Quinoline-Flanked Diketopyrrolopyrrole Copolymers Breaking through Electron Mobility over 6 cm2 V?1 s?1 in Flexible Thin Film Devices

Article abstract of DOI:10.1002/adma.201704843

Herein, the design and synthesis of novel π-extended quinoline-flanked diketopyrrolopyrrole (DPP) [abbreviated as QDPP] motifs and corresponding copolymers named PQDPP-T and PQDPP-2FT for high performing n-type organic field-effect transistors (OFETs) in flexible organic thin film devices are reported. Serving as DPP-flankers in backbones, quinoline is found to effectively tune copolymer optoelectric properties. Compared with TDPP and pyridine-flanked DPP (PyDPP) analogs, widened bandgaps and strengthened electron deficiency are achieved. Moreover, both hole and electron mobility are improved two orders of magnitude compared to those of PyDPP analogs (PPyDPP-T and PPyDPP-2FT). Notably, featuring an all-acceptor-incorporated backbone, PQDPP-2FT exhibits electron mobility of 6.04 cm² V^?1 s^?1, among the highest value in OFETs fabricated on flexible substrates to date. Moreover, due to the widened bandgap and strengthened electron deficiency of PQDPP, n-channel on/off ratio over 10⁵ with suppressed hole transport is first realized in the ambipolar DPP-based copolymers.

Full text of DOI:10.1002/adma.201704843

COMMUNICATION
Flexible Electronics
www.advmat.de
Quinoline-Flanked Diketopyrrolopyrrole Copolymers
Breaking through Electron Mobility over 6 cm2 V−1 s−1
in Flexible Thin Film Devices
Zhenjie Ni, Huanli Dong, Hanlin Wang, Shang Ding, Ye Zou, Qiang Zhao,
Yonggang Zhen, Feng Liu, Lang Jiang, and Wenping Hu*
Over the past years, flexible devices
have gained wide attention to satisfy the
Herein, the design and synthesis of novel π-extended quinoline-flanked diketopyr-
rolopyrrole (DPP) [abbreviated as QDPP] motifs and corresponding copolymers
named PQDPP-T and PQDPP-2FT for high performing n-type organic field-effect
transistors (OFETs) in flexible organic thin film devices are reported. Serving
as DPP-flankers in backbones, quinoline is found to effectively tune copolymer
optoelectric properties. Compared with TDPP and pyridine-flanked DPP (PyDPP)
analogs, widened bandgaps and strengthened electron deficiency are achieved.
Moreover, both hole and electron mobility are improved two orders of magnitude
compared to those of PyDPP analogs (PPyDPP-T and PPyDPP-2FT). Notably,
featuring an all-acceptor-incorporated backbone, PQDPP-2FT exhibits electron
mobility of 6.04 cm2 V−1 s−1, among the highest value in OFETs fabricated on flex-
ible substrates to date. Moreover, due to the widened bandgap and strengthened
electron deficiency of PQDPP, n-channel on/off ratio over 105 with suppressed
hole transport is first realized in the ambipolar DPP-based copolymers.
mechanical requirements of wearable elec-
tronics and flexible display.[1,2] As the key
element for driving and logic operations,
high mobility and solution-processable
organic field-effect transistors (OFETs),
especially with polymer channel layer,
are of great interests to realize low-cost
and high-performing flexible devices.[3–5]
Among these polymers, diketopyrrolopyr-
role (DPP) presents a most adopted unit in
copolymer synthesis.[6,7] DPP’s good pla-
narity facilitates intermolecular interchain
interactions and π-electron delocalization
to enhance carrier transport. Moreover,
due to its electron deficiency, copolymeri-
zation of DPP with donor units can poten-
tially lead to ambipolar materials.[8–10]
Dr. Z. J. Ni, Prof. H. L. Dong, H. L. Wang, Dr. Y. Zou, Q. Zhao,
Prof. Y. G. Zhen, Prof. L. Jiang, Prof. W. P. Hu
Beijing National Laboratory for Molecular Sciences
Key Laboratory of Organic Solids
Institute of Chemistry
Chinese Academy of Sciences
To date, thiophene-flanked diketopyrrolopyrrole (TDPP)-
based polymers have been extensively investigated.[4,5] Espe-
cially, TDPP copolymers with common thiophene-derived
donors have exhibited remarkably high hole mobilities in past
reports.[11,12] However, electron mobility of these materials
is largely lag behind their hole mobilities, most probably due
to relatively weak electron deficiency and insufficient lowest
unoccupied molecular orbitals (LUMO) levels for electron
injection and transport. To address this issue, substitution of
electron donors with acceptors, such as benzothiazole (BTz),[13]
difluorothiophene (2FT),[14] tetrafluorobenzene (TFB),[15] and
1,2-bis(3,4-difluorothiophen-2-yl)ethene (4FTVT)[16] were car-
ried out. Unfortunately, copolymers derived from this protocol
generally display balanced ambipolar transport by identical
hole/electron mobilities and dominant n-transporting ones
are rare.[17] Furthermore, adoption of TDPP in the backbone of
copolymers usually leads to narrowed bandgap, thereby deterio-
rating their n-channel on/off ratio (less than 1000).[6] Besides
acceptor substitution, another route features molecular modi-
fication on DPP flankers. Electron-withdrawing units, such as
pyridine (Py),[14,18] thiazole (Tz),[19] and π-extended DPP core[20]
are adopted to strengthen polymer electron deficiency. How-
ever, these attempts fail to give high electron mobility products.
Moreover, a majority of high electron mobility DPP polymers
are fabricated on rigid substrates, restricting their application
under flexible conditions. Hence, the acquisition of n-type DPP
copolymers that simultaneously accommodate high electron
Beijing 100190, P. R. China
E-mail: huwp@iccas.ac.cn, huwp@tju.edu.cn
Dr. Z. J. Ni, Prof. W. P. Hu
Tianjin Key Laboratory of Molecular Optoelectronic Sciences
Department of Chemistry
School of Science
Tianjin University, and Collaborative Innovation Center of Chemical
Science and Engineering (Tianjin)
Tianjin 300072, P. R. China
Prof. H. L. Dong, S. Ding
Beijing Key Laboratory for Optical Materials and Photonic Devices
Department of Chemistry
Capital Normal University
Beijing 100048, P. R. China
H. L. Wang, Q. Zhao, Prof. Y. G. Zhen, Prof. L. Jiang
School of Chemistry and Chemical Engineering
University of Chinese Academy of Sciences
Beijing 100049, P. R. China
Prof. F. Liu
Department of Physics and Astronomy
Shanghai Jiaotong University
Shanghai 200240, P. R. China
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adma.201704843.
DOI: 10.1002/adma.201704843
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Figure 1. a) Molecular structures of the novel copolymers, PPyDPP-T, PPyDPP-2FT, PQDPP-T, and PQDPP-2FT. b) Synthetic procedures of the copoly-
mers PQDPP-T and PQDPP-2FT.
mobility and on/off ratio on flexible substrates presents an
urgent and demanding task.
mobility of 6.04 cm2 V−1 s−1, among the highest value in OFETs
fabricated on flexible substrates up to date. Moreover, due to
the widened bandgap and strengthened electron deficiency
of PQDPP, n-channel on/off ratio over 105 with suppressed
hole transport is first realized in the ambipolar DPP-based
copolymers.
The synthetic routes for PQDPP-T and PQDPP-2FT are
depicted in Figure 1b. The important intermediate 6-bro-
moquinoline-2-carbonitrile 2 was synthesized via a one-
step iodine-catalyzed ammoxidation of 6-bromo-2-meth-
ylquinoline 1 reported by Cheng.[22] However, the yield of 2
decreased obviously, when this procedure was carried out in
gram scale. An alternative multistep protocol for compound
2 has been developed. The intermediate 2 was obtained
from direct cyanation of 6-bromoquinoline N-oxide using a
Herein, to address aforementioned limitations, we report
the design and synthesis of novel π-extended quinoline-flanked
DPP (abbreviated as QDPP) motif and corresponding copoly-
mers named PQDPP-T and PQDPP-2FT (Figure 1a) for high-
performing n-type OFETs in flexible organic thin film devices.
Serving as DPP flankers in backbones, quinoline is found to
effectively tune copolymer optoelectric properties. Compared
with TDPP and pyridine flanked DPP (PyDPP) analogs,[14,21]
widened bandgaps and strengthened electron deficiency
are achieved. Moreover, both hole and electron mobility are
improved two orders of magnitude than those of PyDPP ana-
logs (PPyDPP-T and PPyDPP-2FT). Notably, featuring an all-
acceptor-incorporated backbone, PQDPP-2FT exhibits electron
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Figure 2. a,b) UV–vis–NIR absorption spectra of PPyDPP-T and PQDPP-T, PPyDPP-2FT and PQDPP-2FT. c) Secondary electron cutoff UPS spectra of
polymers deposited on gold film. d) Valence band spectra.
less toxic trimethylsilyl cyanide as the cyano source.[23] Fol-
lowed quinoline flanked DPP 5 was prepared by condensa-
tion reaction of 2 with diisopropyl succinate. The quinolone-
flanked DPP monomer 6 was obtained after the N-alkylation
of 5 with branched 2-decyltetradecyl chain, which ensures
the sufficient solubility of the quinolone-flanked DPP poly-
mers. Finally, polymers PQDPP-T and PQDPP-2FT were
synthesized by a modified Stille polymerization of 6 with
bis-stannylated thiophene or bis-stannylated difluorothio-
phene in high yield within only 10 min. For control experi-
ment, reference polymers PPyDPP-T and PPyDPP-2FT were
prepared by the similar procedure. The detailed synthetic
procedures of polymers are described in the Supporting
Information. Number-averaged molar mass (Mn) and dis-
persity (Ð) of 119.9 KDa and 1.84 for PQDPP-T, 67.4 KDa
and 2.01 for PQDPP-2FT, 27.2 KDa and 2.92 for PPyDPP-T,
and 20.2 KDa and 1.90 for PPyDPP-2FT were obtained after
the removal of low molecular weight oligomers through Sox-
hlet extraction. Thermogravimetric analysis demonstrated
that all polymers were thermally stable with a degradation
temperature (Td) higher than 350 °C (Figure S1, Supporting
Information).
UV–vis spectroscopy was used to determine the bandgap of
the polymers. Calculated from absorption onset in Figure 2a,b,
bandgaps of PPyDPP-T and PPyDPP-2FT were 1.71 and 1.78 eV,
respectively. Substitution of pyridine by quinoline flankers led
to slightly widened bandgaps, which were 1.74 and 1.80 eV
for PQDPP-T and PQDPP-2FT, respectively. The highest occu-
pied molecular orbitals (HOMO) were measured by ultraviolet
photoelectron spectroscopy (UPS) (Figure 2c,d) and sum-
marized in Table 1. PPyDPP-2FT and PQDPP-2FT’s HOMO
levels are −5.72 and −5.64 eV, respectively. Reduction of optical
bandgaps from HOMO levels gives LUMO levels. Due to an all-
acceptor alternating structure, their LUMO levels are −3.94 and
−3.84 eV for PPyDPP-2FT and PQDPP-2FT, respectively, and
notably lower than those of thiophene-flanked DPP polymers.
Hence, enhanced electron transport over reported DPP poly-
mers is highly anticipated. For comparison, density functional
theory (DFT) calculation for methyl-substituted trimers were
conducted by B3LYP/6-31G (d,p). The optimized structures
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Table 1. Bandgaps and energy levels of the copolymers.a)
to 10−4 cm2 V−1 s−1. This is probably due to the large hole injec-
tion barrier of 1.02 eV in PPyDPP-2FT/Au interface due to the
low-lying HOMO level (−5.72 eV) of PPyDPP-2FT, making hole
transport injection limited.
Polymer
Eg [eV]
1.71
HOMO [eV]
−5.33
LUMO [eV]
−3.62
PPyDPP-T
PPyDPP-2FT
PQDPP-T
PQDPP-2FT
In contrast to PPyDPPs, PQDPP-T showed much improved
and balanced ambipolar charge transport with hole and electron
mobilities of 0.50 and 0.72 cm2 V−1 s−1, respectively (Figure S4,
Supporting Information). Though PQDPP-2FT’s LUMO level
(−3.84 eV) is 0.1 eV higher than PPyDPP-2FT (Table 1), an
unexpectedly high electron mobility of 6.04 cm2 V−1 s−1 is
obtained (Figure 4). Similar to PPyDPP-2FT’s dominant elec-
tron transport property, PQDPP-2FT demonstrates an evidently
suppressed hole channel with mobility of 0.21 cm2 V−1 s−1, giving
a μe/μh ratio of 30. (Table 2). Contact resistance was acquired
by the transfer-line method and calculated to be 20.4 kΩ cm
for PQDPP-2FT and 117.4 kΩ cm for PQDPP-T, which is in
good accordance with their LUMO level (Figure S5, Supporting
Information). Note that reported TDPP polymers with a
donor–acceptor or acceptor–acceptor backbone prototype are
generally p- or ambipolar-transporting.[6,7] To our knowledge,
PQDPP-2FT is one of the few DPP polymers demonstrating
dominant n-channel features. These findings indicate that:
(i) Quinoline flankers are more advantageous over pyridine or
thiophene for highly efficient n-channel DPP-based polymers.
(ii) 2FT presents a powerful electron accepting unit. Conjunc-
tion of 2FT unit with QDPP core enables an all-acceptor con-
taining polymer backbone. Therefore, PQDPP-2FT possesses
strong electron deficiency, potentially facilitating electron trans-
port and n-channel formation.
Furthermore, a correlation between electron-channel onset
voltage (Ve, onset) and LUMO level is uncovered. Among four
polymers, PPyDPP-2FT shows the lowest Ve,onset of 20 V
(LUMO, −3.94 eV), while PQDPP-T and PPyDPP-T require
high VG (over 40 V) to turn-on electron channel (Table 2). This
result imply a low-lying LUMO level is potentially beneficial
for Ve,onset reduction. Similar correlation between HOMO and
hole-channel onset voltage is also found and shown in Table 2.
Though a large electron injection barrier are to be expected
between PPyDPP-T and PQDPP-T/Au interface (0.98 and
0.92 eV), output characterisitics at low VDS region do not sug-
gest similar conclusion (Figures S3 and S4, Supporting Infor-
mation). Therefore, we postulate that high thin film quality and
microstruture are other factors governing OFET performance.
Due to fused heterocycles (quinoline) in PQDPP-2FT back-
bone, its operation under various illumination conditions was
investigated. Under 365 nm (6.22 mW cm−2) and 550 nm
(9.54 mW cm−2) light exposure, PQDPP-2FT displays limited
VOnset shift (2–3 V) and IOff increase by several ten-fold to 10−8
A and retains its original n-channel operation when illumina-
tion is ceased (Figure S6, Supporting Information), implying
a tolerable photosensitivity for practical uses. Control experi-
ments on PQDPP-2FT and P(NDI2OD-T2)[3] were also con-
ducted for comparison. Under identical biasing conditions,
P(NDI2OD-T2) exhibits μe of 0.50 cm2 V−1 s−1, on/off ratio
of 103 and subthreshold swing of 7.5 V per decade, implying
PQDPP-2FT a superior candidate as n-type OFETs (Figure S7,
Supporting Information). Transport property of PQDPP-2FT is
tested on 2 mm PET, its bending stress with a radius of 8 mm
was conducted in Figure S8 (Supporting Information). After
1.78
−5.72
−3.94
1.74
−5.42
−3.68
1.80
−5.64
−3.84
a)Bandgaps of polymers were measured by absorption onset (Eg = 1240/λ) by UV–
vis spectroscopy. HOMO levels were obtained by ultraviolet photoelectron spec-
troscopy. LUMO levels were calculated by subtraction of bandgaps from HOMO
levels.
and frontier molecular orbitals of four trimers are displayed
in Figure S2 (Supporting Information). Their HOMO and
LUMO were well delocalized along their backbones. The DFT
calculation showed that PPyDPP-T, PPyDPP-2FT, PQDPP-T,
and PQDPP-2FT trimers’ HOMO were −5.12, −5.23, −5.17,
and −5.25 eV, respectively, and their LUMO levels were −3.09,
−3.24, −3.05, and −3.15, respectively. Though simulation ener-
getic levels of four trimers are different from UPS results, they
share the identical tendency by: (i) Quinoline flankers deliv-
ered widened the polymer bandgaps. (ii) Deeper LUMO energy
levels in PPyDPP-2FT and PQDPP-2FT, resulting from syner-
gistic effect of electron-deficient pyridine/quinoline flankers
and 3,4-difluorothiophene units.
The ambipolar transport properties of PPyDPP- and PQDPP-
based copolymers were evaluated by OFET characterization. To
facilitate electron channel stable in ambient atmosphere, OFETs
were fabricated with a top-gated architecture on polyethylene
terephthalate (PET) (Figure 3a,b). Polymer active layers were
spin-coated from o-dichlorobenzene (o-DCB) solution on pre-
defined gold contacts. Then, 900 nm polymethylmethacrylate
(PMMA) served as dielectric[17] (Ci, 3.3 nF cm−2) and 50 nm
thermally-deposited aluminum was used as gate. Saturation
mobility was extracted using IDS square root dependence on
gate voltage (VG) under a VDS of 80 V. Overall, PQDPPs exhibit
evidently higher hole and electron mobility than those of PPy-
DPPs by two orders of magnitude, as summarized in Table 2.
Hole/electron mobilities of PPyDPP-T are rather low ranged
from 10−4 to 10−3 cm2 V−1 s−1 (Figure S3, Supporting Informa-
tion). With the introduction of a strong electron-accepting unit,
2FT in the polymer backbone, PPyDPP-2FT showed enhanced
electron mobility tenfold times higher than that of PPyDPP-T,
up to 0.021 cm2 V−1 s−1. Meanwhile, its hole mobility is reduced
Figure 3. a) OFET array fabricated on flexible PET substrate. b) 3D sche-
matic illustrating the top-gated OFET structure for the characterization
of the copolymers.
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Table 2. Thin film device characteristics of copolymers.a)
By contrast, PPyDPP-T and PPyDPP-2FT possess
Ǻ
a value of 3.60 and 3.53 . This observation is in
μh (cm2 V−1 s−1
)
μe
Polymer
Ion
p-channel
/
Vh, onset
[V]
Ion
n-channel
/
Ve, onset
[V]
good agreement with close π–π spacing effectively
promotes charge transport by reducing interchain
charge hopping barrier and leads to high mobili-
ties. Crystal coherence length is a parameter quan-
tifying the polymer crystalline order range, which is
calculated using the Scherrer equation.[24] Polymers
with 2FT segment display higher range of crystal-
line order. In-plane (010) coherence lengths for
PPyDPP-T, PPyDPP-2FT, PQDPP-T, and PQDPP-
2FT were 32.2, 41.8, 29.4, and 65.2 Å, respectively.
off
off
[cm2 V−1 s−1
]
PPyDPP-T
PPyDPP-2FT
PQDPP-T
102
102
37.5
20.0
45.8
35.0
5–8 × 10−4
1–3 × 10−4
0.28–0.50
0.13–0.21
−38.0
−59.0
−35.5
−47.7
2–4 × 10−3
10
0.015–0.021
0.51–0.72
4.25–6.04
103
103
103
PQDPP-2FT
103
105
a)OFETs were characterized within a VG range from 0 to 90 V and a VDS of 80 V.
200 times bending, it nearly retained its n-channel transfer
curve unchanged.
These results clearly indicate: (i) With π-extended conjugation
length, quinoline flankers deliver stronger intermolecular inter-
actions than pyridine in DPP polymer backbone. (ii) 2FT unit
render denser polymer packing, as well as crystalline structure
with greater range than thiophene unit. This is probably due
to the formation of hydrogen bonding between fluorine atoms
on 2FT and aromatic hydrogen atoms on quinoline/pyridine
flankers. Such an intramolecular interaction can enhance the
planarity of polymer backbone to facilitate efficient interchain
charge transport. Besides above findings, all polymers except
PQDPP-2FT exhibit a more pronounced (010) diffraction pat-
tern in out-of-plane direction than in-plane. In other words,
these three polymers are inclined to adopt a preferential face-on
We proceed to study thin film crystallization with grazing-
incidence X-ray diffraction (GIXD) (Figure 5). Both PPyDPPs
and PQDPPs exhibit strong crystallization feature. In out-of-
plane orientation, both PPyDPPs and PQDPPs evidently display
a succession of five (h00) peaks, implying an ordered lamellar
packing in thin film state. Moreover, (010) diffraction peaks
were also present in out-of-plane direction, indicating a mixed
orientation of face-on and edge-on. π–π stacking distance was
calculated using their in-plane (010) peaks. Especially, shorter
in-plane π–π stacking distance was observed in PQDPPs, which
Ǻ
was 3.49 and 3.45 for PQDPP-T and PQDPP-2FT, respectively.
Figure 4. a) n-type transfer characteristics of PQDPP-2FT. b) n-type output characteristics of PQDPP-2FT. c) A summary of ambipolar mobilities of the
four copolymers. d) Ve, onset and Vh, onset of the four copolymers.
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Experimental Section
Synthesis of PQDPP-2FT: Under an argon
atmosphere, (3,4-difluorothiophene-2,5-diyl)
bis(trimethylstannane) (45.7 mg, 0.10 mmol),
3,6-bis(6-bromoquinolin-2-yl)-2,5-bis(2-
decyltetradecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-
dione (122.1 mg, 0.10 mmol), Pd2(dba)3 (2.7 mg,
0.003 mmol, 3 mol %), and (o-Tol)3P (2.7 mg,
0.009 mmol, 9 mol %) were dissolved in degassed
toluene (3 mL) and NMP (0.6 mL) in a Schlenk
tube. The reaction was stirred at 110 °C for 10 min,
followed by addition of 2-bromothiophene (0.3 mL)
to react with the trimethylstannyl end group.
The mixture was further stirred at 100 °C for 1 h.
After cooling to room temperature, the mixture
was precipitated into chilled methanol (20 mL).
Then the crude polymer was collected by filtration
and purified by Soxhlet extraction with acetone,
hexane and the remaining product was dissolved
with refluxing 1,1,2,2-tetrachloroethane. The
tetrachloroethane solution was then concentrated
by evaporation and precipitated into methanol,
dried over vacuum. Finally, the desired polymer
was obtained. 90% yield; GPC(1,2-dichlorobenzene,
120 °C): Mn = 67.4 KDa, Mw = 135.8 KDa, Ð = 2.01;
Anal. Calcd. for C76H108F2N4O2S, C, 77.37; H, 9.23;
N, 4.75; Found: C, 77.20; H, 9.20; N, 4.49.
Device Fabrication: A top gate, bottom contact
configuration was used to evaluate the polymer
semiconductors. 200 μm thick PET substrates
were rinsed with deionized water, ethanol,
acetone, then dried by nitrogen before device
fabrication. Next, 20 nm gold interdigitated
fingers (channel width 4500 μm, channel length
90 μm) were deposited by thermal evaporation.
Figure 5. 2D-GIXD diffraction images of a) PPyDPP-T, b) PPyDPP-2FT, c) PQDPP-T, and
d) PQDPP-2FT films.
All polymers were dissolved in 1,2-dichlorobenzene (o-DCB) with a
concentration of 4 mg mL−1. The polymer solution was spin-coated
on PET at a speed of 1800 rpm and dried at 150 °C for 10 min on a
hotplate. PMMA dissolved in n-butyl acetate (60 mg mL−1) served as the
dielectric and dried at 90 °C for 30 min. To complete the fabrication,
100 nm thick aluminum was thermally deposited through shadow mask
as gate contact. OFET characteristics were carried out in ambient using
a Keithley 4200 semiconductor characterization system.
packing in thin film. By contrast, this feature is less significant
in the case of PQDPP-2FT. Edge-on rather than face-on packing
is reported to be beneficial for highly efficient charge transport
(in horizontal direction from source to drain) in OFETs, which
accounts for the superior electron mobility in PQDPP-2FT. Thin
film morphology was studied by atomic-force microscopy in
Figure S9 (Supporting Information). PPyDPP-2FT, PQDPP-T,
and PQDPP-2FT showed smooth surfaces with root-square-
mean roughness below 1 nm. PPyDPP-T’s surface is notably
uneven (2.71 nm).
Supporting Information
In conclusion, a quinoline-flanked DPP acceptor was
designed and synthesized efficiently. Copolymerization
with thiophene/difluorothiophene afforded two copolymers
PQDPP-T and PQDPP-2FT with widened bandgaps and
strengthened electron deficiency compare to their PyDPP
and TDPP analogs. Moreover, in this manuscript, we show:
(i) As indicated by X-ray diffraction, PQDPPs display
enhanced intermolecular interaction by shortened π–π
stacking distances, which is advantageous for achieving
high-performing polymers. (ii) OFET characterization and
ultraviolet photoelectron spectroscopy uncover a preferential
electron transport rather than hole and deep-lying LUMO
in PQDPP. The all-acceptor containing copolymer PQDPP-
2FT exhibits an electron mobility over 6.00 cm2 V−1 s−1 with
on/off ratio over 105, which is among the highest value in
OFETs fabricated on flexible substrates to date. Our results
demonstrate that QDPP is a superb building unit for high-
performance OFET polymers.
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
Z.J.N., H.L.D., H.L.W., and S.D. contributed equally to this work.
The authors thank Dr. Yang Li and Dr. Yanfeng Dang for the DFT
calculations. This work was supported financially by the Ministry of
Science and Technology of China (2016YFB0401100, 2017YFA0204503,
2013CB933403, and 2013CB933504), the National Natural Science
Foundation of China (51633006, 51733004, 91433115, 91222203,
91233205, 51303185, and 21473222), and the Chinese Academy of
Sciences (XDB12030300).
Conflict of Interest
The authors declare no conflict of interest.
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Keywords
charge transport, conjugated copolymers, electron mobility, flexible
devices
[14] C. J. Mueller, C. R. Singh, M. Fried, S. Huettner, M. Thelakkat, Adv.
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Received: August 24, 2017
Revised: December 12, 2017
Published online:
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