Indoloindole as a new building block of a hole transport type host for stable operation in phosphorescent organic light-emitting diodes

Article abstract of DOI:10.1039/c9tc00701f

An organic material for application as a p-type host of phosphorescent organic light-emitting diodes was newly developed using an indoloindole moiety as a hole transport unit. The indoloindole derived organic material showed better hole transport properti

Full text of DOI:10.1039/c9tc00701f

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Fine-tuning of gold nanorod dimensions and plasmonic properties using
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Journal of Materials Chemistry C
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DOI: 10.1039/C9TC00701F
Indoloindole as a new building block of hole transport type host for stable
operation in the phosphorescent organic light-emitting diodes
Ha Lim Lee, Kyung Hyung Lee, Jun Yeob Lee*
School of Chemical Engineering, Sungkyunkwan University
2066, Seobu-ro, Jangan-gu, Suwon-si, Gyeonggi-do, 440-746, Korea
Fax: (+) 82-31-299-4716
E-mail: leej17@skku.edu
* To whom correspondence should be addressed
Abstract
An organic material for application as a p-type host of phosphorescent organic light-emitting
diodes was newly developed using an indoloindole moiety as a hole transport unit. The
indoloindole derived organic material showed better hole transport property than a common
carbazole based organic material. The good hole transport property of the indoloindole
derivative allowed the use of it as the p-type host material in the exciplex type mixed host of
phosphorescent organic light-emitting diodes. The new host extended the lifetime of the yellow
phosphorescent OLEDs by more than 10 times compared with a conventional p-type host while
achieving the similar external quantum efficiency.
Key words : indoloindole, host, mixed host, efficiency
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DOI: 10.1039/C9TC00701F
Introduction
In the device structure of organic light-emitting diodes (OLEDs), several organic materials are being
used and they are hole injection material, hole transport material, electron transport material, host and
emitters.1-14 Except for the emitters, other materials mainly or partially play a role of carrying holes or
electrons and consisted of carrier transport units.1-6, 8-10 Hole carrying units are embedded in the hole
injection material, hole transport material and host material, while electron carrying units are implanted
in the electron transport material and host material. Therefore, many hole and electron carrying units
have been explored to develop the organic materials for OLEDs.
As the hole carrying units, carbazole and aromatic amine have been popular because of efficient hole
generation and transport.9, 15-18 However, the carbazole is a weak hole transport unit and is not appropriate
as the building unit of hole transport materials except for high triplet energy hole transport materials with
triplet exciton blocking function.19 The aromatic amine unit is also common as a strong hole transport
unit and mostly used to build hole transport materials.18-20 Other than the carbazole and aromatic amine
units, indole and acridine units can also be included as the hole transport units, but they were not as
popular as the carbazole and aromatic amine units.21, 22 In fact, not many hole transport units are available
in the design of hole transport and host materials, and more hole transport units are required to diversify
the material design of host and hole transport materials.
In this work, an indole derived unit, indoloindole, was introduced as a new hole transport unit of hole
transport type (p-type) host. The indoloindole was synthesized and used to develop 1,3-bis(6-
phenylindolo[2,3-b]indol-5(6H)-yl)benzene (mIDIDP) host. The indoloindole derived mIDIDP
functioned as a strong p-type host for yellow phosphorescent OLEDs. It was demonstrated that the
indoloindole moiety performed well as the building block of the p-type host and the yellow
phosphorescent OLEDs possessing an exciplex type mixed host built on the mIDIDP p-type host
achieved lifetime improvement by more than 10 times compared with a common exciplex host while
achieving high external quantum efficiency over 20%.
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Journal of Materials Chemistry C
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DOI: 10.1039/C9TC00701F
Results and discussion
The synthetic path of the mIDIDP host derived from a new hole transport moiety is described in
Scheme 1. Indoloindole was synthesized through 3 step synthetic process starting from 1H-indole. 1-
Phenyl-1H-indole was successfully synthesized with high yield of 90% by Ullmann reaction according
to literature.23 Then the subsequent Heck reaction with 1-iodo-2-nitrobenzene was carried out to obtain
a 3-(2-nitrophenyl)-1-phenyl-1H-indole intermediate with a synthetic yield around 60%. After that, a
ring closing reaction using triphenylphosphine was carried out to prepare the new hole transport moiety,
5-phenyl-5,6-dihydroindolo[2,3-b]indole (IDID). The final product, mIDIDP, was synthesized by
Ullman reaction using 1,3-diiodobenzene. After purification, mIDIDP was obtained as a pure product
with a high purity over 99.9% and a synthetic yield around 60%. The mIDIDP was confirmed by analysis
1
using H nuclear magnetic spectrometer (NMR), 13C NMR and mass spectroscopy. The details of
synthetic procedure are summarized in experimental part.
The IDID moiety which has two 1H-indole units fused together was designed for strong donor
character by the electron richness of the indole unit. The fusion of the two indole units may strengthen
the donor character of the IDID moiety, which was estimated by examining the molecular orbital
calculation results of the IDID moiety using B3LYP function and 6-31G(d) basis set. The calculation
result of molecular orbital distribution of the IDID moiety is shown in Figure 1 in comparison with that
of conventional carbazole, diphenylamine, and dimethylacridine moieties. The highest occupied
molecular orbital (HOMO) of the IDID moiety was well spread over the two indole moieties and was
shallower than that of carbazole and diphenylamine moieties, indicating the strong donor character of the
IDID moiety. It was similar to a dimethyacridine moiety in terms of donor character considering the
similar HOMO level of IDID and dimethylacridine.
The electronic orbital distribution of the HOMO and LUMO of the mIDIDP host was also calculated
using the B3LYP 6-31G basis set. Figure 2 shows the HOMO and LUMO orbital distribution of mIDIDP.
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The HOMO was localized on the IDID moiety of the mIDIDP because of electron richness of the IDID
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DOI: 10.1039/C9TC00701F
moiety, whereas the LUMO was observed in the phenyl linker between IDID moieties. The calculated
HOMO level of the mIDIDP host was -4.88 eV, which was shallower than that of 1,3-di(9H-carbazol-9-
yl)benzene (mCP) (-5.41 eV) and 1,3-bis(9,9-dimethylacridin-10(9H)-yl)benzene (mAP) (-4.90 eV).
From the calculations, the mIDIDP host is expected to have stronger electron donating property than
mCP and mAP.
The theoretically estimated HOMO and LUMO of the mIDIDP host were experimentally determined
from the onset of oxidation and reduction scan using cyclic voltammetry. The oxidation and reduction
data in Figure 3 estimated the HOMO and LUMO as -5.64 and -2.38 eV, respectively. As expected from
the calculation result, the mIDIDP showed shallower HOMO level than mCP (-6.10 eV) and mAP (-5.88
eV), supporting the insight that the fusion of the two indole units in the IDID moiety intensify the donor
character of the mIDIDP host.
The photophysical behaviour of the mIDIDP host was studied using ultraviolet-visible (UV-Vis)
absorption measurement and photoluminescence (PL) emission measurement (Figure 4). The UV-Vis
absorption spectrum of mIDIDP showed n-π* transition and π-π* transition in the wavelength region of
250-370 nm. The UV-Vis absorption gap of the mIDIDP host was 3.31 eV from the onset energy of the
absorption spectrum. The PL emission spectrum of mIDIDP in tetrahydrofuran solution (1.0  10-5 M
concentration) at room temperature showed a main emission peak at 369 nm corresponding to singlet
energy of 3.36 eV and vibrational peaks at long wavelength. The PL spectrum at 77 K from frozen
tetrahydrofuran solution with 2 μs delay time exhibited phosphorescent emission at 492 nm
corresponding to triplet energy of 2.52 eV. It can be noted from the triplet energy that the mIDIDP can
be applied as the host of yellow phosphors. The triplet energy of the mIDIDP host was similar to that of
the IDID moiety as shown in Figure S1. The material analysis data are summarized in Table 1.
Thermal properties of mIDIDP were also analysed to understand the thermal stability of mIDIDP.
Figure 5(a) and (b) show differential scanning calorimeter analysis result of glass transition temperature
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Journal of Materials Chemistry C
(Tg) and thermogravimetric analysis output of thermal decomposition temperature (Td) of mIDIDP. Since
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the host materials having low Tg can be deformed or crystallized during electrical operaDtiOoIn: 10o.1f0t3h9/eC9OTCL0E07D01sF,
they should have high Tg for stable operation. High Tg of 137.4 °C was observed in the mIDIDP host in
spite of low molecular weight possibly due to the rigid IDID donor moiety. Also, Td of mIDIDP was
467.9 °C up to 5% weight loss, describing the thermal stability of the mIDIDP host.
The mIDIDP host can be regarded as the strong hole transport type host from the HOMO level of -
5.64 eV. Therefore, it was applied as the p-type host of the mixed host. It was mixed with an electron
transport type host (n-type host) to develop the p-n mixed host. The n-type host for the mixed host was
2,2′,2"-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi). Prior to device application, the
mixed film of mIDIDP and TPBi was analysed by PL measurement to study the nature of the
mIDIDP:TPBi mixed host. The fluorescent emission spectra of each host and mixed host are shown in
Figure 6. The peak wavelengths of the mIDIDP, TPBi and mIDIDP:TPBi hosts were 395, 365 and 461
nm, respectively. The mIDIDP:TPBi mixed film showed broadened and red-shifted PL spectrum
compared with the mIDIDP and TPBi, indicating that the mixed host of mIDIDP and TPBi is an exciplex
type host as reported in other publications24-27
.
In several publications, the exciplex type host could enhance external quantum efficiency (EQE) and
extend operational lifetime of the phosphorescent OLEDs.24-27 To evaluate the performances of the
mIDIDP host as a p-type host in the mIDIDP:TPBi exciplex host, yellow phosphorescent OLEDs were
fabricated using the mIDIDP:TPBi (50:50) mixed host. Iridium(III) bis(4-phenylthieno[3,2-c]pyridinato-
N,C2')acetylacetonate (PO-01) was used as the phosphor to fabricate the phosphorescent OLEDs at a
doping concentration of 5 wt%. Reference host was tris(4-carbazoyl-9-ylphenyl)amine (TCTA):TPBi
(50:50) host which is well known as an exciplex host.27 The details of device structure and energy
diagram are summarized in supporting information (Figure S2). The TCTA p-type host has the
HOMO/LUMO levels of -5.70/-2.40 eV, which are almost the same values as those of mIDIDP.
Therefore, the comparison of the mIDIDP:TPBi and TCTA:TPBi mixed host is suitable for judging the
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performance of the mIDIDP as the p-type host of the exciplex host. The device performances of the
View Article Online
mIDIDP:TPBi and TCTA:TPBi devices are summarized in Figure 7 and Table 2. In tDhOeI:c10u.1r0r3e9n/Ct9dTCe0n0s7i0t1yF
(J)-voltage (V)-luminance (L) curves (Figure 7(a)), the mIDIDP:TPBi device showed higher J and L
than the TCTA:TPBi host. Compared with the TCTA p-type host, the mIDIDP host can be considered as
the strong p-type host judging from the single carrier density of the TCTA and mIDIDP hole only devices
in Figure 8. The strong hole transport property of the mIDIDP host increased the J of the mIDIDP:TPBi
mixed host device. Considering the similar HOMO level of TCTA and mIDIDP, the increase of J in the
mIDIDP:TPBi device is due to the improved hole transport properties rather than hole injection properties
by reduced hole injection barrier. The power efficiency-luminance plots and current efficiency-
luminance plots were shown in Figure S3 and Figure S4.
The EQE of the mIDIDP:TPBi device in Figure 7(b) was equivalent to that of the TCTA:TPBi
device, describing the appropriateness of the mIDIDP host as the p-type host. The maximum EQEs of
the mIDIDP:TPBi and TCTA:TPBi devices were 21.4% and 22.2%, respectively. The EQE drop at high
L was insignificant by preserving the high EQE of the devices. For example, the EQE of the
mIDIDP:TPBi device at 5,000 cd/m2 was 20.9%, which is similar to the maximum EQE. Balance of
holes and electrons along with efficient carrier injection in the mIDIDP:TPBi device enabled the small
efficiency roll-off. The mIDIDP:TPBi and TCTA:TPBi hosts were comparable in terms of energy
transfer because the same electroluminescence (EL) spectra were obtained in the yellow phosphorescent
OLEDs (Figure 7(c)). The peak wavelength of the two phosphorescent OLEDs was 561 nm.
The device lifetime up to 80% of initial L at 1,000 cd/m2 was also examined to evaluate the mIDIDP
host as the lifetime elongating host. The lifetime measurement result of the two devices is shown in
Figure 9. The device lifetime of the mIDIDP:TPBi (226.9 h) device was much longer than that of the
TCTA:TPBi (17.1 h) device. Surprisingly, more than 10 times extension of the device lifetime was noted
by replacing TCTA with mIDIDP in the exciplex host. This result showed that the mIDIDP host in the
mixed host device is much better than the TCTA host as the p-type host.
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Journal of Materials Chemistry C
To figure out the reason for the extended lifetime in the mIDIDP:TPBi device, hole carrier stability
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DOI: 10.1039/C9TC00701F
test of mIDIDP and TCTA was carried out by fabricating single carrier devices. The hole carrier stability
test was performed because the p-type hosts mostly carry holes rather than electrons. The hole only device
was operated at a constant J of 7.5 mA/cm2. As a result of hole carrier stability test at a constant J
condition (Figure 10), the driving voltage of the TCTA was significantly increased, but that of the
mIDIDP device was not increased at all. As the voltage rise during electrical operation is caused by
increased resistance in the organic layer or at the interface by degradation of the organic materials, it can
be stated that the reason of the improved lifetime of the mIDIDP:TPBi device is the good hole carrier
stability of the mIDIDP p-type host. The chemical structure merging two indole units could withstand
the hole carriers during device operation.
Conclusions
New hole type moiety, IDID, was designed and developed for good hole transport property and hole
stability. The mIDIDP host derived from the IDID moiety was synthesized and applied as the p-type host
with TPBi in exciplex type mixed host for yellow phosphorescent OLEDs. The PO-01 doped
mIDIDP:TPBi device showed device lifetime more than 10 times longer than that of the common
TCTA:TPBi device while demonstrating high EQE over 20%. This work demonstrated that the new
mIDIDP host derived from IDID moiety can efficiently work as a p-type host possessing high stability
against the hole carriers.
Experimental
General information
1H-indole, triphenylphosphine, copper iodide, and 1,10-phenathroline were product of Sigma Aldrich
Co.. Iodobenzene, 1-iodo-2-nitrobenzene, and 1,3-diiodobenzene were purchased from Alfa Aesar,
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Thermo Fisher Scientific Inc.. Cesium carbonate, potassium carbonate, 1,4-dioxane, N,N-
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DOI: 10.1039/C9TC00701F
dimethylformamide (DMF), and o-dichlorobenzene (o-DCB) were supplied from Duksan Sci. Co..
Palldium (II) acetate was purchased from P&H Tech Co. Methylene chloride (MC) and n-hexane were
bought from Samchun Pure Chemical Co., Ltd.. All of purchased products were used without any
purification. The 1H and 13C nuclear magnetic resonance (NMR) spectra of intermediate compounds and
final product were measured by using AVANCE III HD (Bruker, 500 MHz) spectrometer. The mass
spectroscopy of all compounds except final product was recorded with Advion, ExpresionL CMS
spectrometer with APCI mode. The final compound analysis was proceeded with fast atom bombardment
(FAB) mode measured by JMS-700 (JEOL). The absorption spectrum and emission spectrum of
compound was measured by using spectrophotometer (JASCO, V-730) and fluorescence
spectrophotometer (PerkinElmer, LS-55) respectively. Purity of the final compound was measured using
high performance liquid chromatography (Younglin Instrument Co.) using a mobile phase of
tetrahydrofuran:water (7:3).
Synthesis
1-Phenyl-1H-indole
Synthetic method of 1-pheyl-1H-indole was already reported in previous literature.23
3-(2-Nitrophenyl)-1-phenyl-1H-indole
1-Phenyl-1H-indole (3.00 g, 15.52 mmol), 1-iodo-2-nitrobenzene (5.41 g, 21.73 mmol), potassium
carbonate (6.44 g, 46.57 mmol) and palladium(II) acetate (0.17 g, 0.78 mmol) were poured into 250 ml
2-neck round-bottomed flask. Then, 1,4-dioxane (100 ml) was added into reaction mixture and then the
mixture was bubbled with a nitrogen gas for 1 h. After degassing, the reaction mixture was heated to
110 °C. After 14 h, the reaction mixture was cooled down and extracted with methylene chloride. The
separated organic layer was then filtered with celite/silica filter and concentrated using a rotatry
evaporator. A crude product was purified by column chromatography using a mixed eluent (n-hexane:
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Journal of Materials Chemistry C
methylene chloride=1:2). After all purification, a yellow powder was obtained. (2.88 g, Yield 59%)
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DOI: 10.1039/C9TC00701F
1H NMR (500 MHz, CDCl3) : δ 7.78 (d, 1H, J=7.00 Hz), 7.70 (d, 1H, J=7.00 Hz), 7.53 (t, 1H, J=7.50
Hz), 7.45 (d, 1H, J=7.50 Hz), 7.42 (t, 1H, J=7.75 Hz), 7.36-7.27 (m, 4H), 7.24-7.18 (m, 4H), 6.74 (s, 1H),
13C NMR (125 MHz, CDCl3) : δ 149.3, 138.5, 137.3, 135.7, 133.5, 132.6, 129.5, 129.1, 128.2, 127.9,
127.5, 124.3, 123.1, 121.2, 121.0, 110.8, 104.7, MS (ASAP) m/z : Found 315.16 [(M+H)+]. Calculated
For C20H14N2O2 : 314.34, Tm=136.6 °C
5-Phenyl-5,6-dihydroindolo[2,3-b]indole
3-(2-Nitrophenyl)-1-phenyl-1H-indole (2.00 g, 6.36 mmol), triphenylphosphine (5.01 g, 19.09 mmol)
and o-dichlorobenzene (20 ml) were added into a round-bottomed flask and heated under reflux condition.
After 24 h, the mixture was cooled down and adsorbed into a silica gel. The adsorbed crude product was
purified by column chromatography using a mixed solvent (n-hexane: methylene chloride=2:1). The final
product showed ivory-white after all purification. (1.25 g, Yield 70%)
1H NMR (500 MHz, DMSO) : δ 11.50 (s, 1H), 7.87 (d, 1H, J=7.00 Hz), 7.75 (d, 2H, J=7.50 Hz), 7.69
(t, 2H, J=7.75 Hz), 7.61 (d, 1H, J=8.00 Hz), 7.56 (d, 1H, J=8.50 Hz), 7.47 (t, 1H, J=7.25 Hz), 7.42 (d,
13
1H, J=8.00 Hz), 7.28-7.19 (m, 3H), 7.02 (t, 1H, J=7.25 Hz), C NMR (125 MHz, DMSO) : δ 140.3,
139.9, 138.5, 130.1, 129.9, 126.4, 126.0, 125.1, 124.8, 122.7, 121.8, 119.7, 118.3, 118.2, 117.5, 115.7,
114.1, 112.5, 110.6 MS (ASAP) m/z : Found 283.09 [(M+H)+]. Calculated For C20H14N2 : 282.34,
Tm=181.5 °C
1,3-Bis(6-phenylindolo[2,3-b]indol-5(6H)-yl)benzene (mIDIDP)
1,3-Diiodobenzene (1.50 g, 4.55 mmol), 5-phenyl-5,6-dihydroindolo[2,3-b]indole (2.82g, 10.00 mmol),
copper iodide (1.73 g, 9.10 mmol), potassium carbonate (1.89 g, 13.64 mmol) and 1,10-phenathroline
(1.64 g, 9.10 mmol) were added into a pressure tube. DMF (30 ml) was added into the pressure tube and
then the pressure tube was heated to 150 °C for 12 h. After the reaction, excess amount of methylene
chloride was added into the reaction mixture and the mixture was filtered with celite/silica gel. The filtrate
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was then concentrated using a rotary evaporator and adsorbed into a silica gel. The crude product was
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purified with column chromatography using a mixed eluent (n-hexane: methylene chDloOrI:i1d0e.1=0319/:C19)T.CA00f7t0e1rF
recrystallization, the product was sublimed with train sublimation machine several times. A white
product was obtained after all purification. (1.71 g, Yield 59%)
1H NMR (500 MHz, CDCl3) : δ 8.14(s, 1H), 7.93-7.86 (m, 3H), 7.76 (d, 6H, J=7.50 Hz), 7.70 (d, 2H,
J=8.00 Hz), 7.64 (t, 6H, J=6.75 Hz), 7.57 (d, 2H, J=8.00 Hz), 7.46 (t, 2H, J=7.50 Hz), 7.26 (t, 4H, J=7.75
Hz), 7.13 (t, 4H, J=7.25 Hz), 13C NMR (125 MHz, CDCl3) : δ 141.1, 141.1, 140.5, 138.9, 131.0, 129.9,
127.2, 127.0 ,126.7, 126.1, 124.3, 123.1, 123.0, 122.9, 120.1, 119.9, 118.8, 118.7, 116.2, 115.8, 111.2,
111.1 MS (HR-FAB) m/z Found : 638.2468 [(M+H)+]. Calculated For C46H30N4 : 638.7572,
Tm=263.1 °C
Device Fabrication and measurements
Patterned ITO substrates were used for all devices fabrication. Organic materials, LiF and Al were
deposited at a high pressure of 1.0 × 10-6 torr.
The device structure is described below.
ITO (50 nm)/ DNTPD (60 nm)/ BPBPA (20 nm)/ PCZAC (10 nm)/ emitting layer (30 nm)/ DBFTrz (5
nm)/ ZADN (30 nm)/ LiF (1.5 nm)/ Al (200 nm)
N4,N4′-Bis[4-[bis(3-methylphenyl)amino]phenyl]-N4,N4′-diphenyl-[1,1′-biphenyl]-4,4′-diamine
(DNTPD) and N,N,N'N'-tetra[(1,10-biphenyl)-4-yl]-(1,10-biphenyl)-4,4'-diamine (BPBPA) were used as
a hole injection layer and a hole transport layer, respectively. The 9,9-dimethyl-10-(9-phenyl-9H-
carbazol-3-yl)-9,10-dihydroacridine (PCZAC) was deposited on BPBPA and used as an exciton blocking
layer. 2,8-Bis(4,6-diphenyl-1,3,5-triazin-2-yl)dibenzo[b,d]furan (DBFTrz) and 9,10-di(naphthalene-2-
yl)anthracen-2-yl-(4,1-phenylene)(1-phenyl-1Hbenzo[d]imidazole (ZADN) were used as an exciton
blocking layer and an electron transport layer, respectively. The hosts of the emission layer were either
mIDIDP:TPBi or TCTA:TPBi. The doping concentration of PO-01 was fixed with 5 wt% in all devices.
The single charge device structure is summarized below.
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Journal of Materials Chemistry C
ITO (50 nm)/ PEDOT:PSS (60 nm)/ mIDIDP or TCTA (50 nm)/ Al (200 nm)
View Article Online
DOI: 10.1039/C9TC00701F
The fabricated devices were analyzed using Keithley 2400 source measurement unit and CS 2000
spectroradiometer at room temperature after encapsulation.
Acknowledgements
This work was supported by Basic Science Research Program (2016R1A2B3008845) and Nano
Materials Research Program (2016M3A7B4909243) through the National Research Foundation of Korea
funded by Ministry of Science, ICT and Future Planning.
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Journal of Materials Chemistry C
Page 14 of 28
List of Table
View Article Online
DOI: 10.1039/C9TC00701F
Table 1. Material property data of mIDIDP
Table 2. Device performance of mixed host devices
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Journal of Materials Chemistry C
Table 1. Material property data of mIDIDP
View Article Online
DOI: 10.1039/C9TC00701F
Tg
Td
EHOMO ELUMO Egap EUv-gap
ES
ET
(°C)
(°C)
(eV)
(eV)
(eV)
(eV)
(eV)
(eV)
-5.64 -2.38
3.26
3.31
3.36
2.52 137.4 467.9
mIDIDP
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Journal of Materials Chemistry C
Page 16 of 28
Table 2. Device performance of mixed host devices
QE(%)
[5000cd/m2]
PE(lm/W)
[5000cd/m2]
CE(Cd/A)
[5000cd/m2]
Vd
(V)
I
LT80
(h)
CIE
(mA/cm2)
[Max]
[Max]
[Max]
mIDIDP:
TPBi
TCTA:
TPBi
5.6
5.7
7.4
7.2
(0.49, 0.51)
(0.49, 0.51)
20.9
21.4
37.8
38.2
52.4
67.7
69.6
70.1
226.9
17.1
21.5
22.2
52.4
71.9
*All data was measured at 5,000 cd/m2
**QE=Quantum Efficiency, PE=Power Efficiency, CE=Current Efficiency, Vd=Driving voltage
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Page 17 of 28
Journal of Materials Chemistry C
List of figures
View Article Online
DOI: 10.1039/C9TC00701F
Scheme 1. Synthetic method for mIDIDP
Figure 1. Calculation data of moieties
Figure 2. Orbital distribution of mIDIDP host
Figure 3. CV measurement of mIDIDP
Figure 4. Uv-Vis absorption spectrum and PL emission spectra of mIDIDP
Figure 5. Thermal property analysis of mIDIDP host with (a) DSC and (b) TGA
Figure 6. PL emission spectra of mIDIDP, TPBi and mixed film
Figure 7. (a) J-V-L curves, (b) EQE-L curves, (c) electroluminescenc spectra of mixed host devices
Figure 8. J-V curves of single charge device
Figure 9. Luminance-lifetime plots of devices
Figure 10. hole stability test of single charge device
17

Journal of Materials Chemistry C
Page 18 of 28
View Article Online
DOI: 10.1039/C9TC00701F
Scheme 1. Synthetic method for mIDIDP
18

Page 19 of 28
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C9TC00701F
Figure 1. Calculation data of moieties
19

Journal of Materials Chemistry C
Page 20 of 28
View Article Online
DOI: 10.1039/C9TC00701F
Figure 2. Orbital distribution of mIDIDP host
20

Page 21 of 28
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C9TC00701F
Figure 3. CV measurement of mIDIDP
21

Journal of Materials Chemistry C
Page 22 of 28
View Article Online
DOI: 10.1039/C9TC00701F
Figure 4. Uv-Vis absorption spectrum and PL emission spectra of mIDIDP
22

Page 23 of 28
Journal of Materials Chemistry C
(a)
View Article Online
DOI: 10.1039/C9TC00701F
(b)
Figure 5. Thermal property analysis of mIDIDP host with (a) DSC and (b) TGA
23

Journal of Materials Chemistry C
Page 24 of 28
View Article Online
DOI: 10.1039/C9TC00701F
Figure 6. PL emission spectra of mIDIDP, TPBi and mixed film
24

Page 25 of 28
Journal of Materials Chemistry C
(a)
View Article Online
DOI: 10.1039/C9TC00701F
(b)
(c)
Figure 7. (a) J-V-L curves, (b) EQE-L curves, (c) electroluminescenc spectra of mixed host devices
25

Journal of Materials Chemistry C
Page 26 of 28
View Article Online
DOI: 10.1039/C9TC00701F
Figure 8. J-V curves of single charge device
26

Page 27 of 28
Journal of Materials Chemistry C
View Article Online
DOI: 10.1039/C9TC00701F
Figure 9. Luminance-lifetime plots of devices
27

Journal of Materials Chemistry C
Page 28 of 28
View Article Online
DOI: 10.1039/C9TC00701F
Figure 10. hole stability test of single charge device
28