Synthetic
Metals
180 (2013) 73–
78
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at
ScienceDirect
Synthetic
Metals
journal
h
om
epage:
www.elsevier.com/locate/synmet
Organic
thin-film
transistors
based
on
thieno[3,4-c]pyrrole-4,6-dione
conjugated
polymer
via
oxidative
polymerization
Guobing
Zhang
a,∗
,
Rui
Peng
a
,
Peng
Li
a
,
Xianghua
Wang
a
,
Hongbo
Lu
a
,
Junsheng
Yu
b
,
Longzhen
Qiu
a
,∗∗
a
Key
Lab
of
Special
Display
Technology,
Ministry
of
Education,
National
Engineering
Lab
of
Special
Display
Technology,
State
Key
Lab
of
Advanced
Display
Technology,
Academy
of
Opto-Electronic
Technology,
Hefei
University
of
Technology,
Hefei
230009,
China
b
State
Key
Lab
of
Electronic
Thin
Films
and
Integrate
Devices,
School
of
Optoelectronic
Information,
University
of
Electronic
Science
and
Technology
of
China
(UETC),
Chengdu
610054,
China
a
r
t
i
c
l
e
i
n
f
o
Article
history:
Received
18
March
2013
Received
in
revised
form
30
June
2013
Accepted
23
July
2013
Available online 3 September 2013
Keywords:
Thieno[3,4-c]pyrrole-4,6-dione
Oxidative
polymerization
Organic
thin-film
transistors
a
b
s
t
r
a
c
t
Thieno[3,4-c]pyrrole-4,6-dione
(TPD)-based
polymer
(PDTTPD)
with
head-to-head
(H-H)
linkage
of
3-
dodecylthiophene
unit
was
synthesized
by
ferric
chloride
oxidative
polymerization.
The
polymer
was
characterized
by
chemical
analysis
as
well
as
thermal
analysis,
optical
spectroscopy
and
cyclic
voltam-
meter.
PDTTPD
polymer
showed
excellent
thermal
stability,
had
significantly
red-shifted
of
absorption
edge
by
its
solid
film
compared
to
its
solution
and
a
deep
highest
occupied
molecular
orbital
(HOMO)
energy
level
of
−5.82
eV.
Polymer
thin-film
microstructures
and
morphologies
were
also
investigated
through
atomic
force
microscope
(AFM)
and
grazing-incidence
X-ray
diffraction
(GIXD)
which
showed
that
the
PDTTPD
film
is
composed
of
rod-like
crystalline
grains
and
ordered
structures.
Organic
thin-
film
transistors
(OTFT)
with
common
architectures
were
fabricated
to
evaluate
OTFT
performance
and
exhibited
the
preliminary
hole
mobility
of
0.019
cm
−2
V
−1
s
−1
.
© 2013 Elsevier B.V. All rights reserved.
1.
Introduction
Over
the
past
decade,
organic
thin-film
transistors
(OTFT)
based
on
conjugated
polymers
have
undergone
significant
progress
due
to
many
advantages
such
as
light
weight,
low-cost,
and
good
compatibility
with
solution-processes
that
are
promis-
ing
for
the
fabrication
of
flexible
large
area
devices
[1–10].
To
obtain
higher
charge
mobilities,
molecular
ordering
of
the
polymer
semiconductors
must
be
improved
when
processed
from
a
solution
[11–13].
Polythiophene
derivatives
such
as
poly(3-hexylthiophene)
(P3HT),
poly(2,5-bis(3-alkylthiophen-2-
yl)thieno[3,2-b]thiophene)
(PBTTT)
possessed
finely
conjugated
and
coplanar
conformation,
and
therefore
possess
a
highly
crys-
talline
thin-film
microstructure.
The
polythiophene-based
device
is
reported
to
have
charge
mobilities
as
high
as
0.1
cm
2
V
−1
s
−1
with
current
on/off
ratio
above
10
6
[11–14].
However,
these
high-
performance
polythiophene
derivatives
were
mostly
constructed
from
electron-rich
groups
and
possessed
a
relatively
high
energy
level
of
the
highest
occupied
molecular
orbitals
(HOMO),
the
air
stability
is
still
to
be
improved
for
practical
applications.
For
∗
Corresponding
author.
Tel.:
+86
55162904748.
∗∗
Corresponding
author.
E-mail
addresses:
gbzhang@hfut.edu.cn
(G.
Zhang),
lzqiu@ustc.edu
(L.
Qiu).
polymer
semiconductors,
lowering
the
HOMO
energy
levels
will
result
in
increasing
the
air
stability.
Therefore,
fine
tuning
of
the
semiconductor
energy
levels
may
be
the
most
effective
way
to
improve
their
device
stability
[15–17]
.
So
far,
conjugated
polymers
with
donor-acceptor
(D-A)
architectures
have
been
an
effective
approach
to
enhanced
the
device
stability.
The
D-A
polymer
which
constructed
by
alternate
electron
rich
and
deficient
units
could
more
easily
produced
a
low
HOMO
energy
level
and
result
in
high
air
stability
[15].
Recently,
the
D-A
polymers
based
on
thieno[3,4-
c]pyrrole-4,6-dione
(TPD)
have
received
much
attention
due
to
its
high
performance
in
polymer
solar
cells
and
organic
thin
film
tran-
sistors
[18–26].
TPD
possesses
a
compact,
symmetric,
and
planar
structure,
the
strong
electron-withdrawing
imide
group
of
TPD
greatly
lowers
the
HOMO
and
the
lowest
unoccupied
molecular
orbital
(LUMO)
energy
levels
[21,25].
If
the
TPD
unit
is
introduced
into
poly(3-alkylthiophene)
backbone,
the
polymers
would
have
lower
HOMO
energy
levels
and
shows
better
air
stability.
Taking
all
of
these
results
into
account,
polymer
(PDTTPD)
based
on
TPD
and
3-dodecylthiophene
units
were
firstly
syn-
thesized
through
ferric
chloride
oxidative
polymerization
in
this
paper
(Scheme
1).
The
3-dodecylthiophene
units
in
PDTTPD
backbone
form
a
head-to-head
(H-H)
conformation
(Fig.
1).
The
thermal,
optical,
electrochemical
properties
and
microstructure
and
morphology
were
also
characterized
in
this
work.
The
polymer
PDTTPD
showed
excellent
thermal
stability,
and
the
film
exhibited
0379-6779/$
–
see
front
matter ©
2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.synthmet.2013.07.019