A distorted lactam unit with intramolecular hydrogen bonds as the electron donor of polymer solar cells

Article abstract of DOI:10.1039/c9tc04014e

A novel distorted lactam motif, namely 4,4′-dialkyl-[6,6′-bithieno[3,2-b]pyridine]-5,5′(4H,4′H)-dione (BTP), could lock itself by intramolecular hydrogen bonds. In view of the potential of the motif, two D-A conjugated polymers, PBDT-BTP-HD and PBDT-BTP-OD, with two different long side chains consisting of 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene (BDT) as a donor unit and BTP as an acceptor unit were designed and synthesized. Furthermore, the photophysical, electrochemical and photovoltaic properties of both polymers were investigated. The morphologies and molecular ordering of the neat polymers and blend films were also probed to relate the side chain structures with aggregation states and device parameters. The device based on PBDT-BTP-OD with IT-M exhibited a power conversion efficiency of up to 9.54% thanks to the synergistic effect of the building blocks and side-chain engineering. As a result, it is successfully demonstrated that the novel distorted lactam BTP is a promising building block in organic solar cells.

Full text of DOI:10.1039/c9tc04014e

Journal of
Materials Chemistry C
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A distorted lactam unit with intramolecular hydrogen
bonds as the electron donor of polymer solar cells†
Cite this: J. Mater. Chem. C, 2019,
7, 12290
Hua-Chun Wang,a Minrun Ren,b Jian Cao,a Hong-Bo Yin,a Guichuan Zhang,b
b
a
Jingyang Xiao,b Xiancheng Ren,a Hin-Lap Yip
and Yun-Xiang Xu
*
A
novel distorted lactam motif, namely 4,40-dialkyl-[6,60-bithieno[3,2-b]pyridine]-5,50(4H,40H)-dione
(BTP), could lock itself by intramolecular hydrogen bonds. In view of the potential of the motif, two D–A
conjugated polymers, PBDT-BTP-HD and PBDT-BTP-OD, with two different long side chains consisting
of 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b0]dithiophene (BDT) as a donor unit and BTP
as an acceptor unit were designed and synthesized. Furthermore, the photophysical, electrochemical
and photovoltaic properties of both polymers were investigated. The morphologies and molecular
ordering of the neat polymers and blend films were also probed to relate the side chain structures with
aggregation states and device parameters. The device based on PBDT-BTP-OD with IT-M exhibited a
power conversion efficiency of up to 9.54% thanks to the synergistic effect of the building blocks and
side-chain engineering. As a result, it is successfully demonstrated that the novel distorted lactam BTP is
a promising building block in organic solar cells.
Received 23rd July 2019,
Accepted 17th September 2019
DOI: 10.1039/c9tc04014e
rsc.li/materials-c
Introduction
Bulk heterojunction polymer solar cells (PSCs) consisting of
electron donors and electron acceptors have drawn consider-
able interest due to their unique features, including flexibility,
large-area fabrication, low cost and light weight.1–12 At present, the
power conversion efficiencies (PCEs) based on non-fullerene
single-junction PSCs have exceeded 15%, which is benefited from
Scheme 1 Chemical structure of IID, DTP, DPP and BTP.
the optimization of the device structure and the development of backbone.21–28 Nevertheless, the highly planar building blocks often
active layer materials, especially non-fullerene small molecular lead to excessive aggregation when the film is formed, which is not
acceptor materials.13–17 To match well with non-fullerene conducive to obtaining an optimized phase morphology for
acceptors with strong absorption from 600 to 800 nm, it is very PSCs.29,30 On the other side, an extensively distorted skeleton also
essential to design highly efficient wide bandgap polymer leads to poor device performance due to insufficient intramolecular
donors with suitable energy levels.7,18–20
charge transport properties.31–33 As a balance, a rigid distorted
Among the high-performance polymer donors, lactam skeletons, skeleton with a certain dihedral angle may be a desirable motif to
such as isoindigo (IID), dithieno[3,2-b:20,30d]pyridin-5(4H)-one (DTP) achieve appropriate polymer chain conformation and aggregation
and diketopyrrolopyrrole (DPP) (Scheme 1), have been considered as states.34,35 Traditionally, DPP lactam units are propitious to
some of the most versatile and promising building blocks due to diminish the degree of conformational rotation due to the
their strong electron-withdrawing properties and excellent planar intramolecular hydrogen bonds leading to increased planarity
and conjugation.36,37 If a similar intramolecular locking could
be introduced into the distorted lactam units, the desired motif
would be harvested. Herein, an isomer of DPP was designed
with two six-membered rings connected, named 4,40-dialkyl-
a College of Polymer Science & Engineering, State Key Laboratory of Polymer
Materials Engineering, Sichuan University, Chengdu 610065, China.
E-mail: yxxu@scu.edu.cn
b State Key Laboratory of Luminescent Materials and Devices, School of Materials
Science and Engineering, South China University of Technology,
Guangzhou 510640, China
[6,60-bithieno[3,2-b]pyridine]-5,50(4H,40H)-dione (BTP) (Scheme 1).
This new lactam motif is supposed to lock itself by intramolecular
hydrogen bonds but with a distorted angle due to the steric
hindrance of the increased ring size.
Besides, in ordinary organic solvents, the solubility of the
conjugated polymers based on lactam skeletons can be well
† Electronic supplementary information (ESI) available: Details of the experimental
section, device fabrication and characterization, carrier mobility measurements, and
other figures and tables. CCDC 1941412. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c9tc04014e
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regulated by incorporating alkyl side chains at the N-atom by condensation reaction between succinyl dichloride and
position.38,39 Further selection of the optimum side chains N-alkylthiophen-3-amine. Subsequently, the intermediate amides
could slightly adjust the frontier molecular orbital energy levels of were cyclized using the Vilsmeier reagent to afford the desired
the organic semiconductors, regulate the intermolecular packing products BTP in good yields. The synthesis of key comonomers
and optimize the blend film morphology.38,40–42 Consequently, great BTP-T-HD-diBr and BTP-T-OD-diBr consisted of three steps,
efforts have been devoted to developing a high-performance including bromination of intermediate BTPs, coupling with
conjugated polymer by side-chain engineering.40,43–45 Specifically, 2-tributylstannyl-thiophene and bromination of the products
the length of the alkyl side chains plays a critical role in boosting the again. Finally, the alternating polymers PBDT-BTP-HD and
optoelectronic properties of the organic semiconductors.40,43,46 It PBDT-BTP-OD were gained by copolymerizing lactam monomers
would be critical to attach specific alkyl side chains on newly with 2,6-bis(trimethytin)-4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo-
designed lactam units to provide the solubility and form appropriate [1,2-b:4,5-b0]dithiophene (BDT-diTin) using Pd2(dba)3 and P(o-tol)3
morphology resulting in optimum device performance in PSCs.
as catalysts. The resulting polymers had good solubility in
In this work, a novel distorted lactam unit BTP was designed chlorinated solvents, such as chloroform (CHCl3), chlorobenzene
and synthesized with intramolecular hydrogen bonds proved by (CB) and dichlorobenzene (DCB). The number-average molecular
single-crystal analysis. In addition, BTP allowed for introducing weight (Mn) of PBDT-BTP-HD and PBDT-BTP-OD was 7.05 and
alkyl side chains of different lengths at the N-atom position. 7.85 kDa with a polydispersity index (PDI) of 3.33 and 2.93,
Based on the above advantages of BTP, two D–A conjugated respectively, evaluated by high-temperature gel permeation chroma-
polymers PBDT-BTP-HD and PBDT-BTP-OD with two different long tography at 150 1C by using 1,2,4-trichorobenzene as the eluent and
side chains using 4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2- linear polystyrene as the reference.
b:4,5-b0]dithiophene (BDT) as the donor unit and BTP as the
Thermogravimetric analysis (TGA) and differential scanning
acceptor unit were prepared. Furthermore, the photophysical, calorimetry (DSC) were used to investigate the thermal properties
electrochemical and photovoltaic properties of both polymers of PBDT-BTP-HD and PBDT-BTP-OD. The resulting curves are
were investigated to reveal the potential of BTP as a building shown in Fig. S1, ESI.† Both the polymers presented good
block in PSCs.
thermal stability and the thermal decomposition temperatures
(Td, 5% weight loss) were over 390 1C, which was sufficient for
application in polymer solar cells. There were no obvious thermal
transitions during heating up to 250 1C, which implied that
PBDT-BTP-HD and PBDT-BTP-OD possessed amorphous nature.
The analysis of single crystal X-ray diffraction (XRD) was
Results and discussion
The detailed synthetic route of monomers and polymers is
shown in Scheme 2. The intermediate amides were obtained performed to obtain insight into the conformation of lactam
Scheme 2 The synthetic route of PBDT-BTP-HD and PBDT-BTP-OD.
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which is far greater than that in the DPP-diBr single crystal
(3.320 Å), indicating that the p–p interaction is weaker in
BTP-diBr than in DPP-diBr.
The UV-vis absorption spectra of PBDT-BTP-HD and PBDT-
BTP-OD in CB solution at different temperatures are depicted
in Fig. 2a and b. As the temperature of the polymer solution
increased from 25 to 95 1C, the absorption strength of the
shoulder peak gradually weakened. The phenomenon could be
ascribed to the dissociation of intermolecular aggregation or
the weakening of the polymer backbone coplanarity. To clarify
this phenomenon, the dependence of absorbance with con-
centration was measured for PBDT-BTP-HD and PBDT-BTP-OD
at 583 nm. The results showed a linear relationship between
absorbance and concentration (Fig. S3a, ESI†), indicating
Fig. 1 (a) Single crystal structure and (b) molecular stacking structure of
BTP-diBr. C (grey), H (white), O (red), N (blue), S (yellow), Br (brown). Hꢀ ꢀ ꢀO
and p–p distance are marked and the unit is Å. Free solvent is hidden to
provide an unobstructed view of BTP-diBr.
unit BTP. Single crystals of the hexyl-substituted BTP-diBr were that no intermolecular aggregation occurred in the diluted CB
gained by the slow diffusion of methanol into the chloroform solution. Therefore, it is speculated that both the polymers
solution. The molecular stacking of BTP-diBr is shown in Fig. 1, possessed strong intramolecular hydrogen bonds in CB solution
and the crystallographic data are listed in Table S2 (CDCC at low temperatures. With the elevation of the temperature, the
1941412) (ESI†). The monoclinic crystal structure with space intramolecular hydrogen bonds were gradually weakened and
group P21/c was displayed in the single crystal of BTP-diBr. The the coplanarity of the backbone was reduced. Therefore, the
backbone of BTP-diBr shows non-planar conformation with the shoulder peak was diminished. Compared with the polymer
torsional angle (37.311) in favour of weakening intermolecular solution, the films showed slightly red-shifted absorption peaks
aggregation. There are two types of intramolecular hydrogen (Fig. 2c), demonstrating that further intermolecular aggregation
bonds (Hꢀ ꢀ ꢀO) observed and the Hꢀ ꢀ ꢀO bond distances are 2.350 occurred. Notably, the annealed films of both the polymers
and 2.369 Å, respectively. Therefore, BTP-diBr possessed a rigid showed lowered shoulder peaks (Fig. S3b, ESI†) compared to the
and distorted conformation. In contrast, DPP-diBr displays a unannealed one, which was probably originated from the
quasi-planar structure with the torsional angle of 6.971 (CCDC weakening of intramolecular hydrogen bonding. According to
1020305, see Fig. S2 in ESI†).47 Furthermore, intermolecular the calculation results (Fig. 3), the dihedral angles among the
p–p stacking occurs for the half-unit of BTP-diBr owing to the units are below 251, much lower than the values observed in the
non-planar structure. And the p–p stacking distance is 3.529 Å single crystal. It is possible that the packing of polymer chains
Fig. 2 (a and b) Temperature dependent UV-vis absorption spectra of PBDT-BTP-HD and PBDT-BTP-OD in chloorobenzene solution; (c) UV-vis film
absorption spectra, (d) energy level diagram and (e) chemical structure of PBDT-BTP-HD, PBDT-BTP-OD and IT-M.
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Fig. 4 (a) The J–V curves of the PSCs based on PBDT-BTP-HD:IT-M
and PBDT-BTP-OD:IT-M and (b) the EQE spectra of the corresponding
PSCs.
and PBDT-BTP-OD films displayed the diffraction peaks at
2y = 24.401 and 24.281 before annealing corresponding to p–p
stacking distance of 3.645 and 3.663 Å, respectively. The results
implied that PBDT-BTP-HD with a short side chain had more
compact stacking, which might lead to a higher hole mobility.
Fig. 3 Optimized molecular conformations and energy levels of polymer
calculated by DFT at the B3LYP/6-31G* level.
will force the lactam unit to rotate into a larger dihedral angle, After annealing, the PBDT-BTP-HD and PBDT-BTP-OD films
thus resulting in lower conjugation in the solid state. It is also presented a smaller p–p stacking distance of 3.639 and 3.660 Å
encouraging that both the polymers possessed complementary (2y = 24.441 and 24.301), which implied that annealing was
absorption with the electron acceptor, IT-M (Fig. 2c and Fig. S4a, conducive to polymer stacking.
ESI†), which is beneficial for the light absorption of devices. The
key optical parameters are summarized in Table 1.
To evaluate the photovoltaic properties of PBDT-BTP-HD
and PBDT-BTP-OD as donor materials in BHJ polymer solar cells,
The molecular energy levels were measured by using the the devices were fabricated with the inverted configuration indium
cyclic voltammetry (CV) method. The CV curves of PBDT-BTP- tin oxide (ITO)/ZnO/donor polymer:IT-M/MoO3/Ag. The current
HD and PBDT-BTP-OD are shown in Fig. S4b, ESI.† The density–voltage (J–V) curves of the PSCs were measured under
corresponding highest occupied molecular orbital (HOMO) simulated AM 1.5G illumination at 100 mW cmꢁ2 and shown in
and the lowest unoccupied molecular orbital (LUMO) energy Fig. 4a and associated data of the PSCs are presented in Table 2.
levels of PBDT-BTP-HD and PBDT-BTP-OD were ꢁ5.22/ꢁ3.03 The optimized conditions of device fabrication are summarized in
and ꢁ5.30/ꢁ3.05 eV, respectively. The LUMO levels remain similar Tables S3–S5 (ESI†). The maximum PCE for PBDT-BTP-HD and
but the HOMO levels tend to decrease as the length of the side PBDT-BTP-OD devices was obtained by adding 1% (v/v) 1,8-diiodo-
chains increases. This suggests that the steric hindrance of the octane (DIO) as additive followed by a thermal annealing at
longer side chains led to looser packing and reduced electronic 120 1C and 140 1C for 10 min, respectively. The PSC based on
coupling between the polymer backbones. The HOMO/LUMO PBDT-BTP-HD : IT-M (1 : 1, w/w) showed an impressive PCE of
levels of both polymers matched well with IT-M for PSCs. The 9.47%, with an open-circuit voltage (Voc) of 0.89 V, a short-
electrochemical band gaps of PBDT-BTP-HD and PBDT-BTP-OD circuit current density ( Jsc) of 14.82 mA cmꢁ2, and a fill factor
were estimated to be 2.19 and 2.25 eV (Table 1) respectively, which (FF) of 71.78%. Besides, the device based on PBDT-BTP-OD :
was consistent with their optical bandgaps. Density functional IT-M (1 : 1.5, w/w) generated a comparable PCE of 9.54%, with
theory (DFT) calculation at the B3LYP/6-31G* level was performed slightly enhanced Voc of 0.91 V and FF of 72.66%, and
to obtain optimized geometries and energy levels of three repetitive decreased Jsc of 14.38 mA cmꢁ2. The improved Voc value
units of polymer. As shown in Fig. 3, both HOMO and LUMO originated from the lower-lying HOMO energy level of PBDT-
orbitals were reasonably delocalized along the polymer backbone BTP-OD and the diminished Jsc might be attributed to weaker
in the optimal geometries. The calculated HOMO and LUMO absorbance of PBDT-BTP-OD. The PSC devices based on PBDT-
energy levels of the polymer are ꢁ4.74 and ꢁ2.54 eV, which agrees BTP-HD:IT-M and PBDT-BTP-OD:IT-M exhibited
a broad
with the trend of the cyclic voltammetry test. response from 300 to 800 nm because of good complementary
The X-ray diffraction (XRD) analysis was carried out to study absorption. The external quantum efficiency (EQE) measure-
the stacking in PBDT-BTP-HD and PBDT-BTP-OD films before ments were used to verify the Jsc values and are shown in Fig. 4b
and after annealing. As shown in Fig. S5 (ESI†), PBDT-BTP-HD and Fig. S6, ESI.† The calculated Jsc values ( Jcal) by integration of
Table 1 Optical and electrochemical properties of PBDT-BTP-HD and PBDT-BTP-OD
Polymer
lmax,solution (nm)
esolution (Mꢁ1 cmꢁ1
)
lmax,film (nm)
ledge (nm)
Eogpt (eV)
EHOMO (eV)
ELUMO (eV)
Ecgv (eV)
PBDT-BTP-HD
PBDT-BTP-OD
554, 583
551, 584
5.4 ꢂ 104
558, 586
555, 587
652
645
1.90
1.92
ꢁ5.22
ꢁ5.30
ꢁ3.03
ꢁ3.05
2.19
2.25
4.5 ꢂ 104
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Table 2 Device parameters of the PSCs based on PBDT-BTP-HD:IT-M and PBDT-BTP-OD:IT-M
Jsc (mA cmꢁ2
)
Jcal (mA cmꢁ2
)
FF (%)
PCEmax (PCEave
)
(%)
a
b
Active layer
Voc (V)
PBDT-BTP-HD:IT-M
PBDT-BTP-OD:IT-M
0.89
0.91
14.82
14.38
14.09
13.56
71.78
72.66
9.47 (9.18 ꢃ 0.20)
9.54 (9.25 ꢃ 0.17)
a
b
The Jcal values were determined from the integration of the related EQE curves. The average PCE was obtained from at least 10 devices.
Fig. 5 Photoluminescence spectra for (a) PBDT-BTP-HD and blend films excited at 555 nm; (b) PBDT-BTP-OD and blend films excited at 555 nm;
(c) IT-M and blend films excited at 705 nm.
The hole and electron mobility (mh and me) of the active layers
were measured through the space charge limited current (SCLC)
method, and the related charts are depicted in Fig. S7 and Table
S6, ESI.† The blend films of PBDT-BTP-HD:IT-M exhibited higher
hole mobility (7.67 ꢂ 10ꢁ4 cm2 Vꢁ1 sꢁ1) than those of the PBDT-
BTP-OD:IT-M films (7.30 ꢂ 10ꢁ4 cm2 Vꢁ1
s
ꢁ1), but the former
presented lower electron mobility (1.12 ꢂ 10ꢁ4 cm2 Vꢁ1 sꢁ1) than
the latter (5.42 ꢂ 10ꢁ4 cm2 Vꢁ1
s
ꢁ1). As a result, the mh/me ratio
based on the PBDT-BTP-OD:IT-M film (1.35) was more balanced
than that of the PBDT-BTP-HD:IT-M film (6.85), which could be
responsible for the higher FF (72.66%) of related devices.
The morphologies of the active layers were investigated by
using an atomic force microscope (AFM). As shown in Fig. 6,
the PBDT-BTP-OD:IT-M film appeared with a slightly smoother
surface with the root mean square (RMS) roughness of 2.30 nm
compared with the PBDT-BTP-HD:IT-M film (RMS = 2.48 nm).
The higher roughness could be derived from a more compact
stacking of the PBDT-BTP-HD film as proved in the XRD
pattern. The molecular orientation and packing of the pristine
and blend films were investigated through grazing incidence
wide-angle X-ray scattering (GIWAXS) measurements. The
Fig. 6 AFM height (left) and phase (right) images of (a and b) PBDT-BTP-
HD:IT-M and (c and d) PBDT-BTP-OD:IT-M blend films with DIO as additive.
the EQE curves were in good agreement with those obtained GIWAXS patterns and their corresponding line-cut profiles are
from the J–V measurements. shown in Fig. 7 and Fig. S8 (ESI†), respectively. PBDT-BTP-HD
The exciton dissociation and charge transfer in the active and PBDT-BTP-OD pristine films showed an obvious p–p stacking
layers were estimated by photoluminescence (PL) quenching peak (010) at 1.68 and 1.66 Åꢁ1 (3.74 and 3.79 Å) along the out-of-
experiments. As illustrated in Fig. 5, the emissions for PBDT- plane direction, which indicated that the neat polymer films took
BTP-HD:IT-M and PBDT-BTP-OD:IT-M were highly quenched face-on orientation. IT-M was also inclined to adopt face-on
when excited at 555 nm, revealing an effective electron transfer orientation. While in the blend films, PBDT-BTP-OD:IT-M still
from polymers to acceptors. The emission quenching for the maintained face-on orientation which was in favour of vertical
PBDT-BTP-HD:IT-M film was more notable than that of the charge transport, resulting in a more balanced carrier mobility
PBDT-BTP-OD:IT-M film when excited at 705 nm. The results and a higher FF. In comparison, the PBDT-BTP-HD:IT-M blend
suggested that devices based on PBDT-BTP-HD:IT-M could film showed mixed face-on and edge-on orientation, which
form more efficient charge separation, which agreed well with explains the inferior balance of hole and electron transport and
higher Jsc in the related PSCs.
lower FF value.
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Fig. 7 The GIWAXS patterns of (a) PBDT-BTP-HD; (b) PBDT-BTP-OD; (c) IT-M; (d) PBDT-BTP-HD:IT-M and (e) PBDT-BTP-OD:IT-M.
3 L. Meng, Y. Zhang, X. Wan, C. Li, X. Zhang, Y. Wang, X. Ke,
Z. Xiao, L. Ding, R. Xia, H.-L. Yip, Y. Cao and Y. Chen,
Science, 2018, 361, 1094–1098.
4 P. Cheng, G. Li, X. Zhan and Y. Yang, Nat. Photonics, 2018,
Conclusions
A novel distorted lactam skeleton BTP with intramolecular
Hꢀ ꢀ ꢀO interactions was synthesized and characterized. Two
conjugated polymers PBDT-BTP-HD and PBDT-BTP-OD, composed
12, 131–142.
of BDT as a donor unit and BTP as an acceptor unit, were
¨
5 J. Hou, O. Inganas, R. H. Friend and F. Gao, Nat. Mater.,
developed with two different long side chains. PBDT-BTP-OD
exhibited a deeper HOMO level and more balanced carrier
mobility than PBDT-BTP-HD, but the latter exhibited a higher
absorption coefficient and more compact stacking than the
former. Taking the above factors, both the polymers demon-
strated comparable PCEs. As a result, the non-fullerene PSCs
based on PBDT-BTP-OD with IT-M showed power conversion
efficiency of up to 9.54% benefitting from side-chain engineering.
Thus, it is strongly believed that the novel distorted lactam BTP is
a promising skeleton in organic solar cells.
2018, 17, 119.
6 C. Yan, S. Barlow, Z. Wang, H. Yan, A. K. Y. Jen, S. R. Marder
and X. Zhan, Nat. Rev. Mater., 2018, 3, 18003.
7 K. Feng, J. Yuan, Z. Bi, W. Ma, X. Xu, G. Zhang and Q. Peng,
iScience, 2019, 12, 1–12.
8 G. Zhang, J. Zhao, P. C. Y. Chow, K. Jiang, J. Zhang, Z. Zhu,
J. Zhang, F. Huang and H. Yan, Chem. Rev., 2018, 118, 3447–3507.
9 B. Kan, H. Feng, H. Yao, M. Chang, X. Wan, C. Li, J. Hou and
Y. Chen, Sci. China: Chem., 2018, 61, 1307–1313.
10 H. Zhang, H. Yao, J. Hou, J. Zhu, J. Zhang, W. Li, R. Yu,
B. Gao, S. Zhang and J. Hou, Adv. Mater., 2018, 30, 1800613.
11 H. Yao, Y. Cui, D. Qian, C. S. Ponseca, Jr., A. Honarfar, Y. Xu,
J. Xin, Z. Chen, L. Hong, B. Gao, R. Yu, Y. Zu, W. Ma,
P. Chabera, T. Pullerits, A. Yartsev, F. Gao and J. Hou, J. Am.
Chem. Soc., 2019, 141, 7743–7750.
Conflicts of interest
There are no conflicts to declare.
12 J. Yuan, Y. Zhang, L. Zhou, C. Zhang, T. K. Lau, G. Zhang, X. Lu,
H. L. Yip, S. K. So, S. Beaupre, M. Mainville, P. A. Johnson,
M. Leclerc, H. Chen, H. Peng, Y. Li and Y. Zou, Adv. Mater., 2019,
31, 1807577.
13 B. B. Fan, D. F. Zhang, M. J. Li, W. K. Zhong, Z. M. Y. Zeng,
L. Ying, F. Huang and Y. Cao, Sci. China: Chem., 2019, 62,
746–752.
Acknowledgements
Y.-X. X. acknowledges the financial support from the National
Natural Science Foundation of China (51403135) and Sichuan
Science and Technology Program (Grant No. 2019YJ0123).
14 Y. Cui, H. Yao, L. Hong, T. Zhang, Y. Xu, K. Xian, B. Gao, J. Qin,
J. Zhang, Z. Wei and J. Hou, Adv. Mater., 2019, 31, 1808356.
15 J. Yuan, Y. Zhang, L. Zhou, G. Zhang, H.-L. Yip, T.-K. Lau,
X. Lu, C. Zhu, H. Peng, P. A. Johnson, M. Leclerc, Y. Cao,
J. Ulanski, Y. Li and Y. Zou, Joule, 2019, 3, 1140–1151.
Notes and references
1 G. Yu, J. Gao, J. C. Hummelen, F. Wudl and A. J. Heeger,
Science, 1995, 270, 1789.
2 Z. Xiao, X. Jia and L. Ding, Sci. Bull., 2017, 62, 1562–1564.
This journal is ©The Royal Society of Chemistry 2019
J. Mater. Chem. C, 2019, 7, 12290--12296 | 12295

View Article Online
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Paper
16 Y. Cui, H. Yao, J. Zhang, T. Zhang, Y. Wang, L. Hong, K. Xian, 32 Y. Qin, S. Liu, H. Gu, W. Dai and X. Luo, Sol. Energy, 2018,
B. Xu, S. Zhang, J. Peng, Z. Wei, F. Gao and J. Hou, Nat.
Commun., 2019, 10, 2515.
17 X. Xu, K. Feng, Z. Bi, W. Ma, G. Zhang and Q. Peng, Adv.
Mater., 2019, 31, 1901872.
166, 450–457.
33 S. Ko, E. T. Hoke, L. Pandey, S. Hong, R. Mondal, C. Risko,
Y. Yi, R. Noriega, M. D. McGehee, J. L. Bredas, A. Salleo and
Z. Bao, J. Am. Chem. Soc., 2012, 134, 5222–5232.
18 D. Liu, B. Yang, B. Jang, B. Xu, S. Zhang, C. He, H. Y. Woo 34 H. Li, Y. J. Hwang, B. A. Courtright, F. N. Eberle, S. Subramaniyan
and J. Hou, Energy Environ. Sci., 2017, 10, 546–551. and S. A. Jenekhe, Adv. Mater., 2015, 27, 3266–3272.
19 S. Li, L. Ye, W. Zhao, H. Yan, B. Yang, D. Liu, W. Li, H. Ade 35 D. Meng, H. Fu, C. Xiao, X. Meng, T. Winands, W. Ma,
and J. Hou, J. Am. Chem. Soc., 2018, 140, 7159–7167.
20 S. Zhang, Y. Qin, J. Zhu and J. Hou, Adv. Mater., 2018,
30, 1800868.
21 Y. Deng, J. Liu, J. Wang, L. Liu, W. Li, H. Tian, X. Zhang,
Z. Xie, Y. Geng and F. Wang, Adv. Mater., 2014, 26, 471–476.
W. Wei, B. Fan, L. Huo, N. L. Doltsinis, Y. Li, Y. Sun and
Z. Wang, J. Am. Chem. Soc., 2016, 138, 10184–10190.
36 L. Dou, J. Gao, E. Richard, J. You, C. C. Chen, K. C. Cha,
Y. He, G. Li and Y. Yang, J. Am. Chem. Soc., 2012, 134,
10071–10079.
22 W. Yue, R. S. Ashraf, C. B. Nielsen, E. Collado-Fregoso, 37 L. Dou, W. H. Chang, J. Gao, C. C. Chen, J. You and Y. Yang,
M. R. Niazi, S. A. Yousaf, M. Kirkus, H. Y. Chen, A. Amassian, Adv. Mater., 2013, 25, 825–831.
J. R. Durrant and I. McCulloch, Adv. Mater., 2015, 27, 4702–4707. 38 W. Li, K. H. Hendriks, A. Furlan, W. S. Roelofs, S. C. Meskers,
23 X. Song, N. Gasparini, M. M. Nahid, S. H. K. Paleti, C. Li, W. Li,
H. Ade and D. Baran, Adv. Funct. Mater., 2019, 29, 1902441.
24 M. An, F. Xie, X. Geng, J. Zhang, J. Jiang, Z. Lei, D. He,
Z. Xiao and L. Ding, Adv. Energy Mater., 2017, 7, 1602509.
M. M. Wienk and R. A. Janssen, Adv. Mater., 2014, 26, 1565–1570.
39 W. S. Yoon, D. W. Kim, J.-M. Park, I. Cho, O. K. Kwon,
D. R. Whang, J. H. Kim, J.-H. Park and S. Y. Park, Macro-
molecules, 2016, 49, 8489–8497.
25 D. Li, Z. Xiao, S. Z. Wang, X. J. Geng, S. F. Yang, J. F. Fang, 40 J. Shin, G. E. Park, D. H. Lee, H. A. Um, T. W. Lee, M. J. Cho and
H. Yang and L. M. Ding, Adv. Energy Mater., 2018, 8, 1800397. D. H. Choi, ACS Appl. Mater. Interfaces, 2015, 7, 3280–3288.
26 A. M. Schneider, L. Lu, E. F. Manley, T. Zheng, V. Sharapov, 41 Z.-G. Zhang and Y. Li, Sci. China: Chem., 2014, 58, 192–209.
T. Xu, T. J. Marks, L. X. Chen and L. Yu, Chem. Sci., 2015, 6, 42 L. Yang, H. Zhou and W. You, J. Phys. Chem. C, 2010, 114,
4860–4866.
16793–16800.
27 W. Li, K. H. Hendriks, M. M. Wienk and R. A. Janssen, Acc. 43 I. Meager, R. S. Ashraf, S. Mollinger, B. C. Schroeder,
Chem. Res., 2016, 49, 78–85.
28 H.-C. Wang, J. Tao, W.-Y. Bai, Z.-Y. Xie, H. Li, X. Ren and
Y.-X. Xu, Eur. J. Org. Chem., 2018, 1218–1223.
H. Bronstein, D. Beatrup, M. S. Vezie, T. Kirchartz,
A. Salleo, J. Nelson and I. McCulloch, J. Am. Chem. Soc.,
2013, 135, 11537–11540.
29 P. E. Hartnett, A. Timalsina, H. S. Matte, N. Zhou, X. Guo, 44 L. Lu, T. Zheng, Q. Wu, A. M. Schneider, D. Zhao and L. Yu,
W. Zhao, A. Facchetti, R. P. Chang, M. C. Hersam, M. R. Chem. Rev., 2015, 115, 12666–12731.
Wasielewski and T. J. Marks, J. Am. Chem. Soc., 2014, 136, 45 S. Nishinaga, H. Mori and Y. Nishihara, Macromolecules,
16345–16356. 2015, 48, 2875–2885.
30 W. Wu, G. Zhang, X. Xu, S. Wang, Y. Li and Q. Peng, Adv. 46 X. Sun, Z. Zhang, R. Hou, M. Huang, B. Zhao and S. Tan,
Funct. Mater., 2018, 28, 1707493. Dyes Pigm., 2017, 139, 403–411.
31 Y. Duan, X. Xu, H. Yan, W. Wu, Z. Li and Q. Peng, Adv. 47 J. Roth-Barton and J. M. White, CCDC 1020305: Experimental
Mater., 2017, 29, 1605115.
Crystal Structure Determination, 2014, DOI: 10.5517/cc137q24.
12296 | J. Mater. Chem. C, 2019, 7, 12290--12296
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