SUPPORTING INFORMATION
Dithienocarbazole and benzothiadiazole based donor-acceptor
conjugated polymers for bulk heterojunction polymer solar cells
RONG ZiQing1,2, DENG YunFeng1,2, XIE ZhiYuan1, GENG YanHou1* & WANG FoSong1
1
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China;
2
University of Chinese Academy of Sciences, Beijing 100049, P. R. China
*Corresponding author (email: yhgeng@ciac.ac.cn)
1
Synthesis of monomers and polymers
N-(1-Octylnonyl)-2,7-dibromocarbazole (1) and 4,7-bis(5-bromothiophen-2-yl)-5,6-bis
(dodecyloxy)benzo[c][1,2,5]thiadiazole (11) were synthesized according to the procedures
reported in literatures [1–3]. The synthesis of 5 was reported previously [3].
N-(1-Octylnonyl)-dithieno[3,2-b;6,7-b]carbazole (9) and its stannyl derivative 10 were
synthesized following the procedure reported before [4–6].
Scheme S1 Molecular structures and synthetic procedures of monomers and polymers: (i)
KI, KIO3, AcOH, 80 oC, 5 h; (ii) (trimethylsilyl)acetylene, Pd(PPh3)2Cl2, CuI, Et3N, THF, RT,
48 h; (iii) Na2S.9H2O, NMP, 230 oC, 12 h; (iv) n-BuLi, Me3SnCl, THF, –78 oC to RT,
overnight; (v) 1) CH3SCH3, (CF3SO2)2O, CH2Cl2, –40 oC, 2 h to RT, 3 h; 2) Et3N, CH3CN,
RT, 3 h; (vi) (trimethylsilyl)acetylene, Pd(PPh3)2Cl2, CuI, Et3N, 80 oC, 48 h; (vii) 1) I2,
CH2Cl2, reflux; 2) trifluoroacetic acid, benzene, RT; (viii) n-BuLi, THF, –78 oC, 1 h then H2O,
–78 oC to RT; (ix) n-BuLi, Me3SnCl, THF, –78 oC to RT, overnight; (x) Pd2(dba)3, P(o-tolyl)3,
toluene, 115 oC, 48 h
N-(1-Octylnonyl)-2,7-dibromo-3,6-dimethylthiocarbazole (6)
Trifluoromethanesulfonic anhydride (7.47 mL, 41 mmol) was dissolved in CH2Cl2 (110 mL)
under argon at –40 oC and dimethyl sulfide (3.01 mL, 41 mmol) was added to the solution. A
solution of 1 (11 g, 19.52 mmol) in CH2Cl2 (55 mL) was added through drop funnel to the
mixture. The temperature was kept at –40 oC for 3 h and then raised to ambient temperature
for 1 h. Acetonitrile (80 mL) was added to re-dissolve the residue after CH2Cl2 was removed
under vacuum. Then, triethylamine (40 mL) was added at 0 oC. The resulting solution was
stirred overnight at room temperature. The solvent was evaporated and the mixture was
extracted with CH2Cl2. The crude product was purified by column chromatography on silica
gel with petroleum ether: CH2Cl2=10:1 as eluent to afford 6 as a viscous yellow solid (3.2 g,
25%). 1H NMR (400 MHz, CDCl3): δ (ppm) 7.96 (s, 2H), 7.78 (s, 1H), 7.62 (s, 1H), 4.40–
4.32 (m, 1H), 2.59 (s, 6H), 2.21–2.12 (m, 2H), 1.92–1.85 (m, 2H), 1.22–1.13 (m, 22H), 0.95–
0.91 (m, 2H), 0.83 ( t, J = 8 Hz, 6H). 13C NMR (400 MHz, CDCl3): δ (ppm) 141.34, 137.65,
128.60, 128.35, 123.02, 122.53, 121.74, 121.54, 120.16, 115.92, 113.68, 57.18, 33.56, 31.73,
29.26, 29.11, 26.69, 22.59, 17.88, 17.81, 14.06. Elemental analysis (%) calculated for
C31H45Br2NS2 (655.6): C, 56.74; H, 6.87; N, 2.13. found: C, 56.85; H, 6.86; N, 2.08. MS
(MALDI-TOF, reflection mode): m/z 653.1 (M)+.
N-(1-Octylnonyl)-2,7-di(trimethylsilylethynyl)-3,6-dimethylthiocarbazole (7)
Et3N (40 mL) was added to a mixture of 6 (2.6g, 3.97 mmol), Pd(PPh3)2Cl2 (140 mg, 0.20
mmol) and CuI (76 mg, 0.40 mmol). Trimethylsilylacetylene (1.23 mL, 8.72 mmol) was
added by the syringe slowly. The solution was stirred at 80 oC for 48 h in the absence of light,
and then poured into aqueous ammonium chloride solution and extracted with CH2Cl2. After
the solvent was evaporated, the residue was purified by column chromatography on silica gel
with petroleum ether: CH2Cl2 = 4:1 as the eluent to yield 7 as a yellow solid (1.92 g,
70% ).1H NMR (400 MHz, CDCl3): δ (ppm) 7.89 (s, 2H), 7.64 (s, 1H), 7.50 (s, 1H), 4.43–
4.39 (m, 1H), 2.59 (s, 6H), 2.24–2.13 (m, 2H), 1.92–1.85 (m, 2H), 1.26–1.13 (m, 22H), 0.96–
0.88 (m, 2H), 0.83 (t, J = 8 Hz, 6H), 0.33 (s, 18H). 13C NMR (400 MHz, CDCl3): δ (ppm)
140.63, 136.93, 131.01, 130.56, 123.87, 122.35, 120.98, 120.30, 118.98, 116.03, 113.78,
103.83, 100.29, 100.17, 57.05, 33.72, 31.72, 29.35, 29.30, 29.12, 26.78, 22.57, 16.98, 16.79,
14.05. Elemental analysis (%) calculated for C41H63NS2Si2 (690.25): C, 71.28; H, 9.13; N
2.03, found: C, 71.12; H, 9.10; N, 1.97. MS (MALDI-TOF, reflection mode): m/z 689.4 (M)+.
N-(1-Octylnonyl)-3,8-diiodo-dithieno[3,2-b;6,7-b]carbazole (8)
Iodine (2.38 g, 9.39 mmol) was added to a solution of 7 (1.62 g, 2.35 mmol) in CH2Cl2 (24
mL) when the solvent started to reflux. The mixture was poured into saturated sodium
thiosulfate aqueous solution after stirring 1 h and extracted with CH2Cl2. The combined
organic layers were washed with saturated sodium chloride aqueous solution and dried over
anhydrous MgSO4. After the solvent was evaporated, the residue was dissolved in benzene
(19 mL) and trifluoroacetic acid (3.5 mL) was added. Water was added to quench the reaction
until it was complete. The mixture was extracted with CH2Cl2 and dried over anhydrous
MgSO4. After the solvent was removed, the crude product was purified by column
chromatography on silica gel with petroleum ether as the eluent to give 8 as a light yellow
solid (1.39 g, 77%). 1H NMR(400 MHz, CDCl3): δ (ppm) 8.57 (d, J = 4 Hz, 2H), 7.87 (s, 1H),
7.69 (s, 3H), 4.81–4.74 (m, 1H), 2.54–2.45 (m, 2H), 2.07–2.00 (m, 2H), 1.30–1.03 (m, 24H),
0.78 (t, J = 4 Hz, 6H). 13C NMR (400 MHz, CDCl3): δ (ppm) 143.35, 139.64, 139.47, 139.28,
129.83, 129.34, 123.25, 122.04, 113.93, 113.69, 106.68, 104.03, 56.70, 33.20, 31.73, 29.38,
29.28, 29.16, 26.67, 22.57, 14.03. Elemental analysis (%) calculated for C33H41I2NS2 (769.62):
C, 51.45; H, 5.33; N, 1.82, found: C, 51.50; H, 5.41; N, 1.70. MS (MALDI-TOF, reflection
mode): m/z 769.1 (M)+.
N-(1-Octylnonyl)-dithieno[3,2-b;6,7-b]carbazole (9)
n-BuLi (1.66 mL, 4.14 mmol, 2.5 M in hexane) was added to a solution of 8 (1.3 g, 1.69
mmol) in THF (35 mL) at –78 oC. The reaction was quenched with saturated aqueous
solution of ammonium chloride after 1 hour. The mixture was extracted with CH2Cl2 and the
combined organic layers were washed with brine. After the solvent was eliminated, the crude
product was purified by column chromatography on silica gel with petroleum ether as the
eluent to afford 9 as a pale yellow solid (0.7 g, 80%). 1H NMR (400 MHz, CDCl3): δ (ppm)
8.59 (d, J = 8 Hz, 2H ), 7.90 (s, 1H), 7.74 (s, 1H), 7.49 (d, J = 4 Hz, 2H), 7.43 (d, J = 4 Hz,
2H), 4.66–4.58 (m, 1H), 2.45–2.35 (m, 2H), 1.99–1.91(m, 2H), 1.26–1.03 (m, 24H), 0.79 (t, J
= 4 Hz, 6H). 13C NMR (400 MHz, CDCl3): δ (ppm) 142.68, 138.84, 138.75, 138.47, 130.95,
130.90, 126.69, 123.71, 123.09, 121.89, 113.69, 113.37, 104.39, 101.67, 56.63, 33.28, 31.73,
29.46, 29.31, 29.14, 26.89, 22.56, 14.02. Elemental analysis (%) calculated for C33H43NS2
(517.83): C, 76.47; H, 8.30; N, 2.70, found: C, 75.86; H, 8.46; N, 2.60. MS (MALDI-TOF,
reflection mode): m/z 517.3 (M)+.
N-(1-Octylnonyl)-2,8-bis(trimethylstannyl) dithieno[3,2-b;6,7-b]carbazole (10)
n-BuLi (1.0 ml, 2.55 mmol, 2.5 M in hexane) was added to a solution of 9 (550 mg) in THF
(6.4 mL) slowly at –78 oC. The mixture was stirred for 30 min at this temperature and then
warmed to ambient temperature for continuing reaction for 2 h. Then trimethyltin chloride
(508 mg, 2.55 mmol) was added at –78 oC. After stirring overnight, the mixture was poured
into potassium fluoride aqueous solution and extracted with CH2Cl2. The organic extracts
were washed with brine, dried over anhydrous MgSO4 before the solvent was removed. The
residue was recrystallized from methanol to give 10 as a yellow solid (0.81 g, 90%). 1H NMR
(400 MHz, CDCl3): δ (ppm) 8.58 (d, J = 8 Hz, 2H), 7.87 (s, 1H), 7.70 (s, 1H), 7.51 (s, 2H),
4.65–4.57 (m, 1H), 2.44–2.37 (m, 2H), 1.97–1.90 (m, 2H), 1.26–1.02 (m, 24H), 0.79 (t, J = 8
Hz, 6H), 0.45 (s, 18H). 13C NMR (400 MHz, CDCl3): δ (ppm) 142.88, 141.04, 140.23,
139.87, 138.90, 135.37, 135.30, 131.69, 122.80, 121.64, 112.96, 112.64, 103.35, 100.58,
56.52, 33.29, 31.74, 29.47, 29.32, 29.15, 26.87, 22.57, 14.04. Elemental analysis (%)
calculated for C39H59NS2Sn2 (843.44): C, 55.49; H, 7.00; N, 1.65. found: C, 55.58; H, 7.21; N,
1.55. MS (MALDI-TOF, reflection mode): m/z 845.2 (M)+.
P(BT-C1)
Toluene (13 ml) was added to a Schlenk tube charged with 5 (156 mg, 188.67 umol),
11(162.3 mg, 192.44 mol), tris(dibenzylideneacetone) dipalladium (Pd2(dba)3, 3.45 mg, 3.77
mol) and tri-o-tolylphosphine (P(o-tolyl)3, 9.19 mg, 30.19 mol) under argon. The solution
was stirred 48 h at 115 oC then bromobenzene (1 mL) was added to for end-capping. After 12
h and then cooled to room temperature, the polymerization solution was added into methanol
dropwise to precipitate the polymer. The polymer was purified by Soxhlet extraction with
ethanol, acetone, hexane and chloroform in succession. The final product was obtained by
precipitation from o-dichlorobenzene solution into methanol as a dark purple solid (202 mg,
90%). 1H NMR (400 MHz, C2D2Cl4, 120 oC): δ (ppm) 8.56 (s, 4H), 7.88 (s, 2H), 7.69 (s, 2H),
7.47 (s, 2H), 4.66 (s, 1H), 4.34 (s, 4H), 2.44 (br, 2H), 2.11 (s, 6H), 1.47–1.26 (m, 60H), 0.92
(t, J = 8 Hz, 12H). Elemental analysis (%) calculated for (C71H95N3O2S5)n (1182.87): C, 72.02;
H, 8.03; N, 3.55, found: C,71.49; H, 8.11; N 3.39.
P(BT-C2)
The polymerization procedure was similar to that of P(BT-C1) and the product was obtained
as a dark purple solid (286 mg, 94%). 1H NMR (400 MHz, C2D2Cl4, 120 oC): δ (ppm) 8.55 (s,
4H), 7.82 (s, 2H), 7.69 (s, 2H), 7.51 (s, 2H), 4.69 (s, 1H), 4.33 (s, 4H), 2.48 (br, 2H), 2.10 (s,
6H), 1.48-1.28 (m, 60H), 0.92 (t, J = 8 Hz, 12H). Elemental analysis (%) calculated for
(C71H95N3O2S5)n (1182.87): C, 72.02; H, 8.03; N, 3.55, found: C, 70.92; H, 8.05; N, 3.34.
2
1
Measurements and instruments
H and 13C NMR spectra were measured with a Bruker Ascend 400 MHz spectrometer with
tetramethylsilane (TMS) as an internal reference and CDCl3 or C2D2Cl4 as the solvent.
Matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectra were
measured using a Bruker/AutoflexIII Smartbean MALDI mass spectrometer. Elemental
analysis was carried out using a VarioEL elemental analysis system. Gel permeation
chromatography (GPC) measurements was conducted on a PL-GPC 220 system at 150 °C
with polystyrene and 1,2,4-trichlorobenzene as standard and eluent, respectively. Thermal
stability was studied by thermogravimetric analysis (TGA) on a Perkin-Elmer TGA7 at a
heating rate of 10 °C/min under nitrogen atmosphere. Differential scanning calorimetric
(DSC) was performed under N2 flow on a Perkin-Elmer DSC 7 in a temperature range of 20–
290 oC at a heating/cooling rate of 10/–10 °C/min. Thin film XRD diffraction was taken on a
Bruker D8 Discover thin-film diffractometer with a monochromatized Cu Kα radiation (λ =
1.54056 Å) operated at 40 kV and 40 mA. UV-vis absorption spectra was performed on a
Shimadzu UV-3600 UV-vis-NIR spectrometer, the optical bandgap Egopt was calculated
according to the equation Egopt = 1240/λonset eV in which λonset is the film absorption onset.
Film cyclic voltammetry was carried out on a CHI660a electrochemical analyzer in
anhydrous acetonitrile with Bu4NPF6 as the electrolyte at a scan rate of 100 mV/s. A
three-electrode system was used with glassy carbon electrode, saturated calomel electrode
and Pt wire as the working, reference and counter electrodes, respectively. The Gaussian 09
package program in B3LYP/6–31G mode was used to study the conformation and molecular
orbitals of the polymers. All alkyl side chains were replaced with methyl groups in order to
simplify the calculations. The morphology of blend films were investigated by atomic force
microscopy (AFM) in tapping mode on a SPA400HV instrument controlled by a SPI 3800
controller.
3
Fabrication and characterization of OTFT devices
OTFT devices were prepared on heavily doped n-type Si wafer with a thermally grown SiO2
layer (300 nm, Ci = 10 nF/cm2). The substrates were cleaned according to the procedure
reported before and modified with trichlorooctadecylsilane (ODTS) [5]. The organic
semiconductor layers were deposited by spin-coating the polymer solution in
o-dichlorobenzene (5.0 mg/mL) at a speed of 800 rpm for 1 min. Au drain and source
electrodes (thickness of 40 nm) were deposited on the top of active layer by vacuum
evaporation through a shadow mask. The channel width (W) and length (L) of the devices are
3000 and 100 μm, respectively. Thermal annealing of the polymer films were operated in the
glovebox at different temperature for 20 min. Field-effect characteristics were measured at
room temperature in ambient atmosphere by using two Keithley 236 source/measure units.
4
Fabrication and characterization of solar cells
ITO was cleaned with detergent and deionized water, then dried in oven before UV-ozone
treatment for 25 min. PEDOT: PSS layer was prepared by spin-casting its aqueous solution
with 4000 rpm for 1 min. An o-DCB solution consisting of polymers (5 mg/mL) and PC71BM
were spin-casted on the top of PEDOT: PSS layer to prepare the blend active layer. LiF and
the negative electrode (Al) were deposited on the active layer through a shadow mask in
vacuum affording a device with a structure of ITO/PEDOT:PSS (40 nm)/polymer:PC71BM
(90 nm)/LiF (1 nm)/Al (80 nm). The devices were encapsulated in the glovebox with the
device area of 0.125 cm2 before measuring in ambient atmosphere. The illuminated current
density-voltage (J-V) characteristics and external quantum efficiency (EQE) profiles of the
photovoltaic cells were measured following the procedure reported previously [7].
Weight ratio (%)
100
P(BT-C1)
P(BT-C2)
80
60
40
200
Figure S1
400
600
o
Temperature ( C)
800
TGA plots of the polymers at a heating rate of 10 oC/min under a nitrogen
atmosphere.
(a)
50
Figure S2
(b)
P(BT-C1)
100
150
200
250
o
Temperature ( C)
300
P(BT-C2)
50
100
150
200
250
o
Temperature ( C)
300
DSC diagrams of the polymers at a scan rate of ±10 oC/min under a nitrogen
atmosphere.
(a)
P(BT-C1)
P(BT-C2)
5
Figure S3
Intensity
Intensity
(b)
10
15
20
2Theta degree)
25
30
P(BT-C1)
P(BT-C2)
5
10
15
20
2 Theta (degree)
25
30
Thin film XRD patterns of the polymer films before (a) and after annealing at
200 oC for 20 min (b). The films were prepared by spin-casting o-DCB solutions with a
concentration of 5 mg/mL on Si/SiO2 substrates.
Table S1
OTFT devices performance of the polymers
Polymer
P(BT-C1)
P(BT-C2)
Annealing
temperature
μh max
(cm2V-1s-1)
VT (V)
Ion/Ioff
Pristine
1.9 × 10-3
–9.7
9.5 × 102
100 oC
1.1 × 10-3
–10.5
9.3 × 102
150 oC
1.1 × 10-3
–4.1
8.3 × 102
Pristine
2.7 × 10-3
–3.3
4.0 × 103
100 oC
3.1 × 10-3
–1.9
3.0 × 103
150 oC
3.9 × 10-3
–1.2
1.2 × 103
200 oC
5.4 × 10-3
–4.9
1.6 × 103
Table S2 Device performance of the PSCs based on P(BT-C1) with different blend ratios
P(BT-C1):
PC71BM
VOC
(V)
JSC
(mA/cm2)
FF
PCE
(%)
Thickness
(nm)
1:1
0.66
3.9
0.56
1.4
39
1:2
0.69
6.2
0.59
2.5
50
1:3
0.70
7.8
0.62
3.4
58
1:4
0.70
9.2
0.65
4.2
70
1:4
0.70
10.7
0.65
4.9
91
Table S3 Device performance of the PSCs based on P(BT-C2) with different blend ratios
P(BT-C2):
PC71BM
VOC
(V)
JSC
(mA/cm2)
FF
PCE
(%)
Thickness
(nm)
1:1
0.83
8.3
0.40
2.7
67
1:2
0.80
10.1
0.55
4.4
78
1:3
0.79
10.5
0.56
4.6
86
1:4
0.79
10.3
0.62
5.0
93
References
1
2
3
4
5
6
7
Blouin N, Michaud A, Leclerc M. A low-bandgap poly(2,7-carbazole) derivative for use in
high-performance solar cells. Adv Mater, 2007, 19: 2295–2300
Chen HY, Yeh SC, Chen CT, Chen CT. Comparison of thiophene- and selenophenebridged donor-acceptor low bandgap copolymers used in bulk-heterojunction organic
photovoltaics. J Mater Chem, 2012, 22: 21549–21559
Deng YF, Chen YG, Liu J, Liu LH, Tian HK, Xie ZY, Geng YH, Wang FS.
Low-band-gap
conjugated
polymers
of
dithieno[2,3-b:7,6-b]carbazole
and
diketopyrrolopyrrole: effect of the alkyl side chain on photovoltaic properties. ACS Appl
Mater Interfaces, 2013, 5: 5741–5747
Chen YG, Liu CF, Tian HK, Bao C, Zhang XJ, Yan DH, Geng YH, Wang FS. Novel
conjugated polymers based on dithieno[3,2-b:6,7-b]carbazole for solution processed
thin-film transistors. Macromol Rapid Commun, 2012, 33: 1759–1764
Deng YF, Chen YG, Zhang XJ, Tian HK, Bao C, Yan DH, Geng YH, Wang FS.
Donor-acceptor conjugated polymers with dithienocarbazoles as donor units: effect of
structure on semiconducting properties. Macromolecules, 2012, 45: 8621–8627
Deng YF, Liu J, Wang JT, Liu LH, Li WL, Tian HK, Zhan XJ, Xie ZY, Geng YH, Wang
FS. Dithienocarbazole and isoindigo based amorphous low bandgap conjugated polymers
for efficient polymer solar cells. Adv Mater, 2014, 26: 471–476
Shao SY, Liu J, Zhang JD, Zhang BH, Xie ZY, Geng YH, Wang LX. Interface-induced
crystalline ordering and favorable morphology for efficient annealing-free
poly(3-hexylthiophene): fullerene derivative solar cells. ACS Appl Mater Interfaces, 2012,
4: 5704–5710