show how ultrafast
electron transfer excites coherent vibration of the first layer of TiO2
surface atoms, whose collective atomic motions can be followed in real
time.
Bio
Will received his bachelor’s degree in Chemical Engineering (magna cum
laude) from the University of Delaware in 2005 and is currently pursuing a
Ph.D. in Chemical Engineering at the University of Minnesota under the
direction of Professors David Norris, Eray Aydil, and Xiaoyang Zhu (now at
the University of Texas – Austin). He is the recipient of an NSF IGERT
Fellowship and a University of Minnesota Doctoral Dissertation Fellowship.
His research interests lie in the understanding of excited state dynamics
near surfaces and interfaces and the application of this understanding
toward development of novel photovoltaic technologies.