A novel bis-lactam acceptor with outstanding molar extinction coefficient and structural planarity for donor-acceptor type conjugated polymer

Article abstract of DOI:10.1021/acs.macromol.6b01680

A novel electron-accepting bis-lactam building block, 3,7-dithiophen-2-yl-1,5-dialkyl-1,5-naphthyridine-2,6-dione (NTDT), and a conjugated polymer P(NTDT-BDT) comprising NTDT as an electron acceptor and benzo[1,2-b:4,5-b′]dithiophene (BDT) as an electron donor are designed and synthesized for producing efficient organic solar cells. The thermal, electronic, photophysical, electrochemical, and structural characteristics of NTDT and P(NTDT-BDT) are studied in detail and compared with those of the widely used bis-lactam acceptor 3,6-dithiophen-2-yl-2,5-dialkylpyrrolo[3,4-c]pyrrole-1,4-dione (DPPT) and its polymer P(DPPT-BDT). Compared to DPPT derivatives, NTDT and P(NTDT-BDT) exhibit remarkably higher absorption coefficients, deeper highest occupied molecular orbital energy levels, and more planar conformations. A bulk heterojunction solar cells based on P(NTDT-BDT) exhibit power conversion efficiency of up to 8.16% with high short circuit current (J_sc) of 18.51 mA cm^-2, one of the highest J_sc values yet obtained for BDT-based polymer. Thus, it is successfully demonstrated that the novel bis-lactam unit NTDT is a promising building block for use in organic photovoltaic devices.

Full text of DOI:10.1021/acs.macromol.6b01680

Article
pubs.acs.org/Macromolecules
A Novel Bis-Lactam Acceptor with Outstanding Molar Extinction
Coefficient and Structural Planarity for Donor−Acceptor Type
Conjugated Polymer
Won Sik Yoon, Dong Won Kim, Jun-Mo Park, Illhun Cho, Oh Kyu Kwon, Dong Ryeol Whang,
Jin Hong Kim, Jung-Hwa Park, and Soo Young Park*
Center for Supramolecular Optoelectronic Materials, Department of Materials Science and Engineering, Seoul National University, 1
Gwanak-ro, Gwanak-gu, Seoul, 151-744, Korea
S
* Supporting Information
ABSTRACT: A novel electron-accepting bis-lactam building
block, 3,7-dithiophen-2-yl-1,5-dialkyl-1,5-naphthyridine-2,6-
dione (NTDT), and a conjugated polymer P(NTDT-BDT)
comprising NTDT as an electron acceptor and benzo[1,2-
b:4,5-b′]dithiophene (BDT) as an electron donor are designed
and synthesized for producing efficient organic solar cells. The
thermal, electronic, photophysical, electrochemical, and struc-
tural characteristics of NTDT and P(NTDT-BDT) are studied
in detail and compared with those of the widely used bis-lactam
acceptor 3,6-dithiophen-2-yl-2,5-dialkylpyrrolo[3,4-c]pyrrole-
1,4-dione (DPPT) and its polymer P(DPPT-BDT). Compared
to DPPT derivatives, NTDT and P(NTDT-BDT) exhibit
remarkably higher absorption coefficients, deeper highest
occupied molecular orbital energy levels, and more planar conformations. A bulk heterojunction solar cells based on
P(NTDT-BDT) exhibit power conversion efficiency of up to 8.16% with high short circuit current (Jsc) of 18.51 mA cm−2, one of
the highest Jsc values yet obtained for BDT-based polymer. Thus, it is successfully demonstrated that the novel bis-lactam unit
NTDT is a promising building block for use in organic photovoltaic devices.
and A units, enhance the charge-carrier mobility owing to the
strong π-stacking interactions28 and (b) the light absorptivity of
these polymers scales with the oscillator strength of the
conjugated backbone, which, in turn, is modulated by the
transition dipole moments of the D and A units.29 To this end,
numerous studies have reported the synthesis as well as the
optoelectrical properties of conjugated polymers comprising
different D and A building blocks and also the characteristics of
devices based on these polymers.30−37 However, while many D
building blocks have been studied, only a few A building blocks
have been reported so far. These include benzothiadiazole,38−40
quinoxaline,41−43 thieno[3,4-c]pyrrole-4,6-dione,44,45 and lac-
tam moieties.46−51 Therefore, it is imperative that more A
building blocks should be developed through the proper design
strategy for high-performance D−A type conjugated polymers.
In this context, planar bis-lactam-based materials, such as
thiophenyl substituted diketopyrrolopyrrole (DPPT),52−54
isoindigo (IID),55,56 and isoDPPT57,58 (Figure 1) have
attracted much attention lately as desirable electron-accepting
building blocks because of their unique features, which include
1. INTRODUCTION
Over the past few decades, π-conjugated polymer semi-
conductors have drawn great attention for use in solution-
processed organic photovoltaic devices owing to their
applicability in flexible, large-area devices.1−5 Recently, bulk
heterojunction (BHJ) type polymer solar cells (PSCs) with a
power conversion efficiency (PCE) greater than 10% have been
reported.6−12 Although a PCE of this level for PSCs is quite
impressive, further improvements in the conversion efficiency
are necessary for these devices to find practical use. To this end,
great efforts are being devoted not only to optimizing the
device architecture13,14 but also to developing high-perform-
ance materials.15−17
Donor−acceptor (D−A) type conjugated polymers, involv-
ing intramolecular charge transfer via an alternative combina-
tion of D and A building blocks along the π-conjugated
backbone, are being investigated intensively for use in PSCs,
since these materials allow for the facile control of the
electronic characteristics based on the rational choice of the D
and A units.18−25 A large number of studies have revealed that
the photovoltaic properties of D−A conjugated polymers are
closely associated with the characteristics of both the D and the
A moieties in the polymer backbone:26,27 (a) the quasi-planar
conjugated backbones of these polymers, which contain the D
Received: August 3, 2016
Revised: October 24, 2016
© XXXX American Chemical Society
A
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which was first synthesized by Rapoport in 197160 and barely
used as monomer of conjugated polymer.61,62 While both
NTDT and DPPT are expected to be electron deficient, based
on the bis-lactam unit, their electronic and photophysical
properties are probably different, owing to the difference in the
ring sizes of their lactam units. Interestingly, density functional
theory (DFT) calculations and single-crystal analyses have
revealed that the optimized geometry of NTDT corresponds to
a coplanar conformation. It is worth noting that, through time-
dependent DFT (TD-DFT) calculations, we found that NTDT
has a higher oscillator strength (f value) than that of DPPT,
which is known to be a compound with a high molar
absorption coefficient. In addition, NTDT allows for alkylation
through the introduction of various solubilizing side groups at
the lactam N-position. This could allow for the realization of
simple solubility control without having to use any solubilizing
comonomers.
Figure 1. Molecular structures of widely used bis-lactam acceptors and
NTDT.
(a) a high electron affinity because of the electron-withdrawing
effect of the lactam units, (b) high degree of π−π stacking,
which is driven by their quasi-planar backbone structure, and
(c) the possibility of controlling their solubility by incorporat-
ing suitable alkyl and aryl side chains in the lactam N-atom
position.59
Inspired by such beneficial effects of bis-lactam compounds,
we attempted to develop a high-performance bis-lactam
compound of 3,7-dithiophen-2-yl-1,5-dialkyl-1,5-naphthyri-
dine-2,6-dione (NTDT) (Figure 1) in this work. NTDT is
structurally based on 1,5-dihydro-1,5-naphthyridine-2,6-dione,
Given these advantages of NTDT, we designed and
synthesized a new D−A type conjugated copolymer P-
(NTDT-BDT) with NTDT as a novel bis-lactam-based A
Scheme 1. Synthesis of P(NTDT-BDT) and P(DPPT-BDT)
B
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Table 1. Characteristics of NTDT, DPPT, P(NTDT-BDT), and P(DPPT-BDT)
c
d
e
g
h
i
λmax,sol
ε at λmax × 104
absorption coefficient at HOMO/LUMO HOMO/LUMO
Egopt
/film
a
a
b
f
Mn (kDa) PDI
Td (°C)
(nm)
(M−1cm−1
)
λmax × 104 (cm−1
)
(eV)
(eV)
(eV)
NTDT
−
−
60.7
−
−
3.15
350
316
358
343
497/533
549/601
651/667
748/754
5.10
3.14
−
−
−
31.7
−5.15/−2.56
−4.97/−2.52
−4.89/−2.86
−4.79/−2.93
−5.42/−3.13
−5.22/−3.26
−5.33/−3.67
2.29
1.96
1.66
1.32
DPPT
P(NTDT-BDT)
P(DPPT-BDT)
59.3
2.84
−
15.7
−5.23/−3.91
a
b
c
Determined by GPC using polystyrene standards in CHCl3. 5% weight-loss temperature measured by TGA under nitrogen flow. Measured in
d
e
CHCl3 solution (5 × 10−5 M). Thin film was spin-coated from CHCl3 solution onto a quartz substrate. Measured from solution absorption spectra
f
g
h
at λmax. Measured from solution absorption spectra at λmax
.
Determined from DFT calculations. HOMO: measured by cyclic voltammetry.
i
LUMO: HOMO + Egopt. Determined from the onset of UV−vis absorption spectra.
building block and the representative D unit of benzo[1,2-b:4,5-
b′]dithiophene (BDT) as the first example of an NTDT-
incorporating polymer semiconductor. P(DPPT-BDT)63−65
was also synthesized as a reference sample for P(NTDT-BDT),
since the DPPT unit has extensively been used as the most
efficient bis-lactam unit in the D−A type conjugated polymer.
Furthermore, the electronic, thermal, photophysical, electro-
chemical, structural, and photovoltaic properties of P(NTDT-
BDT) were studied in depth, in order to demonstrate the high
potential of NTDT for use in organic optoelectronics.
a small thiophene-core dihedral angle (<1°), which facilitated
charge-carrier transport via strong π−π stacking interactions.67
The calculated highest occupied molecular orbital (HOMO)/
lowest unoccupied molecular orbital (LUMO) values for the
two building blocks were found to be −5.15/-2.56 eV (for
NTDT) and −4.97/-2.52 eV (for DPPT) (Table 1).
Furthermore, to be able to predict the optimized geometries
of P(NTDT-BDT) and P(DPPT-BDT), we performed
calculations on double-repeat units ((NTDT-BDT)2 and
(DPPT-BDT)2) of the two polymers with methyl-substituted
alkyl chains (Figure S2, parts c and d, Supporting Information).
The computational results confirmed that they also had highly
planar geometries, with the NTDT-based molecules having
deeper HOMO levels than those of the DPPT-based
molecules.
2. RESULTS AND DISCUSSION
Synthesis and Characterization. The route for synthesiz-
ing the thienyl-substituted NTD monomer (NTDT) is
depicted in Scheme 1. 6-methoxy-1,5-naphthyridin-2(1H)-one
(2) was synthesized as reported.66 The subsequent O-
demethylation of 2 with hydrogen bromide yielded the 1,5-
dihydro-1,5-naphthyridine-2,6-dione compound 3, which was
then N-alkylated with 1-bromooctane in the presence of cesium
carbonate to obtain 1,5-dioctyl-1,5-naphthyridine-2,6-dione (4,
NTD). This compound was brominated with bromine to
obtain 3,7-dibromo-1,5-dioctyl-1,5-naphthyridine-2,6-dione
(5), which was then reacted with tributyl(thiophen-2-yl)-
stannane under typical Stille coupling reaction conditions; this
yielded the NTDT monomer 6. The copolymers containing the
NTDT and DPPT building blocks, namely, P(NTDT-BDT)
and P(DPPT-BDT), were prepared through Stille-coupling
polymerization using BDT as an electron-rich counterpart. The
number-average molecular weight (Mn) and polydispersity
index (PDI) values of P(NTDT-BDT) and P(DPPT-BDT)
were determined by gel permeation chromatography (GPC).
The results revealed that both polymers had a high molecular
weight (Mn = 60.7 kDa, PDI = 3.15 for P(NTDT-BDT) and
Mn = 59.3 kDa, PDI = 2.84 for P(DPPT-BDT)). Thermal
gravimetric analysis (TGA) measurements were performed to
investigate the thermal stabilities of the monomers (NTDT and
DPPT) and polymers (P(NTDT-BDT) and P(DPPT-BDT)).
As shown in Figure S1 (Supporting Information), the NTDT-
based materials (NTDT thermally stable up to 350 °C and
P(NTDT-BDT)) up to 358 °C) exhibited higher thermal
stabilities than the DPPT-based materials (DPPT thermally
stable up to 316 °C and P(DPPT-BDT) up to 343 °C).
Theoretical Calculations. The molecular structures and
optimized geometries of the electron-deficient building blocks
(NTDT and DPPT (R = Me)) were analyzed through
theoretical quantum chemical calculations, which were
performed using Gaussian 09 at the B3LYP level with the
basis set of 6-31G**, as shown in Figure S2, parts a and b
(Supporting Information), respectively. As expected, both
NTDT and DPPT exhibited a higher degree of planarity with
Single Crystal Analysis. To gain a deeper insight into the
conformations of these core units, single-crystal X-ray
diffraction analyses were conducted. Single crystals of NTDT
and DPPT were prepared by the solvent diffusion crystal
growth method using a dichloromethane/methanol (7:3 v/v for
NTDT and 8:2 v/v for DPPT) solution. As shown in Figure 2,
the single-crystal XRD structures of both NTDT (Figure 2a)
Figure 2. Crystal structures and molecular stacking structures of (a)
NTDT and (b) DPPT.
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Figure 3. UV−vis absorption spectra of (a, b) NTDT and DPPT and (c, d) P(NTDT-BDT) and P(DPPT-BDT) in CHCl3 solution and thin-film
form on glass substrates. Energy level diagrams of (e) NTDT and DPPT and (f) P(NTDT-BDT) and P(DPPT-BDT). Light bars denote data
obtained from DFT calculations while dark bars represent experimental data.
and DPPT (Figure 2b) belong to the monoclinic crystal system
(see Tables S1 and S2 for the crystallographic data, Supporting
Information). It can be seen clearly that, in DPPT, intra-
molecular hydrogen-bonded (O···H) interactions occur with
the bond distance being 2.28 Å. In contrast, in NTDT, S···O
interactions occur between the sulfur of the thiophene molecule
and the oxygen of the carbonyl group, with the bond distance
being 2.69 Å. These results indicated that the energetically
preferable conformations of the two units are determined by
different nonbonding interactions, which, in turn, are
influenced by the steric factor, inter- and intramolecular
interactions, and the degree of π-conjugation.68 Interestingly,
the single crystal of NTDT showed a quasi-planar structure,
with the torsional angle (1.38°) between thiophene and the
mean plane of the NTDT core being much smaller than that in
the case of DPPT (10.93°). In addition, the intermolecular
π−π distance in the NTDT crystal (3.40 Å) is slightly smaller
than that in DPPT (3.42 Å), indicating that the π−π
interaction in the NTDT is as strong as DPPT, owing to the
rigid molecular structure.
determined molar extinction coefficients. Parts c and d of
Figure 3 show the UV−vis absorption spectra of P(NTDT-
BDT) and P(DPPT-BDT); As for the solid-state film, the
absorption spectra of both polymers are broadly spanned and
extended to the longer wavelength region compared to the
solution-state absorption region. However, both polymers
showed different degrees of bathochromically shifted maximum
absorption (Δ λmaxabs) in the solid states from those in solution
(16 nm for P(NTDT-BDT) and 6 nm for P(DPPT-BDT)
(Table 1)). Compared to P(DPPT-BDT), P(NTDT-BDT)
showed a larger solution-to-thin film peak shift, indicating that
the intermolecular π−π stacking of P(NTDT-BDT) is more
efficient than that of P(DPPT-BDT) in the solid state. Most
significantly, P(NTDT-BDT) exhibits absorption maximum in
the shorter-wavelength but with much higher absorption
coefficient when compared with P(DPPT-BDT) (317 000
cm−1 for P(NTDT-BDT) and 157 000 cm−1 for P(DPPT-
BDT)) in the film state). It should be noted that this value of
the absorption coefficient is one of the highest reported for D−
A type copolymers and would ensure that the material is
suitable for harvesting photons and increasing the short-circuit
current (Jsc) in photovoltaic devices.
To estimate the frontier MO energies of the core units and
polymers, cyclic voltammetry (CV) analyses were performed
on the solutions (CH2Cl2/0.1 M Bu4NBF4) and solid-state
films (spin-coated on indium tin oxide (ITO) substrates) of the
compounds (Figure S4, Supporting Information). From the CV
analyses, the HOMO energy levels of NTDT, DPPT,
P(NTDT-BDT), and P(DPPT-BDT) were determined to be
−5.42, −5.22, −5.33, and −5.23 eV, respectively. In addition,
the LUMO energy levels of these molecules were evaluated
from their HOMO levels and optical band gaps (Egopt of
NTDT, 2.29 eV; Egopt of DPPT, 1.96 eV; Egopt of P(NTDT-
BDT), 1.66 eV; Egopt of P(DPPT-BDT), 1.32 eV), as depicted
in Figure 3, parts e and f. The experimental HOMO/LUMO
values of these molecules were in good agreement with the
calculated ones. Specifically, the NTDT monomer and its
polymer were found to exhibit relatively deeper HOMO levels
than those of the corresponding DPPT derivatives. This should
make the former suitable for increasing the open-circuit voltage
(Voc) of PSCs.
Optical and Electrochemical Properties. The photo-
physical properties of the bis-lactam monomers (NTDT and
DPPT) as well as the polymers (P(NTDT-BDT) and
P(DPPT-BDT)) were examined by UV−vis absorption
spectroscopy both in the solution state (1.0 × 10−5 M,
CHCl3) and in the film state (using spin-cast films formed on
quartz substrates). NTDT exhibited the maximum absorption
(λmaxabs) at 497 nm in solution (533 nm in film form) whereas
that of DPPT was observed at 549 nm (601 nm in film form)
(Figure 3a and Table 1), indicating that NTDT exhibits a
relatively weaker intramolecular charge transfer (ICT)
transition between the NTD unit and the flanked thiophene
unit than that seen in DPPT. However, NTDT showed a
markedly larger molar extinction coefficient (51 000 M−1 cm−1)
abs
at the λmax level in solution form than that of DPPT, which
was 31 400 M−1 cm−1 (Figure 3b). To elucidate the reason for
these differences in the absorption characteristics, TD-DFT
calculations were performed for NTDT and DPPT. As shown
in Figure S3 (Supporting Information), the S0−S1 transition
energy spectra of the two units matched well with the
corresponding experimental results. Furthermore, the com-
puted oscillator strength indicated that the f value of NTDT
(=0.9064) was much larger than that of DPPT (=0.4773); this
was consistent with the trend observed in the experimentally
Photovoltaic Properties. PSCs were fabricated using each
of the two polymers as the electron donor and PC71BM as the
electron acceptor. The structure of the devices was that of a
D
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Figure 4. (a) Current density−voltage (J−V) curves and (b) IPCE spectra of optimized inverted photovoltaic devices based on P(NTDT-
BDT):PC71BM and P(DPPT-BDT):PC71BM blends.
a
Table 2. Photovoltaic Parameters of Optimized P(NTDT-BDT):PC71BM and P(DPPT-BDT):PC71BM BHJ Devices
b
c
c
c
c
material
Voc (V)
Jsc (mA cm−2
)
FF
PCE (%)
P(NTDT-BDT):PC71BM
P(DPPT-BDT):PC71BM
0.70 (0.70 0.01)
18.51 (17.10 0.89)
7.24 (6.74 0.35)
0.63 (0.64 0.01)
0.68 (0.67 0.01)
8.16 (7.64 0.27)
3.26 (2.95 0.18)
0.66 (0.65 0.01)
a
b
c
ITO/ZnO/PEI/polymer:PC71BM/MoO3/Ag. Weight ratio of polymer:PC71BM is 1:2. Average values were obtained from 10 devices.
conventional BHJ device: ITO/PEDOT:PSS/poly-
mer:PC71BM/Ca/Al. In order to optimize the performances
of the PSCs, we fabricated the devices under different
conditions by varying the solvent conditions and polymer
concentrations. To optimize the charge-transporting network of
the photoactive layer, we also used various additives, such as
1,2-dichlorobenzene (DCB) and 1,8-diiodooctane (DIO)
(Table S3, Supporting Information).69,70 The PSC devices
without an additive were found to exhibit low PCEs; this was
the case for both P(NTDT-BDT) and P(DPPT-BDT). The
device formed using P(NTDT-BDT)/PC71BM = 1:2 (w/w)
and in which DCB was added to CHCl3 (CHCl3/DCB = 85:15
v/v) showed the best performance, with the Voc of 0.72 V, the
Jsc of 16.99 mA cm−2, the fill factor (FF) of 0.58, and the PCE
of 7.11% (Table S3 and Figure S5a, Supporting Information).
In the case of the P(DPPT-BDT)-based device, the addition of
DIO to CHCl3 (CHCl3/DIO = 95:5 v/v) resulted in the
optimization of its performance, with Voc of 0.66 V, Jsc of 7.72
mA cm−2, FF of 0.60, and PCE of 3.08% (Table S3 and Figure
S5b, Supporting Information); these values are comparable to
previously reported results.63−65 The higher Voc value of the
P(NTDT-BDT):PC71BM device was consistent with the fact
that the HOMO level of P(NTDT-BDT) was lower than that
of P(DPPT-BDT).
spectrum (18.06 mA cm−2 for P(NTDT-BDT) device and 7.22
mA cm−2 for P(DPPT-BDT) device) are well matched with
the Jsc values obtained from their J−V curves.
Morphology Investigation. To investigate the ordered
structures of solid-state films of these polymers, grazing
incidence wide-angle X-ray scattering (GIWAXS) measure-
ments were carried out on pristine films of the polymers as well
as polymer:PC71BM blended films and polymer:PC71BM
blended films with additives (Figure 5). The GIWAXS pattern
of the pristine P(NTDT-BDT) film showed interlamellar
stacking (h00) peaks in the in-plane direction and a π−π
stacking peak (010) in the out-of-plane direction at qz = 1.68
To further improve the performance of the P(NTDT-BDT)
device, inverted devices were fabricated with the ITO/ZnO/
polyethylenimine/polymer:PC71BM/MoO3/Ag configuration.
Figure 4a shows the current−voltage (J−V) characteristics of
the optimized inverted PSC device; the other related data are
listed in Table 2. The inverted device exhibited higher Jsc (18.51
mA cm−2) and FF (0.63) than those of the conventional cell.
To the best of our knowledge, this Jsc value of P(NTDT-BDT)
is the highest value yet reported for BDT-based polymer in
PSCs.71 As a result, the inverted device exhibited the highest
PCE, which was 8.16%. The corresponding incident photon-to-
current efficiency (IPCE) of the polymer:PC71BM devices
under the optimized conditions are displayed in Figure 4b; it
can be seen that the integrated current values from the IPCE
Figure 5. Two-dimensional GIWAXS images of pristine films of (a)
P(NTDT-BDT) and (b) P(DPPT-BDT), films of (c) P(NTDT-
BDT):PC71BM and (d) P(DPPT-BDT):PC71BM blends and
optimized films of (e) P(NTDT-BDT):PC71BM with 15 vol %
DCB and (f) P(DPPT-BDT):PC71BM with 5 vol % DIO blends.
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Figure 6. (a−d) AFM height images (5 μm × 5 μm) of (a) P(NTDT-BDT):PC71BM blend film, (b) P(NTDT-BDT):PC71BM:additive (DCB; 15
vol %) blend film, (c) P(DPPT-BDT):PC71BM blend film, and (d) P(DPPT-BDT):PC71BM:additive (DIO; 5 vol %) blend film; (e−h) TEM
images of (e) P(NTDT-BDT):PC71BM blend film, (f) P(NTDT-BDT):PC71BM:additive (DCB; 15 vol %) blend film, (g) P(DPPT-
BDT):PC71BM blend film, and (h) P(DPPT-BDT):PC71BM:additive (DIO; 5 vol %) blend film.
Å−1, which corresponded to face-on π−π stacking. The face-on
orientation of P(NTDT-BDT) is suitable for increasing the
vertical charge-carrier mobility and resulted in a high Jsc value in
the corresponding PSCs.72−74 On the other hand, the GIWAXS
pattern of the pristine P(DPPT-BDT) film displayed weak and
broad interlamellar scattering (h00) and (010) peaks in both
the in-plane and the out-of-plane directions, indicating that
P(DPPT-BDT) exhibits a mix of face-on and edge-on
orientations. Furthermore, the π−overlap distances (dπ) in
the pristine polymer films were calculated to be 3.74 Å (qz =
1.68 Å−1) and 3.78 Å (qz = 1.66 Å−1) for P(NTDT-BDT) and
P(DPPT-BDT), respectively. When P(NTDT-BDT) was
blended with PC71BM (Figure 5c) and PC71BM/DCB additive
(Figure 5e), the intensities of the π−π stacking peak (010) in
the out-of-plane direction somewhat decreased; however, the
blended films exhibited diffraction patterns similar to those of
the pristine polymer films; the only difference was that the
diffraction pattern of PC71BM was present in the case of the
blended films, indicating that the blend films maintain the face-
on orientation due to the highly crystalline nature of P(NTDT-
BDT). In case of P(DPPT-BDT), however, diffraction patterns
of the blended films were quite different from those of the
pristine film. As shown in Figure 5d, the π−π stacking peak
(010) in the qz direction disappered, indicating that the
molecular ordering of P(DPPT-BDT) could be easily affected
by the presence of PC71BM. After adding the DIO additive
(Figure 5f), however, the molecular orientation largely changed
to normal to the substrate plane again, which is beneficial for
vertical charge transport.
Although the additive treatment of P(DPPT-BDT):PC71BM
blend was also effective to form the nanoscale morphology,
they showed poorer film homogeneity with high root-mean-
square roughness (6.23 nm) than the P(NTDT-
BDT):PC71BM blend film (1.02 nm). Thus, the more extensive
and homogeneous interface formed in the P(NTDT-
BDT):PC71BM blend film led to more efficient charge
separation, resulting in the Jsc values of the PSC devices
based on this blend film being higher than those of the devices
based on the P(DPPT-BDT):PC71BM blend film.
Charge Carrier Transport Properties. To further
elucidate the charge-transport characteristics of the polymers,
their charge-carrier mobilities were investigated by using the
space-charge-limited current (SCLC) model as well as organic
field-effect transistors (OFETs). The measured SCLC hole
mobilities of P(NTDT-BDT) and P(DPPT-BDT) were found
to be 3.4 × 10−3 cm2 V−1 s−1 and 2.5 × 10−4 cm2 V−1 s−1,
respectively (Figure S6, Supporting Information). The field-
effect mobilities of the two polymers were determined by using
the polymers for the active layers in typical bottom-gate top-
contact OFETs. As shown in Figure S7 (Supporitng
Information), P(NTDT-BDT) and P(DPPT-BDT) exhibited
p-type organic semiconductor characteristics (hole mobility of
5.8 × 10−3 cm2 V−1 s−1 for P(NTDT-BDT) and 1.2 × 10−2 cm2
V−1 s−1 for P(DPPT-BDT)). That is to say, P(NTDT-BDT)
exhibited a much higher hole mobility than P(DPPT-BDT) in
the vertical direction (SCLC method; the charge carriers flowed
in the vertical direction), while P(DPPT-BDT) showed a
higher hole mobility than P(NTDT-BDT) in the lateral
direction (OFET; the charge carriers flowed in the lateral
direction). From these results, it was concluded that the
preferentially face-on oriented P(NTDT-BDT) film was more
suitable for vertical charge transport than the mixed (face-on +
edge-on) orientation P(DPPT-BDT) film. This leads to a
higher Jsc values for P(NTDT-BDT).
Atomic force microscopy (AFM) and transmission electron
microscopy (TEM) were used for investigating the nanoscale
morphologies of the two polymers (Figure 6). The effect of the
additive treatment could be visualized through the AFM and
TEM images. When an additive was not used, both the
P(NTDT-BDT):PC71BM and P(DPPT-BDT):PC71BM blend
films exhibited macroscopic phase separation between the
polymer and PC71BM. After treatment with an additive,
however, bicontinuous network with finer nanoscale features
was observed in the P(NTDT-BDT):PC71BM blend film.
3. CONCLUSION
We synthesized and characterized a novel bis-lactam-based A
building block, NTDT, for D−A type conjugated polymers.
F
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Article
Enables Multiple Cases of High-Efficiency Polymer Solar Cells. Nat.
Commun. 2014, 5, 5293.
The NTDT unit exhibits a high coplanarity of the conjugated
backbone owing to the intramolecular S···O interactions. The
electron-deficient nature and quasi-planar structure with
remarkably high molar extinction coefficient of the NTDT
unit could allow for the realization of high efficient D−A
copolymer. In fact, the NTDT incorporated conjugated
polymer P(NTDT-BDT) exhibited a deeper HOMO level,
higher absorption coefficient, and higher vertical charge-carrier
mobility than those of the widely used copolymer P(DPPT-
BDT). Furthermore, P(NTDT-BDT) also exhibited the
appropriate nanoscale morphology and the proper ordered
structure with a coplanar geometry. All these factors ensured
that the PSCs based on P(NTDT-BDT) exhibited better
performance. As a result, a BHJ PSC device based on
P(NTDT-BDT) with PC71BM showed an high PCE of
8.16% with a high Jsc value of 18.51 mA cm−2. This Jsc value
is one of the highest values yet obtained for BDT-based
polymer in PSCs. On the basis of these results, we strongly
believe that the NTDT is a promising A building block for
conjugated polymers and can potentially replace DPPT in
organic solar cells.
(8) He, Z.; Xiao, B.; Liu, F.; Wu, H.; Yang, Y.; Xiao, S.; Wang, C.;
Russell, T. P.; Cao, Y. Single-Junction Polymer Solar Cells with High
Efficiency and Photovoltage. Nat. Photonics 2015, 9, 174−179.
(9) Liu, C.; Yi, C.; Wang, K.; Yang, Y.; Bhatta, R. S.; Tsige, M.; Xiao,
S.; Gong, X. Single-Junction Polymer Solar Cells with Over 10%
Efficiency by a Novel Two-Dimensional Donor−Acceptor Conjugated
Copolymer. ACS Appl. Mater. Interfaces 2015, 7, 4928−4935.
(10) Zhou, H. Q.; Zhang, Y.; Mai, C. K.; Collins, S. D.; Bazan, G. C.;
Nguyen, T.-Q.; Heeger, A. J. Polymer Homo-Tandem Solar Cells with
Best Efficiency of 11.3%. Adv. Mater. 2015, 27, 1767−1773.
(11) Zhao, J.; Li, Y.; Yang, G.; Jiang, K.; Lin, H.; Ade, H.; Ma, W.;
Yan, H. Efficient Organic Solar Cells Processed from Hydrocarbon
Solvents. Nat. Energy 2016, 1, 15027.
(12) Zhao, W.; Qian, D.; Zhang, S.; Li, S.; Inganas, O.; Gao, F.; Hou,
̈
J. Fullerene-Free Polymer Solar Cells with over 11% Efficiency and
Excellent Thermal Stability. Adv. Mater. 2016, 28, 4734−4739.
(13) Hau, S. K.; Yip, H.-L.; Jen, A. K.-Y. A Review on the
Development of the Inverted Polymer Solar Cell Architecture. Polym.
Rev. 2010, 50, 474−510.
(14) Cao, W.; Xue, J. Recent Progress in Organic Photovoltaics:
Device Architecture and Optical Design. Energy Environ. Sci. 2014, 7,
2123−2144.
(15) Facchetti, A. π-Conjugated Polymers for Organic Electronics
and Photovoltaic Cell Applications. Chem. Mater. 2011, 23, 733−758.
(16) Bian, L.; Zhu, E.; Tang, J.; Tang, W.; Zhang, F. Recent Progress
in The Design of Narrow Bandgap Conjugated Polymers for High-
Efficiency Organic Solar Cells. Prog. Polym. Sci. 2012, 37, 1292−1331.
(17) Benten, H.; Mori, D.; Ohkita, H.; Ito, S. Recent Research
Progress of Polymer Donor/Polymer Acceptor Blend Solar Cells. J.
Mater. Chem. A 2016, 4, 5340−5365.
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.macro-
mol.6b01680.
Experimental details, Figures S1−S7, and Tables S1−S3
(PDF)
Structure of NTDT (CIF)
(18) Svensson, M.; Zhang, F.; Veenstra, S. C.; Verhees, W. J. H.;
Hummelen, J. C.; Kroon, J. M.; Inganas, O.; Andersson, M. R. High-
̈
Structure of DPPT (CIF)
Performance Polymer Solar Cells of an Alternating Polyfluorene
Copolymer and a Fullerene Derivative. Adv. Mater. 2003, 15, 988−
991.
AUTHOR INFORMATION
Corresponding Author
*E-mail: parksy@snu.ac.kr (S.Y.P.).
■
́
(19) Thompson, B. C.; Frechet, J. M. J. Polymer−Fullerene
Composite Solar Cells. Angew. Chem., Int. Ed. 2008, 47, 58−77.
(20) Cheng, Y.-J.; Yang, S.-H.; Hsu, C.-S. Synthesis of Conjugated
Polymers for Organic Solar Cell Applications. Chem. Rev. 2009, 109,
5868−5923.
Notes
The authors declare no competing financial interest.
(21) Li, G.; Zhu, R.; Yang, Y. Polymer Solar Cells. Nat. Photonics
2012, 6, 153−161.
(22) Subramaniyan, S.; Xin, H.; Kim, F. S.; Murari, N. M.;
Courtright, B. A. E.; Jenekhe, S. A. Thiazolothiazole Donor−Acceptor
Conjugated Polymer Semiconductors for Photovoltaic Applications.
Macromolecules 2014, 47, 4199−4209.
(23) Liu, C.; Wang, K.; Gong, X.; Heeger, A. J. Low Bandgap
Semiconducting Polymers for Polymeric Photovoltaics. Chem. Soc. Rev.
2016, 45, 4825−4846.
(24) Li, Y.; Xue, L.; Li, H.; Li, Z.; Xu, B.; Wen, S.; Tian, W. Energy
Level and Molecular Structure Engineering of Conjugated Donor−
Acceptor Copolymers for Photovoltaic Applications. Macromolecules
2009, 42, 4491−4499.
(25) Li, Y.; Chen, Y.; Liu, X.; Wang, Z.; Yang, X.; Tu, Y.; Zhu, X.
Controlling Blend Film Morphology by Varying Alkyl Side Chain in
Highly Coplanar Donor−Acceptor Copolymers for Photovoltaic
Application. Macromolecules 2011, 44, 6370−6381.
(26) Lu, L.; Zheng, T.; Wu, Q.; Schneider, A. M.; Zhao, D.; Yu, L.
Recent Advances in Bulk Heterojunction Polymer Solar Cells. Chem.
Rev. 2015, 115, 12666−12731.
ACKNOWLEDGMENTS
■
This work was supported by the National Research Foundation
of Korea (NRF) through a grant funded by the Korean
Government (MSIP; No. 2009-0081571[RIAM0417-
20150013]).
REFERENCES
■
(1) Gunes, S.; Neugebauer, H.; Sariciftci, N. S. Conjugated Polymer-
̈
Based Organic Solar Cells. Chem. Rev. 2007, 107, 1324−1338.
(2) Krebs, F. C. Fabrication and Processing of Polymer Solar Cells: A
Review of Printing and Coating Techniques. Sol. Energy Mater. Sol.
Cells 2009, 93, 394−412.
(3) Brabec, C. J. Organic Photovoltaics: Technology and Market. Sol.
Energy Mater. Sol. Cells 2004, 83, 273−292.
(4) Darling, S. B.; You, F. The Case for Organic Photovoltaics. RSC
Adv. 2013, 3, 17633−17648.
(5) Scharber, M. C.; Sariciftci, N. S. Efficiency of Bulk-
Heterojunction Organic Solar Cells. Prog. Polym. Sci. 2013, 38,
1929−1940.
(6) You, J. B.; Dou, L. T.; Yoshimura, K.; Kato, T.; Ohya, K.;
Moriarty, T.; Emery, K.; Chen, C.-C.; Gao, J.; Li, G.; Yang, Y. A
Polymer Tandem Solar Cell with 10.6% Power Conversion Efficiency.
Nat. Commun. 2013, 4, 1446.
(27) Kroon, R.; Lenes, M.; Hummelen, J. C.; Blom, P. W. M.; de
Boer, B. Small Bandgap Polymers for Organic Solar Cells (Polymer
Material Development in the Last 5 Years). Polym. Rev. 2008, 48,
531−582.
(28) Kranthiraja, K.; Gunasekar, K.; Cho, W.; Song, M.; Park, Y. G.;
Lee, J. Y.; Shin, Y.; Kang, I.-N.; Kim, A.; Kim, H.; Kim, B.; Jin, S.-H.
Alkoxyphenylthiophene Linked Benzodithiophene Based Medium
(7) Liu, Y. H.; Zhao, J. B.; Li, Z. K.; Mu, C.; Ma, W.; Hu, H.; Jiang,
K.; Lin, H. R.; Ade, H.; Yan, H. Aggregation and Morphology Control
G
DOI: 10.1021/acs.macromol.6b01680
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
Band Gap Polymers for Organic Photovoltaics: Efficiency Improve-
ment upon Methanol Treatment Depends on the Planarity of
Backbone. Macromolecules 2014, 47, 7060−7069.
(44) Piliego, C.; Holcombe, T. W.; Douglas, J. D.; Woo, C. H.;
Beaujuge, P. M.; Frechet, J. M. J. Synthetic Control of Structural Order
́
in N-Alkylthieno[3,4-c]pyrrole-4,6-dione-Based Polymers for Efficient
Solar Cells. J. Am. Chem. Soc. 2010, 132, 7595−7597.
́ ́
(45) Zou, Y.; Najari, A.; Berrouard, P.; Beaupre, S.; Reda Aïch, B. R.;
(29) Carsten, B.; Szarko, J. M.; Son, H. J.; Wang, W.; Lu, L.; He, F.;
Rolczynski, B. S.; Lou, S. J.; Chen, L. X.; Yu, L. Examining the Effect of
the Dipole Moment on Charge Separation in Donor-Acceptor
Polymers for Organic Photovoltaic Applications. J. Am. Chem. Soc.
2011, 133, 20468−20475.
Tao, Y.; Leclerc, M. A Thieno[3,4-c]pyrrole-4,6-dione-Based Copoly-
mer for Efficient Solar Cells. J. Am. Chem. Soc. 2010, 132, 5330−5331.
(46) Li, Y.; Sonar, P.; Murphy, L.; Hong, W. High Mobility
Diketopyrrolopyrrole (DPP)-Based Organic Semiconductor Materials
for Organic Thin Film Transistors and Photovoltaics. Energy Environ.
Sci. 2013, 6, 1684−1710.
(30) Blouin, N.; Michaud, A.; Gendron, D.; Wakim, S.; Blair, E.;
̂
Neagu-Plesu, R.; Belletete, M.; Durocher, G.; Tao, Y.; Leclerc, M.
Toward a Rational Design of Poly(2,7-Carbazole) Derivatives for Solar
Cells. J. Am. Chem. Soc. 2008, 130, 732−742.
(47) Li, W.; Hendriks, K. H.; Wienk, M. M.; Janssen, R. A. J.
Diketopyrrolopyrrole Polymers for Organic Solar Cells. Acc. Chem. Res.
2016, 49, 78−85.
(31) Hou, J.; Chen, H.-Y.; Zhang, S.; Li, G.; Yang, Y. Synthesis,
Characterization, and Photovoltaic Properties of a Low Band Gap
Polymer Based on Silole-Containing Polythiophenes and 2,1,3-
Benzothiadiazole. J. Am. Chem. Soc. 2008, 130, 16144−16145.
(32) Huang, Y.; Huo, L.; Zhang, S.; Guo, X.; Han, C. C.; Li, Y.; Hou,
J. Sulfonyl: A New Application of Electron-Withdrawing Substituent in
Highly Efficient Photovoltaic Polymer. Chem. Commun. 2011, 47,
8904−8906.
(48) Cao, J.; Liao, Q.; Du, X.; Chen, J.; Xiao, Z.; Zuo, Q.; Ding, L. A
Pentacyclic Aromatic Lactam Building Block for Efficient Polymer
Solar Cells. Energy Environ. Sci. 2013, 6, 3224−3228.
(49) Cao, J.; Qian, L.; Lu, F.; Zhang, J.; Feng, Y.; Qiu, X.; Yip, H.-L.;
Ding, L. A Lactam Building Block for Efficient Polymer Solar Cells.
Chem. Commun. 2015, 51, 11830−11833.
(33) Wu, Y.; Li, Z.; Ma, W.; Huang, Y.; Huo, L.; Guo, X.; Zhang, M.;
Ade, H.; Hou, J. PDT-S-T: A New Polymer with Optimized Molecular
Conformation for Controlled Aggregation and π-π Stacking and Its
Application in Effi cient Photovoltaic Devices. Adv. Mater. 2013, 25,
3449−3455.
(34) Kim, J.-H.; Song, C. E.; Kim, B.; Kang, I.-N.; Shin, W. S.;
Hwang, D.-H. Thieno[3,2-b]thiophene-Substituted Benzo[1,2-b:4,5-
b′]dithiophene as a Promising Building Block for Low Bandgap
Semiconducting Polymers for High-Performance Single and Tandem
Organic Photovoltaic Cells. Chem. Mater. 2014, 26, 1234−1242.
(35) Kroon, R.; Diaz de Zerio Mendaza, A.; Himmel-berger, S.;
(50) Cao, J.; Zuo, C.; Du, B.; Qiu, X.; Ding, L. Hexacyclic Lactam
Building Blocks for Highly Efficient Polymer Solar Cells. Chem.
Commun. 2015, 51, 12122−12125.
(51) Qian, L.; Cao, J.; Ding, L. A Hexacyclic Ladder-Type Building
Block for High-Performance D−A Copolymers. J. Mater. Chem. A
2015, 3, 24211−24214.
(52) Subramaniyan, S.; Kim, F. S.; Ren, G.; Li, H.; Jenekhe, S. A.
High Mobility Thiazole-Diketopyrrolopyrrole Copolymer Semicon-
ductors for High Performance Field-Effect Transistors and Photo-
voltaic Devices. Macromolecules 2012, 45, 9029−9037.
(53) Choi, H.; Ko, S. J.; Kim, T.; Morin, P. O.; Walker, B.; Lee, B. H.;
Leclerc, M.; Kim, J. Y.; Heeger, A. J. Small-Bandgap Polymer Solar
Cells with Unprecedented Short-Circuit Current Density and High Fill
Factor. Adv. Mater. 2015, 27, 3318−3324.
(54) Ma, T.; Jiang, K.; Chen, S.; Hu, H.; Lin, H.; Li, Z.; Zhao, J.; Liu,
Y.; Chang, Y.-M.; Hsiao, C.-C.; Yan, H. Efficient Low-Bandgap
Polymer Solar Cells with High Open-Circuit Voltage and Good
Stability. Adv. Energy Mater. 2015, 5, 1501282.
(55) Stalder, R.; Mei, J.; Graham, K. R.; Estrada, L. A.; Reynolds, J. R.
Isoindigo, a Versatile Electron-Deficient Unit For High-Performance
Organic Electronics. Chem. Mater. 2014, 26, 664−678.
(56) Deng, P.; Zhang, Q. Recent Developments on Isoindigo-Based
Conjugated Polymers. Polym. Chem. 2014, 5, 3298−3305.
(57) Lu, S.; Drees, M.; Yao, Y.; Boudinet, D.; Yan, H.; Pan, H.; Wang,
J.; Li, Y.; Usta, H.; Facchetti, A. 3,6-Dithiophen-2-yl-diketopyrrolo[3,2-
b]pyrrole (isoDPPT) as an Acceptor Building Block for Organic
Opto-Electronics. Macromolecules 2013, 46, 3895−3906.
(58) Guo, X.; Puniredd, S. R.; He, B.; Marszalek, T.; Baumgarten, M.;
Bergqvist, J.; Backe, O.; Faria, G. C.; Gao, F.; Obaid, A.; Zhuang, W.;
̈
Gedefaw, D.; Olsson, E.; Inganas, O.; Salleo, A.; Muller, C.;
̈
̈
Andersson, M. R. A New Tetracyclic Lactam Building Block for
Thick, Broad-Bandgap Photovoltaics. J. Am. Chem. Soc. 2014, 136,
11578−11581.
(36) Wang, M.; Wang, H.; Yokoyama, T.; Liu, X.; Huang, Y.; Zhang,
Y.; Nguyen, T.-Q.; Aramaki, S.; Bazan, G. C. High Open Circuit
Voltage in Regioregular Narrow Band Gap Polymer Solar Cells. J. Am.
Chem. Soc. 2014, 136, 12576−12579.
(37) Saito, M.; Osaka, I.; Suda, Y.; Yoshida, H.; Takimiya, K.
Dithienylthienothiophenebisimide, a Versatile Electron-Deficient Unit
for Semiconducting Polymers. Adv. Mater. 2016, 28, 6921−6925.
(38) Beaujuge, P. M.; Pisula, W.; Tsao, H. N.; Ellinger, S.; Mullen, K.;
̈
Reynolds, J. R. Tailoring Structure-Property Relationships in
Dithienosilole-Benzothiadiazole Donor-Acceptor Copolymers. J. Am.
Chem. Soc. 2009, 131, 7514−7515.
(39) Subbiah, J.; Purushothaman, B.; Chen, M.; Qin, T. S.; Gao, M.;
Vak, D.; Scholes, F. H.; Chen, X. W.; Watkins, S. E.; Wilson, G. J.;
Holmes, A. B.; Wong, W. W. H.; Jones, D. J. Organic Solar Cells Using
a High-Molecular-Weight Benzodithiophene−Benzothiadiazole Co-
polymer with an Efficiency of 9.4%. Adv. Mater. 2015, 27, 702−705.
(40) Sonar, P.; Williams, E. L.; Singh, S. P.; Dodabalapur, A.
Thiophene−Benzothiadiazole−Thiophene (D−A−D) Based Poly-
mers: Effect of Donor/Acceptor Moieties Adjacent to D−A−D
Segment on Photophysical and Photovoltaic Properties. J. Mater.
Chem. 2011, 21, 10532−10541.
Pisula, W.; Mullen, K. Combination of Two Diketopyrrolopyrrole
̈
Isomers in One Polymer for Ambipolar Transport. Chem. Mater. 2014,
26, 3595−3598.
(59) Guo, X.; Facchetti, A.; Marks, T. J. Imide- and Amide-
Functionalized Polymer Semiconductors. Chem. Rev. 2014, 114,
8943−9021.
(60) Frydman, B.; Los, M.; Rapoport, H. Synthesis of Substituted
1,5- and l,7-Naphthyridines and Related Lactams. J. Org. Chem. 1971,
36, 450−454.
(41) Wang, E. G.; Hou, L.; Wang, Z.; Hellstrom, S.; Zhang, F. L.;
(61) Mishra, A. K.; Vaidyanathan, S.; Noguchi, H.; Doetz, F.; Guan,
Y. Semiconductor Materials Based on Diketopiperidinopiperidine
Copolymers. PCT Int. Appl. WO 2012146574 A1, November 1, 2012.
(62) Nanson, L.; Blouin, N.; Mitchell, W.; Tierney, S.; Cull, T.
Organic Semiconductors Containing One or More Units Derived from
1,5-Disubstituted-1,5-dihydro-[1,5]naphthyridine-2,6-dione. PCT Int.
Appl. WO 2013182262 A1, December 12, 2013.
(63) Huo, L. J.; Hou, J.; Chen, H.-Y.; Zhang, S. Q.; Jiang, Y.; Chen,
T. L.; Yang, Y. Bandgap and Molecular Level Control of The Low-
Bandgap Polymers Based on 3,6-Dithiophen-2-yl-2,5-dihydropyrrolo-
[3,4-c]pyrrole-1,4-dione Toward Highly Efficient Polymer Solar Cells.
Macromolecules 2009, 42, 6564−6571.
̈
Inganas, O.; Andersson, M. R. An Easily Synthesized Blue Polymer for
̈
High-Performance Polymer Solar Cells. Adv. Mater. 2010, 22, 5240−
5244.
(42) Zhou, E.; Cong, J.; Tajima, K.; Hashimoto, K. Synthesis and
Photovoltaic Properties of Donor-Acceptor Copolymers Based on 5,8-
Dithien-2-yl-2,3-diphenylquinoxaline. Chem. Mater. 2010, 22, 4890−
4895.
(43) Zhang, Y.; Zou, J.; Yip, H.-L.; Chen, K.-S.; Zeigler, D. F.; Sun,
Y.; Jen, A. K.-Y. Indacenodithiophene and Quinoxaline-Based
Conjugated Polymers for Highly Efficient Polymer Solar Cells.
Chem. Mater. 2011, 23, 2289−2291.
H
DOI: 10.1021/acs.macromol.6b01680
Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
(64) Peng, Q.; Huang, Q.; Hou, X.; Chang, P.; Xu, J.; Deng, S.
Enhanced Solar Cell Performance by Replacing Benzodithiophene
with Naphthodithiophene in Diketopyrrolopyrrole-based Copolymers.
Chem. Commun. 2012, 48, 11452−11454.
(65) Woong Jung, J.; Woong Jo, J.; Liu, F.; Russell, T. P.; Ho Jo, W.
A Low Band-gap Polymer Based on Unsubstituted Benzo[1,2-b:4,5-
b′]-dithiophene for High Performance Organic Photovoltaics. Chem.
Commun. 2012, 48, 6933−6935.
(66) Hameed P, S; Patil, V.; Solapure, S.; Sharma, U.; Madhavapeddi,
P.; Raichurkar, A.; Chinnapattu, M.; Manjrekar, P.; Shanbhag, G.;
Puttur, J.; Shinde, V.; Menasinakai, S.; Rudrapatana, S.; Achar, V.;
Awasthy, D.; Nandishaiah, R.; Humnabadkar, V.; Ghosh, A.; Narayan,
C.; Ramya, V. K.; Kaur, P.; Sharma, S.; Werngren, J.; Hoffner, S.;
Panduga, V.; Kumar, C. N. N.; Reddy, J.; Kumar KN, K.; Ganguly, S.;
Bharath, S.; Bheemarao, U.; Mukherjee, K.; Arora, U.; Gaonkar, S.;
Coulson, M.; Waterson, D.; Sambandamurthy, V. K.; de Sousa, S. M.
Novel N-Linked Aminopiperidine-Based Gyrase Inhibitors with
Improved hERG and in Vivo Efficacy against Mycobacterium
Tuberculosis. J. Med. Chem. 2014, 57, 4889−4905.
(67) Hultell, M.; Stafstrom, S. Impact of Ring Torsion on The
̈
Intrachain Mobility in Conjugated Polymers. Phys. Rev. B: Condens.
Matter Mater. Phys. 2007, 75, 104304.
(68) Jackson, N. E.; Savoie, B. M.; Kohlstedt, K. L.; Olvera de la
Cruz, M.; Schatz, G. C.; Chen, L. X.; Ratner, M. A. Controlling
Conformations of Conjugated Polymers and Small Molecules: The
Role of Nonbonding Interactions. J. Am. Chem. Soc. 2013, 135,
10475−10483.
(69) Liao, H.-C.; Ho, C.-C.; Chang, C.-Y.; Jao, M.-H.; Darling, S. B.;
Su, W.-F. Additive for Morphology Control in High-Efficiency Organic
Solar Cells. Mater. Today 2013, 16, 326−336.
(70) Li, C.; Chen, Y.; Zhao, Y.; Wang, H.; Zhang, W.; Li, Y.; Yang,
X.; Ma, C.; Chen, L.; Zhu, X.; Tu, Y. Acceptor−Donor−Acceptor-
based Small Molecules with Varied Crystallinity: Processing Additive-
Induced Nanofibril in Blend Film for Photovoltaic Applications.
Nanoscale 2013, 5, 9536−9540.
(71) Yao, H.; Ye, L.; Zhang, H.; Li, S.; Zhang, S.; Hou, J. Molecular
Design of Benzodithiophene-Based Organic Photovoltaic Materials.
Chem. Rev. 2016, 116, 7397−7457.
(72) Murphy, L.; Sun, B.; Hong, W.; Aziz, H.; Li, Y. Study of Vertical
and Lateral Charge Transport Properties of DPP-Based Polymer/
PC61BM Films Using Space Charge Limited Current (SCLC) and
Field Effect Transistor Methods and their Effects on Photovoltaic
Characteristics. Aust. J. Chem. 2015, 68, 1741−1749.
(73) Chen, M. S.; Niskala, J. R.; Unruh, D. A.; Chu, C. K.; Lee, O. P.;
́
Frechet, J. M. J. Control of Polymer-Packing Orientation in Thin
Films through Synthetic Tailoring of Backbone Coplanarity. Chem.
Mater. 2013, 25, 4088−4096.
(74) Vohra, V.; Kawashima, K.; Kakara, T.; Koganezawa, T.; Osaka,
I.; Takimiya, K.; Murata, H. Efficient Inverted Polymer Solar Cells
Employing Favourable Molecular Orientation. Nat. Photonics 2015, 9,
403−409.
I
DOI: 10.1021/acs.macromol.6b01680
Macromolecules XXXX, XXX, XXX−XXX