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Plastic Solar Cells
Thuc-Quyen NguyenDepartment of Chemistry and Biochemistry
Center for Polymers and Organic Solids (CPOS)University of California, Santa Barbara
Exciton
1) Light absorption
create the excited
state named exciton
(electron-hole pair)
2) Exciton diffusion
3) Charge separationor electron transfer at
donor-acceptor
interfaces
4) Charge transport
5) Charge Collection
Bulk Heterojunction Polymer Solar Cells
ITO
Aluminum
Polymer(Donor) Fullerene(Acceptor)
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Organic Solar Cell Fabrication
Challenges- Material Design and Synthesis: Need strategy, theory to
guide synthesis, take a long time to optimize new materials,
material reproducibility
- Material Characterization: nanoscale morphology of blended
materials, interfaces, charge generation, charge transport,
charge recombination, defects, etc.
- Device Physics
- Degradation, Lifetime
- Modeling/Calculation: materials and devices
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Issues with Conjugated Polymers
1) Batch to batch variation
- Molecular weight (MW)
- Polydispersity- Chain end variation
2) Impurity
3) Difficult to purify
4) Weak molecular packing
Gui Bazan (UCSB), Nature Chemistry, in press
Mn ~ 7K kg/mol
% ~ 1.2%
Mn ~14K kg/mol
Mn ~ 34K kg/mol
% ~ 5.9%
Advantages of Molecular Donors
Molecular Donors: No batch to batch variation, easy to
purify and to functionalize
S S
SiEt3
SiET3
PCE = 1%
PCE = 0.8%
S
S S
S SS S
S S
S S
OC6H13
OC6H13
C6H13O
C6H13O
PCE = 1.1%
N
S
S
S
S
S
O
O
PCE = 0.8%
S S
SiEt3
SiET3
PCE = 1%
PCE = 0.8%
S
S S
S SS S
S S
S S
OC6H13
OC6H13
C6H13O
C6H13O
PCE = 1.1%
N
S
S
S
S
S
O
O
PCE = 0.8%
G. Malliaras, Mater. Today2007, 10, 34.
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New Materials
Strong Molecular
Order
Donor Materials
Thermal/Photo/
Electrochemical
Stability
High Charge
Carrier Mobility
Solution
Processable
Strong Absorbing
Chromophore
Low Band Gap
SS
SS
SS
Building Blocks
vacuum deposited on SiO2
h ~ 0.2 cm2/V.s
Muccini, et al., Nature Materials
4, 81-85 (2005)
R2N
NR1 O
O
R3
R4
Wallquist, Olof; Lenz, R. 20 years of
DPP pigments - future perspectives.
Macromolecular Symposia (2002), 187,
617-629
Diketopyrrolopyrrole
(DPP)Sexithiophene
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Applications of DPP: Paint Pigments
Diketopyrrolopyrrole (DPP)
High thermal stability
Incorporate the Best of Both Worlds
+
Diketopyrrolopyrrole
Strong absorbing unit
Strong Intermolecular
Interactions
OligothiopheneHigh charge mobility unit
Functionalization Solution Process
SS
SS
SS
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Effect of the End Unit
N
N
O
O
SO
S
O
DPP(TBFu)2
T.-Q. Nguyen et al. Adv. Funct. Mater. 2009, 19, 3063.
Optical Properties
N
N
O
O
SO
SO
1.6
1.2
0.8
0.4
0.0
Intensity
(a.u.
)
700600500400
Wavelength (nm)
DPP(TBFu)2 Solution
DPP(TBFu)2 Film
PC71BM Film
0.5
0.4
0.3
0.2
0.1Absorbance(a.u.)
700600500400
Wavelength (nm)
30:7050:5060:4070:30
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Effect of Blend Ratio on Annealed Film
Morphology
rms ~2.4nmrms ~2.2nmrms ~2.1nm
Image size: 5 m 5 m
70:30 50:50 30:70
Annealed at 100 C for 10 min
0.5
0.4
0.3
0.2
0.1
0.0
IPCE(electrons/photon)
800700600500400300Wavelength (nm)
30:7050:5060:4070:30
Effect of Different Blend Ratios
As-cast Annealed
30-70 50-50 60-40 70-30 30-70 50-50 60-40 70-30JSC
(mA/cm2)6.64 4.13 1.45 0.68 5.70 8.38 10.7 9.01
VOC (V) 0.87 0.93 0.96 0.81 0.89 0.89 0.92 0.92
FF 0.32 0.29 0.24 0.23 0.33 0.38 0.37 0.43
% 1.85 1.12 0.33 0.12 1.67 2.87 4.33 3.54
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-8
-6
-4
-2
0
2
4
J(mA/cm
2)
1.00.80.60.40.20.0-0.2-0.4Potential (V)
30:70 as-cast
50:50 as-cast
60:40 as-cast
70:30 as-cast
30:70 Annealed
50:50 Annealed
60:40 Annealed
70:30 Annealed
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Film Morphology of Annealed Blend
rms ~0.5nm rms ~1.1nm rms ~2.3nm
Image Size: 2 m 2 m Blend Ratio: 70:30
As-cast 90 C 100 C
Temp (C) 90 100 110 120 130 140
Jsc 10.9 10.7 11.9 10.5 9.2 8.0
Voc 0.92 0.92 0.92 0.92 0.92 0.92
FF 0.34 0.37 0.37 0.39 0.41 0.40
3.97 4.33 4.79 4.42 4.12 3.43
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-8
-6
-4
-2
0
2
CurrentDensity(mA/cm
2)
1.00.80.60.40.20.0-0.2-0.4Potential (V)
90 C100 C110 C120 C130 C140 C
Effect of Thermal Annealing on Device
Performance (60:40 blend ratio)
0.6
0.5
0.4
0.3
0.2
0.1
0.0
IPC
E
(electrons
/photon)
900800700600500400300Wavelength (nm)
As-cast80 C100 C110 C150 CP3HT
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Adv. Funct. Mater. 2009, 19, 3063
AcknowledgementsStudents:
Bright Walker
Mark Dante
Jason Lin
Mananya Tantiwiwat
Jessica Sherman
Corey Hoven
Chi-Yen LinMichele Guide
Daniel Kamkar
Postdocs:
Dr. Arnold Tamayo
Dr. Chunki Kim
Dr. Junghwa Seo
Dr. Xuan-Dung Dang
Dr. Karolina Siskova
Dr. Jihua Yang
Dr. Peng WangDr. Mungsoo Lee
Dr. Andres Garcia
Undergraduates:
Peter Zalar
Tyler Kent
Ngoc Luu
Duc Duong
Janine Boucher
Calvin Peng
Alexandra PolosukhinaAlissa Walker Bell
Jaime Salazar
Armando Lagunas
Dorian Mattrey
Victoria Crockett
Manuel Schnabel
Jennifer Swift
Frank Proa
Collaborators: Jeff Peet, Gui Bazan, FredWudl, Alan Heeger, Ed Kramer, Harold Ade,
Lynn Loo, Darryl Smith
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Funding
- Office of Naval Research Young Investigator Award
- Camille Dreyfus Teacher Scholar Award
- Alfred Sloan Research Award
- DOE: BES, Energy Frontier Research Centers (EFRCs)
- NSF-MRSEC
- California NanoSystem Institute at UCSB
- Army Office of Research/Institute for Collaborative
Biotechnologies