This presentation has been moved. To view this presentation, please visit http://pubs.acs.org/iapps/liveslides/pages/index.htm?mscNo=jz300723h Sulfated Graphene Oxide as a Hole-Extraction Layer in High-Performance Polymer Solar Cells J. Phys. Chem. Lett., 2012, 3 (14), pp 1928–1933 DOI: 10.1021/jz300723h In this study, we have rationally designed and successfully developed sulfated graphene oxide (GO–OSO3H) with −OSO3H groups attached to the carbon basal plane of reduced GO surrounded with edge-functionalized −COOH groups. The resultant GO–OSO3H is demonstrated to be an excellent hole extraction layer (HEL) for polymer solar cells (PSCs) because of its proper work function for Ohmic contact with the donor polymer, its reduced basal plane for improving conductivity, and its −OSO3H/–COOH groups for enhancing solubility for solution processing. Compared with that of GO, the much improved conductivity of GO–OSO3H (1.3 S m–1 vs 0.004 S m–1) leads to greatly improved fill factor (0.71 vs 0.58) and power conversion efficiency (4.37% vs 3.34%) of the resulting PSC devices. Moreover, the device performance of GO–OSO3H is among the best reported for intensively studied poly(3-hexylthiophene):[6,6]-phenyl-C61 butyric acid methyl ester (P3HT:PCBM) devices. Our results imply that judiciously functionalized graphene materials can be used to replace existing HEL materials for specific device applications with outstanding performance.

1. Sulfated Graphene Oxide as a Hole-Extraction
Layer in High-Performance Polymer Solar Cells
Jun Liu, Yuhua Xue and Liming Dai*
COOH
COOH
HOOC COOH
HOOC COOH
Al OH O
OH
OSO3H
OSO3H
Ca HOOC
O
OH
COOH
HOOC
OH
COOH
O OH
P3HT:PCBM HOOC
COOH
COOH HOOC
OSO3H COOH
COOH
GO GO-OSO3H
ITO
Department of Macromolecular Science and Engineering, Department of Chemical
Engineering, Case Western Reserve University, Cleveland, OH 44106, USA
J. Phys. Chem. Lett. 2012, 3, 1928 -1933. 1

2. Hole-Extraction Layer
Requirement for Hole-Extraction Layer:
Minimizing hole extraction barrier;
Blocking electrons; Al
Alter morphology of the active layer; Ca
Solution processability; P3HT:PCBM
High conductivity.
ITO
Graphene oxide as for Hole-Extraction Layer:
Low conductivity;
Large series resistance and low fill factor of the devices.
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3. Design of GO-OSO3H
COOH COOH
HOOC COOH HOOC COOH
OH
OH O OSO3H O
O
H2SO4 (SO3)
OSO3H
HOOC COOH HOOC COOH
OH
O OH OSO3H O
HOOC COOH HOOC COOH
COOH COOH
GO GO-OSO3H
 Reduced basal plane: improved conductivity;
 -OSO3H groups: improved acidicity;
 -OSO3H and –COOH groups: improved solubility.
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4. Reduced Basal Plane
O1s GO C-O C-C
C1s GO
C=O
160 200 240 COOH
C1s O1s
GO-OSO3H C-C
GO-OSO3H
C-O
160 200 240 C-S
S2p S2s COOH
0 200 400 600 290 285 280
Binding energy (eV) Binding Energy (eV)
XPS: Less O content XPS C1s: Less C-O/C-C ratio
11.5o GO
GO GO-OSO3H
Conductivity:
diffraction (a.u.)
intensity (a.u.)
GO-OSO3H
22.6
o GO: 0.004 S/m
GOOSO3H: 1.3 S/m
500 1000 1500 2000 20 40 60 80
-1
wavenumber (cm ) 2 (deg)
Raman: larger ID/IG ratio XRD: smaller π- π distance
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5. Solution Processability
High quality film
Single-layer graphene sheets after spincoating
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6. Device Efficiency
HEL VOC JSC FF PCE Rs
(V) (mA/cm2) (%) ( cm2)
PEDOT:PSS 0.60 10.35 0.71 4.39 1.4
GO 0.61 9.64 0.58 3.34 3.1
GO-OSO3H 0.61 10.15 0.71 4.37 1.2
0
Compared with the GO-based
current density (mA/cm2)
-3 PEDOT:PSS
device, its GO−OSO3H counterpart GO
GO-OSO3H
-6
exhibits a much lower series
-9
resistance and hence significantly
improved FF and PCE. -12
0.0 0.2 0.4 0.6
voltage (V)
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7. Thicknesses Dependence
GO-OSO3H GO
current density (mA/cm )
current density (mA/cm )
2
2
0 0
-3 2 nm 2 nm
-3
4 nm 4 nm
6 nm 6 nm
-6 -6
-9 -9
-12 -12
0.0 0.2 0.4 0.6 0.0 0.2 0.4 0.6
voltage (V) voltage (V)
No dependence Efficiency decrease
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8. Conclusions
Rational-design and preparation of GO-OSO3H.
The reduced basal plane, the increased acidicity, and the good
solution processability of GO-OSO3H.
GO-OSO3H is an excellent hole extraction material for PSCs.
Acknowledgement
Air Force Office of Scientific Research (FA9550-12-1-
0069) under the Program Manager – Dr. Charles Lee
Wenzhou Medical College,
Zhejiang Innovation Team from Department of Education (T200917),
Ministry of Education of China (IRT1077, 211069, and 20103321120003),
National “Thousand Talents Program” of China,
Ministry of Science and Technology of China (2009DFB30380), NSFC-
NSF MWN (NSF-DMR 1106160)
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