Supporting Information
A Novel Crystallizable Low Band Gap Polymer for High-efficiency
Polymer Photovoltaic Cells
Xiaoli Zhao,ab Hongying Lv,abc Dalei Yang,abc Zidong Li,abc Zhaobin Chen,a and Xiaoniu
Yangab*
aPolymer
Composites Engineering Laboratory, Changchun Institute of Applied
Chemistry, Chinese Academy of Sciences, Changchun 130022, P. R. China
bState
Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P.R. China
cUniversity
of Chinese Academy of Sciences, Beijing 100049, P. R. China
*Correspondence to: X.N. Yang (E-mail: xnyang@ciac.ac.cn)
1
Materials and characterization
All reagents were used as received without any purification unless stated
otherwise. Chlorobenzene (CB, anhydrous, 99%) and 1-chloronaphthalene (CN) were
purchased from Sigma-Aldrich Company and Tokyo Chemical Industry CO., respectively.
PC71BM was purchased from American Dye Source Inc. PBDT-DTFFBT (Mn = 35 kDa,
PDI = 1.96) was prepared according to our previous work.1
The molecular weight of polymer was measured by gel permeation chromatography
(GPC) on a PL-GPC220 equipment. Electrochemical properties of polymer film were
performed on a CHI600D electrochemical analyzer in anhydrous acetonitrile at a scan
rate 50 mV s-1 under nitrogen. A glass carbon electrode covered with the copolymer
thin film was used as the working electrode, whereas a Pt wire and Ag/AgNO 3
electrode were used as the counter and reference electrodes, respectively.
Thermogravimetric
analysis
(TGA)
was
performed
on
a
METTLER
TOLEDOTGA/DSC1/1100 LF apparatus operated at a heating rate of 10 oC min-1 under
nitrogen. UV-Vis absorption spectra were recorded on a Lambda 750 spectrometer
(Perkin-Elmer). TEM were conducted on a JEOL JEM-1011 transmission electron
microscope operated at an acceleration voltage of 100 KV. XRD was obtained on a
Bruker D8 Discover Reflector with a 40 kV tube voltage and 40 mA tube current. The
diffraction was taken at a –2 symmetry scanning mode with the scan angle 2 from
3o-25o. The J-V characteristics of photovoltaic devices were measured by Keithley-2400
source meter in a glove box using a solar simulator (SAN-EI, XES-70S1) at AM 1.5 G
illumination of 100 mW cm-². The IPCE of these devices was measured in atmospheric
environment, using a calibrated silicon solar cell as a reference.
2
Experimental Section
Synthesis of the polymer
Synthesis of poly[benzo[1,2-b:3,4-b’:5,6-d”]trithiophene-alt-5,6-difluoro-4,7-bis(4-(2ethylhexyl)-2-thienyl)-2,1,3-benzothiadiazole] (BTT-DTFFBT) copolymer. The BTT-Sn
(0.732 g, 0.81 mmol) and DTFFBT-Br (0.582 g, 0.81 mmol) were dissolved in 50 mL of
anhydrous toluene. After be flushed with argon for 15 min, Pd2(dba)3 (18.4 mg) and
P(o-Tolyl)3 (39.2 mg) as the catalysts were added in the solution, which was then
flushed with argon for another 15 min. This reaction medium was heated and allowed
to stand at 120 oC for 48 h under argon protection. After reaction, the crude product
was subsequently end-capped with 2-(tributylstannyl)-thiophene (20 L) and 2bromothiophene (20L), and then precipitated in methanol. The precipitates were
collected by filtration, and purified by Soxhlet extraction using methanol, acetone,
hexane, tetrahydrofuran and chloroform. Then the residual fraction was collected and
dried in vacuum to get a dark solid as the product BTT- DTFFBT copolymer (400 mg,
43%). 1H-NMR (400 MHz, C2D2Cl4, 120 oC, ppm): 8.12 (s, br, 2H), 7.77 (s, br, 1H), 7.62
(s, br, 1H), 7.38 (s, br, 1H), 2.91 (s, br, 1H), 1.76-0.79 (m, br, 48H). Molecular weight:
Mn=11.0 kg mol-1, Mw=13.5 kg mol-1, and PDI=1.22. (Figure S1 and Figure S2)
Device fabrication
Polymer solar cells (PSCs) with standard device structure of indium-tin oxide
(ITO)/poly(ethylenedioxythiophene)(PEDOT):poly(styrenesulfonate)(PSS)/BTTDTFFBT:PC71BM/LiF/Al were fabricated as follows: the PEDOT:PSS layer with thickness
3
of ca. 30 nm was first spin-coated on pre-cleaned ITO-coated glass substrate, and then
baked at 150 oC for 10 min. The BTT-DTFFBT/PC71BM (1/1, w/w) blend was dissolved
in CB, ODCB or ODCB/CF mixture with CN (1 vol.% or 3 vol.%) with a polymer
concentration of 5 mg ml-1, while the blend of PBDT-DTFFBT/PCBM (1/1, w/w) was
dissolved in ODCB with a total concentration of 20mg ml-1, and the resultant solutions
were spin-coated on the PEDOT:PSS layer to fabricate the ca. 90 nm photoactive layer.
For the hole-only devices, a ca. 40 nm polymer film was spin-coated on the PEDOT:PSS
substrate. Afterwards, the photoactive layers were thermally annealed at different
conditions in a glove box. The solar cells were completed by evaporation of a 1 nm LiF
layer topped with a 100nm Al layer on the photoactive layers, while the hole-only
device was finished by evaporation of a 50 nm Au layer and subsequently a 100 nm Al
layer. The photoactive area for each device was 9 mm², as defined by a shadow mask.
The SCLC hole mobility was estimated by fitting the hole-only I-V curves with SCLC
model and the Mott-Gurney law:
ln(I / V2) = 0.89β(V / L)1/2 + ln(9με0εS / (8L3))
(1)
where I is the current, V is the applied voltage, β is the field-activation factor, L is the
thickness of polymer film, μ is the mobility, ε0 is the permittivity of free space, ε is the
relative permittivity, and S is the area of polymer film.[2-4]
4
Figure S1. 1H NMR spectrum of BTT-DTFFBT copolymer.
5
Figure S2. Molecular weight distribution plot of BTT-DTFFBT copolymer.
6
Weight Lose (%)
100
90
80
70
60
50
40
100
200
300
Temperature (oC)
400
500
Figure S3. TGA curve of BTT-DTFFBT copolymer under nitrogen atmosphere at a
heating rate of 10 oC min-1.
7
Current
Polymer
2+
Fe/Fe
-2
-1
0
1
+
2
Potential (V vs Ag/Ag )
Figure S4. CV of BTT-DTFFBT copolymer as thin film on a glass carbon electrode in
anhydrous acetonitrile at a scan rate 50 mV s-1 under nitrogen.
8
(b) -5.0
(a)
Polymer
Polymer/PC71BM
0.1
I (A)
2
ln (I/V )
-5.1
Polymer
Polymer/PC71BM
0.01
-5.2
-5.3
1E-3
2
4
6
2.5
8
V (V)
2.6
2.7
V
2.8
1/2
Figure S5. (a) Hole-only I–V curves of BTT-DTFFBT polymer and composite films. (b)
linear fits for the plots of ln(I/V2) versus V1/2 based on the SCLC model.
9
0
(b)
0 vol.% CN
0
-3
-2
-2
J (mA cm )
-3
Pristine
o
130 C
o
150 C
o
180 C
o
200 C
J (mA cm )
(a)
-6
-6
Pristine
o
130 C
o
150 C
o
180 C
o
200 C
1 vol.% CN
-9
-9
-12
0.0
0.2
0.4
0.6
0.8
0.0
0.2
0
-6
(d)
3 vol.% CN
-3
-9
-12
0.0
0.6
0.8
0
-2
J (mA cm-2)
-3
Pristine
o
130 C
o
150 C
o
180 C
o
200 C
J (mA cm )
(c)
0.4
V (V)
V (V)
0min
10min
20min
30min
40min
1 vol.% CN
-6
-9
-12
0.2
0.4
0.6
0.8
V (V)
0.0
0.2
0.4
0.6
0.8
V (V)
Figure S6. J–V characteristics of BTT-DTFFBT /PC71BM devices: (a) 0 vol.% CN, (b) 1 vol.%
CN, (c) 3 vol.% CN under different thermally annealed temperature for 10min, and (d)
different thermally annealed time at 180 oC (1 vol.% CN), respectively.
10
(a) 0
(b)
0
o
TA@180 C/0min
o
TA@180 C/10min
TA@180 C/0min
o
TA@180 C/10min
-2
J (mA cm )
-3
-2
J (mA cm )
-3
o
-6
-9
-12
0.0
0.2
0.4
0.6
-6
-9
-12
0.0
0.8
0.2
0.4
0.6
0.8
V (V)
V (V)
Figure S7. J–V characteristics of BTT-DTFFBT /PC71BM devices using (a) ODCB and (b)
ODCB/CF=1/1 as solvents and 1vol.% CN as solvent additive under different thermally
annealed time at 180 oC, respectively.
11
0
PFN
ZnO
-2
J (mA cm )
-3
-6
-9
-12
0.0
0.2
0.4
V (V)
0.6
0.8
Figure S8. J-V characteristics of BTT-DTFFBT BHJ inverted solar cells fabricated using CB
as solvent with 1 vol. % CN as the processing additive and thermal annealing at 180 oC
for 10 minutes ( Inverted Device Structure: ITO/PFN/Active layer/MoOx/Ag and
ITO/ZnO/Active layer/MoOx/Ag) .
12
a)
0
b)
Pristine
o
-3
TA@180 C for 60min
-2
-2
J (mA cm )
-3
J (mA cm )
0
-6
PBDT-DTFFBT
-9
-12
0.0
-6
BTT-DTFFBT
Pristine
o
TA @180 C for 60min
-9
-12
0.3
0.6
0.0
0.9
0.2
0.4
0.6
0.8
V (V)
V (V)
Figure S9. J-V characteristics of the device based on a) PBDT-DTFFBT and b) BTTDTFFBT before and after accelerated durability tests and c) the molecular structure of
PBDT-DTFFBT.
13
Table S1. Photovoltaic performance of BTT-DTFFBT devices under different condition.
Jsc
Voc
Condition
FF (%)
PCE (%)
(mA cm-2)
(V)
Pristine
9.33
0.72
0.39
2.62
CN
9.54
0.72
0.41
2.80
TA
10.07
0.78
0.61
4.79
CN+TA
11.79
0.78
0.61
5.61
14
Table S2. Photovoltaic performance of BTT-DTFFBT devices under different condition.
Condition
0 vol.% CN
TA temperature
1 vol.% CN
TA temperature
3 vol.% CN
TA temperature
1 vol.% CN
180 oC
Variable
Jsc
(mA cm-2)
Voc
(V)
FF (%)
PCE (%)
Pristine
9.33
0.72
0.39
2.62
130
9.89
0.78
0.54
4.18
150
10.09
0.78
0.58
4.56
180
10.07
0.78
0.61
4.79
200
9.93
0.78
0.58
4.49
Pristine
9.54
0.72
0.41
2.80
130
11.14
0.76
0.46
3.86
150
11.89
0.78
0.53
4.89
180
11.79
0.78
0.61
5.61
200
11.81
0.78
0.59
5.44
Pristine
10.09
0.74
0.42
3.11
130 oC
11.14
0.76
0.45
3.81
150 oC
11.54
0.76
0.53
4.64
180 oC
11.59
0.78
0.59
5.34
200 oC
11.70
0.76
0.58
5.17
0 min
9.54
0.72
0.41
2.80
10 min
12.15
0.78
0.58
5.51
20 min
11.51
0.78
0.61
5.45
30 min
10.79
0.78
0.63
5.28
40 min
10.42
0.78
0.61
4.98
15
Table S3. Photovoltaic performance of BTT-DTFFBT devices using different solvents.
Condition
ODCB
1 vol.% CN
180 oC
ODCB/CF=1/1
1 vol.% CN
180 oC
Variable
Jsc
(mA cm-2)
Voc
(V)
FF (%)
PCE (%)
0 min
6.11
0.74
0.61
2.74
10 min
10.8
0.74
0.69
5.48
0 min
6.67
0.74
0.59
2.93
10 min
10.8
0.74
0.65
5.21
16
Table S4. Device performance parameters for inverted BHJ PSCs with the device
structure:
Glass/ITO/PFN/Active
layer/MoOx/Ag
and
Glass/ITO/ZnO/Active
layer/MoOx/Ag.
condition
CB
1 Vol.% CN
180 oC/10min
Device
Structure
Jsc
(mA cm-2)
Voc
(V)
FF (%)
PCE(%)
PFN
11.2
0.76
0.66
5.62
ZnO
11.3
0.74
0.60
5.02
17
Table S5. Device performance parameters for BHJ PSCs based on PBDT-DTFFBT and
BTT-DTFFBT.
Polymer
Condition
Jsc
(mA cm2)
Voc
(V)
FF (%)
PCE (%)
PBDT-
Pristine
10.15
0.82
0.69
5.77
DTFFBT
TAa
4.53
0.82
0.55
2.04
BTT-
Pristineb
11.79
0.78
0.61
5.61
DTFFBT
TAa
9.87
0.78
0.61
4.70
Thermal
Stabilityc
65%
16%
a) Annealing for 60 min at 180 °C; b) Annealing for 10 min at 180 °C as the pristine device; C) The
loss ratio of PCEs, after annealing for 60min at 180 °C.
[1] Z. Li, F. Wu, H. Lv, D. Yang, Z. Chen, X. Zhao, X. Yang, Adv. Mater. 2015, DOI:10.1002/adma.201502900
[2] Murgatro.Pn, J. Phys. D: Appl. Phys. 1970, 3, 151.
[3] G. H. Lu, H. W. Tang, Y. A. Huan, S. J. Li, L. G. Li, Y. Z. Wang, X. N. Yang, Adv. Funct. Mater. 2010, 20,
1714.
[4] H. Lv, X. Zhao, W. Xu, H. Li, J. Chen, X. Yang, Org. Electron. 2013, 14, 1874.
18