Synthesis and photovoltaic properties of novel alternating phenylenevinylene or fluorenevinylene copolymers containing perylene bisimide

Article abstract of DOI:10.1016/j.reactfunctpolym.2010.04.005

Two novel alternating phenylenevinylene copolymers P6 and P12 as well as one fluorenevinylene copolymer F connected at the 1,7 bay positions with perylene bisimide were synthesized by Heck coupling. They were characterized by GPC, FT-IR, ¹H NMR, TGA, TMA, UV-vis, cyclic voltammetry and photoluminescence (PL) emission spectra. The copolymers were soluble in common organic solvents and thermally stable up to ～300 °C. Their glass transition temperatures were 48-60 °C. The long wavelength absorption maximum was located at 510-542 nm with optical band gaps of ～2.0 eV. The PL emission maximum of P6 and P12 was red-shifted relative to F. The photovoltaic performance of P6, P12 and F was also investigated.

Full text of DOI:10.1016/j.reactfunctpolym.2010.04.005

Reactive & Functional Polymers 70 (2010) 426–432
Contents lists available at ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Synthesis and photovoltaic properties of novel alternating phenylenevinylene
or fluorenevinylene copolymers containing perylene bisimide
b
b
b
John A. Mikroyannidis a, , Kai Yin Cheung , Man Kin Fung , Aleksandra B. Djurišic
*
´
a Chemical Technology Laboratory, Department of Chemistry, University of Patras, GR-26500 Patras, Greece
b Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two novel alternating phenylenevinylene copolymers P6 and P12 as well as one fluorenevinylene copoly-
mer F connected at the 1,7 bay positions with perylene bisimide were synthesized by Heck coupling. They
were characterized by GPC, FT-IR, 1H NMR, TGA, TMA, UV–vis, cyclic voltammetry and photolumines-
cence (PL) emission spectra. The copolymers were soluble in common organic solvents and thermally sta-
ble up to ꢀ300 °C. Their glass transition temperatures were 48–60 °C. The long wavelength absorption
maximum was located at 510–542 nm with optical band gaps of ꢀ2.0 eV. The PL emission maximum
of P6 and P12 was red-shifted relative to F. The photovoltaic performance of P6, P12 and F was also
investigated.
Received 22 February 2010
Received in revised form 7 April 2010
Accepted 10 April 2010
Available online 24 April 2010
Keywords:
Conjugated polymers
Perylene bisimide
Phenylenevinylene
Fluorenevinylene
Photophysics
Ó 2010 Elsevier Ltd. All rights reserved.
Polymer solar cells
Synthesis
1. Introduction
electronics and optoelectronics devices such as organic LEDs
[11f,11g,12], light-harvesting arrays [13], photovoltaic cells [14]
In recent years, conjugated polymers and organic materials
have attracted much attention for their applications in light-emit-
ting diodes (LEDs) and plastic solar cells [1–3]. Poly(p-phenylene-
vinylene) (PPV) and its derivatives are one of the most promising
classes of conjugated polymers for LEDs due to their high lumines-
cence and easy modification of the chemical structure [4–8]. Do-
nor–acceptor conjugated complexes or oligomers have attracted
intense scientific investigation due to their unique optical and elec-
trical properties with potential applications in many fields such as
molecular electronics, optoelectronics, and artificial photosyn-
thetic systems [9].
Perylene bisimides are potential candidates as electron-accept-
ing materials in organic photovoltaic solar cells [10]. They represent
a class of highly thermostable n-type semiconductors with rela-
tively high electron affinity and excellent transport property. More
and more attention has been focused on the modification of pery-
lene bisimide structures through high-yield synthetic routes to im-
prove their chemical and physical properties [11]. These molecules
and their derivatives have been used not only as building blocks for
but also for studying the photoinduced energy and electron-transfer
process [15]. Both PPV and perylene bisimide chromophores
have been applied in bulk-heterojunction-like solar cell configura-
tions as donor and as acceptor materials, respectively [15b,16]. Re-
cently, a new class of donor–acceptor polymers consisting of
alternating oligo(p-phenylenevinylene) and perylene bisimide con-
nected via saturated spacers was synthesized [14g]. Moreover, two
copolymers containing perylene bisimide and PPV and triphenyl-
amine segments were synthesized and used for photovoltaic cells
[17]. Furthermore, two n-type conjugated polymers based on pery-
lene bisimide were synthesized by Stille coupling reaction [18].
Finally, an alternating phenylenevinylene copolymer bearing
perylene bisimide moieties along the backbone was synthesized
in our laboratory and used as electron acceptor in photovoltaic cells
[19].
In this investigation we describe the synthesis, characterization,
photophysics and photovoltaic properties of three novel conju-
gated alternating copolymers based on perylene bisimide. Specifi-
cally, two phenylenevinylene copolymers P6 and P12 with
hexyloxy and dodecyloxy side groups, respectively, and one fluo-
renevinylene copolymer F were successfully synthesized by Heck
coupling. These donor–acceptor copolymers showed that charge
transfer from the excited state takes place.
* Corresponding author. Tel.: +30 2610 997115; fax: +30 2610 997118.
E-mail addresses: mikroyan@chemistry.upatras.gr, mikroyan@googlemail.com
(J.A. Mikroyannidis).
1381-5148/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.reactfunctpolym.2010.04.005

J.A. Mikroyannidis et al. / Reactive & Functional Polymers 70 (2010) 426–432
427
2.4. Preparation of copolymers
2. Experimental
The preparation of P6 is given as a typical example for the prep-
aration of copolymers.
2.1. Characterization methods
A flask was charged with a mixture of 2 (0.1298 g, 0.182 mmol),
3a (0.0602 g, 0.182 mmol), Pd(OAc)2 (0.0017 g, 0.007 mmol), P(o-
tolyl)3 (0.0128 g, 0.042 mmol), DMF (8 mL) and triethylamine
(3 mL). The flask was degassed and purged with N2. The mixture
was heated at 90 °C for 24 h under N2. Then, it was filtered and
the filtrate was poured into methanol. The purple precipitate was
filtered and washed with methanol. The crude product was puri-
fied by dissolving in THF and precipitating into methanol (0.14 g,
87%).
IR spectra were recorded on a Perkin-Elmer 16PC FT-IR spec-
trometer with KBr pellets. 1H NMR (400 MHz) spectra were ob-
tained using a Brucker spectrometer. Chemical shifts (d values)
are given in parts per million with tetramethylsilane as an internal
standard. UV–vis spectra were recorded on a Beckman DU-640
spectrometer with spectrograde THF. The PL spectra were obtained
with a Perkin-Elmer LS45 luminescence spectrometer. The PL spec-
tra were recorded with the corresponding excitation maximum as
the excitation wavelength. TGA was performed on a DuPont 990
thermal analyzer system. Ground samples of about 10 mg each
were examined by TGA and the weight loss comparisons were
made between comparable specimens. Dynamic TGA measure-
ments were made at a heating rate of 20 °C/min in atmospheres
of N2 at a flow rate of 60 cm3/min. Thermomechanical analysis
(TMA) was recorded on a DuPont 943 TMA using a loaded penetra-
tion probe at a scan rate of 20 °C/min in N2 with a flow rate of
60 cm3/min. The TMA experiments were conducted at least in
duplicate to ensure the accuracy of the results. The TMA specimens
were pellets of 10 mm diameter and ꢀ1 mm thickness prepared by
pressing powder of sample for 3 min under 8 kp/cm2 at ambient
temperature. The Tg is assigned by the first inflection point in the
TMA curve and it was obtained from the onset temperature of this
transition during the second heating. Elemental analyses were car-
ried out with a Carlo Erba model EA1108 analyzer.
FT-IR (KBr, cmꢁ1): 2926, 2852, 1694, 1590, 1450, 1420, 1336,
1258, 1206, 1188, 1033, 984, 896, 810, 750, 568.
1H NMR (CDCl3, ppm) (Fig. 2 top): 8.73–7.64 (broad, 6H, aro-
matic ‘‘i”); 7.15–7.00 (m, 4H, olefinic ‘‘f”); 6.92 (m, 2H, aromatic
‘‘e”); 3.96 (m, 4H, aliphatic ‘‘d”); 2.47 (s, 2H, aliphatic ‘‘h”); 1.91
(m, 4H, aliphatic ‘‘c”); 1.78, 1.48 (m, 20H, aliphatic ‘‘g”); 1.35 (m,
12H, aliphatic ‘‘b”); 0.90 (t, J = 7.2 Hz, 6H, aliphatic ‘‘a”).
Anal. Calcd. for (C58H60N2O6)n: C, 79.06; H, 6.86; N, 3.18. Found:
C, 78.12; H, 6.94; N, 3.25.
Copolymer P12 was similarly prepared in 80% yield from the
reaction of 2 with 3b.
FT-IR (KBr, cmꢁ1) (Fig. 1): 2928, 2852, 1694, 1654, 1590, 1456,
1420, 1338, 1258, 1202, 1132, 1036, 985, 896, 810, 752, 568.
1H NMR (CDCl3, ppm): 8.74–7.66 (broad, 6H, aromatic of pery-
lene bisimide); 7.14–7.00 (m, 4H, olefinic); 6.93 (m, 2H, aromatic
ortho to OC12H25); 3.95 (m, 4H, aliphatic OCH2(CH2)10CH3); 2.48 (s,
2H, aliphatic of cyclohexyl rings close to the nitrogen); 1.79, 1.48
(m, 20H, other aliphatic of cyclohexyl rings); 1.71 (m, 4H, aliphatic
2.2. Reagents and solvents
N,N-Dimethylformamide (DMF) and tetrahydrofuran (THF)
were dried by distillation over CaH2. Triethylamine was purified
by distillation over KOH. All other reagents and solvents were com-
mercially purchased and were used as supplied.
2.3. Preparation of monomers
2.3.1. 1,7-Dibromo-3,4,9,10-perylenetetracarboxylic dianhydride (1)
Compound 1 was prepared by bromination of 3,4,9,10-peryl-
enetetracarboxylic dianhydride by means of bromine and a cata-
lytic amount of iodine in sulfuric acid according to the literature
[20]. The 1,7-dibromo derivative was the predominant isomer
which was obtained as reaction product.
2.3.2. 1,7-Dibromo-N,N00-dicyclohexyl-3,4,9,10-perylenetetracarboxylic
dianhydride (2)
Compound 2 was prepared from the reaction of 1 with excess of
cyclohexylamine (mol ratio 1:3) in N-methyl-2-pyrrolidone (NMP)
in the presence of glacial acetic acid [20].
2.3.3. 1,4-Divinyl-2,5-bis(hexyloxy)-benzene (3a) and 1,4-divinyl-2,5-
bis(dodecyloxy)-benzene (3b)
Compounds 3a and 3b were synthesized by Stille coupling
reaction [21] of 1,4-dibromo-2,5-bis(hexyloxy)-benzene and 1,4-
dibromo-2,5-bis(dodecyloxy)-benzene, respectively, with tributyl-
vinyltin [22].
2.3.4. 9,9-Dihexyl-2,7-divinylfluorene (4)
Compounds 4 was synthesized by Stille coupling reaction [21]
of 9,9-dihexyl-2,7-dibromofluorene with tributylvinyltin in the
presence of PdCl2(PPh3)2 as catalyst and a few crystals of 2,6-di-
tert-butylphenol as polymerization inhibitor utilizing toluene as
reaction medium. The synthesis and characterization of 4 has been
described in our previous publication [23].
Fig. 1. FT-IR spectra of monomers 1 (top), 2 (middle) and copolymer P12 (bottom).

428
J.A. Mikroyannidis et al. / Reactive & Functional Polymers 70 (2010) 426–432
OCH2CH2(CH2)9CH3); 1.30 (m, 36H, aliphatic OCH2CH2(CH2)9CH3);
0.93 (t, J = 7.2 Hz, 6H, aliphatic OCH2(CH2)10CH3).
Anal. Calcd. for (C70H84N2O6)n: C, 80.11; H, 8.07; N, 2.67. Found:
C, 79.56; H, 8.12; N, 2.56.
nate) (PEDOT:PSS)/polymer:(phenyl-C61-butyric acid methyl es-
ter) PCBM (1:5) or polymer:poly(3-hexylthiophene) (P3HT) (1:1)/
Al. PCBM and P3HT were purchased from American Dyes. PED-
OT:PSS (Baytron VPAI 4083) was purchased from H.C. Starck. The
Copolymer F was similarly prepared in 79% yield from the reac-
tion of 2 with 4.
patterned ITO glass substrates (10 X per square) were cleaned by
sonication in toluene, acetone, ethanol and deionized water. Then
the cleaned substrates were dried in the vacuum oven at 100 °C
and exposed to UV ozone for 300s before spin-coating. PEDOT:PSS
FT-IR (KBr, cmꢁ1): 2926, 2854, 1696, 1654, 1592, 1458, 1338,
1258, 1188, 986, 896, 812, 752, 568.
1H NMR (CDCl3, ppm) (Fig. 2 bottom): 8.80–8.25 (broad, 6H,
aromatic ‘‘g”); 7.62 (m, 2H, aromatic ‘‘e”); 7.37 (m, 4H, aromatic
‘‘d”); 7.15–7.07 (m, 4H, olefinic ‘‘f”); 2.48 (s, 2H, aliphatic ‘‘i”);
2.10 (m, 4H, aliphatic ‘‘c”); 1.95, 1.36 (m, 20H, aliphatic ‘‘h”);
1.03 (m, 16H, aliphatic ‘‘b”); 0.76 (t, J = 7.2 Hz, 6H, aliphatic ‘‘a”).
Anal. Calcd. for (C65H64N2O4)n: C, 83.30; H, 6.88; N, 2.99. Found:
C, 82.56; H, 6.95; N, 3.10.
aqueous solution (passed through the 0.45 lm filter) was spin-
coated on patterned ITO substrates at 5000 r.p.m. for 3 min. The
substrates were then baked in a nitrogen atmosphere at 150 °C
for 15 min. A 20 mg/ml chlorobenzene solution of (P6, P12 and
F):PCBM (1:5) and (P6, P12 and F):P3HT (1:1) were then spin-
coated at 1000 r.p.m. for 2 min. The substrates were dried at room
temperature in low vacuum (vacuum oven) for 1 h, and then stored
in high vacuum (10ꢁ5 to 10ꢁ6 Torr) overnight. The substrates were
transferred to a thermal evaporator where Al electrode (100 nm)
was then evaporated through a shadow mask. The effective active
area of the devices is 3.14 mm2.
The measurement of the prepared polymer solar cells was per-
formed in air. I–V curves were measured in the dark and under illu-
mination from a solar simulator (Oriel 66002 solar light simulator)
with an AM 1.5 (AM = air mass) spectral filter. The light intensity
(100 mW cmꢁ2) was measured by a Molectron Power Max 500D la-
ser power meter. The power conversion efficiency was determined
from the J–V curve and the electrical measurement was performed
using a Keithley 2400 sourcemeter.
2.5. Electrochemical characterization
Cyclic voltammetry was used to measure the highest occupied
molecular orbital (HOMO) and the lowest unoccupied molecular
orbital (LUMO) levels of copolymers. The HOMO and LUMO were
calculated using the half-wave potentials determined from electro-
chemical measurements. The experiments were performed by
coating the copolymer films on the ITO/glass as working electrode
with a Ag/AgCl wire as the reference electrode, at a scan rate of
50 mV sꢁ1. The solvent in all measurements was acetonitrile, and
the supporting electrolyte was 0.1 M TBABF4.
2.6. Solar cell fabrication and characterization
3. Results and discussion
Device structure of polymer solar cell (PSCs) was indium tin
oxide (ITO)/poly(3,4-ethylene-dioxythiophene):poly(styrene sulfo-
3.1. Synthesis and characterization
Scheme 1 outlines the synthesis of monomers 1 [20] and 2 [20].
The alternating copolymers P6, P12 and F were synthesized by
Heck coupling [24] of dibromide 2 with divinyls 3a, 3b [22] and
4 [23], respectively (Scheme 2). Copolymers P6 and P12 are PPV
derivatives with hexyloxy and dodecyloxy side groups, respec-
tively, while F is fluorenevinylene derivative. The copolymers have
the donor–acceptor (D–A) architecture with the electron-rich 2,5-
dialkoxybenzene or 9,9-dialkylfluorene as D unit and the elec-
tron-deficient perylene bisimide as A unit. Even thought perylene
bisimide is a polynuclear segment of low solubility, the copolymers
were very soluble in THF, dichloromethane, chloroform, toluene
and other common organic solvents. The alkoxy or alkyl side chains
and the cyclohexyl rings which were attached to the perylene bisi-
mide enhanced the solubility of copolymers.
P6
The preparation yields were 79–87% and the number-average
molecular weights (Mn) which were determined by GPC were
7500–10,300 with polydispersity of 1.5–1.8 (Table 1). The copoly-
mers derived from the Heck reaction present usually low degree of
polymerization [25]. Two related copolymers containing perylene
bisimide and PPV and triphenylamine moieties [17] which have
been synthesized by means of Wittig reaction showed Mn of
ꢀ6800. In the present case the bulky and rigid dibromide 2 with
the two bromines at the 1,7 bay positions of perylene bisimide
may present low reactivity towards the divinyls.
F
The synthesis of copolymers could be monitored by FT-IR and
1H NMR spectroscopy. Fig. 1 presents the IR spectra of monomers
1 and 2 and copolymer P12. Monomer 1 showed characteristic
absorption bands at 1772, 1736 and 1038 cmꢁ1 associated with
the anhydride structure, while 2 and P12 lacked of these absorp-
tions. Monomer 2 and copolymer P12 displayed common absorp-
tions at 2928, 2852 (C–H stretching of aliphatic moieties) and
1694, 1654 cmꢁ1 (imide structure). Copolymer P12, as compared
to 2, exhibited additional absorptions at 1202 and 985 cmꢁ1 as-
Fig. 2. 1H NMR spectra in CDCl3 solution of copolymers P6 (top) and F (bottom).
The solvent peak is denoted by an asterisk.

J.A. Mikroyannidis et al. / Reactive & Functional Polymers 70 (2010) 426–432
429
Scheme 1. Synthesis of monomers 1 and 2.
Scheme 2. Synthesis of copolymers P6, P12 and F.
Table 1
Molecular weights, thermal and optical properties of copolymers.
Copolymer
P6
P12
F
a
Mn
10,300
1.8
375
51
9100
1.7
367
39
7500
1.5
378
57
a
Mw/Mn
b
Td (°C)
c
Yc (%)
d
Tg
55
48
60
e
ka,max in solution (nm)
kf,max in solution (nm)
ka,max in thin film (nm)
Eogpt
422, 510, 542
564
400, 512, 541
556
382, 513, 542
530
f
e
427, 527
405, 522
386, 520
2.02 eV (614 nm)h
1.99 eV (623 nm)h
2.00 eV (620 nm)h
g
HOMO (eV)
LUMO (eV)
Eegl (eV)
i
ꢁ5.75
ꢁ3.75
2.00
ꢁ5.76
ꢁ3.78
1.98
ꢁ5.77
ꢁ3.76
2.01
The PL emission spectra were recorded at 490 nm excitation wavelength.
a
Molecular weights determined by GPC using polystyrene standard.
Decomposition temperature corresponding to 5% weight loss in N2 determined by TGA.
Char yield at 800 °C in N2 determined by TGA.
Glass transition temperature determined by TMA.
b
c
d
e
ka,max: The absorption maxima from the UV–vis spectra in THF solution or in thin film.
f
kf,max: The PL maxima in THF solution.
Eogpt: The optical band gap calculated from the onset of thin film absorption spectrum.
g
h
Numbers in parentheses indicate the onset of thin film absorption spectrum.
Eegl: Electrochemical band gap determined from cyclic voltammetry.
i

430
J.A. Mikroyannidis et al. / Reactive & Functional Polymers 70 (2010) 426–432
signed to the ether bond of the dodecyloxy chains and the out-of-
plane bending mode of the trans-vinylene groups, respectively.
Fig. 2 depicts the 1H NMR spectra of copolymers P6 and F.
Copolymer P6 showed an upfield broad resonance at 8.73–
7.64 ppm assigned to the six perylene bisimide protons labeled
‘‘i”. The olefinic protons ‘‘f” and the aromatic protons ‘‘e” gave sig-
nals at 7.15–7.00 and 6.92 ppm, respectively. The cyclohexyl pro-
tons ‘‘g” gave multiplets at 1.78 and 1.48 ppm, while the
cyclohexyl protons ‘‘h” gave a signal at 2.47 ppm. Finally, the ali-
phatic protons ‘‘a”, ‘‘b”, ‘‘c” and ‘‘d” of the hexyloxy chains reso-
nated at 0.90, 1.35, 1.91 and 3.96 ppm, respectively. Similarly, F
showed a broad signal at 8.80–8.25 ppm from the perylene bisi-
mide protons ‘‘g”. The fluorene protons ‘‘e” and ‘‘d” and the olefinic
protons ‘‘f” resonated at 7.62, 7.37 and 7.15–7.07 ppm, respec-
tively. The cyclohexyl protons ‘‘h” and ‘‘i” gave similar resonances
with those of cyclohexyl protons of P6. Finally, the aliphatic pro-
tons ‘‘a”, ‘‘b” and ‘‘c” of the hexyl chains resonated at 0.76, 1.03
and 2.10 ppm, respectively. It is noteworthy that the small dou-
blets between 5 and 6 ppm appeared in both 1H NMR spectra are
assigned to the protons CH2@CHA of the vinyl terminal groups.
The thermal properties of copolymers were studied by TGA and
TMA (Fig. 3). The decomposition temperature (Td), the char yield
(Yc) at 800 °C in N2 by TGA as well as the glass transition temper-
ature (Tg) by TMA are listed in Table 1. The copolymers were stable
up to about 300 °C and gave Yc of 39–57%. Their Tg ranged from 48
to 60 °C. On the basis of the Td and Yc values, the thermal stability
of copolymers was of the order F > P6 > P12. The Tg values followed
also the same trend. This suggests that the 9,9-dihexylfluorene
moiety was more thermally stable and rigid than the 2,5-dihexyl-
oxy- and didodecyloxy-benzene unit. P6, as compared to P12, dis-
played higher thermal stability and rigidity because carried shorter
alkoxy side chains. The Tg values of the present copolymers are
lower than that (103 °C) of another related perylene-containing
PPV [17], since the latter carried octyl instead of cyclohexylamine
groups and an additional phenylene ring along the backbone. A Tg
value of ꢀ65 °C has been reported for 2-methoxy-5-(2-ethylhexyl-
oxy)-1,4-phenylenevinlylene (MEH-PPV) [26].
3.2. Photophysical properties
Fig. 4. Normalized UV–vis absorption spectra of copolymers in 10ꢁ5 M THF solution
(a) and thin film (b).
Figs. 4 and 5 present the normalized UV–vis absorption spectra
of copolymers in both dilute (10ꢁ5 M) THF solution and thin films.
The latter were prepared from THF solutions by spin-coating on
quartz substrate. Table 1 summarizes the photophysical character-
istics of copolymers.
Fig. 3. TGA thermograms of copolymers in N2. The inset shows the TMA traces of
copolymers. Conditions: N2 flow, 60 cm3/min; heating rate, 20 °C/min.
Fig. 5. Normalized PL emission spectra of polymers in 10ꢁ5 M THF solution. The PL
emission spectra were recorded by excitation at 490 nm.

J.A. Mikroyannidis et al. / Reactive & Functional Polymers 70 (2010) 426–432
431
The absorption spectra of copolymer solutions (Fig. 4) showed
similar curves with three maxima (ka,max) at about 400, 510 and
540 nm. The short wavelength absorption (ꢀ400 nm) is associated
with the perylene segment, while the long wavelength absorptions
(ꢀ510, 540 nm) correspond to the
p–p* transitions of the conju-
gated main chain. The copolymer thin films displayed two distinct
ka,max around 400 and 520 nm. The absorption edges of copolymer
thin films were bathochromic shifted in comparison with those of
the corresponding polymer solutions, as a result of the interchain
interactions in the polymer films. The visible absorption band of
copolymers covers a broad wavelength range approximately from
300 to 600 nm which bodes well for their photovoltaic properties.
The absorption onset in thin film of copolymers P6, P12 and F
were 614 and 623 and 620 nm, respectively, from which the opti-
cal band gaps ðEogptÞ of the copolymers were determined to be 2.02,
1.99 and 2.00 eV, respectively. The Eogpt of the present copolymers is
slightly lower than that of MEH-PPV [26] (2.10 eV). A Eogpt value of
2.13 eV has been reported for donor–acceptor type thiophene–per-
ylene–thiophene polymer [27]. Finally,
p-conjugated polymers
composed of phenothiazine, bithiophene, and perylene moieties
which were prepared by the Suzuki coupling reaction had Eogpt of
2.26–2.33 eV [28].
Fig. 6. J–V curves of the best polymer solar cells with polymer (P6, P12 and
F):PCBM (1:5) and (P6, P12 and F):P3HT (1:1) active layers under simulated AM 1.5
solar irradiation.
Band gaps of copolymers were also estimated from cyclic vol-
tammetry measurements. From the onset values of oxidation po-
tential (Eonset,ox) and reduction potential (Eonset,red), the HOMO
and LUMO as well as the electrochemical band gaps (Eegl) of the
copolymers were calculated from to the following equations:
Table 2
Solar cell performance of polymer blend devices (P6, P12 and F):PCBM (1:5) and (P6,
P12 and F):P3HT (1:1).
a
b
c
Voc (V)
Jsc (mAcmꢁ2
)
FF
g
(%)d
1:5 PCBM
EHOMO ¼ ꢁðEox þ 4:72Þ eV
ELUMO ¼ ꢁðEred þ 4:72Þ eV;
P6
P12
F
0.30
0.35
0.34
0.10
0.11
0.15
0.26
0.23
0.24
0.008
0.009
0.012
1:1 P3HT
where the unit of potential is V versus Ag/AgCl. Obtained results are
shown in Table 1.
The electrochemically estimated band gaps of copolymers were
1.98–2.01 eV and they were in agreement with the optically esti-
mated band gaps.
The copolymer solutions emitted yellow-orange light with
maximum (kf,max) at 530–564 nm when they photoexcited at
490 nm (Fig. 5). P6 and P12 had comparable kf,max which supports
that the length of the alkoxy side chains did not influence their
emission considerably. In contrast, the kf,max of P6 and P12 was sig-
nificantly red-shifted by 34 and 26 nm, respectively, relative to F
because of the presence of the electron-donating alkoxy side
chains that usually causes a bathochromic shift. The emission spec-
tra of copolymer thin films were not recorded because they were
not fluorescent to a detectable extent. This feature could be attrib-
uted to aggregate quenching because of strong intramolecular
interactions in solid state.
P6
P12
F
0.38
0.35
0.34
0.009
0.013
0.007
0.20
0.17
0.20
0.0007
0.0008
0.0005
a
b
c
Voc: Open circuit voltage.
Jsc: Short circuit current.
FF: Fill factor.
d
g
: Efficiency.
All the devices exhibited relatively low fill factor and short cir-
cuit current density, so that resulting photovoltaic efficiency is low
in spite of good absorption coverage of the visible part of the solar
spectrum. However, the resistance of the cells was rather large,
which indicates either inferior mobility of the materials or unfa-
vorable phase separation leading to poor charge transport and
large recombination losses, and thus low values of Jsc and FF. The
efficiency could possibly be improved by increasing the degree of
polymerization to improve film quality and charge transport, as
well as by modifying the chemical structure of the polymer to fur-
ther enhance charge transport and induce favorable phase separa-
tion in the blends. In some cases, efficiencies of the order ꢀ1% have
been obtained for blends of polymers containing perylene diimide
and a polythiophene derivative [31], which indicates that by tailor-
ing the molecular structures and blend compositions efficiencies of
solar cells based on this class of compounds can be further
increased.
3.3. Photovoltaic behavior
Photovoltaic devices were fabricated using pure polymers as
well as polymer blends (P6, P12 and F):PCBM (1:5) and (P6, P12
and F):P3HT (1:1) as active layers. Pure polymers in all cases exhib-
ited very poor photovoltaic performance. Since blends containing
perylene derivatives both with PCBM [29] and P3HT [30] have been
reported, we have tried both of these materials. Fig. 6 shows the J–
V curve of the PSCs under AM 1.5 illumination (100 mW cmꢁ2), and
Table 2 lists the photovoltaic performance parameters. Better re-
sults have been obtained for (P6, P12 and F):PCBM (1:5) compared
to (P6, P12 and F):P3HT (1:1). The best result was obtained for
F:PCBM 1:5 blends, resulting in open circuit voltage Voc = 0.34 V,
4. Conclusions
Two phenylenevinylene copolymers P6 and P12 as well as one
fluorenevinylene copolymer F were synthesized by means of the
Heck reaction. The introduction of the dialkoxyphenylene or dial-
kylfluorene moieties into the bay positions of the perylene bisi-
mide and the cyclohexyl rings attached to the perylene bisimide
short circuit current density Jsc = 0.15 mA cmꢁ2
FF = 0.24, and efficiency = 0.012%. An efficiency value of 0.07
has been reported for a related perylene-containing PPV [17].
, fill factor
g

432
J.A. Mikroyannidis et al. / Reactive & Functional Polymers 70 (2010) 426–432
(b) S.I. Yang, S. Prathapan, M.A. Miller, J. Seth, D.F. Bocian, J.S. Lindsey, D.
Holten, J. Phys. Chem. B 105 (2001) 8249;
(c) K. Tomizaki, R.S. Loewe, C. Kirmaier, J.K. Schwartz, J.L. Retsek, D.F. Bocian, D.
Holten, J.S. Lindsey, J. Org. Chem. 67 (2002) 6519;
(d) K. Muthukumaran, R.S. Loewe, C. Kirmaier, E. Hindin, J.K. Schwartz, I.V.
Sazanovich, J.R. Diers, D.F. Bocian, D. Holten, J.S. Lindsey, J. Phys. Chem. B 107
(2003) 3431;
enhanced the solubility of copolymers. The Tg’s were relatively low
(48–60 °C) and the optical band gap was ꢀ2.0 eV. The absorption
was broad and extended approximately from 300 to 600 nm. Pho-
tovoltaic cells prepared from the polymer blends for all three
materials exhibited relatively low efficiency.
(e) M.A. Miller, R.K. Lammi, S. Prathapan, D. Holten, J.S. Lindsey, J. Org. Chem.
65 (2000) 6634.
[14] (a) C.W. Tang, Appl. Phys. Lett. 48 (1986) 183;
References
(b) B.A. Gregg, R.A. Cormier, J. Am. Chem. Soc. 123 (2001) 7959;
(c) S. Ferrere, A. Zaban, B.A. Gregg, J. Phys. Chem. B 101 (1997) 4490;
(d) P. Peumans, V. Bulovic´, S.R. Forrest, Appl. Phys. Lett. 76 (2000) 2650;
(e) J.J. Dittmer, E.A. Marseglia, R.H. Friend, Adv. Mater. 12 (2000) 1270;
(f) R. de Bettignies, Y. Nicolas, P. Blanchard, E. Levillain, J.-M. Nunzi, J. Roncali,
Adv. Mater. 15 (2003) 1939;
(g) E.E. Neuteboom, S.C. J Meskers, P.A. van Hal, J.K.J. van Duren, E.W. Meijer,
R.A.J. Janssen, H. Dupin, G. Pourtois, J. Cornil, R. Lazzaroni, J.-L. Brédas, D.
Beljonne, J. Am. Chem. Soc. 125 (2003) 8625.
[1] (a) M.A. Baldo, D.F. O’Brien, Y. You, A. Shoustikov, S. Sibley, M.E. Thompson, S.R.
Forrest, Nature (London) 395 (1998) 151;
(b) M.A. Baldo, M.E. Thompson, S.R. Forrest, Nature (London) 403 (2000) 750.
[2] C.J. Brabec, N.S. Sariciftci, J.C. Hummelen, Adv. Funct. Mater. 11 (2001) 15.
[3] (a) S. Zheng, J. Shi, R. Mateu, Chem. Mater. 12 (2000) 1814;
(b) A.P.H.J. Schenning, A.C. Tsipis, S.C.J. Meskers, D. Beljonne, E.W. Meijer, J.L.
Brédas, Chem. Mater. 14 (2002) 1362;
(c) L. Tan, M.D. Curtis, M.D. Francis, Chem. Mater. 15 (2003) 2272;
(d) F. Huang, H. Wu, D. Wang, W. Yang, Y. Cao, Chem. Mater. 16 (2004) 708.
[4] A. Kraft, A.C. Grimsdale, A.B. Holmes, Angew. Chem. Int. Ed. 37 (1998) 402.
[5] U. Mitschke, P. Bäuerle, J. Mater. Chem. 10 (2000) 1471.
[6] (a) Z. Yang, I. Sokolik, F.E. Karasz, Macromolecules 26 (1993) 1188;
(b) Z.K. Chen, H. Meng, Y.H. Lai, W. Huang, Macromolecules 32 (1999) 4351;
(c) T. Ahn, S.Y. Song, H.K. Shim, Macromolecules 33 (2000) 6764.
[7] (a) S. Jin, M. Jang, H. Suh, H. Cho, J. Lee, Y. Gal, Chem. Mater. 14 (2002) 643;
(b) Z. Liang, M. Rackaitis, K. Li, E. Manias, Q. Wang, Chem. Mater. 15 (2003)
2699.
[8] (a) H.M. Li, Y.L. Li, J. Zha, G.L. Cui, H.B. Liu, S.Q. Xiao, Y. Liu, F.S. Lu, L. Jiang, D.B.
Zhu, Chem. Eur. J. 9 (2003) 6031;
(b) H.M. Li, C.H. Xiang, Y.L. Li, S.Q. Xiao, H.J. Fang, D.B. Zhu, Synth. Met. 135
(2003) 483.
[9] M.R. Wasielewski, Chem. Rev. 92 (1992) 435.
[10] G. Hoprowitz, F. Kouki, P. Spearman, D. Fichou, C. Nogues, X. Pan, F. Garnier,
Adv. Mater. 8 (1996) 242.
[11] (a) K.-Y. Law, Chem. Rev. 93 (1993) 449;
[15] (a) H. Langhals, S. Saulich, Chem. Eur. J. 8 (2002) 5630;
(b) A.P.H.J. Schenning, J. van Herrikhuyzen, P. Jonkheijm, Z. Chen, F. Würthner,
E.W. Meijer, J. Am. Chem. Soc. 124 (2002) 10252;
(c) J. Qu, N.G. Pschirer, D. Liu, A. Stefan, F.C. De Schryver, K. Müllen, Chem. Eur.
J. 10 (2004) 528;
(d) F. Würthner, C. Thalacker, A. Sautter, Adv. Mater. 11 (1999) 754.
[16] A. Syamakumari, A.P.H.J. Schenning, E.W. Meijer, Chem. Eur. J. 8 (2002) 3353.
[17] Y. Liu, C. Yang, Y. Li, Y. Li, S. Wang, J. Zhuang, H. Liu, N. Wang, X. He, Y. Li, D.
Zhu, Macromolecules 38 (2005) 716.
[18] L. Huo, Y. Zhou, Y. Li, Macromol. Rapid Commun. 29 (2008) 1444.
[19] J.A. Mikroyannidis, M.M. Stylianakis, G.D. Sharma, P. Balraju, M.S. Roy, J. Phys.
Chem. C 113 (2009) 7904.
[20] F. Würthner, V. Stepanenko, Z. Chen, C.R. Saha-Möller, N. Kocher, D. Dietmar
Stalke, J. Org. Chem. 69 (2004) 7933.
[21] D.R. McKean, G. Parrinello, A.F. Renaldo, J.K. Stille, J. Org. Chem. 52 (1987) 422.
[22] Q. Peng, M. Li, X. Tang, S. Lu, J. Peng, Y. Cao, J. Polym. Sci. Part A: Polym. Chem.
45 (2007) 1632.
[23] J.A. Mikroyannidis, Y.-J. Yu, S.-H. Lee, J.I. Jin, J. Polym. Sci. Part A: Polym. Chem.
44 (2006) 4494.
[24] C.B. Ziegler Jr., R.F. Heck, Org. Chem. 43 (1978) 2941.
[25] A. Hilberer, J.-H. Brouwer, B.J. Van der Scheer, J. Wildeman, G. Hadziioannou,
Macromolecules 28 (1995) 4525.
[26] X. Li, Y. Zhang, R. Yang, J. Huang, W. Yang, Y. Cao, J. Polym. Sci. Part A: Polym.
Chem. 43 (2005) 2325.
[27] S. Kuyuncu, M. Kus, S. Demic, I. Kaya, E. Ozdemir, S. Icli, J. Polym. Sci. Part A:
Polym. Chem. 46 (2008) 1974.
[28] W. Tang, L. Ke, Z.-K. Chen, J. Phys. Chem. B 112 (2008) 3590.
[29] J. Cremer, P. Bäuerle, J. Mater. Chem. 16 (2006) 874.
[30] W.S. Shin, H.-H. Jeong, M.-K. Kim, S.-H. Jin, M.-R. Kim, J.-K. Lee, J.W. Lee, Y.-S.
Gal, J. Mater. Chem. 16 (2006) 384.
(b) D. Dotcheva, M. Klapper, K. Müllen, Macromol. Chem. Phys. 195 (1994)
1905;
(c) H. Quante, Y. Geerts, K. Müllen, Chem. Mater. 9 (1997) 495;
(d) R.A. Cormier, B.A. Gregg, Chem. Mater. 10 (1998) 1309;
(e) F. Würthner, C. Thalacker, A. Sautter, W. Schärtl, W. Ibach, O. Hollricher,
Chem. Eur. J. 6 (2000) 3871;
(f) M. Thelakkat, P. Pösch, H.-W. Schmidt, Macromolecules 34 (2001) 7441;
(g) C. Ego, D. Marsitzky, S. Becker, J. Zhang, A.C. Grimsdale, K. Müllen, J.D.
MacKenzie, C. Silva, R.H. Friend, J. Am. Chem. Soc. 125 (2003) 437.
[12] (a) P. Ranke, I. Bleyl, J. Simmerer, D. Haarer, A. Bacher, H.W. Schmidt, Appl.
Phys. Lett. 71 (1997) 1332;
(b) X.Z. Jiang, Y.Q. Liu, S.G. Liu, W.F. Qiu, X.Q. Song, D.B. Zhu, Synth. Met. 91
(1997) 253;
(c) K.D. Belfield, K.J. Schafer, M.D. Alexander, Chem. Mater. 12 (2000) 1184.
[13] (a) S. Prathapan, S.I. Yang, J. Seth, M.A. Miller, D.F. Bocian, D. Holten, J.S.
Lindsey, J. Phys. Chem. B 105 (2001) 8237;
[31] Z. Tan, E. Zhou, X. Zhan, X. Wang, Y. Li, S. Barlow, S.R. Marder, Appl. Phys. Lett.
93 (2008) 073309.