Synthesis and characterization of carbazole-based copolymers containing benzothiadiazole derivative for polymer light-emitting diodes

Article abstract of DOI:10.1080/15421406.2012.702439

A new thermally robust electroluminescent (EL) carbazole-based-conjugated copolymer, including poly[3,7-(N-hexylcarbazole)-co-4,7-{5,6-bis(3,7- dimethyloctylo-xymethyl)-2,1,3-(benzothiadiazole)}] (PCz-co-P2C₁₀BT) was synthesized and used to fabricate the efficient polymer light-emitting diodes (PLEDs). The glass transition temperature of the PCz-co-P2C ₁₀BT (105C) was found to be higher than that of poly(9,9- dialkylfluorene) derivatives. We fabricated PLEDs in ITO/PEDOT/light-emitting polymer/Alq₃/LiF/Al configuration. The new copolymer was found to have green emission color (523nm). The maximum brightness and external quantum efficiency of PCz-co-P2C₁₀BT were 260 cd/m² at 14V and 0.22%, respectively.

Full text of DOI:10.1080/15421406.2012.702439

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Synthesis and Characterization of
Carbazole-based Copolymers Containing
Benzothiadiazole Derivative for Polymer
Light-Emitting Diodes
a
a
b
c
Jin Su Park , Sung-Ho Jin , Yeong-Soon Gal , Jun Hee Lee & Jae
d
Wook Lee
a
Department of Chemistry Education, Interdisciplinary Program of
Advanced Information and Display Materials , Institute for Plastic
Information and Energy Materials , Busan , 609-735 , Korea
b
Polymer Chemistry Lab , Kyungil University , Hayang , 712-701 ,
Korea
c
Department of Advanced Materials Engineering , Dong-A
University , Busan , 604-714 , Korea
d
Department of Chemistry , Dong-A University , Busan , 604-714 ,
Korea
Published online: 17 Sep 2012.
To cite this article: Jin Su Park , Sung-Ho Jin , Yeong-Soon Gal , Jun Hee Lee & Jae Wook Lee (2012)
Synthesis and Characterization of Carbazole-based Copolymers Containing Benzothiadiazole Derivative
for Polymer Light-Emitting Diodes, Molecular Crystals and Liquid Crystals, 567:1, 102-109, DOI:
10.1080/15421406.2012.702439
To link to this article: http://dx.doi.org/10.1080/15421406.2012.702439
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Mol. Cryst. Liq. Cryst., Vol. 567: pp. 102–109, 2012
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2012.702439
Synthesis and Characterization of Carbazole-based
Copolymers Containing Benzothiadiazole Derivative
for Polymer Light-Emitting Diodes
1
1,∗
2
JIN SU PARK, SUNG-HO JIN, YEONG-SOON GAL,
3
4
JUN HEE LEE, AND JAE WOOK LEE
1Department of Chemistry Education, Interdisciplinary Program of Advanced
Information and Display Materials, and Institute for Plastic Information and
Energy Materials, Busan 609-735, Korea
2
Polymer Chemistry Lab, Kyungil University, Hayang 712-701, Korea
Department of Advanced Materials Engineering, Dong-A University,
3
Busan 604-714, Korea
4
Department of Chemistry, Dong-A University, Busan 604-714, Korea
A new thermally robust electroluminescent (EL) carbazole-based π-conjugated
copolymer, including poly[3,7-(N-hexylcarbazole)-co-4,7-{5,6-bis(3,7-dimethyloctylo-
xymethyl)-2,1,3-(benzothiadiazole)}] (PCz-co-P2C10BT) was synthesized and used
to fabricate the efficient polymer light-emitting diodes (PLEDs). The glass transi-
◦
tion temperature of the PCz-co-P2C10BT (105 C) was found to be higher than that
of poly(9,9-dialkylfluorene) derivatives. We fabricated PLEDs in ITO/PEDOT/light-
emitting polymer/Alq /LiF/Al configuration. The new copolymer was found to have
3
green emission color (523 nm). The maximum brightness and external quantum
2
efficiency of PCz-co-P2C10BT were 260 cd/m at 14 V and 0.22%, respectively.
Keywords benzothiadiazole; carbazole; polymer light-emitting diodes; PhOLEDs;
Introduction
Ever since Tang and Vanslyke constructed organic light-emitting diodes (OLEDs) using
organic materials as emitters, OLEDs continue to attract intensive interest because of their
numerous applications in full-color flat-panel displays and other lighting sources [1,2].
Polymer light-emitting diodes (PLEDs) have received remarkable scientific and in-
dustrial attention due to their potential applications in large area flat-panel displays [3].
π-Conjugated polymers are attractive because of their applicability to PLEDs [4]. Among
the various types of π-conjugated polymers reported, poly(N-alkylcarbazole) (PCz) and
its derivatives exhibit the most promise for PLED applications and have been widely
used, because of their chemical and thermal stability, high photoluminescent (PL) quantum
efficiency, and ease of property tuning by copolymerization with various comonomers.
∗
Address correspondence to Sung-Ho Jin, Department of Chemistry Education, Interdisciplinary
Program of Advanced Information and Display Materials, and Center for Plastic Information System,
Pusan National University, Busan 609-735, Korea. E-mail: shjin@pusan.ac.kr and Jae Wook Lee,
Department of Chemistry, Dong-A University, Busan, 604-714, Korea. E-mail: jlee@donga.ac.kr
[304]/102

Benzothiadiazole Derivative for PLEDs
[305]/103
PCz derivatives have strong absorption in the near UV region and a low redox potential.
The electrochemical and spectroscopic properties of PCz derivatives have been extensively
investigated [5]. Normally, PCz derivatives emit blue light with a wide band gap. However,
by incorporating a narrow band gap comonomers into the carbazole backbone, the emission
colors of PCz derivatives could be tuned over the entire visible range [6]. The most com-
monly used comonomer is the electron deficient 2,1,3-benzothiadiazole (BT) unit, which
emits the green color in PLEDs [7,8]. In this article, we report the synthesis and charac-
terization of a new EL polymer, consisting of poly[3,7-(N-Hexylcarbazole)-co-4,7-{5,6-
bis(3,7-dimethyloctyloxymethyl)-2,1,3-(benzothiadiazole)}] (PCz-co-P2C10BT), aimed
at increasing the solubility of resulting copolymer, tuning the emission color from blue
to green, and improving the PLED performance. The new copolymer was synthesized
with palladium-catalyzed Suzuki polymerizations and was fully characterized. The new
EL polymer was used to fabricate efficient PLEDs using PCz-co-P2C10BT as an emitting
layer with ITO/PEDOT/polymer/Alq3/LiF/Al configuration.
Experimental
Characterization
Carbazole, N-bromosuceinimide (NBS), sodium hydride, 1-bromohexane, n-butyl lithium,
2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, Alq3, LiF, and aluminum were pur-
chased from Aldrich Co., and used without further purification unless otherwise noted.
Solvents were dried and purified by fractional distillation over sodium/benzophenone and
handled in a moisture-free atmosphere. The moisture content of THF was below 10 ppm.
1
Column chromatography was performed using silica gel (Merck, 250–430 mesh). The H-
NMR spectra were recorded on an Inova-500 spectrometer and the chemical shifts were
recorded in ppm units with chloroform as the internal standard. The UV-visible and the
emission spectra were recorded with a Shimadzu UV-3100 and Hitachi F-4500 fluorescence
spectrophotometers. The solid state emission measurements were carried out by supporting
each film on a quartz substrate, which was mounted to receive front-face excitation at an
o
angle < 45 . Polymer film was excited with several portions of the visible spectrum using a
xenon lamp. The molecular weight and polydispersity of the polymer were determined by
gel permeation chromatography (GPC) using a PL gel 5 µm MIXED-C column on an Agi-
lent 1100 series liquid chromatography system with THF as an eluent and calibration with
polystyrene standards. Thermal analyses were carried out on a Mettler Toledo TGA/SDTA
◦
8
51, DSC 822 analyzer under an N2 atmosphere at a heating rate of 10 C/min. Cyclic
voltammetry (CV) was carried out in a 0.1 M solution of tetrabutylammonium tetrafluo-
roborate (Bu4NBF4) in anhydrous chloroform using a CHI600C at a potential scan rate
of 50–100 mV/s. Polymer film was coated onto a Pt disc electrode (diameter: 0.2 cm) by
dipping the electrode into the polymer solution (10 mg/mL). A platinum wire was used as
the counter electrode and Ag/AgNO3 electrode was used as the reference electrode. All
electrochemical experiments were performed at room temperature in a glove box in an Ar
atmosphere.
Synthesis of 3,6-Dibromo-9H-Carbazole (1)
To a solution of carbazole (5 g, 29.9 mmol) in anhydrous tetrahydrofurane (THF) was
added NBS (10.64 g, 59.8 mmol) at room temperature. The reaction mixture was stirred at

104/[306]
J. S. Park et al.
◦
8
5 C for 48 h. Then the reaction mixture was diluted with water and extracted with ethyl
acetate. The combined organic layers were washed with brine, dried anhydrous MgSO4
1
and concentrated. The product was purified by recrystallization. (1.9 g, 98%) H-NMR
13
(
Acetone-d6, δ ppm): 7.20–7.31 (m, 4H), 8.41 (s, 2H); C-NMR (CDCl3, δ ppm): 129.2,
121.1, 121.0, 119.7, 117.0, 113.3. Anal. Calcd for (C12H7Br2N) : C 44.35, H 2.17, N 4.31
Found : C 46.12, H 2.24, N 4.13.
Synthesis of 3,6-Dibromo-N-Hexylcarbazole (2)
60 mL of dried THF in a 100 mL three neck flask was purged with a continuous N2 flow.
Sodium hydride (0.2 g, 7.6 mmol) was added into the flask to be stirred. 3,6-Dibromo-
9
7
H-carbazole (3 g, 9.2 mmol) was added slowly into the mixture. 1-Bromohexane (1.1 g,
.6 mmol) diluted by THF (10 mL) was added dropwise into the flask and the content in the
flask was refluxed for 12 h. The reactant was cooled to room temperature and then the solvent
was stripped off by evaporation. The residue was mixed with H2O (60 mL) and extracted
with ethyl acetate. The extracted solution was dried with anhydrous MgSO4 and then filtrate.
Yellowish viscous liquid was obtained by evaporation of the solvent and was purified by
employing a silica gel column with an eluent of an ethyl acetate:hexane:methylene chloride
1
(
1:7:2). The product was purified by recrystallization (4.36 g, 80%). H-NMR (CDCl3,
δ ppm): 0.84 (m, 3H), 1.33 (m, 6H), 1.81 (m, 2H), 4.20 (t, 2H), 7.24 (d, 2H), 7.56 (q, 2H),
.76 (d, 1H), 7.86 (s, 1H), 8.17 (s, 1H). 1 C-NMR (CDCl3, δ ppm): 130.3, 121.1, 121.0,
20.0, 117.0, 113.3, 60.9, 31.5, 30.4, 27.0, 22.7, 14.01. Anal. Calcd for (C18H19Br2N) : C
2.84, H 4.68, N 3.42 Found : C 50.94, H 4.86, N 3.55.
3
7
1
5
Synthesis of 3,6-bis(4,4,5,5-Tetramethyl-1,3,2-Tioxaborolan-2-yl)-N-Hexylcarbazole (3)
To a solution of 3,6-dibromo-N-hexylcarbazole (0.2 g, 0.49 mmol) in anhydrous THF
◦
◦
(
10 mL) at −78 C, n-butillithium was added by syringe. The mixture was stirred at −78 C
for 2 hr. 2-Isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (0.2 ml, 1.1 mmol) was
◦
added slowly to the solution and the mixture was stirred for 2 h at −78 C. The resulting
mixture was warmed to room temperature and stirred for 24 h. The mixture was poured into
water and was extracted with diethyl ether. The organic layer was washed with brine and
dried over anhydrous MgSO4. The solvent was removed by distillation and the residue was
1
purified by column chromatography. The product was white solid in 43% yield. H-NMR
(
(
CDCl3, δ ppm): 0.86 (t, 3H), 1.41 (m, 30H), 1.83 (t, 2H), 4.29 (t, 2H), 7.39 (d, 2H), 7.98
d, 2H), 8.78 (s, 2H). 13C-NMR (CDCl3, δ ppm): 130.8, 122.0, 121.0, 120.0, 118.9, 111.1,
8
8
3.1, 60.9, 31.5, 30.4, 27.0, 22.7, 21.3, 14.1. Anal. Calcd for (C30H43B2NO4) : C 71.59, H
.61, N 2.78, O 12.72 Found : C 74.31, H 8.95, N 2.89.
4,7-Dibromo-5,6-bis(Decyloxymethyl)Benzo[c][1,2,5]thiadiazole (4)
1
H-NMR (CDCl3, δ ppm): 0.92 (m, 6H), 1.31–1.36 (m, 30H), 1.86–1.88 (m, 4H), 3.38
13
(
t, 4H), 4.72 (d, 4H). C-NMR (CDCl3, δ ppm): 159.7, 142.3, 114.2, 72.0, 68.2, 31.8, 30.0,
9.6, 29.3, 25.9, 22.7, 14.1. Anal. Calcd for (C28H46Br2N2O2S) : C 53.0, H 7.31, N 4.41,
O 5.04 Found : C 51.04, H 7.60, N 4.56.
2

Benzothiadiazole Derivative for PLEDs
[307]/105
Synthesis of Poly[3,7-(N-Hexylcarbazole)-co-4,7-{5,6-bis(3,7-Dimethyloctyloxymethyl)-
,1,3-(Benzothiadiazole)}] (PCz-co-P2C10BT) (1:1 mol%)
2
The copolymer was prepared by the Suzuki coupling reaction between 3,6-
bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-N-hexylcarbazole (3) and 5,6-bis(3,7-
dimethyloctyloxymethyl)-4,7-dibromo-2,1,3-benzothiadiazole (4). A mixture of compound
3
(0.3 g, 0.6 mmol), compound 4 (0.38 g, 0.6 mmol) and Pd(PPh3)4 (20 mg, 0.025 mmol) in
◦
toluene (5 mL) was stirred at 95 C. To this flask, aqueous 2M Na2CO3 (0.5 mL) was added
and the mixture was stirred for 48 h at 100 C. The polymer was end-capped by adding a
◦
small amount of bromobenzene to remove the boronic ester end group, followed by stirring
for 2 h. The polymerization solution was poured into methanol (500 mL) and the crude
polymer was successively Soxhlet extracted with methanol, isopropyl alcohol and hexane
to remove the unreacted monomers, impurities and oligomers. The collected powder was
◦
dried under vacuum overnight at 40 C to afford PCz-co-P2C10BT (70 mg, 37%) as a dark
1
purple powder. H-NMR (CDCl3, δ ppm): 8.0–7.4 (br, 6H, aromatic protons), 4.8–4.5 (br,
4
3
H, methoxy protons next to oxygen), 4.5–4.2 (br, 2H, methoxy protons next to nitrogen),
.6–3.2 (br, 4H, methylene protons next to oxygen), 1.8–0.6 (br, 47H, aliphatic protons).
Anal. Calcd for (C46H67N3O2S)n : C, 79.58; H, 9.26; N, 6.33; S, 4.83 Found : C, 73.35; H,
.40; N, 8.65: S, 3.72.
5
Fabrication of PLED and Measurements
Optical thin film of the PCz-co-P2C10BT was obtained by spin-coating from their toluene
solutions. Polymer solution was filtered with 0.45 µm PP syringe filter (Whatman) prior to
spin-coating. Film for optical absorption and PL measurement was spin-coated onto quartz
◦
2
substrates and dried over 10 min at 120 C under N2 atmosphere. Glass substrate coated with
ITO, whose conductivity was 15 ꢀ/cm (Samsung Corning) served as anode electrode. The
ITO substrates were cleaned successive rinsing with acetone and wiping with non-woven
tissues to remove adhering glass particle from cutting and ultrasonic treatment with distilled
water, acetone, isopropyl alcohol, and finally distilled water and dried with N2 gas. The
PEDOT/PSS (Baytron CH8000, 30 nm) as a hole injection and decreasing roughness of ITO
surface was spin-coated from aqueous solution with 10 wt% of isopropyl alcohol. A solution
of PCz-co-P2C10BT (0.5–1.5 wt% in toluene) was filtered through 0.45 µm PP syringe
filter and deposited by spin coating onto the PEDOT/PSS layer with uniform and pinhole
free films as a thickness around 100 nm. Finally, cathode electrode, Alq3 (15 nm)/LiF
−
6
(
1 nm)/Al (200 nm) triple layer, was vacuum (1 × 10 torr) evaporated onto the resulting
2
emitting layer. The active area of the PLED was approximately 4 mm . The thickness of
the active layer was measured using a KLA Tencor Alpha-step IQ surface profilometer. For
the measurements of device characteristics, current density-voltage-luminescence (J-V-L)
characteristics were measured using a current/voltage source (Keithly 238) and an optical
power meter (CS-1000, LS-100). All processes and measurements mentioned above were
carried out in the open air at room temperature.
Results and Discussion
Carbazole-based polymers have many advantages such as good hole injection and trans-
porting properties, thermal stability and tuning the emission colors. Its unique chemical
properties are effectively raise the highest occupied molecular orbital (HOMO) energy level
and reduce the barrier height for hole injection between the anode layer and the emitting

106/[308]
J. S. Park et al.
O
Br
B
O
O
Br
Br
B
NaH, (CH
2
)
6
Br
O
n-BuLi, THF
Br
N
N
THF
N
O
O
B
O
(
1)
(2)
(3)
Br
Br
NH2
N-Thionylaniline
toluene, reflux
N
N
N
Br , I (cat.)
NBS, BPO (initiator)
CCl , reflux
2
2
S
S
NH2
N
MC
4
Br
Br
Br
-
+
C10H21
N
N
C10H21O Na
N
S
N
Br
Br
O
O
S
C H21: 3,7-dimethyloctyl-
10
THF
C10H21
Br
(4)
O
C10H21
C10H21
B
O
O
O
O
B
Pd(II)acetate, tricyclohexylphosphine
Tetraethylammonium hydroxide
O
+
Br
Br
N
N
N
S
(3)
(4)
C10H21O
OC10H21
*
n
N
N
N
S
PCz-co-P2C10BT
Scheme 1. Synthetic process of the PCz-co-P2C10BT
layer in PLEDs. Scheme 1 outlines the synthetic routes of the monomer and the PCz-
co-P2C10BT. Compound (2) was prepared from bromination of carbazole, followed by
alkylation. Finally we introduced boronic acid at the position of 3- and 6- in compound (3)
for Suzuki polymerization by treating n-BuLi. 5,6-Bis(3,7-dimethyloctyloxymethyl)-4,7-
dibromo-2,1,3-benzothiadiazole (4) was synthesized according to the published procedures
[9]. The polymerization was carried out using palladium(II) acetate, tricyclohexylphos-
phine, tetraethylammonium hydroxide aqueous solution (20%w/w) in dried toluene under

Benzothiadiazole Derivative for PLEDs
[309]/107
N2 atmosphere for 48–72 h. During the polymerization, the fluorescent light was observed
without any precipitation. The PCz-co-P2C10BT was completely soluble in various organic
solvents such as chloroform, chlorobenzene, toluene, and THF. Molecular structures of the
1
13
monomer and the PCz-co-P2C10BT were identified by H- and C-NMR and elemen-
tal analysis. To improve color purity and PLED performance, the PCz-co-P2C10BT was
further purified by multiple soxhlet extraction with different solvents including methanol,
acetone and finally chloroform to remove unreacted monomers and inorganic impurities.
The solution of PCz-co-P2C10BT was filtered through the methanol precipitation and
then dried in vacuo. From these processes, the highly purified and narrow polydispersity
of PCz-co-P2C10BT was obtained. The weight-average molecular weight (Mw) and the
polydispersity of the PCz-co-P2C10BT were 5,570 and 1.21, respectively. The glass tran-
◦
sition temperature of PCz-co-P2C10BT was 105 C. TGA thermogram was measured at
◦
temperature of 5% weight loss for PCz-co-P2C10BT and showed the stable up to 279 C.
Higher thermal stability of the light emitting polymer is one of the most critical require-
ments to operate the PLED especially for blue light emitting it needs higher turn on voltage
compared to other color light emitting polymers.
The absorption and PL spectra of the PCz-co-P2C10BT in CHCl3 solution and the
polymer film spin-coated onto quartz with CHCl3 solution were measured at room temper-
ature. Figure 1 shows the optical absorption, PL spectrum of PCz-co-P2C10BT in solution
state and EL spectra in film state. The PCz-co-P2C10BT exhibited two absorption peaks
at 287 nm and 419 nm which can be attributed to the carbazole and 2,1,3-benzothiadiazole
segments in the polymer. The absorption and emission peaks in film state were slightly
red shifted comparing with the solution state because of the interchain aggregation. The
absorption, emission maxima and energy band gap of PCz-co-P2C10BT in solution and
film states are summarized in Table 1.
To investigate the charge injection and transport in PCz-co-P2C10BT, it is very impor-
tant to determine the energy band diagrams of the HOMO and LUMO binding energy levels
with respect to the ferrocene standard by using cyclic voltammetry (CV) measurements
and the band gaps obtained from the optical absorption spectrum. The ionization potential
PCz-co-P2C BT (Abs, sol)
1
0
PCz-co-P2C BT (PL, sol)
1
0
PCz-co-P2C BT (EL)
1
0
3
00
400
500
600
700
800
Wavelength [nm]
Figure 1. UV-visible absorption, PL and EL spectra of PCz-co-P2C10BT.

108/[310]
J. S. Park et al.
Table 1. Electro-Optical properties of PCz-co-P2C10BT.
Abs (nm)a
PL (nm)a
Polymer
Solution
407
Film
419
Solution
489
Film
515
EL(nm)b
522
Eg(eV)c
PCz-co-P2C10BT
2.64
aMeasured in the thin film onto the quartz substrate.
b
EL spectras were measured cathode using by LiF/Al as cathode.
c
Band gap estimated from the onset wavelength of the optical absorption.
(IP) and electron affinity (EA) or their associated HOMO and LUMO energy levels were
estimated from the onset oxidation data and optical band edges. IP/HOMO = Eox+4.8 eV
and EA/LUMO = EHOMO+Eg, where an SCE energy level of -4.8 eV below the vacuum
level was used [10]. The HOMO energy level and optical band gap of PCz-co-P2C10BT
were 5.55 eV and 2.63 eV, respectively. The major carriers in PCz-co-P2C10BT are holes
rather than electrons, due to the lower band offset between the ITO and HOMO energy
levels. The band offset was 0.80 eV for hole injection at the interface of the ITO/HOMO
state.
To investigate the PLED performance of PCz-co-P2C10BT as an emitting layer, we fab-
ricated PLED with a configuration of ITO/PEDOT/PCz-co-P2C10BT/Alq3/LiF (1 nm)/Al
(120 nm). The maximum EL peak of PCz-co-P2C10BT was slightly red-shifted with re-
spect to the PL peak of film state as shown in Figure 1. The red-shifted EL spectrum was
attributed to the injected current density, which extended the effective conjugation length.
The maximum emission peak of PCz-co-P2C10BT was at 523 nm, which corresponded to
a green color.
Figure 2 shows the current density-voltage-luminescence characteristics of the
ITO/PEDOT/PCz-co-P2C10BT/Alq3/LiF (1 nm)/Al (120 nm) device. The turn-on volt-
age of PCz-co-P2C10BT was 10 V. The PLED performances of PCz-co-P2C10BT are
1
00
2
1
0
1
1
1
1
1
0
0
0
0
0
8
6
4
2
0
0
0
0
0
-
-
1
2
0
2
4
6
8
10
12
14
Bias [V]
Figure 2. Current density-Luminescence-voltage (J-V-L) characteristic of PCz-co-P2C10BT.

Benzothiadiazole Derivative for PLEDs
[311]/109
Table 2. PLED Performance of PCz-co-P2C10BT.
a
b
2
Polymer
Turn-on (V)
10
PE (lm/W)
Lmax (cd/m )
260
EQE (%)
PCz-co-P2C10BT
0.18
0.22
aMaximum power efficiency.
b
Maximum luminescence.
summarized in Table 2. The maximum brightness, power efficiency and external quantum
2
efficiency of PCz-co-P2C10BT were 260 cd/m , 0.18 lm/W and 0.22%, respectively.
Conclusions
This study focused on the molecular design and synthesis of bipolar struc-
ture of poly[3,7-(N-Hexylcarbazole)-co-4,7-{5,6-bis(3,7-dimethyloctyloxymethyl)-2,1,3-
(
benzothiadiazole)}] (PCz-co-P2C10BT) for PLED applications. The resulting EL poly-
mer was highly soluble in common organic solvents, which allowed being easily spin-
coated onto glass substrates with high quality optical thin films. We fabricated PLEDs
in ITO/PEDOT/PCz-co-P2C10BT/Alq3/LiF (1 nm)/Al (120 nm) configuration. The max-
2
imum brightness and power efficiency were 260 cd/m at 14 V and 0.18 lm/W at 11 V,
respectively.
Acknowledgements
This work was supportedbyBasicScienceResearchProgramthroughthe National Research
Foundation of Korea (NRF) grant funded from the Ministry of Education, Science and
Technology (MEST) of Korea for the Center for Next Generation Dye-sensitized Solar Cells
(No. 2011–0001055) and the New & Renewable Energy program of the Korea Institute
of Energy Technology Evaluation and Planning (KETEP) grant (No. 20103020010050)
funded by the Ministry of Knowledge Economy, Republic of Korea.
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