Synthesis and photovoltaic characteristics of novel copolymers containing poly(phenylenevinylene) and triphenylamine moieties connected at 1,7 bay positions of perylene bisimide

Article abstract of DOI:10.1021/ma048491l

Two novel copolymers containing PPV and triphenylamine moieties connected at 1,7 bay positions of perylene bisimide were successfully synthesized by means of the Wittig reaction. Both of them were characterized by FT-IR, ¹H NMR, UV-vis, and FL

Full text of DOI:10.1021/ma048491l

716
Macromolecules 2005, 38, 716-721
Synthesis and Photovoltaic Characteristics of Novel Copolymers
Containing Poly(phenylenevinylene) and Triphenylamine Moieties
Connected at 1,7 Bay Positions of Perylene Bisimide
Yang Liu,†,‡ Chunhe Yang,† Yongjun Li,†,‡ Yuliang Li,*,† Shu Wang,†
Junpeng Zhuang,† Huibiao Liu,† Ning Wang,†,‡ Xiaorong He,†,‡ Yongfang Li,† and
Daoben Zhu*,†
CAS Key Laboratory of Organic Solids, Center for Molecular Sciences, Institute of Chemistry,
Chinese Academy of Sciences, Beijing 100080, P.R. China, and Graduate School of Chinese
Academy of Sciences
Received July 23, 2004; Revised Manuscript Received November 8, 2004
ABSTRACT: Two novel copolymers containing PPV and triphenylamine moieties connected at 1,7 bay
positions of perylene bisimide were successfully synthesized by means of the Wittig reaction. Both of
1
them were characterized by FT-IR, H NMR, UV-vis, and FL spectra as well as GPC, TGA, and DSC
measurements. The introduction of PPV and TPA moieties into the bay positions of perylene bisimide
enhanced the solubility of polymers and quenched the fluorescence of perylene bisimide obviously. The
photovoltaic devices ITO/PEDOT:PSS/copolymers/Ca/Al were fabricated, and their I-V characteristics
indicated that the copolymerization in PERY-PPV and PERY-PPV-TPA improved the device perform-
ance for some extent.
Introduction
bisimide led to polymers with good solubility compared
with that of perylene bisimide, which may be a useful
strategy for the synthesis of other functional polymers.
These polymer donor-acceptor molecular systems have
shown that the charge transfer from the excited state
occurs. These data imply fabricating improved polymer
photovoltaic cells with higher efficiency. We hope that
these new designed donor-acceptor copolymers could
be of importance for future studies on polymer materials
applied in the field of photoelectric devices.
In recent years, conjugated polymers and organic
materials have attracted much attention for their ap-
plications in light-emitting diodes (LEDs) and plastic
solar cells.1-3 Poly(phenylenevinylene) (PPV) and its
derivatives are one of the most promising classes of
conjugated polymers for LEDs due to their high lumi-
nescence and easy modification of the chemical struc-
ture.4-8 Triphenylamine (TPA) and its derivatives, with
excellent solubility, good stability, and high PL ef-
ficiency, have been extensively used as hole-transport-
ing species in photoelectronic devices.9 Perylene bisim-
ides represent a class of organic semiconductors with a
variety of different structures,10-13 with possible ap-
plications such as optical switching,14 photovoltaic
devices,15 and dye lasers.16 They have excellent chemi-
cal, thermal, and photochemical stability. Perylene
bisimides are potential candidates as electron-accepting
materials in organic photovoltaic solar cells.17 Both PPV
and perylene bisimide chromophores have been applied
in bulk-heterojunction-like solar cell configurations as
donor and as acceptor materials, respectively.18,19 Re-
cently, Janssen’s group reported a new class of donor-
acceptor polymers consisting of alternating oligo(p-
phenylenevinylene) (OPV) and perylene bisimide connec-
ted via saturated spacers.20 However, little attention
was paid to the synthesis of copolymers containing PPV
and TPA moieties covalently introduced into bay posi-
tions of perylene bisimide.13 In this paper, we present
the synthesis and characterization of two copolymers
containing perylene bisimide and PPV and TPA moi-
eties. The PPV and TPA groups were connected through
ether linkages at 1,7 bay positions of perylene bisimide,
and the photovoltaic characteristics of two copolymers
were measured. In our case, introducing moieties with
different properties into the bay positions of perylene
Experimental Section
Materials. Most of chemical reagents were purchased from
Acros or Aldrich Corp. and were utilized as received unless
indicated otherwise. N,N′-Dioctyl-1,7-dibromoperylene-3,4,9,-
10-tetracarboxylic acid bisimide (1), 1,4-bis(triphenylphospho-
nionmethyl)-2,5-bis(octyloxy)benzene dibromide (3), and triph-
enylamine diandehyde (4) were prepared according to literature
procedures.21-23 All solvents were purified using standard
procedures.
N,N′-Dioctyl-1,7-bis(4-formalphenoxy)perylene-3,4,9,-
10-tetracarboxylic Acid Bisimide (PERY) (2). A mixture
of p-hydroxybenzaldehyde (97.6 mg, 0.8 mmol), K2CO3 (442
mg, 3.2 mmol), and 18-crown-6 (1.69 g, 6.4 mmol) was stirred
under nitrogen in toluene (50 mL) at room temperature. Then
N,N′-dioctyl-1,7-dibromoperylene-3,4,9,10-tetracarboxylic acid
bisimide (1) (154 mg, 0.2 mmol) was added. The reaction
mixture was refluxed with stirring for 5 h. After cooling to
room temperature, the reaction mixture was filtered and
filtrate was collected. The crude product was obtained by
drying solvent and purified by column chromatography on
silica with CH2Cl2 to give 2 (98.3 mg, 58%): 1H NMR (400
MHz, CDCl3, 25 °C) δ: 10.00 (s, 2H), 9.44 (d, 2H, J ) 9.5 Hz),
8.64 (d, 2H, J ) 9.5 Hz), 8.36 (s, 2H), 7.96 (d, 4H, J ) 9.5 Hz),
7.24 (d, 4H, J ) 9.5 Hz), 4.15 (t, 4H, J ) 7.7 Hz), 1.71 (m,
4H), 1.40-1.26 (m, 20H), 0.86 (m, 6H). UV/vis (CHCl3) λmax
:
526, 492, 392 nm. Fluorescence (CHCl3) λmax: 562 nm. FT-IR
(KBr), ν [cm-1]: 2733, 1700, 1659, 853. MS (MALDI-TOF):
854.9 (M-). Elemental analysis calcd (%) for C54H50N2O8
(854.4): C, 75.86; H, 5.89; N, 3.28. Found: C, 75.61; H, 6.02;
N, 3.36.
† Chinese Academy of Sciences.
‡ Graduate School of Chinese Academy of Science.
* Corresponding author. E-mail: ylli@iccas.ac.cn.
Synthesis of Copolymer PERY-PPV (5). To a solution
of 17.1 mg (0.02 mmol) of compound 2 and 20.8 mg (0.02 mmol)
10.1021/ma048491l CCC: $30.25 © 2005 American Chemical Society
Published on Web 01/14/2005

Macromolecules, Vol. 38, No. 3, 2005
Novel Copolymers Containing PPV 717
Scheme 1. Synthesis of Monomer and Copolymersa
a Reaction conditions: (a) p-hydroxybenzaldehyde, K2CO3, 18-crown-6, toluene, nitrogen, reflux, 5 h, 58%; (b) compound 3,
CHCl3, EtOH, EtONa/EtOH, at room temperature, 48 h, 45%; (c) compounds 3 and 4, CHCl3, EtOH, EtONa/EtOH, at room
temperature, 24 h, 12%.
of compound 3 in 40 mL of dry CHCl3 and 10 mL of anhydrous
EtOH, 10 mL of fresh EtONa/EtOH (10 mL of EtOH + 115
mg of Na) was added. The reaction mixture was stirred at room
temperature for 48 h. Then the resulting solution was poured
into 50 mL of 2 N hydrochloric acid. The organic phase was
collected and washed with ethanol/water (3/1) to remove the
byproducts triphenylphosphine oxide and NaBr. The product
was extracted by dichloromethane and dried by anhydrous
sodium sulfate. The solvent was removed, and the residue was
redissolved in CH2Cl2 and precipitated in methanol and dried
in a vacuum to give 17.2 mg of dark solid. 1H NMR (400 MHz,
CDCl3, 25 °C) δ: 9.44 (br, 2H), 8.63 (br, 2H), 8.39 (s, 2H), 7.95
(d, 4H), 7.65-7.46 (br, 2H), 7.23-7.17 (br, 4H), 7.05-6.72 (br,
4H), 4.14 (br, 4H), 4.04-3.85 (br, 4H), 1.71 (m, 8H), 1.55-
1.24 (m, 40H), 0.86 (m, 12H). UV/vis (CHCl3) λmax: 536, 502,
394 nm. Fluorescence (CHCl3) λmax: 565 nm. FT-IR (KBr), ν
[cm-1]: 1700, 1659, 984. GPC (THF, g/mol): Mn, 6801; Mw,
15 419; Mz ) 35 380; PDI: 2.27.
Characterization. UV/vis spectra were taken on a Hitachi
U-3010 spectrometer, and fluorescence spectra were measured
on a Hitachi F-4500 spectrofluorometer. 1H NMR spectra were
obtained on a Bruker Avance DPS-400(400 MHz) spectrom-
eter. FT-IR spectra were measured on a Bruker EQUINOX55
spectrometer. MALDI-TOF mass spectrometric measure-
ments were performed on Bruker Biflex MALDI-TOF. El-
emental analyses were carried out on the Carlo-Erba 1160
elemental analyzer. Gel permeation chromatography (GPC)
analysis was performed on a Waters 2410 GPC instrument,
using THF as eluant and polystyrene standards for calibration.
Thermal gravimetric analysis (TGA) was carried out using
Perkin-Elmer 7 series thermal analysis system. Differential
scanning calorimetry (DSC) was run on a DSC822e at a
heating rate of 10 °C/min in nitrogen. The current-voltage
(I-V) measurements of photovoltaic devices were conducted
on a computer-controlled Keithley 236 source measure unit.
A xenon lamp simulated a white-light source; the optical power
at the sample was 75 mW/cm2.
Synthesis of Copolymer PERY-PPV-TPA (6). A mix-
ture of compound 2 (17.2 mg, 0.02 mmol), compound 3 (104.2
mg, 0.1 mmol), and compound 4 (24 mg, 0.08 mmol) was
dissolved in 50 mL of dry chloroform and 10 mL of anhydrous
EtOH. Then 10 mL of fresh EtONa/EtOH (10 mL of EtOH +
115 mg of Na) was added. The reaction mixture was stirred
at room temperature for 24 h. Then the resulting solution was
poured into 50 mL of 2 N hydrochloric acid. The organic phase
was collected and washed with water. The product was
extracted by chloroform and dried by anhydrous sodium
sulfate. The solvent was removed by reduced pressure. The
residue was redissolved in CHCl3 and precipitated in methanol
to purification. The product was dried in a vacuum to give 17.3
Results and Discussion
Scheme 1 outlines the synthetic routes of monomer 2
and two copolymers 5 and 6. The monomer 2 was
prepared by the nucleophilic substitution of the two
bromine atoms of compound 1 using p-hydroxybenzal-
dehyde. Two copolymers 5 and 6 can be obtained by
Wittig polycondensation reaction.24
Figure 1 showed the FT-IR spectra of the dialdehyde
monomer PERY and the two copolymers PERY-PPV
and PERY-PPV-TPA. In Figure 1a, the dialdehyde
monomer PERY showed the characteristic absorption
peak of aldehyde group at 2733 cm-1. But in Figure 1b,
the absorption peak at 2733 cm-1 disappeared after
polymerization. At the same time, a weak absorption
peak at 984 cm-1 corresponding to the out-of-plane
bending mode of the trans-vinylene groups appeared,
suggesting that the generated double bonds are mainly
1
mg of dark solid. H NMR (300 MHz, CDCl3, 25 °C) δ: 9.60
(br, 2H), 8.66 (br, 2H), 8.39 (s, 2H), 7.98 (d, 4H), 7.68-7.42
(br, 2H), 7.23-7.17 (br, 12H), 7.05-6.72 (br, 6H), 4.15 (br, 4H),
4.01-3.75 (br, 4H), 1.72 (m, 8H), 1.43-1.20 (m, 40H), 0.86 (m,
12H). UV/vis (CHCl3) λmax: 539, 518, 509, 389 nm. Fluores-
cence (CHCl3) λmax: 568, 530 nm. FT-IR (KBr), ν [cm-1]: 1700,
1659, 968. GPC (THF, g/mol): Mn, 6849; Mw, 16 769; Mz )
35 203; PDI: 2.45.

718 Liu et al.
Macromolecules, Vol. 38, No. 3, 2005
Figure 3. UV-vis absorbance spectra of PERY, PERY-PPV,
and PERY-PPV-TPA in CHCl3.
Figure 1. FT-IR spectra of PERY (a), PERY-PPV (b), and
PERY-PPV-TPA (c).
resonance of protons on the newly formed vinylene
group, and broad peaks at about 4.04-3.75 ppm ap-
peared due to the resonance of protons on -OCH2-
linked to aromatic ring. These results indicate that the
Wittig reaction is successful and complete.
The UV-vis absorption spectra of monomer PERY
and two copolymers in CHCl3 are shown in Figure 3.
The main absorption band of pure PERY showed a peak
at 526 nm. The absorption maximum of PERY-PPV
and PERY-PPV-TPA were red-shifted by 10 and 13
nm compared with that of pure PERY, respectively. This
is similar to the phenomenon that perylene bisimides
exhibit a red shift upon aggregation.25 It was found that
UV-vis spectra of both copolymers were broader at
around 400 nm due to the π-π* transition of the PPV
conjugated backbone.26
Figure 4 showed the fluorescence spectra of pure
PERY and two copolymers in chloroform at excitation
wavelength 402 nm. Pure monomer PERY showed
intense fluorescence, and the fluorescence of PERY-
PPV and PERY-PPV-TPA showed significant quench-
ing compared with that of pure PERY (Figure 4a). This
is due to electron transfer from the PPV moiety to the
perylene unit leading to strong fluorescent quenching.20
As shown in Figure 4b, PERY-PPV-TPA also showed
obvious quenching compared with that of PERY-PPV.
Significant quenching of the emission in the triad of
copolymer indicates interaction and electron transfer
from the PPV and TPA moieties to the perylene unit.
In CHCl3 solution, PERY-PPV and PERY-PPV-TPA
displayed poor fluorescence with maximum at 565 and
568 nm, which were slightly but distinctly red-shifted
by 3 and 6 nm compared to that of pure PERY,
respectively. As can be seen in Figure 4a, the shoulder
peak of the fluorescence spectrum of pure PERY was
at 598 nm, which almost disappeared in the fluorescence
spectra of PERY-PPV and PERY-PPV-TPA. And a
new shoulder peak of the fluorescence spectrum of
PERY-PPV-TPA at 530 nm was observed (Figure 4b),
which may be caused by the conjugated structure of PPV
backbone and TPA moiety.27
Figure 2. Partial 1H NMR spectra of PERY, PERY-PPV, and
PERY-PPV-TPA in CDCl3 at room temperature.
the trans configuration. Figure 1c also showed a weak
absorption peak at 968 cm-1, corresponding to the out-
of-plane bending mode of the trans-vinylene groups.
Figure 2 shows the partial 1H NMR spectra of PERY,
PERY-PPV, and PERY-PPV-TPA. Figure 2a repre-
sents the spectrum of monomer PERY. The character-
istic peaks at δ 10.00, 9.44-8.36, and 7.96-7.17 ppm
are due to the resonance of protons on formyl group,
perylene ring, and aromatic rings, respectively. And the
triplets of -CH2- linked to the imide group are at 4.15
ppm. In Figure 2b,c, we can see that the peaks of
copolymers are broader than those of monomer. It can
be found that the characteristic peak for the formyl
proton of monomer PERY disappeared completely, while
a new peak at about 6.8 ppm appeared, which is the
GPC analysis was performed on a Waters 2410 GPC
instrument, using THF as eluant and polystyrene
standards for calibration. Table 1 displayed polymeri-
zation results and molecular weights of PERY-PPV and
PERY-PPV-TPA. The number-average and weight-
average molecular weights for PERY-PPV were 6801

Macromolecules, Vol. 38, No. 3, 2005
Novel Copolymers Containing PPV 719
Figure 5. TGA spectrum of copolymer PERY-PPV.
Figure 4. Fluorescence spectra of PERY, PERY-PPV, and
PERY-PPV-TPA in CHCl3 (λex ) 402 nm).
Table 1. Polymerization Results and Molecular Weights
of Copolymers PERY-PPV and PERY-PPV-TPAa
Figure 6. DSC scan for copolymers PERY-PPV and PERY-
PPV-TPA in flowing nitrogen at a heating rate of 10 °C/min.
Mn
Mw
Mz
copolymers
(g/mol) (g/mol) (g/mol) PDI yield (%)
PERY-PPV
6801
6849
15 419 35 380 2.27
16 769 35 203 2.45
45
12
coating of the polymer layer onto an ITO-coated glass
substrate. Each of the copolymers was sandwiched
between PEDOT:PSS-covered indium tin oxide (ITO)
and calcium and aluminum electrodes. The organic
active layers were prepared by spin-coating from toluene
solutions. In Figure 6 the current-voltage (I-V) char-
acteristics of the photovoltaic devices were plotted in a
logarithmic and linear scale. Figure 7A showed that the
characteristic data of the ITO/PEDOT:PSS/PERY-PPV/
Ca/Al device were a short-circuit current (ISC) of 0.45
mA/cm2, an open-circuit voltage (VOC) of 0.3 V, the fill
factor (FF, defined as (IV)max/(ISCVOC) where (IV)max is
the maximum power rectangle32) of 36%, and the power
conversion efficiency (ηe) of 0.07% under illumination
at an intensity of 75 mW/cm2. However, reported
polymers20 introducing OPV moieties into the imide of
perylene bisimides had ISC of 0.008-0.012 mA/cm2, VOC
of 0.97-1.20 V, and the fill factors of 25-26%. Figure
7B displayed that the characteristic data of the ITO/
PEDOT:PSS/PERY-PPV-TPA/Ca/Al device were a
short-circuit current (ISC) of 0.0167 mA/cm2, an open-
circuit voltage (VOC) of 0.42 V, and a fill factor of 28%.
The relevant data of the I-V characteristics of photo-
voltaic devices are shown in Table 2. The ISC of the
PERY-PPV photocell was almost 30 times higher than
that of the PERY-PPV-TPA photocell, probably be-
cause of the much higher content of perylene in PERY-
PPV than that in PERY-PPV-TPA. The absorber in
PERY-PPV-TPA
a GPC in THF using polystyrene standards.
and 15 419, respectively, whereas those for PERY-
PPV-TPA were 6849 and 16 769, respectively. In fact,
two copolymers were partially soluble in THF; their
actual molecular weights should be higher than the
measured values because the insoluble parts possessed
higher molecular weights. The thermal property of
PERY-PPV was measured by TGA measurement (Fig-
ure 5), which showed thermal stability up to 370 °C.
Figure 6 showed the DSC curves of two copolymers at
a heating rate of 10 °C/min under flowing nitrogen.
PERY-PPV-TPA showed a higher glass transition
temperature (Tg) of 146 °C than PERY-PPV (103 °C),
owing to the attachment of the triphenylamine unit that
can efficiently enhance the Tg of the polymers.9c These
values of Tg were comparable with those of PPV deriva-
tives with bulky pendants (140 °C,27 106 and 122 °C28)
but lower than those of PPV derivatives with cyano-
phenyl pendant (180 and 192 °C).29 The Tg values of the
present copolymers were around 40-80 °C higher than
that of MEH-PPV (∼65 °C)30 but lower than those of
some main chain copolyimides containing perylene units
(170-210,31a 340-360,31b and 374 °C31c).
The ITO/PEDOT:PSS (50 nm)/copolymers/Ca (5 nm)/
Al (88 nm) devices were fabricated by sequential spin-

720 Liu et al.
Macromolecules, Vol. 38, No. 3, 2005
TGA, and DSC measurements. The introduction of PPV
and TPA moieties into the bay positions of perylene
bisimide enhanced the solubility of polymers and
quenched the fluorescence of perylene bisimide obvi-
ously. The photovoltaic devices, ITO/PEDOT:PSS/
copolymers/Ca/Al, were fabricated, and their I-V char-
acteristics indicated that the copolymerization in PERY-
PPV and PERY-PPV-TPA improved the device per-
formance for some extent.
Acknowledgment. This work was supported by the
Major State Basic Research development Program and
the National Natural Science Foundation of China
(20151002, 50372070, 90101025).
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Figure 7. I-V characteristics under illumination at an
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ISC (mA/cm2)
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PERY-PPV
0.45
0.3
36
28
PERY-PPV-TPA
0.0167
0.42
these two coplymers should be mainly perylene unit,
since the stilbene or triphenylamine was almost trans-
parent in the visible region. Therefore, the content of
perylene units in the copolymers played an important
role for the performance of the photocells. To investigate
the copolymerization effect on the photovoltaic perfor-
mance, the photovoltaic cell with the blend of PERY and
TPA (weight ratio of 1:1) as the active layer was also
fabricated and characterized. The ISC and VOC of the
photovoltaic cell were 0.013 mA/cm2 and 0.12 V, respec-
tively. The performance of the device based on the blend
of PERY and TPA was poorer than that of the device
based on PERY-PPV-TPA, indicating that the copo-
lymerization in PERY-PPV and PERY-PPV-TPA
improved the device performance for some extent.
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Two novel copolymers PERY-PPV and PERY-PPV-
TPA were successfully synthesized by means of the
Wittig reaction. Both of them were characterized by FT-
1
IR, H NMR, UV-vis, and FL spectra as well as GPC,

Macromolecules, Vol. 38, No. 3, 2005
Novel Copolymers Containing PPV 721
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