Efficient
quantum
dot
light
emitting
devices
with
ethanol
treated
PEDOT:
PSS
hole
injection
layer
Jia
Wang
a,b
,
Han
Zhang
b
,
Wenyu
Ji
a,
*
,
Hanzhuang
Zhang
b,
*
a
State
Key
Laboratory
of
Luminescence
and
Applications,
Changchun
Institute
of
Optics,
Fine
Mechanics
and
Physics,
Chinese
Academy
of
Sciences,
Changchun
130033,
China
b
Department
of
Physics,
Jilin
University,
Changchun
130023,
China
A
R
T
I
C
L
E
I
N
F
O
Article
history:
Received
6
June
2015
Received
in
revised
form
25
August
2015
Accepted
31
August
2015
Available
online
xxx
Keywords:
Quantum
dots
Light
emitting
diodes
Hole-injection
layer
PEDOT:PSS
A
B
S
T
R
A
C
T
The
conductivity
of
poly(3,4-ethylenedioxythiophene)-poly(styrene
sulfonate)
(PEDOT:PSS)
film
is
improved
by
simply
mixing
PEDOT:PSS
solution
with
ethanol
for
the
film
deposition,
and
the
performance
of
quantum-dot
light-emitting
diodes
(QD-LEDs)
is
significantly
enhanced
with
ethanol
treated
(ET-
treated)
PEDOT:PSS
as
the
hole
injection
layer
(HIL).
Comparing
with
the
pristine
PEDOT:PSS
based
device,
the
current
density
of
device
with
ET-treated
PEDOT:PSS
as
the
HIL
is
increased
by
18%,
from
50
to
59
mA/cm
2
,
at
operating
voltage
of
5
V,
and
the
maximum
current
efficiency
is
enhanced
by
12.5%,
from
10.4
to
11.7
cd/A,
which
is
due
to
the
improved
conductivity
of
ET-treated
PEDOT:PSS
film.
With
atomic
force
microscopy
(AFM)
measurements,
we
demonstrate
that
the
improvement
of
the
conductivity
of
PEDOT:PSS
film
is
due
to
the
decreased
PSSH
amount
after
solvent
treatment,
reducing
the
thickness
of
PSSH
insulating
shell,
leading
to
an
efficient
charge
transport
across
the
PEDOT
chains.
ã
2015
Elsevier
B.V.
All
rights
reserved.
1.
Introduction
Due
to
unique
optoelectronic
properties
and
high
emission
quantum
yield,
which
are
strongly
dependent
on
their
size,
semiconductor
II–VI
quantum
dots
have
been
paid
extensively
attention
to
the
potential
applications
in
flat
panel
displays
and
solid-state
lighting
sources
[1–6].
Especially,
quantum
dot
light-
emitting
devices
(QD-LEDs)
with
near
100%
internal
quantum
efficiency
was
reported
by
Shirasaki
et
al.
[6],
offering
significant
advantages
over
organic
LEDs
[7,8].
Many
efforts
were
devoted
to
the
QD-LED
field
to
improve
the
device
performance,
closing
to
that
of
organic
LEDs
[9,10].
To
date,
the
most
efficient
device
is
achieved
through
a
hybrid
structure,
consisting
of
organic
carrier
transport
layers
combined
with
an
inorganic
metal
oxide
electron
transport
layer
(ETL),
such
as
poly(3,4-ethylenedioxythiophene)-
poly(styrene
sulfonate)
(PEDOT:PSS)
hole
injection
layer
(HIL),
CBP
hole
transport
layer
(HTL),
poly[-bis(4-butylphenyl)–bis(phenyl)
benzidine]
(poly-TPD)
HTL,
ZnO
nanoparticle
ETL,
and
TiO
2
electron
transport
layer
[9–16].
Recently,
an
efficient
QD-LEDs
with
an
external
quantum
efficiency
(EQE)
of
20.5%
was
reported
by
employing
ZnO
nanoparticle
as
the
ETL
combined
with
organic
HTLs
[10],
benefitting
from
the
outstanding
properties
of
ZnO
ETL,
including
high
electron
mobility,
matched
energy
level
with
QDs
and
good
stability.
Meanwhile,
the
QDs/ZnO
interface
was
modified
by
a
thin
poly(methylmethacrylate)
layer
to
suppress
the
exciton
quenching
induced
by
the
ZnO,
which
plays
an
important
role
in
improving
the
device
efficiency.
So
far
the
ZnO
nanoparticle
film
is
demonstrated
the
best
candidate
as
the
ETL
and
highly
efficient
QD-LEDs
have
been
fabricated
[10–18].
Enlightened
from
the
effect
of
efficient
electron
injection
and
interface
engineering
achieved
by
the
ZnO
ETL
on
the
device
performance
[10],
optimizing
HTL/HIL
to
achieve
efficient
hole
injection
must
be
a
feasible
strategy
to
improve
the
QD-LED
performance.
In
common
QD-LEDs,
the
PEDOT:PSS
is
often
used
as
the
HIL
to
enhance
the
ITO
work
function
and
hole
injection
from
ITO
to
HTL.
It
has
been
widely
accepted
that
high
resistivity
of
the
PEDOT:PSS
film
could
lead
to
a
higher
average
electric
field
across
the
device,
and
more
Joule
heating,
which
would
substantially
deteriorate
the
device
performance
[19] .
Therefore,
increasing
the
conductivity
of
PEDOT:PSS
is
beneficial
to
improve
device
performance.
It
is
well
known
that
the
conjugated
polymer
PEDOT
is
positively
doped,
and
the
sulfonate
anionic
groups
of
PSS
are
used
as
the
counterions
to
balance
the
doping
charges.
PEDOT:PSS
films
after
secondary
doping
with
some
inert
solvents,
such
as
sorbitol
[20,21],
N-methylpyrrolidone
[22],
(poly)-ethylene
glycol
and
other
alcohols
[19,23,24],
dimethyl
sulfoxide
(DMSO),
N,N-dimethylfor-
mamide,
and
tetrahydrofuran
[25],
lead
to
a
conductivity
increase
*
Corresponding
author.
E-mail
addresses:
jiwy@ciomp.ac.cn,
jlu__jwy@163.com
(W.
Ji),
zhanghz@jlu.edu.cn
(H.
Zhang).
http://dx.doi.org/10.1016/j.synthmet.2015.08.033
0379-6779/ ã
2015
Elsevier
B.V.
All
rights
reserved.
Synthetic
Metals
209
(2015)
484–489
Contents
lists
available
at
ScienceDirect
Synthetic
Metals
journal
homepage:
www.else
vie
r.com/locat
e/synme
t