1
Supporting Information for:
Doping of Donor-Acceptor Polymers with Long
Side Chains via Solution Mixing for Advancing
Thermoelectric Properties
Eui Hyun Suh, Yong Jin Jeong, Jong Gyu Oh, Kyumin Lee, Jaemin Jung, Yong Soo Kang and
Jaeyoung Jang*
Department of Energy Engineering, Hanyang University, Seoul 04763, Republic of Korea.
Author Information
* Corresponding Author
E-mail address: [email protected] (J. Jang)
2
OFET fabrication and characterization
Top-contact bottom-gate OFETs were fabricated from both the neat and 5 mol% doped
PCDTFBT, PCDTPT, and P3HT films. Heavily doped Si wafers coated with a SiO2 (300-nm)
dielectric layer were used as the gate substrates, which were cleaned with piranha solution,
rinsed multiple times with DI water, and then treated with octadecyltrichlorosilane (ODTS).
The solutions of neat polymers or the polymer/F4TCNQ mixtures were spin-coated onto the
ODTS-treated substrates and subsequently annealed at 150 °C for 10 min inside an N2-filled
glove box. To fabricate the source and drain electrodes, 100 nm thick Au layers were deposited
on the tops of the spin-coated films by thermal evaporation through a shadow mask. The
channel length (L) and width (W) were 100 and 300 μm, respectively. Total of 58 OFETs were
tested under each condition, and the obtained carrier mobilities were averaged. The electrical
properties of the produced OFETs were determined inside the N2-rich glove box using a
Keithley 4200-SCS parameter analyzer. The field-effect mobility was calculated in the
saturation regime from the slope of the plot of the square root of the drain current (ID1/2) versus
the gate voltage (VG) using the equation ID = CiW(2L)−1(VG − Vth)2, where Ci was the
capacitance per unit area (10.0 nF cm2), and Vth was the threshold voltage.
3
Fig. S1. Cyclic voltammograms of (a) ferrocene and (b) F4TCNQ recorded versus the Ag/AgCl
reference electrode.
-0.4 0.0 0.4 0.8 1.2
-5
-4
-3
-2
-1
0
1
2
3
Cu
rren
t (
A)
Potential (V) (vs Ag/AgCl)
F4TCNQ
0.0 0.2 0.4 0.6 0.8-15
-10
-5
0
5
10
15
20 Ferrocene
Cu
rre
nt
(A
)
Potential (V) (vs Ag/AgCl)
a b
4
Fig. S2. Solution stability of the polymer-dopant mixture. (Top) Photographs of the polymer
solutions mixed with the F4TCNQ solutions. UV-vis-NIR spectra of the (a) PCDTFBT, (b)
PCDTPT, and (c) P3HT solutions obtained before/after mixing with the F4TCNQ solutions (30
mol% for PCDTFBT and PCDTPT; 20 mol% for P3HT).
400 600 800 1000 1200 1400
0.0
0.2
0.4
0.6
0.8
1.0 PCDTFBT Before mixing After mixing
No
rmal
ized
ab
sorb
an
ce
(a.u
.)
Wavelength (nm)400 600 800 1000 1200 1400
0.0
0.2
0.4
0.6
0.8
1.0
Wavelength (nm)
PCDTPT Before mixing After mixing
No
rmal
ized
ab
sorb
an
ce
(a.u
.)
400 600 800 1000 1200 1400
0.0
0.2
0.4
0.6
0.8
1.0
Wavelength (nm)
P3HT Before mixing After mixing
No
rmal
ized
ab
sorb
an
ce
(a.u
.)
a b c
1000 1200 1400 1200 1400
5
Fig. S3. Fourier transform infrared (FTIR) spectra (FT/IR-4200, JASCO Inc.) for (a) neat
polymers (PCDTFBT, PCDTPT, and P3HT), and (b) F4TCNQ and F4TCNQ-doped polymers
(30 mol% for PCDTFBT, 38 mol% for PCDTPT, and 20 mol% for P3HT).
To investigate the dominant doping mechanism of our system, we used Fourier
transform infrared (FTIR) spectroscopy, which is widely used to analyze the degree of charge
transfer between organic semiconductors and molecular dopants including F4TCNQ [S1-S4].
Because the absorption band of cyano groups (C≡N) in F4TCNQ is highly sensitive to the
amount of negative charges, the shift of the absorption band can be used as an indicator of the
extent of charge transfer between organic semiconductors and F4TCNQ. As shown in Fig. S3(b),
the absorption band of cyano groups for neutral F4TCNQ appeared at ~2226 cm-1. Interestingly,
the peaks for all the three doped polymers were observed at ~2192 cm-1, indicating the peak
shift of about 33 cm-1. This amount of peak shifts (~33 cm-1) is known to result from integer
charge transfer between organic semiconductors and F4TCNQ [S4]. As a comparison, other
F4TCNQ-doped D-A polymers have shown less amounts of band shift than F4TCNQ-doped
P3HT (i.e. partial charge transfer [S3]). We think that the superior electrical conductivity of our
D-A polymers after F4TCNQ doping could be achieved because the doping was based on the
integer charge transfer, along with their good charge transport properties.
2260 2240 2220 2200 2180 2160 2140
2192 cm-1
DopedPCDTPT
DopedPCDTFBT
Ab
sorb
ance
(a.
u.)
Wavenumber (cm-1)
2226 cm-1
NeatF
4TCNQ
Doped P3HT
2260 2240 2220 2200 2180 2160 2140
Ab
sorb
ance
(a.
u.)
Wavenumber (cm-1)
Neat PCDTPT
Neat PCDTFBT
Neat P3HT
a b
6
Fig. S4. Extraction of Seebeck coefficient. Linear plots of the thermo-voltage versus the
temperature difference obtained for the PCDTFBT (30 mol%), PCDTPT (30 mol%), and P3HT
(20 mol%) films doped with F4TCNQ. The R2 is a factor related with measurement error (its
value close to 1 indicates accurate measurement). The center of each temperature difference
was maintained at 300 K.
2 3 4 5200
400
600
800
1000V
olt
age
(V
)
Temperature difference (K)
PCDTFBT (30 mol%)Seebeck = 213 V/K
R2 = 0.998
2 3 4 5200
400
600
800
1000
Temperature difference (K)
Vo
ltag
e (
V)
PCDTPT (30 mol%)Seebeck = 192 V/K
R2 = 0.999
2 3 4 5200
400
600
800
1000
Temperature difference (K)
Vo
ltag
e (
V)
P3HT (20 mol%)Seebeck = 86.2 V/K
R2 = 0.998
a b c
7
Fig. S5. Optical microscopy images of the neat and doped PCDTFBT and PCDTPT films.
8
Fig. S6. Distributions of power factors of optimally doped PCDTFBT (30 mol%) and PCDTPT
(38 mol%) films.
PCDTFBT PCDTPT
0
10
20
30
40
50
Po
wer
fac
tor
(W
m-1
K-2)
9
Table S1. Room-temperature thermoelectric properties of various soluble p-type and n-type
conjugated polymers (including the materials used in this study).
Material Doping methoda
Electrical conductivity
(S cm1)
Seebeck coefficient(μV K-1)
Max. power factor (μW m1 K2)
Thermal conductivity (W m-1 K-2)
Max. ZT Ref. #
PCDTFBT +F4TCNQ
Solution mixing 6.91 213 31.5 0.22c 0.043 This
work
PCDTPT +F4TCNQ
Solution mixing 5.13 211 21.8 0.25c 0.026 This
work
P3HT +F4TCNQ
Solution mixing 0.56 116 0.76 This
work
PBTTT +F4TCNQ
Solution mixing 3.51 60 1.3 S5
PCDTBT +FeCl3
Solution mixing 63 38 9 1.00c 0.0026 S6
PDTDE12 +F4TCNQ
Solution mixing 140 22 11 0.23d 0.014 S7
p(g42T-T) +F4TCNQ
Solution mixing 90 26 6 S2
P3HT+PEO +F4TCNQ
Solution mixing 0.3 60 0.1 0.33e 0.0001 S8
P3HT +F4TCNQ
Sequential process 3.5 52 0.95 S9
P3HT +F4TCNQ
Sequential process 22.5 61 8.5 S10
P3HT +F4TCNQ
Vapor doping 12.7 46 2.7 S11
PBTTT +F4TCNQ
Vapor doping 220670 3942 32120 S5
FBDPPV +N-DMBI
Solution mixing 14 -141b 28 S12
TEG-N2200 +N-DMBI
Solution mixing 0.17 -111b 4.6 S13
PNDI2TEG-2Tz +N-DMBI
Solution mixing 1.8 -159b 4.6 S14
a Samples prepared via one-step solution mixing were preferentially summarized, and a few sequentially processed samples using F4TCNQ dopant were also included for comparison. b N-type data. c In-plane thermal conductivity d Out-of-plane thermal conductivity e Bulk thermal conductivity
10
Fig. S7. Air stability of the thermoelectric properties of the doped PCDTFBT (30 mol%),
PCDTPT (30 mol%), and P3HT (9 mol%) films. Time dependences of the relative (a) electrical
conductivity ( ), (b) Seebeck coefficient (S), and (c) power factor (P) calculated with respect
to their initial values. The samples were stored in ambient air with average temperature and
relative humidity of 24 4 °C and 20 5%, respectively.
As compared to the D-A polymers, the doped P3HT films exhibited opposite trends for σ and
S. The slight increase in σ observed for the doped P3HT at the early stage can be attributed to
its re-doping after the thermal annealing at 150 °C (it has been reported previously that the
F4TCNQ-doped P3HT films undergo some de-doping when heated to temperatures over 80 °C)
[S5, S15]. We hypothesize that some amounts of the de-doped F4TCNQ participated again in
doping with time, resulting in the increase in σ.
0 20 40 60 80 100 120 1400.0
0.5
1.0
1.5
2.0
2.5
3.0
/0
Time (day)
PCDTFBT (30 mol%) PCDTPT (30 mol%) P3HT (9 mol%)
0 20 40 60 80 100 120 1400.0
0.5
1.0
1.5
2.0
2.5
3.0
Time (day)
S/S
0
PCDTFBT (30 mol%) PCDTPT (30 mol%) P3HT (9 mol%)
0 20 40 60 80 100 120 1400.0
0.5
1.0
1.5
2.0
2.5
3.0
Time (day)
P/P
0
PCDTFBT (30 mol%) PCDTPT (30 mol%) P3HT (9 mol%)
a b c
11
Fig. S8. Thermoelectric properties as a function of bending cycles for the doped PCDTFBT (30
mol%), PCDTPT (38 mol%), and P3HT (20 mol%) films: the relative (a) electrical conductivity,
(b) Seebeck coefficient, and (c) power factor as a function of bending cycles. The bending
radius and corresponding tensile strain were 8 mm and 0.9 %, respectively. All films were
prepared on polyethylene terephthalate substrates and their fabrication procedures were exactly
the same with those of the samples fabricated on glass substrates.
0 100 2000.0
0.5
1.0
1.5
2.0
Bending cycles
/
0 PCDTFBT (30 mol%) PCDTPT (38 mol%) P3HT (20 mol%)
0 100 2000.0
0.5
1.0
1.5
2.0 PCDTFBT (30 mol%) PCDTPT (38 mol%) P3HT (20 mol%)
S/S
0
Bending cycles0 100 200
0.0
0.5
1.0
1.5
2.0
P/P
0
PCDTFBT (30 mol%) PCDTPT (38 mol%) P3HT (20 mol%)
Bending cycles
a b c
12
Fig. S9. OFET characteristics of the polymers before and after doping. Transfer characteristics
(drain voltage VD = 80 V) and average values of the OFETs fabricated from (ac) neat and
the (df) doped (5 mol%) polymers: (a, d) PCDTFBT, (b, e) PCDTPT, and (c, f) P3HT.
-80 -40 0 40 80
0.0
3.0x10-3
6.0x10-3
9.0x10-3
ID1/
2 (
A1
/2)
h =
0.26 0.06
I D (
A)
VG (V)
10-15
10-13
10-11
10-9
10-7
10-5
10-3
PCDTFBT(5 mol%)
-80 -40 0 40 80
0.0
3.0x10-3
6.0x10-3
9.0x10-3
ID1/
2 (
A1/
2 )
h =
0.23 0.05
I D (
A)
VG (V)
10-15
10-13
10-11
10-9
10-7
10-5
10-3
PCDTPT(5 mol%)
-80 -40 0 40 80
0.0
3.0x10-3
6.0x10-3
9.0x10-3
h =
0.38 0.0810-15
10-13
10-11
10-9
10-7
10-5
10-3
ID1
/2 (
A1/
2 )
Neat PCDTPT
I D (
A)
VG (V)
-80 -40 0 40 80
0.0
3.0x10-3
6.0x10-3
9.0x10-3
ID1
/2 (
A1/
2 )
h = 0.0057 0.0009
Neat P3HT
I D (
A)
VG (V)
10-15
10-13
10-11
10-9
10-7
10-5
10-3
-80 -40 0 40 80
0.0
3.0x10-3
6.0x10-3
9.0x10-3
h = 0.0015 0.0003
P3HT(5 mol%)
10-15
10-13
10-11
10-9
10-7
10-5
10-3
ID1/
2 (
A1
/2)
I D (
A)
VG (V)
-80 -40 0 40 80
0.0
3.0x10-3
6.0x10-3
9.0x10-3
10-15
10-13
10-11
10-9
10-7
10-5
10-3
h =
0.33 0.06
Neat PCDTFBTV
D = -80 V
ID1
/2 (
A1/
2 )
I D (
A)
VG (V)
a b c
d e f
13
Fig. S10. Absorption spectra and thermoelectric properties of spin-coated PCDTFBT films
doped with F4TCNQ. (a) UV-vis-NIR spectra recorded for spin-coated PCD TFBT films as a
function of F4TCNQ molar ratio. (b) Electrical conductivity and Seebeck coefficient and (c)
power factor of spin-coated PCDTFBT films containing 30 mol% F4TCNQ. The dotted lines
denote corresponding average values for the drop-cast films.
0
1
2
3
4
5
6
7
PCDTFBT (30 mol%)
Co
nd
uct
ivit
y (
) (S
cm-1)
0
100
200
300
400
500
Average S (drop-cast)
See
bec
k co
effi
cien
t (S
) (
V K
-1)
Average (drop-cast)
500 1000 1500 2000
0.0
0.2
0.4
0.6
0.8
1.0N
orm
aliz
ed
Ab
sorb
an
ce (
a.u
.)
Wavelength (nm)
0 mol% 2 mol% 5 mol% 9 mol% 13 mol% 20 mol% 30 mol%
PCDTFBT
0
5
10
15
20
25
30
35
PCDTFBT (30 mol%)
Po
wer
fac
tor
(W
m-1
K-2)
Average (drop-cast)
a b c
14
Fig. S11. 2D-GIXD patterns obtained for the PCDTFBT films with doping ratios ranging from
0 to 45 mol%. All diffraction intensities were normalized with respect to the probed material
volumes and X-ray exposure times.
15
Fig. S12. 2D-GIXD patterns obtained for the PCDTPT films with doping ratios ranging from 0
to 45 mol%. All diffraction intensities were normalized with respect to the probed material
volumes and X-ray exposure times.
16
Fig. S13. 2D-GIXD patterns obtained for the P3HT films with doping ratios ranging from 0 to
13 mol%. All diffraction intensities were normalized with respect to the probed material
volumes and X-ray exposure times.
17
Fig. S14. 2D-GIXD line scans obtained from the results presented in Fig. S7S9 at various
doping ratios. Cross-sectional intensity profiles recorded along the qz (out-of-plane) direction
at a given qxy (in-plane) value for the (a) PCDTFBT, (b) PCDTPT, and (c) P3HT films. Cross-
sectional intensity profiles recorded along the qxy (in-plane) direction at given qz (out-of-plane)
values for the (d) PCDTFBT, (e) PCDTPT, and (f) P3HT films.
0.5 1.0 1.5
0
2000
4000
6000
F4TCNQ crystal
45 mol%
PCDTPTOut-of-plane
0 mol%
Inte
ns
ity
(a.u
.)
qz (Å-1)
0.5 1.0 1.5 2.0
0
2000
4000
6000
0 mol%
PCDTFBTOut-of-plane
Inte
ns
ity
(a.
u.)
qz (Å-1)
45 mol%
0.5 1.0 1.5
0
1000
2000
3000
400045 mol%
PCDTFBTIn-plane
0 mol%
F4TCNQ crystal
Inte
ns
ity
(a.u
.)
qxy
(Å-1)
a
b
c
d
e
f
0.5 1.0 1.5 2.0
0
1000
2000
3000
13 mol%
P3HTIn-plane
0 mol%
Inte
ns
ity
(a.u
.)
qxy
(Å-1)0.5 1.0 1.5
0
1000
2000
3000
13 mol%
P3HTOut-of-plane
0 mol%
Inte
ns
ity
(a.u
.)
qz (Å-1)
0.5 1.0 1.5
0
1000
2000
3000
4000
0 mol%
PCDTPTIn-plane 45 mol%
Inte
ns
ity
(a.u
.)
qxy
(Å-1)
18
Fig. S15. Surface morphologies of the doped polymer films. Atomic force microscopy
topographic images of the doped (a) PCDTFBT (5 mol%), (b) PCDTPT (5 mol%), and (c)
P3HT (5 mol%) films with root-mean-square roughness (Rq) values, which were obtained with
a XE-150 microscope, Park Systems.
19
Table S2. Variations of the (100) d-spacing values of the PCDTFBT, PCDTPT, and P3HT
films observed after doping with F4TCNQ.
F4TCNQ ratio
(mol%)
PCDTFBT PCDTPT P3HT
qz (Å-1) d (Å) qz (Å-1) d (Å) qz (Å-1) d (Å)
0 0.2816 22.3 0.2707 23.2 0.3830 16.4
2 0.2780 22.6 0.2688 23.4 0.3559 17.7
5 0.2725 23.1 0.2670 23.5 0.3541 17.7
9 0.2780 22.6 0.2707 23.2 0.3505 17.9
13 0.2725 23.1 0.2725 23.1 0.3487 18.0
20 0.2725 23.1 0.2688 23.4
30 0.2743 22.9 0.2634 23.9
38 0.2725 23.1 0.2670 23.5
45 0.2670 23.5 0.2579 24.4
20
Fig. S16. Pole figures obtained from the (100) diffraction peaks of neat and the doped (a)
PCDTFBT, (b) PCDTPT, and (c) P3HT polymers. All data were extracted from the 2D-GIXD
patterns depicted in Fig. S7S9.
0 20 40 60 80
0 mol% 2 mol% 5 mol% 9 mol% 13 mol%
P3HT
(degree)
Inte
ns
ity
(a.u
.)
0 20 40 60 80 (degree)
Inte
ns
ity
(a.u
.)
0 mol% 2 mol% 5 mol% 9 mol% 13 mol% 20 mol% 30 mol% 38 mol% 45 mol%
PCDTPT
0 20 40 60 80
0 mol% 2 mol% 5 mol% 9 mol% 13 mol% 20 mol% 30 mol% 38 mol% 45 mol%
PCDTFBT
Inte
ns
ity
(a.u
.)
(degree)
a b c
21
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22
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