Synthesis and photovoltaic properties of conjugated D-A copolymers based on thienyl substituted pyrene and diketopyrrolopyrrole for polymer solar cells

Article abstract of DOI:10.1002/pola.27378

A new donor-acceptor conjugated copolymer (PDTPyDPP), comprising 2,7-di-2-thienyl-4,5,9,10-tetrakis(hexyloxy)pyrene as a donor and diketopyrrolopyrrole (DPP) as an acceptor, was synthesized. PDTPyDPP showed good solubility in common organic solvents, broad visible absorption from 300 to 900 nm, and a moderate hole mobility up to 6.3 × 10^-3 cm² V^-1 s^-1. The power conversion efficiency of the photovoltaic device based on the PDTPyDPP/PC₇₁BM photoactive layer reached 4.43% with 0.66 V of open-circuit voltage (V_oc), 10.52 mA cm^-2 of short-circuit current (J_sc) and 64.11% of fill factor.

Full text of DOI:10.1002/pola.27378

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Synthesis and Photovoltaic Properties of Conjugated D–A Copolymers
Based on Thienyl Substituted Pyrene and Diketopyrrolopyrrole for
Polymer Solar Cells
Ning Wang,1 Xichang Bao,1 Yan Yan,2 Dan Ouyang,1 Mingliang Sun,2,3 V. A. L. Roy,2
Chun Sing Lee,2 Renqiang Yang1
1CAS Key Laboratory of Bio-based Materials, Qingdao Institute of Bioenergy and Bioprocess Technology, Chinese Academy of
Sciences, Qingdao 266101, China
2Center of Super-Diamond and Advanced Films (COSDAF), City University of Hong Kong, Tat Chee Ave, Hong Kong
3Institute of Materials Science and Engineering, Ocean University of China, Qingdao 266100, China
Correspondence to: R. Yang (E-mail: yangrq@qibebt.ac.cn)
Received 10 July 2014; accepted 16 August 2014; published online 8 September 2014
DOI: 10.1002/pola.27378
ABSTRACT: A new donor-acceptor conjugated copolymer
(PDTPyDPP), comprising 2,7-di-2-thienyl-4,5,9,10-tetrakis(hexy-
loxy)pyrene as a donor and diketopyrrolopyrrole (DPP) as an
acceptor, was synthesized. PDTPyDPP showed good solubility
in common organic solvents, broad visible absorption from
300 to 900 nm, and a moderate hole mobility up to 6.3 3 1023
cm2 V21 s21. The power conversion efficiency of the photovol-
taic device based on the PDTPyDPP/PC71BM photoactive layer
reached 4.43% with 0.66 V of open-circuit voltage (Voc), 10.52
mA cm22 of short-circuit current (Jsc) and 64.11% of fill factor.
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KEYWORDS: charge transfer; conjugated polymers; diketopyrro-
lopyrrole; photovoltaic; pyrene; structure-property relations
aggregation.19,20 Some conjugated polymers21–24 or small
molecules25,26 containing pyrene moieties have been prepared
and showed excellent performance in organic electronics. For
example, Hwang and coworkers reported that the incorpora-
tion of the pyrene units to the donor-acceptor (D-A) conju-
gated polymer backbone would improve the hole mobility and
decrease the highest occupied molecular orbital (HOMO)
energy level of the copolymer, which resulted in a highest PCE
of 5.04% obtained.21 However, diketopyrrolopyrrole (DPP) is
INTRODUCTION Polymer solar cells (PSCs) have been exten-
sively studied in recent years, owing to their low cost, light
weight, and flexibility.1–7 Recently, PSCs based on conjugated
polymers and fullerene derivatives have shown a remarkable
breakthrough, the power conversion efficiencies (PCEs) over
8% have been obtained.8–10 In PSCs, the bulk heterojunction
device structure, in which the active layer consists of nano-
scale bicontinuous phase-separated electron donor and
acceptor components, has been proven to be the most suc-
cessful structure.11,12 As for the active layer materials, many
research efforts have been devoted to design and synthesis
novel polymer donor materials with good solubility, broad
absorption, optimized energy levels and high mobility.13–15
The conjugated polymers with alternating electron-rich units
(D) and electron-deficient segments (A), known as D–A
structured polymers,16–18 are one of the most efficient struc-
tures. Therefore, many electron-rich and electron-deficient
building blocks have been used in the design and synthesis
of novel D–A copolymer photovoltaic materials. Among vari-
ous donor units in the D–A copolymers, pyrene is a com-
pletely planar electron-rich moiety, and has prominent
optical and electronic properties such as high quantum yield,
good thermal stability and strong propensity to form p stack
a
strong electron-deficient segment with two electron-
deficient carbonyl groups. DPP-based conjugated polymers
have shown intense absorption in near infrared region and
excellent performance in photovoltaic devices.27–30
Herein, we designed and synthesis a D-A copolymer contain-
ing 2,7-di22-thienyl-4,5,9,10-tetrakis(hexyloxy)pyrene as a
donor moiety and DPP as an acceptor unit (Scheme 1). The
inclusion of two thiophene spacers at 2, 7 position of pyrene
was expected to broaden the absorption and enhance the
light harvesting ability of the conjugated polymer. The four
hexyloxy side chains at 4, 5, 9, 10 position of pyrene would
improve the solubility of the conjugated polymer in common
organic solvent. The thermal, optical, electrochemical, and
Additional Supporting Information may be found in the online version of this article.
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SCHEME 1 Synthesis route of PDTPyDPP.
photovoltaic properties of the polymer were investigated
systematically. The polymer exhibited a high decomposition
temperature of 350 ꢀC, a broad absorption in the range of
300–900 nm, and a HOMO energy level of 25.16 eV. Finally,
performed using a TA-Q600 analyzer with a heating rate of
10 ꢀC min21 under a nitrogen atmosphere. The ultraviolet-
visible (UV–vis) spectra were measured on a Varian Cary 50.
The electrochemical behaviour of the polymer was investi-
gated by cyclic voltammogram (CV). The CV was performed
in a solution of tetrabutylammonium hexafluorophosphate
(Bu4NPF6; 0.1 M) in acetonitrile. A three-electrode cell con-
sisting of a glassy carbon working electrode, a Pt counter
electrode and an Ag/AgCl reference electrode was used. The
scan rate was 100 mV s21. The polymer solution was dipped
on the glassy carbon electrode. The potential of ferrocene/
ferrocenium (Fc/Fc1) was measured to be 0.43 V compared
with the Ag/AgCl electrode under the same conditions. It is
assumed that the redox potential of Fc/Fc1, has an absolute
energy level of 24.8 eV under vacuum. Atomic force micros-
copy (AFM) images were obtained on an Agilent 5400 scan-
ning probe microscope using AC mode.
the PSC device based on this polymer and [6,6]-phenyl-C71
-
butyric acid methyl ester (PC71BM) showed the best power
conversion efficiency (PCE) of 4.43% with an open-circuit
voltage (Voc) of 0.66 V, a short-circuit current density (Jsc) of
10.52 mA cm22 and a fill factor (FF) of 64.11%.
EXPERIMENTAL
Materials
All reagents were bought from commercial sources and were
used without further purification. The solvents were purified
with standard methods. All air and water sensitive reactions
were performed under an argon atmosphere. Silica gel (200–
300 mesh) was used for column chromatography. New prod-
ucts were characterized by 1H NMR, 13C NMR, and Atmos-
pheric Pressure Chemical Ionization-Time of Flight (APCI-
TOF) high resolution mass spectra (HRMS). Compound 1,31
2-tributylstannylthiophene,32 were synthesized according to
the corresponding literatures.
Fabrication of Photovoltaic Devices
Photovoltaic devices with
a layered structure of ITO/
PEDOT:PSS/PDTPyDPP:PC71BM blend/Ca (10 nm)/Al
(100 nm) were fabricated on ITO coated glass substrates (15
3 15 mm2). The ITO coated glasses were cleaned in an
ultrasonic bath with detergent, ultra pure water, acetone,
and isopropyl alcohol sequentially for 20 min, and then oxy-
gen plasma treated for 20 min. The substrates were spin
coated with PEDOT:PSS at 5000 rpm, and dried at 120 ꢀC
for 20 min. PDTPyDPP and PC71BM were dissolved in deoxy-
genated anhydrous o-dichlorobenzene (o-DCB) in the weight
ratios of 1:1, 1:1.5, and 1:2, respectively and stirred over-
night in glovebox at 90 ꢀC. An active layer consisting of the
blend of PDTPyDPP and PC71BM was then spin coated on
Characterization
1H NMR and 13C NMR spectra were recorded on a Bruker
DRX-600 spectrometer. APCI-TOF HRMS were performed on
Bruker Maxis UHR-TOF (both positive and negative ion
reflector mode). The molecular weight and polydispersity
were determined by size exclusion chromatography (SEC)
analysis using an ELEOS System, with monodisperse polysty-
rene as standard and THF as eluent at a flow rate of 1.0 mL
min21 at 35 ꢀC. Thermogravimetric analysis (TGA) and dif-
ferential scanning calorimetry (DSC) measurements were
PEDOT:PSS.
A typical concentration of the PDTPyDPP/
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PC71BM blending solution was 24 mg mL21. Subsequently
Ca (10 nm) and Al (100 nm) were thermally evaporated in a
vacuum of 2 3 1024 Pa on top of the active layer as cathode.
Photovoltaic performance was characterized under illumina-
tion with an AM 1.5G (100 mW cm22) in a nitrogen atmos-
phere, and the current–voltage curves were recorded using a
Keithley 2400 source meter. The external quantum efficien-
cies (EQE) of solar cells were analyzed using a certified New-
port incident photon conversion efficiency measurement
system.
(APCI-TOF): [M 1 H]1 Calcd for: C40H57Br2O4 759.2623;
found: 759.2597.
Synthesis of DTPy4C6
Compound
2
(7.61
g,
10
mmol)
and
2-
tributylstannylthiophene (8.20 g, 22 mmol) were added in a
50 mL three-necked flask. After purging with argon, bis(tri-
phenylphosphine)palladium(II) chloride (350.96 mg, 0.5
mmol) and THF (30 mL) were added. The reaction mixture
was stirred at 80 ꢀC for 12 h. After cooling down to room
temperature, the products were extracted with chloroform
three times, washed with water, and then dried over sodium
sulfate. After filtration, the solution was evaporated and the
product mixture was purified by silica gel flash column chro-
matography using a mixture of dichloromethane/petroleum
ether (1/1, v/v) as an eluent. Finally, the recrystallization of
the product using chloroform/methanol afforded DTPy4C6
as pale yellow solid (5.98 g, 7.79 mmol) in 78% yield. 1H
NMR (600 MHz, CDCl3) d (ppm) 5 8.66 (s, 4H), 7.64 (dd,
J1 5 3.60 Hz, J2 5 0.98 Hz, 2H), 7.40 (dd, J1 5 5.16 Hz,
J2 5 0.98 Hz, 2H), 7.20 (dd, J1 5 5.16 Hz, J2 5 3.60 Hz, 2H),
4.36 (t, J 5 6.76 Hz, 8H), 2.02–1.96 (m, 8H), 1.71–1.65 (m,
8H), 1.47–1.37 (m, 16H), 0.94 (t, J 5 7.04 Hz, 12H). 13C NMR
Fabrication of Field-Effect Transistors (FET) Devices
Bottom-gate/bottom-contact transistors were fabricated on
Au-patterned SiO2/Si substrate. After standard cleaning (15
min ultrasonic process in acetone, isopropanol and DI-water,
sequentially), 5 mg mL21 polymer dissolved in chloroben-
zene was spin-coated on the substrates at a speed of
1200 rpm for 1 ꢀmin. Then, substrates were annealed on a
hot plate at 120 C for 30 min before device test. I–V curves
were measured by a Keithley 6212 source meter, Agilent
4155C semiconductor parameter analyzer and HP 4284A
LCR meter in nitrogen glove-box under dark conditions.
(150 MHz, CDCl3),
d (ppm) 5 151.38, 144.25, 138.46,
Synthesis of Compound 1
137.42, 131.11, 125.18, 124.02, 121.56, 117.23, 73.93, 31.87,
30.64, 26.26, 22.80, 14.14. HRMS (APCI-TOF): [M 1 H]1
Calcd for: C48H63O4S2 767.4238; found: 767.4235.
To a solution of pyrene-4,5,9,10-tetranoes (13 g, 50 mmol)
in 500 mL of 85% H2SO4, n-bromosuccinimide (NBS) (27 g,
0.15 mol) was added. The mixture was stirred for 4 h at
room temperature, and then was poured into 2 L water and
stirred overnight. The precipitated was filtered and dried
under vacuum to afford compound 1 as pale yellow solid
Synthesis of DTPy4C6Sn
DTPy4C6 (1.53 g, 2 mmol) was added in a 50 mL dry flask.
After purging with argon, fresh distilled THF (30 mL) was
added. The reaction mixture was cooled down to 0 ꢀC, and
n-butyllithium (1.6 M in n-hexane, 2.6 mL, 4.2 mmol) was
added dropwise. After 1 h of stirring at this temperature, the
neat trimethylstannyl chloride (1.0 M in n-hexane, 4.8 mL,
and 4.8 mmol) was added. The solution was allowed to
warm to room temperature and stirred for another 12 h, fol-
lowed by dilution with hexane and washing with brine. The
organic layer was collected and dried over anhydrous
Na2SO4, then, the solvent was removed in vacuum. The
recrystallization of the crude product using isopropanol
afforded DTPy4C6Sn as pale yellow solid (1.88 g, 1.72
1
(18.1 g, 86%). H NMR (600 MHz, DMSO-d6) d (ppm) 5 8.35
(s, 4H). 13C NMR (150 MHz, DMSO-d6), d (ppm) 5 165.28,
147.65, 139.72, 135.29, 125.75. HRMS (APCI-TOF): [M 1 H]1
Calcd for: C16H5Br2O4 418.8467; found: 418.8432.
Synthesis of Compound 2
To a solution of compound 1 (8.40 g, 20 mmol) in THF
(340 mL) and H2O (210 mL) were added tetra-n-butylammo-
nium bromide (3.22 g, 10 mmol) and Na2S2O3 (18.96 g, 120
mmol). After 15 min, a solution of KOH (16 g, 69.7 mmol) in
H2O (210 mL) was added to the reaction mixture followed
by 1-bromohexane (14.85 g, 90 mmol). The red colour reac-
tion mixture was stirred at 100 ꢀC for 4.5 h. The reaction
mixture was cooled and extracted with EtOAc (100 mL). The
organic layers were separated and the aqueous phase was
extracted with EtOAc (3 3 100 mL). The combined EtOAc
extracts were washed with water followed by brine and
dried over Na2SO4. The solvent was removed under reduced
pressure. The crude product was purified by silica gel flash
column chromatography using a mixture of dichlorome-
thane/petroleum ether (1/2, v/v) as an eluent to afford com-
pound 2 as white solid (10.18 g, 13.4 mmol) in 67% yield.
1H NMR (600 MHz, CDCl3) d (ppm) 5 8.54 (s, 4H), 4.32 (t,
J 5 6.72 Hz, 8H), 2.00–1.94 (m, 8H), 1.67–1.60 (m, 8H),
1.46–1.40 (m, 16H), 0.97 (t, J 5 6.98 Hz, 12H). 13C NMR (150
MHz, CDCl3), d (ppm) 5 151.49, 144.27, 138.97, 137.01,
125.34, 74.05, 32.15, 30.64, 26.22, 23.78, 14.17. HRMS
mmol) in 86% yield. 1H NMR (600 MHz, CDCl3),
d
(ppm) 5 8.66 (s, 4H), 7.74 (d, J 5 3.36 Hz, 2H), 7.28 (d,
J 5 3.36 Hz, 2H), 4.35 (t, J 5 6.40 Hz, 8H), 2.02–1.95 (m, 8H),
1.73–1.67 (m, 8H), 1.47–1.38 (m, 16H), 0.95 (t, J 5 6.94 Hz,
12H), 0.45 (s, 18H). 13C NMR (150 MHz, CDCl3),
d
(ppm) 5 151.32, 144.27, 138.46, 136.48, 132.21, 129.18,
125.01, 120.09, 116.46, 73.93, 31.87, 30.64, 26.26, 22.80,
14.14, 28.26. HRMS (APCI-TOF): [M 1 H]1 Calcd for:
C54H79O4S2Sn2 1093.3469; found: 1093.3463.
Synthesis of PDTPyDPP
DTPy4C6Sn (218 mg, 0.2 mmol) and 2BrDPP32 (178 mg,
0.2 mmol) were dissolved in 8 mL toluene. The mixture was
purged with argon for 30 min, then Pd2(dba)3 (4 mg) and
P(o-tol)3 (8 mg) were added. After being purged with argon
for another 30 min, the reaction mixture was heated to 100
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tion for the polymer before 350 ꢀC. The high decomposition
and thermal transition temperatures prevent the deformation
and degradation of the polymer film when the active layer
was annealed, indicating sufficient thermal stability for PSCs
application.33
Optical Properties
The absorption spectra of PDTPyDPP in 1,2-dichlorobenzene
and in film are shown in Figure 2. A maximum peak at
700 nm with two shoulder peaks at 778 and 643 nm was
observed in the spectrum of the polymer in 1,2-dichloroben-
zene solution, meanwhile, two peaks at 422 and 367 nm
were showed in short wavelength region. Compared with the
weak absorption for the p–p* transition in the 300–500 nm
range, the intense absorption in the range of 550–900 nm
was attributed to the intramolecular charge transfer (ICT)
from electron-donating units (pyrene and thiophene) to
electron-withdrawing unit (DPP) in the conjugated main
chain.34 In the solid film, the peak of maximum ICT absorp-
tion was at 715 nm, which was red-shifted by 15 nm in com-
parison with their solution absorption. Interestingly, the
solid absorption spectrum demonstrates a more pronounced
shoulder peak at long wavelength (797 nm) and a weaker
shoulder peak at short wavelength (653 nm), which indi-
cates an increased interchain p–p* stacking for planar poly-
mer chain in the solid state. The optical band-gap of the
polymer was estimated as 1.33 eV from the onset of the UV–
vis absorption in the thin film.
FIGURE 1 TGA and DSC curves of PDTPyDPP.
ꢀC and stirred for 12 h under an argon atmosphere. Then
the mixture was cooled down to ambient temperature and
the polymer was precipitated by the addition of 150 mL
methanol. The crude product was then subjected to Soxhlet
extraction with methanol, hexane, and chlorobenzene. The
polymer recovered from chlorobenzene was precipitated by
the addition of 150 mL methanol. Then the product was
dried under vacuum for 1 day to give the target polymer
PDTPyDPP as a dark solid (242 mg, yield 75.6%, Mn 5 14.5
kDa, PDI 5 1.4). 1H NMR (600 MHz, CDCl3), d (ppm) 5 9.50–
7.35 (br, 12H), 5.0–3.5 (br, 12H), 2.5–1.1 (br, 80H), and 1.1–
0.5 (br, 24H).
Electrochemical Properties
RESULTS AND DISCUSSION
Electronic energy levels of the polymers are crucial for their
application in PSCs. To evaluate the redox behaviours of the
synthesized conjugated polymer, the electrochemical prop-
erty of PDTPyDPP was measured by CV with 0.1 M Bu4NPF6
as the supporting electrolyte. As shown in Figure 3, the poly-
mer film exhibited an irreversible reduction wave in the neg-
ative potential range and a quasi-reversible wave in the
positive potential range (vs. Ag/AgCl). The HOMO and lowest
unoccupied molecular orbital (LUMO) energy levels of the
conjugated polymer film were estimated from the onset
Synthesis and Characterization
The synthesis of the monomer and the target polymer is
depicted in Scheme 1. 2,7-Dibromo-4,5,9,10-tetra-hexyloxy-
pyrene (compound 2) was prepared conveniently via reduc-
tive alkylation with Na2S2O3 and 1-bromohexane according
to the modified procedure reported previously.31 DTPy4C6
was synthesized by the Stille coupling reaction between
compound 2 and 2-tributylstannylthiophene. Then it was
stannated with trimethyltinchloride to produce the monomer
DTPy4C6Sn. 2BrDPP32 was commercial available. Finally, the
D–A structured polymer (PDTPyDPP) was synthesized via
Stille coupling polymerization between DTPy4C6Sn and
2BrDPP32 in the presence of Pd2(dba)3 catalyst and tri(o-tol-
yl)phosphine ligand with a yield of 75.6%. The synthesized
potentials
according
to
the
equation
HOMO
1
polymer was characterized by H NMR (Supporting Informa-
tion Fig. S1) and the number-average molecular weight (Mn)
was measured by SEC to be 14.5 kDa with a polydispersity
index (PDI) of 1.4. PDTPyDPP can be dissolved in common
organic solvent such as chloroform, chlorobenzene, and 1, 2-
dichlorobenzene.
Thermal Stability
The thermal properties of the polymer PDTPyDPP were
measured by TGA and DSC. As shown in Figure 1, TGA indi-
cates that PDTPyDPP has good thermal stability and the
decomposition temperature (Td) at 5% weight loss is about
FIGURE 2 Normalized UV–vis absorption spectra of PDTPyDPP
ꢀ
350 C. DSC reveals that there is no apparent thermal transi-
in 1,2-dichlorobenzene solution and in the thin solid film.
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FIGURE 3 CV of PDTPyDPP.
(LUMO) 5 2[ðEonset
oxðredÞ2EfocÞ1Eref
] (eV), where Efoc is the
potential of the external standard, the ferrocene/ferrocenium
ion (Foc/Foc1) couple, and Eref is the reference energy level
of ferrocene (4.8 eV below the vacuum level; the vacuum level
is defined as zero). The HOMO and LUMO energy levels of
PDTPyDPP calculated in this way are 25.16 and 23.81 eV.
The energy band-gap calculated from the HOMO and LUMO
levels is 1.35 eV, which is consistent with the optical band gap
(1.33 eV) estimated from absorption onset in the thin film.
FIGURE 4 J–V characteristics of PSCs based on the
PDTPyDPP:PC71BM blend film with (a) different ratios and (b) dif-
ferent amount of DIO as additive when PDTPyDPP:PC71BM 5 1:1.5.
Polymer Solar Cell Performance
Photovoltaic property of PDTPyDPP was investigated with a
device structure of ITO/PEDOT:PSS/PDTPyDPP:PC71BM/Ca/
Al under the illumination of AM 1.5G at 100 mA cm22. The
devices fabrication conditions, such as the weight ratio of
polymer to PC71BM, and the amount of the 1,8-diiodooctane
(DIO) additive were carefully optimized. As shown in Table 1
and Figure 4(a), the Voc values kept almost stable while the
ratio of PDTPyDPP to PC71BM increased from 1:1 to 1:1.5,
and then to 1:2, however, the device showed the highest Jsc
and FF values at 1:1.5, and the PCE of the device reached
PC71BM blend films were prepared at the above optimized
composite ratio from o-dichlorobenzene solution with addi-
tion of 1, 1.5, 2, 2.5, and 3% (volume) DIO as additive,
respectively. As shown in Table 1 and Figure 4(b), while
1.5% volume ratio of DIO was used as the additive, the PCE
of the PDTPyDPP:PC71BM based device increased to 4.43%
with Voc 5 0.66 V, Jsc 5 10.52 mA cm22, and FF 5 64.11%.
We also use PC61BM as acceptor to investigate the device
performance of our polymer. As shown in Supporting Infor-
mation Figure S2 and Table S1, the devices with PDTPyDPP
as donor and PC61BM as acceptor showed the best PCE of
3.45%, with
Voc 5 0.66 V,
J
sc 5 8.01 mA cm22
,
and
FF 5 64.95%. To further investigate the effect of processing
additive on the performance of devices, the PDTPyDPP/
1.86 %, with
Voc 5 0.63 V, J , and
sc 5 5.01 mA cm22
TABLE 1 Device Performance of the Copolymer
FF 5 58.80%, when the weight ratio of PDTPyDPP to
Voc
Jsc
(mA cm22
FF
PCE
(%)
PC61BM was 2:3 with addition of 1.5% DIO as additive.
Ratioa
Solvent
(V)
)
(%)
The photoresponse curve of the optimized device based on
PDTPyDPP was investigated, which showed a relatively
broad photoresponse range between 300 and 800 nm (Fig.
5). The maximum EQE value of 50% at 460 nm was
observed. The integrated JSC from EQE spectrum is 10.01 mA
cm22, which is consistent with the measured JSC value
(10.52 mA cm22).
1:1
o-DCB
0.66
0.66
0.66
0.67
0.66
0.65
0.67
0.66
7.89
8.01
7.42
8.97
10.52
9.99
9.58
9.00
61.32
64.95
61.29
64.81
64.11
59.67
60.07
59.51
3.18
3.45
2.99
3.90
4.43
3.87
3.83
3.55
1:1.5
1:2
o-DCB
o-DCB
1:1.5
1:1.5
1:1.5
1:1.5
1:1.5
o-DCB 1 1.0%DIO
o-DCB 1 1.5%DIO
o-DCB 1 2.0%DIO
o-DCB 1 2.5%DIO
o-DCB 1 3.0%DIO
Hole Mobility
The hole mobility of the polymer is tested by FET device.
Figure 6 shows the transfer curve of the FET device based
a
The weight ratio of the PDTPyDPP to PC71BM.
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FIGURE 5 EQE curve of device based on PDTPyDPP/PC71BM
FIGURE 6 ID versus VG transfer characteristic of PDTPyDPP
(1:1.5, w/w) with 1.5% DIO as additive.
based FET device.
on PDTPyDPP. The calculated mobility of the polymer is 6.3
3 1023 cm2 V21 s21 with on/off ratio of 1 3 105 and VTh of
8 V for the FET device. Obviously, the high efficiency of the
PSC based on PDTPyDPP should be as a benefit of the high
hole mobility and broad absorption of PDTPyDPP.
All the films were prepared under the same conditions with
the optimized photovoltaic devices. As shown in Figure 7(a),
the surface root mean square (RMS) roughness for the blend
film of PDTPyDPP: PC71BM is 0.80 nm. While the blend films
are spin-coated from o-dichlorobenzene solution containing
1.5% DIO as additive, the RMS data is greatly increased to
2.07 nm, which indicates that adding DIO as additive in the
mixture leads to rougher surface than that of the pristine
blend film. Notably, the fibrous networks phase images are
observed in the blending films with DIO additive, indicating
AFM Images
The morphologies of the blend films of PDTPyDPP and
PC71BM (1:1.5, w/w) have been investigated by tapping-
mode AFM. Figure 7 showed the topographic and phase
images of the films with or without DIO additive treatment.
that
a well-ordered interpenetrating network between
FIGURE 7 AFM topography height (a and c), phase (b and d) images of the PDTPyDPP:PC71BM (1:1.5, w/w) film without (a and b)
and with (c and d) 1.5% DIO as additive (scan size: 2 3 2 lm2).
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12 J.-H. Kim, C. E. Song, H. U. Kim, I.-N. Kang, W. S. Shin, M.-
J. Park, D.-H. Hwang, J. Polym. Sci. Part A: Polym. Chem. 2013,
51, 4136–4149.
polymer and acceptor is formed [Fig. 7(d)], which would be
helpful in the charge collection efficiency in the active layer
of the device, finally, resulted in higher Jsc (Fig. 4 and Table
1).35,36
13 B. Qi, J. Wang, Phys. Chem. Chem. Phys. 2013, 15, 8972–
8982.
14 S. L. Shen, L. Gao, C. He, Z. J. Zhang, Q. J. Sun, Y. F. Li,
Org. Electron. 2013, 14, 875–881.
CONCLUSIONS
In conclusion, we synthesized a new D-A conjugated copoly-
mer from two easily accessible monomers, pyrene derivative
and DPP. The obtained polymer showed broad visible
absorption from 300 to 900 nm, a moderate field hole mobil-
ity up to 1023 order, a high decomposition temperature of
350 ꢀC, and a HOMO energy level of 25.16 eV. The PSC
device based on this polymer and PC71BM gave the PCE of
4.43%, one of the highest efficiencies among pyrene-based
polymers. Our preliminary experiment results show that
thienyl substituted pyrene with suitable side chains is a
promising donor building block in constructing D-A conju-
gated polymers for the photovoltaic applications.
15 H. B. Pan, L. J. Zuo, W. F. Fu, C. C. Fan, B. Andreasen, X. Q.
Jiang, K. Norrman, F. C. Krebs, H. Z. Chen, Org. Electron. 2013,
14, 797–803.
16 L. J. Huo, Z. A. Tan, X. Wang, Y. Zhou, M. F. Han, Y. F. Li, J.
Polym. Sci. Part A: Polym. Chem. 2008, 46, 4038–4049.
17 X. Zhao, D. Yang, H. Lv, L. Yin, X. Yang, Polym. Chem.
2013, 4, 57–60.
18 P. Shen, H. J. Bin, Y. Zhang, Y. F. Li, Polym. Chem. 2014, 5,
567–577.
19 J. Xiao, X. Xiao, Y. Zhao, B. Wu, Z. Liu, X. Zhang, S. Wang,
X. Zhao, L. Liu, L. Jiang, Nanoscale 2013, 5, 5420–5425.
20 S. X. Qu, M. H. Li, L. X. Xie, X. Huang, J. G. Yang, N. Wang,
S. F. Yang, ACS Nano 2013, 7, 4070–4081.
21 J. H. Kim, H. U. Kim, I. N. Kang, S. K. Lee, S. J. Moon, W. S.
Shin, D. H. Hwang, Macromolecules 2012, 45, 8628–8638.
ACKNOWLEDGMENTS
22 D. S. Yang, K. H. Kim, M. J. Cho, J. I. Jin, D. H. Choi, J.
Polym. Sci. Part A: Polym. Chem. 2013, 51, 1457–1467.
This work was supported by National Natural Science Founda-
tion of China (21204097, 21274134, 51173199, and
61107090), Ministry of Science and Technology of China
(2014CB643501 and 2010DFA52310), Shandong Provincial
Natural Science Foundation (ZR2011BZ007), and Qingdao
Municipal Science and Technology Program (11-2-4–22-hz).
23 C. E. Song, I. N. Kang, J. H. Kim, D. H. Hwang, J. C. Lee, T.
Ahn, W. S. Shin, S. J. Moon, S. K. Lee, J. Polym. Sci. Part A:
Polym. Chem. 2013, 51, 1512–1519.
24 J. H. Kim, S. Lee, I. N. Kang, M. J. Park, D. H. Hwang, J.
Polym. Sci. Part A: Polym. Chem. 2012, 50, 3415–3424.
25 J. W. Mun, I. Cho, D. Lee, W. S. Yoon, O. K. Kwon, C. Lee,
S. Y. Park, Org. Electron. 2013, 14, 2341–2347.
REFERENCES AND NOTES
26 O. P. Lee, A. T. Yiu, P. M. Beaujuge, C. H. Woo, T. W.
Holcombe, J. E. Millstone, J. D. Douglas, M. S. Chen, J. M. J.
1 G. Yu, J. Gao, J. C. Hummelen, F. Wudl, A. J. Heeger, Sci-
ence 1995, 270, 1789–1791.
ꢀ
Frechet, Adv. Mater. 2011, 23, 5359–5363.
ꢀ
27 R. Zhou, Q. D. Li, X. C. Li, S. M. Lu, L. P. Wang, C. H. Zhang,
J. Huang, P. Chen, F. Li, X. H. Zhu, W. C. H. Choy, J. B. Peng,
Y. Cao, X. Gong, Dyes Pigments 2014, 101, 51–57.
2 P. M. Beaujuge, J. M. J. Frechet, J. Am. Chem. Soc. 2011,
133, 20009–20029.
3 J. H. Hou, H. Y. Chen, S. Q. Zhang, R. I. Chen, Y. Yang, Y.
Wu, G. Li, J. Am. Chem. Soc. 2009, 131, 15586–15587.
28 Z. Zeng, Y. Li, J. F. Deng, Q. Huang, Q. Peng, J. Mater.
Chem. A 2014, 2, 653–662.
4 H. Tan, X. Deng, J. Yu, J. Chen, K. Nie, Y. Huang, Y. Liu, Y.
Wang, M. Zhu, W. Zhu, J. Polym. Sci. Part A: Polym. Chem.
2013, 51, 1051–1057.
29 J.-H. Kim, C. E. Song, I.-N. Kang, W. S. Shin, D.-H. Hwang,
Chem. Commun. 2013, 49, 3248–3250.
30 W. Li, A. Furlan, W. S. C. Roelofs, K. H. Hendriks, G. W. P.
van Pruissen, M. M. Wienk, R. A. J. Janssen, Chem. Commun.
2014, 50, 679–681.
5 Y. Z. Lin, Y. F. Li, X. W. Zhan, Chem. Soc. Rev. 2012, 41,
4245–4272.
6 X. Guan, K. Zhang, F. Huang, G. C. Bazan, Y. Cao, Adv. Func.
Mater. 2012, 22, 2846–2854.
31 S.-i. Kawano, M. Baumgarten, D. Chercka, V. Enkelmann, K.
Muellen, Chem. Commun. 2013, 49, 5058–5060.
7 Q. Liu, X. C. Bao, S. G. Wen, Z. K. Du, L. L. Han, D. Q. Zhu, Y. H.
Chen, M. L. Sun, R. Q. Yang, Polym. Chem. 2014, 5, 2076–2082.
32 Q. Ye, J. Chang, K.-W. Huang, C. Chi, Org. Lett. 2011, 13,
5960–5963.
8 Z. C. He, C. M. Zhong, S. J. Su, M. Xu, H. B. Wu, Y. Cao, Nat.
Photonics 2012, 6, 591–595.
33 S. Wen, X. Bao, W. Shen, C. Gu, Z. Du, L. Han, D. Zhu, R.
Yang, J. Polym. Sci. Part A: Polym. Chem. 2014, 52, 208–215.
9 L. Dou, J. You, J. Yang, C. C. Chen, Y. J. He, S. Murase, T.
Moriarty, K. Emery, G. Li, Y. Yang, Nat. Photonics 2012, 6, 180–185.
34 K.-H. Ong, S.-L. Lim, J. Li, H.-K. Wong, H.-S. Tan, T.-T. Lin,
L. C. H. Moh, J. C. de Mello, Z.-K. Chen, Polym. Chem. 2013, 4,
1863–1873.
10 J. You, L. Dou, K. Yoshimura, T. Kato, K. Ohya, T. Moriarty,
K. Emery, C.-C. Chen, J. Gao, G. Li, Y. Yang, Nat. Commun.
2013, 4, 1446.
35 Y. Wang, Y. Liu, S. J. Chen, R. X. Peng, Z. Y. Ge, Chem.
Mater. 2013, 25, 3196–3204.
11 R. S. Kularatne, H. D. Magurudeniya, P. Sista, M. C. Biewer,
M. C. Stefan, J. Polym. Sci. Part A: Polym. Chem. 2013, 51,
743–768.
36 X. C. Bao, T. Wang, A. L. Yang, C. P. Yang, X. W. Dou, W. C.
Chen, N. Wang, R. Q. Yang, Mater. Sci. Eng. B 2014, 180, 7–11.
3204
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2014, 52, 3198–3204