Synthesis and application of H-Bonded cross-linking polymers containing a conjugated pyridyl H-Acceptor side-chain polymer and various carbazole-based H-Donor dyes bearing symmetrical cyanoacrylic acids for organic solar cells

Article abstract of DOI:10.1016/j.polymer.2010.10.018

A series of novel hydrogen-bonded (H-bonded) cross-linking polymers were generated by complexing various proton-donor (H-donor) solar cell dyes containing 3,6- and 2,7-functionalized electron-donating carbazole cores bearing symmetrical thiophene linkers

Full text of DOI:10.1016/j.polymer.2010.10.018

Polymer 51 (2010) 6182e6192
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
Synthesis and application of H-Bonded cross-linking polymers containing
a conjugated pyridyl H-Acceptor side-chain polymer and various carbazole-based
H-Donor dyes bearing symmetrical cyanoacrylic acids for organic solar cells
,
c
Duryodhan Sahu a, Harihara Padhy a, Dhananjaya Patra a, Dhananjay Kekuda b, Chih-Wei Chu b
,
,
I-Hung Chiang a, Hong-Cheu Lin a
*
a Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, Taiwan, ROC
b Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan, ROC
c Department of Photonics, National Chiao Tung University, Hsinchu, Taiwan, ROC
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel hydrogen-bonded (H-bonded) cross-linking polymers were generated by complexing
various proton-donor (H-donor) solar cell dyes containing 3,6- and 2,7-functionalized electron-donating
carbazole cores bearing symmetrical thiophene linkers and cyanoacrylic acid termini with a proton-
acceptor (H-acceptor) side-chain homopolymer carrying pyridyl pendants (with 1/2 M ratio of H-donor/
H-acceptor). The supramolecular H-bonded structures between H-donor dyes and the H-acceptor side-
chain polymer were confirmed by FTIR measurements. The effects of the supramolecular architecture on
optical, electrochemical, and organic photovoltaic (OPV) properties were investigated. From DFT (density
functional theory) calculations, the optimized geometries of organic dyes reflected that the carbazole
cores of H-donor dyes were coplanar with the conjugated thiophenes and cyanoacrylic acids, which is
essential for strong conjugations across the donor-acceptor units in D1eD4 dyes. Under 100 mW/cm2 of
AM 1.5 white-light illumination, bulk heterojunction (BHJ) OPV cell devices containing an active layer of
H-bonded polymers (PDFTP/D1eD4) as an electron donor blended with [6,6]-phenyl C61-butyric acid
methyl ester (PCBM) as an electron acceptor in a weight ratio of 1:1 were explored. From the preliminary
investigations, the OPV device containing 1:1 weight ratio of H-bonded polymer PDFTP/D2 and PCBM
showed the best power conversion efficiency (PCE) value of 0.31% with a short-circuit current (Jsc) of
1.9 mA/cm2, an open-circuit voltage (Voc) of 0.55 V, and a fill factor (FF) of 29%, which has a higher PCE
value than the corresponding H-donor D2 dye (PCE ¼ 0.15%) or H-acceptor PDFTP homopolymer
(PCE ¼ 0.02%) blended with PCBM in 1:1 weight ratio.
Received 12 August 2010
Received in revised form
4 October 2010
Accepted 10 October 2010
Available online 26 October 2010
Keywords:
H-bonded polymer network
Solar cell
Self-assembly
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
area processible [8,9] alternatives to silicon-based solar cells, though
their efficiencies are not comparable to those of silicon-based tech-
In order to overcome the growing global energy needs, extensive
researches on environment friendly and renewable sources of ener-
gies have been made during the past decade [1,2]. As an ecologically
sustainable and renewable source of energies, solar energy led to
a greater attention for the scientists to develop solar energy conver-
nologies. In fact, different solar cell architectures have been devel-
oped, including dye sensitized solar cells [10e12], donor-acceptor
BHJs of polymer blends [13e19] and block copolymers [20], supra-
molecular ensemble of small molecule/small molecule [21] etc.
However, the interests on oligomers with easy purification processes
and lack of problems in molecular weight distributions etc. are
generally auxiliary to their polymer analogues due to the better
solvent processabilities and film morphologies in photovoltaic cells
[22]. Therefore, in order to get the advantages of both oligomeric and
polymeric properties, an attractive approach would be the well-
sion devices [3,4]. Since then, p-conjugated oligomers and polymers
were applied as advanced materials for the development of organic
photovoltaic (OPV) devices for future applications [5,6]. After the
breakthrough work of Heeger and coworkers in 1995 [7], bulk het-
erojunction (BHJ) solar cells became a low-cost, flexible, and large-
defined supramolecular architectures of
p-conjugated oligomers
with the processabilities of polymers [23].
Since conjugated polymers with electron donor-acceptor (D-A)
architectures had proved as the highly efficient solar cell polymers
* Corresponding author. Tel.: þ8863 5712121x55305; fax: þ8863 5724727.
E-mail address: linhc@cc.nctu.edu.tw (H.-C. Lin).
0032-3861/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.polymer.2010.10.018

D. Sahu et al. / Polymer 51 (2010) 6182e6192
6183
that built intramolecular charge transfer (ICT) transitions from the
electron donor to acceptor and thus to lower the band gaps of solar
cell polymers [24]. Carbazole-based oligomers and polymers as
semiconducting materials have been attracted attentions for its
good chemical stability, easy functionalization with a large variety
of substituents to modulate the carbazole properties without
increasing the steric hindrance, and cheap availabilities of starting
materials towards organic materials applications of organic light-
emitting diodes (OLEDs) [25], organic field effect transisters
(OFETs) [26] and organic photovoltaics (OPVs) [27]. The electron
rich nitrogen and sulphur atoms in carbazole and thiophene units
respectively enhance their potentials as efficient p-type trans-
porting moieties in those applications. After the successful
synthesis of N-alkyl-2,7-diiodocarbazole by Leclerc at.el [28], 2,7-
functionalized carbazole became the promising candidate with
intramolecular charge transfer interactions from the electron
donors to the electron acceptors and thus to increase the PCE
values.
As shown in Fig. 1, a series of symmetrical carbazole-based
conjugated dyes (D1eD4) containing carbazole cores functional-
ized at two different (i.e., 3,6- and 2,7-substituted) positions linked
to cyanoacrylic acid termini (as double H-donors) via p-conjugated
oligo-thiophenes were synthesized, which were complexed with
a side-chain homopolymer (PDFTP) bearing pyridyl pendants (as
H-acceptors). Then, double H-donors of D1eD4 dyes and H-
acceptors of side-chain homopolymer PDFTP can be self-assembled
into H-bonded cross-linking polymers, and the schematic illustra-
tion is demonstrated in Fig. 2. The supramolecular (H-bonded)
polymer networks (PDFTP/D1eD4) of carbazole-based H-donor
dyes (D1eD4) complexed with side-chain H-acceptor homopol-
ymer (PDFTP) were confirmed by FTIR spectroscope. The active
layer of blended polymers of H-bonded polymer networks PDFTP/
D1eD4 as electron donors and (6,6)-phenyl C61-butyric acid methyl
ester (PCBM) as an electron acceptor (in a weight ratio of 1:1) were
subjected to BHJ photovoltaic investigations (under AM 1.5 irradi-
ation, 100 mW/cm2). From the preliminary results, the solar cell
device containing H-bonded polymer network PDFTP/D2 produced
the best PCE value of 0.31%, which was obviously doubled the PCE
value (0.15%) of the active layer of D2 dye alone blended with PCBM,
fabricated and measured under similar conditions.
more planar and well delocalized
p-electron structure for the
applications of organic photovoltaics [29]. There are many reports
of carbazole-based polymers or oligomers in the field of bulk het-
erojunction (BHJ) organic photovoltaics (OPVs) [30]. However, in
order to get high power conversion efficiency (PCE) values, self-
assembles of
into well-defined and organized D-A supramolecular structures
remain challenge [23]. Previously, Meijer and coworkers
p-conjugated oligomers with processable polymers
a
employed a supramolecular H-bonded polymer containing oligo(p-
phenylene vinyene) and ureido-pyrimidinone units (as H-bonded
groups) for the applications in OPV devices [22a,31]. Furthermore,
we reported on supramolecular assemblies of H-bonded side-chain
polymers which were prepared by complexation of light-emitting
dendrimers or solar cell dyes bearing carboxylic acids as proton-
donors (H-donors) with side-chain polymers bearing pyridyl
pendants as proton-acceptors (H-acceptors) for the applications in
OLEDs and OPVs [32]. In general, different attempts of utilizing
conjugated oligomers/polymers or both have been made to
design electron donor-acceptor architectures to enhance the
2. Experimental
2.1. Materials
Chemicals and solvents were reagent grades and purchased
from Aldrich, ACROS, TCI, Strem, Fluka, and Lancaster Chemical Co.
THF and dichloromethane were distilled over sodium/benzophe-
none and calcium hydride respectively and freshly distilled before
Fig. 1. Structures of H-acceptor side-chain polymer (PDFTP) and H-donor dyes (D1eD4) used in supramolecular (H-bonded) cross-linking polymers.

6184
D. Sahu et al. / Polymer 51 (2010) 6182e6192
Fig. 2. Schematic illustration of H-bonded polymer networks (PDFTP/D1eD4) containing H-donor dyes (D1eD4) and H-acceptor side-chain polymer (PDFTP).
use. Tetra-n-butyl ammonium hexafluorophosphate (TBAPF6) was
recrystallized twice from absolute ethanol and further dried for two
days under vacuum. N-bromosuccinimide was recrystallized from
distilled water and dried under vacuum. The other chemicals were
used without further purification. Chromatography was performed
with Merck silica gel (mesh 70e230) and basic aluminum oxide,
deactivated with water. The chemical structures for all products
were confirmed by 1H NMR spectroscopy, mass spectra (FAB) and
elemental analyses.
2.3. Quantum chemistry computation
The predicted structures of the molecules were optimized by
using B3LYP hybrid functional [33] and 6-31G* basis sets [34]. For
each of the molecules, a number of conformational isomers were
examined and the one with the lowest energy was used. All of the
analyses were performed under Gaussian 03 (G03) (revision E.01)
program package [35] by using density functional theory (DFT).
2.4. Fabrication and characterization of OPV devices
2.2. Measurements
Solar cells were fabricated on indium tin oxide (ITO)-coated
glass substrates through a following procedure: The ITO coated
glass substrate was first cleaned with a detergent and sonicated in
an ultrasonic bath, and they were dried overnight in an oven. After
this cleaning procedure, the substrates were subjected to UV ozone
cleaning for 15 min. PEDOT: PSS (Baytron PH) was spin coated onto
the substrates at 4000 rpm. The films were dried on a hotplate at
120 ꢀC for 30 min. The samples were then transferred to the
nitrogen filled glove box for the active layer deposition. A solution
containing hydrogen-bonded polymer networks (PDFTP/Dx, where
x vary from 1 to 4) and PCBM were prepared (2 wt%, 1:1) and were
kept overnight digitally controlled hotplate at 60 ꢀC for the uniform
mixing. The solutions were used for the active layer deposition and
were spin coated on the substrates at 1500 rpm for 60 s. The films
were allowed to dry in a covered Petri dish. No thermal annealing
treatment was given to the active layers prior to the cathode
deposition. Finally, a 20 nm Ca and 50 nm Al cathodes were
deposited using a thermal evaporator at a base pressure of 1 ꢂ10ꢁ6
Torr. The device area was 0.1 cm2. The devices were then trans-
ferred to the nitrogen filled glove box. The current-voltage char-
acteristics of the devices were measured using HP 4156
semiconductor parameter analyzer. Air mass 1.5 Global (AM 1.5 G)
solar simulator was used for the photo illumination of the devices.
1H NMR spectra were recorded on a Varian unity 300 MHz
spectrometer using d-DMSO as solvents. Elemental analyses were
performed on a HERAEUS CHN-OS RAPID elemental analyzer.
Fourier transform infrared (FT-IR) spectra were performed
a Nicolet 360 FT-IR spectrometer. Thermo gravimetric analyses
(TGA) were conducted on a Du Pont Thermal Analyst 2100
system with a TGA 2950 thermo gravimetric analyzer at a heat-
ing rate of 20 ꢀC/min under nitrogen. Gel permeation chroma-
tography (GPC) analyses were conducted with a Water 1515
separations module using polystyrene as a standard and THF as
an eluent. UVevisible absorption spectra were recorded in dilute
THF solutions (10ꢁ5 M) on an HP G1103A spectrophotometer.
Fourier transform infrared (FTIR) spectra of samples dispersed
in KBr disks were recorded on a PerkineElmer Spectrum 100
Series [32a].
Thin films of UVevis were spin-coated on quartz substrates
from THF solutions with a concentration of 1 wt%. Cyclic voltam-
metry (CV) measurements were performed using a BAS 100
electrochemical analyzer with a standard three-electrode electro-
chemical cell in a 0.1 M tetrabutylammonium hexafluorophosphate
(TBAPF6) solution at room temperature with a scanning rate of
100 mV/s. During the CV measurements, the solutions were purged
with nitrogen for 30 s. In H-bonded cross-linking polymers,
a carbon working electrode coated with a thin layer of H-bonded
polymer, and for dyes in solution (THF) a platinum wire as the
counter electrode, and a silver wire as the quasi-reference electrode
were used, and Ag/AgCl (3 M KCl) electrode was served as a refer-
ence electrode for all potentials quoted herein. The redox couple of
ferrocene/ferrocenium ion (Fc/Fcþ) was used as an external stan-
dard. The corresponding highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO) levels
were calculated using Eox/onset and Ered/onset. The onset potentials
were determined from the intersections of two tangents drawn at
the rising currents and background currents of the cyclic voltam-
metry (CV) measurements.
2.5. Synthesis of monomer and dyes
Carbazole-based donor dyes D1eD4 (as shown in Fig. 1) were
synthesized from 9-hexyl-3,6-bis(4,4,5,5-tetramethyl-1,3,2-dioxa-
borolan-2-yl)-9H-carbazole(D1eD2) [36] and 9-(heptadecan-9-yl)-
2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-carbazole
(D3eD4) [37]. Intermediates 7e10 were synthesized by the similar
Suzuki coupling conditions, and one of the synthetic procedures (for
intermediate 7) has been described. The monomers D1eD4 were
acquired from the previous intermediates via Knoevenagel
condensation reaction. Their synthetic routes are shown in Scheme
S1 and detailed procedures for intermediates are described in the

D. Sahu et al. / Polymer 51 (2010) 6182e6192
6185
supporting information. Monomer DFTP was synthesized from 2,7,
dibromofluorene as a starting material and polymerized with free
radical polymerization using AIBN as an initiator are shown in
Scheme 1. The 1H NMRs of the monomer DFTP and side-chain
homopolymer (PDFTP) are shown in Fig. 3 and the detailed proce-
dures for monomer DFTP and homopolymer PDFTP are described as
follows:
with water followed by a little brine. Then, the organic layer was
dried over anhydrous MgSO4 (worked up). The solvent was
removed by rotary evaporator, and the crude product was purified
by column chromatography (silica) using hexane as an eluent to
yield a white solid (13.40 g, 88%). 1H NMR (300 MHz, CDCl3),
d
(ppm): 7.50 (s, 2H), 7.46 (d, J ¼ 1.5 Hz, 2H), 7.44 (d, J ¼ 1.8 Hz, 2H),
1.93e1.88 (m, 4H), 1.17 (m, 4H), 1.13e1.03 (m, 12H), 0.78 (t,
J ¼ 6.9 Hz, 6H).
2.5.1. 2,7-Dibromo-9,9-dihexyl-9H-fluorene (1)
A mixture of 2,7-dibromofluorene (10 g, 30.86 mmol) and
potassium-tert-butoxide (10.37 g, 92.58 mmol) were stirred in
120 ml of dry THF under nitrogen for 1 h, then 1-bromohexane
(11 ml, 78.00 mmol) was added drop wise and refluxed for
overnight. Excess of THF was removed by rotary evaporator. Next,
the compound was extracted with dichloromethane and washed
2.5.2. 2,2’-(9,9-Dihexyl-9H-fluorene-2,7-diyl)dithiophene (2)
Compound 1 (5 g,10.15 mmol), thiophen-2-ylboronic acid (3.3 g,
25.78 mmol), K2CO3 (4.2 g, 30.40 mmol) were reacted in 300 ml of
toluene and ethanol (3:1) and degassed for 10 min then Pd(PPh3)4
(293 mg, 0.253 mmol) was added and then the resulting mixture
was stirred under reflux for 4 h. The reaction mixture was worked
Scheme 1. Synthetic route of H-acceptor side-chain polymer (PDFTP).

6186
D. Sahu et al. / Polymer 51 (2010) 6182e6192
Fig. 3. 1H NMR spectra of monomer DFTP and H-acceptor polymer PDFTP in CDCl3. (* indicates the solvent peak).
up, then the excess solvent was concentrated under vacuum.
Subsequently, the compound was purified by column chromatog-
raphy (silica) using hexane as an eluent to yield a white solid (4.8 g,
NMR (300 MHz, CDCl3),
d
(ppm): 7.33 (d, J ¼ 9.0 Hz, 2H), 6.75 (d,
J ¼ 9.0 Hz, 2H), 3.89 (t, J ¼ 6.3 Hz, 2H), 3.62 (t, J ¼ 6.6 Hz, 2H),
1.78e1.69 (m, 2H), 1.59e1.50 (m, 2H), 1.41e1.29 (m, 12H).
96%). 1H NMR (300 MHz, CDCl3),
d
(ppm): 7.69 (d, J ¼ 7.8 Hz, 2H),
7.63e7.57 (m, 4H) 7.40 (d, J ¼ 3 Hz, 2H), 7.30 (d, J ¼ 5.2 Hz, 2H),
7.13e7.10 (m, 2H), 2.05e2.00 (m, 4H),1.14e1.06 (m,12H), 0.78e0.69
(m, 10H).
2.5.5. [10-(4-Bromo-phenyl)-decyloxy]-tert-butyl-dimethyl-silane (5)
Mixture of compound 4 (5 g, 15.18 mmol) and imidazole (2.00 g,
30.30 mmol) were dissolved in 100 ml of dry dichloromethane and
degassed for 10 min. Tert-butyl-chloro-dimethyl-silane (4.57 g,
30.30 mmol) was added at 0 ꢀC under nitrogen atmosphere and
stirred further to react for 4 h at room temperature, then the reacting
mixture was worked up and the excess solvent was removed using
rotary evaporator. Subsequently, the crude product was purified by
column chromatography (silica) using mixture of hexane and
dichloromethane (4:1) as eluent, to get a colorless liquid (5.5 g,
2.5.3. 5,5’-(9,9-Dihexyl-9H-fluorene-2,7-diyl)bis(2-
bromothiophene) (3)
Compound 2 (5 g, 10 mmol) was dissolved in 120 ml of DMF, to
that N-bromosuccinimide (4.1 g, 23.05 mmol, freshly purified by
recrystallization from water) was added portion wise and stirred
for overnight at room temperature, sequentially. The reaction
mixture was worked up and the solvent was removed under
vacuum. Then, the compound was purified by column chroma-
tography (silica) using hexane as an eluent to yield a white solid
82%).1H NMR (300 MHz, CDCl3),
d
(ppm): 7.34 (d, J ¼ 12 Hz, 2H), 6.76
(d, J ¼ 8.1 Hz, 2H), 3.90 (t, J ¼ 15 Hz, 2H) 3.60 (t, J ¼ 15 Hz, 2H),1.73(m,
2H), 1.30e1.51 (m, 14H), 0.89 (s, 9H), 0.05 (s, 6H).
(6.1 g, 93%). 1H NMR (300 MHz, CDCl3),
2H), 7.50 (d, J ¼ 1.5 Hz, 1H) 7.48 (d, J ¼ 1.5 Hz, 1H), 7.45 (d, J ¼ 1.5 Hz,
2H), 7.11 (d, J ¼ 3.9 Hz, 2H), 7.05 (d, J ¼ 3.9 Hz, 2H), 2.01e1.96 (m,
4H), 1.14e1.04 (m, 12H), 0.77e0.63(m, 10H).
d
(ppm): 7.66 (d, J ¼ 7.8 Hz,
2.5.6. 2-{4-[10-(Tert-butyl-dimethyl-silanyloxy)-decyl]-phenyl}-
4,4,5,5-tetramethyl-[1,3,2] dioxaborolane (6)
5 g of compound 5 (11.27 mmol) was dissolved in 100 ml of dry
THF and the solution was cooled to ꢁ 78 ꢀC under nitrogen atmo-
sphere then 9 ml of n-BuLi (2.5 M in hexane, 22.54 mmol) was
added. The solution was warmed up to room temperature and
stirred for 2 h and cooled again to ꢁ 78 ꢀC, then 6.13 ml
(22.54 mmol) of 2-Isopropoxy-4,4,5,5-tetramethyl- [1,3,2] dioxa-
borolane was injected promptly in to the flask and the resulting
mixture was stirred overnight at room temperature. The reaction
was quenched by adding 50 ml of water then extracted with
dichloromethane, and a little of brine. Thereafter the organic
solvent was dried over anhydrous MgSO4 and the solvent was
removed by rotary evaporator. The crude product was purified by
2.5.4. 10-(4-Bromo-phenoxy)-decanol (4)
4-Bromophenol (10 g, 57.8 mmol), 10-bromo decanol (16.45 g,
69.36 mmol), and K2CO3 (23.96 g, 173.33 mmol) was dissolved in
150 ml of dry acetone and stirred under reflux for 24 h. After
cooling to room temperature, the potassium salt was filtered off
and the solvent was removed by rotary evaporator followed by
similar work up procedure, then the excess solvent was removed
using rotary evaporator. The crude product was purified by column
chromatography (silica) using mixture of hexane and ethyl acetate
(4:1) as an eluent, to get low melting semi solid (15.2 g, 80%).1H

D. Sahu et al. / Polymer 51 (2010) 6182e6192
6187
column chromatography (silica) using mixture of hexane and
dichloromethane (4:1) as eluent to yield a low melting white solid
a mixture of hexane and ethyl acetate (5:1) as eluent, to get a yellow
oil (0.45 g, 80%) 1H NMR (300 MHz, CDCl3),
(ppm): 8.56 (d,
J ¼ 4.8 Hz, 2H), 7.60 (d, J ¼ 3.3 Hz, 1H), 7.48 (d, J ¼ 6.3 Hz, 2H), 7.19
(d, J ¼ 3.3 Hz, 1H), 1.64e1.53 (m, 6H), 1.39e1.26 (m, 6H), 1.17e1.11
(m, 6H), 0.90 (t, J ¼ 7.5 Hz, 9H).
d
(3.5 g, 63%). 1H NMR (300 MHz, CDCl3),
d
(ppm): 7.72 (d, J ¼ 8.4 Hz,
2H), 6.87(d, J ¼ 8.7 Hz, 2H), 3.95(t, J ¼ 12.9 Hz, 2H), 3.57(t,
J ¼ 13.5 Hz, 2H), 1.73(qn, J ¼ 6.9 Hz, 2H), 1.54e1.22 (m, 26H), 0.86 (s,
9H), 0.02 (s, 6H).
2.5.11. 4-(50-(7-(5-(4-(10-(tert-Butyldimethylsilyloxy)decyloxy)
phenyl)thiophen-2-yl)-9,9-dihexyl-9H-fluoren-2-yl)-2,20-
bithiophen-5-yl)pyridine (11)
Mixture of compound 7 (2 g, 2.12 mmol), compound 10 (1 g,
2.22 mmol) and Pd(PPh3)4 (0.3 g, 0.26 mmol) were added to
toluene (200 ml) and degassed for 10 min. Then the mixture was
heated to reflux for 24 h under nitrogen atmosphere. The solvent
was removed under vacuum. After the similar work up procedure,
the solvent was concentrated by rotary evaporator, and then the
compound was purified by column chromatography (Al2O3) using
dichloromethane as eluent, to get a yellow solid (1.3 g, 60%) 1H NMR
2.5.7. (10-(4-(5-(7-(5-Bromothiophen-2-yl)-9,9-dihexyl-9H-
fluoren-2-yl)thiophen-2-yl)phenoxy)decyloxy) (tert-butyl)
dimethylsilane (7)
Mixture of compound 3 (3 g, 4.56 mmol), 6 (1.9 g, 3.9 mmol),
and K2CO3 (0.7 g, 5.03 mmol) were dissolved in 80 ml of toluene
and ethanol (3:1) and degassed for 10 min. Then Pd(PPh3)4 (115 mg,
0.10 mmol) was added and the resulting mixture was stirred under
reflux for overnight. The solvent was removed under vacuum, and
after being worked up the solvent was concentrated by rotary
evaporator. Then, the compound was purified by column chroma-
tography (silica) using a mixture of hexane and dichloromethane
(9:1) as an eluent, to get a yellow solid (2.00 g, 55%) 1H NMR
(300 MHz, CDCl3),
d
(ppm): 8.57 (d, J ¼ 6.3 Hz, 2H), 7.70 (d, J ¼ 3 Hz,
1H), 7.67 (d, J ¼ 3 Hz,1H), 7.62e7.50(m,10H), 7.32 (d, J ¼ 3.6 Hz, 2H),
7.25 (d, J ¼ 5.7 Hz, 1H), 7.18 (d, J ¼ 3.9 Hz, 1H), 6.90 (d, J ¼ 9 Hz, 2H),
3.96 (t, J ¼ 6.9 Hz, 2H), 3.58 (t, J ¼ 6.6 Hz, 2H), 2.13e2.05 (m, 4H),
1.80e1.76 (m, 2H), 1.49e1.28 (m, 16H), 1.11e1.05 (m, 10H), 0.88 (s,
9H), 0.75e0.67 (m, 10H), 0.042 (s, 6H).
(300 MHz, CDCl3),
d
(ppm): 7.66 (d, J ¼ 7.8 Hz, 2H), 7.59e7.53(m, 5H)
0.7.36 (dd, J ¼ 3.6 Hz, J ¼ 1.2 Hz,1H), 7.31 (d, J ¼ 3.9 Hz,1H), 7.27 (dd,
J ¼ 5.1 Hz, J ¼ 1.2 Hz, 1H), 7.18 (d, J ¼ 3.9 Hz, 1H), 7.10e7.08 (m, 1H),
6.90 (d, J ¼ 9 Hz, 2H), 3.97 (t, J ¼ 6.6 Hz, 2H), 3.58(t, J ¼ 13.5 Hz, 2H),
2.03e1.97 (m, 4H), 1.83e1.76 (m, 2H), 1.51e1.25 (m, 16H), 1.13e1.05
(m, 10H), 0.88 (s, 9H), 0.75e0.67 (m, 10H), 0.035 (s, 6H).
2.5.12. 10-(4-(5-(9,9-Dihexyl-7-(50-(pyridin-4-yl)-2,20-bithiophen-
5-yl)-9H-fluoren-2-yl)thiophen-2-yl)phenoxy)decan-1-ol (12)
Compound 11 (0.9 g, 0.88 mmol) was dissolved in 30 ml of dry
THF, to this 1.75 ml (1.76 mmol) of 1M TBAF was added under an
ice-cold water bath. The reaction mixture was stirred for 10 min
then further 12 h at room temperature. THF was removed by rotary
evaporator, the product was extracted with excess of dichloro-
methane followed by brine wash .The organic solvent was dried
over anhydrous magnesium sulphate then the solvent was
removed using rotary evaporator. The crude product was purified
by column chromatography on Al2O3 using mixture of dichlor-
omethane:THF (20:1) as an eluent to yield a yellow solid (0.65 g,
2.5.8. 4-(Thiophen-2-yl) pyridine (8)
Mixture of compound 4-iodopyridine (2 g, 9.75 mmol), thio-
phen-2-ylboronic acid (1.5 g, 11.7 mmol), K2CO3 (1.8 g, 13 mmol)
were dissolved in 120 ml of toluene and ethanol (3:1) and degassed
for 10 min then Pd(PPh3)4 (225 mg, 0.195 mmol) was added and
then the resulting mixture was stirred under reflux for overnight.
The solvent was removed under vacuum followed by work up
procedure, then the solvent was concentrated under vacuum.
Thereafter, the compound was purified by column chromatography
(Al2O3) using mixture of hexane and dichloromethane (9:1) as
eluent, to get a white solid (1.4 g, 86%) 1H NMR (300 MHz, CDCl3),
d
81%) 1H NMR (300 MHz, CDCl3),
d
(ppm): 8.70 (d, J ¼ 5.4 Hz, 2H),
(ppm): 8.57 (d, J ¼ 6 Hz, 2H), 7.50e7.46 (m, 3H), 7.40 (d, J ¼ 5.1 Hz,
8.05 (d, J ¼ 3.9 Hz, 2H), 7.96 (d, J ¼ 6.3 Hz, 2H), 7.82e7.73 (m, 4H),
7.66e7.54 (m, 7H), 7.40 (d, J ¼ 3.6 Hz, 1H), 6.95 (d, J ¼ 8.7 Hz, 2H),
3.99 (t, J ¼ 6.6 Hz, 2H), 3.64 (t, J ¼ 6.6 Hz, 2H), 2.06e2.01 (m, 4H),
1.82e1.77 (m, 2H), 1.59e1.53 (m, 2H), 1.47e1.43 (m, 14H), 1.15e1.07
(m, 10H), 0.77e0.72 (m, 10H).
1H), 7.12 (t, J ¼ 4.2 Hz, 1H).
2.5.9. 4-(5-Bromothiophen-2-yl) pyridine (9)
4-(thiophen-2-yl)pyridine (8) (1 g, 6.2 mmol) was dissolved in
50ml ofdichloromethane, tothat, bromine(0.63ml,12.4mmol)with
10 mlof dichloromethanewasadded slowly for 10 minandstirred for
additional 15 min at room temperature. The reaction was quenched
with 50 ml of 10% K2CO3 followed by extraction from dichloro-
methaneanddriedoveranhydrous MgSO4. Subsequently, thesolvent
wasconcentratedby rotaryevaporator. Afterthat, the compound was
purified by column chromatography on Al2O3 using mixture of
hexane and dichloromethane (10:1) as eluent, to get white solid
2.5.13. 10-(4-(5-(9,9-Dihexyl-7-(50-(pyridin-4-yl)-2,20-bithiophen-
5-yl)-9H-fluoren-2-yl)thiophen-2-yl)phenoxy)decyl methacrylate
(DFTP)
To a schlenk tube, compound 12 (1.0 g, 1.10 mmol), vinyl
methacrylate (0.37 g, 3.3 mmol), 1,3-dichloro-1,1,3,3-tetrabu-
tyldistannoxane (0.30 mg, 0.05 mmol), and 2,6-di-tert-butyl-4-
methylphenol (24 mg, 0.110 mmol) in dry THF (2 mL) were purged
with nitrogen for 15 min at room temperature. The tube was sealed
and stirred at 50 ꢀC for 2 days. After cooling to room temperature,
the reaction mixture was extracted using dichloromethane, and the
extract was washed with water, dried over Mg2SO4, and then
evaporated. The crude product was purified by column chroma-
tography using dichloromethane as eluent and then washed with
hexane. to yield yellow solid (0.84 g, 81%) 1H NMR (300 MHz,
(1.2 g, 81%) 1H NMR (300 MHz, CDCl3),
7.45 (d, J ¼ 6 Hz, 2H), 7.30 (d, J ¼ 3 Hz, 1H), 7.11 (d, J ¼ 3 Hz, 1H).
d
(ppm): 8.60 (d, J ¼ 6 Hz, 2H),
2.5.10. 2-Tri-n-butylstannyl-5-(4-pyridyl) thiophene (10)
4-(5-bromothiophen-2-yl) pyridine (9) (0.3 g, 1.24 mmol) was
dissolved in 80 ml of THF and the solution was cooled to - 78 ꢀC.
0.75 ml (2.5 M in hexane, 1.87 mmol) of n-BuLi was added over
a period of 3 min under nitrogen atmosphere. After stirring the
solution for 30 min at - 78 ꢀC, Bu3SnCl (0.5 ml, 1.87 mmol) was
added and the reaction mixture was stirred for further 1 h. It was
then allowed to warm up to room temperature and stirred for
additional 3 h then the reaction was quenched with water (30 ml).
THF was removed in rotary evaporator and worked up, then the
solvent was removed in rotary evaporator. Afterward, the
compound was purified by column chromatography(Al2O3) using
CDCl3),
d(ppm): 8.60 (d, J ¼ 5.7 Hz, 2H), 7.68 (d, J ¼ 7.8 Hz, 2H),
7.62e7.56 (m, 8H) 7.47e7.44 (m, 2H), 7.34e7.32 (m, 2H), 7.25 (d,
J ¼ 2.7 Hz,1H), 7.21 (d, J ¼ 2.7 Hz,1H), 6.95 (d, J ¼ 8.7 Hz, 2H), 3.99 (t,
J ¼ 6.6 Hz, 2H), 3.64 (t, J ¼ 6.6 Hz, 2H), 2.06e2.01 (m, 4H), 1.95 (s,
3H) 1.82e1.77 (m, 2H), 1.59e1.53 (m, 2H), 1.47e1.43 (m, 14H),
1.15e1.07 (m, 10H), 0.77e0.72 (m, 10H). MS (FAB): m/z [Mþ] 975;
calcd m/z [Mþ] 974.46. Anal. Calcd for C62H71NO3S3: C, 76.42; H,
7.34; N, 1.44; Found: C, 76.49; H, 7.36; N, 1.92.

6188
D. Sahu et al. / Polymer 51 (2010) 6182e6192
2.6. Synthesis of H-acceptor polymer
range of 381e386 ꢀC, which are adequate for their applications in
polymer solar cells and other optoelectronic devices.
2.6.1. Poly[10-(4-(5-(9,9-dihexyl-7-(50-(pyridin-4-yl)-2,20-
bithiophen-5-yl)-9H-fluoren-2-yl)thiophen-2-yl)phenoxy)decyl
methacrylate] (PDFTP)
3.2. FT-IR spectroscopy of H-Bonded cross-linking polymers
The polymerization was carried out by the free radical poly-
merization described as follows. To a Schlenk tube, 1.5 g of mono-
mer DFTP was dissolved in 20 wt% monomer concentration of dry
THF (7.5 mL) with AIBN (5 mg, 2 mol % the monomer concentration)
as an initiator. The solution was degassed by three freeze-pump-
thaw cycles and then sealed off. The reaction mixture was stirred
and heated at 60 ꢀC for 48 h. After polymerization, the polymer was
precipitated into methanol. The precipitated polymer was
collected, washed with diethyl ether, and dried under high vacuum.
Yield: 1.2 g (80%). Mn ¼ 25128 and PDI (Mw/Mn) ¼ 1.72 (by GPC). 1H
H-acceptor side-chain homopolymer PDFTP and H-donor dyes
D1eD4 were complexed in an appropriate molar ratio of 2:1 to
form H-bonded cross-linking polymers by slow evaporation
processes (ambient temperature) in THF solutions followed by
drying under reduced pressure in vacuum. The formation of
hydrogen bonds in H-bonded cross-linking polymers originated
from COOH groups of H-donor dyes and pyridyl groups of H-
acceptor polymer were confirmed by FTIR spectroscopy. Fig. 4
shows the IR spectra of H-donor dye D1, H-acceptor homopol-
ymer PDFTP, and H-bonded polymer network PDFTP/D1. In
contrast to the characteristic OeH stretching vibrations at 2490 and
2650 cmꢁ1 of pure D1 dye, the weaker OeH bands observed at 2500
and 1900 cmꢁ1 are indicative of strong hydrogen bonding between
the pyridyl groups of H-acceptor polymer PDFTP and carboxylic
acids of H-donor D1 dye [32,38]. In addition, the C]O stretching
vibration at 1723 cmꢁ1 of H-bonded polymer network PDFTP/D1
showed that the carbonyl group was in a less associated state than
that in pure D1 which appeared at 1678 cmꢁ1 [32b]. The above
results implied that the hydrogen bonds were formed between H-
acceptor polymer PDFTP and H-donor D1 dye in the solid state of
H-bonded polymer network PDFTP/D1. The other H-bonded cross-
linking polymers also have the similar consequences as the H-
bonded structure of H-bonded polymer network PDFTP/D1
demonstrated here.
NMR (300 MHz, CDCl3), d(ppm): 8.51 (br, s, 2H), 7.55e7.46 (br, m,
4H), 7.32e7.11 (br, m, 10H), 6.95e6.91 (br, m, 2H), 6.81 (br, s, 2H),
3.99 (br, m, 2H), 3.83 (br, m, 2H), 1.95 (br, m, 4H), 1.72 (br, m, 4H),
1.33 (br, m, 12H), 0.98 (br, m, 12H), 0.64 (br, m, 10H). Anal. Calcd for
C62H71NO3S3: C, 76.42; H, 7.34; N, 1.44; Found: C, 75.89; H, 7.11; N,
2.05.
2.6.2. Preparation of H-Bonded polymer networks (PDFTP/D1eD4)
Proton-acceptor polymer PDFTP and proton-donor dye
(D1eD4) 2:1 M ratio were dissolved in minimum amount of THF to
make a clear solution. Then the solvent was evaporated under
ambient temperature, and was followed by drying in a vacuum
oven at 60 ꢀC for several hours. The complexation of donor and
acceptor through hydrogen bonding occurred during the solvent
evaporation. Similar procedure was followed for all the H-bonded
polymers.
3.3. Optical properties
The normalized UVevis absorption spectra of H-acceptor poly-
mer PDFTP and H-donor dyes D1eD4 in THF solutions (10ꢁ5 M) are
shown in Fig. 5 and their data are listed in Table 1. H-donor dyes
D1eD4 showed the maximum absorption wavelengths in the range
from 468 to 480 nm and were attributed to the intramolecular
charge transfer (ICT) from the donor carbazole core to the cya-
noacrylic acid termini. Regardless of the increased conjugation
lengths (with one more symmetrical thiophene unit) from D1 to D2
3. Results and discussion
3.1. Structural characterization
All H-donor dyes D1eD4, monomer DFTP, and H-acceptor side-
chain homopolymer PDFTP were satisfactorily characterized by 1H
NMR, FAB, and elemental analyses. The weight average molecular
weight (Mw) of H-acceptor polymer PDFTP was determined by gel
permeation chromatography (GPC) with THF as the eluting solvent
and polystyrene as a standard. Fig. 3 shows 1H NMR spectra of
monomer DFTP and polymer PDFTP. The number average molec-
ular weight (Mn) and polydispersity index (PDI) of polymer PDFTP
were 25128 g/mol and 1.72, respectively. The decomposition
temperatures (Td) of H-bonded polymer networks PDFTP/D1-D4
and H-acceptor polymer PDFTP were measured by TGA and
summarized in Table 1. H-bonded cross-linking polymers showed
good thermal stabilities with decomposition temperatures in the
Table 1
Photophysical Properties and Optical Band gaps of H-Donor Dyes (D1eD4), H-
Acceptor Polymer (PDFTP), and H-Bonded Polymer Networks (PDFTP/D1eD4).
Compound labs,sol (nm)a labs,film (nm)a lonset,abs (nm)b Eg,opt (eV)b Td (ꢀC)
D1
D2
D3
D4
PDFTP
PDFTP/D1
PDFTP/D2
PDFTP/D3
PDFTP/D4
470
468
480
470
414
e
513
513
530
526
416
426
463
445
431
646
663
639
655
480
586
648
604
598
1.91
1.87
1.94
1.89
2.57
2.11
1.91
2.05
2.07
e
e
e
e
e
381
384
386
386
e
e
e
a
Absorption spectra were recorded in THF solutions.
Estimated from the onset wavelengths of absorption spectra in solid films.
Fig. 4. FT-IR spectra of H-acceptor polymer PDFTP, H-donor dye D1, and H-bonded
polymer network PDFTP/D1 at room temperature.
b

D. Sahu et al. / Polymer 51 (2010) 6182e6192
6189
Fig. 5. Normalized UVevisible absorption spectra of H-donor dyes D1eD4 and H-
acceptor polymer PDFTP in THF solutions.
and from D3 to D4, the presence of lateral alkyl chains in the
thiophene units resulted in 2 and 10 nm blue shifts, respectively,
which was presumably increased the disorder in the conjugated
system of the dyes due to the steric hindrance imparted by those
alkyl side chains. However, the onset absorption wavelengths
were increased by the increased conjugation effect [39]. Relative to
the solution state in Fig. 5, the solid film absorption spectra of dyes
(D1eD5) in Fig. 6 a were red-shifted by a range of 43e56 nm (see
Table 1), thus the red-shifts of the absorption peaks suggest the
enhanced p-p stacking in terms of inter-chain characteristics [40]
in solid state. As anticipated, the red-shifts from D1 to D3 (10 nm
in solutions and 17 nm in solid films) and D2 to D4 (2 nm in
solutions and 13 nm in solid films) were possible due to the
enhanced
of D3 and D4 over non-planar 3,6-carbazole cores of D1 and D2
[29e]. Evidently, the poor stacking interactions in H-acceptor
p-p stacking assisted by the coplanar 2,7-carbazole cores
p-p
polymer PDFTP, due to presence of longer flexible alkyl chain
resulted in negligible (2 nm) red shift in the absorption spectrum of
solid film compared with that in solution. As shown in Fig. 6 b, the
maximum absorption peak of H-bonded polymer networks PDFTP/
D1eD4 on solid quartz films were blue shifted in contrast to those
of H-donor dyes (D1eD4) and the blue shifts (blue shifted to
a range of 50e87 nm) were ascribed to the dilution effect of H-
acceptor polymer as solid solvent for dyes as solutes in the H-
bonded cross-linking polymers. However, the broader absorption
spectra of H-bonded cross-linking polymers (compared with
PDFTP) extending to longer wavelength regions (Fig. 6 b) favored
better light harvesting and increased the photocurrent response
region. In addition, the broadening of absorption spectra in the H-
bonded cross-linking polymers increased their lonset, thus the
decrease of optical band gaps in solid films was observed. Among
all H-bonded polymer networks, PDFTP/D2 has the longest
broadening of the absorption spectrum. Thus, the lowest band gap
(1.91 eV) of H-bonded polymer network PDFTP/D2 was observed,
which further reflected as the most superior performance among
all photovoltaic devices. Furthermore, it is supported by the fact
that there were significant PL quenching observed in the H-bonded
polymer networks (see Fig. S1 of the supporting information) and
the degrees of quenching were consistent with their PCE values
(PDFTP/D2 > PDFTP/D1 > PDFTP/D3 > PDFTP/D4). The largest PL
quenching of PDFTP/D2 was a symptom of better photo-induced
charge transfer in H-bonded polymer network PDFTP/D2, which
will reflect later to show the best PCE value.
Fig. 6. Normalized UVevisible absorption spectra of (a) H-donor dyes (D1eD4) (b) H-
acceptor polymer (PDFTP) and H-bonded polymer networks (PDFTP/D1eD4) in solid
films coated onto fused quartz plates.
3.4. Electrochemical properties
Cyclic voltammetric (CV) method was used to investigate the
electrochemical characteristics of H-donor dyes (D1eD4), H-
acceptor polymer PDFTP, and the H-bonded polymer networks
(PDFTP/D1eD4). The relevant CV data of dyes are presented in
Table 2
Electrochemical Properties of H-Acceptor Polymer (PDFTP) and H-Bonded Polymer
Networks (PDFTP/D1eD4).
Polymer
Eox/onset (V)a Ered/onset (V)a HOMO (eV)b LUMO (eV)b Eg,cv (eV)c
PDFTP
1.28
ꢁ 0.90
ꢁ 0.94
ꢁ 0.83
ꢁ 0.96
ꢁ 0.83
ꢁ 5.63
ꢁ 5.51
ꢁ 5.37
ꢁ 5.41
ꢁ 5.49
ꢁ 3.45
ꢁ 3.41
ꢁ 3.52
ꢁ 3.39
ꢁ 3.52
2.21
2.10
1.85
2.02
1.97
PDFTP/D1 1.16
PDFTP/D2 1.02
PDFTP/D3 1.06
PDFTP/D4 1.14
a
Oxidation and reduction potentials were measured by cyclic voltammetry in
solid films.
b
Estimated from the onset potentials using empirical equations: HOMO/
LUMO ¼ [ꢁ(Eox/red onset ꢁ E1/2 (ferrocene) þ 4.8)] eV, where 4.8 eV is the energy level of
ferrocene below the vacuum level.
c
Band gaps measured by cyclic voltammograms.

6190
D. Sahu et al. / Polymer 51 (2010) 6182e6192
Table 3
Photovoltaic Performance of PSC Devicesa Based on H-Bonded Polymer Networks
PDFTP/D1-D4 Measured Under AM 1.5 Irradiation, 100 mW/cm2.
Polymer network
Voc (V)
Jsc (mA/cm2)
FF (%)
PCE (%)
PDFTP/D1
PDFTP/D2
PDFTP/D3
PDFTP/D4
0.56
0.55
0.57
0.59
1.76
1.90
1.40
1.13
27
29
30
24
0.27
0.31
0.24
0.16
a
PSC devices with the configuration of ITO/PEDOT:PSS/(PDFTP/D1-D4):PCBM/Ca/
Al where H-bonded polymer network:PCBM ¼ 1:1 by weight.
ꢁ 5.51/ꢁ 3.41, ꢁ 5.37/ꢁ 3.52, ꢁ 5.41/ꢁ 3.39, and ꢁ 5.49/ꢁ 3.52 eV,
respectively, with electrochemical band gaps (Eg,cv) of 2.10, 1.85,
2.02, and 1.97 eV, correspondingly. The attained LUMO and HOMO
levels in these H-bonded polymer networks with good air stabili-
ties are suitable as a donor for electron injection and transporting
to PCBM acceptor [42]. Moreover, electrochemical band gaps (Eg,cv
)
were very close to those obtained from the absorption spectra of
solid polymer films (Eg,opt). To gain insight into the geometries of H-
donor dyes D1eD4, we performed DFT (density functional theory)
calculations using Gaussian 03 program package. The optimized
geometries in ground state and the dihedral angles formed
between the carbazole-thiophene and thiophene-cyanoacrylate
units are shown in Fig. S3 and Table S2 of the supporting infor-
mation. From the calculated dihedral angles, it is noticeable that the
thiophene units are found to be coplanar with the cyanoacrylic acid
groups, which are important characteristics in the conceptions of
materials in photovoltaic applications.
Fig. 7. Cyclic voltammograms of H-bonded polymer networks PDFTP/D1eD4 in
acetonitrile at a scan rate of 100 mV/s.
Table S1 and Fig. S2 (see the supporting information), and those of
polymers are also illustrated in Table 2 and Fig. 7. Cyclic voltam-
mograms of the dyes are measured in deoxygenated THF solutions
containing 0.1 M TBAPF6 at 25 ꢀC in volts versus Ag/AgNO3 (0.01 M
in MeCN; the scan rate is 100 mV sꢁ1). All dyes (D1eD4) exhibited
quasi-reversible oxidation and reduction potential (see Fig. S2 of
the supporting information). The calculated HOMO and LUMO
levels of those H-donor dyes D1eD4 were found in the range
of ꢁ 5.44 to ꢁ 5.56 eV and ꢁ 3.31 to ꢁ 3.34 eV, respectively, with
electrochemical band gap of 2.11e2.22 eV. Cyclic voltammograms
of H-acceptor polymer PDFTP and H-bonded polymer networks
PDFTP/D1eD4 were measured in solid films with Ag/AgCl as a
reference electrode, which were calibrated by ferrocene (E1/2
3.5. Photovoltaic properties
To demonstrate the potential application of the H-bonded
polymer networks (PDFTP/D1eD4) as electron donors in photo-
voltaic devices, we fabricated devices by spin-coating from 2 wt%
N-methylpyrrolidone (NMP) solutions of polymer blends contain-
ing H-bonded polymer networks PDFTP/D1eD4 (as electron
donors) and PCBM (as an electron acceptor) in 1:1 weight ratio with
¼ 0.45 mV vs Ag/AgCl). The HOMO and LUMO levels of all
(ferrocene)
a
configuration of ITO/PEDOT:PSS/H-bonded polymer net-
polymers were estimated by the oxidation and reduction potentials
from the reference energy level of ferrocene (4.8 eV below the
vacuum level) according to the following equation [41]: EHOMO/
works:PCBM (1:1 w/w)/Ca/Al (under AM 1.5 irradiation, 100 mW/
cm2). Fig. 8 shows the current density versus voltage (JeV) curves
and the results are illustrated in Table 3. As shown in Table 3, the
short-circuit current density (Jsc), open-circuit voltage (Voc), fill
factor (FF), and PCE values of the OPV devices containing H-bonded
¼ [-(Eonset - 0.45) - 4.8] eV. The HOMO/LUMO levels of H-
LUMO
bonded polymer networks PDFTP/D1eD4 were estimated to be
Fig. 8. Current density-voltage curves of illuminated solar cells incorporating H-
bonded polymer networks PDFTP/D1eD4 with PCBM in 1:1 (w/w) ratio under AM
1.5G, 100 mW/cm2.
Fig. 9. Current density-voltage curves of illuminated solar cells incorporating D2, D3,
or PDFTP with PCBM in 1:1 (w/w) ratio under AM 1.5G, 100 mW/cm2.

D. Sahu et al. / Polymer 51 (2010) 6182e6192
6191
Table 4
molecules and polymers via H-bonding are very encouraging for
the future research on donor-acceptor supramolecular architec-
Photovoltaic Performance of PSC Devicesa Based on H-Donor Dyes D2-D3 or H-
Acceptor Polymer PDFTP Measured Under AM 1.5 Irradiation, 100 mW/cm2.
tures of oligomeric dyes H-bonded with processable
polymers in organic solar cell applications.
p-conjugated
Compound
Voc (V)
Jsc (mA/cm2)
FF (%)
PCE (%)
D2
D3
PDFTP
0.26
0.27
0.22
1.85
1.31
0.30
32
31
26
0.15
0.11
0.02
Appendix. Supplementary material
a
PSC devices with the configuration of ITO/PEDOT:PSS/D2,D3, or PDFTP:PCBM/
Ca/Al where Compound:PCBM ¼ 1:1 by weight.
Supplementary data related to this article can be found online at
doi:10.1016/j.polymer.2010.10.018.
polymer networks PDFTP/D1eD4 were in the range of
1.13e1.9 mA/cm2, 0.55e0.59 V, 24e30%, 0.16e0.31%, respectively.
Due to the negligible difference in their HOMO values, all the
devices containing H-bonded polymer networks (PDFTP/D1eD4)
showed similar Voc values. As described before, due to the longest
broadening of absorption spectra in PDFTP/D2, it had the best light
harvesting and the highest photocurrent response and hence to
appeal a highest Jsc value (1.9 mA/cm2) among all H-bonded poly-
mer networks (PDFTP/D1eD4). As a contributing parameter for the
net PCE value, the fill factors of the OPV devices were low, which
could be associated with the large series resistance of the devices.
In addition, the behavior of the solar cell properties can be well
analyzed from the surface topography of the active layer. On the
whole, the OPV device containing blended H-bonded polymer
network PDFTP/D2:PCBM resulted the best overall PCE value of
0.31% with Jsc ¼ 1.9 mA/cm2, Voc ¼ 0.55 V, and FF ¼ 29%, which was
mainly because of its broader absorption and better utilization of
the solar spectrum, and also supported by the largest quenching of
PL spectra (see Fig. S1 of the supporting information) which
increased the photo-induced charge transfer in H-bonded polymer
network PDFTP/D2 [14b,19c]. In general, the poor solubilities of H-
bonded polymer networks might be one of the reasons for the
lower PCE values. In order to demonstrate the contribution of
supramolecular structures in H-bonded cross-linking polymers, we
fabricated OPV devices with only H-donor D2eD3 dyes or H-
acceptor polymer PDFTP blended with PCBM in 1:1 weight ratio
measured under similar conditions as those of the blended H-
bonded cross-linking polymers and the J-V curves are shown in
Fig. 9 and the data are listed in Table 4. Interestingly, it is noticeable
that the PCE values of D2 (0.15%), D3 (0.11%), and PDFTP (0.02%)
were much lower than those of H-bonded polymer networks
PDFTP/D2 (0.31%) and PDFTP/D3 (0.24%). In general, the approach
in self-assembly of H-donor dyes with H-acceptor polymers via
hydrogen bonding was proven to enhance OPV properties by the
unique non-covalent-bonded practical applications.
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