High-efficiency exciplex-based white organic light-emitting diodes with a new tripodal material as a co-host

Article abstract of DOI:10.1039/c9tc01326a

Exciplex-forming co-hosts have been reported to be a potentially suitable material for organic light-emitting diodes (OLEDs). However, they might not be able to provide optimal low voltage and maximal power efficiency (PE), when used in white organic light-emitting diodes (WOLEDs). Herein, a novel strategy using multi-exciplex-forming co-hosts (MEHs) is introduced to achieve enhanced efficiency and low operating voltage. To realize this strategy, a new tripodal bipolar compound CNTPA-DPA was synthesized and used as a co-host in the devices. As a result, the orange light-emitting component in WOLEDs provides 27% external quantum efficiency (EQE), 2.1 V turn-on voltage, and 115.5 lm W^-1 PE, which are among the best values of orange color emission in OLEDs. And then this orange light emitting component was adopted in the MEH strategy to construct WOLEDs, achieving 19.5% EQE and 73 lm W^-1 PE at the maximum, which are 45.7% and 19.6% higher than those using a single exciplex as the host, respectively. Moreover, the well-matched energy alignment endows the device with a very low operating voltage of 3.8 V at 1000 cd m^-2. These results indicate that the performance of the exciplex-based WOLEDs can be remarkably enhanced by using the MEH strategy.

Full text of DOI:10.1039/c9tc01326a

View Article Online
View Journal
Journal of
M at erials Chemistry C
Accepted Manuscript
This article can be cited before page numbers have been issued, to do this please use: Y. Zhang, Q. Ran,
Q. Wang, J. Fan and L. Liao, J. Mater. Chem. C, 2019, DOI: 10.1039/C9TC01326A.
Volume
4
Number
1
7
January 2016 Pages 1–224
This is an Accepted Manuscript, which has been through the
Royal Society of Chemistry peer review process and has been
accepted for publication.
Journal of
Materials Chemistry C
Materials for optical, magnetic and electronic devices
www.rsc.org/MaterialsC
Accepted Manuscripts are published online shortly after
acceptance, before technical editing, formatting and proof reading.
Using this free service, authors can make their results available
to the community, in citable form, before we publish the edited
article. We will replace this Accepted Manuscript with the edited
and formatted Advance Article as soon as it is available.
You can find more information about Accepted Manuscripts in the
author guidelines.
Please note that technical editing may introduce minor changes
to the text and/or graphics, which may alter content. The journal’s
standard Terms & Conditions and the ethical guidelines, outlined
in our author and reviewer resource centre, still apply. In no
event shall the Royal Society of Chemistry be held responsible
for any errors or omissions in this Accepted Manuscript or any
consequences arising from the use of any information it contains.
ISSN 2050-7526
PAPER
~
Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
the Hofmeister effects
rsc.li/materials-c

Page 1 of 7
J Po lue r an sael od fo Mn aot et rai ad l js u Cs ht emm ai rs gt ri yn sC
View Article Online
DOI: 10.1039/C9TC01326A
ARTICLE
High-Efficiency Exciplex-Based White Organic Light-Emitting
Diodes with a New Tripodal Material as a Co-Host
‡
a
‡a
a
ab
ab
Yuan-Lan Zhang, Quan Ran, Qiang Wang, Jian Fan* and Liang-Sheng Liao*
Received 00th January 20xx,
Accepted 00th January 20xx
The exciplex-forming co-hosts have been reported to be potentially suitable host for organic light-emitting diodes (OLEDs).
However, it might not be able to achieve optimal low voltage and maximal power efficiency (PE), when it comes to white
organic light-emitting diodes (WOLEDs). Herein, a novel strategy called multi-exciplex-forming co-hosts (MEHs) is introduced
to achieve enhanced efficiency with low operating voltage. To realize this strategy, a new tripodal bipolar compound CNTPA-
DPA was synthesized and used as a co-host in the devices. As a result, the orange light-emitting component in the WOLEDs
DOI: 10.1039/x0xx00000x
-
1
reaches 27% in external quantum efficiency (EQE), 2.1 V in turn-on voltage, and 115.5 lm W in PE, which is among the best
values of orange color emission in OLEDs. And then this orange light emitting component was adopted in the MEHs strategy
-
1
to construct WOLEDs, achieving 19.5% of EQE and 73 lm W of PE at the maximum, which are 45.7% and 19.6% higher than
those of using a single exciplex as the host, respectively. Moreover, the well-matched energy alignment endows the device
-
2
with a very low operating voltage of 3.8 V at 1000 cd m . These results indicate that the performance of the exciplex-based
WOLEDs can be remarkably enhanced by using the strategy of MEHs.
transported via the lowest unoccupied molecular orbital
(LUMO) of acceptors and the highest occupied molecular orbital
1
. Introduction
2
1
(HOMO) of donors, respectively. In addition, the exciplex-
White organic light-emitting diodes (WOLEDs) have attracted
close attention as an outstanding candidate for future displays
and solid‐state lighting sources owing to their superior inherent
properties, such as flexibility, light weight, fast response time,
and power conservation. With the development of hosts and
emitters, the performance of WOLEDs has been gradually
enhanced to satisfy the demand of real commercialization for
cellphones, lamps and televisions. However, achieving high
power efficiency (PE) is still a great challenge. At present, the PE
of WOLEDs have been achieved beyond 100 lm W with
outcoupling technology. It should be mentioned that reducing
forming co-host not only maintains effective exciton harvesting
from host to dopants but also broadens the recombination zone
of excitons which will substantially improve the efficiency and
1
1, 12
device stability.
1
-4
However, the situation of WOLEDs is more complicated than
that of monochromatic OLEDs, because there are two or more
guests doped into the exciplex-forming co-host. In the emitting
layer (EML) of the conventional exciplex-based WOLEDs, only
5
single exciplex-forming co-host is usually employed.1
3-15, 20
In
-
1
order to ensure the high triplet (T ) of exciplex co-host, it
1
6
requires deep-lying HOMO of electron-donating materials and
shallow LUMO of electron-accepting material. As a result, it will
create high charge injection barrier between the hole- or
electron-transporting layer and the exciplex. In brief, the driving
voltage of WOLEDs using single exciplex-forming co-host would
result in high voltage.
the operating voltage is critically important to improve the PE.7
Many efforts have been taken in optimizing the performance of
WOLEDs, but only a few of them could realize ideal luminance
under low driving voltages to achieve high PE. The high voltage
issue usually occurs in single-host-based WOLEDs because high
carrier injection barrier exists when the wide band gap host
materials are used, and the energy loss is hardly avoided
Here in this work, we aim to further decrease the driving voltage
of the exciplex-based WOLEDs. A strategy of multi-exciplex-
forming co-hosts (MEHs) was developed in the WOLEDs. In two-
color components, the cascade HOMO level alignment of the
adjacent exciplex hosts could form “staircases” to remove the
hole injection barrier. The triplet energy levels from the lower
energy level (for orange emitter) to the higher energy level (for
blue emitter) could ensure effective exciton harvesting of
different dopants in WOLEDs. As a result, a very low driving
8-
between single host and guests in the energy transfer process.
10
On the other hand, when using exciplex-forming co-host, the
voltage could be lower than that of the conventional single host
since the electrons and holes are directly injected to and
a.Institute of Functional Nano & Soft Materials (FUNSOM), Jiangsu Key Laboratory
for Carbon-Based Functional Materials & Devices, Soochow University, Suzhou,
Jiangsu 215123, China. *E-mail: lsliao@suda.edu.cn; jianfan@suda.edu.cn
-2
voltage of 3.8 V under operating brightness of 1000 cd m could
b.
Institute of Organic Optoelectronics, Jiangsu Industrial Technology Research
be achieved, and both the external quantum efficiency (EQE)
and the power efficiency (PE) could be substantially improved.
Institute (JITRI), 1198 Fenhu Avenue, Wujiang, Suzhou, Jiangsu, P. R. China.
†
Electronic
DOI: 10.1039/x0xx00000x
These two authors contributed equally to this work.
Supplementary
Information
(ESI)
available.
See
‡
Please do not adjust margins

J Po lue r an sael od fo Mn aot et rai ad l js u Cs ht emm ai rs gt ri yn sC
Page 2 of 7
ARTICLE
Journal Name
2
. Experimental Details
View Article Online
DOI: 10.1039/C9TC01326A
2
.1. Synthesis of New Tripodal Bipolar Compound CNTPA-DPA
Synthesis of 4-(phenylamino)benzonitrile. A mixture of aniline
5.12 g, 55 mmol), 4-bromobenzonitrile (10 g, 55 mmol),
(
tris(dibenzylideneacetone)dipalladium (504 mg 0.55 mmol), 2-
Dicyclohexylphosphino-2',6'-dimethoxy-1,1'-biphenyl (452 mg,
1
.1 mmol) and sodium tert-butoxide (10.6 g, 110 mmol) in 300
Scheme 1 The synthetic route of CNTPA-DPA.
ml of toluene were heated at 80 °C overnight under argon. After
cooling down to room temperature, the mixture was extracted
with dichloromethane. The combined organic extracts were
The OLEDs were fabricated through vacuum deposition under
dried over Na
2
SO
4
and evaporated under reduced pressure. The
-6
vacuum of 4×10 Torr and on commercially pre-patterned ITO-
crude product was purified by column chromatography on silica
gel using petroleum ether/ dichloromethane (PE/DCM, 8/1, v/v)
as the eluent to afford the target compound (8 g, 75 %). H NMR
coated glass substrates (32 mm×32 mm×0.7 mm) with the ITO
thickness of 135 nm and a sheet resistance of 15 Ω per square.
The emitting area of each device is 0.09 cm . The ITO substrates
were ultrasonically cleaned with acetone and ethanol for 15 min
subsequently, and then dried in an oven at 110 °C for 1 h and
finally treated by UV-ozone for 15 min. The deposition rate was
1
2
(400 MHz, CDCl
3
) δ 7.48 (d, J = 8.6 Hz, 2H), 7.36 (t, J = 7.8 Hz,
H), 7.17 (d, J = 7.8 Hz, 2H), 7.12 (t, J = 7.4 Hz, 1H), 6.97 (d, J =
.7 Hz, 2H), 6.10 (s, 1H).
2
8
1
1
3
3
Synthesis of 5-chloro-N ,N ,N ,N -tetraphenylbenzene-1,3-
diamine. A mixture of 1,3-dibromo-5-chlorobenzene (2 g, 7.41
mmol),
controlled
hexaazatriphenylenehexacarbonitrile (HAT-CN), 0.2-0.4 Å/s for
-hydroxyquinolatolithium (Liq), 1-2 Å/s for other organic layers
at
0.3-0.4
Å/s
for
1,4,5,8,9,11-
diphenylamine
(2.63
g,
15.56
mmol),
8
tris(dibenzylideneacetone)dipalladium (339 mg, 0.37 mmol), 2-
dicyclohexylphosphino-2',6'-dimethoxy-1,1'-biphenyl (457 mg,
1
1
After cooling down to room temperature, the mixture was
extracted with dichloromethane. The combined organic
extracts were dried over Na
pressure. The crude product was purified by column
chromatography on silica gel using petroleum
and 6-8 Å/s for Al anode. The Electroluminescence (EL) spectra,
efficiencies, Commission Internationale de L’Eclairage (CIE)
coordinates, current density-voltage-luminance curves, current
efficiencies and power efficiencies of the OLEDs were measured
with a programable spectra scan photometer (PHOTO
RESEARCH, PR 655) and a constant current source meter
.11 mmol) and sodium tert-butoxide (2.85 g, 29.64 mmol) in
00 ml of toluene were heated at 80 °C for 4 hours under argon.
2 4
SO and evaporated under reduced
(
KEITHLEY 2400) at room temperature.
ether/dichloromethane (PE/DCM, 4/1, v/v) as the eluent to 3. Results and Discussion
1
afford the target compound with a yield of 50%. H NMR (400
3.1. Material Properties
MHz, CDCl
3
) δ 7.22 (t, J=7.8 Hz, 8H), 7.06 (d, J=7.8 Hz, 8H), 7.00
CNTPA-DPA has a tripodal structure, and three functional
groups are attached to 1,3,5-positions of the central benzene
ring, which are shown in Fig. 1a. In this novel bipolar compound,
diphenylamine (DPA) and benzonitrile are applied as electron-
donating and electron-withdrawing groups, respectively,
offering independent channels for hole and electron transport.
The density functional theory (DFT) calculations were also
carried out. As shown in Fig. 1b, the HOMOs of the material are
mainly located on the DPA units, while the LUMOs are mainly
distributed on the benzonitrile and the central benzene motif.
The UV-Vis absorption and photoluminescence (PL) spectra of
CNTPA-DPA were also collected to study the photophysical
properties as shown in Fig. 1c. The strong structureless
absorption for CNTPA-DPA at approximately 305 nm could be
corresponding to the π-π* absorption from the backbone.
Estimated from the peaks of fluorescence and phosphorescence
(
t, J=7.3 Hz, 4H), 6.65 (s, 1H), 6.56 (d, J=1.8 Hz, 2H).
1
1
3
3
Synthesis of CNTPA-DPA. A mixture of 5-chloro-N ,N ,N ,N -
tetraphenylbenzene-1,3-diamine (1.05 g, 2.36 mmol), 4-
(phenylamino)benzonitrile
(551
mg,
2.84
mmol),
tris(dibenzylideneacetone)dipalladium (109 mg, 0.12 mmol),
tri-t-butylphosphonium tetrafluoroborate (104 mg, 0.36 mmol)
and sodium tert-butoxide (910 mg, 9.48 mmol) in 100 ml of
toluene were heated at 110 °C overnight under nitrogen. After
cooling down to room temperature, the mixture was extracted
with dichloromethane. The combined organic extracts were
dried over Na SO and evaporated under reduced pressure. The
2 4
crude product was purified by column chromatography on silica
gel using petroleum ether/ dichloromethane (PE/DCM, 1/1, v/v)
1
as the eluent to afford a white solid (717 mg, 68 %). H NMR
400 MHz, DMSO-d ) δ 7.56 (d, J=8.7 Hz, 2H), 7.34 (t, J=7.7 Hz,
H), 7.23 (t, J=7.8 Hz, 8H), 7.13 (dd, J=7.7 Hz, 3H), 7.05 – 6.91
(
2
6
1
3
1 1
spectra, the S and T energies were about 3.01 and 2.74 eV,
(m, 14H), 6.29 (s, 1H), 6.23 – 6.14 (m, 2H). C NMR (151 MHz,
respectively. Besides, Cyclic voltammetry (CV) was carried out
at room temperature to estimate the HOMO energy level of
CNTPA-DPA and the calculated result was about -5.76 eV (Fig.
S5, ESI†). Given the difference of HOMO and LUMO energy level
is nearly about the value of the corresponding optical bandgap,
the LUMO could also be calculated to be -2.49 eV. Moreover,
thermogravimetric analysis (TGA) and differential scanning
CDCl ) δ 151.03, 149.43, 147.07, 146.93, 145.39, 132.95,
3
1
1
C
29.60, 129.10, 125.99, 125.07, 124.17, 123.04, 119.80, 119.47,
15.04, 114.89, 102.21. MALDI-TOF-MS: m/z: calcd for
43 32 4
H N : 604.76, found: 604.19. The complexes were fully
1
13
characterized by H and C NMR (Fig. S1-S4, ESI†) and MALDI-
TOF mass spectrometry.
2.2. OLED Fabrication and Measurements
2
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 3 of 7
J Po lue r an sael od fo Mn aot et rai ad l js u Cs ht emm ai rs gt ri yn sC
Journal Name
ARTICLE
deposited mCP: PO-T2T mixed film also indicated the succeed
View Article Online
DOI: 10.1039/C9TC01326A
of exciplex.
Simplified device structures doped with orange phosphor
Iridium(III) bis(4-phenylthieno[3,2-c]pyridinato-N, C2’) (PO-01)
based on this new exciplex-forming co-host were designed,
which was established as ITO/HAT-CN (10 nm)/TAPC (40
nm)/TCTA (10 nm)/CNTPA-DPA: PO-T2T: PO-01 (1:1 6 wt%, 20
nm)/PO-T2T (50 nm)/Liq (2 nm)/Al (120 nm). Fig. 3a shows the
device structure and energy-level diagram. Here, HAT-CN and
Liq are the hole- and electron-injecting layer. Di[4-(N,N-ditolyl-
amino)-phenyl]cyclohexane (TAPC) and tris(4-(9Hcarbazol-9-
yl)phenyl)amine (TCTA) act as the hole-transporting layers. PO-
T2T is the electron transporting layer. PO-01 is the dopant as
guest. The device structure of orange phosphorescent organic
light-emitting diodes was well optimized and the turn-on
voltage was as low as 2.1 V. A high maximum power efficiency
-1
of 115.5 lm W and maximum EQE of 27% were achieved, which
16-17, 19
is among the highest values to our knowledge.
The high
efficiency of this orange OLEDs indicated that excitons
generated from the exciplex-forming co-host could be
efficiently harvested by PO-01 in the emitting-layer.
Fig. 1 (a) Molecular structures of CNTPA-DPA. (b) Frontier molecular
orbitals distribution of CNTPA-DPA. (c) UV-Vis absorption, fluorescence
(
300 K), and phosphorescence (77 K) spectra of CNTPA-DPA.
In traditional exciplex-based WOLEDs structure, the donor of
1
exciplex-forming co-host must have a high T to block the
generated excitons for the harvesting in the EML and should has
a deep HOMO to form exciplex-forming co-host with acceptor
for the effective energy transfer to all the dopants, especially
the blue one. The conventional exciplex system cannot avoid
the energy loss from exciplex-forming co-host to different
dopants. For instance, because the orange phosphor PO-01 has
a narrow energy band gap, the excitons generated by the holes
on HOMOs of mCP and the electrons on the LUMOs of PO-T2T
will have excessive energy for it and there must be energy loss
in the transfer. In addition, the sharp change in HOMO between
TCTA and mCP severely hinder the hole injection, which will
calorimetry (DSC) measurements have been tested as shown in
Fig. S6 (ESI†). Hole-only devices of CNTPA-DPA and 1,3-bis(N-
carbazolyl)benzene (mCP) were also fabricated to compare
their hole-injection (Fig. S7, ESI†). The hole current densities of
CNTPA-DPA is much higher than that of mCP, indicating a better
hole-injection, which will contribute to enhance the device
efficiency. Based on the space-charge-limited-current (SCLC)
model, the hole mobility of CNTPA-DPA was calculated to be
-8
2
-1 -1
7
.8×10 cm V s . All physical properties of CNTPA-DPA were
summarized in Table S1 (ESI†).
.2. Photophysical & Electroluminescent Properties
3
We employed CNTPA-DPA as the donor to form a new exciplex-
forming co-host with a conventional acceptor (1,3,5-triazine-
2
,4,6-triyl)tris(benzene-3,1-diyl)tris-(diphenylphosphineoxide)
(PO-T2T). The molecular structures of mCP and PO-T2T are
shown in Fig. 2a, respectively. The PL spectra of the material
CNTPA-DPA, mCP, PO-T2T, CNTPA-DPA co-deposited with PO-
T2T film and mCP co-deposited with PO-T2T film are shown in
Fig. 2b. Since CNTPA-DPA and PO-T2T have an emission peak at
4
26 nm and 395 nm, respectively, the CNTPA-DPA: PO-T2T
mixed film showed a feature-less broad emission, peaked at 535
nm and a bathochromic shift compared with either CNTPA-DPA
or PO-T2T. It indicated an intermolecular D-A interaction and
the successful formation of new exciplex. In order to calculate
1
the T energy of CNTPA-DPA: PO-T2T, we tested the
phosphorescence spectra at 77K as shown in Fig. S11. From the
peak of the phosphorescence spectra, the triplet energy of
CNTPA-DPA: PO-T2T was determined to be 2.32 eV. The PL
lifetime spectra of CNTPA-DPA: PO-T2T mixed film in Fig. 2c
further proved this phenomenon, including a fast decay
component of 61.3 ns and a much slower decay with lifetime
longer than 4.2 μs. The PL spectra and PL lifetime spectra of co-
Fig. 2 (a) Molecular structures of mCP and PO-T2T. (b) PL spectra of
CNTPA-DPA, mCP, PO-T2T, CNTPA-DPA:POT2T, mCP:PO-T2T, all of solid
films were measured at 280 nm excitation. (c) Transient PL decay curve
of CNTPA-DPA:PO-T2T, mCP:PO-T2T co-doped film (measured at 300K).
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 3
Please do not adjust margins

J Po lue r an sael od fo Mn aot et rai ad l js u Cs ht emm ai rs gt ri yn sC
Page 4 of 7
ARTICLE
Journal Name
transfer routes of MEHs system is shown in Fig. S10. Owing to
View Article Online
DOI: 10.1039/C9TC01326A
the well-matched HOMO level alignment between TCTA,
CNTPA-DPA and mCP, the hole-injection/transport is enhanced
compared to W2. Besides, the hole mobility of CNTPA-DPA is
faster than mCP, which will further enhance the efficiency.
Benefited from CNTPA-DPA and MEHs strategy, a remarkable
enhancement of efficiency could be achieved. W1 achieved an
enhancement of PE by 45.7% and EQE by 19.6% at the
maximum in contrast to W2. Besides, the well-matched energy
alignment endows the device W1 with a very low operating
-2
voltage of 3.8V at 1000 cd m , which is decreased by 0.3 V in
comparison with W2. In addition, W1 exhibits slightly cooler
white-emission with correlated color temperature (CCT) ≈ 4000
K contrast to 3500 K of W2 and the CIE coordinates were
optimized from (0.44, 0.48) to (0.41, 0.48), this enhancement
may due to the better hole-injection and transport in the EML.
It should be noted that the CIE coordinates shift from (0.46, 0.50)
to (0.34, 0.46) with driving voltage varying from 3 V to 6 V in W1,
which might be due to the increasing exciton harvesting in the
blue part of the multi-EML. To further investigate the effect of
the intermediate HOMO level of CNTPA-DPA in the MEHs
strategy, we exchanged the sequence of blue emitting layer and
orange emitting layer and fabricated W3 with a configuration of
ITO/HAT-CN (10 nm)/TAPC (40 nm)/TCTA (10 nm)/ mCP: PO-
T2T: FIrpic (1:1 15 wt%, 20 nm)/CNTPA-DPA: PO-T2T: PO-01 (1:1
Fig. 3 EL characteristics of the orange OLEDs. (a) Schematic diagram of the device
structure and energy level. (b) PE-L-CE curve. (c) EL spectral at 5 mA/cm . (d)
EQE-L curve.
2
bring the charge injection barrier and high driving voltage.
CNTPA-DPA has a high T
excitons and its suitable HOMO (-5.76 eV) would provide a
staircase” for the hole-injection/transport from TCTA to mCP,
1
(2.74 eV) to block the generated
“
which decrease the carrier injection barrier. More importantly,
it has quite high hole mobility than mCP, indicating better hole
injection/transport to further improve the efficiency. What’s
more, CNTPA-DPA and PO-T2T successfully form an effective
exciplex as host of PO-01, which was confirmed in the former
part.
4
wt%, 3 nm)/PO-T2T (45 nm)/Liq (2 nm)/Al (120 nm) (Fig. S8,
ESI†). Impressively, W3 exhibits higher color stability with a
slight shift in the CIE coordinated ΔCIE = (0.02, 0.00) from (0.40,
-
2
-2
0
.47) at 1000 cd m to (0.38, 0.47) at 8000 cd m . In addition,
benefited from the MEHs strategy, W3 also shows high
To explore its possibility of utility value in WOLEDs, we designed
and fabricated white devices by utilizing the MEHs strategy.
mCP and PO-T2T could successfully form exciplex as host of a
blue phosphor Iridium(III)[bis(4,6-difluorophenyl)-pyridinato-
-
2
performance with a maximum EQE of 16.8%. At 1000 cd m ,
there was a negligible decrease for EQE of 16.5%, with a roll-off
1
8
N,C2′] picolinate (FIrpic). In traditional structure of exciplex-
based WOLEDs, this exciplex could be used as the host of blue
and orange emitters because mCP and PO-T2T both have highly
enough T1 to block the excitons for effective harvesting. But the
high energy level of T1 also brings the high voltage. To solve this
problem and further improve the performance, we employed
the strategy of MEHs, The optimized device structure was
fabricated as following (W1, shown in Fig. 4a): ITO/HAT-CN (10
nm)/TAPC (40 nm)/TCTA (10 nm)/CNTPA-DPA: PO-T2T: PO-01
(1:1 4 wt%, 3 nm)/mCP: PO-T2T: FIrpic (1:1 15 wt%, 20 nm)/PO-
T2T (45 nm)/Liq (2 nm)/Al (120 nm). For comparison with
traditional exciplex-based WOLEDs, W2 was fabricated as
following: ITO/HAT-CN (10 nm)/TAPC (40 nm)/TCTA (10
nm)/mCP: PO-T2T: PO-01 (1:1 4 wt%, 3 nm)/mCP: PO-T2T: FIrpic
(1:1 15 wt%, 20 nm)/PO-T2T (45 nm)/Liq (2 nm)/Al (120 nm). In
the multi-EML, the white emission composed of orange
emission and blue emission. The difference of these two
WOLEDs focused on the orange part. In reference device W2,
the orange dopant simply adopted the same exciplex-forming
co-host as the blue part, which will result in high voltage and
energy loss. While in W1, blue and orange dopant were
allocated to distinct exciplex-forming co-hosts, and the one for
orange dopants was more efficient and could avoid the energy
loss in the energy transfer. The schematic diagram of the energy
Fig. 4 EL characteristics of W1, W2. (a, b) Schematic diagram of the device
structure W1, W2. (c) Current Density-Voltage-Luminance (J-V-L) curves of W1,
W2. (d) PE-Luminance-EQE (PE-L-EQE) curves of W1, W2. (e, f) Normalized EL
spectra at various luminance of 1000, 2000, 4000 and 8000 cd m−2 and the
corresponding CIE values of W1, W2.
4
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 5 of 7
J Po lue r an sael od fo Mn aot et rai ad l js u Cs ht emm ai rs gt ri yn sC
Journal Name
ARTICLE
Table 1 EL Performance of Three Different WOLEDs.
Conflicts of interest
View Article Online
DOI: 10.1039/C9TC01326A
The authors declare no competing financial interest.
Acknowledgements
The authors acknowledge the financial support from the
National Natural Science Foundation of China (51821002,
of just 1.8%. Unfortunately, owing to the sharp change in HOMO
between TCTA and mCP, W3 shows higher turn-on voltage and
driving voltage than W1, which represents the critical effect of
the suitable energy level matches. Moreover, we also fabricated
W4 based on single exciplex-forming co-host composed of
CNTPA-DPA and PO-T2T. As shown in Fig. S9 (ESI†), the device
W4 was fabricated as ITO/HAT-CN (10 nm)/TAPC (40 nm)/TCTA
6
1575136) and the National Key R&D Program of China
(2016YFB0400700). This work was also funded by the
Collaborative Innovation Centre of Suzhou Nano Science and
Technology (Nano-CIC), Priority Academic Program
Development of Jiangsu Higher Education Institutions (PAPD),
and “111” Project of The State Administration of Foreign
Experts Affairs of China.
(10 nm)/CNTPA-DPA: PO-T2T: FIrpic (1:1 15 wt%, 20
nm)/CNTPA-DPA: PO-T2T: PO-01 (1:1 4 wt%, 3 nm)/PO-T2T (45
nm)/Liq (2 nm)/Al (120 nm). Unfortunately, due to the low
triplet energy (2.32 eV) of the exciplex-forming co-host (CNTPA-
DPA: PO-T2T), the device W4 exhibits only orange emission with
negligible blue component. All the performance of the white
devices was summarized in Table 1. To sum up, the maximum
References
1
2
3
4
5
6
7
B. W. D'Andrade and S. R. Forrest, Advanced Materials, 2004,
16, 1585-1595.
Y. Sun, N. C. Giebink, H. Kanno, B. Ma, M. E. Thompson and S.
R. Forrest, Nature, 2006, 440, 908-912.
H. Uoyama, K. Goushi, K. Shizu, H. Nomura and C. Adachi,
Nature, 2012, 492, 234-238.
C. W. Tang and S. A. VanSlyke, Applied Physics Letters, 1987,
51, 913-915.
H. Sasabe and J. Kido, Journal of Materials Chemistry C, 2013,
1, 1699.
K. Udagawa, H. Sasabe, F. Igarashi and J. Kido, Advanced
Optical Materials, 2016, , 86-90.
H. Sasabe, H. Nakanishi, Y. Watanabe, S. Yano, M. Hirasawa,
Y.-J. Pu and J. Kido, Advanced Functional Materials, 2013, 23
-1
-1
PEs and EQEs of W1, W2 and W3 were 73 lm W , 47.5 lm W ,
-
1
4
9.3 lm W and 19.5%, 16.3%, 16.8%, respectively. At 1000 cd
-
2
-1
m , the PEs and EQEs could maintain levels as 41.9 lm W , 31.2
lm W , 32.7 lm W and 16%, 13.9%, 16.5%, respectively, with a
slight efficiency roll-off. Device W1 achieved a very low
operating voltage of about 3.8 V at 1000 cd m , while 4.1 V for
Device W2 and 4.9 V for Device W3. These results confirmed the
superiority for utilizing the strategy of MEHs in exciplex-based
WOLEDs.
-1
-1
-2
4
,
5
550-5555.
8
X. Tang, X. Y. Liu, Y. Yuan, Y. J. Wang, H. C. Li, Z. Q. Jiang and L.
S. Liao, ACS applied materials & interfaces, 2018, 10, 29840-
4
. Conclusions
2
9847.
In conclusion, a new tripodal bipolar compound CNTPA-DPA
was synthesized and employed to assist this strategy of multi-
exciplex-forming co-hosts (MEHs) in exciplex-based WOLEDs.
Benefited from the valuable properties of CNTPA-DPA,
especially the high hole mobility and suitable HOMO, the
9
1
1
E. Mondal, W.-Y. Hung, H.-C. Dai and K.-T. Wong, Advanced
Functional Materials, 2013, 23, 3096-3105.
0 A. Chaskar, H. F. Chen and K. T. Wong, Adv Mater, 2011, 23
876-3895.
1 P. Xiao, J. Huang, Y. Yu, J. Yuan, D. Luo, B. Liu and D. Liang,
Applied Sciences, 2018, , 1449.
,
3
8
orange color emitting component for the WOLEDs could reach 12 Y.-S. Park, S. Lee, K.-H. Kim, S.-Y. Kim, J.-H. Lee and J.-J. Kim,
2
7% in external quantum efficiency (EQE), 2.1 V in turn-on
Advanced Functional Materials, 2013, 23, 4914-4920.
13 Z. Chen, X.-K. Liu, C.-J. Zheng, J. Ye, C.-L. Liu, F. Li, X.-M. Ou, C.-
S. Lee and X.-H. Zhang, Chemistry of Materials, 2015, 27, 5206-
-1
voltage, and 115.5 lm W in power efficiency, which is believed
among the best values of orange color emission in OLEDs. By
utilizing the strategy of MEHs, we alleviate the problem of high
voltage and energy loss in traditional WOLEDs using single
exciplex-forming co-host. As a result, we realize considerable
enhancement in efficiency and decrease in operating voltage.
The optimized WOLEDs showed enhancement of PE by 45.7%
and EQE by 19.6% at the maximum in contrast to the traditional
5
211.
1
4 X. K. Liu, Z. Chen, J. Qing, W. J. Zhang, B. Wu, H. L. Tam, F. Zhu,
X. H. Zhang and C. S. Lee, Advanced Materials, 2015, 27, 7079-
7085.
1
1
5 N. Sun, Q. Wang, Y. Zhao, Y. Chen, D. Yang, F. Zhao, J. Chen
and D. Ma, Adv Mater, 2014, 26, 1617-1621.
6 S. Lee, K. H. Kim, D. Limbach, Y. S. Park and J. J. Kim, Advanced
Functional Materials, 2013, 23, 4105-4110.
single exciplex-based WOLEDs. Particularly, the well-matched 17 R. Wang, D. Liu, H. Ren, T. Zhang, H. Yin, G. Liu and J. Li, Adv
energy alignment endows the device with a very low operating
Mater, 2011, 23, 2823-2827.
-2
18 J.-H. Lee, S.-H. Cheng, S.-J. Yoo, H. Shin, J.-H. Chang, C.-I. Wu,
K.-T. Wong and J.-J. Kim, Advanced Functional Materials,
voltage of 3.8 V at 1000 cd m , which is decreased by 0.3 V.
These results showed obvious improvement of performance in
WOLEDs and the effective strategy of MEHs offered a new
option for WOLEDs structure characteristics and showed
another way to design materials for exciplex-employing in high-
performance WOLEDs.
2
015, 25, 361-366.
1
9 T. Xu, Y. X. Zhang, B. Wang, C. C. Huang, I. Murtaza, H. Meng
and L. S. Liao, ACS Appl. Mater. Interfaces, 2017, 9, 2701-
2710.
2
0 T. Xu, J.-G. Zhou, M.-K. Fung and H. Meng, Organic Electronics,
2
018, 63, 369-375.
This journal is © The Royal Society of Chemistry 20xx
J. Name., 2013, 00, 1-3 | 5
Please do not adjust margins

J Po lue r an sael od fo Mn aot et rai ad l js u Cs ht emm ai rs gt ri yn sC
Page 6 of 7
ARTICLE
Journal Name
2
1 T. Xu, J. G. Zhou, C. C. Huang, L. Zhang, M. K. Fung, I. Murtaza,
H. Meng and L. S. Liao, ACS Appl. Mater. Interfaces, 2017, 9,
0955-10962.
View Article Online
DOI: 10.1039/C9TC01326A
1
6
| J. Name., 2012, 00, 1-3
This journal is © The Royal Society of Chemistry 20xx
Please do not adjust margins

Page 7 of 7
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C9TC01326A
Table of Contents Graphic
An evident enhancement of performance in exciplex-based WOLEDs utilizing the
effective strategy of multi-exciplex-forming co-hosts (MEHs) was achieved.