Narrow band-gap donor-acceptor copolymers based on diketopyrrolopyrrole and diphenylethene: Synthesis, characterization and application in field effect transistor

Article abstract of DOI:10.1016/j.dyepig.2015.12.015

Three low band-gap diketopyrrolopyrrole based polymers with varying donor groups of furan, thiophene and phenyl were synthesized and then copolymerized with diphenylethene. We investigate the influence of different donor groups and comonomers on the band-gap and field effect transistors. The efficient synthesis of the diketopyrrolopyrrole based copolymers was clearly characterized by a variety of measurements. Two dimensional Grazing Incident X-ray Diffraction was measured to prove that furan and thiophene based copolymers have ordered edge-on structure. These copolymers exhibited strong π-π stacking and excellent hole mobilities when applied in the electric double layer field effect transistors. The high mobility of 2.36 cm² V^-1 s^-1 with an on/off ratio of 10³ was achieved.

Full text of DOI:10.1016/j.dyepig.2015.12.015

Dyes and Pigments 127 (2016) 37e44
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Narrow band-gap donoreacceptor copolymers based on
diketopyrrolopyrrole and diphenylethene: Synthesis, characterization
and application in field effect transistor
Haoyun Zhu, Wei Huang, Yuli Huang, Junwei Yang, Weizhi Wang*
State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Collaborative Innovation Center of Polymers and
Polymer Composite Materials, Fudan University, Shanghai 200433, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Three low band-gap diketopyrrolopyrrole based polymers with varying donor groups of furan, thiophene
and phenyl were synthesized and then copolymerized with diphenylethene. We investigate the influence
of different donor groups and comonomers on the band-gap and field effect transistors. The efficient
synthesis of the diketopyrrolopyrrole based copolymers was clearly characterized by a variety of mea-
surements. Two dimensional Grazing Incident X-ray Diffraction was measured to prove that furan and
Received 4 October 2015
Received in revised form
30 November 2015
Accepted 16 December 2015
Available online 30 December 2015
thiophene based copolymers have ordered edge-on structure. These copolymers exhibited strong
pep
stacking and excellent hole mobilities when applied in the electric double layer field effect transistors.
The high mobility of 2.36 cm2 Vꢀ1 sꢀ1 with an on/off ratio of 103 was achieved.
© 2015 Elsevier Ltd. All rights reserved.
Keywords:
Diketopyrrolopyrrole
Donor
Acceptor
Diphenylethene
Field effect transistor
Oxidization
1. Introduction
such as thiophene, phenyl, selenophene and furan have been
employed in DPP based copolymers [28e30]. DPP based co-
In recent years, donoreacceptor (DeA)
p
-conjugated polymers
polymers can be prepared with the desired comonomer via either
Suzuki coupling or Stille coupling [31e35]. Variation of the como-
nomer provides vast possibilities with different unit combination
which may cause promising properties for semiconducting devices
[36e38]. The enthusiasm towards various DPP based polymers
accelerates the development of many applications in the polymer
solar cells (PSCs) and field effect transistors (FETs) [39e43]. For
instance, Sonar and co-workers have reported three DPP based
copolymers using furan as the donor group and alternatively using
phenylene, naphthalene or anthracene as donor comonomer blocks
which finally achieved a mobility of 0.11 cm2 Vꢀ1 sꢀ1 [44]. Shahid
and co-workers have reported the synthesis of two alternating
copolymers of thiophene and selenophene flanked DPP with
dithienothiophene which exhibited great charge transport prop-
with narrow-band-gap have emerged as promising candidates for
optoelectronic devices [1e8]. Diketopyrrolopyrrole (DPP) was mostly
used as an electron acceptor to form DeA copolymers for its highly
conjugated lactam structure, electron withdrawing capability and a
high degree of planarity [9,10]. The polymers involving DPP units have
showed enhancing intramolecular charge transport via extended
delocalized p-electron distribution along the backbone [11e15]. The
low band-gap which originates from coplanarity and well conjugated
structure of DPP based copolymers makes these polymers as the key
materials for semiconducting application [16e20].
Molecular packing of donoreacceptor has a great effect on the
performance of electronic device [21e25]. By carefully selecting the
electron donating groups on the lactam ring or the comonomer, its
highest occupied molecular orbitals (HOMO) and lowest occupied
molecular orbitals (LUMO) can be tuned which leads to innovative
low band-gap materials [26,27]. Various electron donating groups,
erties with high mobility up to 0.23 cm2 ꢀ1 sꢀ1 [29]. Yun and co-
V
workers have reported that by introducing nitrile group as an
electron withdrawing unit and vinyl as linkage in the DPP-based
copolymer, a high mobility of 7.0 cm2 Vꢀ1 sꢀ1 was obtained when
applied in field-effect transistors [45].
We are interested in systematically investigating the effects of
different flanking block and comonomers on lowering the band
* Corresponding author.
E-mail address: weizhiwang@fudan.edu.cn (W. Wang).
http://dx.doi.org/10.1016/j.dyepig.2015.12.015
0143-7208/© 2015 Elsevier Ltd. All rights reserved.

38
H. Zhu et al. / Dyes and Pigments 127 (2016) 37e44
gap. Here, furan, thiophene and phenyl were used to attach on the
DPP electron accepting moiety and then copolymerized with
diphenylethene units which were shorted as PFDPP, PTDPP and
PPDPP. Diphenylethene have been used in many materials with
high charge carrier mobilities [46,47]. The chemical structures of
three DPP based copolymers PFDPP, PTDPP and PPDPP are shown
in Scheme 1. The values of aromatic resonance energy for furan,
thiophene and phenyl are 0.70 eV, 1.26 eV and 1.56 eV, respectively.
The electron donating strength suggests the effective conjugation
length and enhancement of planarity which would decrease the
band-gap of organic semiconducting devices [48]. With dipheny-
lethene units, DDP derivatives provide a longer effective conjuga-
tion length and promote a more delocalized HOMO distribution
along the backbone which would enhance the intermolecular
charge-carrier hopping [35]. To further study the electron donating
comonomers, diphenylethene was oxidized to become a rigid
structure. The three oxidized copolymers O-PFDPP, O-PTDPP and
O-PPDPP are shown in Scheme 1. Lei and co-workers have
substituted the donor part of conjugated polymers which showed
the rotatable donor groups provided better FET performance than
the rigid donor groups [24]. Here we demonstrate that comonomer
with rigid structure leads to a larger band gap due to worse
pep
stacking and intermolecular interaction which originates from the
increasing torsional angle. The copolymers were characterized by
nuclear magnetic resonance spectroscopy (NMR), gel permeation
chromatography (GPC), thermogravimetric analysis (TGA), UVevis
absorption and cyclic voltammetry (CV). PFDPP, PTDPP and PPDPP
based electric double layer transistors exhibited a p-channel per-
formance with high mobilities. The peak mobility value of
2.36 cm2 Vꢀ1 sꢀ1 can be reached when PFDPP was applied to field
effect transistors.
2. Experimental
2.1. Materials and instruments
Unless otherwise stated, all of reagents and chemicals used were
purchased from Aldrich or Sinopham Chemical Reagent Company.
Scheme 1. Procedures for the synthesis of the monomer and the polymer. Conditions: (a) t-BuOK, t-amyl alcohol, 110 ꢁC, 4 h, under argon; (b) 2-ethyhexyl bromide, DMF, potassium
carbonate, 145 ꢁC, 15 h, under argon; (c) NBS, chloroform, rt, 40 h; under argon; (d) Pt(PPh3)4, DMF, 90 ꢁC,24 h; (e) Pd(PPh3)4, 2 M K2CO3(aq), toluene, 110 ꢁC, 8 h; (f) FeCl3, CHCl3,
3 min.

H. Zhu et al. / Dyes and Pigments 127 (2016) 37e44
39
1H NMR and 13C NMR spectra were measured on a Bruker
3. Results and discussion
AVANCE III HD 300 MHz. FT-NMR spectrometer in dimethyl sulf-
oxide-d6 and deuterated chloroform (CDCl3). Chemical shifts are in
The synthetic route of the monomers and target polymers is
clearly outlined in Scheme 1. Monomer 1, monomer 2 and mono-
mer 3 were synthesized through the condensation reaction [49]. To
increase the solubility and film-forming ability, two octyl groups
were attached at the 2, 5 position of the DPP moiety. It was
necessary to improve the solubility of these DPP based copolymers
since they are poorly soluble in common organic solvents which
ppm units using tetramethylsilane (TMS;
d
¼ 0) as an internal
standard. The samples were analyzed by AB SCIEX 5800 matrix
assisted laser desorption ionization-time of flight mass spec-
trometer (MALDI-TOF). Gel permeation chromatography (GPC)
measurements were recorded on an Agilent/Wyatt 1260 gel
permeation chromatographer. The calibration was managed by
employing commercially available polystyrene. Thermal gravi-
metric analysis (TGA) measurements were done on a Perkin Elmer
Pyris 1 thermogravimetric analyzer heating from 50 to 800 ꢁC
with a warming rate of 10 ꢁC/min, under dry N2 flow. Cyclic vol-
tammetry was operated on a T30/FRA2 electrochemical worksta-
tion. Using ferrocene (4.8 eV under vacuum) as the internal
standard, the measurements of the products films coated on a
glassy carbon electrode (0.08 cm2) were performed in an elec-
results from strong hydrogen-bonding structure and
pep inter-
molecular interaction [50]. M1 and M2 were then obtained through
bromination using n-bromosuccinimide (NBS) in CHCl3 at room
temperature. M4 was obtained via a simple addition reaction with
the help of a platinum catalyst. By Suzuki coupling reaction in
toluene using Pd(PPh3)4 as a catalyst, Aliquat 336 as a phase
transfer catalyst at 110 ꢁC for 8 h, the target polymers PFDPP,
PTDPP and PPDPP were obtained. This achievable and efficient
synthesis strategy gave polymers in good yield with good solubility
in organic solvents including tetrahydrofuran, chlorobenzene,
chloroform and 1,2-dichlorobenzene. All the details of the synthesis
procedure of PFDPP, PTDPP and PPDPP are described
in Supplementary data (S1).
All the monomers and copolymers were characterized by nu-
clear magnetic resonance spectra (NMR). Every detailed spectrum
of 1H NMR and 13C NMR has been shown in Supplementary data
(Figs. S9eS29) to prove the successful synthesis. As shown in the
1H NMR spectra of PFDPP, PTDPP and PPDPP, we can obviously
find that the peaks coincide with their corresponding copolymers.
For instance, the spectrum in the range of 7.0e8.0 for PPDPP shows
a continuous multi peaks while the peaks at 8.2 arise for PFDPP and
at 8.7 arise for PTDPP. The mass spectrometric data of monomers
demonstrate the successful synthesis of expected products as
shown in the supporting information (Figs. S1eS8).
The values of weight-average molecular weight (Mw), the
number average molecular weight (Mn) and the polydispersity in-
dex (PDI) for PFDPP, PTDPP and PPDPP were determined by
permeation chromatography (GPC) with tetrahydrofuran as the
eluent and polystyrene as the standard. As revealed in Table 1, the
values of Mn for PFDPP, PTDPP and PPDPP were measured to be
7400, 8500 and 3900 and the polydispersity indexes (PDIs) of
PFDPP, PTDPP and PPDPP were measured to be 1.67, 1.56 and
1.51 (see GPC profiles in Fig. S30 in Supplementary data). The
PPDPP has relatively lower Mn of 3900 with PDI of 1.51 which may
be due to the reactivity and steric hindrance of the donor segments.
To measure the thermal stability of the resulting polymers, ther-
mogravimetric analysis (TGA) has been performed under nitrogen.
As shown in Fig. 1, PFDPP, PTDPP and PPDPP showed a 5% weight
loss at 374 ꢁC, 310 ꢁC and 215 ꢁC, respectively, which indicates good
thermal stability of PFDPP and PTDPP.
trolyte of 0.1
M
tetrabutylammonium hexaflurophosphate
(TBAPF6) in acetonitrile at a scan rate of 100 mV/s at room tem-
perature under the protection of N2. The reference electrode was
a Ag/AgNO3 electrode and a platinum wire was applied as the
counter electrode. A PerkineElmer Lambda 750 UVevisible spec-
trophotometer was employed for UV spectra in CHCl3 solution.
Synchrotron-based two-dimensional gazing-incidence X-ray
diffraction data (2D GIXRD) were recorded at BL14B1, Shanghai
Synchrotron Radiation Facility, with the gazing-incidence
angle ¼ 0.25ꢁ and
l
¼ 0.124 nm. Samples were spin-coated on
SiO2 (300 nm)/Si substrates at 3000 r/m for 60 s from 0.1 wt%
chloroform solution of the copolymers. Data processing was
implemented by means of the program SAINT, meanwhile a pro-
gram of SADABS was employed for scaling of the diffraction data,
an experiential absorption correction based on redundant re-
flections and the utilization of a decay correction. The final
structures of the products were resolved by utilizing the straight-
ways procedure in the program library of Bruker SHELXL and
clarified by the least-squares full-matrix approaches on F2. All of
the non-hydrogen atoms were refined using the anisotropic
thermal parameters. Simultaneously, hydrogen atoms were com-
bined as fixed contributors at calculated positions, with the
isotropic thermal parameters based on carbon atoms where they
were bonded.
2.2. FET device fabrication
Some commercially available highly p-doped SiO2 (300 nm)/Si
wafers were washed by acetone and methanol, H2O2/H2SO4 and
deionized water in turn. The conjugated polymers in CHCl3 so-
lution (2 mg/mL) were spin-coated on these clean SiO2/Si wafers
at the rotating speed of 7000 r/min. The thin films as the semi-
conductor were placed in a vacuum environment for a while to
evaporate the surplus solvent. The 50 nm thick gold drain and
source electrodes (the typical channel length is 0.6 mm, and
width is 1 mm) were vapor-deposited on the polymer thin film.
The top gate dielectric was formed with a kind of ion gel which
consists of an ionic liquid, 1-ethyl-3-methylimidazolium bis(tri-
fluoromethylsulfonyl)imide, a triblock copolymer, poly(styrene
Fig. 2(a) shows the intensity-normalized UVevis absorption
spectra in dilute chloroform solution. The absorption peaks (lmax
)
at 789 nm, 627 nm and 500 nm for PFDPP, PTDPP and PPDPP are
attributed to a strong intermolecular charge transfer (ICT). The
shoulder peaks of PFDPP and PTDPP in Fig. 2(a) may be related to
Table 1
GPC data of PFDPP, PTDPP and PPDPP.
block-methyl
methacrylate-block
styrene)
(PS-PMMA-PS;
MPS ¼ 3 kg molꢀ1, MPMMA ¼ 8.5 kg molꢀ1, Mw ¼ 14 kg molꢀ1) and
ethyl acetate solution. The weight ratio of the ionic liquid, solvent
and the polymer was 10:20:0.7. The prepared ionic solution was
drop-cast to cover both the surfaces of the copolymer and the
drain and source electrodes. Then the top-gate electrode was
formed by covering a 0.03 mm foil of Al on the transistor
channels.
Polymer
Mna/g molꢀ1
Mwb/g molꢀ1
PDIs
PFDPP
PTDPP
PPDPP
7400
8500
3900
10700
13300
5900
1.67
1.56
1.51
a
The value of number-average molecular weight.
The value of weight-average molecular weight.
b

40
H. Zhu et al. / Dyes and Pigments 127 (2016) 37e44
whereas the torsional angle between the DPP units and phenyl ring
(33ꢁ) is much more higher. In our study, M3 has formed long and
sharp needle-like crystals while M1 and M2 didn't form any crystals
(see single crystal X-ray diffraction data of M3 in Table S1 and the
schematic diagram in Fig. S31 in Supplementary data). The large
torsional angle of 35ꢁ between the phenyl and the lactam ring of
M3 is close to the previous report. The large torsional angle renders
the lower absorption wavelength as compared to the other two
derivatives for the weak
pep interaction. We deduce that the
torsional angle for PFDPP and PTDPP was also much smaller than
that of PPDPP which is verified by the UV absorption wavelength.
Joydeep and co-workers have proved that the phenyl-based poly-
mers were non-planar as they synthesized three vinylene linked
DPP based copolymers with phenyl, thienyl, and selenyl units as
donors which supported our studies [17].
To further study the influence of the donor moieties, we
attempted to oxidize the diphenylethene by using the anhydrous
FeCl3 as an oxidant which has been regularly used for the synthesis
of some polycyclic aromatic hydrocarbon [47]. In Fig. 2(a), we can
observe that the spectra of O-PFDPP, O-PTDPP and O-PPDPP show
unusual blue-shift absorption maximum in dilute chloroform so-
lution compared to PFDPP, PTDPP and PPDPP. The result may be
attributed to the increasing torsional angle between the DeA unit
and diphenylethene comonomer moiety of these oxidized co-
polymers. The large torsional angle leads to worse coplanarity of
Fig. 1. The TGA spectra of PFDPP, PTDPP and PPDPP.
the intermolecular aggregation state which results from the strong
polarity of the lactam groups of DPP units or a spectral feature of
the polymer chain [33]. Judging from the onset of absorption
spectra (lonset), the optical band-gaps of PFDPP, PTDPP and PPDPP
are calculated as 1.36 eV, 1.57 eV, and 2.12 eV, respectively. A
gradual bathochromic shift can be observed from PPDPP to PTDPP
to PFDPP, indicating the decrease of the band-gap which results
from the different electronic properties and structure effects of all
these copolymers. The repulsive interaction between the phenyl
rings and the DPP units would lead to a twisted structure with less
the whole backbone, worse pep stacking and less effective orbital
overlap. Above all, we presume that rigid comonomer which re-
strains the rotation of the phenyl and hence influence coplanarity
of the backbone, accordingly affect the
gation of DDP based copolymers.
pep stacking and aggre-
efficient
pep stacking whereas thiophene and furan rings on the
DPP core help alleviate the repulsive interaction [48]. We speculate
the interaction between the C]O on the DPP core and the O atom
from the furan analogs was stronger than the interaction between
the C]O on the DPP core and the S atom from the thiophene an-
alogs, while the interaction between the C]O on the DPP core and
the CeH of the phenyl ring was much weaker. As a result, the
torsional angle increased as well as the absorption wavelength
reduced. Yuan and co-workers have reported that the furan based
DPP copolymer had stronger intermolecular interactions than
thiophene based copolymers which agrees well with our study [51].
To investigate the solid state packing and crystal structure of
DPP based polymers, single crystal X-ray diffraction was measured
by recrystallizing the polymers in n-hexane/acetone solution. As
described in the report of Dhar and co-workers, the torsional angle
between the DPP group and donating group changes by substitut-
ing the donor moieties [48]. The torsional angle for thiophene
based polymer and selenophene based polymer is 9ꢁ and 12ꢁ
The photographs in Fig. 2(b) show their fluorescent pictures in
the solid state under 365 nm UV irradiation and the solution state
in the daylight. It is obvious to find the color of PFDPP, PTDPP and
PPDPP changes after oxidization by locking up the phenyl rings.
PFDPP shows the weakest PL emission while PPDPP shows the
strongest PL emission which may be due to the different state of
coplanarity for these copolymers. The coplanarity of PFDPP makes
the charge transport much easier than PPDPP, as a result, PPDPP
shows the strongest PL emission which was caused by the blocked
electron transport. Furthermore, the oxidized copolymers O-
PFDPP, O-PTDPP and O-PPDPP in Fig. 2(b) show relatively stronger
PL emission for the worse coplanarity as we have mentioned above.
As a result, poor effects on the field effect transistors properties
could be achieved for the weaker charge transfer among the
oxidized copolymers.
In order to study the molecular packing and crystallinity of
different electron donating groups on solid molecular packing and
Fig. 2. (a) Normalized UVevis absorption spectra in CHCl3 of PFDPP, O-PFDPP, PTDPP, O-PTDPP, PPDPP and O-PPDPP. (b) The photographs of the CHCl3 solutions of PFDPP, O-
PFDPP, PTDPP, O-PTDPP, PPDPP and O-PPDPP in the daylight and under 365 nm UV irradiation.

H. Zhu et al. / Dyes and Pigments 127 (2016) 37e44
41
Table 2
ordering, two dimensional Grazing Incident X-ray Diffraction (2D
GIXRD) measurements were conducted on the spin-coated thin
film held at room temperature. In the 2D GIXRD patterns, qxy and qz
represent the in-plane and out-of-plane components of the scat-
tering vector q, respectively. As shown in Fig. 3(a) and (b), PFDPP
and PTDPP films exhibit Bragg peaks of 001 along the out-of-plane
direction, indicating that PFDPP and PTDPP have an ordered edge-
on structure. But no diffraction peak in the 2D GIXRD pattern is
observed in the case of PPDPP. The (100) layer distance of each
polymer, the d-spacing ð¼ 2p=qz*Þ, is derived from the out-of plane
intensity profiles at qxy ¼ 0. The layer distances of PFDPP and
PTDPP are 1.50 and 1.31 nm, respectively.
Electrochemical properties of PFDPP, O-PFDPP, PTDPP, O-PTDPP, PPDPP and O-
PPDPP.
Polymer
Eg (eV)
HOMO (eV)
Eonset-ox (eV)
LUMO (eV)
PFDPP
O-PFPDD
PTDPP
O-PTDPP
PPDPP
O-PPDPP
1.36
1.39
1.57
1.69
2.12
2.28
ꢀ5.09
ꢀ5.81
ꢀ5.11
ꢀ5.26
ꢀ5.42
ꢀ5.60
0.34
1.06
0.36
0.51
0.67
0.85
ꢀ3.73
ꢀ4.42
ꢀ3.54
ꢀ3.57
ꢀ3.30
ꢀ3.32
a negative impact on enhancing the intermolecular interactions.
The observation of the low band-gap of PFDPP has great impor-
tance in developing high performance field effect transistors.
The electrical properties of these polymers were measured by
electric double layer transistors (EDLT). EDLT was known as a good
method to measure the mobility because the electric double layer is
able to accumulate a high carrier concentration with a low gate bias
which is hard to be obtained by a solid insulator gate [51,52]. Unlike
the typical inorganic oxides, the extraordinary high capacitance
allows a low voltage to decrease the quantity of the heat generated
by the working device [53,54]. Fig. 4(a) shows a schematic diagram
of the thin-film top-gated FET with an electric double layer as gate
dielectric and aluminum as the top gate. The synthesized co-
polymers were utilized as the semiconductor layer in FETs. Fig. 4(b)
shows the photograph of the practical ELDTs. The application of a
gate voltage induces the formation of an electrical double layer at
the interface between ion gel and thin film. A charged plane, called
Helmholtz plane can be formed when an electrical bias is applied
between two electrodes of opposite charge which are driven by the
electric field. Two parallels oppositely charged layers are formed
between the gate and the thin film. The field-effect mobility can be
calculated from the following equation for the saturation regime:
HOMO and LUMO energy levels of these polymers were
measured by electrochemical cyclic voltammetry (CV). Typically, a
three-electrode cell, equipped with a Ag/AgNO3 reference elec-
trode,
a Pt-wire counter electrode and a glassy carbon
electrode which was coated with polymer, was employed in an
electrolyte of 0.1 M TBAPF6 in acetonitrile using ferrocene as the
internal standard. The cyclic voltammetry analyses were carried on
under the argon atmosphere at a scan rate of 100 mV sꢀ1. From the
value of onset oxidation potential (Eonset), the HOMO and LUMO
energy levels of the polymers can be calculated by the equation:
HOMO ¼ ꢀe(Eonset-ox ꢀ 0.0468 V)ꢀ4.8 eV, LUMO ¼
where Eonset-ox is determined from cyclic voltammetry, the value
0.0468 V is for ferrocene/ferrocenium vs Ag/Agþ and the
Eg is
D
Eg þ HOMO,
D
evaluated from the UVevis absorption onset. The results from
calculating and CV measurement are listed in Table 2 and the cyclic
voltammograms can be found in Supplementary data (Fig. S32).
Table 2 shows that in the order of PFDPP, PTDPP and PPDPP, the
HOMO energy levels slightly decrease, the LUMO energy levels
slightly increase. The results of HOMO for PFDPP, PTDPP and
PPDPP were determined to be ꢀ5.09 eV, ꢀ5.11 eV and ꢀ5.42 eV,
respectively. The stronger donating strength of furan and thio-
phene raises the HOMO energy levels as compared to phenyl which
improve the coupling ability between donor and acceptor units. On
the other side, the LUMO energy levels of PFDPP and PTDPP are
stabilized for the lower electron affinity of furan and thiophene.
Hence, we can conclude that inclusion of chalcogen atoms affects
the electronic properties to a great extent. In order to make a clear
comparison, results of cyclic voltammetry analyses for the oxida-
tive organic copolymers were measured and listed in Table 2. The
results of HOMO for O-PFDPP, O-PTDPP and O-PPDPP were
determined to be ꢀ5.81 eV, ꢀ5.26 eV and ꢀ5.60 eV, respectively.
The results indicate that oxidation of these copolymers leads to the
increasing band-gap because the rigid structure of comonomer has
mWCi
2L
IDS
¼
ðVG ꢀ VthÞ2
where W and L are the channel width and length, respectively, Ci is
the capacitance per unit area of the dielectric layer. VTH is the
threshold voltage. Ci of the prepared ion gel in this work was
measured to be 20 m
F/cm2. Fig. 5(b) shows the output drain cur-
rentedrain voltage (IDSeVD) characteristics of the thin film FET
device with the ion gel as the gate dielectric. The IDS value increases
with the increasing gate voltage (VD). The IDSeVD characteristic
shows a typical p-channel transistor behavior. Fig. 5(a) shows the
Fig. 3. The 2D GIXRD patterns of (a) PFDPP and (b) PTDPP. The insets in (a) and (b) are schematic diagrams of the orientations of the aggregation structure with respect to the
substrate in the films.

42
H. Zhu et al. / Dyes and Pigments 127 (2016) 37e44
Fig. 4. (a) The 3D model showing the geometric structure of the fabricated top-gate EDLT. (b) The photograph of the practical ELDTs.
Fig. 5. Output characteristics of the ELDTs consist of (a) PFDPP, (c) PTDPP and (e) PTDPP. Transfer characteristic curve at VDS ¼ ꢀ1 V of the ELDTs consist of (b) PFDPP, (d) PTDPP
and (f) PTDPP.

H. Zhu et al. / Dyes and Pigments 127 (2016) 37e44
43
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transfer characteristics curves and output characteristic curves of
PTDPP and PPDPP are shown in Fig. 5(c)e(f). The on/off ratio,
threshold voltage (Vth) and mobilities are calculated and listed in
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crystallinity of diketopyrrolopyrrole-based terpolymers for highly efficient
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the Supplementary data (Table S2). The average value of
m is
2.11 cm2 Vꢀ1 sꢀ1, 1.52 cm2 Vꢀ1 sꢀ1 and 1.14 cm2 Vꢀ1 sꢀ1 for PFDPP,
PTDPP and PPDPP with the similar Ion/Ioff of 103. Among them,
PFDPP exhibits the highest mobility of 2.36 cm2 Vꢀ1 sꢀ1 among all
these copolymers which may be resulted from stronger intra-
molecular interaction, better charge carrier transport and lower PL
depletion. The figure about the calculated mobility plots versus the
related gate voltages for PFDPP, PTDPP and PPDPP can be found
in Supplementary data (Fig. S33). For oxidized copolymers, no field
effect mobility was observed. Hence, the rigid structure of the
oxidized copolymers significantly hinders the charge carrier
transport properties.
€
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Acknowledgment
This work was financially supported by the National Natural
Science Foundation of China (21274027, 20974022) and the Inno-
vation Program of Shanghai Municipal Education Commission
(15ZZ002). The synchrotron-based 2D GIXRD measurements at
beamline BL14B1 were supported by the Shanghai Synchrotron
Radiation Facility (15ssrf00474).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2015.12.015.
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