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: jyjang15@hanyang.ac.kr (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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