Easily attainable phenothiazine-based polymers for polymer solar cells: Advantage of insertion of S,S-dioxides into its polymer for inverted structure solar cells

Article abstract of DOI:10.1021/ma202661b

Two donor-(D-) acceptor (A) type polymers based on a soluble chromophore of phenothiazine (PT) unit that is a tricyclic nitrogen-sulfur heterocycle, have been synthesized by introducing an electron-deficient benzothiadiazole (BT) building block copolymerized with either PT or phenothiazine-S,S-dioxide (PT-SS) unit as an oxidized form of PT. The resulting polymers, PPTDTBT and PPTDTBT-SS are fully characterized by UV-vis absorption, electrochemical cyclic voltammetry, X-ray diffraction (XRD), and DFT theoretical calculations. We find that the maximum absorption of PPTDTBT is not only markedly red-shifted with respect to that of PPTDTBT-SS but also its band gap as well as molecular energy levels are readily tuned by the insertion of S,S-dioxides into the polymer. The main interest is focused on the electronic applications of the two polymers in organic field-effect transistors (OFETs) as well as conventional and inverted polymeric solar cells (PSCs). PPTDTBT is a typical p-type polymer semiconductor for OFETs and conventional PSCs based on this polymer and PC₇₁BM show a power conversion efficiency (PCE) of 1.69%. In case of PPTDTBT-SS, the devices characteristics result in: (i) 1 order of magnitude higher hole mobility (μ = 6.9 × 10^-4 cm² V^-1 s ^-1) than that obtained with PPTDTBT and (ii) improved performance of the inverted PSCs (1.22%), compared to its conventional devices. Such positive features can be accounted for in terms of closer packing molecular characteristics owing either to the effects of dipolar intermolecular interactions orientated from the sulfonyl groups or the relatively high coplanarity of PPTDTBT-SS backbone.

Full text of DOI:10.1021/ma202661b

Article
pubs.acs.org/Macromolecules
Easily Attainable Phenothiazine-Based Polymers for Polymer Solar
Cells: Advantage of Insertion of S,S-dioxides into its Polymer for
Inverted Structure Solar Cells
†
†
‡
§
†
,†
Gyoungsik Kim, Hye Rim Yeom, Shinuk Cho, Jung Hwa Seo, Jin Young Kim, and Changduk Yang*
†Interdisciplinary School of Green Energy and KIER-UNIST Advanced Center for Energy, Low Dimensional Carbon Materials
Center, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, South Korea
‡Department of Physics and EHSRC, University of Ulsan, Ulsan 680-749, South Korea
§Department of Materials Physics, Dong-A University, Busan 604-714, South Korea
*
S Supporting Information
ABSTRACT: Two donor− (D−) acceptor (A) type polymers based on a soluble chromophore of phenothiazine (PT) unit that
is a tricyclic nitrogen−sulfur heterocycle, have been synthesized by introducing an electron-deficient benzothiadiazole (BT)
building block copolymerized with either PT or phenothiazine-S,S-dioxide (PT-SS) unit as an oxidized form of PT. The resulting
polymers, PPTDTBT and PPTDTBT-SS are fully characterized by UV−vis absorption, electrochemical cyclic voltammetry, X-
ray diffraction (XRD), and DFT theoretical calculations. We find that the maximum absorption of PPTDTBT is not only
markedly red-shifted with respect to that of PPTDTBT-SS but also its band gap as well as molecular energy levels are readily
tuned by the insertion of S,S-dioxides into the polymer. The main interest is focused on the electronic applications of the two
polymers in organic field-effect transistors (OFETs) as well as conventional and inverted polymeric solar cells (PSCs).
PPTDTBT is a typical p-type polymer semiconductor for OFETs and conventional PSCs based on this polymer and PC BM
7
1
show a power conversion efficiency (PCE) of 1.69%. In case of PPTDTBT-SS, the devices characteristics result in: (i) 1 order of
−4
2
−1 −1
magnitude higher hole mobility (μ = 6.9 × 10 cm V s ) than that obtained with PPTDTBT and (ii) improved performance
of the inverted PSCs (1.22%), compared to its conventional devices. Such positive features can be accounted for in terms of
closer packing molecular characteristics owing either to the effects of dipolar intermolecular interactions orientated from the
sulfonyl groups or the relatively high coplanarity of PPTDTBT-SS backbone.
INTRODUCTION
metal oxides (e.g., TiO and ZnO) as electron collecting
x
■
15,16
bottom electrodes.
Thus, with advances made on the
The dramatic growing need for renewable energy supply is
increasing the demand for new technologies for photovoltaic
energy conversion. Polymeric solar cells (PSCs) have attracted
much attention due to their potentials for low cost, lightweight,
and good compatibility with the roll-to-roll process for making
flexible large area devices. So far, the most efficient polymer
solar cell system is built on the concept of bulk-heterojunction
BHJ) structure, which uses a blend of an electron-donor
aforementioned efficiency front, the lifetime and reliability of
PSCs are also envisaged by utilizing the inverted PSC
configuration through the replacement of the low work-
function metal cathode and the elimination of PEDOT:PSS
layer.
1
−5
Recently, several classes of narrow bandgap donor− (D−)
acceptor (A) type polymers have been developed to better
harvest the solar spectrum with deeper HOMO energies that
can be helpful in realizing high open circuit voltage (VOC) and
PCEs, as the VOC value of PSCs is directly proportional to the
offset between the HOMO level of electron donor and the
(
3
polymer and an electron-acceptor fullerene. Recently, power
conversion efficiencies (PCEs) of 6−8% have been realized by
6
−10
using new conjugated polymer donors
or novel fullerene-
11−13
derived acceptors.
5
,17−19
LUMO level of electron acceptor.
Among them,
Aside from achieving higher PCEs, improving the stability of
PSCs is equally important. In general, conventional PSCs are
comprised of a BHJ active layer sandwiched between an acidic
poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)- (PE-
DOT:PSS-) coated indium tin oxide (ITO) anode and a low
work-function metal cathode (e.g., Al and Ca). In such a device
structure, not only does the cathodes easily oxidize in air but
also the acidic PEDOT:PSS-ITO can suffer interfacial
degradation over the operating lifetime. As alternative to
the regular device configuration, PSCs with an inverted device
structure have been developed, which enables the use of stable
and printable high work-function metals (e.g., Ag and Au) as
hole collecting top electrodes and n-type low work-function
poly(2,7-carbazole-alt-dithienylbenzothiadiazole) (PCDTBT)
showed particularly interesting achievement of a PCE in excess
of 6% from a BHJ cell with VOC value approaching 0.9 V as well
as remarkable stability at higher temperature for extended
1
7,20
periods of time.
More recently, efficient, air-stable inverted
BHJ solar cells based on PCDTBT fabricated with a low-
temperature annealed sol−gel-derived ZnO film as an electron
15
14
transport layer have also been demonstrated.
Received: December 8, 2011
Revised: January 15, 2012
Published: February 3, 2012
©
2012 American Chemical Society
1847
dx.doi.org/10.1021/ma202661b | Macromolecules 2012, 45, 1847−1857

Macromolecules
Article
Figure 1. Molecular structures of PCDTBT and phenothiazine-based polymers. Schematic depiction of the conventional structure (a) and inverted
structure (b) of the PSCs used by our research group.
However, to prepare the tricyclic 2,7-carbazole monomer,
Herein, we report two new polymers incorporating either
phenothiazine or its oxidized analogue phenothiazine-S,S-
dioxide as the donor and benzothiadiazole as the acceptor,
namely poly(N-(2-decyltetradecyl)-3,7-phenothiazine-alt-5,5-
(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)) (PPTDTBT) and
poly(N-(2-decyltetradecyl)-3,7-phenothiazine-S,S-dioxide-alt-
5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)) (PPTDTBT-
SS), respectively (Figure 1). These polymers are tested in
both conventional and inverted solar cell devices using the
fullerene derivative (see Figure 1a and b). We find that PSCs
based on PPTDTBT in a conventional architecture can reach
PCE as high as 1.69%, whereas the utilization of its oxidized
form PPTDTBT-SS into inverted solar cells shows improved
performance (PCE = 1.22%), when compared to that of its
conventional devices. The results obtained here are very helpful
for molecular design strategies to obtain inverted solar cells
with higher device performance.
4
,4′-dibromobiphenyl must first undergo a nitration reaction
21
followed by a Cadogan ring closure reaction. The relatively
long synthetic routes will limit their future commercial
application in PSCs. To realize potentially low manufacturing
costs, it is critical to obtain readily synthesized polymers from
commercial products.
In this regard, we focused our attention to the well-known
phenothiazine building block, considering the following: (i)
Heterocyclic phenothiazine unit is structurally similar to the
carbazole moiety but it contains an additional sulfur atom. As a
more powerful electron-rich molecule, the phenothiazine is
better suited for the development of enhanced intramolecular
charge transfer (ICT) polymers. In addition, its “butterfly”
nonplanar structure impedes π-stacking aggregation and
intermolecular excimer formation, resulting in diverse opto-
22−26
electronic applications.
(ii) Not only is phenothiazine
cheap and commercially available but also it can be easily
tailored by connecting solubilizing groups to the N atom to
improve solubility. This is important since the barrier for
preparation of materials in terms of a cost effectiveness must be
overcome to realize the commercial potentials of PSCs. (iii)
Following oxidation of phenothiazines to phenothiazine-S,S-
dioxides, the electron-withdrawing sulfones would reduce the
electron density in the polymer backbone, most likely rendering
it more resistant toward the oxidation while simultaneously
tuning the electronic properties. In particular, we hypothesized
RESULTS AND DISCUSSION
■
(
The synthetic routes to the intermediates and the polymers
PPTDTBT and PPTDTBT-SS) are outlined in Scheme 1.
Synthesis of 4,7-dibromo-2,1,3-benzothiadiazole (1), 4,7-di-2-
thienyl-2,1,3-benzothiadiazole (2), and 4,7-bis(5-bromo-2-
thienyl)-2,1,3-benzothiadiazole (3) were prepared by following
27
the literature procedures. In order to guarantee good
solubility of phenothiazine-based polymers, the bulky branched
side chain (2-decyltetradecyl) was introduced onto the nitrogen
atom on the phenothiazine unit. Dibromination of 4 by N-
bromosuccinimide (NBS) in DMF afforded 3,7-dibromo-N-(2-
decyltetradecyl)phenothiazine (5) in 93% yield which was
transformed into the corresponding diboronic ester 6 via
lithiation and subsequent quenching with 2-isopropoxy-4,4,5,5-
that the hydrophilicity of the SO groups can promote the
2
compatibility and low contact resistance through the potential
interaction with oxides in the inverted BHJ solar cells integrated
with metal oxide materials as an electron transport and an hole
transport between the ITO/BHJ and BHJ/metal interfaces.
1
848
dx.doi.org/10.1021/ma202661b | Macromolecules 2012, 45, 1847−1857

Macromolecules
Article
a
Scheme 1. Synthesis of PPTDTBT and PPTDTBT-SS
a
Reagents and conditions: (i) Br , HBr, reflux; (ii) 2-(tributylstannyl)thiophene, THF, Pd(pph ) , reflux; (iii) NBS, DMF, RT; (iv) 2-
2
3 4
Decyltetradecyl bromide, NaN, DMF, RT; (v) NBS, DMF, RT; (vi) n-BuLi, THF, −78 °C, 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane;
(
vii) H O , acetic acid, 90 °C; (viii) Bis(pinacolato)diboron, DMF, KOAc, PdCl (dppf), reflux; (ix) Suzuki polymerization, toluene, H O, K PO ,
2
2
2
2
3
4
P(o-tol) , Pd (dba) , 90 °C.
3
2
3
3
3
tetramethyl-1,3,2-dioxaborolane (58%) to generate the como-
nomer. Separately, compound 5 was oxidized with hydrogen
peroxide under acetic acid (52%) according to a previously
reported protocol to obtain phenothiazine-S,S-dioxide 7.
Treatment of 7 with bis(pinacolato)diboron under
mass (M ) of 9.8 × 10 and 7.6 × 10 g/mol and polydispersity
n
(PDI) of 1.27 and 1.21 for PPTDTBT and PPTDTBT-SS,
respectively.
28
Optical and Electrochemical Properties. The UV−vis
spectra of two polymers (PPTDTBT and PPTDTBT-SS) in
chloroform solution and solid films on the quartz are shown in
Figure 2. The spectroscopic data of the polymers are
summarized in Table 1. PPTDTBT film are characterized
with a strong, broad and structureless absorption band at 582
nm, corresponding to the intramolecular charge-transfer (ICT)
transition, together with a strong absorption band at shorter
wavelength (∼395 nm) due to higher energy transitions such as
π−π* transitions. Notably, such optical features are remarkable
similarity to those of the analogous PCDTBT (λ = 398 and
576 nm), but PPTDTBT has a slightly lower optical band gap
(Eg = 1.79 eV) from the absorption edge of the thin film than
PCDTBT (1.88 eV). Compared to PPTDTBT showing the
absorption maxima, PPTDTBT-SS in the solid state exhibits a
nearly identical high-energy peak at 387 nm but a
hypsochromic shift of the ICT band at 535 nm, resulting in a
larger optical band gap (1.95 eV). This indicates that, as
expected, the donating strength of phenothiazine-S,S-dioxide
PdCl (dppf)/KOAc/DMF led to the phenothiazine-S,S-dioxide
2
diboronic ester 8 in 64% yield.
With all the monomers ready, Suzuki polycondensations
(Scheme 1) were carried out at 90 °C for 72 h in degassed
toluene/water using K PO as an organic base, Pd (dba) as a
3
4
2
3
catalyst, and P(o-tol) as the corresponding ligand, affording
3
PPTDTBT and PPTDTBT-SS respectively. The target
polymers were purified by reprecipitation and Soxhlet
extraction with methanol, acetone, and chloroform. They
show good solubility in common solvents such as chloroform,
dichloromethane, toluene, THF, and chlorobenzene. Note that
PPTDTBT-SS has somewhat lower solubility in the nonpolar
solvents than that of PPTDTBT because of the increased
polarity as well as the hydrophilicity that result from the
introduction of the sulfone groups in the polymer backbone.
Gel-permeation chromatography (GPC) analysis against
polystyrene standard exhibits a number-averaged molecular
max
opt
1
849
dx.doi.org/10.1021/ma202661b | Macromolecules 2012, 45, 1847−1857

Macromolecules
Article
due to the insertion of the additional electron-rich sulfur atoms.
For PPTDTBT-SS interchanged the phenothiazine with a
phenothiazine-S,S-dioxide segment, the HOMO (−5.6 eV) is
found to be lower than of that of PPTDTBT owing to the
presence of the electron-deficient SO groups in the polymer
2
backbone, which can be beneficial to the better air-stability and
30
higher VOC of the PSCs based on the polymer as donor.
X-ray Analyses. To evaluate the crystallinity of the
polymer, X-ray diffraction (XRD) measurements were taken
of thick films prepared from chlorobenzene on SiO /Si
2
substrate. The thickness of the films was determined to be
1
.5−55 μm by profilometry. Figure 4 shows the XRD data of
the thin films of PPTDTBT and PPTDTBT-SS, respectively.
PPTDTBT-SS reveals a distinct primary diffraction feature at
2
θ = 4.67°, corresponding to d-spacing of 18.9 Å and a
secondary broad peak at 2θ = 21.2° (d = 4.2 Å) related to π−π
stacking between the polymer main chains is also observed.
Contrastingly, the XRD pattern of PPTDTBT exhibits only the
secondary broad peak shifting to 17.51° (d = 5.10 Å). These
results suggest a higher structural organization in the solid state
for PPTDTBT-SS compared to PPTDTBT.
Organic Field Effect Transistors. To investigate the
potential of the two new polymers in plastic electronics, organic
field-effect transistors (OFETs) were fabricated in the top
contact geometry as described in the Experimental Section
(
Figure 5). Figure 5b shows the transfer characteristics, |I | vs
ds
1/2
V and |I | vs V (both at V = −60 V), of OFETs fabricated
using PPTDTBT and PPTDTBT-SS, respectively, as the active
layer. These I vs V curves obtained from both PPTDTBT
gs
ds
gs
ds
Figure 2. UV−vis absorption spectra of PPTDTBT (a) and
PPTDTBT-SS (b).
ds
gs
and PPTDTBT-SS exhibit clear signature of p-type behavior.
The saturated charge carrier mobilities of the polymers are
that contains the electron-withdrawing sulfonyl group is weaker
than that of the phenothiazine moiety, leading to relatively
reduced ICT character in PPTDTBT-SS.
calculated using the saturation current equation: I = (μWC /
ds
i
2
31
−5
2
L)(V − V ) . An hole mobility (μ) as high as 9.8 × 10
Electrochemical cyclic voltammetry (CV) was performed to
determine the highest occupied molecular orbital (HOMO)
and lowest unoccupied molecular orbital (LUMO) energy
levels of the polymers (Figure 3). The CV curves were
recorded referenced to an Ag/Ag+ (0.1 M n-Bu NPF )
gs
T
2
−1 −1
cm V
s
(threshold voltage (V
) = −11.5 V) with a current
T
2
on/off ratio (Ion/Ioff) of 2.5 × 10 is estimated for OFETs
produced from PPTDTBT. Interestingly, despite the insertion
of the electron-deficient SO groups as well as the relatively
2
lower molecular weight, the hole carrier mobility is increased by
4
6
electrode, which was calibrated by a ferrocene-ferrocenium
+
(
Fc/Fc ) redox couple (4.8 eV below the vacuum level). The
about 1 order of magnitude in PPTDTBT-SS OFETs (μ = 6.9
−4
2
−1 −1
2
electrochemical characteristics of the estimated energy levels
× 10 cm V s , V
T
= −21.0 V, Ion/Ioff = 7.7 × 10 ),
elec
(
HOMO and LUMO) and electrochemical band gap (Eg
)
compared to PPTDTBT. Although a concrete evidence of the
high performance with PPTDTBT-SS OFETs is lacking at this
stage, we think this is partially contributed either from (i) the
reduced contact resistance between the semiconductor and the
source/drain electrodes arising from the favorable interfacial
dipoles between S,S-dioxide groups and Au electrodes or (ii)
the well-interconnected thin film morphology due to the
interaction between the polar S,S-dioxides. The enhanced
intermolecular interactions would bring the polymer chain into
a close proximity as evidenced by the XRD results, which can
facilitate charge hopping in the polymer.
are listed in Table 1. The HOMO and LUMO energy levels are
calculated to be −5.41 and −3.63 eV for PPTDTBT and −5.60
and −3.60 eV for PPTDTBT-SS, respectively. Considering the
relatively low HOMO levels of the polymers, a high V can be
OC
2
9
expected. The LUMO levels of the polymers are positioned
.3 eV above the PC BM (−4.3 eV) to ensure a downhill
driving force for charge separation to PC BM. The electro-
0
7
1
7
1
chemical HOMO−LUMO gaps of the both polymers are very
similar to those of optical band gaps. Apparently, the LUMO
value of PPTDTBT matches well with that of PCDTBT (−3.6
eV) whereas its higher HOMO level, in comparison with
PCDTBT (−5.5 eV), indicates the increase of donor strength
DFT Electronic Structure Calculations. To shed light on
the difference in the electronic properties and energies of
Table 1. UV−Vis Absorption and Electrochemical Properties of the Polymers
Egopt (eV)a
HOMO (eV)
b
LUMO (eV)
b
Egelec (eV)
polymer
λmax [nm] solution
λmax [nm] film
PPTDTBT
390, 564
377, 515
395, 582
387, 535
1.79
1.95
−5.41
−5.60
−3.63
−3.60
1.78
2.00
PPTDTBT-SS
a
Calculated from the absorption band edge of the copolymer film, Egopt=1240/λedge
ferrocene at 50 mVs . HOMO and LUMO estimated from the onset oxidation and reduction potentials, respectively, assuming the absolute energy
level of ferrocene/ferrocenium to be 4.8 eV below vacuum. Eg (eV) = −(LUMO − HOMO).
b
. Thin films in CH CN/n-Bu NPF , versus ferrocenium/
3 4 6
−1
elec
1
850
dx.doi.org/10.1021/ma202661b | Macromolecules 2012, 45, 1847−1857

Macromolecules
Article
Figure 3. (a) Cyclic voltammograms of PPTDTBT (top) and PPTDTBT-SS (bottom) thin films on the Pt electrode in 0.1 M n-Bu NPF
4
6
acetonitrile solution at room temperature. (b) Energy level diagrams of individual layers used in conventional and inverted structure.
Polymer Solar Cells. To demonstrate potential applica-
tions of the two polymers in PSCs, we used PPTDTBT and
PPTDTBT-SS as an electron donor and PC BM as an
7
1
electron acceptor and fabricated conventional PSCs with a BHJ
structure of ITO/PEDOT:PSS/polymers:PC BM/Al. The
7
1
main focus of the current study is to elucidate the improved
device performance of inverted PSCs by introducing SO2
functionality in the polymer backbone through potential
interaction with oxide materials. Thus, the PSCs with inverted
configuration stacked from bottom to top (ITO/TiOx/
polymers:PC BM/MoO /Au) were also prepared, where
7
1
3
MoO as the hole transport layer and TiO as the electron
3
x
transport layer were deposited. TiO was employed as the
x
Figure 4. X-ray diffraction (XRD) patterns of drop-cast films of
electron selective layer due to its high electron affinity (LUMO
32
polymers on SiO /Si substrates.
= ∼4.4 eV). Since the valence band edge of TiO is much
2
x
lower than those of HOMOs of both the polymers and
PC BM, the TiO layer serves also as a hole blocking layer.
frontier orbitals between the two polymers, computational
studies using density functional theory (DFT) approaches were
carried out. Oligomers (PTDTBT) and (PTDTBT-SS) with
71
x
Similarly, the MoO layer was used to block the electron flow
3
n
n
because of its small electron affinity and to enhance hole
33
n = 1 and 2 were subjected to the calculations, with the alkyl
chains replaced by methyl groups for simplicity. The optimized
geometries and electron density distributions of the polymers
were calculated with the B3LYP function and 6-31G* basis
transport to the anode. The device structures of regular and
inverted polymer solar cells are shown in Figure 1, parts a and
b, and Figure 3b illustrates the energy level diagrams for each
component, respectively. All data were obtained under white
light AM1.5G illumination from a calibrated solar simulator
(
Figure 6 and Figure S1 in the Supporting Information). As
shown in Figure 6, the HOMO isosurfaces of the both
PTDTBT) and (PTDTBT-SS) are well spread over the
2
with irradiation intensity of 100 mW/cm . The active layers
(
through a very broad altering range from 1:1 to 1:4 (w/w) of
n
n
whole conjugated backbones, whereas the LUMOs are mainly
localized on BT units, respectively, which verifies the p-type
behaviors obtained from the OFET study. In addition, the
calculated bandgaps for (PTDTBT)2 (1.80 eV) and
polymer:PC BM in either chlorobenzene (CB) or o-
dichlorobenzene (ODCB) were evaluated. The optimized
7
1
weight ratios of polymer to PC BM for PPTDTBT and
71
PPTDTBT-SS are 1:2 and 1:1.5, respectively. Device current
density/voltage (J − V) characteristics are shown in Figure 7
and the parameters listed in Table 2.
(
PTDTBT-SS) (1.99 eV) are in considerable coincidence
2
with the electrochemical analyses above. It is found that the
phenothiazine and phenothiazine-S,S-dioxide rings are folded
along the S···N vector, having the aspect angles of 21° and 15°,
respectively, in qualitative agreement with their single crystal X-
PCEs up to 1.69% is observed for the conventional
PPTDTBT:PC BM solar cells with a V of 0.77 V, a short
7
1
OC
−2
circuit current density (J ) of 5.75 mA cm , and a fill factor
SC
28
ray diffraction studies. We note a relatively larger dihedral
angle between PT and DTBT-SS units (θ = 160°) in the
optimized geometry, when compared to that between PT and
DTBT (θ = 153°). So it can be seen from the data that the
coplanarity of PPTDTBT-SS is better than that in PPTDTBT.
This implies that the backbone of PPTDTBT-SS brings about
larger effective π−π interactions in the solid state, which
matches qualitatively well with the XRD data. Furthermore, this
can explain satisfactorily our interpretation of the better
PPTDTBT-SS OFET results above.
(FF) of 38%. Under the same white light illumination, the
PPTDTBT-SS:PC BM-based regular cell exhibits a J of 4.03
7
1
SC
−2
mA cm , a V of 0.81 V, and a FF of 30%. It yields a
OC
substantially lower PCE of 0.97% because of its decreased
photocurrent, when compared to that of PPTDTBT:PC BM.
7
1
This can be mainly attributed to PPTDTBT-SS’s intrinsic
absorption limit in the visible region due to the relatively large
energy bandgap. It is worthy to mention that as expected from
the oxidation potential, the VOC for the cell with PPTDTBT-SS
is higher than that of PPTDTBT.
1
851
dx.doi.org/10.1021/ma202661b | Macromolecules 2012, 45, 1847−1857

Macromolecules
Article
Figure 5. (a) Chemical structures of the polymers and schematic representation of OFETs structure (L = 50 μm, W = 1.5 mm). (b) Transfer curves
in saturated regime with PPTDTBT (black line) and PPTDTBT-SS (red line). The output characteristics of PPTDTBT (c) and PPTDTBT-SS
(
d), respectively.
Figure 6. DFT-optimized geometries and charge-density isosurfaces for the HOMO and LUMO levels of (a) (PTDTBT) and (b) (PTDTBT-SS)
2
2
model systems (top) and optimized structures of phenothiazine and phenothiazine-S,S-dioxide rings and their top views, respectively (bottom).
2
Despite the aforementioned advantages of the inverted cells,
the majority studies on the inverted cells were based on P3HT
illumination (AM1.5 G, 100 mW/cm ) are shown in Figure 7.
The corresponding PCE is 1.47 and 1.22% for
PPTDTBT:PC BM and PPTDTBT-SS:PC BM, respectively
(Table 2). In the both inverted devices, despite the fact that the
absorption spectra of the active layer films in the two device
types are identical, a decrease in the JSC (4.80 mA cm for
PPTDTBT:PC BM and 4.11 mA cm for PPTDTBT-
SS:PC BM, respectively) is clearly observed, resulting the
3
2,34
as active materials,
had been tested in such configuration.
while only few new conjugated polymers
71
71
1
5,35,36
Therefore,
comparison of the photovoltaic properties of new materials in
both conventional and inverted cells is very important to fully
evaluate the performance of new polymers. The J−V curves for
the inverted polymer solar cells obtained under white light
−2
−
2
71
71
1
852
dx.doi.org/10.1021/ma202661b | Macromolecules 2012, 45, 1847−1857

Macromolecules
Article
efficiency (IPCE) of the devices. Figure 8 shows the IPCE
curves of both the conventional and inverted PSCs fabricated
under the optimized conditions as those used for the J−V
Figure 8. Incident photon-to-current efficiency (IPCE) spectra of the
polymer:PC BM solar cells.
71
measurements. All devices show a broad photoresponse
spreading from 300 to 700 nm, with maximum around 570
nm. However, the IPCE of the device is within 40% for almost
the whole absorption range. From this observation, we believe
that the IPCE of the devices can be improved by increasing the
thickness of the active layer without hampering charge
separation and transport properties. However, because of
their more or less limited solubility for the fabrication of
practical PSCs, it is difficult to obtain high thickness for the
active layer by using high concentration of the polymer blends.
Currently, the preparation of dithienylbenzothiadiazole with
two flexible alkoxyl chains in an effort to improve solubility is
ongoing. Obviously, the IPCE value for the conventional
Figure 7. J − V characteristics of the PSCs based on PPTDTBT (a)
2
and PPTDTBT-SS (b) under illumination of AM1.5G, 100 mW/cm .
low overall performances. One possible explanation for this
phenomenon is that, in the inverted cell, a small fraction of the
incident light is observed by the evaporated Au top electrode. It
is roughly estimated that 30% of the incident light with
wavelength <650 nm is not absorbed by the active layer on the
first pass, so clearly the reflectivity of the top electrode plays a
non-negligible role in the total number of photons absorbed by
the blend. Thus, it is plausible that the enhanced reflectivity of
the Al electrodes used in the normal cell causes the
PPTDTBT:PC BM is the highest, which agrees with the
71
highest JSC value of the devices. To evaluate the accuracy of the
photovoltaic results, the JSC values were calculated by
integrating the IPCE data with the AM 1.5G reference
spectrum. The JSC values obtained using integration and J-V
measurements are rather close (within 7% error), which
indicates that the photovoltaic results are reliable.
37
photocurrent to be slightly higher.
Surprisingly, in contrast, the inverted cell of PPTDTBT-
SS:PC BM exhibits a slight improved J and a much higher
71
SC
VOC value (0.92 eV) than that of the conventional configuration
with PPTDTBT:PC BM, which suggests that the recombina-
7
1
Morphology. The nanoscale morphologies of both the
tion behavior and morphology are different for the two
architectures. A likely rationale for this positive effect may be
attributed to a combination of the following factors: The
conventional and inverted polymer/PC BM films were studied
71
using tapping-mode atomic force microscopy (AFM). Surface
topography (left) and phase images (right) were taken for each
film and are shown in Figure 9. Both the regular and inverted
PPTDTBT:PC71BM blends are very similar and exhibit a rather
uniform smooth film formation which suggests the absence of
large features that might reduce the interface between polymer
hydrophilicity of SO groups would facilitate intimate contact
2
on both the electrodes and thus facilitate efficient charge
transfer between the active layer and the electrodes. In addition,
we cannot rule out that the dipole moment induced by the
polar SO units in PPTDTBT-SS could be the origin of the
2
3
8,39
improvement in the device performance since a higher VOC can
and fullerene potentially limiting device performance.
In
32
indicate a larger electrostatic field across the device structure,
contrast, PPTDTBT-SS:PC71BM blends in both conventional
and inverted structures (Figure 9, c and d) give very
inhomogeneous features in which voids with a diameter of
∼300 nm are present. This indicates poor miscibility between
PPTDTBT-SS and PC BM. This implies that the presence of
although other explanations are still possible. Further
investigation of these films using electrostatic force and surface
potential microscopy in underway.
The accuracy of the photovoltaic measurements can be
confirmed by the incident photon-to-electron conversion
71
SO groups makes PPTDTBT-SS strongly hydrophilic, which
2
Table 2. Photovoltaic Performance of Blends of the Polymers with Fullerenes
a
JSC (mA cm−2
device structure
conventional
composite
d (nm)
)
VOC (V)
FF
PCE (%)
PPTDTBT:PC BM (1:2)
50
50
28
32
5.75
4.03
4.80
4.11
0.77
0.81
0.78
0.92
0.38
0.30
0.39
0.32
1.69
0.97
1.47
1.22
7
1
PPTDTBT-SS:PC BM (1:1.5)
7
1
inverted
PPTDTBT:PC BM (1:2)
71
PPTDTBT-SS:PC BM (1:1.5)
7
1
a
Thickness of the active layer.
1
853
dx.doi.org/10.1021/ma202661b | Macromolecules 2012, 45, 1847−1857

Macromolecules
Article
Figure 9. Tapping-mode AFM images (5 μm × 5 μm) of PPTDTBT:PC BM (conventional (a); inverted (b)) and PPTDTBT-SS:PC BM
71
71
(
conventional (c); inverted (d)) films used in making the devices (under optimized device conditions). The topography of each film is shown in the
left panels, and the corresponding phase images in the right panels.
is, in large part, responsible for the relatively low PCEs in the
conventional cells, but this can positively affect the inverted
PSCs adopting transporting metal oxides between the ITO/
BHJ and BHJ/metal interfaces because of the potential
interaction with oxides. This observation is in good agreement
with the J-V characteristics tested in this study.
On the other hand, despite the fact that relatively low-lying
HOMO of PPTDTBT-SS enhances the VOC, the current
density in the PPTDTBT-SS:PC BM-based regular cell is low
71
and limits the PCE to 0.97%. This is likely a consequence of a
reduced solar absorption of PPTDTBT-SS’s caused by the
relatively large energy bandgap. Delightfully, when it comes to
incorporating PPTDTBT-SS into the inverted configuration
cell with TiO and MoO as electron-selective and hole-
CONCLUSIONS
x
3
■
selective layers, respectively, the estimated PCE of 1.22% is
achieved from the combination with the improved VOC and JSC.
Current work on π-conjugated polymer structural modification
has been aimed at understanding the influence of polymer
polarity in inverted solar cells. Our results indicate that the
introduction of S,S-dioxide units into the polymer backbone is a
useful strategy for the design of high performance inverted solar
cells.
Considering low cost PSCs into account, an easily accessible
donor, phenothiazine, which is stronger than commonly used
2
,7-carbazole donors due to an additional sulfur atom, has been
copolymerized with electron-deficient benzothiadiazole build-
ing block to yield new conjugated polymer PPTDTBT. By
virtue of the enhanced strength of ICT, the “strong donor−
acceptor” polymer (PPTDTBT) shows more bathocromically
shifted absorption spectrum (λ = 582 nm) and lower band
max
elec
gap (Eg = 1.78 eV) in comparison with its analogous polymer
EXPERIMENTAL SECTION
(PCDTBT) that in particular has been subject to increasing
■
interest in the polymer research community. Through the
sulfur oxidation in the phenothiazine unit, the corresponding
oxidized form polymer PPTDTBT-SS is also prepared and
characterized in parallel following our design motif. The strong
Materials and Instruments. All starting materials were purchased
either from Aldrich or Acros and used without further purification.
THF was distilled over sodium/benzophenone. H NMR and
1
13
C
NMR spectra were recorded on a Varian VNRS 600 MHz (Varian
USA) spectrophotometer using CDCl as solvent and tetramethylsi-
3
polarity of SO groups would enhance the compatibility and
2
lane (TMS) as the internal standard and MALDI MS spectra were
obtained from Ultraflex III (Bruker, Germany). UV−vis-NIR spectra
were taken on Cary 5000 (Varian USA) spectrometer. Number-
average (M ) and weight-average (M ) molecular weights, and
low contact resistance in the inverted BHJ solar cells integrated
two metal oxides. Both the PPTDTBT and PPTDTBT-SS
show moderate mobilities as p-type polymer semiconductors in
OFETs. Interestingly, the carrier mobility of PPTDTBT-SS is
about 1 order of magnitude higher than that of PPTDTBT,
which is presumably ascribed to the closer packing driven either
from the dipolar intermolecular interactions associated with the
presence of the sulfonyl groups or the relatively enhanced
coplanarity of PPTDTBT-SS, supported by the DFT
calculations as well as XRD results. The performance of the
PSCs containing the polymer PPTDTBT reaches PCEs of
n
w
polydispersity index (PDI) of the polymer products were determined
by gel permeation chromatography (GPC) with Agilent 1200 HPLC
Chemstation using a series of mono disperse polystyrene as standards
in THF (HPLC grade) at 308 K. Cyclic voltammetry (CV)
measurements were performed on AMETEK VersaSTAT 3 with a
three-electrode cell in a nitrogen bubbled 0.1 M tetra-n-butylammo-
nium hexafluorophosphate (n-Bu NPF ) solution in acetonitrile at a
4
6
+
scan rate of 50 mV/s at room temperature. A used as the Ag/Ag (0.1
M of AgNO in acetonitrile) reference electrode, platinum counter
3
1.69% and 1.47% for conventional and inverted structure
electrode and polymer-coated platinum working electrode, respec-
+
devices when using PC BM as electron acceptor, respectively.
tively. The Ag/Ag reference electrode was calibrated using a
7
1
1
854
dx.doi.org/10.1021/ma202661b | Macromolecules 2012, 45, 1847−1857

Macromolecules
Article
and removed under reduced pressure. The crude product was purified
by column chromatography (silica gel, hexane) to afford 13.6 g (82%)
1
of 4 as a colorless oil. H NMR (600 MHz, CDCl ): δ (ppm) 7.14 (m,
3
onset
onset
4H), 6.92−6.86 (m, 4H), 3.73 (d, 2H, J = 6.6 Hz), 2.00 (m, 1H),
13
1.41−1.26 (m, 40H), 0.91−0.88 (t, 6H, J = 7.2 Hz). C NMR (150
MHz, CDCl ): δ (ppm) 145.94, 127.66, 127.17, 126.03, 122.43,
3
116.05, 51.65, 36.25, 34.60, 32.10, 31.81, 30.11, 29.94, 29.86, 29.83,
29.81, 29.80, 29.77, 29.74, 29.73, 29.63, 29.62, 29.53, 29.51, 28.00,
26.40, 22.86, 14.29, 14.27. Anal. Calcd: C, 80.68; H, 10.72; N, 2.61; S,
5.98. Found: C: 80.91, H: 10.82, N: 2.74, S: 5.71. MALDI−TOF−MS
+
•
m/z: [M] = 535.34; calcd, 535.91.
Synthesis of 3,7-Dibromo-N-2-decyltetradecylphenothia-
zine (5). N-Bromosuccinimide (3.65 g, 20.53 mmol) was slowly
added to a solution of 4 (5.0 g, 9.33 mmol) in anhydrous DMF (50
mL). The reaction mixture was stirred at room temperature overnight,
which was quenched by water and extracted with diethyl ether. The
separated organic layer was washed with water and brine, then dried
thermal evaporation using a shadow mask. The thickness of source and
drain electrodes was 50 nm. Channel length (L) and channel width
over MgSO . The solvent was removed under reduced pressure. The
4
crude product was purified by column chromatography(silica gel,
1
(
W) was 50 μm and 1.5 mm, respectively. Electrical characterization
was performed using a Keithley semiconductor parametric analyzer
Keithley 4200) under N atmosphere. The electron mobility (μ) was
hexane) to afford 6.0 g (93%) of 5 as a yellow oil. H NMR (600
MHz, CDCl ): δ (ppm) 7.25 (m, 4H), 6.69 (d, 2H, J = 1.8 Hz), 3.64
3
(
(d, 2H, J = 7.2 Hz), 1.89 (m, 1H), 1.36−1.22 (m, 40H), 0.89 (t, 6H, J
2
= 7.2 Hz). 13C NMR (150 MHz, CDCl ): δ (ppm) 144.75, 130.20,
determined using the following equation in the saturation regime
3
1
29.99, 127.49, 117.30, 114.91, 51.88, 34.60, 32.09, 32.08, 31.66,
30.06, 29.85, 29.82, 29.77, 29.75, 29.59, 29.52, 29.50, 26.33, 22.85,
4.28. Anal. Calcd: C, 62.33; H, 7.99; Br, 23.04; N, 2.02; S, 4.62.
I
= (WC /2L) × μ × (V − VT)2
ds
i
gs
1
Found: C: 63.34, H: 8.11, N: 2.17, S: 4.53. MALDI−TOF−MS m/z:
where C is the capacitance per unit area of the SiO dielectric (C = 15
i
2
i
+
•
2
[M] = 693.17; calcd, 693.7.
nF/cm ) and V is the threshold voltage.
T
Synthesis of N-2-Decyltetradecyl-3,7-bis(4,4,5,5-tetrameth-
yl-1,3,2-dioxaborolanyl)phenothiazine (6). A portion of 4.43 mL
of n-butyllithium (1.6 M in hexane, 7.08 mmol) was added dropwise to
a solution of 5 (2.0 g, 2.83 mmol) in anhydrous THF (40 mL) under
argon atmosphere at −78 °C. After 30 min, 2-isopropoxy-4,4,5,5-
tetramethyl-1,3,2-dioxaborolane (1.32 mL, 7.08 mmol) was injected to
the reaction mixture. The resulting mixture was warmed up to room
temperature and stirred overnight. Then, the reaction was quenched
by water and extracted with a diethyl ether. The separated organic
Fabrication of Conventional and Inverted Photovoltaic
Cells. Two-type photovoltaic cells were fabricated on ITO-coated
glass substrates. The ITO-coated glass substrates were first cleaned
with detergent, ultrasonicated in water, acetone and isopropyl alcohol,
and dried overnight in an oven. In conventional cells, PEDOT:PSS(Al
4083) was spin-cast on cleaned ITO substrates after a UV-ozone
treatment for 15 min and heated at 140 °C for 10 min in air.
Subsequently, the active layer was coated in a glovebox. The solution
containing a mixture of PPTDTBT:PC BM (1:2) in a solvent
71
(
chlorobenzene) with a concentration of 11 mg/mL and PPTBTDT-
layer was washed with water and brine, then dried over MgSO and
4
SS:PC BM (1:1.5) in a solvent (dichlorobenzene) with a concen-
removed under reduced pressure. The crude product was purified by
column chromatography (silica gel, 10% ethyl acetate in hexane) to
71
tration of 13 g/mL was spin-cast on top of PEDOT:PSS film. After
then, the top electrode (Al) was deposited on the active layer in a
1
afford 1.3 g (58%) as a yellow-green sticky solid. H NMR (600 MHz,
−6
vacuum (<10 Torr) thermal evaporator. Inverted solar cells were
CDCl
3.74 (d, 2H, J = 6.6 Hz), 1.94 (m, 1H), 1.37−1.2 (m, 64H), 0.89 (t,
6H, J = 6.6 Hz). 13C NMR (150 MHz, CDCl
): δ (ppm) 148.07,
3
): δ (ppm) 7.56 (d, 4H, J = 7.8 Hz), 6.83 (d, 2H, J = 7.8 Hz),
fabricated on ITO-coated glass substrates. A TiO precursor solution
x
was prepared using the sol−gel method. The TiO precursor solution
3
x
was spin-cast on cleaned ITO substrates after a UV-ozone treatment
for 15 min and heated at 80 °C for 10 min in air for conversion to
TiO by hydrolysis. Subsequently, the TiO -coated substrates were
134.07, 133.98, 125.27, 115.46, 83.80, 34.79, 32.09, 32.07, 31.78,
30.11, 29.81, 29.75, 29.62, 29.51, 29.48, 26.43, 24.99, 22.48. Anal.
Calcd: C, 73.18; H, 10.11; B, 2.74; N, 1.78; O, 8.12; S, 4.07; Found: C:
73.44, H: 10.01, N: 1.94, S: 3.86, O: 7.82. MALDI−TOF−MS m/z:
x
x
transferred into a glovebox. A solution containing a mixture of
+
•
PPTDTBT:PC BM (1:2) in a solvent (chlorobenzene) with a
[M] = 787.53; calcd, 787.83.
71
concentration of 11 mg/mL was spin-cast on top of TiO films at 1500
Synthesis of 3,7-Dibromo-N-2-decyltetradecylphenothia-
zine-S,S-dioxide (7). Hydroperoxide (35%, 10 mL) was added
dropwise to a solution of 5 (2 g, 2.9 mmol) in acetic acid (30 mL) was
stirred at 90 °C overnight. After cooled down, the water was added
and extracted with ethyl acetate. The separated organic layer was and
x
rpm 60 s and PPTBTDT-SS:PC BM (1:1.5) in a solvent
7
1
(
dichlorobenzene) with a concentration of 13 g/mL was spin-cast
on top of TiO films at 600 rpm 60 s. Then, a thin layer of MoO film
x
3
(
≈5 nm) was evaporated on top of the active layer. Finally, the anode
−6
(
Au, ≈95 nm) was deposited on the active layer in a vacuum (<10
washed with water and brine, then dried over MgSO and removed
4
Torr) thermal evaporator. The cross-sectional area of each of the
under reduced pressure. The crude product was purified by column
2
electrode defines the active area of the device as 13.5 mm .
chromatography (silica gel, 10% ethyl acetate in hexane) to afford 1.1 g
1
Photovoltaic cell measurements were carried out inside the glovebox
using a high quality optical fiber to guide the light from the solar
simulator equipped with a Keithley 2635A source measurement unit.
The J−V curves for the devices were measured under AM 1.5G
(52%) of 7 as a colorless solid. H NMR (600 MHz, CDCl ): δ (ppm)
3
8.17 (d, 2H, J = 2.4 Hz), 7.67 (d, 2H, J = 7.2 Hz), 7.24 (s, 2H), 4.04
(d, 2H, J = 6.6 Hz), 1.94 (m, 1H), 1.29−1.20 (m, 40H), 0.89 (t, 6H, J
= 7.2 Hz). 13C NMR (150 MHz, CDCl ): δ (ppm) 140.83, 135.92,
3
−2
illumination at 100 mW cm . The IPCE spectra for the PSCs were
measured on an IPCE measuring system.
126.99, 126.41, 119.03, 114.72, 32.06, 30.90, 29.95, 29.84, 29.80,
29.74, 29.71, 29.62, 29.51, 29.49, 26.22, 22.84, 14.27. Elemental
Analysis: C, 59.58; H, 7.64; Br, 22.02; N, 1.93; O, 4.41; S, 4.42;
Found: C: 59.84, H: 7.70, N: 2.01, S: 4.21, O: 4.22. MALDI-TOF-MS
Synthesis of N-2-Decyltetradecylphenothiazine (4). To a
mixture of phenothiazine (6.2 g, 31.1 mmol) and sodium hydride
+
•
(
60% in mineral oil, 1.0 g, 41.7 mmol) in anhydrous DMF (40 mL), 2-
m/z: [M] = 727.23; calcd, 725.7.
decyltetradecyl bromide (16.8 g, 40.2 mmol) was slowly added at
room temperature under argon. The mixture was stirred at room
temperature overnight, which was poured into water and extracted
with diethyl ether. The separated organic layer was dried over MgSO4
Synthesis of N-2-decyltetradecyl-3,7-bis(4,4,5,5-tetrameth-
yl-1,3,2-dioxaborolanyl)phenothiazine-S,S-dioxide (8). Com-
pound 7 (0.7 g, 0.96 mmol), bis(pinacolato)diboron (0.97 g, 3.84
mmol), potassium acetate (0.66 g, 6.72 mmol), and Pd Cl (dppf) (42
2
1
855
dx.doi.org/10.1021/ma202661b | Macromolecules 2012, 45, 1847−1857

Macromolecules
Article
mg, 57.6 μmol) in anhydrous DMF (20 mL) were stirred at 120 °C
overnight. The reaction was quenched by water and extracted with
ethyl acetate. The separated organic layer was washed with water and
ACKNOWLEDGMENTS
■
This work was supported by Basic Science Research Program
through the National Research Foundation of Korea (NRF)
funded by the Ministry of Education, Science and Technology
2010-0002494) and the National Research Foundation of
Korea Grant funded by the Korean Government (MEST)
brine, then dried over MgSO and removed under reduced pressure.
4
The crude product was purified by column chromatography (silica gel,
3
0% ethyl acetate in hexane) to afford 0.5 g (64%) of 8 as light-yellow
(
1
solid. H NMR (600 MHz, CDCl ): δ (ppm) 8.58 (s, 2H), 7.97 (d,
3
2
H, J = 8.4 Hz), 7.33 (d, 2H, J = 8.4 Hz), 4.13 (d, 2H, J = 7.2 Hz),
(
(
2010-0019408), (2010-0026163), (2010-0026916), and
NRF-2009-C1AAA001-0093020).
13
1
.98 (m, 1H), 1.35−1.19 (m, 64H), 0.88 (t, 6H, J = 7.2 Hz). C NMR
(
150 MHz, CDCl ): δ (ppm) 143.64, 138.72, 131.02, 125.88, 116.21,
3
8
2
1
4.28, 32.08, 31.05, 29.99, 29.80, 29.71, 29.67, 29.51, 29.47, 25.18,
5.02, 22.84, 14.28. Anal. Calcd: C: 70.32, H: 9.71, B: 2.64, N: 1.71, O:
1.71, S: 3.91. Found: C: 70.52, H: 9.68, N: 1.88, S: 3.61, O: 11.62.
REFERENCES
■
+
•
(1) Cheng, Y. J.; Yang, S. H.; Hsu, C. S. Chem. Rev. 2009, 109, 5868.
2) Gunes, S.; Neugebauer, H.; Sariciftci, N. S. Chem. Rev. 2007, 107,
324.
3) Yu, G.; Gao, J.; Hummelen, J. C.; Wudl, F.; Heeger, A. J. Science
995, 270, 1789.
4) Kim, G.; Yun, M. H.; Anant, P.; Cho, S.; Jacob, J.; Kim, J. Y.;
Yang, C. Chem.Eur. J. 2011, 17, 14681.
5) Cheedarala, R. K.; Kim, G. H.; Cho, S.; Lee, J.; Kim, J.; Song, H.
K.; Kim, J. Y.; Yang, C. J. Mater. Chem. 2011, 21, 843.
(6) Wang, E. G.; Ma, Z. F.; Zhang, Z.; Vandewal, K.; Henriksson, P.;
Inganas, O.; Zhang, F. L.; Andersson, M. R. J. Am. Chem. Soc. 2011,
133, 14244.
MALDI−TOF−MS m/z: [M] = 819.53; calcd, 819.83.
(
Poly(N-(2-decyltetradecyl)-3,7-phenothiazine-alt-5,5-(4′,7′-
di-2-thienyl-2′,1′,3′-benzothiadiazole)) (PPTDTBT). In a Schlenk
flask, monomer 6 (0.21 g, 0.266 mmol) and 4,7-bis(5-bromothio-
phenyl)-2,1,3-benzothiadiazole (0.12 g, 0.266 mmol) was dissolved in
toluene (7 mL), to this a solution of K PO (286 mg, 1.34 mmol), trio-
1
(
1
(
3
4
tolylphosphine (10 mg, 0.03 mmol) and deionized water (1.5 mL) was
added. The mixture was vigorously stirred at room temperature under
argon. After 30 min, Pd (dba) (10 mg, 0.011 mmol)was added to the
reaction mixture and stirred at 90 °C for 3 days (end-capped with
phenylboronic acid and bromobenzene). Finally, the solution was
precipitated in a mixture of methanol and ammonia (4:1 v/v, 250 mL).
This was filtered off through 0.45 μm nylon filter, washed on Soxhlet
apparatus with methanol (1 d) and acetone (1 d). Then, 160 mg
(
2
3
(7) Price, S. C.; Stuart, A. C.; Yang, L. Q.; Zhou, H. X.; You, W. J.
Am. Chem. Soc. 2011, 133, 4625.
(
1
72%) of the polymer was recovered as a violet-powder (M = 9.8 ×
(8) Huo, L. J.; Zhang, S. Q.; Guo, X.; Xu, F.; Li, Y. F.; Hou, J. H.
Angew. Chem., Int. Ed. 2011, 50, 9697.
(9) Piliego, C.; Holcombe, T. W.; Douglas, J. D.; Woo, C. H.;
Beaujuge, P. M.; Frechet, J. M. J. J. Am. Chem. Soc. 2010, 132, 7595.
́
(10) Chen, H. Y.; Hou, J. H.; Zhang, S. Q.; Liang, Y. Y.; Yang, G. W.;
n
3
1
0 g/mol, PDI = 1.27). H NMR (600 MHz, CDCl ): δ (ppm) 8.11
3
(
br, 2H), 7.88 (br, 2H), 7.50 (br, 2H), 7.32 (br, 4H) 6.91 (br, 2H),
3
0
.79 (br, 2H), 2.04 (br, 1H), 1.8 (br, 6H), 1.42−1.24 (br, 40H), 0.87−
.84 (br, 6H).
Poly(N-(2-decyltetradecyl)-3,7-phenothiazine-S,S-dioxide-
Yang, Y.; Yu, L. P.; Wu, Y.; Li, G. Nat. Photonics 2009, 3, 649.
alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole))
(11) Zhao, G. J.; He, Y. J.; Li, Y. F. Adv. Mater. 2010, 22, 4355.
(PPTDTBT-SS). In a Schlenk flask, monomer 8 (0.214 g, 0.266 mmol)
(12) Cheng, Y. J.; Hsieh, C. H.; He, Y. J.; Hsu, C. S.; Li, Y. F. J. Am.
and 4,7-bis(5-bromothiophenyl)-2,1,3-benzothiadiazole (0.12 g, 0.266
mmol) was dissolved in toluene (7 mL), to this a solution of K PO4
Chem. Soc. 2010, 132, 17381.
13) He, Z.; Zhong, C.; Huang, X.; Wong, W.-Y.; Wu, H.; Chen, L.;
Su, S.; Car, Y. Adv. Mater. 2011, 23, 4636.
14) Jørgensen, M.; Norrman, K.; Krebs, F. C. Sol. Energy Mater. Sol.
Cells. 2008, 92, 686.
15) Sun, Y. M.; Seo, J. H.; Takacs, C. J.; Seifter, J.; Heeger, A. J. Adv.
Mater. 2011, 23, 1679.
16) Hau, S. K.; Yip, H.-L.; Leong, K.; Jen, A. K.-Y. Org. Electron.
009, 10, 719.
17) Park, S. H.; Roy, A.; Beaupre, S.; Cho, S.; Coates, N.; Moon, J.
3
(
(286 mg, 1.34 mmol), trio-tolylphosphine (10 mg, 0.03 mmol) and
deionized water (1.5 mL) was added. The mixture was vigorously
stirred at room temperature under argon. After 30 min, Pd (dba) (10
(
2
3
mg, 0.011 mmol) was added to the reaction mixture and stirred at 90
C for 3 days (end-capped with phenylboronic acid and
(
°
bromobenzene). Finally, the solution was precipitated in a mixture
of methanol and ammonia (4:1 v/v, 250 mL). This was filtered off
through 0.45 μm nylon filter, washed on Soxhlet apparatus with
(
2
(
methanol (1 d) and acetone (1 d). Then 0.14 g (61%) of the polymer
was recovered as a deep-red powder (M = 7.6 × 10 g/mol, PDI =
1
2
1
3
S.; Moses, D.; Leclerc, M.; Lee, K.; Heeger, A. J. Nat. Photonics 2009,
3, 297.
n
1
.21). H NMR (600 MHz, CDCl ): δ (ppm) 8.42 (br, 2H), 8.15 (br,
3
(18) Blouin, N.; Michaud, A.; Gendron, D.; Wakim, S.; Blair, E.;
H), 7.93 (br, 4H), 7.50−7.40 (br, 4H) 4.16 (br, 2H), 2.07 (br, 1H),
.27−1.23 (br, 40H), 0.90−0.85 (br, 6H).
Neagu-Plesu, R.; Belletete, M.; Durocher, G.; Tao, Y.; Leclerc, M. J.
Am. Chem. Soc. 2008, 130, 732.
(
19) Svensson, M.; Zhang, F. L.; Veenstra, S. C.; Verhees, W. J. H.;
Hummelen, J. C.; Kroon, J. M.; Inganas, O.; Andersson, M. R. Adv.
Mater. 2003, 15, 988.
20) Cho, S.; Seo, J. H.; Park, S. H.; Beaupre, S.; Leclerc, M.; Heeger,
A. J. Adv. Mater. 2010, 22, 1253.
21) Cadogan, J. I. G.; Cameron-Wood, M.; Mackie, R. K.; Searle, R.
J. G. J. Chem. Soc. 1965, 4831.
22) Padhy, H.; Huang, J. H.; Sahu, D.; Patra, D.; Kekuda, D.; Chu,
ASSOCIATED CONTENT
■
̈
* Supporting Information
S
(
DFT-optimized geometries and charge-density isosurfaces for
the HOMO and LUMO levels of (a) (PTDTBT) and (b)
1
(
1
(
PTDTBT-SS)1 model, H NMR spectra of polymers,
polymers:PCBM blend transistors, solar cell performance of
polymer:PC BM, and GPC data. This material is available free
of charge via the Internet at http://pubs.acs.org.
(
61
C. W.; Lin, H. C. J. Polym. Sci., Part A: Polym. Chem. 2010, 48, 4823.
(23) Sang, G. Y.; Zou, Y. P.; Li, Y. F. J. Phys. Chem. C 2008, 112,
1
(
2058.
24) Liu, Y.; Cao, H.; Li, J.; Chen, Z.; Cao, S.; Xiao, L.; Xu, S.; Gong,
AUTHOR INFORMATION
■
*
+
Q. J. Polym. Sci., Part A: Polym. Chem. 2007, 45, 4867.
(25) Cho, N. S.; Park, J. H.; Lee, S. K.; Lee, J.; Shim, H. K.; Park, M.
J.; Hwang, D. H.; Jung, B. J. Macromolecules 2006, 39, 177.
Corresponding Author
E-mail: yang@unist.ac.kr. Telephone: +82-52-217-2920. Fax:
82-52-217-2909.
(
26) Kong, X. X.; Kulkarni, A. P.; Jenekhe, S. A. Macromolecules 2003,
6, 8992.
27) Liu, B.; Najari, A.; Pan, C. Y.; Leclerc, M.; Xiao, D. Q.; Zou, Y.
P. Macromol. Rapid Commun. 2010, 31, 391.
3
(
Notes
The authors declare no competing financial interest.
1
856
dx.doi.org/10.1021/ma202661b | Macromolecules 2012, 45, 1847−1857

Macromolecules
Article
(
28) Kamtekar, K. T.; Dahms, K.; Batsanov, A. S.; Jankus, V.;
Vaughan, H. L.; Monkman, A. P.; Bryce, M. R. J. Polym. Sci., Part A:
Polym. Chem. 2011, 49, 1129.
(
29) Scharber, M. C.; Wu
Waldauf, C.; Heeger, A. J.; Brabec, C. L. Adv. Mater. 2006, 18, 789.
30) Brabec, C. J.; Cravino, A.; Meissner, D.; Sariciftci, N. S.;
̈
hlbacher, D.; Koppe, M.; Denk, P.;
(
Fromherz, T.; Rispens, M. T.; Sanchez, L.; Hummelen, J. C. Adv.
Funct. Mater. 2001, 11, 374.
(
31) Kang, S.-M.; Leblebici, Y. CMOS Digital Integrated Circuits:
Analysis and Design; McGraw-Hill: New York, 1996.
32) Chen, L. M.; Hong, Z. R.; Li, G.; Yang, Y. Adv. Mater. 2009, 21,
434.
33) Sun, Y. M.; Takacs, C. J.; Cowan, S. R.; Seo, J. H.; Gong, X.;
Roy, A.; Heeger, A. J. Adv. Mater. 2011, 23, 2226.
34) Ma, H.; Yip, H.-L.; Huang, F.; Jen, A. K.-Y. Adv. Funct. Mater.
010, 20, 1371.
35) Zhang, Y.; Hau, S. K.; Yip, H.-L.; Sun, Y.; Acton, O.; Jen, A. K.-
Y. Chem. Mater. 2010, 22, 2696.
36) Hsieh, C.-H.; Cheng, Y.-J.; Li, P.-J.; Chen, C.-H.; Dubosc, M.;
Liang, R.-M.; Hsu, C.-S. J. Am. Chem. Soc. 2010, 132, 4887.
37) Waldauf, C.; Morana, M.; Denk, P.; Schilinsky, P.; Coakley, K.;
Choulis, S. A.; Brabec, C. J. Appl. Phys. Lett. 2006, 89, 233517.
38) van Duren, J. K. J.; Yang, X. N.; Loos, J.; Bulle-Lieuwma, C. W.
T.; Sieval, A. B.; Hummelen, J. C.; Janssen, R. A. J. Adv. Funct. Mater.
004, 14, 425.
39) Wienk, M. M.; Kroon, J. M.; Verhees, W. J. H.; Knol, J.;
Hummelen, J. C.; van Hal, P. A.; Janssen, R. A. J. Angew. Chem., Int. Ed.
(
1
(
(
2
(
(
(
(
2
(
2
003, 42, 3371.
NOTE ADDED AFTER ASAP PUBLICATION
This article posted ASAP on February 3, 2012. Scheme 1 has
been revised. The correct version posted on February 7, 2012.
■
1
857
dx.doi.org/10.1021/ma202661b | Macromolecules 2012, 45, 1847−1857