Supporting Information
Fluorine Substituted Conjugated Polymer of Medium Band Gap Yields
7% Efficiency in Polymer-Fullerene Solar Cells
Samuel C. Price
1
, Andrew C. Stuart
1
, Liqiang Yang
2
, Huaxing Zhou
1
, and Wei You
1,2, *
1. Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North
Carolina 27599-3290
2. Curriculum in Applied Sciences and Engineering, University of North Carolina at Chapel Hill,
Chapel Hill, North Carolina 27599-3287
*
To whom all correspondence should be addressed. Email: wyou@email.unc.edu.
S1
Table of Contents
1. Experimental section (S3-S8).
2. NMR Spectra (S9-S18).
3. Photographs of polymer solutions (S19).
4. Supplemental Cyclic Voltammetry, Reduction Curves (S20).
5. SCLC Hole Mobility Measurement Graph (S20).
6. X-Ray Diffraction Spectroscopy (S21).
7. Atomic Force Microscopy Film Characterization (S22).
8. Energy Dispersive Spectroscopy (S23).
9. Film Thickness Measurements via SEM (S24-25).
10. Reference (S26)
S2
Reagents. All solvents are ACS grade unless otherwise noted. Anhydrous THF was obtained
by distillation from sodium/benzophenone prior to use. Diisopropylamine was distilled from
potassium hydroxide prior to use. 4,7-dibromo-2-(2-butyloctyl)-2H-benzo[d][1,2,3]triazole,
1,2
2,6-Bis(trimethyltin)-4,8-(3-butylnonyl)benzo[1,2-b:4,5-b’]dithiophene,
3
2-butyloctylbromide,
4
and 5,6-difluoro-1H-benzo[d][1,2,3]triazole
5
were prepared according to modified literature
procedures. All reagents were purchased from VWR, Fisher Scientific, Dynamic Absorbents,
Silicycle, Accela ChemBio Inc., and were used without further purification.
4,7-bis(5-bromothiophen-2-yl)-2-(2-butyloctyl)-2H-benzo[d][1,2,3]triazole (HTAZ).
Thiophene (3.01 g, 2.5 eq) was dissolved in dry THF (40 mL) in a flame dried flask under argon.
The mixture was cooled to 0°C in an ice bath, and 1.6M n-BuLi in hexanes (22.8 mL, 2.55 eq)
was added dropwise over 3 minutes. The solution was stirred for 35 min maintaining the
temperature at 0°C, and then anhydrous ZnCl
2
(5.07 g, 2.6 eq) was added as a solution in 40 mL
dry THF. The reaction was stirred for 5 min at 0°C, and then Pd(PPh
3
)
2
Cl
2
(602 mg, 6 mol %)
was added in one portion. 4,7-dibromo-2-(2-butyloctyl)-2H-benzo[d][1,2,3]triazole (6.39 g, 1.0
eq) was then added via cannula as a solution in 20 mL of dry THF. The reaction mixture was
then heated to reflux, and stirred for 16 h. The reaction mixture was then poured into water and
extracted with ethyl acetate. The organic layer was then washed with water (3x), dried (MgSO
4
),
filtered, concentrated in vacuo, and purified by column chromatography on silica gel using 4:1
hexanes:CH
2
Cl
2
as the eluent. The resulting fluorescent yellow solid was then dissolved into
THF (80 mL), and N-bromosuccinimide (2.89 g, 2.0 eq) was added in one portion. The reaction
mixture was stirred for 3.5 h, and then poured into saturated NaHCO
3
solution and extracted with
ethyl acetate. The organic phase was then washed with water (3 ×), dried (MgSO
4
), filtered, and
S3
concentrated in vacuo. The material was then purified by column chromatography on silica gel,
using 3:1 hexanes:chloroform as the eluent. The resulting yellow solid (HTAZ) was then
recrystallized twice from isopropanol to yield a yellow powder. Yield (2 steps): 2.79 g (32%).
Fluorescent yellow solid; mp 70°C.
1
H NMR (CDCl
3
, 400 MHz, δ): 7.76 (d,
3
J
HH
= 3.6 Hz, 2H),
7.46 (s, 2H), 7.10 (d,
3
J
HH
= 4 Hz, 2H), 4.71 (d,
3
J
HH
= 6.4 Hz, 2H), 2.27 (m, 1H), 1.26 (m, 16H),
0.90 (t,
3
J
HH
= 7.2 Hz, 3H), 0.86 (t,
3
J
HH
= 6 Hz, 3H).
13
C NMR (CDCl
3
, 100 MHz, δ): 141.55,
141.24, 130.80, 126.81, 122.90, 122.01, 113.16, 59.88, 39.09, 31.82, 31.38, 31.15, 29.56, 28.45,
26.17, 22.96, 22.65, 14.09. Anal. Calcd for C
26
H
31
Br
2
N
3
S
2
: C, 51.24; H, 5.13; N, 6.89. Found: C,
51.52; H, 4.95; N, 6.88.
Polymerization of PBnDT-HTAZ. 2,6-Bis(trimethyltin)-4,8-(3-butylnonyl)benzo[1,2-b:4,5-
b’]dithiophene (132 mg, 1.0 eq), HTAZ (91.4 mg, 1.0 eq), Pd
2
(dba)
3
(2.8 mg, 0.02 eq), and
tri(o-tolyl)phosphine (7.2 mg, 0.16 eq) were combined in a dry microwave vial. The vial was
sealed with a septum cap, and then evacuated and refilled with argon three times. Dry, oxygen
free o-xylene (0.75 mL) was added. The mixture was then reacted in a microwave reactor for 20
min, at 200°C (at 300W), and then cooled to room temperature. The reaction mixture was diluted
with chlorobenzene (3 mL), and then the polymer solution was precipitated into methanol (100
mL) at room temperature. The resulting purple-black solid was filtered into a Soxhlet thimble,
and extracted with methanol, ethyl acetate, hexanes, and chloroform until the wash from each
extraction was colorless. When there was no solid remaining in the thimble, the chloroform
fraction was concentrated, and chlorobenzene was added (5 mL). The polymer solution was then
precipitated into methanol at room temperature, filtered, and dried under vacuum at 0.5 mmHg.
Yield: 143 mg (95%). Purple metallic solid.
1
H NMR @ 400K (C
2
D
2
Cl
4
, 400 MHz, δ): 7.86,
S4
7.23, 4.87, 3.14, 2.41, 1.87, 1.50, 1.08. GPC (1,2,4-trichlorobenzene at 135°C): M
n
= 47.6
kg/mol, M
w
= 133.4 kg/mol, PDI = 2.57.
2-(2-butyloctyl)-5,6-difluoro-2H-benzo[d][1,2,3]triazole (2). 5,6-difluoro-1H-
benzo[d][1,2,3]triazole (8.04 g, 1.0 eq), potassium tert-butoxide (5.87 g, 1.01 eq), and 2-
butyloctylbromide (13.04 g, 1.01 eq) were dissolved in 130 mL of methanol. The reaction was
heated to reflux for 17 h. The reaction mixture was then poured into saturated NH
4
Cl solution,
and extracted with ethyl acetate. The organic layer was washed with water (2x), dried (Na
2
SO
4
),
filtered, concentrated in vacuo, and purified by column chromatography on silica gel using 10:1
hexanes:ethyl acetate as the eluent. Yield: 2.88 g (17%). Colorless oil.
1
H NMR (CDCl
3
, 400
MHz, δ): 7.59 (t,
3
J
HF
= 8.4 Hz, 2H), 4.58 (d,
3
J
HH
= 6.8 Hz, 2H), 2.22 (m, 1H), 1.28 (m, 16H),
0.86 (t,
3
J
HH
= 5.6 Hz, 6H).
4,7-dibromo-2-(2-butyloctyl)-5,6-difluoro-2H-benzo[d][1,2,3]triazole (3). 1.6M n-BuLi in
hexanes (12.5 mL, 2.25 eq) was added dropwise over 3 min to a solution of diisopropylamine
(3.10 mL, 2.5 eq) and dry THF (90 mL) under argon at -78°C. The solution was stirred for 15
min, and then a solution of Compound 2 (2.88 g, 1.0 eq) and trimethylsilyl chloride (3.1 mL,
2.75 eq) in dry THF (35 mL) was added dropwise over 10 minutes at -78°C. -78°C was
maintained while the reaction was stirred for 3 h, and then the reaction was quenched with 10
mL of saturated NH
4
Cl. The reaction was warmed to room temperature and poured into saturated
NH
4
Cl. The mixture was extracted with ethyl acetate, washed with water (3x), dried (MgSO
4
),
and concentrated in vacuo. The residue was then dissolved into CHCl
3
(30 mL), and bromine
(3.6 mL, 8.0 eq) was added in one portion, and the reaction was stirred for 16 h at room
temperature, shielded from light. The reaction was then poured into a mixture of 10% NaOH and
ice, and extracted with methylene chloride. The organic layer was washed with brine, dried
S5