High-Performance Ambipolar Polymers Based on Electron-Withdrawing Group Substituted Bay-Annulated Indigo

Article abstract of DOI:10.1002/adfm.201804839

For donor–acceptor conjugated polymers, it is an effective strategy to improve their electron mobilities by introducing electron-withdrawing groups (EWGs, such as F, Cl, or CF₃) into the polymer backbone. However, the introduction of different EWGs always requires a different synthetic approach, leading to additional arduous work. Here, an effective two-step method is developed to obtain EWG substituted bay-annulated indigo (BAI) units. This method is effective to introduce various EWGs (F, Cl, or CF₃) into BAI at different substituted positions. Based on this method, EWG substituted BAI acceptors, including 2FBAI, 2ClBAI, and 2CF₃BAI, are reported for the first time. Furthermore, four polymers of PBAI-V, P2FBAI-V, P2ClBAI-V, and P4OBAI-V are developed. All the polymers show ambipolar transport properties. Particularly, P2ClBAI-V exhibits remarkable hole and electron mobilities of 4.04 and 1.46 cm² V^?1 s^?1, respectively. These mobilities are among the highest values for BAI-based polymers.

Full text of DOI:10.1002/adfm.201804839

FULL PAPER
Polymeric Semiconductors
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High-Performance Ambipolar Polymers Based
on Electron-Withdrawing Group Substituted
Bay-Annulated Indigo
Jie Yang, Yaqian Jiang, Zeyi Tu, Zhiyuan Zhao, Jinyang Chen, Zhengran Yi,
Yifan Li, Shuai Wang,* Yuanping Yi,* Yunlong Guo,* and Yunqi Liu*
the field of low-cost, flexible, and printed
optoelectronic devices such as organic
photovoltaics (OPVs)[1] and organic field-
effect transistors (OFETs).[2] Currently,
the most effective synthetic strategy for
high-performance polymers is to design
donor–acceptor (D–A) molecular struc-
tures.[3] There is extensive literature of
high-performance p-type D–A polymers
based on the well-known units such as
diketopyrrolopyrrole (DPP),[4,5] isoindigo
(IID),[6] and benzothiadiazole (BTZ).[7] In
contrast, the development of ambipolar
polymers lags behind that of p-type coun-
terparts due to the lack of strong electron-
withdrawing units.[8,9] However, ambipolar
polymers are of great significance for real-
izing several important electronic devices,
such as complementary metal–oxide–
semiconductor (CMOS)-like logic circuits
For donor–acceptor conjugated polymers, it is an effective strategy to
improve their electron mobilities by introducing electron-withdrawing groups
(EWGs, such as F, Cl, or CF3) into the polymer backbone. However, the
introduction of different EWGs always requires a different synthetic approach,
leading to additional arduous work. Here, an effective two-step method
is developed to obtain EWG substituted bay-annulated indigo (BAI) units.
This method is effective to introduce various EWGs (F, Cl, or CF3) into BAI
at different substituted positions. Based on this method, EWG substituted
BAI acceptors, including 2FBAI, 2ClBAI, and 2CF3BAI, are reported for the
first time. Furthermore, four polymers of PBAI-V, P2FBAI-V, P2ClBAI-V,
and P4OBAI-V are developed. All the polymers show ambipolar transport
properties. Particularly, P2ClBAI-V exhibits remarkable hole and electron
mobilities of 4.04 and 1.46 cm2 V−1 s−1, respectively. These mobilities are
among the highest values for BAI-based polymers.
and light-emitting field-effect transistors (LFETs).[2,10]
1. Introduction
Most of reported ambipolar or n-type polymers are based
on strong electron-withdrawing units such as naphthalenedi-
imide (NDI)[3] or benzodifurandione-based oligo(p-phenylene
vinylene) (BDOPV).[6] Introducing EWGs into the polymer back-
bone is an effective strategy to improve the electron mobilities
(µe) of the polymers containing moderate electron-deficient
units such as DPP, IID, or BTz (Figures S1 and S2, Supporting
Information). The introduction of EWGs can effectively lower
the lowest unoccupied molecular orbital (LUMO) energy
levels of the polymers, which can promote the electron injec-
tion and thus improve the µe. Among these EWGs, F and Cl
have been adopted. In fact, high-performance EWG substituted
polymers are mostly focused on fluorinated units (Figure S1,
Supporting Information), whereas chlorinated polymers are
ignored (Figure S2, Supporting Information). In fact, it is fairly
difficult to synthesize EWG substituted units, especially for
EWG substituted acceptors.[11] Substituted acceptors with each
different EWG always require a different synthetic approach.
For example, the synthetic route to fluorinated IID is noneffec-
tive for chlorinated IID, leading to additionally arduous works
(Figure S3, Supporting Information).[12,13] On the other hand,
the mobilities of chlorinated semiconductors are much infe-
rior compared to fluorinated counterparts (Figures S1 and S2,
Supporting Information). For example, there is no chlorinated
small molecule or polymer with a µe over 1 cm2 V−1 s−1 due to
Solution-processable conjugated polymers have attracted
increasing attention because of their potential applications in
J. Yang, Prof. S. Wang
Key Laboratory of Material Chemistry for Energy
Conversion and Storage
Ministry of Education
School of Chemistry and Chemical Engineering
Huazhong University of Science and Technology
Wuhan 430074, China
E-mail: chmsamuel@hust.edu.cn
J. Yang, Y. Jiang, Dr. Z. Tu, Dr. Z. Zhao, J. Chen, Y. Li,
Prof. Y. Yi, Prof. Y. Guo, Prof. Y. Liu
Beijing National Laboratory for Molecular Sciences
Key Laboratory of Organic Solids
Institute of Chemistry
Chinese Academy of Sciences
Beijing 100190, China
E-mail: ypyi@iccas.ac.cn; guoyunlong@iccas.ac.cn; liuyq@iccas.ac.cn
Dr. Z. Yi
School of Chemical Engineering and Pharmacy
Wuhan Institute of Technology
Wuhan 430205, China
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adfm.201804839.
DOI: 10.1002/adfm.201804839
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condensation reaction between indigo deriva-
tives and 2-thienylacetyl chloride. Several
routes were developed to synthesize indigo
derivatives. For example, three routes to tyrian
purple (6,6′-dibromoindigo) were reported
(Figure S4, Supporting Information). We
selected the simplest route 1 to obtain indigo
derivatives. The targeted indigo derivatives
were synthesized using commercially avail-
able substituted 2-nitrobenzaldehydes as pre-
cursors, which reacted with acetone in NaOH
aqueous solution. As shown in Table S1
in the Supporting Information, we found
that plenty of water and enough reaction
time could obviously increase the yield of
2F-indigo-5. To demonstrate the universality
of the two-step method, we attempted to
synthesize different types of substituted BAI
derivatives (Figure 1). 2X4BAI-4 was derived
from BAI with the 1,8-position substituted by
Cl atoms (Figure 1a). 2X5BAI-5 was derived
from BAI with the 2,9-position substituted
by halogen atoms (F, Cl, Br) (Figure 1a).
2X6BAI-6 was derived from BAI with the
3,10-position substituted by halogen atoms
(F, Cl, Br), or CF3 (Figure 1a). 2X4BAI-4,
2X5BAI-5, and 2X6BAI-6 were all single-sub-
stituted BAI derivatives. 4OBAI was derived
Figure 1. An effective two-step approach to different types of BAI acceptors, a) single-
substituted BAI derivatives with different substituted positions b) double-substituted BAI
derivative (4OBAI).
the steric hindrance effect of big-size Cl atom.[13,14] However, we
wonder whether high performance can be achieved in a well-
designed chlorinated polymer with negligible steric hindrance.
The first bay-annulated indigo (BAI) compound was reported
in 1914.[15] Recently, Liu and co-workers developed a BAI-based
polymer, which showed a hole mobility (µh) and µe of 1.5 and
0.41 cm2 V−1 s−1, respectively.[16] However, the research on
BAI-based polymers is still limited.[16–21] For example, there
is no report of BAI-based polymers with both µh and µe over
1.0 cm2 V−1 s−1. Here, we developed an effective two-step
approach (Figure 1) to obtain EWG substituted acceptors based
on the BAI unit. This approach was effective to introduce various
EWGs (such as F, Cl, or CF3) into BAI at different substituted
positions. Four polymers of PBAI-V, P2FBAI-V, P2ClBAI-V,
and P4OBAI-V were developed by this method. All the poly-
mers showed ambipolar transport behaviors. Particularly,
P2ClBAI-V showed a remarkable µh/µe of 4.04/1.46 cm2 V−1 s−1.
Moreover, we performed theoretical calculations on the effec-
tive masses (m*) of the polymers. P2ClBAI-V showed small
effective masses, indicating that it is a promising unit for high-
performance polymers.
from BAI with dioxolane rings fused to the benzene rings
(Figure 1b). 4OBAI was an example among the double-sub-
stituted derivatives of BAI although the dioxolane ring was an
electron-donating group. Interestingly, the synthesis of 4OBAI
started from piperonal (Supporting Information), which is a
natural product existing in some plants such as pepper and sas-
safras. We successfully synthesized ten BAI derivatives by the
two-step approach, demonstrating it was a general method.
Bromination of 2FBAI-5 using N-bromosuccinimide (NBS)
in chloroform yielded 2FBAI-2Br-5 in 71% yield, which
underwent Stille coupling with 3-(2-octyldodecyl)-5-tributyl-
stannylthiophene to give 2FBAI-2T-5. Unfortunately, the Stille
coupling reaction showed moderate yield (<30%) due to the
poor solubility of 2FBAI-2Br-5 in the reaction solution. As
shown in Table S1 in the Supporting Information, we con-
ducted the Stille coupling reaction in different solvents. Similar
yields (about 11%) were found in toluene and toluene/DMF
(v/v, 4:1). Higher yield (15.2%) was achieved in chlorobenzene.
In o-dichlorobenzene, the reaction showed the highest yield of
21.7%. Other soluble products, BAI-2T, 2ClBAI-2T-4, 2ThBAI-5,
2ClBAI-2T-5, 2ClBAI-2T-6, 2FBAI-2T-6, and 4OBAI-2T were
synthesized following the similar procedures as 2FBAI-2T-5.
From the eight soluble BAI derivatives, we selected 2FBAI-
2T-5, BAI-2T, 2ClBAI-2T-5, and 4OBAI-2T to further develop
their monomers and polymers (Scheme 1). Bromination of
above four products gave the corresponding monomers. Stille
coupling polymerization between the four monomers and
trans-1,2-bis(tributylstannyl)ethene afforded the corresponding
polymers. Vinyl group was selected as the donor because it
could form a coplanar molecular structure with the adjacent
alkylated thiophenes (Figure S23, Supporting Information).
2. Results and Discussion
2.1. Synthesis
As shown in Figure 1, various substituted BAI derivatives were
developed based on an effective two-step method. The two-step
approach was composed of two reactions. The first step was
synthesis of indigo derivatives. The second step was a one-pot
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Scheme 1. An effective route to four BAI-based monomers and polymers.
We conducted solubility tests (Figure S6, Supporting Informa-
tion) of the polymers in common chlorinated solvents. PBAI-V,
P2ClBAI-V, and P4OBAI-V showed good solubility in chlo-
roform (≈25 mg mL−1), chlorobenzene (≈15 mg mL−1), and
o-dichlorobenzene (≈15 mg mL−1). However, the fluorinated
polymer, P2FBAI-V showed inferior solubility in chloroform
(≈10 mg mL−1) and was hardly soluble (<3 mg mL−1) ins chlo-
robenzene and o-dichlorobenzene. The results indicated that
fluorination of polymers decreased the solubility in chlorin-
ated solvents. As shown in Table 1, number-average molecular
weights (Mn) of PBAI-V, P2FBAI-V, P2ClBAI-V, and P4OBAI-
V were 25.2, 17.9, 32.5, and 18.0 kDa, respectively. Thermao-
gravimetric analysis (TGA) curves indicated that the polymers
exhibited good thermal stability (Figure S7, Supporting
Information).
2.2. Optical and Electrochemical Properties
The UV–vis absorption spectra of the polymers were meas-
ured both in chloroform solution and in thin film. As shown
in Figure 2, the polymers showed broad absorption bands
from 600 to 1100 nm, which were attributed to the π–π* tran-
sitions and the intramolecular charge transfer (ICT).[22,23] As
shown in Figure S6 in the Supporting Information, all the
BAI-based polymers were green in solution, similar to DPP-
based polymers. The absorption maxima (λmax) of P2ClBAI-V
in chloroform solution and in film red shifted compared to
those of PBAI-V. For instance, the λmax of solution increased
from 827 nm for PBAI-V to 918 nm for P2ClBAI-V. The red
shift of λmax could be attributed to the enhanced “push–pull”
interactions between the 2ClBAI and neighboring thiophenes
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Table 1. Number average molecular weights, polydispersity index (PDI), wavelength of
absorption maxima, bandgaps, HOMO, and LUMO energy levels of the polymers.
−5.58 eV. The HOMO and LUMO energy
levels of P4OBAI-V increased to −5.16 and
−3.57 eV compared to PBAI-V due to the
electron-donating characteristic of substi-
tuted dioxolane rings.
Polymer
PBAI-V
Mn [kDa]/PDI
25.2/2.03
17.9/1.83
32.5/1.93
18.0/1.82
Egopt a) [eV]
1.16
HOMOb) [eV]
−5.22
LUMOb) [eV]
−3.65
λ
max [nm]
827c)/794d)
699/714
918/897
785/773
P2FBAI-V
P2ClBAI-V
P4OBAI-V
1.15
−5.58
−3.72
1.04
−5.32
−3.70
2.3. Field-Effect Transistor Devices
1.19
−5.16
−3.57
Field-effect transistors (FETs) with top-gate
bottom-contact (TGBC) configuration were
fabricated on glass substrates to inves-
tigate the carrier transport properties of
a)Determined from the onset of thin-film absorption; b)Determined from the onset of oxidation and
reduction potentials of cyclic voltammetry; c)Absorption maximum in chloroform solution; d)Absorption
maximum in film.
because 2ClBAI was more electron-deficient than BAI.[24]
Similarly, P4OBAI-V showed blue-shift λmax compared to
PBAI-V due to the electron-donating characteristic of substi-
tuted dioxolane rings. However, the λmax of P2FBAI-V in solu-
tion blue shifted to 699 nm after introducing fluorine atoms,
which was unusual and needed further studies. As shown in
Table 1, all the polymers showed narrow film optical bandgaps
(Egopt) of about 1.2 eV. In particular, P2ClBAI-V exhibited a
the polymers. The device configuration of TGBC OFETs is
shown in Figure S10 in the Supporting Information. Gold
source/drain electrodes and aluminum gate electrodes were
thermally evaporated via a shadow mask. Polymethyl meth-
acrylate (PMMA) served as a dielectric layer. For OFETs
based on PBAI-V, P2ClBAI-V, and P4OBAI-V, the semicon-
ducting layers were spin-coated from o-dichlorobenzene
solutions. In comparison, P2FBAI-V was processed in chlo-
roform solution due to its poor solubility in o-dichloroben-
zene (Figure S6, Supporting Information). The fabrication
procedures of FET devices are provided in the Experimental
Section. As shown in Table S2 in the Supporting Infor-
mation, P2ClBAI-V showed the highest mobilities when
annealed at 180 °C, which was determined as the optimal
annealing temperature. Figure 3 and Figures S11–S13 (Sup-
porting Information) show the output and transfer curves of
the annealed polymers. Saturation mobilities were extracted
using IDS square root dependence on gate voltage (VG)
under VDS of 60 V. As shown in Figures S14–S17 in the
Supporting Information, the mobilities extracted from the
transfer curves of all the polymers showed weak dependence
on VG.[27]
All the polymers showed ambipolar transport behav-
iors with typical V-shaped transfer curves (Figure 3 and
Figures S11–S13, Supporting Information). The carrier mobili-
ties, threshold voltages, and on/off current ratios were extracted
from the transfer curves in the saturation regimes and were
shown in Table 2. We calculated reliability factors of satu-
rated mobility for the polymers to ensure the reliability of
mobility data.[27] PBAI-V showed ambipolar performance
with a maximum µh/µe of 1.30/0.34 cm2 V−1 s−1. In contrast,
P2FBAI-V was almost an n-type semiconductor with a µe of
opt
Eg of 1.04 eV, which was among the smallest values for the
reported D–A polymers.[3] In addition, temperature-dependent
UV–vis absorption spectra of the polymers in chlorobenzene
solution were performed to investigate aggregation prop-
erty of each polymer (Figure S8, Supporting Information).
Upon increasing solution temperature, the λmax at ICT band
of PBAI-V, P2ClBAI-V, and P4OBAI-V only showed slight
blue shifts (<10 nm), indicating that the polymers exhibited
weak aggregation in chlorobenzene solution.[25,26] Meanwhile,
the λmax of P2FBAI-V showed no obvious change at different
temperatures.
The electrochemical properties of the polymers were eval-
uated by cyclic voltammetry (CV) (Figure S9, Supporting
Information). All the polymers exhibited intense oxidative
and reductive peaks. The highest occupied molecular orbital
(HOMO) and LUMO energy levels of the polymers were
calculated from the onsets of oxidative and reductive peaks,
respectively. The HOMO and LUMO energy levels of PBAI-V
were −5.22 and −3.65 eV, respectively. Fluorination and chlo-
rination can lower both the HOMO and LUMO energy levels
due to the electron-withdrawing characteristics of F and Cl
atoms. For instance, the LUMO energy levels of P2FBAI-V
and P2ClBAI-V decreased to −3.72 and −3.70 eV, respectively.
Notably, P2FBAI-V showed a deep HOMO energy level of
Figure 2. UV−vis absorption spectra of the polymers a) in chloroform solution and b) in thin film.
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Figure 3. a,b) Output and c,d) transfer characteristics of a TGBC device based on P2ClBAI-V.
0.16 cm2 V−1 s−1 and a negligible µh of 10−4 cm2 V−1 s−1. The
HOMO energy level of P2FBAI-V was −5.58 eV, which was unfa-
vorable for hole injection from the Au electrodes (work function
≈5.1 eV).[28] Interestingly, the chlorinated polymer, P2ClBAI-V
showed significantly improved performance with a µh/µe of
4.04/1.46 cm2 V−1 s−1. These mobilities were among the highest
values for BAI-based polymers and were comparable to those of
well-known DPP-based polymers.[16,18,29] P4OBAI-V showed infe-
rior performance with µh and µe of 0.17 and 0.085 cm2 V−1 s−1,
respectively. In addition, we fabricated bottom-gate bottom-con-
tact (BGBC) devices based on P2ClBAI-V. Highly-doped SiO2/Si
wafers were used as substrates. The SiO2 surface was modified
with octadecyltrichlorosilane (OTS) to minimize surface charge
trapping. As shown in Figure S18 in the Supporting Information,
P2ClBAI-V based BGBC devices showed ambipolar performance
with a maximum µh/µe of 1.06/0.53 cm2 V−1 s−1 in nitrogen
atmosphere. Compared with the TGBC devices, the inferior per-
formance for the BGBC devices was attributed to charge trap-
ping at the interface between the semiconductor and the silicon
dioxide dielectric.[18,30,31] We further evaluated the performance
of BAI-based polymers by comparing them with the reported
DPP and IID-based polymers. PBAI-V, PDPP-(E)-2-(2-(thiophen-
2-yl)vinyl)thiophene (TVT), and PIID-TVT were selected as the
targeted polymers because all of them contained similar TVT
donors (Figure S19, Supporting Information). PDPP-TVT and
PIID-TVT were nearly unipolar p-type polymers.[29,30] In compar-
ison, PBAI-V showed obvious n-type performance with a µe of
0.34 cm2 V−1 s−1 due to its lowest LUMO energy level (−3.65 eV)
among the three polymers. Therefore, BAI units would be prom-
ising building blocks for ambipolar polymers.
2.4. Film Crystallinity and Morphology
2D grazing incident X-ray diffractions (2D-GIXRD) were
conducted to explore the crystalline nature of the polymers.
2D-GIXRD patterns of annealed films at 180 °C on glass sub-
strates are shown in Figure 4. For all the polymers, (h00) diffrac-
tion peaks corresponding to lamellar diffractions were observed
along the in-plane (qxy) and out-of-plane (qz) directions.
The out-of-plane (100) diffraction of PBAI-V was found at
2θ = 4.64°, corresponding to a lamellar d-spacing of 19.0 Å.
Similarly, the lamellar d-spacings of P2FBAI-V, P2ClBAI-V,
and P4OBAI-V were 20.4, 19.9, and 19.7 Å, respectively. For
all the polymers, (010) diffraction peaks corresponding to the
π–π stacking were observed along the out-of-plane and in-plane
direction (Figure S20, Supporting Information), suggesting
that the π–π stacking crystallites adopted a bimodal distribu-
tion of edge-on and face-on orientations. PBAI-V, P2ClBAI-V,
and P4OBAI-V showed π-stacking spacings of 3.53, 3.54, and
3.52 Å, respectively, which were calculated from the (010) dif-
fraction peaks. The π-stacking spacings of the three polymers
were among the smallest values for D–A polymers,[4] promising
effective intermolecular charge transport for carriers. The com-
parative π-stacking spacings of PBAI-V and P2ClBAI-V indicated
that chlorination of BAI did not cause obvious steric hindrance
to hinder the intermolecular stacking although the chlorine
atom has a large atom size.[13] Surprisingly, P2FBAI-V showed
a much larger π-stacking spacing of 3.68 Å than the other three
polymers. Different from DPP or IID-based polymers,[4,6] these
BAI-based polymers exhibited (00l) diffraction peaks, which
corresponded to planes resulting from repeat polymer units in
Table 2. TGBC OFET performance of the polymers.
µhb) [cm2V−1s−1
]
µeb) [cm2V−1s−1
]
Polymer
p-type
Vthd) [V]
n-type
Vthd) [V]
p/n ratioa)
c)
e)
c)
e)
rsat
Ion/Ioff
rsat
Ion/Ioff
103−104
102−103
102−103
103−104
58 ( 3)
43 ( 5)
39 ( 4)
66 ( 4)
102−103
103−104
102−103
102−103
PBAI-V
1.30 (0.94)
0.561
0.854
0.691
0.508
0.34 (0.28)
0.16 (0.12)
1.46 (1.01)
0.085 (0.037)
0.759
0.718
0.734
0.757
3.36
5.6 × 10−3
2.79
−33 ( 2)
−14 ( 4)
−36 ( 4)
−24 ( 1)
8.4 × 10−4 (6.7 × 10−4
4.04 (2.82)
)
P2FBAI-V
P2ClBAI-V
P4OBAI-V
0.17 (0.15)
4.05
a)Ratio of average hole and electron mobility; b)Maximum mobilities extracted from the transfer curves in the saturation regimes. The average values are listed in parentheses.
c)
The mobility values were calculated from the high gate voltage region;
r
sat
represents reliability factor of saturated mobility; d)Threshold voltage; e)On–off current ratio.
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Figure 4. 2D-GIXRD patterns of a) PBAI-V, b) P2FBAI-V, c) P2ClBAI-V, and d) P4OBAI-V films annealed at 180 °C.
an ordered mainchain backbone.[18,19] All the polymers except
P2FBAI-V showed (001) and (002) diffraction peaks. PBAI-V,
P2ClBAI-V, and P4OBAI-V showed close (001) d-spacings of
22.43, 22.60, and 22.37 Å, respectively. The theoretical calculated
length of a repeat unit of each polymer was almost the same
(≈22.67 Å) (Figure S23, Supporting Information). The backbone-
direction (001) d-spacing of each polymer was very close to the
theoretical calculated length of a repeat unit, indicating that the
polymer backbone should be entirely extended (not twisted)
along the conjugated direction in solid state, thus resulting in
better intramolecular carrier transport characteristics.[18,32]
Figures S21 and S22 in the Supporting Information show the
atomic force microscopy (AFM) images of annealed polymer
films on glass substrates. All the polymer films showed well-
interconnected domains that could minimize the intergranular
charge hopping barriers. The films of all the polymers except
P2FBAI-V exhibited relatively low root-mean-square (RMS)
surface roughness of below 1 nm. Particularly, P2ClBAI-V
showed fairly smooth interface with a small RMS of 0.12 nm.
The smooth interface was beneficial for charge transport in
top-gate OFETs, consistent with the results in reported high-
performance ambipolar polymers.[33]
2.5. Theoretical Calculations
Charge transport in semiconducting polymers includes intra-
molecular charge transport along the conjugated backbone
and intermolecular charge transport through π–π stacking.
It is difficult to evaluate intramolecular charge transport by
experimental methods, which plays an important role in high-
mobility polymers. Recently, we introduced the concept “m*”
to evaluate intramolecular charge transport, where a small m*
reveals effective intramolecular charge transport.[34] The m*
can be obtained by theoretical calculations. Here, we calcu-
lated the m* of the four polymers based on their simulative 1D
crystalline structures. Figure S23 in the Supporting Informa-
tion shows the planarity data of the polymers. All the polymers
showed similar planarity with the maximum torsion angles
between the BAI core and adjacent thiophenes being about
27°, which was comparable to IID-based polymers (≈22°)[12]
but smaller than NDI-based counterparts (≈40°).[35] Notably, the
large-size chlorine atoms in P2ClBAI-V did not lead to worse
planarity. Figure 5d–g shows the calculated band structures and
densities of states (DOS). Hole and electron effective masses
(mh* and me*) of the polymers were calculated based on the
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Figure 5. a) Average hole and electron mobilities of the polymers extracted from the transfer curves. b) HOMO and LUMO energy levels of the polymers
determined from CV. c) Hole and electron effective masses (mh* and me*) obtained from the theoretical calculations. Band structures and partial
density of states (DOS) of d) PBAI-V, e) P2FBAI-V, f) P2ClBAI-V, and g) P4OBAI-V.
second derivative of band structures. As shown in Table 2,
all the polymers showed small mh* and me*. PBAI-V showed
small mh* and me* of 0.098 and 0.137 me, respectively. In com-
parison, P2FBAI-V and P2ClBAI-V showed slightly smaller mh*
and me*, indicating that both fluorination and chlorination of
the BAI could promote more effective intramolecular charge
transport. P4OBAI-V showed much larger mh* and me* than
those of PBAI-V. Table S5 in the Supporting Information shows
calculated m* of IID and NDI-based polymers. We noted that
P2FBAI-V and P2ClBAI-V showed comparable m* to IID-based
polymers but much smaller m* than NDI-based counterparts.
The results revealed that the intramolecular charge transport
in P2FBAI-V or P2ClBAI-V was as effective as in IID-based
counterparts. In consideration that IID unit was a well-known
acceptor for high-mobility polymers, we believed that 2FBAI or
2ClBAI would be a promising building block for high-perfor-
mance ambipolar polymers.
Here, we tried to explain the trend of the polymers’ mobili-
ties from the aspects of charge injection and transport based
on above results of CV, GIXRD, and AFM. P2FBAI-V showed
inferior performance, which could be attributed to its infe-
rior solubility in chloroform. Similar phenomena could be
found in BDOPV-based polymers.[36,37] Moreover, P2FBAI-V
showed bad crystallinity with weak (h00) and (010) peaks and
a large π-stacking spacing of 3.68 Å, indicating inferior inter-
molecular charge transport in P2FBAI-V. We are attempting
to design other 2FBAI-based polymers with good solubility for
better device performance. Compared with PBAI-V, P2ClBAI-V
showed improved hole and electron mobilities. Several reasons
were responsible for the results: 1) P2ClBAI-V showed lower
LUMO energy level than PBAI-V (Figure 5b), thus promoting
the electron injection. 2) GIXRD results indicated that chlorina-
tion of BAI did not cause obvious steric hindrance to hinder
the intermolecular stacking. 3) Different from F atom, Cl atom
has empty 3d orbitals, which can accept π-electrons from the
donors. As a result, strong intermolecular interactions would
form in chlorinated polymers, which can modulate their film
crystallinity or morphology.[38–40] AFM results indicated that
P2ClBAI-V showed more smooth interface compared with
PBAI-V. The smoother interface was beneficial for better charge
transport in top-gate OFETs.[33]
3. Conclusion
In conclusion, we developed a general two-step method to obtain
EWG substituted acceptors based on BAI units. This method
was effective to introduce various EWGs (such as F, Cl, or CF3)
into BAI at different substituted positions. Four new poly-
mers of PBAI-V, P2FBAI-V, P2ClBAI-V, and P4OBAI-V were
developed by this approach. All the polymers showed ambi-
polar transport behaviors. Particularly, P2ClBAI-V exhibited
remarkable performance with a µh/µe of 4.04/1.46 cm2 V−1 s−1.
These mobilities were the best values achieved for chlorinated
semiconductors (including small molecules and polymers).
Theoretical calculations and GIXRD indicated that the intro-
duction of Cl atoms in P2ClBAI-V did not distort the backbone
coplanarity and not hinder the π–π stacking. For the first time,
our results demonstrate that chlorination can be a promising
strategy for high-performance ambipolar polymers. Moreover,
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next purification of the polymer was similar to PBAI-V. The chloroform
fraction was concentrated by evaporation and precipitated into methanol
(100 mL) and filtered off to afford the green polymer (79.4 mg,
87.5%). GPC: Mn = 32.5 kDa, Mw = 57.2 kDa, PDI = 1.93. Anal. calcd.
for C78H96Cl2N2O2S4: C 72.47, H 7.49, N 2.17; found: C 71.46, H 7.55,
N 2.15.
the effective two-step approach can achieve various EWG sub-
stituted BAI acceptors, which will significantly enrich the
library of ambipolar polymers.
P4OBAI-V: 4OBAI-2T-2Br (100.0 mg, 0.069 mmol), trans-1,2-
bis(tributylstannyl)ethene (41.9 mg, 0.069 mmol), Pd2(dba)3 (2.0 mg),
P(o-tol)3 (5.2 mg), and toluene (6 mL) were added to a Schlenk tube.
The tube was charged with argon through a freeze–pump–thaw cycle
for three times. The mixture was stirred for 24 h at 110 °C. The next
purification of the polymer was similar to PBAI-V. The chloroform
fraction was concentrated by evaporation and precipitated into
methanol (100 mL) and filtered off to afford the green polymer
(52.3 mg, 57.6%). GPC: Mn = 18.0 kDa, Mw = 29.6 kDa, PDI = 1.82.
Anal. calcd. for C80H98N2O6S4: C 73.24, H 7.53, N 2.14; found: C 72.48,
H 7.57, N 2.16.
TGBC OFET Fabrication and Characterization: Polymer FETs with a
TGBC configuration were fabricated on Corning glass substrates. The
substrates were rinsed by deionized water, ethanol, acetone under
ultrasonication and dried by nitrogen before device fabrication. The
source–drain gold electrodes were prepared by vacuum evaporation
technique. The channel width and length of all FET devices were
4500 and 50 µm, respectively. PBAI-V, P2ClBAI-V, and P4OBAI-V were
dissolved in 1,2-dichlorobenzene (10 mg mL−1). P2FBAI-V was dissolved
in chloroform (10 mg mL−1). In a nitrogen glovebox, the polymer
solutions were spin-coated onto the substrates, yielding polymer films.
Then the film samples were further annealed at 180 °C for 10 min.
Next, PMMA (MW = 996 kDa) solution in anhydrous n-butyl acetate
(60 mg mL−1) was spin-coated onto the surface of the polymer films
(PMMA thickness ≈900 nm, capacitance ≈2.56 nF cm−2).[41] The samples
were dried at 90 °C for 50 min in glove box. Finally, the aluminum gate
electrodes (thickness ≈80 nm) were evaporated onto PMMA through a
shadow mask. All the FET devices were determined under the ambient
4. Experimental Section
Characterization: Nuclear magnetic resonance (NMR) spectra were
recorded on a Bruker DMX-300 (300 MHz) spectrometer. 1HNMR
chemical shifts were referenced to internal tetramethylsilane (TMS,
0 ppm). High-resolution mass spectroscopy (HRMS) measurements
were collected using electron-impact mass spectra (EIMS) on a Bruker
BIFLEX III mass spectrometer. Matrix-assisted laser desorption/
ionization time-of-flight (MALDI-TOF) mass spectra were collected
on an Autoflex III (Bruker Daltonics Inc.) MALDI-TOF spectrometer.
Molecular weights were determined by gel permeation chromatography
(GPC) at 120 °C on a PL-220 system using 1,2,4-tricholorobenzene as
the eluent. TGA measurements were carried out on a PerkinElmer series
7 thermal analysis system under N2 at a heating rate of 10 °C min−1
.
UV–vis absorption spectra were measured on polymer solutions in
chloroform and polymer films cast onto quartz glass using a Jasco-
570 spectrophotometer. CV was carried out on an electrochemical
workstation (CHI660c) using a three-electrode cell. The glassy carbon
electrode coated with a thin film layer of polymer was used as working
electrode. Ag/AgCl (Ag in a 0.01 mol L−1 KCl) electrode was used as the
reference electrode. Platinum wire was used as the counter electrode.
Anhydrous and N2 saturated solution 0.1
m tetrabutylammonium
hexylfluorophosphate (n-Bu4NPF6) in acetonitrile was employed as
the electrolyte. AFM measurements were carried out on a Nanoscope
V instrument. AFM samples were identical to those used in FET
performance analysis. GIXRD was performed on 1W1A Station of Beijing
Synchrotron Radiation Facility (λ = 1.5418 Å).
Polymer Synthesis: PBAI-V: BAI-2T-2Br (100.0 mg, 0.074 mmol),
trans-1,2-bis(tributylstannyl)ethene (44.6 mg, 0.074 mmol), Pd2(dba)3
(2.0 mg), P(o-tol)3 (5.2 mg), and chlorobenzene (6 mL) were added to a
Schlenk tube. The tube was charged with argon through a freeze–pump–
thaw cycle for three times. The mixture was stirred for 48 h at 130 °C,
cooled down to room temperature, and poured into methanol (100 mL)
containing hydrochloric acid (5 mL) and stirred for 3 h. The precipitated
product was filtered and purified via Soxhlet extraction with methanol
(10 h), acetone (10 h), hexane (10 h), and was finally collected with
chloroform. The chloroform fraction was concentrated by evaporation
and precipitated into methanol (100 mL) and filtered off to afford the
green polymer (85.2 mg, 94.6%). GPC: Mn = 25.2 kDa, Mw = 46.3 kDa,
polydispersity index (PDI) = 2.03. Anal. calcd. for C78H98N2O2S4: C 76.55,
H 8.07, N 2.29; found: C 74.74, H 8.00, N 2.27.
P2FBAI-V: 2FBAI-2T-2Br-5 (200.0 mg, 0.144 mmol), trans-1,2-
bis(tributylstannyl)ethene (87.0 mg, 0.144 mmol), Pd2(dba)3 (3.9 mg),
P(o-tol)3 (10.5 mg), and toluene (12 mL) were added to a Schlenk tube.
The tube was charged with argon through a freeze–pump–thaw cycle for
three times. The mixture was stirred at 110 °C for several minutes (about
4 min) before being gelled, cooled down to room temperature, and
poured into methanol (200 mL) containing hydrochloric acid (10 mL)
and stirred for 3 h. The precipitated product was filtered and purified via
Soxhlet extraction with methanol (10 h), acetone (10 h), hexane (10 h),
chloroform (10 h), chlorobenzene (5 h), and finally o-dichlorobenzene
(5 h). The chlorinated fractions were concentrated by evaporation and
precipitated into methanol (200 mL) and filtered off to afford the green
polymers: chloroform fraction (81.2 mg, 45.0%), chlorobenzene fraction
(very less), o-dichlorobenzene fraction (very less). GPC: Mn = 17.9 kDa,
Mw = 29.9 kDa, PDI = 1.83. Anal. calcd. for C78H96F2N2O2S4: C 74.36, H
7.68, N 2.22; found: C 69.91, H 7.23, N 2.18.
conditions using
a Keithley 4200 SCS semiconductor parameter
analyzer. The field-effect mobility in saturation region (µsat) is calculated
according to the Equation (1)
2
(1)
IDS = W/2L C µ V −V
)
(
)
(
i
sat
G
th
where IDS is the drain current; W and L are the semiconductor channel
width and length, respectively; Ci is the capacitance per unit area of the
gate dielectric layer; and VG and Vth are the gate voltage and threshold
voltage, respectively.
BGBC OFET Fabrication and Characterization: BGBC FETs were
fabricated on highly-doped silicon wafer with 300 nm SiO2 insulator.
Silicon was used as bottom gate electrode. The gold (gold/titanium,
30 nm/5 nm) electrodes were served as source–drain electrodes,
which were prepared by photolithography. The gate dielectric layer has
a capacitance of ≈11.5 nF cm−2. The substrates were first subjected
to cleaning by ultrasonication in acetone, deionized water, and
ethanol. Next, OTS modification was performed in solution (hexane:
OTS = 100:1) to form an OTS self-assembled monolayer on the surface
of the dielectric. After removing the extra OTS by hexane, polymer
semiconductor was deposited by spin coating from
a preheated
polymer solution in o-dichlorobenzene (10 mg mL−1) in N2 glovebox.
The samples were further annealed on a hotplate at 180 °C in N2 for
10 min. BGBC FETs were measured in N2 by using a Keithley 4200 SCS
semiconductor parameter analyzer. Channel length (L) and width (W) of
the devices were 20 and 1400 µm, respectively.
Reliability Factor Calculations: Reliability factors of saturated mobility
(rsat) for the polymers are calculated according to Equation (2)[27]


2

max
off

2
P2ClBAI-V: 2ClBAI-2T-2Br-5 (100.0 mg, 0.070 mmol), trans-1,2-
bis(tributylstannyl)ethene (42.5 mg, 0.070 mmol), Pd2(dba)3 (2.0 mg),
P(o-tol)3 (5.2 mg), and chlorobenzene (6 mL) were added to a Schlenk
tube. The tube was charged with argon through a freeze–pump–thaw
cycle for three times. The mixture was stirred for 48 h at 130 °C. The
IDS
−
I
∂
IDS
∂VG
DS
off






rsat
=
/




(2)
VG max − VG


where IDSoff is minimum current at the off-state.
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Theoretical Calculations: For simplicity, the alkyl chains at the
thiophenes were replaced by methyl groups. The geometry structures
of isolated polymer chain with 1D periodicity were optimized at
HSE06-D3 functional with the CRYSTAL17 Package.[42] Uniform 5 × 1 × 1
Monkhorst–Pack k-point mesh was employed for all the polymers. To
generate the band structures, 50 k-points were calculated between the
gamma point (center of the Brillouin zone (BZ)) and the edge of the first
BZ. m* for 1D crystal was calculated by means of Sperling’s centered
difference method with dk = 0.01 Bohr−1 using the following definition
[3] X. Guo, A. Facchetti, T. J. Marks, Chem. Rev. 2014, 114, 8943.
[4] Z. Yi, S. Wang, Y. Liu, Adv. Mater. 2015, 27, 3589.
[5] Z. Liu, G. Zhang, D. Zhang, Acc. Chem. Res. 2018, 51, 1422.
[6] T. Lei, J.-Y. Wang, J. Pei, Acc. Chem. Res. 2014, 47, 1117.
[7] K.-H. Ong, S.-L. Lim, H.-S. Tan, H.-K. Wong, J. Li, Z. Ma,
L. C. H. Moh, S.-H. Lim, J. C. de Mello, Z.-K. Chen, Adv. Mater.
2011, 23, 1409.
[8] Y. Zhao, Y. Guo, Y. Liu, Adv. Mater. 2013, 25, 5372.
[9] J. Yang, Z. Zhao, S. Wang, Y. Guo, Y. Liu, Chem 2018, 4, 2748.
[10] J. Zaumseil, R. H. Friend, H. Sirringhaus, Nat. Mater. 2006, 5, 69.
[11] T. Bura, S. Beaupré, O. A. Ibraikulov, M.-A. Légaré, J. Quinn,
P. Lévêque, T. Heiser, Y. Li, N. Leclerc, M. Leclerc, Macromolecules
2017, 50, 7080.
[12] T. Lei, J.-H. Dou, Z.-J. Ma, C.-H. Yao, C.-J. Liu, J.-Y. Wang, J. Pei,
J. Am. Chem. Soc. 2012, 134, 20025.
[13] T. Lei, J.-H. Dou, Z.-J. Ma, C.-J. Liu, J.-Y. Wang, J. Pei, Chem. Sci.
2013, 4, 2447.
[14] R. Schmidt, J. H. Oh, Y.-S. Sun, M. Deppisch, A.-M. Krause,
K. Radacki, H. Braunschweig, M. Könemann, P. Erk, Z. Bao,
F. Würthner, J. Am. Chem. Soc. 2009, 131, 6215.
m* = h2/(d2E/dk2)
(3)
where E is the band energy and k is the electron wave vector along the
backbone direction.
The mobility can be evaluated according to Equation (4)
µ = eτ/m*
(4)
where e is the electron charge and τ is the effective scattering time. τ
is limited by energetic disorder, dynamic disorder, and chain ends.[43]
According to this equation, smaller m* suggests better intramolecular
charge transport along the polymer backbone, which is favorable to
obtain high mobility.
[15] G. Engi, Z. Angew. Chem. 1914, 27, 144.
[16] B. He, A. B. Pun, D. Zherebetskyy, Y. Liu, F. Liu, L. M. Klivansky,
A. M. McGough, B. A. Zhang, K. Lo, T. P. Russell, L. Wang, Y. Liu,
J. Am. Chem. Soc. 2014, 136, 15093.
[17] K. J. Fallon, N. Wijeyasinghe, N. Yaacobi-Gross, R. S. Ashraf,
D. M. E. Freeman, R. G. Palgrave, M. Al-Hashimi, T. J. Marks,
I. McCulloch, T. D. Anthopoulos, H. Bronstein, Macromolecules
2015, 48, 5148.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
[18] K. J. Fallon, N. Wijeyasinghe, E. F. Manley, S. D. Dimitrov,
S. A. Yousaf, R. S. Ashraf, W. Duffy, A. A. Y. Guilbert,
D. M. E. Freeman, M. Al-Hashimi, J. Nelson, J. R. Durrant,
L. X. Chen, I. McCulloch, T. J. Marks, T. M. Clarke,
T. D. Anthopoulos, H. Bronstein, Chem. Mater. 2016, 28, 8366.
[19] K. J. Fallon, A. Santala, N. Wijeyasinghe, E. F. Manley, N. Goodeal,
A. Leventis, D. M. E. Freeman, M. Al-Hashimi, L. X. Chen,
T. J. Marks, T. D. Anthopoulos, H. Bronstein, Adv. Funct. Mater.
2017, 27, 1704069.
[20] M. A. Kolaczkowski, B. He, Y. Liu, Org. Lett. 2016, 18, 5224.
[21] J. Brebels, K. C. C. W. S. Klider, M. Kelchtermans, P. Verstappen,
M. Van Landeghem, S. Van Doorslaer, E. Goovaerts, J. R. Garcia,
J. Manca, L. Lutsen, D. Vanderzande, W. Maes, Org. Electron. 2017,
50, 264.
Acknowledgements
J.Y. and Y.J. contributed equally to this work. This work was financially
supported by the National Natural Science Foundation of China (Grant
No.s: 61890940, 51873216, 21504026, and 21633012), the National
Key R&D Program of “Strategic Advanced Electronic Materials”
(No. 2016YFB0401100), and the Strategic Priority Research Program of
the Chinese Academy of Sciences (No. XDB12030100 and XDB30000000)
and Key Research Program of Frontier Sciences, CAS, Grant No.
QYZDY-SSW-SLH029 and Beijing Nova program (Z181100006218034).
2D-GIXRD results were obtained at 1W1A Station of Beijing Synchrotron
Radiation Facility. The authors gratefully acknowledge the assistance of
scientists of the Diffuse X-ray Scattering Station during the experiments.
[22] B. He, W. T. Neo, T. L. Chen, L. M. Klivansky, H. Wang, T. Tan,
S. J. Teat, J. Xu, Y. Liu, ACS Sustainable Chem. Eng. 2016, 4, 2797.
[23] B. He, D. Zherebetskyy, H. Wang, M. A. Kolaczkowski,
L. M. Klivansky, T. Tan, L. Wang, Y. Liu, Chem. Sci. 2016, 7,
3857.
Conflict of Interest
The authors declare no conflict of interest.
[24] H. Li, F. S. Kim, G. Ren, S. A. Jenekhe, J. Am. Chem. Soc. 2013, 135,
14920.
[25] R. S. Ashraf, I. Meager, M. Nikolka, M. Kirkus, M. Planells,
B. C. Schroeder, S. Holliday, M. Hurhangee, C. B. Nielsen,
H. Sirringhaus, I. McCulloch, J. Am. Chem. Soc. 2015, 137,
1314.
[26] H. Chen, Z. Liu, Z. Zhao, L. Zheng, S. Tan, Z. Yin, C. Zhu, Y. Liu,
ACS Appl. Mater. Interfaces 2016, 8, 33051.
Keywords
ambipolar transistors, bay-annulated indigo, electron-withdrawing group
substituted, high performance
Received: July 15, 2018
Revised: November 25, 2018
Published online:
[27] H. H. Choi, K. Cho, C. D. Frisbie, H. Sirringhaus, V. Podzorov, Nat.
Mater. 2017, 17, 2.
[28] Y. Zhou, C. Fuentes-Hernandez, J. Shim, J. Meyer, A. J. Giordano,
H. Li, P. Winget, T. Papadopoulos, H. Cheun, J. Kim, M. Fenoll,
A. Dindar, W. Haske, E. Najafabadi, T. M. Khan, H. Sojoudi,
S. Barlow, S. Graham, J.-L. Brédas, S. R. Marder, A. Kahn,
B. Kippelen, Science 2012, 336, 327.
[29] J. Yang, H. Wang, J. Chen, J. Huang, Y. Jiang, J. Zhang, L. Shi,
Y. Sun, Z. Wei, G. Yu, Y. Guo, S. Wang, Y. Liu, Adv. Mater. 2017, 29,
1606162.
[1] L. Lu, T. Zheng, Q. Wu, A. M. Schneider, D. Zhao, L. Yu, Chem. Rev.
2015, 115, 12666.
[2] A. C. Arias, J. D. MacKenzie, I. McCulloch, J. Rivnay, A. Salleo,
Chem. Rev. 2010, 110, 3.
©
Adv. Funct. Mater. 2018, 1804839
1804839 (9 of 10)
2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

www.advancedsciencenews.com
www.afm-journal.de
[30] Y. Gao, Y. Deng, H. Tian, J. Zhang, D. Yan, Y. Geng, F. Wang, Adv.
Mater. 2017, 29, 1606217.
[38] H. Wang, P. Chao, H. Chen, Z. Mu, W. Chen, F. He, ACS Energy
Lett. 2017, 2, 1971.
[31] B. Sun, W. Hong, Z. Yan, H. Aziz, Y. Li, Adv. Mater. 2014, 26, 2636.
[32] B. Kang, R. Kim, S. B. Lee, S.-K. Kwon, Y.-H. Kim, K. Cho, J. Am.
Chem. Soc. 2016, 138, 3679.
[39] Z. Hu, H. Chen, J. Qu, X. Zhong, P. Chao, M. Xie, W. Lu,
A. Liu, L. Tian, Y.-A. Su, W. Chen, F. He, ACS Energy Lett. 2017, 2,
753.
[33] A. J. Kronemeijer, E. Gili, M. Shahid, J. Rivnay, A. Salleo, M. Heeney,
H. Sirringhaus, Adv. Mater. 2012, 24, 1558.
[40] M. Chu, J.-X. Fan, S. Yang, D. Liu, C. F. Ng, H. Dong, A.-M. Ren,
Q. Miao, Adv. Mater. 2018, 30, 1803467.
[34] J. Yang, Z. Zhao, H. Geng, C. Cheng, J. Chen, Y. Sun, L. Shi, Y. Yi,
Z. Shuai, Y. Guo, S. Wang, Y. Liu, Adv. Mater. 2017, 29, 1702115.
[35] H. Chen, Y. Guo, Z. Mao, G. Yu, J. Huang, Y. Zhao, Y. Liu, Chem.
Mater. 2013, 25, 3589.
[41] Z. Mao, Y. Guo, H. Chen, W. Zhang, G. Yu, Polymer 2016, 99,
496.
[42] A. Erba, J. Baima, I. Bush, R. Orlando, R. Dovesi, J. Chem. Theory
Comput. 2017, 13, 5019.
[36] Z. Yan, B. Sun, Y. Li, Chem. Commun. 2013, 49, 3790.
[37] T. Lei, J.-H. Dou, X.-Y. Cao, J.-Y. Wang, J. Pei, Adv. Mater. 2013, 25,
6589.
[43] B. B.-Y. Hsu, C.-M. Cheng, C. Luo, S. N. Patel, C. Zhong, H. Sun,
J. Sherman, B. H. Lee, L. Ying, M. Wang, G. Bazan, M. Chabinyc,
J.-L. Brédas, A. Heeger, Adv. Mater. 2015, 27, 7759.
©
Adv. Funct. Mater. 2018, 1804839
1804839 (10 of 10)
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