Post on 22-Jan-2018
Surface Potential Heterogeneity in Organic Semiconductors
Paula HoffmannACS CERM
October 29, 2014
Semiconductor IndustryInorganic Organic
synthetically tailorable
low cost
highly processable
wide-‐spread industry
high stability
ef8icient
Forrest, S.R., Nature, 2004, 428, 911-918; http://www.solarpanels.net.in/
Semiconductor IndustryInorganic Organic
synthetically tailorable
low cost
highly processable
wide-‐spread industry
high stability
ef8icient
Forrest, S.R., Nature, 2004, 428, 911-918; http://www.solarpanels.net.in/
high cost low ef9iciency
Semiconductor Disorder
Typical disorder caused by:
defects
traps and barriers
molecular motion/
vibration
ACS Nano, 2011 5 pp. 8579
J Phys Chem C, 2012 116 pp.11852
!Z!Scanning!
Laser
Photodiode Detector
Cantilever
Height Feedback
Potential Feedback
X*Y!Scanning!Bias Feedback Control
Sample
Sample Holder
Height and Potential Images
Atomic Force Microscopy
Advantages: Spatial resolution Versatile-‐ many techniques
Disadvantages Instrument artifacts Max scan area-‐ 20 x 20 μm2
Substrate
Cantilever
Substrate
Kelvin Probe AFM5
4
3
2
1
0
µm
543210µm
-10
0
10
nm
5
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1
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µm
543210µm
888684828078
mV
Height Scan Potential Scan
Potential Histogram
Kelvin Probe AFM5
4
3
2
1
0
µm
543210µm
-10
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nm
5
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1
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µm
543210µm
888684828078
mV
10008006004002000
Cou
nts
100mV90807060Potential (V)
Height Scan Potential Scan
Potential Histogram
Kelvin Probe AFM5
4
3
2
1
0
µm
543210µm
-10
0
10
nm
5
4
3
2
1
0
µm
543210µm
888684828078
mV
10008006004002000
Cou
nts
100mV90807060Potential (V)
Height Scan Potential Scan
Potential Histogram
10008006004002000
Cou
nts
100mV90807060Potential (V)
Kelvin Probe AFM5
4
3
2
1
0
µm
543210µm
-10
0
10
nm
5
4
3
2
1
0
µm
543210µm
888684828078
mV
Height Scan Potential Scan
Potential Histogram
10008006004002000
Cou
nts
100mV90807060Potential (V)
5004003002001000
Cou
nts
80nm400-40Height (nm)
Height Histogram
Surface Potential Distributions
J. Phys. Chem. C, 2013 117 pp. 18367
P3HT%
PEDOT:PSS%%
A)#Varying#Materials#(ITO)#
3T%
NiPS% MgO%
SiO2%
B)#Varying#Substrates#(P3HT)#
ITO%
Au%
NN
N
NN
N
N
NNi
SO3--O3S
SO3--O3S
SSS
S
OO
SO3-
S
Positive charges form nanoscale trap “islands” Negative charges morehomogeneous
distances
probability
-+
-
-
+
+
Energy (eV)
Surface PotentialDistribution
J. Phys. Chem. C, 2013 117 pp. 18367
Spatially Inhomogeneous Trapping
Experimental KPFM
Simulated Surface Potentials
Experiment vs. Simulation: Mixed Disorder
J. Phys. Chem. C, 2013 117 pp. 18367
Imprinting Process
20
15
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µm
20151050µm
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nm
20nm
0
-20
Height
20µm151050Position
Org. Electron. 2011 12 pp.1241
Patterned P3HT
20
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20151050µm
-100-50050100
nm
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nm
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20151050µm
-100-50050100
nm
20
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20151050µm
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nm
P3HT-‐PCBM Patterns20
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µm
20151050µm
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nm
20
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20151050µm
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nm20
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20151050µm
-196
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mV
5 µm dot
2 µm dotHeight Potential
P3HT-‐PCBM Patterns
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nm20
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nm20
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5 µm dot
2 µm dotHeight Potential
4003002001000
Cou
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80mV6040200-20-40Potential (mV)
P3HT-‐PCBM Patterns
20
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nm20
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5 µm dot
2 µm dotHeight Potential
8006004002000
Cou
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-0.21V -0.20 -0.19 -0.18 -0.17Potential (V)
4003002001000
Cou
nts
80mV6040200-20-40Potential (mV)
P3HT-‐PCBM Patterns20
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µm
20151050µm
-20
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nm
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20151050µm
-150
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mV
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1086420µm
-20-1001020
nm10
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µm
1086420µm
280
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mV
2 µm lines
StarHeight Potential
P3HT-‐PCBM Patterns
20
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µm
20151050µm
-20
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nm
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20151050µm
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mV
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-20-1001020
nm10
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1086420µm
280
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mV
2 µm lines
StarHeight Potential
600
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Cou
nts
-0.160V -0.155 -0.150 -0.145 -0.140 -0.135Potential (V)
P3HT-‐PCBM Patterns
20
15
10
5
0
µm
20151050µm
-20
0
20
nm
20
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µm
20151050µm
-150
-148
-146
-144
-142
-140
mV
10
8
6
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2
0
µm
1086420µm
-20-1001020
nm
10
8
6
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2
0
µm
1086420µm
280
260
240
220
mV
2 µm lines
StarHeight Potential
600
400
200
0
Cou
nts
0.30V0.280.260.240.220.20Potential (V)
600
400
200
0
Cou
nts
-0.160V -0.155 -0.150 -0.145 -0.140 -0.135Potential (V)
Patterning and Potential Distributions
20
15
10
5
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µm
20151050µm
-40
-20
0
20
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nm
5004003002001000
Cou
nts
-0.40V -0.38 -0.36 -0.34 -0.32 -0.30Potential (V)
20
15
10
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µm
20151050µm
-0.37
-0.36
-0.35
-0.34
V
Height Potential
5004003002001000
Cou
nts
-0.40V -0.38 -0.36 -0.34 -0.32 -0.30Potential (V)
Implications for Transport
Evidence of “hot pathways” for transport
Long time scans show changing
shape
ConclusionsAsymmetry in potential distributions not always
due to morphological disorder. Indicative of an electronic disorder not commonly
observed
Electronic disorder likely exists in two time domains
Future experiment:?
Thanks! Questions?
Acknowledgements
Additional work done by: Izzy Ortiz
Rachel Wilson Dr. Geoff Hutchison
Other group members: Chris Marvin
Ilana Kanal Kyle Reese Michelle Hu
Michael Moody