Optimizing the Structure of Conjugated Polymer Films for Transistors & Photovoltaic Cells



Dinner Lecture

Tuesday, Nov. 11
Michael's Restaurant
Mountain View

Prof. Michael McGehee
Department of Materials Science and Engineering
Stanford University

"Optimizing the Structure of Conjugated Polymer
Films for Transistors and Photovoltaic Cells."

One of the greatest challenges we face is that of finding a way to provide energy
without releasing carbon dioxide into the atmosphere. If the cost of photovoltaic
cells could be reduced by a factor of five, they would compete favorably with
conventional sources of electricity and could provide a significant fraction of our
energy without generating carbon dioxide. Since organic semiconductors and
inorganic nanocrystals can be deposited at low cost they provide a means to
lower the costs of photovoltaic cells. The key to making efficient cells with these
materials is to interpenetrate two semiconductors with offset energy levels at the
10-nm length scale so that photogenerated excitons can be split by electron
transfer before they recombine. The network must also be designed to enable
efficient collection of the charge by the electrodes. Our plans for making ideal
structures and our progress towards making these structures will be presented.

Regioregular poly (3-hexylthiophene) (P3HT) has one of the highest field-effect
mobilities of any semiconducting polymer and is one of the leading candidates to
replace amorphous silicon as the active layer of low-cost thin-film transistors.
We have discovered that the field-effect mobility of this polymer increases by four
orders of magnitude as the molecular weight is increased from 3.2 kD to 36.5 kD.
To determine the mechanisms underlying this surprising trend, we have characterized
the structure of the films with atomic force microscopy, x-ray diffraction, UV-vis
absorption spectroscopy and photoluminescence spectroscopy. Collectively, the
results of these experiments show that low-molecular-weight samples form highly
crystalline nanorods that are poorly connected to each other, while high-molecular-
weight samples form less ordered structures. They suggest that the high molecular
weight films have higher mobility since polymer chains are better connected to each
other. Control experiments rule out other explanations for the mobility versus molecular
weight trend, such as end group trapping, chemical defects, polydispersity effects and
regioregularity effects. This study points out the importance of optimizing the molecular
weight of regioregular P3HT for making high-mobility transistors and sheds light on
how charge moves through this polymer.



DATE: Tuesday, Nov. 11

Location: Michael's at Shoreline Park, Mountain View

Timing: 6 PM social hour
7 PM dinner
8 PM lecture

Cost: $30 with advance registration
half price students, retired, unemployed
free for just the lecture at 8PM
(but please let us know for headcount)

$35 at the door, with no guarantee
of admission or dinner choice

PLEASE NOTE: we accept cash or checks, but are unable to
accept payment by credit card at this time.

Deadline for registration:
5 PM Friday Nov. 7

Please register on the web site

Or, contact:
Damian Hajduk

You should receive confirmation of your registration; if not,
please contact us again.


Dinner choices:
grilled salmon
eggplant Parmesian
chicken Saltimbocco (w/ prosciutto & provolone)

Note that we must request that you be liable for your
registration fee if you register and do not attend;
cancellation is allowed up to the registration deadline.


Restaurant's web page directions

From 101 in Mountain View, take the Shoreline Boulevard
Exit, turning toward the bay. Drive past the Shoreline
Amphitheater and go straight ahead, entering into
Shoreline Park. After a mile or so inside the park,
a sign for Michael's will direct you to turn left into
the parking lot for Michael's.
Address: 2960 N Shoreline Blvd.
Restaurant phone: 650-962-1014
(do not call restaurant for reservations)


Upcoming GGPF meetings:

Dec. 11, Faz Restaurant, Sunnyvale
Prof. Tim Patten
U. C. Davis Chemistry Dept.
"Synthesis and Assembly of Polymer-Grafted

Jan 2004
William J. Orts, Ph.D.
Research Leader, Bioproduct Chemistry & Engineering
USDA-ARS-WRRC, speaks on the topic of wheat/rice-based
starch as a drop-in replacement for polystyrene.

Feb 2004
Prof. Benny Freeman
Chemical Engineering Dept., U. of Texas, Austin
on a polymer diffusion related topic, details tba.


OTHER EVENTS of possible interest to the
GGPF audience:


Oct. 14, San Francisco
joint meeting of the Northern California Society for Microscopy
and the San Francisco Microscopical Society
"Applications of Light and Electron Microscopy for
Genetic Therapy Research", Kenneth C. Moore, Univ. of Iowa
For information, contact
(web page does not have meeting information)

Oct. 15, Santa Clara/Mountain View
SAMPE tour of 2 Phase Technolgies & dinner afterwards

Oct. 15, Millbrae
BioScience Forum Meeting:
"Drug Delivery; Achilles Heel of Biotechnology"
Prof. Francis Szoka, UCSF

Oct. 15, San Francisco
nanoSIG event, nanoSoftware and Tools Forum
Prof. Dorian Liepmann, Depts of Bioengineering
& Mechanical Engineering, U.C. Berkeley,
"Micro Electro Mechanical Systems applied
to fluid dynamics"; and Dr. Ephraim Suhir, on
the proposed Nano-Optics Research Center (NORC)
at UC Santa Cruz.

Oct. 19-22, Oakland
55th Pacific Coast Regional meeting of the
American Ceramic Society

Oct. 20- 21, San Francisco
COTS MEMS meeting (Commercial Off-The-Shelf MEMS)

Oct. 22, Sunnyvale
AVS Thin Films Users Group meeting
(afternoon meeting)
Focus of meeting is on "low-k" dielectric films & processing

Oct. 24-26, Palo Alto
IMAPS (International Microelectronics & Packaging Society)
Advanced Technology Workshop on "Thermal Management for
High-Performance Computing & Wireless Applications"

Oct. 30, Dublin
ACS California Section dinner meeting
"Nano-science and Nano-engineering: The Science and Technology
is 'Out-of-the-Bottle!', Nano-Sensors for Medicine, Environment,
Security & Industry" by
Joseph R. Stetter, Ph.D. Nanomix, Emeryville, CA &
Illinois Institute of Technology


Nov. 4, Mountain View
NorCal AIChE southBay dinner meeting,
"Design of a Transdermal Glucose Monitoring System",
Janet Tamada, Cygnus

Nov. 10-13, San Francisco
Nanocomposites 2003

Nov 16-20, San Francisco
Annual Fall National AIChE meeting

Nov. 18, Millbrae
Bio E2E "First Annual Career Fair."
afternoon event

Nov. 19, San Francisco
nanoSIG event
Lawrence H. Dubois , SRI, Vice President of the Physical Sciences Division,
will speak about the nanotechnology focus at SRI.


Dec. 10, Mountain View
AIChE SouthBay meeting
tour of ALZA

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