Increased Exciton Dipole Moment Translates into Charge-transfer Excitons in Thiophene-fluorinated Low-bandgap Polymers for Organic Photovoltaic Applications

Elisa Collado-Fregoso1, Pierre Boufflet

1, Zhuping Fei

1*, Eliot Gann

2,3 Shahid Ashraf

1, Zhe

Li1,4

, Christopher R. McNeill3, James R. Durrant

1,4* and Martin Heeney

1*

1 Centre for Plastic Electronics, Department of Chemistry, Imperial College London, Exhibition Road, London

SW7 2AZ, United Kingdom 2 Australian Synchrotron, 800 Blackburn Road, Clayton, VIC 3169, Australia

3 Materials Science and Engineering, Monash University, Wellington Road, Clayton, VIC 3800, Australia

4 SPECIFIC IKC, College of Engineering, Swansea University, Central Avenue, Baglan, Port Talbot, SA12

7AX, U.K.

Supporting Information

1. UV absorption coefficient

2. Theoretical calculations

3. Crystallinity and morphology of neat and blend materials

4. Transient absorption spectroscopy

1. UV absorption coefficient

400 600 800 1000

0

1x104

2x104

3x104

4x104

5x104

Ab

so

rpti

on

Co

eff

icie

nt

[cm

-1]

Wavelength [nm]

F0

F4

Figure S1. UV-vis absorption coefficient of 0F and 4F in 1,2-dichlorobenzene solution at RT.

2. Theoretical calculations

Table S1. Calculations for ground and excitated state dipole using B3LYP/6-31G(d) (top) or

WB97XD/6-311G(d,p) (bottom) for one donor-acceptor repeat unit.

B3LYP/6-31G(D)

μg (D) μe (D) Δμge (D)

x y z overall x y z overall

Change

DTBT/0F anti -1.5588 2.1497 0.0014 2.66

-13.9781 4.2876 0.0009 14.62

12.60

DTBT/0F syn -0.8005 -0.0617 -0.1016 0.81

-11.7771 -2.5768 -0.051 12.06

11.26

DTBT/0F anti-syn -0.8914 0.9518 0.0001 1.30

-11.8078 -1.8924 -0.0013 11.96

11.28

DTBT/0F syn-anti -2.0608 3.0285 0.0576 3.66

-14.4379 4.8541 0.0423 15.23

12.51

TFDTBT/4F anti -2.8344 4.6342 -1.0927 5.54

-22.9772 6.0996 -1.8319 23.84

20.21

TFDTBT/4F syn -2.575 3.6763 -0.0001 4.49

-15.4222 0.8998 0.0001 15.45

13.14

TFDTBT/4F anti-syn -2.1712 2.8211 -0.9099 3.67

-21.4436 4.6244 0.2784 21.94

19.39

TFDTBT/4F syn-anti 2.0844 -1.2319 0.9196 2.59

15.99 1.0761 0.5618 16.04

14.10

WB97XD/6-311G(d,p)

μg (D)

μe (D)

Δμge (D)

x y z overall x y z overall Change

DTBT/0F anti -0.8423 1.9511 0.8163 2.28

-6.0514 3.6606 0.0884 7.07

5.53

DTBT/0F syn -0.2332 0.0528 0.1709 0.29

-4.955 -2.1051 0.3117 5.39

5.19

DTBT/0F anti-syn -0.1794 0.6776 1.0092 1.23

-4.6341 -1.3617 2.1752 5.30

5.04

DTBT/0F syn-anti -1.2793 2.8506 0.5975 3.18

-6.6675 4.454 0.5013 8.03

5.62

TFDTBT/4F anti 2.1444 -4.5918 -1.3456 5.24

9.8617 -5.448 -1.8206 11.41

7.78

TFDTBT/4F syn -1.895 4.1948 -0.0011 4.60

-7.8955 2.2322 0.0011 8.20

6.31

TFDTBT/4F anti-syn 1.4053 -1.5798 1.8657 2.82

8.2774 0.0165 1.8936 8.49

7.06

TFDTBT/4F syn-anti -1.4838 2.4949 -0.7663 3.00

-8.226 3.9304 0.081 9.12

6.95

3. Crystallinity and morphology of neat and blend materials

Figure S2. AFM Topography and phase images of F0/PC70BM 1:2 blend (a) and (b), and F4/PC70BM

1:2 blend (c) and (d). Size: 1x1 µm.

Figure S3. Top: R-SoXS scattering profiles taken of 4F:PC70BM and 0F:PC70BM blend films taken

at 284 eV. The scattering profile of the 0F blend is peaked at a lower q-value indicating a larger

domain spacing, with the top axis giving the corresponding real-space size. Intergration of the

scattering profiles reveals a ratio of 1:1.45 0F:4F or relative purities of 100% for 4F and 68.6% for 0F

Bottom: Contrast functions calcualted from the optical constatns of 0F, 4F and PC70BM that were

used to determin the energy of maximum materials constrate (284 eV).

Figure S4. Grazing incidence wide-angle x-ray scattering of neat F0 and F4 and F0/PC70BM and

F0/PC70BM blends along with out-of-plane and in-plane line-outs.

PCBM

4. Transient absorption spectroscopy

Figure S5.Sub-picosecond resolved TAS traces at the excitation energy densities presented in this

study (3 uJ/cm2) and lower energy intensities (1 uJ/cm

2) showing that the dynamics are comparable

over this range. a) F0/PC70BM 1:2 blend films and b) F4/PC70BM 1:2 blend films.

Figure S6. Microsecond-resolved transients taken exciting at 660 nm with 5 J/cm2 and probing at

1160 nm for F0 neat film (a) and F0 blend film (c) and at 1060 for F4 neat film (b) and F4 blend film

baa

100f 1p 10p 100p 1n0.0

0.5

1.0

1.5

2.0

O

D / m

OD

t / s

F4 blend, 1 uJ/cm2 x 3.6

F4 blend, 3 uJ/cm2

100f 1p 10p 100p 1n0.0

0.5

1.0

1.5

2.0

O

D / m

OD

t / s

F0 blend, 1 uJ/cm2 x 3.1

F0 blend, 3 uJ/cm2

a

1 101E-5

1E-4

1E-3

0.01

0.1

O

D [m

OD

]

t [s]

F0 blend N2

F0 blend O2

c

1 101E-5

1E-4

1E-3

0.01

0.1

O

D [m

OD

]

t [s]

F4 blend N2

F4 blend O2

d

0 2 4 6 8 10

0.00

0.01

0.02

0.03

0.04

O

D [m

OD

]

t [s]

F4 neat N2

F4 neat O2

0 2 4 6 8 10

0.00

0.01

0.02

0.03

O

D [m

OD

]

t [s]

F0 neat N2

F0 neat O2

a b

(d) showing the presence of triplets in F4 neat, and the absence of them in both blends. See main text

for the discussion on F0 neat. The blends were plotted in log-log scales to emphasize the linear

behaviour, characteristic of polarons.

1 10 100 10000.0

0.2

0.4

0.6

0.8

1.0

1.2

No

rm

OD

[a.u

.]

t [ps]

950 nm

1100 nm

1150 nm

1200 nm

Figure S7. Probed-wavelength dependence of the F4 exciton dynamics showing the the blue-shift of

the signal in the first 10 ps, after excitation at 710 nm with an intensity of 3 J/cm2. In red, best-

triexponential fits.

Table S2. Best tri-exponential fits, 𝑦 = 𝑦0 + 𝐴1𝑒−𝑥 𝜏1⁄ + 𝐴2𝑒−𝑥 𝜏2⁄ + 𝐴3𝑒−𝑥 𝜏3⁄ to the IR exciton

decays for different probed wavelentghts. Values are reported ± standard error.

prob (nm) 𝒚𝟎

(a.u.)

𝑨𝟏

(a.u.)

𝝉𝟏

(ps)

𝑨𝟐

(a.u.)

𝝉𝟐

(ps)

𝑨𝟑

(a.u.)

𝝉𝟑

(ps)

950 0.000±0.008 -0.14±0.01 5.3±1.3 0.62±0.11 227±39 0.40±0.08 961±192

1100 0.042±0.005 0.09±0.03 0.6±0.3 0.53±0.05 217±17 0.40±0.04 1002±112

1150 0.047±0.005 0.15±0.02 1.1±0.2 0.47±0.03 153±13 0.38±0.03 921±101

1200 0.046±0.005 0.19±0.01 2.2±0.2 0.43±0.03 129±11 0.34±0.02 861±96

100f 1p 10p 100p 1n

0

1

2

3

= 1.8 0.1 ps

= 1.7 0.1 ps

O

D /

mO

D

t / s

F0blend, 1332

F0blend, 788

Figure S8. Singlet exciton dynamics at 1332 nm and polaron signal accumulation at 788 nm for the

F0/PC70BM 1:2 blend films. The latter wavelength was used since it does not show any singlet

absorption in the neat film. The traces were fitted with single exponential functions with characteristic

times that match within the error of the measurment.

100f 1p 10p 100p 1n0.0

0.2

0.4

0.6

0.8

1.0

No

rma

lize

d

OD

/ a

.u.

t / s

F0 blend, 1170 nm

F0 blend, 740 nm negative

Figure S9. Normalized polaron trace at 1170 nm and ground state bleach trace (negative) at 740 nm

for F0/PC70BM 1:2 blend films, showing matching decay dynamics and therefore recombination of

polarons back to the ground state.

Figure S10. Transient absorption kinetics in the late nanosecond and microsecond scale, after

excitation at 660 nm, for a) 1:2 F0/PC70BM blend, probed at 1160 nm b) 1:2 F4/PC70BM blend,

probed at 1060 nm. All signals have been corrected for polymer blend absorbance at the excitation

wavelength.

b

a

100n 1µ 10µ1E-4

1E-3

0.01

0.1

1

t / s

O

D / m

OD

O

D / m

OD

30 uJ/cm2

2.4 uJ/cm2

0.48 uJ/cm2

1E-4

1E-3

0.01

0.1

1

O

D / m

OD

30 uJ/cm2

2.5 uJ/cm2

0.42 uJ/cm2

1E-4 / 1