2D coherent charge transport in highly ordered conducting ......PBTTT is one of the most widely...

Supplementary Materials for

2D Coherent Charge Transport in Highly Ordered Conducting Polymers

Doped by Solid State Diffusion

Keehoon Kang∗, Shun Watanabe†, Katharina Broch, Alesandro Sepe, Adam Brown, Iyad

Nasrallah, Mark Nikolka, Zhuping Fei, Martin Heeney, Daisuke Matsumoto, Kazuhiro

Marumoto, Hisaaki Tanaka, Shin-ichi Kuroda, and Henning Sirringhaus‡

∗ These authors contributed equally to this work† These authors contributed equally to this work

‡ To whom correspondence should be addressed; E-mail:[email protected]

This PDF file includes:

A. Materials

B. Composition analysis with X-ray photoelectron spectroscopy (XPS)

C. Device preparations

D. Controllability of doping

E. Generality of doping

F. Details of Hall effect measurements

G. Analysis of magnetoconductance

H. Electron spin resonance measurements

I. Temperature dependence of conductivity of PBTTT/F4-TCNQ

Figures S1 to S20

Tables S1 to S3

A. Materials

PBTTT is one of the most widely investigated semiconducting polymers and exhibits a

high p-type, field-effect mobility up to 1.0 cm2 V−1 s−1. PBTTT-C16 was synthesized and

purified via a standard Stille copolymerization,1 where molecular weight and polydispersity

1

2D coherent charge transport in highly ordered conducting polymers doped by solid state diusion

SUPPLEMENTARY INFORMATIONDOI: 10.1038/NMAT4634

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http://dx.doi.org/10.1038/nmat4634

were measured to be 41 kDa and 1.5. The molecular weight was determined by Agilent

Technologies 1200 series GPC running in chlorobenzene at 80 ◦C, using two PL mixed B

columns in series, and calibrated against narrow polydispersity polystyrene standards. The

PBTTT film was spin-coated from a 10 mg ml−1 1,2-dichlorobenzene solution in a nitrogen

glovebox. The resulting 40-nm thick film was annealed in a nitrogen atmosphere at 180◦C for 20 min, then slowly cooled down to room temperature. The origin of the relatively

high carrier mobility is PBTTT’s semicrystalline lamellar microstructure.1 In addition to the

grazing incidence wide angle X-ray scattering (GI-WAXS) measurements shown in Fig.1 d

in the main text, we confirmed that the present PBTTT film forms a highly-ordered lamellar

structure with well-defined terraces. Figure S1a shows an atomic force microscopy (AFM)

image of the PBTTT film that was spin-coated on a sapphire substrate. The surface is

homogeneous with an r.m.s. surface roughness of 1.9 ± 0.1 nm. The terrace morphology

can be confirmed in the height distribution histogram (Fig. S1b), where the observed step

height ∼ 2.0 ± 0.2 nm is consistent with the molecular step between each polymer lamellae

∼ 2.29 nm.2 Note that there are no morphological differences of PBTTT films on any given

substrates (sapphire, Corning glass, and SiO2/Si substrate).

0 1 2

0

1

2

a

0

10

(nm)

x (µm)

y (

µm

)

b

0 5 10 15 200

1000

2000

3000

4000

Height (nm)

He

igh

t in

ten

sity (

a.u

.)

Figure S1: Terrace-like surface morphology of semicrystalline PBTTT a 2 µm × 2 µm

AFM image of PBTTT spin-coated on a sapphire substrate. b A typical height distribution

histogram. The film thickness and r.m.s. surface roughness were measured to be approximately 40

± 2 nm and 1.9 ± 0.1 nm.

F4-TCNQ is an organic small molecule having a strong electron affinity, which originates

2


from its fluorinated core structure. The powder was purchased from Sigma-Aldrich, and was

used without any purification (purity ∼ 97 %). The film was deposited via evaporation at

a base pressure of 2 × 10−7 mbar with a rate of 1 - 2 Å s−1 (nominal thickness was 25 nm).

The dopant molecules diffuse into the bulk of the PBTTT film during the evaporation and

storage of the film at room temperature after deposition, nearly all the way down to the

substrate, which is confirmed by X-ray photoemission spectroscopy (XPS) measurements,

as shown in Section B.

Figures S2a and b show AFM images of the PBTTT (40 nm) films that were spin-coated

on a sapphire substrate. The observed surface is homogeneous in the large-area scan shown

in Fig. S2a. The terrace morphology can also be seen in a small-area scan shown in Fig. S2b.

In contrast to the smooth surface of the PBTTT film, a typical 3D small molecule grain

morphology is confirmed for F4-TCNQ films deposited onto sapphire substrates (Figs. S2c

and d); the grain size is estimated to be 500 nm. When F4-TCNQ was evaporated onto a

pre-deposited film of PBTTT (Figs. S2e and f) in excess, such that in spite of the diffusion

of F4-TCNQ molecules into the polymer film, grains of pure F4-TCNQ remained on the

surface, we found a similar 3D growth mode on the surface of the PBTTT film as on the

sapphire substrates. The surface morphology of the F4-TCNQ films deposited on PBTTT is

subtly different from those deposited on sapphire substrates, presumably because of different

substrate surface energy.

One of the most significant discoveries demonstrated in the study is an enhanced struc-

tural order in the lamellar structure for PBTTT by the introduction of the F4-TCNQ small

molecule. The observation that the lamellar spacing along the side-chain direction increases

after depositing the F4-TCNQ molecules, while the corresponding π-stacking diffraction

does not change, shows that the F4-TCNQ molecules intercalate preferentially into the

layer of side chains of PBTTT. This can be rationalised by comparing the size of a F4-

TCNQ molecule, which is small enough (approximately 1.6 nm)3 to the side-chain distance

of PBTTT (2.0 nm). To be able to further justify the bulk doping in the present case, we

performed angle of incidence dependent GI-WAXS measurements on films fabricated onto

a SiO2 (100 nm)/Si substrate, shown in Fig. S3 and Fig. S4. 2D-GIWAXS images both for

the doped and pristine PBTTT films were taken with the same condition as shown Fig.1 in

the main text and they were evaluated using HipIES. The peaks along the direction of qz,

3


54321

5

4

3

2

1

0 5 10 150

5

10

15a

0

20

(nm)

x (µm)

y (

µm

)

00

b

0

15

(nm)

y (

µm

)

54321

5

4

3

2

1

0 5 10 150

5

10

15c

0

50

(nm)

x (µm)

y (

µm

)

00

d

0

40

(nm)

y (

µm

)

x (µm) x (µm)54321

5

4

3

2

1

0 5 10 150

5

10

15e

0

120

(nm)

x (µm)

y (

µm

)

00

f

0

100

(nm)

y (

µm

)

x (µm)

Figure S2: Surface image of PBTTT/F4TCNQ. a, b AFM images of PBTTT spin-coated

on a sapphire substrate. c, d Similar scale AFM images of F4-TCNQ thermally-evaporated on the

sapphire substrate. e, f AFM image of the surface of F4-TCNQ directly deposited on top of the

PBTTT layer.

which represents a characteristic d-spacing of each lamellae parallel to the substrate surface,

are observed to be independent of the X-ray incidence angle. The penetration depth of

the incident X-ray is estimated to be roughly 1 nm at 0.1◦, 10 nm at the critical angle of

0.15◦ and much larger at angles above the critical angle.4 This strongly suggests that the

heterostructure of PBTTT and F4-TCNQ retains a highly ordered structure all the way

down to the substrate with a uniform lamellar spacing throughout the film. The change in

the intensity of the peaks for incidence angles above/below and close to the critical angle

of the sample of 0.15 degrees is caused by the enhancement of the scattered intensity by a

factor of 3 - 4 for measurements with an angle of incidence close to the critical angle.5 More

details are shown in the out-of-plane scattering profiles in Figs. S4a and b.

4


0.13 O

0.0 0.5 1.0 1.5 2.0

0.0

0.5

1.0

1.5

2.0

qz

(Å-1)

qxy

(Å-1)

0.10 O

0.0 0.5 1.0 1.5 2.0

0.0

0.5

1.0

1.5

2.0

qz

(Å-1)

qxy

(Å-1)

0.20 O

0.0 0.5 1.0 1.5 2.0

0.0

0.5

1.0

1.5

2.0

qz

(Å-1)

qxy

(Å-1)

0.16 O

0.0 0.5 1.0 1.5 2.0

0.0

0.5

1.0

1.5

2.0

qz

(Å-1)

qxy

(Å-1)

0.0 0.5 1.0 1.5 2.0

0.0

0.5

1.0

1.5

2.0

qz

(Å-1)

qxy

(Å-1)

0.0 0.5 1.0 1.5 2.0

0.0

0.5

1.0

1.5

2.0

qz

(Å-1)

qxy

(Å-1)0.0 0.5 1.0 1.5 2.0

0.0

0.5

1.0

1.5

2.0

qz

(Å-1)

qxy

(Å-1)0.0 0.5 1.0 1.5 2.0

0.0

0.5

1.0

1.5

2.0

qz

(Å-1)

qxy

(Å-1)

Figure S3: Angular dependence of GI-WAXS images. 2D-GIWAXS images on thin films

of PBTTT/F4-TCNQ (top) and pristine PBTTT (bottom), where the angle of grazing incidence

was adjusted to be 0.10, 0.13, 0.16, and 0.20◦ (from left to right). Each thin film was deposited on

a silicon substrate following the same process as described above.

5


0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.20 0.25 0.30 0.35 0.40 0.45 0.50

0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.18 0.19 0.2 0.3

Inte

gra

ted

In

ten

sity

(a

.u.)

0.10 0.11 0.12 0.13 0.14 0.15 0.16 0.18 0.19 0.2 0.3

Inte

gra

ted

In

ten

sity

(a

.u.)

q (Å-1) q (Å-1)

PBTTT F4TCNQ PBTTT

a b

Figure S4: Out-of-plane scattering profiles on semicrystalline PBTTT. Out-of-plane

diffraction along qz on a, PBTTT/F4-TCNQ, and b, pristine PBTTT, with different grazing inci-

dence angles.

6


The second target system under investigation is PEDOT:PSS. A commercially available

water-based ink of PEDOT:PSS (Clevios PH1000, Heraeus) was used. Dimethyl sulfoxide

(DMSO, Sigma-Aldrich) and Dynol 607 were mixed into the ink as additional dopant and

surfactant to optimize the electrical conductivity. A compositional ratio was adjusted to

be 94.5 wt% PEDOT:PSS, 5 wt% DMSO, 0.5 wt% DynolTM607. After the spin-coating,

the resulting films were then annealed in a nitrogen atmosphere at 180 ◦C for 2 hours.

Figures S5a and b show 15 µm × 15 µm and 3 µm × 3 µm AFM images of the PEDOT:PSS

films that were fabricated on a SiO2 (300 nm)/Si substrate. A mesh-like surface morphology

can be observed with brighter and darker regions, which have been interpreted as PEDOT-

rich and PSS-rich regions, respectively.6 In contrast to the surface of the semicrstalline

PBTTT films, no terrace morphology is seen in the height distribution histogram shown in

Fig. S5c.

0 5 10 150

5

10

15a

0

20

(nm)

x (µm)

y (

µm

)

b

0

15

(nm)

y (

µm

)

x (µm)0 1 2 3

0

1

2

3

c

0 5 10 15 200

500

1000

1500

Height (nm)

He

igh

t in

ten

sity (

a.u

.)

Figure S5: Surface of disordered PEDOT:PSS a 15 µm × 15 µm and b 3 µm × 3 µm

AFM images of PEDOT:PSS spin-coated on a SiO2 (300 nm)/Si substrate. c A typical height

distribution histogram. The film thickness and r.m.s. surface roughness were measured to be

approximately 50 ± 5 nm and 3.5 ± 0.2 nm.

B. Composition analysis with X-ray photoelectron spectroscopy (XPS)

Identification of elements with XPS

From GIWAXS measurements, it has already been shown that F4-TCNQ molecules are

likely to reside in the side-chain region and increase the lamellar stacking distance. To

corroborate this structural model XPS depth profiling measurements were performed to

7


determine the composition ratio of PBTTT to F4-TCNQ as function of depth in the film.

The sample was prepared on a SiO2 (300nm)/Si substrate in the same way as described in

Section A. XPS measurements were used to determine the atomic composition by fitting

XPS scans which are shown in Fig. S6. The scans clearly show that the film is composed of a

mixture between PBTTT and F4-TCNQ. The carbon composition is from both PBTTT and

F4-TCNQ, sulphur from PBTTT, nitrogen and fluorine from F4-TCNQ. A small contribu-

tion of silicon is likely to originate from siloxane impurities in the atmosphere, in the polymer

starting material or introduced during processing.7 The oxygen contamination is expected

to originate from unintentional atmospheric exposure or from contaminants such as siloxane.

1200 1000 800 600 400 200 0

0

2

4

6

8

10

12

14

300 290 280

410 400 390

110 100540 530

170 160700 690 680

Co

un

ts (

10

4 s

-1)

Binding Energy (eV)

10

00

20

00

0

10

00

50

01

00

00

40

00

Binding Energy (eV)

Co

un

ts (

s-1)

C K

L1

F K

L1 F 1

s

N 1

s

C 1

sS

2s

S 2

p

a

b

F 1s N 1s

O 1s C 1s

S 2p

Si 2p

Figure S6: XPS Scans for identifying constituent elements a Survey scans showing peaks

for different elements b High resolution XPS scans for F 1s, N 1s and S 2p (top row), O 1s, C 1s

and Si 2p (bottom row). The XPS measurements were performed with ESCALAB 250Xi X-ray

Photoelectron Spectrometer (XPS) produced by Thermo ScientificTM in a high vacuum condition.

Molecular ratio and charge density PBTTT/F4-TCNQ (25nm)

8


In addition to the survey scan, spectra around the peaks for each element were measured

by integrating 20 times to give an accurate atomic composition shown in Fig. S7a. The

atomic composition obtained from the scan shown was used to determine the composition

of the film in terms of the ratio of the number of F4-TCNQ molecules to PBTTT repeat

units. The depth profile of the composition ratio was characterised by measuring XPS scans

while etching the film with an in-situ Ar ion-beam. The Ar ion-beam etches the film all the

way down to the substrate as confirmed from the composition of silicon and oxygen which

rises to a significant value at 40 nm. The ratio of F4-TCNQ to PBTTT molecules can be

calculated by relative atomic composition percentage of N and F atoms compared to C and

S, based on the molecular formula of PBTTT-C16 , (C46H70S4)n, and F4-TCNQ, C12F4N4.

The resulting depth profile of the ratio is shown in Fig. S7c which shows a large ratio at

the surface (bigger than 1) which represents an excess layer of F4-TCNQ formed on top of

the PBTTT film. The ratio decreases deeper in the film but a finite ratio in the ratio down

to 40 nm implies a dopant penetration all the way down to the substrate. According to the

molecular formula, the ratio of the nitrogen composition should be the same as that of the

fluorine. The discrepancy is due to the error in fitting and was represented as the error in

the molecular ratio as shown in Fig. S7c. The same analysis was done for a thinner layer

of F4-TCNQ (15 nm) eavaporated on PBTTT to produce Fig. 1c of the main manuscript

which is explained further in the section below.

The nearly-ideal Hall effect demonstrated in the work relies on an accurate determina-

tion of the mobile charge carriers. The charge density of 3.3 ± 0.2 × 1020 cm−3 from

ESR measurement (Section F) corresponds to 39 ± 3 % of the PBTTT monomer units

doped; for this we estimated the PBTTT monomer density in the film from unit cell val-

ues for PBTTT-C168 and measured π-π stacking distance and out-of-plane d-spacing. The

estimate of 3.3 ± 0.2 × 1020 cm−3 from ESR was found to be consistent with two other

independent measurements. The depth profile of the XPS provides the average molecular

ratio of F4-TCNQ to PBTTT of 0.62 ± 0.13 which can be used to calculate the anion

density when combined with the fraction of the number of F4-TCNQ− ions to the total

number of F4-TCNQ molecules, which is accessible by both XPS and Fourier transform

infrared spectroscopy (FTIR) absorption measurements. The high resolution N 1s XPS

9


scan provides information about the degree of charge transfer in F4-TCNQ molecules, and

hence the fraction of F4-TCNQ− ions. The spectrum can be decomposed into two peaks

centred at binding energies of 398 and 399 eV, corresponding to the contribution from F4-

TCNQ molecules that have undergone charge transfer and that have not, respectively.9,10

This analysis can be applied throughout the whole film, as shown in the depth profile of

the scans in the Fig. S7b. The fraction of F4-TCNQ− ions out of total F4-TCNQ molecules

can then be determined at each depth from integrating both peaks. The fraction is small

at the uppermost surface (0 nm) which implies that the top excess layer of F4-TCNQ is

electrically neutral. The fraction then increases and stays nearly constant down to 40 nm

which represents a nearly constant degree of charge transfer in the bulk of the film. The

average fraction in the film is calculated to be 0.34 ± 0.20 from the depth profile shown

in Fig. S7d. This agrees with an independent estimate of this fraction obtained from FTIR

absorption spectra as shown in Fig. S7e. The vibration feature at 2227 cm−1 arises from b1u

ν18 modes of C≡N and C=C bond stretching of neutral F4-TCNQ molecules.11 The peak at

2193 cm−1 corresponds to b2u ν32 mode of charged species, and therefore it is only present

in PBTTT/F4-TCNQ spectrum. The peak at 2227 cm−1 is significantly bleached for the

doped film compared to the neutral F4-TCNQ film and the fraction of charged F4-TCNQ

molecules can be determined to be 0.65 ± 0.12 from comparing the peak intensities, which

agrees with the value obtained from the XPS N 1s scans within the error. The fraction of

F4-TCNQ− ions can then be combined with the molecular ratio of F4-TCNQ to PBTTT

monomer to calculate the percentage of doped PBTTT monomers in the film as 21 ± 13

% from XPS and 40 ± 12 % from FTIR, respectively, assuming every F4-TCNQ that has

undergone charge transfer donates one hole to PBTTT. These values are both in reasonable

agreement with the percentage value of 39 ± 3 % from ESR.

In addition, the UV-Vis absorption spectrum shown in Fig. 1b of the main text

shows a significant bleaching of the neutral transition at 555nm. The reduction in

the peak is roughly 50 % in intensity when the background absorption of the neutral

F4-TCNQ molecules is taken into account. This is higher than 39 % determined from

ESR which reflects a sufficient charge carrier delocalisation that bleaches half of the active

PBTTT sites12; each charge carrier on PBTTT is delocalised over more than one repeat unit.

10


0 10 20 30 400.1

1

10

100

A

tom

ic C

om

postion (

%)

Depth (nm)

C 1s

N 1s

F 1s

S 2p

O 1s

Si 2p

a b c

d

2150 2200 225076.4

76.6

76.8

77.0

77.2

77.4

77.6

F4-TCNQ

PBTTT

PBTTT/F4-TCNQ

Ab

so

rba

nce

(%

)

Wavenumebr (cm-1)

e

0 10 20 30 400.0

0.5

1.0

1.5

2.0

2.5

Depth (nm)

(F

4-T

CN

Q/P

BT

TT

)

Mo

lecu

lar

Ra

tio

0 10 20 30 400.0

0.2

0.4

0.6

0.8

1.0

Depth (nm)

405 400 395Binding Energy (eV)

0 nm

0.8 nm

1.6 nm

4.9 nm

6.6 nm

10.3 nm

15.2 nm

25.0 nm

35.0 nm

5000

Co

un

ts (

s-1)

Ra

tio

(ch

arg

ed

/to

tal F

4-T

CN

Q)

Figure S7: Depth profile of XPS and doping ratio a Depth profile of the atomic composition

in the film b N 1s scans(top) and the fit for the scans (bottom)at different depths from 0.1 to 35

nm. The black lines represent the limits between which the peak binding energies are distributed

for each spectrum. c Molecular ratio of number of F4-TCNQ molecules to PBTTT repeat units

at different depths. The error is from the fitting. d Ratio of the number of F4-TCNQ molecules

that have undergone charge transfer out of the total number of F4-TCNQ molecules. The error

bars represent error from the fitting. e FTIR absorption spectra of three different thin films,

pristine PBTTT (blue), doped PBTTT (red) and F4-TCNQ (green), used to determine the degree

of charge transfer between F4-TCNQ and PBTTT. All samples were fabricated as described in

Section A on silicon substrates with a native oxide of 2 nm. The PBTTT film for both pristine and

doped samples were prepared at the same time. The 20 nm of thermally evaporated F4-TCNQ was

deposited at the same time in neutral F4-TCNQ sample and doped PBTTT sample so that equal

amount of F4-TCNQ molecules were deposited. The peak at 2227 cm−1 for the neutral F4-TCNQ

is bleached in the doped PBTTT, representing charge transfer of F4-TCNQ.All FTIR spectra were

recorded in transmission mode with a Thermo Nicolet Nexus 870 FTIR spectrometer while the

sample chamber was constantly purged with nitrogen.

Comparison with PBTTT/F4-TCNQ (15nm) and doping ratio profile

The XPS result shown above is measured with 25 nm of F4-TCNQ deposited on top

of PBTTT film. As seen from the AFM image in Figs. S2c and d, the excess F4-TCNQ

molecules that have not penetrated form a neutral layer on the surface with a rms roughness

11


of 23 nm. This potentially limits the depth resolution of the depth profile data of XPS mea-

surements. To confirm the resolution of the depth profile in the XPS, AFM measurements

were performed in conjunction with the XPS measurement for a doped PBTTT film with a

smaller thickness of F4-TCNQ (15 nm) deposited on top of the PBTTT layer.

The thinner film of F4-TCNQ resulted in a smoother surface with a rms surface roughness

of 15.5 nm on the surface (Fig. S8a). However, the roughness decreased to 5 nm as the film

was etched with the Ar ion beam for 150 s (Fig. S8b), and decreased further to 2 nm when

etched for 300 s (when roughly 5 nm of the film was etched from the surface). As shown in

Fig. S8c, the roughness becomes small enough such that horizontal streaks that represent

the scans of Ar ion beam can be seen. Therefore, the depth resolution for the XPS data

presented in Fig. S8d would be fine enough to represent the steps of 2 nm from the film

depth of 5 nm onwards. This justifies the accuracy of the depth profile of the molecular

ratio data shown in the Fig. 1 c of the main manuscript. The smaller roughness could result

from preferential sputtering of F4-TCNQ molecules compared to PBTTT molecules due to

a lower molecular mass of F4-TCNQ. This can also result in underestimating the ratio of

F4-TCNQ molecules to PBTTT at each depth, and therefore the obtained ratio values in

Fig. 1c of the main manuscript are the lower limit. The molecular ratio is calculated to

be much smaller on the surface (0 nm) but only slightly smaller in the bulk compared to

Fig. S7c, representing a thinner excess neutral F4-TCNQ layer on top of the PBTTT on the

surface, but only slightly less F4-TCNQ penetration to the PBTTT film.

The F4-TCNQ molecules were confirmed to penetrate all the way down to the substrate

as before from a finite molecular ratio down to 40 nm in the depth profile. From the same

analysis of the N 1s peaks as above, the fraction of F4-TCNQ molecules that have undergone

charge transfer were found to be slightly higher in the bulk than PBTTT/F4-TCNQ (25nm)

as shown in Fig. S7d. Combining the two ratios, the fraction of the doped PBTTT

monomers (doping ratio) can be calculated by multiplying the molecular ratio of F4-TCNQ

to PBTTT monomers with the fraction of charged F4-TCNQ molecules to the total number

of F4-TCNQ molecules (see above section). Variation of the resultant doping ratio with

depth is shown in Fig. S8f for the two different thicknesses of F4-TCNQ deposited on

PBTTT. The depth profile reveals a smaller doping ratio at the surface which reveals the

neutral F4-TCNQ layer, again. Although the doping ratio increases initially for the first

few nm, the doping ratio remains fairly constant throughout the film, representing a nearly

12


uniform charge concentration in the bulk. Especially, below 5 nm, the doping ratio changes

by less than factor of 2. The doping ratios for the two different F4-TCNQ thicknesses agree

within the error except the first few nm of the film, implying a similar charge concentration

profile in the two films. The average percentage of doped PBTTT monomers is found to be

20 ± 10% which is in a reasonable agreement with the estimates in the above section.

0 10 20 30 40

0.1

1

10

100

Ato

mic

Co

mp

ostio

n (

%)

Depth (nm)

C 1s

N 1s

F 1s

S 2p

O 1s

Si 2p

d e f

0 10 20 30 400.0

0.2

0.4

0.6

0.8

1.0

Ra

tio

Depth (nm)

0 10 20 30 400.0

0.2

0.4

0.6

0.8

1.0

25 nm

15 nm

Depth (nm)

a

0

140

(nm)

b c

0

100

(nm)

0

20.4

(nm)

t = 0 s (0 nm) t = 150 s (2.6 nm) t = 300 s (5.2 nm)

(ch

arg

ed

/to

tal F

4-T

CN

Q)

Do

pin

g r

atio

(do

pe

d/to

tal P

BT

TT

)

Figure S8: Comparison of doping ratio for PBTTT/F4-TCNQ (15nm) AFM images at

different Ar ion beam etching times while measuring depth profile at a 0 s, b 150 s and c 300 s. The

probed depths are calculated to be 0 nm, 2.6 nm and 5.2 nm, respectively. d Depth profile of the

atomic composition in the film. e Ratio of the number of F4-TCNQ molecules that have undergone

charge transfer out of the total number of F4-TCNQ molecules calculated from the same analysis

of N 1s peaks at each depth (Fig. S7b). The error bars represent error from the fitting. f The

depth profile of the fraction of doped PBTTT monomers (doping ratio) for PBTTT/F4-TCNQ

(15nm) in black and PBTTT/F4-TCNQ (25nm) in red circles. The doping ratios for the two films

agree very well in the bulk of the film. The error was calculated from error propagation of the

errors from fitting of the molecular ratio and fraction of F4-TCNQ anions.

13


C. Device preparations

Hall effect and magnetotransport measurements were performed using a Hall bar

architecture, where the conductive PBTTT/F4-TCNQ layer was patterned in order to

accurately measure local potential of probes. The fabrication process for the Hall bars

was as follows: A 0.5 mm-thick sapphire substrate was cleaned by a sonication cleaning

processes in deionized water, acetone, and isopropanol. After further cleaning by an oxygen

plasma treatment (250 W for 10 mins), electrodes were lithographically formed via a

standard double-layer lift off process. The electrode consisting of chromium (Cr, 1.5 nm)

and gold (Au, 20 nm) were thermally evaporated at the base pressure of 1 × 10−6 mbar

with a rate of 0.2 Å s−1. Here, the Cr layer was to improve adhesion between Au and

the sapphire substrates. Channel length (L) and width (W ) were 240 µm and 80 µm.

Four probes were mounted in between source and drain electrodes, where the distance

between two longitudinal probes along the channel length (defined as L∗) was designed to

be either 80 or 120 µm. The width of the probe was 15 µm. After completing the elec-

trodes, the PBTTT layer was spin-coated onto the sapphire substrates, then F4-TCNQ was

thermally evaporated directly on the top of the PBTTT layer (the details were shown above).

In order for the PBTTT/F4-TCNQ layer to form a precise Hall bar geometry, the second

photolithographic process was performed as follows.13,14 A 100 nm-thick CYTOP (Asahi

Glass) was spin-coated on the PBTTT/F4-TCNQ layer immediately after the F4-TCNQ

deposition. In addition to the CYTOP layer, a 1.5 nm-thick aluminum (Al) was thermally

deposited and exposed to air, forming native oxide, resulting in the surface of the CYTOP

layer being hydrophobic. The second lithography process involved oxygen plasma ashing

(300 W for 30 mins) which etched away the PBTTT/F4-TCNQ layer where the second

photoresist layer was not covered. The second photoresist layer remained as a protection

layer for the active channel. All processes were carried out under cleanroom conditions with

controlled humidity and temperature. The Hall bar devices were used to confirm an efficient

nature of doping; upon doping, the conductivity increases by six orders of magnitude as

shown in Fig. S9. The current is linear with the applied voltage, indicating that the doped

film achieves an Ohmic contact with the gold electrodes.

14


-1.0 -0.5 0.0 0.5 1.0

10-7

Voltage (V)

10-11

10-9

10-5

10-3

|Cu

rre

nt | (A

)

Linear fitF4-TCNQ

Doped

PBTTT

Figure S9: Current-Voltage (I-V ) characteristics of Hall bars a I-V characteristics of pris-

tine PBTTT (blue), doped PBTTT (red) and F4-TCNQ devices fabricated in Hall-bar geometry.

The solid lines represent linear I-V curves (Ohm’s law) which demonstrate the Ohmic contacts

achieved. I-V traces were measured with a Hall bar geometry, where the channel length (L) and

width (W ) were 240 µm and 80 µm.

15


D. Controllability of doping

The doping method employed is not only highly efficient but controllable such that the

conductivity can be tuned to a range of values. The degree of doping can be controlled

both by controlling the amount of F4-TCNQ deposited during thermal evaporation as

shown in Fig. S10 and de-doping by annealing the films after the evaporation (Fig. S11).

The amount of F4-TCNQ was varied by varying the nominal thickness of the F4-TCNQ

deposited in the evaporation. The conductivity achieved for 10 nm of F4-TCNQ deposited

was 200 S cm−1 and the conductivity saturates (Fig. S10b) as the thickness increases

further, indicating that the doping level is also saturated.

-0.1 0.0 0.1

Voltage (V)

Co

nd

uctivity (

S/c

m)

10 nm 5 nm 3 nm 2 nm

F4-TCNQ nominal thickness (nm)

a b

10-7

10-8

10-5

10-4

|Cu

rre

nt | (A

)

10-6

10-9

1000

100

10

10 5 10 15 20 25 30

Figure S10: Conductivity variation with degree of doping a I-V characteristics of doped

PBTTT films with 2 nm (blue), 3 nm (green), 5 nm (pink) and 10 nm (red) of F4-TCNQ deposited

in the evaporation fabricated into Hall bar geometry. I-V traces were measured with a Hall bar

geometry, where the channel length (L) and width (W ) were 240 µm and 80 µm. b The resulting

conductivity change with the different thicknesses of F4-TCNQ evaporated on PBTTT.

In order to investigate the dopant penetration/doping ratio profile in the polymer

film, conductivity was measured for devices with different thicknesses of PBTTT film

16


b c

-0.1 0.0 0.1

Voltage (V)

10-7

10-10

10-8

10-5

10-4|C

urr

en

t | (A

)

10-6

10-9

10-11

10-12

10-13

10-14

a

60 °C and 90 °C

120 °C

150 °C

180 °C

Post-annealing temperature (°C)

60 80 100 120 140 160 180

100

10-3

10-1

102

103

Co

nd

uctivity (

S c

m-1) 101

10-2

10-4

10-5

0.1

0.3

0.4

Ab

so

rba

nce

(a

.u.)

0.2

0.0

Wavelength (nm)

200 400 600 800 1000 1200

90 °C120 °C150 °C180 °C

60 °C

Figure S11: Tuning conductivity by dedoping a I-V characteristics of doped PBTTT films

after annealing sequentially for 30 minutes each at 60◦C (red), 90◦C (pink), 120 ◦C (orange), 150 ◦C

(green) and 180 ◦C (blue). b The resulting conductivity change by the dedoping at each annealing

temperature. c UV-Vis absorption spectrum taken after the annealing at each temperature. The

spectrum for 180 ◦C is almost the same as that of a pristine PBTTT, reflecting the full range of

doping achievable by the dedoping method.

with the same amount of F4-TCNQ evaporated. The thickness of the PBTTT film was

varied by varying the spin-coating speed which allowed the range of thicknesses from 20

nm to 94 nm, as shown in Figs. S12a and b. The measured conductivity is relatively

constant up to the thickness of 60 nm and it decreases significantly at the thickness of

94 nm (Fig. S12c). This indicates that the depth profile of the doping is nearly constant

for the films thinner than 60 nm, and therefore the films are nearly uniformly doped.

It also means that the depth profile of conductivity in the films are nearly the same,

with a uniform conductivity profile in the bulk. If we assume a nearly uniform charge

density in the bulk (see Section B), the mobility profile is also expected to be uniform

in the bulk. The conductivity of the film of 94 nm thickness is almost half of that of

the fully doped films, suggesting the dopants only diffuse half-way through the thick-

ness. The lower conductivity values of the devices in general is due to a lower amount of

F4-TCNQ deposited (6 nm, instead of 10 nm which is required to saturate the conductivity).

17


200 400 600 800 1000

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 1000 2000 3000 4000 5000

20

40

60

80

100

Ab

so

rba

nce

(A

U)

Wavelength (nm)

500 rpm

750 rpm

1000 rpm

1500 rpm

3000 rpm

5000 rpm

Th

ickn

ess (

nm

)rpm

10 20 30 40 50 60 70 80 90 1000

20

40

60

80

100

120

140

160

Co

nd

uctivity (

S/c

m)

Thickness (nm)

a b c

Figure S12: Thickness dependence of PBTTT a UV-Vis spectrum of different thicknesses

of PBTTT films (prior to doping) prepared by various spin-coating speeds specified in the legend.

b The resulting thickness calibration with the peak absorbance values from a. c Conductivity

measured by four-point probe measurements with Hall bar devices made with the thicknesses of

PBTTT specified in b. A nearly constant conductivity up to 60 nm thickness shows that the

dopants penetrate fully into the polymer film.

18


E. Generality of doping method

The doping method demonstrated in the paper was also found to be an effective doping

method for PBTTT with different lengths of alkyl side-chains and P3HT. Specular scans

were measured by X-ray diffraction (XRD) techniques to show a similar structural change

in the out-of-plane lamellar spacing (along qz) in the different polymer films doped with

F4-TCNQ. From the XRD data in Fig. S13, the lamellar spacing between the polymer

backbones increases upon doping for all the polymers. This implies the same intercalation

structure of F4-TCNQ molecules between the polymer backbones in the alkyl side-chain

regions. The conductivity increase in P3HT is five times bigger than the highest reported

value of 1 S cm−1 for solution-doped P3HT with F4-TCNQ15 although the device was not

optimised. Broad peaks in the diffraction peaks in the XRD data for P3HT also suggest that

the crystallinity in the films can be optimised further. Furthermore, the doping could be

applied to a polycyclopentadithiophene-benzothiadiazole donor-acceptor co-polymer (CDT-

BTZ) with an order of magnitude higher conductivity of S cm−1 than P3HT, demonstrating

diversity of the employed doping method.

Table 1: Comparison of conductivity values

Polymer Conductivity (S cm−1)

PBTTT-C10 161

PBTTT-C14 248

PBTTT-C16 230

P3HT 5.3*

CDT-BTZ 63

Maximum value obtained from measurements

*conductivity value for unoptimised device

19


0.2 0.3 0.40.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

No

rm. in

ten

sity

(a

.u.)

qz (Å-1)

0.5 1.00.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

No

rm. in

ten

sity

(a

.u.)

qz (Å-1)

P3HT

0.5 1.00.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

No

rm. in

ten

sity

(a

.u.)

qz (Å-1)

PBTTT-C10

PBTTT-C14

0.5 1.00.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1.0

No

rm. in

ten

sity

(a

.u.)

qz (Å-1)

PBTTT-C16

pristine doped

a b c

d

pristine doped

pristine doped

pristine doped

0.2 0.3 0.40.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

No

rm. in

ten

sity

(a

.u.)

CPDT-BTZ

pristine doped

qz (Å-1)

e

Figure S13: XRD data for different side-chains of PBTTT and P3HT The XRD measure-

ments show a shift in diffraction peak when pristine films (black line) are doped with F4-TCNQ (red

line) for a PBTTT-C10, b PBTTT-C14, c PBTTT-C16, d P3HT and e CDT-BTZ. This implies

dopant molecules intercalating in the alkyl side-chain regions to facilitate doping.

20


F. Details of Hall effect measurements

Hall effect measurements

After wiring using a wedge bonder, the completed Hall bar was inserted into a He gas-

exchange cryostat with a superconducting magnet, where an external magnetic field B was

applied perpendicular to the sample plane. The magnitude of B and temperature T have

been initially calibrated by a Si diode and GaAs Hall sensor, where uncertainties of T and B

were measured to be less than 0.1 %. The longitudinal voltage ∆Vxx, and transverse ∆Vxy

voltage were recorded with a constant d.c. current, I, when B was ramped up and down

to 8 T and to − 8 T with the sweeping rate of 0.2 T min−1, as shown in Fig. 2b in the

main text. To avoid Joule heating, I was chosen to be less than 5 µA. Prior to the Hall

measurement, we have confirmed that the four probes in the channel measure an ideal local

potential, and a voltage drop due to the contact resistance at the polymer/electrode contacts

was estimated to be less than 0.1 % of the effective voltage applied along the channel length

L. We emphasize that the difference between transverse voltages should be minimized for an

accurate Hall voltage measurement. From the Hall effect measurements, the Hall coefficient,

RH, and Hall mobility, µH, were extracted using the following equations,

|RH| =∆Vxyt

IB, (S1)

|µH| = |RH|σ, (S2)

where t is the thickness of the conductive layer, and σ is the four-point-probe conductivity

measured from σ = IVxx

L∗

Wt. Practically, to minimize the experimental uncertainty in the

eq. (S1), |RH| was extracted by taking a slope of ∆Vxy between 8 and − 8 T, resulting in

|RH| = tId(∆Vxy)dB

. The uncertainties of RH and µH were estimated to be less than 1 % because

the temporal ∆Vxy drift due to device degradation is negligible in the present samples (the

conductivity drift was measured to be less than 0.05 % ). The coherence factor, γH, is

defined as16

γH = ne

|RH|−1 , (S3)

where n is the charge concentration, and e is the elemental charge, and represents degree

21


of phase coherence, and therefore how ideal the measured Hall effect is, i.e. it is 1 when the

transport is ideal which reproduces the ideal Hall effect formula. The coherence factor also

represents a finite deviation of Hall mobility from drift mobility, µD, as

µH = γH ∗ µD, (S4)

where µH is the Hall mobility. Taking account into the coherence factor of 0.6 in

PBTTT/F4-TCNQ at room temperature from Fig. 2f of the main text, the drift mobility is

estimated to be even higher value of 3.2 cm2 V−1 s−1. The Hall coefficient can also deviate

from reciprocal of charge density ( 1ne

in Eq. S3) not due to decoherence but energy dependent

scattering rate which is represented by another factor known as Hall scattering factor, rH, in

the place of γH in Eq. S3. For phonon and alloy scattering or ionised impurity scattering, rH

are either 1.18 or 1.93 for non-degenerate spherically symmetric bands, respectively.17 Due

to a high conentration of F4-TCNQ anions present, we would expect the ionised impurity

scattering would contribute to charge transport. However, the magneto-conductance data

support carrier-carrier scattering mechanism from the temperature dependence of phase co-

herence time (see main Fig. 3c). We can justify this empirical evidence with the fact that

the doping method proposed achieves a spatial isolation of dopants and conduction channels

(i.e. polymer chain) akin to modulation doping. As F4-TCNQ anions reside in the side chain

regions the electric field is likely to be at least partially screened by a large concentration

of charges in the polymer chains. Therefore, it would be still possible to have carrier-carrier

scattering as a dominant scattering path in addition to the expected ionised impurities. The

small discrepancy of charge concentration measured from ESR (3.3 ± 0.2 × 1020 cm−3)

and that extracted from Hall coefficient at lowest temperatures could possibly indicate the

emergence of non-unity Hall scattering factor since γH becomes 1.3 at 25 K (see main

Fig. 2h). However, this is only speculative and close to the measurement accuracy at low

temperatures.

It should be noted that the measured transverse voltage often contains B-independent

offset voltage (∼ a few mV) presumably due to a misalignment of transverse probes. This

is due to an imperfection in the photolithography. At B = 0 T, the offset is purely due to

the misalignment and can be expressed as V offsetxy = I

σ∆x14Wt

, where ∆x14 is distance between

the transverse probes, as shown in the Fig. S14a, and is estimated to be ∼ 1 µm. It is

reasonable because the resolution of the photolithography process is of the same order ∼ 1

22


µm.

The measured magnetoconductance (MC) is positive and more apparent at lower tem-

peratures (below 95K). This B-dependent, longitudinal voltage due to positive MC contam-

inates the transverse voltage though the misalignment, hence defined as;

V measuredxy (B) = V offset

xy + V offset−MCxy (B) + VHall(B), (S5)

where V measuredxy is the measured transverse voltage, V offset−MC

xy the field-dependent offset

voltage due to the contribution of a positive MC, VHall a pure Hall voltage. The magnitude

of the offset voltage is consistent with the measured MC value and the offset at zero field.

Figure S14b shows V measuredxy at 35K. VHall can be extracted from a fitting with a quadratic

polynomial. We should emphasize that optimizing the Hall bar architecture is the key

engineering process to demonstrate an ideal Hall effect, and it is necessary to minimize the

contact resistance, misalignment as well as device degradation.

P1

-2 0 2 4 6 8

1.73

0

20

40a b

1.72

1.71

1.70

1.69

1.68

1.67

1.66

1.65

B (T)

-4-6-8

-20

-40

-30

-10

10

30

VH

all (m

V)

Vxy

me

asu

red (

mV

)

Vxy

measured

VHall

xL

P2L*

L

Vxy

me

asu

red

B = 0

B ≠ 0

∆x14

Vxy

offset

P3P4

x

Figure S14: Extraction of Hall voltage component from measured transverse voltage

a A schematic diagram showing how a finite voltage offset, V offsetxy , arises due to misalignment of

the probes 1 and 4, ∆x14. V offsetxy decreases when a magnetic field, B, is applied due to a positive

magnetoconductance. b Magnetic field dependence of the measured transverse voltage, V measuredxy ,

and the extracted Hall voltage,VHall, at 35K. VHall was extracted from the quadric polynomial

fitting.

Confirmation of the symmetry of Hall effect and low temperature correction

23


An ideal Hall effect in a π-conjugated polymer had rarely been measured.18–22 The

argument in the main text mainly relies on the quality of the Hall effect measurements. To

be able to further justify our measurements, the symmetry of Hall effect was confirmed by

measuring the Hall voltage under the applied voltage and magnetic field sweep. As shown

in Fig. S15a, the sign of the Hall voltage reverses with reversing the applied voltage V , and

with reversing B, which is found to agree with the equation.

Vxy = µHV BW

L∗, (S6)

where µH is the Hall mobility, V the applied voltage, B the magnetic field, W the width

of the channel, L∗ the length of the channel, respectively. The magnitude of the voltage is

linear in both V and B (Figs. S15a and b).

-60 -40 -20 0 20 40 60-30

-20

-10

0

10

20

30

-6 -4 -2 0 2 4 6

-40

-20

0

20

40

V (

mV

)

B (T)

-20

V (mV)

7.6 4.0

-4.0 -7.6

Vxy (

µV

)

Vxy (

µV

)

20B (T)

0.0

a b

Figure S15: Confirmation of Hall effect symmetry a Contour plot of Hall voltage, Vxy,

for different appied voltage,V , and magnetic field, B. b Vxy variation with V , showing a linear

dependence at different magnetic fields (different colours).

24


G. Analysis of magnetoconductance

Different magnetoresistance effects have been studied in organic semiconductors and con-

ductors. The magnetoconductance (MC) reported in OCSs is mostly negative. In table

we summarize the various effects that have been observed and how they differ from positive

MC due weak localization (WL) observed here.

Table 2: Various magnetoconductance effects in organic materials.

Structure Temperature B-dependence Angular dependence

WL presented work 20- 250 K B2 anisotropic (2D)

doped OSCs sub-15K B2 or B1/2 ? anisotropic (2D)/isotropic (3D)

EEI Doped OSCs 1.5 - 30 K −B2 or −B1/2* isotropic

OMAR NM/OSC/NM 4.2 - 300 K ±B2/(|B|+B0)2 isotropic

ES-VRH Electrochemical transistor 1.5 - 50 K −exp(B2) anisotropic/Isotropic

GMR/TMR FM/OSC/FM 1.5 - 300 K switching at coercive field anisotropic

WL = weak localisation, EEI= e-e interaction, OMAR = organic magnetoresistance, ES-VRH = Eflos-

Shklovskii variable-range-hopping, GMR = giant magnetoresistance, TMR = tunnel magnetresistance, NM

= nonmagnetic metal, FM = ferromagnetic metal,

? B2 when B << Be , B1/2 when B >> Be where Be = ~4eDτ and τ is the elastic scattering time.

*B2 in weak field limit, and B1/2 in strong field limit.

MC for weak localisation is positive due to a magnetic field suppression of the construc-

tive interference for backscattering and can be described by the Hikami-Larkin-Nagaoka

formalism of equation (1) in the Methods section of the main manuscript. The magne-

toconductance can be reduced to B2 or B1/2 dependence depending on the magnitude of

Be = ~4eDτ , where τ is the elastic scattering time.23 Previous reports in doped polyacetylene24

and polyaniline25 have shown a B2 dependence at low-field and temperatures below 5 K.

The estimated phase coherence time time is roughly 100 ps at 1 K for polyacetylene which is

similar to that of doped PBTTT (presented work); for polyaniline a phase coherence length

25


of 167 Å at 4.2K has been extracted. In doped poly(p-phenylenevinylene),26 only a lower

limit for the phase coherence length was estimated to be 240 Å at 2 K from the minimum

field value that fits the B1/2 dependence which is an order of magnitude higher than for

doped PBTTT. However, both the phase coherene time and length strongly depend on how

accurately one can determine the diffusion coefficient, D, in Bφ = ~4eDτφ

. What differen-

tiates the present study from previous studies is the ability to determine D from the Hall

mobility directly extracted from Hall effect measurements. This allows a more accurate de-

termination of both phase coherence time and length compared to the estimates reported in

the above literature which required rough assumptions of density of states, charge concen-

tration, etc. The recently reported positive MC in electrolyte-gated PBTTT27 and doped

polyacetylene28 only report qualitative agreement of MC with WL at temperatures below

15 K. In the ref,28 it is interpreted that the MC in 3D-weak localisation formalism29 which

is normally independent of the field-direction in an isotropic system but anisotropic due to

an anisotropic effective mass tensor. All the other studies above interpret anisotropic MC

as 2D weak localisation with the MC signal vanishing when the magnetic field is applied

longitudinally (in the plane of the current axis), which is confirmed for PBTTT/F4-TCNQ

from the angular dependence measurement of the MC in Fig. 3f.

The isotropic, negative component of the measured MC can be explained by electron-

electron interaction effects23 which arise from Zeeman splitting of spin-up and spin-down

bands and therefore have different behaviour in the two limiting cases: When the Zeeman

energy is larger than the thermal energy (gµBB >> kBT ), MC is expected to be propor-

tional to −B2. When gµBB << kBT we expect the MC to be proportional to −B1/2.

The longitudinal negative MC (positive magnetoresistance) has been observed for other

doped polymer systems, polypyrrole,30 poly(p-phenylenevinylene),26 doped polyacetylene,24

polyaniline25 and electrolyte gated PBTTT.27 Since the mechanism relies on Zeeman split-

ting (spin-effect), the resulting MC should be isotropic with respect to the field direction.

Also, the resulting negative MC is more apparent below 30 K in our in-plane magneto-

conductance measurements (i.e. no WL component) because the Zeeman energy becomes

comparable to the thermal energy, kBT (see Fig. S16). The electron-electron interaction can

be treated as an additive term to the weak localisation component and the total measured

MC has two components.

Another mechanism that can give rise to an isotropic MC is organic magnetoresistance

26


150 K

100 K

80 K

60 K

45 K

35 Kθ = 90 °

0.05 Fit

-8 -4 0 4 8

B (T)

∆G

(μ

S)

Figure S16: Temperature dependence of in-plane magnetoconductance Magnetoconduc-

tance for in-plane B (θ = 90 ◦ in Fig. 3f from the main manuscript) at different T . Magnetocon-

ductance is negative (i.e. magnetoresistance is positive) and parabolic when gµBB << kBT , and

therefore more apparent at low temperatures.

(OMAR) for which different explanations have been proposed. One mechanism involves

magnetic field induced change in exciton population in π-conjugated polymer/fullerene

composite. The exciton population is changed by the modulation of the rates of exciton

formation and decay routes. This effect occurs in bi-polar devices with concurrent electron

and hole injection31,32 and is therefore not applicable to our unipolar conduction system

investigated here. However, an OMAR mechanism has also been proposed for unipolar

conduction.33 This involves the magnetic field influencing the rate for bipolaron formation

in the device, which can lead to large magnetoresistance effects particularly in percolation

systems, where certain conduction paths can effectively be switched off by a spin blockade

mechanism. The magnitude of OMAR effects can be large, 0.1 - 50 %, depending on the

materials and temperature. However, importantly the effect saturates already at small

magnetic field ∼ less than 5 mT; it is fit empirically with MC ∼ ±B2/(|B| + B0)2. The

fact that OMAR is a small field effect is attributed to it being mediated by the hyperfine

interaction. Because the MC presented in the paper does not show saturation up to large

field of several T’s allows us to exclude the OMAR effect as a mechanism. In addition our

measured MC is highly anisotropic, which originates from a two-dimensional transport,

whereas OMAR is isotropic. Giant magnetoresistance and tunnel magnetoresistance effects

can be excluded because both appear only in sandwiched structures with ferromagnetic

electrodes.

27


It has been reported that negative MC associated with the variable-range-hopping (VRH)

including Coulomb interaction effects, Efros-Shklovskii (ES) VRH, which is measurably large

in highly doped polymer system.22 The large negative MC due to ES-VRH may originate

from field-induced suppression of wavefunction overlap, and in a weak field limit, it is pre-

dicted to be σ(B)/σ(0) ∼ −exp(B2). The negative MC can be isotropic or anisotropic

depending on the charge transport. The field localises the wavefuction perpendicular to

the field direction. In a completely amorphous system, the charge transport is isotropic

and therefore the MC is also isotropic. In a system with an anisotropic, semicrystalline

microstructure, the localisation extent of the wavefuction could be anisotropic. The field-

induced localisation should cause a reduction in wavefunction-overlap and therefore a neg-

ative MC; it can not explain the positive MC observed for PBTTT/F4-TCNQ while it may

be a dominant process for the negative MC observed in PEDOT:PSS.

H. Electron spin resonance measurements

X-band (9.5 GHz) electron spin resonance (ESR) measurements were performed with

both a Bruker E500 and JEOL JES-FA200 setup. PBTTT/F4-TCNQ and PEDOT:PSS

films were deposited onto a 3 mm wide × 10 - 20 mm long quartz substrate using a

similar process as described above. We confirmed that the used quartz substrates do

not contribute to any signal and background over a wide temperature range (4 − 300

K). The sample was then inserted into a quartz ESR tube and were purged with 100

mbar of helium gas for heat exchange. The ESR tube was placed in a TE011 cylindri-

cal cavity. For low temperature measurements, a continuous helium gas flow cryostat

was used. Microwave power and modulation magnetic field were carefully adjusted

to be 0.1 - 10 mW and 50 µT in order not to saturate the ESR signal. CuSO4 5H2O,

free radical Tempol, and manganese marker were used as a standard spin counting reference.

Figure S17 shows ESR spectra for PBTTT/F4-TCNQ (top), pristine PBTTT (middle),

and pristine F4-TCNQ (bottom) films, where the red and blue curves represent the signal

for the external magnetic field being perpendicular and parallel to the substrate plane.

Measurable, albeit weak, signals are observed even for pristine PBTTT and F4-TCNQ films.

It is because of unintentional charge transfer either from oxygen and/or water, or from

28


-1.0

-0.5

0.0

0.5

1.0

-1.0

-0.5

0.0

0.5

1.0

341 342 343 344

-1.0

-0.5

0.0

0.5

1.0

B (mT)

Nor

mal

ized

ES

R in

tens

ity (

a.u.

)

g|| = 2.002 73

g┴ = 2.002 64

g┴ = 2.002 80

g|| = 2.002 46

g┴ = 2.002 89

g|| = 2.002 87

PBTTT/F4-TCNQ

PBTTT

F4-TCNQ

Figure S17: Angular dependence of ESR spectra ESR spectra for PBTTT/F4-TCNQ (top),

pristine PBTTT (middle), and pristine F4-TCNQ (bottom) films, where the red and blue curves

represent the signal for the external magnetic field being perpendicular and parallel to the substrate

plane.

impurities contaminating the raw materials (the purity of F4-TCNQ powder is 97 %). The

anisotropic g-values observed for PBTTT are consistent with those observed previously34

as shown in the table , suggesting that PBTTT forms edge-on lamellar structure. The g-

values for the F4-TCNQ film are found to be isotropic, meaning that there is no preferential

molecular structure.

Observation of Pauli paramagnetism indicates that a metallic ground-state is indeed

realised in a semicrystalline polymer. Recently, we have demonstrated Pauli param-

agnetism in a semicrystalline polymer doped by fluoroalkylsilane (tridecafluoro-1,1,2,2-

tetrahydrooctyl)trichlorosilane, FTS).36 It is found that the Pauli susceptibility is observable

only at the highly-crystalline, edge-on domain. Surprisingly, with the presented F4-TCNQ

doping, the density of states estimated from the slope of χtotT − T is considerably larger

than those with FTS doping. For instance, the slope of χtotT − T for F4-TCNQ doped

PBTTT is larger by a factor of 25 - 30 compared to that of PBTTT doped by FTS,36 as

shown in Fig. S18a. The enhancement of Pauli susceptibility originates from enlargement

29


Table 3: Comparison of g-values

PBTTT-C16 (this work) PBTTT-C1634

ga⊥ 2.002 80 2.003 1 (2.002 73)c

gb|| 2.002 46 2.001 5 (2.002 13)c

F4-TCNQ (this work) F4-TCNQ35

g⊥ ∼ g|| 2.002 89 2.002 9

a g⊥ corresponds to gz in the ref..34 b g|| is an average of gx and gy, where x-, y-, and z-axes are defined

as pπ-orbital, C-H bond, and polymer-long axis, respectively. c The calculated g-values are also shown.

of highly-crystalline domain homogeneously distributed in the entire bulk of the PBTT

film. It is consistent with the fact that the g-factor measured in F4-TCNQ doped PBTTT

(g ∼ 2.00290) is assigned to a pure edge-on orientation of the polymer, whereas FTS-doped

PBTTT in Fig. S18b comprises a mixture of edge-on and face-on oriented grain giving rise

to a split ESR signal (g ∼ 2.003 and g′ ∼ 2.002).

340 341 342 343 344 3450 100 200 300

0.06

100 200 300 No

rma

lise

d E

SR

in

ten

sity (

a.u

.)

B (mT)T (K)

2.0

3.0

χ T

(1

0-4 e

mu

K c

m-3)

F4-TCNQ

Fit

0.0

1.0

0.04

0.02

00

F4-TCNQ

FTS

FTS (high)

FTS (low)

ba

g = 2.002 90

g = 2.003 03

g’ = 2.001 81

Figure S18: Comparison of Pauli susceptibility a Comparison of χtotT − T plots for F4-

TCNQ-doped (red) and FTS doped (blue and black) PBTTT films, where the latter is taken from

ref.36 (also see the magnified one in the inset). b ESR spectra for PBTTT/F4-TCNQ (red) and

PBTTT/FTS. The measurements were performed in the same manner above.

Our analysis of the χtotT − T plots relies on the assumption that the degree of charge

transfer should be independent of temperature. To test this assumption Figure S19 shows

temperature dependence of UV-vis spectra for the PBTTT/F4-TCNQ film, where no sig-

nificant change is observed at the peak for π-π∗ transition (556 nm) and at doping induced

30


anion peaks (768 and 879 nm) as shown in the inset. This demonstrates that the charge

transfer is indeed temperature independent of temperature for the present system, which is

also expected from energy diagram of the present system,37 i.e. the HOMO level of PBTTT

lies above the LUMO level of F4-TCNQ.

400 600 800 1000 12000.0

0.2

0.4

0.6

0 100 200 3000.15

0.20

0.25

0.30

0.35

Ab

so

rba

nce

Wavelength (nm)

300 K 250 K 200 K 150 K 100 K 50 K 20 K 5.2 K

879

768

556

T (K)

Figure S19: Temperature dependence of UV-vis measurements Temperature dependence

of UV-vis spectra for the PBTTT/F4-TCNQ film. The inset shows temperature variation of the

absorbance at 556 nm (triangles), at 768 nm (squared) and 879 nm (circles), respectively.

I. Temperature dependence of conductivity of PBTTT/F4-TCNQ

The measured conductivity does not exhibit an ideal metallic behaviour (i.e. increasing

conductivity with decreasing temperature) but can be fitted with a general variable-range-

hopping (VRH) model, σ(T ) = σ0 exp(T0T

)− 1d , where T0 is a characteristic temperature. Out

of the possible values for d, d = 2.34 gives the best fit which excludes 3-D VRH (d = 4)

and 2-D VRH (d = 3) as possible mechanisms for charge transport (see Fig. S20a). This

implies that the conduction is not governed by a pure hopping between localised states in

three dimensions which is the case for PEDOT:PSS (see Main Fig. 4e) or hopping of doped

interfacial states, respectively. Efros-Shklovskii variable-range-hopping (ES-VRH) model

predicts d = 2 which is the closest to the best fit with d = 2.34 and differs from a pure Mott

VRH model by taking into account for a ’soft gap’ in the density of states near Fermi energy

due to Coulomb interaction between localised states.38 Such ’soft Coulomb gap’ reduces the

density of states near Fermi energy and plays a role at low temperatures when the energy

31


interval for hopping becomes comparable to the Coulomb gap. Therefore, the effect is ex-

pected to be apparent at low temperatures. The linearisation of the data using logarithmic

derivative of conductivity (see Fig. S20b) indicates a slight contribution of ES-VRH from

the fit with d = 2 below 30K. However, it is not conclusive to attribute the temperature

dependence solely to ES-VRH since several other models have a similar temperature depen-

dence, but with different physical origins, including inter-cluster hopping between metallic

clusters39 and transport dominated by tunnelling due to temperature dependent voltage-

fluctuation-noise.40 Although we would not be able to conclude on a particular mechanism

that is responsible for the whole temperature range, we would like to note that a deviation

from the standard VRH fits might be due to a finite coherent charge transport in the system.

2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0-1.2

-1.0

-0.8

-0.6

-0.4

-0.2

0.0

0.2

0.4

0 50 100 150 200 250 3000

50

100

150

200ln

W

ln T

200200

aa b

(S

cm

-1)

σ

Best fit (d = 2.34)

Experiments

T (K)

Best fit

Experimentsd = 4d = 3

d = 2

d = 4d = 3

d = 2

T = 30 K

(d = 2.34)

Figure S20: VRH fit for temperature dependence of conductivity a Temperature depen-

dence of conductivity for PBTTT/F4-TCNQ film fitted with diffferent exponents, d as defined in

the text. d = 2.34 fits the best over the whole temperature range. b Linearised plot of conductivity

vs temperature graph where w = d(ln σ)/d(lnT ), so that the slope of the line corresponds to d.

The fit for d = 2 for ES-VRH model is only valid at temperatures below 30 K (drawn as a line).

32


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