This presentation is based on the recent publication from our group entitled, "Tracking the Adsorption and Electron Injection Rates of CdSe Quantum Dots on TiO2: Linked versus Direct Attachment," published in 2011 in the Journal of Physical Chemistry C. Presented by Doug Pernik, an undergraduate in the Kamat lab. Figures in this presentation are reprinted with permission from J. Phys. Chem. C, 2011, 115, 13511-13519. Copyright 2011 American Chemical Society. Visit our website, KamatLab.com, for the latest news, publications, and research from our group.

1. Tracking
the
Adsorp2on
and
Electron
Injec2on
Rates
of
CdSe
Quantum
Dots
on
TiO2:
Linked
versus
Direct
ADachment
Douglas
R.
Pernik,
Kevin
Tvrdy,
James
G.
Radich,
Prashant
V.
Kamat
J.
Phys.
Chem.
C,
2011,
115
(27),
pp
13511-­‐13519
Department
of
Chemical
and
Biomolecular
Engineering
Department
of
Chemistry
and
Biochemistry
RadiaHon
Laboratory,
University
of
Notre
Dame

2. Big
Picture
• Quantum
dot
sensiHzed
solar
cells
(QDSSCs)
are
cheap
devices
for
converHng
solar
energy
to
electricity
• Current
QDSSCs
lack
in
efficiency
compared
to
crystalline
silicon
• Improvements
are
needed
at
the
QDSSC
working
electrode
Goals
of
this
work:
–
Understand
quantum
dot
adsorpHon
phenomenon
on
TiO2
–
Examine
charge
carrier
dynamics
for
QD-­‐TiO2
assemblies

3. Goal
1:
Understand
QD
AdsorpHon
Phenomenon
on
TiO2
Experimental
setup
for
monitoring
CdSe
QD
adsorpHon
on
TiO2.
AdsorpHon
is
seen
over
Hme
with
UV-­‐Visible
absorpHon
spectrometry.

4. AdsorpHon
Processes
QDs
begin
to
form
a
monolayer
on
TiO2
before
aggregaHng
on
the
TiO2
surface

5. AdsorpHon
Modeling
0.06 Experimental Adsorption Data
Sub-Monolayer Adsorption
QD Aggregation
Fractional Coverage of TiO2
0.05 Total Fit
0.04
0.03
0.02
0.01
0.00
0 10 20 30 40 50
Time (Hours)
AdsorpHon
is
seen
as
a
combinaHon
of
monolayer
formaHon
and
QD
aggregaHon
on
TiO2

6. Effect
of
Washing
on
QD
AdsorpHon
25
QD Adsorbed Per TiO2 Nanoparticle 5 Washes
20
15
3 Washes
10
5
1 Wash
0
0 10 20 30 40 50
Time (Hours)
Methanol
pretreatment
(washing)
improves
QD
affinity
for
TiO2

7. Goal
2:
Examine
Charge
Carrier
Dynamics
for
QD-­‐TiO2
Assemblies
Flow of Electrons
Electron Electrolyte
Light Transfer
QD
TiO2
Photoanode Photocathode
How
does
the
presence
of
a
molecular
linker
affect
electron
injecHon
rates?

8. Electron
InjecHon
Rates
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()9
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9-/ -// --/ :// :-/ ;// / +/ 9/ :/ 1/ 0//
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Electron
injecHon
is
more
rapid
when
QDs
are
directly
adsorbed
onto
TiO2.
The
linker
molecule
3-­‐MPA
acts
as
a
physical
barrier
to
charge
transfer

9. Summary
• Development
of
a
method
to
monitor
and
model
QD
adsorpHon
onto
TiO2
over
Hme
• Importance
of
QD
washing
to
achieve
high
coverage
of
TiO2
• AdsorpHon
is
seen
as
a
combinaHon
of
monolayer
formaHon
and
parHcle
aggregaHon
• Linker
molecules
have
a
detrimental
effect
on
electron
injecHon
rates
These
findings
will
aid
in
construcHng
quantum
dot
sensiHzed
solar
cells
with
higher
efficiency

10. Special
Thanks
–
U.S.
Department
of
Energy
for
project
funding
–
Vincent
P.
Slac
Fellowship
for
Undergraduate
Research,
provided
by
Notre
Dame
Energy
Center
This
work
is
published
in
the
Journal
of
Physical
Chemistry
C:
J.
Phys.
Chem.
C,
2011,
115
(27),
pp
13511-­‐13519
DOI:
10.1021/jp203055d
AddiHonal
informaHon
about
the
Kamat
group
is
on
the
group
website:
hcp://nd.edu/~pkamat/