All-polymer solar cells with 3.3% efficiency based on naphthalene diimide-selenophene copolymer acceptor

Article abstract of DOI:10.1021/ja4085429

The lack of suitable acceptor (n-type) polymers has limited the photocurrent and efficiency of polymer/polymer bulk heterojunction (BHJ) solar cells. Here, we report an evaluation of three naphthalene diimide (NDI) copolymers as electron acceptors in BHJ solar cells which finds that all-polymer solar cells based on an NDI-selenophene copolymer (PNDIS-HD) acceptor and a thiazolothiazole copolymer (PSEHTT) donor exhibit a record 3.3% power conversion efficiency. The observed short circuit current density of 7.78 mA/cm ² and external quantum efficiency of 47% are also the best such photovoltaic parameters seen in all-polymer solar cells so far. This efficiency is comparable to the performance of similarly evaluated [6,6]-Phenyl-C ₆₁-butyric acid methyl ester (PC₆₀BM)/PSEHTT devices. The lamellar crystalline morphology of PNDIS-HD, leading to balanced electron and hole transport in the polymer/polymer blend solar cells accounts for its good photovoltaic properties.

Full text of DOI:10.1021/ja4085429

Communication
pubs.acs.org/JACS
All-Polymer Solar Cells with 3.3% Efficiency Based on Naphthalene
Diimide-Selenophene Copolymer Acceptor
Taeshik Earmme, Ye-Jin Hwang, Nishit M. Murari, Selvam Subramaniyan, and Samson A. Jenekhe*
Department of Chemical Engineering and Department of Chemistry, University of Washington, Seattle, Washington 98195-1750,
United States
*
S Supporting Information
2
(
4
J < 6.3 mA/cm ) and external quantum efficiency (EQE <
sc
3
ABSTRACT: The lack of suitable acceptor (n-type)
polymers has limited the photocurrent and efficiency of
polymer/polymer bulk heterojunction (BHJ) solar cells.
Here, we report an evaluation of three naphthalene
diimide (NDI) copolymers as electron acceptors in BHJ
solar cells which finds that all-polymer solar cells based on
an NDI-selenophene copolymer (PNDIS-HD) acceptor
and a thiazolothiazole copolymer (PSEHTT) donor
exhibit a record 3.3% power conversion efficiency. The
3%) obtained to date in all-polymer solar cells have also been
far lower than in polymer/fullerene devices.
1
,2
Here, we report all-polymer solar cells with 3.3% PCE
enabled by a novel polymer/polymer blend system composed
of a new NDI-selenophene copolymer acceptor and a
thiazolothiazole-dithienosilole copolymer donor. Three n-type
polymer semiconductors, including an NDI-thiophene copoly-
mer (PNDIT) and two new NDI-selenophene copolymers
(
PNDIS, PNDIS-HD) whose molecular structures are shown in
Figure 1a, are investigated as electron acceptors in BHJ solar
2
observed short circuit current density of 7.78 mA/cm and
external quantum efficiency of 47% are also the best such
photovoltaic parameters seen in all-polymer solar cells so
far. This efficiency is comparable to the performance of
similarly evaluated [6,6]-Phenyl-C -butyric acid methyl
6
1
ester (PC BM)/PSEHTT devices. The lamellar crystal-
60
line morphology of PNDIS-HD, leading to balanced
electron and hole transport in the polymer/polymer blend
solar cells accounts for its good photovoltaic properties.
olution-processed organic photovoltaic devices are promis-
1
S
ing low cost solar energy technologies. Much progress has
been made in developing polymer/fullerene solar cells in the
2
past decade, with efficiencies now approaching 10%. In
contrast, the performance of all-polymer solar cells, composed
of both donor and acceptor polymers and free of fullerenes, has
remained relatively low with no significant advance in the same
3
period. All-polymer active layers of solar cells have potential
advantages over polymer/fullerene systems, including enhanced
absorption coefficients, increased photovoltage, superior photo-
chemical, thermal, and mechanical robustness, and facile
control of solution viscosity and the industrial coating process.
Perylene diimide (PDI) and naphthalene diimide (NDI) have
Figure 1. (a) Molecular structures of acceptor (PNDIT, PNDIS, and
PNDIS-HD) and donor (PSEHTT) polymers. (b) UV−vis absorption
spectra of PNDIT, PNDIS, and PNDIS-HD. (c) LUMO/HOMO
energy levels of PNDIT, PNDIS, PNDIS-HD, PC BM, and PSEHTT.
3
,4
60
been the most widely explored building blocks in the design
and investigation of acceptor (n-type) polymers for all-polymer
3
,4
solar cells. A PDI-based acceptor polymer in combination
with polythiophene derivatives has produced bulk hetero-
junction (BHJ) solar cells with a power conversion efficiency
cells for the first time. We show that these NDI-based
copolymers exhibit unipolar electron transport with high field-
effect and bulk mobilities. The donor polymer, poly[(4,4′-
bis(2-ethylhexyl)dithieno[3,2-b:2′,3′-d]silole)- 2,6-diyl-alt-(2,5-
bis(3-(2-ethylhexyl)thiophen-2-yl)thiazolo[5,4-d]thiazole)]
3
h
(
(
(
(
PCE) of 2.23%.
An NDI-bithiophene copolymer
PNDI2OD-T2) with very high field-effect electron mobilities
2
(
PSEHTT, Figure 1a) has been previously shown to be a
0.1−0.85 cm /(V s)) and moderate bulk electron mobility
−3
2
promising electron donor and hole-conducting material in
polymer/fullerene BHJ solar cells. The morphology of the
∼10 cm /(V s)) has so far shown only low efficiencies of
5
0
.2−1.4% PCE in BHJ solar cells using a P3HT donor
3e,l
polymer. Among the acceptor polymers in BHJ solar cells, a
benzothiadiazole-fluorene copolymer has the highest PCE
Received: August 17, 2013
3k
(2.7%) reported to date. The short circuit current density
©
XXXX American Chemical Society
A
dx.doi.org/10.1021/ja4085429 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
Table 1. Molecular Weight, Thermal Stability, Photophysical, and XRD Properties of NDI-Copolymers
polymer
Mw (kDa)
M (kDa)
n
PDI
Td (°C)
λmaxsol
λmaxfilm
Eg (eV)
d100 (Å)
d010 (Å)
PNDIT
31.5
31.6
23.9
26.1
79.0
1.3
1.2
2.3
430
415
400
326, 542
341, 556
341, 556
341, 598
353, 621
351, 614
1.77
1.70
1.65
24.86
22.92
21.53
4.20
4.16
4.16
PNDIS
PNDIS-HD
177.9
polymer/polymer blends was imaged by AFM. Charge
transport in the active layer blends was investigated by organic
field-effect transistors (OFETs) and space-charge-limited
current (SCLC) measurements. Finally, we show that the all-
polymer solar cells can be as efficient as the similarly evaluated
PC BM/PSEHTT BHJ devices.
PNDIT and PNDIS were synthesized by Stille coupling
copolymerization of 4,9-dibromo-2,7-bis(2-decyltetradecyl)-
benzo[lmn][3,8]-phenanthroline-1,3,6,8-tetraone with 2,5-bis-
S8c) while the corresponding HOMO energy levels were
obtained from the LUMO levels and the optical band gaps.
The electron transport properties of PNDIT, PNDIS, and
PNDIS-HD thin films were characterized by using organic field-
effect transistors (OFETs) with bottom gate/top contact
geometry. The OFETs showed only n-channel transistor
behavior with unipolar electron transport. The average
saturated region field-effect electron mobilities of PNDIT,
6
0
−4
−3
−3
PNDIS, and PNDIS-HD were 2 × 10 , 2 × 10 , and 7 × 10
2
(
trimethylstannyl)thiophene and 2,5-bis(trimethylstannyl)-
cm /(V s), respectively (SI, Figure S9). The order of
magnitude higher electron mobility of PNDIS and PNDIS-
HD compared to PNDIT can be understood from the larger π-
orbitals of selenium compared to sulfur, which improves
overlap of the orbitals. In addition, interaction between Se−Se
atoms could enhance the crystallinity of the copolymers and
selenophene, respectively, in the presence of Pd (dba) and
2
3
P(o-tolyl) in chlorobenzene solvent (Supporting Information
3
(
SI), Figure S1). PNDIS-HD was similarly synthesized as
PNDIS using 4,9-dibromo-2,7-bis(2-hexyldecyl)benzo[lmn]-
3,8]-phenanthroline-1,3,6,8-tetraone with a shorter 2-hexyl-
[
8
interchain charge transport. The higher electron mobility of
decyl (HD) side chain. The monomer and copolymer
1
PNDIS and PNDIS-HD can also be explained by their
favorable solid state morphology and molecular packing with
shorter d100 and d010 spacings compared to PNDIT (Table 1).
The higher electron mobility of PNDIS-HD with shorter
hexyldecyl side chains compared to PNDIS with decyltetradecyl
side chains can be largely understood in terms of the higher
molecular weight and shorter d100 spacing of PNDIS-HD.
We fabricated and evaluated polymer/polymer blend solar
cells with the inverted device structure of ITO/ZnO/blend/
molecular structures were confirmed by H NMR (SI, Figure
S2−S7). The M of PNDIT and PNDIS was 23.9 and 26.1 kDa
n
with a polydispersity index (PDI) of 1.3 and 1.2, respectively.
PNDIS-HD had a much higher M of 79.0 kDa with a PDI of
n
2.3. These polymers had an onset decomposition temperature
(
T ) of 400−430 °C (SI, Figure S8a).
d
X-ray diffraction (XRD) analysis of solution-cast films of
PNDIT, PNDIS, and PNDIS-HD revealed lamellar crystallinity
with an intense (100) peak (SI, Figure S8b). A lamellar d-
spacing (d100) of 24.86, 22.92, and 21.53 Å, respectively, was
observed for PNDIT, PNDIS, and PNDIS-HD. The shorter
d100 spacing compared to the alkyl chain length (2 × 14 C) of
MoO /Ag. The active layer blend was PNDIT:PSEHTT,
3
PNDIS:PSEHTT, or PNDIS-HD:PSEHTT, each spin-coated
from chlorobenzene with an optimum composition of 1:1 w/w.
The optimal composition (1:1 w/w) to focus our detailed
investigation was determined by the initial performance of solar
cells fabricated from different blend compositions (1:0.75, 1:1,
and 1:2 w/w). The photodiodes were fabricated in a glovebox
43.12 Å indicates interdigitation of the alkyl chains. As
expected, PNDIS-HD has a smaller d100 value compared to
the other two polymers with 2-decyltetradecyl side chains. The
shorter d100 spacing of PNDIS compared to PNDIT is due to a
larger torsion angle between NDI and selenophene moieties,
which is a consequence of the larger Se orbitals compared to S.
The observed π−π stacking distance (d010) of 4.16 Å in PNDIS
and PNDIS-HD and 4.2 Å in PNDIT are comparable with
2
and tested under AM 1.5 solar illumination at 100 mW/cm in
ambient conditions. Representative current density−voltage
(
J−V) curves of PNDIT:PSEHTT, PNDIS:PSEHTT, and
PNDIS-HD:PSEHTT solar cells are shown in Figure 2a. The
photovoltaic parameters including the short-circuit current
density (J ), the open-circuit voltage (V ), and fill factor (FF)
6
values seen in other NDI-based copolymers (∼4.0 Å).
sc
oc
Optical absorption spectra of PNDIT, PNDIS, and PNDIS-
−6
are summarized in Table 2.
HD thin films (Figure 1b) and dilute (∼10 M) CHCl3
solutions (SI, Figure S8b) show two distinctive absorption
peaks, one due to π−π* transition at 340−360 nm and the
other centered at 598−621 nm, which is a result of
intramolecular charge transfer (ICT) (Table 1). It is interesting
that the selenophene-linked polymers, PNDIS and PNDIS-HD,
have slightly smaller band gaps and a broader fwhm in the ICT
bands, which imply potentially better near-IR light harvesting
compared to the thiophene-linked PNDIT. At their visible
absorption maxima of 598−621 nm, all three NDI copolymers
4
−1
have an absorption coefficient (α) of (2.7−2.9) × 10 cm . In
5
−1
contrast, an absorption coefficient of 1.1 × 10 cm is observed
at the absorption maximum (584 nm) of the donor polymer
(
PSEHTT). The LUMO/HOMO energy levels of the NDI
Figure 2. (a) Current density (J)−voltage (V) characteristics and (b)
external quantum efficiency (EQE) spectra of all-polymer BHJ solar
cells from 1:1 w/w blend each of PSEHTT:PNDIT, PSEHTT:PNDIS,
and PSEHTT:PNDIS-HD.
7
5
copolymers along with those of PC BM and PSEHTT are
shown in Figure 1c. The LUMO energy levels of the NDI
copolymers were estimated from cyclic voltammetry (SI, Figure
6
0
B
dx.doi.org/10.1021/ja4085429 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
5b
Table 2. Photovoltaic Properties of All-polymer Solar Cells
performance is in good agreement with the previous report.
The EQE spectrum of the optimum PSEHTT:PC BM cell
6
0
active layer
1:1 w/w)
Jsc
Voc
PCEmax
(%)
2
shows the same onset of photocurrent as the above all-polymer
devices; however, the 54% maximum EQE (SI, Figure S11b) is
higher than the 47% observed for the all-polymer BHJ solar
cells. Although the EQE and the photocurrent of PC BM
(
(mA/cm ) (V)
FF
PCEavg (%)
PNDIT:PSEHTT
PNDIS:PSEHTT
3.80
6.53
7.78
0.61
0.75
0.76
0.56
0.60
0.55
1.20 ± 0.09
2.84 ± 0.15
3.16 ± 0.10
1.30
2.96
3.26
6
0
PNDIS-
HD:PSEHTT
devices are higher than those of the polymer acceptor, PNDIS-
HD, the power conversion efficiencies of BHJ solar cells using
the two types of acceptors are identical largely because of the
superior photovoltage of the all-polymer devices.
BHJ devices based on the thiophene-linked PNDIT acceptor
showed the lowest performance among the three NDI
copolymer acceptors, including a maximum 1.30% PCE and a
rather low photocurrent (Table 2). The performance of the
BHJ solar cells increased significantly by using the selenophene-
linked PNDIS acceptor; the observed maximum PCE of 2.96%
means a 2.4-fold increase compared with the PNDIT devices.
This improvement arises from the higher J of 6.53 mA/cm as
well as the increased V of 0.75 V. The best performance, with
a maximum PCE of 3.26%, J = 7.78 mA/cm , and V = 0.76 V,
was observed in PNDIS-HD:PSEHTT blend solar cells, where
the acceptor polymer has smaller hexyldecyl (HD) side chains.
The lower photovoltage of PNDIT cells compared to those of
PNDIS and PNDIS-HD is likely a result of greater charge
recombination due to their much lower carrier mobilities. The
observed FF values of 0.55−0.60 are impressively high among
all-polymer solar cells and are comparable to typical values seen
in polymer/fullerene systems. We note that both the PCE and
photocurrent observed in PNDIS-HD devices are the highest
for all-polymer solar cells reported to date.
The EQE spectra of the photovoltaic devices showed that the
photocurrent generation starts at 720 nm (Figure 2b) and are
consistent with the absorption spectra of the blends. The
PNDIS-HD:PSEHTT device shows the highest photoconver-
sion efficiency with a maximum EQE of 47% with more than
The charge transport properties of the polymer/polymer
blends (PSEHTT:PNDIT, PSEHTT:PNDIS, and
PSEHTT:PNDIS-HD) in the all-polymer solar cells were
investigated by both OFET devices and space-charge-limited
current (SCLC) measurements and are summarized in Table 3.
−4
Field-effect electron mobility in PNDIS-HD blends (1.3 × 10
2
sc
2
cm /(V s)) was slightly better than in PNDIS blends but an
oc
order of magnitude higher than in PNDIT blends. In contrast,
2
sc
oc
the field-effect hole mobility was about the same in all three
−4
2
series of blends (3.5−6.4) × 10 cm /(V s). Hole-only
devices, composed of ITO/PEDOT:PSS/blend/Au, and
electron-only devices, consisting of ITO/ZnO/blend/LiF/Al,
enabled estimation of the bulk charge transport properties of
the BHJ blend films. Electron mobility in the bulk blend film is
−4
2
also highest in the PNDIS-HD blends (1.0 × 10 cm /(V s)),
slightly lower in PNDIS blends (5.8 × 10− cm /(V s)), and a
5
2
factor of 6 lower in the PNDIT blends (1.8 × 10− cm /(V s)).
Balanced and high hole and electron mobilities are thus
observed in the PNDIS-HD blends (Table 3), which can largely
5
2
explain the highest performance in terms of J , EQE, and PCE
sc
values for the BHJ solar cells using this polymer acceptor.
AFM imaging was used to investigate the surface
morphology of the all-polymer solar cells. AFM topographic
and the corresponding phase images taken directly from the
surfaces of devices are shown in Figure 3. The observed phase
separated morphology with domain sizes of 200−500 nm is
identical in all three blend systems (PNDIT, PNDIS, and
PNDIS-HD). The similarity of the morphology of all three
different polymer/polymer BHJ devices implies that the
observed large variation in the photocurrent and PCE does
not originate in the blend morphologies. On the other hand,
the large scale of the observed phase separation in the blends
suggests that there is still room for further improvement of the
photovoltaic properties of PNDIS:PSEHTT and PNDIS-
HD:PSEHTT blends by reducing the domain sizes of the
phase separated blend morphology through strategies such as
4
5% over the 500−650 nm wavelength range. The J calculated
by integrating the EQE spectrum of the PNDIS-HD:PSEHTT
sc
2
solar cell with an AM 1.5 reference spectrum is 7.76 mA/cm ,
which is in excellent agreement with the 7.78 mA/cm2
measured directly from the J−V curve. We note that J values
sc
calculated from the EQE spectra for the PNDIS and PNDIT
devices were also within 3% of the Jsc values from J−V
measurements. The maximum EQE seen in PNDIS-HD
devices is the highest so far in all-polymer solar cells.
We also fabricated polymer/fullerene solar cells with the
PSEHTT:PC BM (1:2 w/w) active layer and the same
inverted device structure as a reference for comparison with
the polymer/polymer blend solar cells. In this case, we used the
previously reported optimized composition and processing
conditions to deposit the PSEHTT:PC BM active layer,
including the 3.0 vol % 1,8-diiodooctane (DIO) additive in o-
dichlorobenzene. From the J−V characteristics (SI, Figure
S11a) we obtained J = 8.46 mA/cm , V = 0.64 V, FF = 0.62,
60
3e,h
9
cosolvents
and processing additives.
In conclusion, two new semicrystalline NDI copolymers
(PNDIS, PNDIS-HD) and a known one (PNDIT) have been
synthesized, characterized, and, for the first time, evaluated as
acceptors in BHJ organic solar cells. We found that all-polymer
solar cells composed of a PNDIS-HD acceptor and PSEHTT
6
0
5
b
2
sc
oc
and a maximum PCE of 3.3% (average PCE 3.23 ± 0.11). This
Table 3. Charge Transport Properties of Polymer/Polymer Blends Used in All-Polymer Solar Cells
a
2
b
2
c
2
d
2
blend (1:1 w/w)
μh (cm /(V s)) (OFET)
μe (cm /(V s)) (OFET)
μh (cm /(V s)) (SCLC)
μe (cm /(V s)) (SCLC)
4.0 × 10−
3.5 × 10−
6.4 × 10−
4
1.0 × 10
−5
4.5 × 10
−5
1.8 × 10
−5
PNDIT:PSEHTT
PNDIS:PSEHTT
PNDIS-HD:PSEHTT
4
−5
−5
−5
7.5 × 10
9.6 × 10
5.8 × 10
4
−4
−4
−4
1.3 × 10
2.0 × 10
1.0 × 10
a
b
c
Average charge carrier mobility of blend from p-channel OFETs. Average charge carrier mobility of blend from n-channel OFETs. Hole mobility
d
of blend extracted from SCLC measurement using single charge carrier devices. Electron mobility of blend extracted from SCLC measurement
using single charge carrier devices.
C
dx.doi.org/10.1021/ja4085429 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX

Journal of the American Chemical Society
Communication
C. M.; Tsang, S.-W.; Lai, T.-H.; Reynolds, J. R.; So, F. Nat. Photon.
2
(
(
012, 6, 115.
3) (a) McNeill, C. R. Energy Environ. Sci. 2012, 5, 5653.
b) Facchetti, A. Mater. Today 2013, 16, 123. (c) Halls, J. J. M.;
Walsh, C. A.; Greenham, N. C.; Marseglia, E. A.; Friend, R. H.;
Moratti, S. C.; Holmes, A. B. Nature 1995, 376, 498. (d) Alam, M. M.;
Jenekhe, S. A. Chem. Mater. 2004, 16, 4647. (e) Schubert, M.; Dolfen,
D.; Frisch, J.; Roland, S.; Steyrleuthner, R.; Stiller, B.; Chen, Z.; Scherf,
U.; Koch, N.; Facchetti, A.; Neher, D. Adv. Energy Mater. 2012, 2, 369.
(
f) Jenekhe, S. A.; Yi, S. Appl. Phys. Lett. 2000, 77, 2635. (g) Zhou, E.;
Tajima, K.; Yang, C.; Hashimoto, K. J. Mater. Chem. 2010, 20, 2362.
h) Zhou, E.; Cong, J.; Wei, Q.; Tajima, K.; Yang, C.; Hashimoto, K.
Angew. Chem., Int. Ed. 2011, 50, 2799. (i) Kietzke, T.; Horhold, H.-H.;
Neher, D. Chem. Mater. 2005, 17, 6532. (j) Holcombe, T. W.; Woo, C.
H.; Kavulak, D. F. J.; Thompson, B. C.; Frechet, J. M. J. J. Am. Chem.
(
̈
́
2
Soc. 2009, 131, 14160. (k) Mori, D.; Benten, H.; Ohkita, H.; Ito, S.;
Miyake, K. ACS Appl. Mater. Interfaces 2012, 4, 3325. (l) Zhan, X.;
Tan, Z. a.; Domercq, B.; An, Z.; Zhang, X.; Barlow, S.; Li, Y.; Zhu, D.;
Kippelen, B.; Marder, S. R. J. Am. Chem. Soc. 2007, 129, 7246.
Figure 3. AFM topographical images (5 × 5 μm ) of the surfaces of
all-polymer solar cells: (a) PNDIT:PSEHTT, (b) PNDIS:PSEHTT,
and (c) PNDIS-HD:PSEHTT; and the corresponding phase images of
d) PNDIT:PSEHTT, (e) PNDIS:PSEHTT, and (f) PNDIS-
(
(
m) Zhou, E.; Cong, J.; Zhao, M.; Zhang, L.; Hashimoto, K.; Tajima,
HD:PSEHTT.
K. Chem. Commun. 2012, 48, 5283. (n) Hwang, Y.-J.; Ren, G.; Murari,
N. M.; Jenekhe, S. A. Macromolecules 2012, 45, 9056. (o) Cao, Y.; Lei,
T.; Yuan, J.; Wang, J.-Y.; Pei, J. Polym. Chem 2013, 4, 5228. (p) Moore,
J. R.; Albert-Seifried, S.; Rao, A.; Massip, S.; Watts, B.; Morgan, D. J.;
Friend, R. H.; McNeill, C. R.; Sirringhaus, H. Adv. Energy Mater. 2011,
1, 230. (q) Brenner, T. J. K.; Hwang, I.; Greenham, N. C.; McNeill, C.
R. J. Appl. Phys. 2010, 107, 114501. (r) Guo, C.; Lin, Y.-H.; Witman,
M. D.; Smith, K. A.; Wang, C.; Hexemer, A.; Strzalka, J.; Gomez, E. D.;
Verduzco, R. Nano Lett. 2013, 13, 2957.
donor have a record performance (PCE = 3.3%, J = 7.78 mA/
cm , and EQE = 47%), which is comparable to similarly
sc
2
evaluated PC BM:PSEHTT BHJ solar cells. Balanced electron
60
and hole transport was observed in the PNDIS-HD:PSEHTT
blend active layers. The superior photovoltaic properties of
3e,n
PNDIS-HD compared to PNDIS and prior NDI copolymers
suggest that unipolar electron transport with high bulk mobility,
good crystallinity, size of alkyl side chains, and molecular weight
are all important factors in the design of suitable acceptor
polymers for BHJ solar cells.
(4) (a) Anthony, J. E.; Facchetti, A.; Heeney, M.; Marder, S. R.;
Zhan, X. Adv. Mater. 2010, 22, 3876. (b) Mishra, A.; Bau
Chem., Int. Ed. 2012, 51, 2020.
5) (a) Subramaniyan, S.; Xin, H.; Kim, F. S.; Shoaee, S.; Durrant, J.
̈
erle, P. Angew.
(
R.; Jenekhe, S. A. Adv. Energy Mater. 2011, 1, 854. (b) Xin, H.;
Subramaniyan, S.; Kwon, T.-W.; Shoaee, S.; Durrant, J. R.; Jenekhe, S.
A. Chem. Mater. 2012, 24, 1995.
ASSOCIATED CONTENT
Supporting Information
Experimental procedures, NMR spectra, TGA thermograms,
UV−vis absorption spectra, cyclic voltammograms (CV), and
XRD patterns of copolymers, OFETs, PSEHTT:PC BM solar
■
*
S
(6) (a) Hwang, Y.-J.; Murari, N. M.; Jenekhe, S. A. Polym. Chem.
2013, 4, 3187. (b) Guo, X.; Kim, F. S.; Seger, M. J.; Jenekhe, S. A.;
Watson, M. D. Chem. Mater. 2012, 24, 1434.
(7) Scharber, M. C.; Mu
C.; Heeger, A. J.; Brabec, C. J. Adv. Mater. 2006, 18, 789.
8) (a) Chen, Z.; Lemke, H.; Albert-Seifried, S.; Caironi, M.; Nielsen,
̈
hlbacher, D.; Koppe, M.; Denk, P.; Waldauf,
6
0
cell, and SCLC device characteristics. This material is available
free of charge via the Internet at http://pubs.acs.org.
(
M. M.; Heeney, M.; Zhang, W.; McCulloch, I.; Sirringhaus, H. Adv.
Mater. 2010, 22, 2371. (b) Hollinger, J.; Jahnke, A. A.; Coombs, N.;
Seferos, D. S. J. Am. Chem. Soc. 2010, 132, 8546.
AUTHOR INFORMATION
Corresponding Author
jenekhe@u.washington.edu
■
(9) Ren, G.; Ahmed, E.; Jenekhe, S. A. Adv. Energy Mater. 2011, 1,
9
46.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This paper is based on work (Excitonic Solar Cells) supported
by the U.S. Department of Energy, Office of Basic Energy
Sciences, Division of Materials Sciences, under Award
DEFG02-07ER46467. The synthesis, characterization, and
charge transport properties of the n-type copolymers were
supported by the Office of Naval Research (ONR) (N00014-
11-1-0317) and the NSF (DMR-1035196).
REFERENCES
■
(
1
1) (a) Gu
07, 1324. (b) Thompson, B. C.; Frec
Ed. 2008, 47, 58. (c) Li, G.; Zhu, R.; Yang, Y. Nat. Photon. 2012, 6,
53.
2) (a) You, J.; Dou, L.; Yoshimura, K.; Kato, T.; Ohya, K.; Moriarty,
T.; Emery, K.; Chen, C.-C.; Gao, J.; Li, G.; Yang, Y. Nat. Commun.
013, 4, 1446. (b) He, Z.; Zhong, C.; Su, S.; Xu, M.; Wu, H.; Cao, Y.
Nat. Photon. 2012, 6, 591. (c) Small, C. E.; Chen, S.; Subbiah, J.; Amb,
̈
nes, S.; Neugebauer, H.; Sariciftci, N. S. Chem. Rev. 2007,
́
het, J. M. J. Angew. Chem., Int.
1
(
2
D
dx.doi.org/10.1021/ja4085429 | J. Am. Chem. Soc. XXXX, XXX, XXX−XXX