1. Surface
Potential
Heterogeneity
in
Organic
Semiconductors
Paula Hoffmann
ACS CERM
October 29, 2014

2. Semiconductor
Industry
Inorganic 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/

3. Semiconductor
Industry
Inorganic 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

4. 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

5. !
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

6. Kelvin
Probe
AFM
5
4
3
2
1
0
µm
543210
µm
-10
0
10
nm
5
4
3
2
1
0
µm
543210
µm
88
86
84
82
80
78
mV
Height Scan Potential Scan
Potential Histogram

7. Kelvin
Probe
AFM
5
4
3
2
1
0
µm
543210
µm
-10
0
10
nm
5
4
3
2
1
0
µm
543210
µm
88
86
84
82
80
78
mV
1000
800
600
400
200
0
Counts
100mV90807060
Potential (V)
Height Scan Potential Scan
Potential Histogram

8. Kelvin
Probe
AFM
5
4
3
2
1
0
µm
543210
µm
-10
0
10
nm
5
4
3
2
1
0
µm
543210
µm
88
86
84
82
80
78
mV
1000
800
600
400
200
0
Counts
100mV90807060
Potential (V)
Height Scan Potential Scan
Potential Histogram
1000
800
600
400
200
0
Counts
100mV90807060
Potential (V)

9. Kelvin
Probe
AFM
5
4
3
2
1
0
µm
543210
µm
-10
0
10
nm
5
4
3
2
1
0
µm
543210
µm
88
86
84
82
80
78
mV
Height Scan Potential Scan
Potential Histogram
1000
800
600
400
200
0
Counts
100mV90807060
Potential (V)
500
400
300
200
100
0
Counts
80nm400-40
Height (nm)
Height Histogram

10. 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%
N
N
N
N
N
N
N
N
Ni
SO3
--O3S
SO3
--O3S
SS
S
S
OO
SO3
-
S

11. Positive
charges
form
nanoscale
trap
“islands”
Negative
charges
more
homogeneous
distances
probability
-
+
-
-
+
+
Energy (eV)
Surface Potential
Distribution
J. Phys. Chem. C, 2013 117 pp. 18367
Spatially
Inhomogeneous
Trapping

12. Experimental
KPFM
Simulated
Surface Potentials
Experiment
vs.
Simulation:
Mixed
Disorder
J. Phys. Chem. C, 2013 117 pp. 18367

13. Imprinting
Process
20
15
10
5
0
µm
20151050
µm
-40
-20
0
20
40
nm
20nm
0
-20
Height
20µm151050
Position
Org. Electron. 2011 12 pp.1241

14. Patterned
P3HT
20
15
10
5
0
µm
20151050
µm
-100
-50
0
50
100
nm
20
15
10
5
0
µm
20151050
µm
-80
-40
0
40
80
nm
20
15
10
5
0
µm
20151050
µm
-100
-50
0
50
100
nm
20
15
10
5
0
µm
20151050
µm
-50
0
50
nm

15. P3HT-­‐PCBM
Patterns
20
15
10
5
0
µm
20151050
µm
-10
0
10
nm
20
15
10
5
0
µm
20151050
µm
-10
0
10
mV
20
15
10
5
0
µm
20151050
µm
-50
0
50
nm
20
15
10
5
0
µm
20151050
µm
-196
-192
-188
-184
mV
5 µm dot
2 µm dotHeight Potential

16. P3HT-­‐PCBM
Patterns
20
15
10
5
0
µm
20151050
µm
-10
0
10
nm 20
15
10
5
0
µm
20151050
µm
-10
0
10
mV
20
15
10
5
0
µm
20151050
µm
-50
0
50
nm
20
15
10
5
0
µm
20151050
µm
-196
-192
-188
-184
mV
5 µm dot
2 µm dotHeight Potential
400
300
200
100
0
Counts
80mV6040200-20-40
Potential (mV)

17. P3HT-­‐PCBM
Patterns
20
15
10
5
0
µm
20151050
µm
-10
0
10
nm 20
15
10
5
0
µm
20151050
µm
-10
0
10
mV
20
15
10
5
0
µm
20151050
µm
-50
0
50
nm
20
15
10
5
0
µm
20151050
µm
-196
-192
-188
-184
mV
5 µm dot
2 µm dotHeight Potential
800
600
400
200
0
Counts
-0.21V -0.20 -0.19 -0.18 -0.17
Potential (V)
400
300
200
100
0
Counts
80mV6040200-20-40
Potential (mV)

18. P3HT-­‐PCBM
Patterns
20
15
10
5
0
µm
20151050
µm
-20
0
20
nm
20
15
10
5
0
µm
20151050
µm
-150
-148
-146
-144
-142
-140
mV
10
8
6
4
2
0
µm
1086420
µm
-20
-10
0
10
20
nm
10
8
6
4
2
0
µm
1086420
µm
280
260
240
220
mV
2 µm lines
StarHeight Potential

19. P3HT-­‐PCBM
Patterns
20
15
10
5
0
µm
20151050
µm
-20
0
20
nm
20
15
10
5
0
µm
20151050
µm
-150
-148
-146
-144
-142
-140
mV
10
8
6
4
2
0
µm
1086420
µm
-20
-10
0
10
20
nm
10
8
6
4
2
0
µm
1086420
µm
280
260
240
220
mV
2 µm lines
StarHeight Potential
600
400
200
0
Counts
-0.160V -0.155 -0.150 -0.145 -0.140 -0.135
Potential (V)

20. P3HT-­‐PCBM
Patterns
20
15
10
5
0
µm
20151050
µm
-20
0
20
nm
20
15
10
5
0
µm
20151050
µm
-150
-148
-146
-144
-142
-140
mV
10
8
6
4
2
0
µm
1086420
µm
-20
-10
0
10
20
nm
10
8
6
4
2
0
µm
1086420
µm
280
260
240
220
mV
2 µm lines
StarHeight Potential
600
400
200
0
Counts
0.30V0.280.260.240.220.20
Potential (V)
600
400
200
0
Counts
-0.160V -0.155 -0.150 -0.145 -0.140 -0.135
Potential (V)

21. Patterning
and
Potential
Distributions
20
15
10
5
0
µm
20151050
µm
-40
-20
0
20
40
nm
500
400
300
200
100
0
Counts
-0.40V -0.38 -0.36 -0.34 -0.32 -0.30
Potential (V)
20
15
10
5
0
µm
20151050
µm
-0.37
-0.36
-0.35
-0.34
V
Height Potential
500
400
300
200
100
0
Counts
-0.40V -0.38 -0.36 -0.34 -0.32 -0.30
Potential (V)

22. Implications
for
Transport
Evidence of “hot pathways” for transport
Long time scans
show changing
shape

23. Conclusions
Asymmetry
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:
?

24. 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