Highly efficient simple-structure blue and all-phosphor warm-white phosphorescent organic light-emitting diodes enabled by wide-bandgap tetraarylsilane-based functional materials

Article abstract of DOI:10.1002/adfm.201400149

Two host materials of {4-[diphenyl(4-pyridin-3-ylphenyl)silyl]phenyl}diphenylamine (p-PySiTPA) and {4-[[4-(diphenylphosphoryl)phenyl](diphenyl)silyl] phenyl}diphenylamine (p-POSiTPA), and an electron-transporting material of [(diphenylsilanediyl)bis(4,1-phenylene)]bis(diphenylphosphine) dioxide (SiDPO) are developed by incorporating appropriate charge transporting units into the tetraarylsilane skeleton. The host materials feature both high triplet energies (ca. 2.93 eV) and ambipolar charge transporting nature; the electron-transporting material comprising diphenylphosphine oxide units and tetraphenylsilane skeleton exhibits a high triplet energy (3.21 eV) and a deep highest occupied molecular orbital (HOMO) level (-6.47 eV). Using these tetraarylsilane-based functional materials results in a high-efficiency blue phosphorescent device with a three-organic-layer structure of 1,1-bis[4-[ N,N- di(p-tolyl)-amino]phenyl]cyclohexane (TAPC)/ p-POSiTPA: iridium(III) bis(4′,6′- difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate (FIr6)/SiDPO that exhibits a forward-viewing maximum external quantum efficiency (EQE) up to 22.2%. This is the first report of three-organic-layer FIr6-based blue PhOLEDs with the forward-viewing EQE over 20%, and the device performance is among the highest for FIr6-based blue PhOLEDs even compared with the four or more than four organic-layer devices. Furthermore, with the introduction of bis(2-(9,9-diethyl-9 H-fluoren-2-yl)-1-phenyl-1 H-benzoimidazol- N,C³) iridium acetylacetonate [(fbi)₂Ir(acac)] as an orange emitter, an all-phosphor warm-white PhOLED achieves a peak power efficiency of 47.2 lm W^?1, which is close to the highest values ever reported for two-color white PhOLEDs.

Full text of DOI:10.1002/adfm.201400149

www.afm-journal.de
www.MaterialsViews.com
Highly Efficient Simple-Structure Blue and All-Phosphor
Warm-White Phosphorescent Organic Light-Emitting
Diodes Enabled by Wide-Bandgap Tetraarylsilane-Based
Functional Materials
Shaolong Gong, Ning Sun, Jiajia Luo, Cheng Zhong, Dongge Ma,* Jingui Qin,
and Chuluo Yang*
for the next-generation flat-panel displays
and lighting sources.[1–3] In particular,
phosphorescent OLEDs (PhOLEDs) have
shown great potentials due to their merit of
higher quantum efficiency compared with
fluorescent OLEDs by utilizing both sin-
glet and triplet excitons.[4–6] Among mono-
chromatic PhOLEDs, the lack of efficient
and stable blue PhOLEDs has become a
major bottleneck to the development of
efficient and stable white PhOLEDs, and
thus restricts the commercialization of
PhOLEDs in lighting sources. In com-
parision with sky-blue PhOLEDs based on
the widely used phosphor of iridium(III)
bis(4,6-(difluorophenyl)pyridine-N,C2′)
Two host materials of {4-[diphenyl(4-pyridin-3-ylphenyl)silyl]phenyl}diphe-
nylamine (p-PySiTPA) and {4-[[4-(diphenylphosphoryl)phenyl](diphenyl)silyl]
phenyl}diphenylamine (p-POSiTPA), and an electron-transporting material
of [(diphenylsilanediyl)bis(4,1-phenylene)]bis(diphenylphosphine) dioxide
(SiDPO) are developed by incorporating appropriate charge transporting
units into the tetraarylsilane skeleton. The host materials feature both high
triplet energies (ca. 2.93 eV) and ambipolar charge transporting nature; the
electron-transporting material comprising diphenylphosphine oxide units and
tetraphenylsilane skeleton exhibits a high triplet energy (3.21 eV) and a deep
highest occupied molecular orbital (HOMO) level (-6.47 eV). Using these
tetraarylsilane-based functional materials results in a high-efficiency blue
phosphorescent device with a three-organic-layer structure of 1,1-bis[4-[N,N-
di(p-tolyl)-amino]phenyl]cyclohexane (TAPC)/p-POSiTPA: iridium(III) bis(4′,6′-
difluorophenylpyridinato)tetrakis(1-pyrazolyl)borate (FIr6)/SiDPO that
exhibits a forward-viewing maximum external quantum efficiency (EQE) up to
22.2%. This is the first report of three-organic-layer FIr6-based blue PhOLEDs
with the forward-viewing EQE over 20%, and the device performance is
among the highest for FIr6-based blue PhOLEDs even compared with the
four or more than four organic-layer devices. Furthermore, with the introduc-
tion of bis(2-(9,9-diethyl-9H-fluoren-2-yl)-1-phenyl-1H-benzoimidazol-N,C3)
iridium acetylacetonate [(fbi)2Ir(acac)] as an orange emitter, an all-phosphor
warm-white PhOLED achieves a peak power efficiency of 47.2 lm W−1, which
is close to the highest values ever reported for two-color white PhOLEDs.
picolinate (FIrpic),[7]
a blue PhOLED
with a deeper blue emission shows more
promise in reducing power consumption
and improving color rendering index for
illumination.[8] Until now, iridium(III)
bis(4′,6′-difluorophenylpyridinato)
tetrakis(1-pyrazolyl)borate
(FIr6)[9–12]
is still one of the typical phosphors for
highly efficient PhOLEDs with a deeper
blue emission. For example, a high-effi-
ciency FIr6-based blue PhOLED with a
peak external quantum efficiency (EQE)
of 22.9% was fabricated by introducing
N,N′-dicarbazolyl-3,5-benzene (mCP):m-
bis(triphenylsilyl)benzene (UGH3) co-host system into the
emitting layer;[10a] a maximum EQE of 20% was achieved by
the FIr6-based blue PhOLED with the incorporation of a double
emissive layer into the p-i-n device structure.[12b]
1. Introduction
High-efficiency organic light-emitting diodes (OLEDs) have
generated considerable interests because of their bright future
Dr. S. Gong, J. Luo, Dr. C. Zhong, Prof. J. Qin,
Prof. C. Yang
N. Sun, Prof. D. Ma
State Key Laboratory of Polymer Physics and Chemistry
Changchun Institute of Applied Chemistry
Chinese Academy of Sciences
Changchun 130022, PR China
E-mail: mdg1014@ciac.jl.cn
Hubei Collaborative Innovation Center for
Advanced Organic Chemical Materials
Hubei Key Lab on Organic and Polymeric Optoelectronic Materials
Department of Chemistry, Wuhan University
Wuhan 430072, PR China
E-mail: clyang@whu.edu.cn
DOI: 10.1002/adfm.201400149
©
wileyonlinelibrary.com
Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201400149
2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1

www.afm-journal.de
www.MaterialsViews.com
Although gains in high EQEs are realized through the
careful device optimization and material selection, at least four
organic layers are required for almost all FIr6-based PhOLEDs
with high efficiencies.[9–12] Except for typical three functional
layers, that is the emitting layer (EML), hole- and electron-
transporting layers (HTL and ETL), more layers are imperative
to facilitate charge injection, transporting or blocking in the
devices, which complicate the device structures and inevitably
cause high operating voltages and increased manufacturing
costs. Therefore, further effort on simplifying device structure
while maintaining high device efficiency is highly desirable
to make low-cost manufacturability amenable to commercial
interests. However, the examples that can achieve satisfactory
device performance in a simple device configuration remain
rare.[13] This is mainly due to the lack of suitable functional
materials to ensure charge balance and exciton confinement
inside the EML in a simple device structure. The most critical
problem to reach this goal is how to systematically manipulate
the singlet and triplet energy levels as well as charge trans-
porting properties of these functional materials used in HTL,
ETL and EML. These functional materials should all have
higher triplet energies (ET) than 2.72 eV[14] of FIr6 to enable
effective exciton confinement inside the EML. Besides this
common requirement, one also expects the host materials to
have ambipolar charge transporting nature to maximize the
radiative recombination of carriers in the EML, and suitable
highest occupied molecular orbital (HOMO) and lowest unoc-
cupied molecular orbital (LUMO) levels to match with the adja-
cent HTL and/or ETL, thus benefiting hole and/or electron
injection into the EML.[6a,15] For the HTL and ETL, the typical
HTL of 1,1-bis[4-[N,N-di(p-tolyl)-amino]phenyl]cyclohexane
(TAPC) has been widely used in blue PhOLEDs because of its
high ET (2.87 eV)[16] and good HT ability;[10,12,13] in contrast,
excellent ET materials with sufficiently high triplet energies
(>2.72 eV) to block exciton leakage are relatively unexplored.[17]
Furthermore, it is desirable that ET materials possess deep
HOMO level to act as a hole-blocking layer (HBL) in terms of
the simplification of device structure. Therefore, the develop-
ment of suitable host and ET materials remains a molecular
designing challenge in efforts to realize high-efficiency blue
PhOLEDs with simple device structure.
Our previous works demonstrated a series of tetraaryl-
silane-based host materials with both relatively high triplet
energies and ambipolar transporting properties for sky-blue
PhOLEDs, which achieved good performance in four-organic-
layer devices.[18] In this work, we develop a series of wide-
bandgap functional materials by incorporating suitable charge-
transporting groups into the tetraarylsilane structure, that is,
two host materials of p-PySiTPA and p-POSiTPA, and an ET
material of SiDPO. The incorporation of electron-donor and
-acceptor units into the tetraphenylsilane skeleton provides the
host materials with high triplet energies (ca. 2.93 eV) and ambi-
polar charge transporting nature; the introduction of diphe-
nylphosphine oxide acceptor into tetraphenylsilane structure
endows the ET material with a high ET (3.21 eV) and a deep
HOMO level (−6.47 eV). Consequently, a high-efficiency blue
phosphorescent device with a three-organic-layer structure of
TAPC/p-POSiTPA:FIr6/SiDPO has been realized with a for-
ward-viewing maximum EQE up to 22.2%. To the best of our
knowledge, this is the first report of three-organic-layer FIr6-
based blue PhOLEDs with the forward-viewing EQE over 20%.
Furthermore, with the introduction of bis(2-(9,9-diethyl-9H-flu-
oren-2-yl)-1-phenyl-1H-benzoimidazol-N,C3)iridium acetylace-
tonate [(fbi)2Ir(acac)] as an orange emitter, an all-phosphor
warm-white PhOLED has been realized with a peak power effi-
ciency of 47.2 lm W−1, which is close to the highest values ever
reported for two-color white PhOLEDs.
2. Results and Discussion
2.1. Synthesis and Characterization
Scheme 1 depicts the synthetic routes and structures of
{4-[diphenyl(4-pyridin-3-ylphenyl)silyl]phenyl}diphenylamine
(p-PySiTPA), {4-[[4-(diphenylphosphoryl)phenyl](diphenyl)silyl]
phenyl}diphenylamine (p-POSiTPA), and [(diphenylsilanediyl)
bis(4,1-phenylene)]bis(diphenylphosphine) dioxide (SiDPO).
Lithiation of 1 with n-butyllithium and subsequent treatment
with excess diiodine afforded the intermediate 2. The C-N cou-
pling reaction of 2 with diphenylamine yielded the key inter-
mediate 3. p-PySiTPA was then synthesized by the Suzuki
cross-coupling reaction of 3 with pyridin-3-ylboronic acid;
whereas p-POSiTPA and SiDPO were prepared through a three-
step procedure of lithiation, phophorization and oxidation from
3 and 1, respectively. 1H and 13C NMR spectroscopies, mass
spectrometry and elemental analysis (see the Experimental
Section) were used to characterize the structures of these
compounds.
2.2. Photophysical Properties
Figure 1 shows the UV-vis absorption, fluorescence and phos-
phorescence spectra of the compounds, and Table 1 sum-
mrizes the key parameters. The optical bandgaps (Eg) of
p-PySiTPA, p-POSiTPA, and SiDPO are estimated as 3.40,
3.41 and 4.26 eV, respectively, from the absorption edge of
the films (Supporting Information Figure S1). The highest-
energy vibronic sub-band of their phosphorescence spectra
at 77 K (Figure 1 and Supporting Information Figure S2)
have allowed us to determine the ET of these compounds
(2.92 eV for p-PySiTPA, 2.93 eV for p-POSiTPA and 3.21 eV
for SiDPO). The higher ET of the compounds than 2.72 eV
of FIr6 could enable good exciton confinement on the blue
phosphor FIr6. The suitability of p-PySiTPA and p-POSiTPA
to host FIr6 are evaluated by measuring the photolumines-
cence quantum yields (PLQYs) of the films which comprise
10 wt% FIr6 in p-PySiTPA and p-POSiTPA, respectively. The
relatively high PLQYs (86.5% for p-PySiTPA:10 wt% FIr6
and 86.8% for p-POSiTPA:10 wt% FIr6) are achieved for the
doped films, which are slightly lower than the PLQY (96%) of
FIr6 in dichoroethane solution.[19] Considering an accepted
value for the light outcoupling efficiency of 25–30% and the
excellent charge balance achieved in FIr6-based PhOLEDs,
the maximum EQE of 22–26% is estimated for p-PySiTPA or
p-POSiTPA:10 wt% FIr6 PhOLEDs, suggesting that p-PySiTPA
and p-POSiTPA are potentially good hosts for FIr6.
©
2
wileyonlinelibrary.com
2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201400149

www.afm-journal.de
www.MaterialsViews.com
Scheme 1. Synthetic routes and structures of p-PySiTPA, p-POSiTPA, and SiDPO.
2.3. Thermal Properties and Film-Forming Ability
The thermal properties of p-PySiTPA, p-POSiTPA and SiDPO
were investigated by the thermogravimetric analysis (TGA)
and the differential scanning calorimetry (DSC) (Figure 2 and
Table 1). The decomposition temperatures (Td, corresponding
to 5% weight loss) are 384, 406 and 476 °C for p-PySiTPA,
p-POSiTPA and SiDPO, respectively. These compounds
show relatively high glass transition temperatures (Tg) of 71
(p-PySiTPA), 94 (p-POSiTPA) and 105 °C (SiDPO), which are
higher than those of previously reported tetraarylsilane com-
pounds (26–53 °C).[14] The good thermal performance could
improve stability of film morphology and reduce possibility
of phase separation upon heating. As shown in Figure 3, the
atomic force microscopy (AFM) images of p-PySiTPA and
p-POSiTPA films doped with FIr6 display smooth and homo-
geneous film morphologies, with the small values of root-
mean-square (RMS) roughness at 0.24 and 0.21 nm. This
indicates that the silicon tetrahedral configuration can provide
Figure 1. UV-vis absorption and fluorescence spectra of p-PySiTPA,
p-POSiTPA, and SiDPO in hexane at 5×10−6 M at room temperature,
and phosphorescence spectra of p-PySiTPA, p-POSiTPA, and SiDPO in
2-methyltetrahydrofuran at 77 K.
Table 1. Physical Properties of p-PySiTPA, p-POSiTPA, and SiDPO
compound
Tg
[°C]a)
Td
[°C]b)
HOMO
[eV]d)
LUMO
[eV]e)
Eg
[eV]f)
ET
[eV]g)
λabs
λem,max
[nm]c)
[nm]c)
p-PySiTPA
p-POSiTPA
SiDPO
71
94
384
406
476
252, 306
307
359
360
307
3.40
3.41
4.26
2.92
2.93
3.21
−5.32
−5.33
−6.47
−1.92
−1.92
−2.21
105
241
a)Obtained from DSC measurements; b)Obtained from TGA measurements; c)Measured in hexane; d)Determined from the onset of oxidation potentials; e)Calculated from
HOMO and Eg; f)Determined from the onset of absorption in film state; g)Measured in 2-methyltetrahydrofuran at 77 K.
©
wileyonlinelibrary.com
Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201400149
2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
3

www.afm-journal.de
www.MaterialsViews.com
Figure 4. Cyclic voltammogram of (a) p-PySiTPA and p-POSiTPA in
Figure 2. (a) TGA traces of p-PySiTPA, p-POSiTPA, and SiDPO recorded
at a heating rate of 10 °C min−1. (b) DSC traces of p-PySiTPA, p-POSiTPA,
CH2Cl2 for oxidation scan, and (b) SiDPO in THF for reduction scan.
and SiDPO recorded at a heating rate of 10 °C min−1
.
p-POSiTPA are −5.32 and −5.33 eV with regard to the energy
level of ferrocene (−4.8 eV below vacuum), respectively, which
well match to the HOMO level (−5.5 eV) of TAPC because of
no hole-injection barriers from TAPC to these hosts.[21] SiDPO
exhibits negligible oxidation signal during the anodic scan in
dichloromethane or dimethylformamide. The LUMO level of
SiDPO is −2.21 eV (Figure 4b), which can facilitate electron-
injection into the EML. Its HOMO level estimated from the
bandgap of SiDPO (4.26 eV) and LUMO is −6.47 eV, indicative
of the potential utilization of SiDPO as an HBL/ETL.
a stabilizing environment for dopants and keep films integrity
throughout the entire fabrication process.
2.4. Electrochemical Properties
Cyclic voltammetry (CV) were performed to investigate the
electrochemical properties of the compounds. p-PySiTPA and
p-POSiTPA exhibit one quasi-reversible, one-electron oxida-
tion process (Figure 4a), which can be assigned to the oxidation
of arylamine moiety.[20] The HOMO levels of p-PySiTPA and
2.5. Electroluminescent Devices
To evaluate the performance of the newly-designed functional
materials in blue PhOLEDs, two types of device structures
were fabricated (Figure 5). The control devices (F1 and F2)
have four-organic-layer structure of ITO/MoO3 (10 nm)/TAPC
(60 nm)/p-PySiTPA or p-POSiTPA: FIr6 (10 wt%, 20 nm)/1,3,5-
tri(m-pyrid-3-yl-phenyl)benzene (Tm3PyPB,
5
nm)/1,3,5-
tris(N-phenylbenzimidazol-2-yl)benzene (TPBI, 30 nm)/LiF
(1 nm)/Al (100 nm). The simplified devices (T1 and T2) have
three-organic-layer structure of ITO/MoO3 (10 nm)/TAPC
Figure 3. AFM images of the doped films prepared by vacuum thermal
deposition with 10 wt% FIr6 in (a) p-PySiTPA and (b) p-POSiTPA.
©
4
wileyonlinelibrary.com
2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201400149

www.afm-journal.de
www.MaterialsViews.com
efficiency roll-off value of only 3.2%; even
at the high luminance of 1000 cd m−2, EQE
remains as high as 17.1%. We have summa-
rized the EL performance of representative
FIr6-based PhOLEDs in Table 3. There are
few examples reported in the literature on
three-organic-layer FIr6-based blue PhOLEDs:
Xue et al. reported a three-organic-layer FIr6-
based blue PhOLED with EQEmax of only
5.5% in the structure of TAPC/UGH2:FIr6/
BCP;[9b] Fukagawa et al. demonstrated PEmax
of 19 lm W−1 and EQEmax of 14% in the struc-
ture of TAPC/Ad-CzPd:FIr6/TmPyPB.[13] To
the best of our knowledge, this work is the
first report of three-organic-layer FIr6-based
blue PhOLEDs with the forward-viewing
EQE above 20%, and the device performance
is among the highest for FIr6-based blue
PhOLEDs even compared with the four or
more than four organic-layer devices.[10–12]
We observed that the device luminescence
went off after ca. 3 hours without encapsula-
tion. The short lifetime of blue phosphores-
Figure 5. (a) Schematic of two type device structures of blue PhOLEDs. (b) Chemical struc-
tures of materials used for fabrication of devices.
(60 nm)/p-PySiTPA or p-POSiTPA: FIr6 (10 wt%, 20 nm)/
SiDPO (35 nm)/LiF (1 nm)/Al (100 nm), where SiDPO acts as
the HBL/ETL to replace Tm3PyPB[22] and TPBI[23] in control
devices. MoO3 and LiF serve as hole- and electron-injecting
layers, respectively; TAPC functions as the HTL; FIr6 doped in
p-PySiTPA or p-POSiTPA is utilized as EML, respectively.
cent OLEDs are generally believed to result from the instability
of blue phosphorescent iridium complexes.[24]
Figure 6 shows the current density-voltage-luminance (J-V-L)
characteristics and efficiency versus luminance curves for the
devices, and Table 2 summarizes the key device performance
parameters. All the devices exhibit relatively low turn-on volt-
ages (Von, recorded at the luminance of 1 cd m−2) in the range
of 3.1–3.3 V, which can be rationalized by the well-matched
HOMO levels of p-PySiTPA and p-POSiTPA with the HTL of
TAPC. Noticablely, the simplified three-organic-layer devices
T1 and T2 exhibit much higher efficiencies than the con-
trol four-organic-layer devices F1 and F2, respectively. For
instance, the p-PySiTPA-based device T1 achieves a maximum
current efficiency (CEmax) of 33.5 cd A−1 (Supporting Infor-
mation Figure S3), a maximum power efficiency (PEmax) of
34.0 lm W−1 and a maximum EQE (EQEmax) of 18.8%, which
outperform those of the control device F1 (CEmax of 22.0 cd
A−1, PEmax of 15.7 lm W−1 and EQEmax of 12.4%). Furthermore,
the p-POSiTPA-based simplified device T2 exhibits better per-
formance than p-PySiTPA-based device T1, with the forward-
viewing CEmax of 40.1 cd A−1, PEmax of 40.5 lm W−1 and EQEmax
of 22.2%. Similarly, p-POSiTPA-based device F2 displays sub-
stantially higher efficiencies (CEmax of 25.9 cd A−1, PEmax of
20.8 lm W−1 and EQEmax of 13.8%) than p-PySiTPA-based device
F1. These results indicates the superiority of host material
p-POSiTPA over p-PySiTPA. Given the fact that the doped films
exhibit almost the same PLQYs (86.5% for p-PySiTPA:10 wt%
FIr6 and 86.8% for p-POSiTPA:10 wt% FIr6), the origin of the
different device performance could be the discrepancy in charge
balance of p-PySiTPA and p-POSiTPA in FIr6-based devices.
Remarkably, device T2 shows rather low efficiency roll-off: at
the luminance of 100 cd m−2, EQE is still up to 21.5% with a
Figure 6. (a) Current density-voltage-luminance characteristics for
devices F1, F2, T1 and T2. (b) External quantum efficiency and power
efficiency versus luminance curves for devices F1, F2, T1 and T2.
©
wileyonlinelibrary.com
Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201400149
2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
5

www.afm-journal.de
www.MaterialsViews.com
Table 2. Summary of EL Performances (Forward-Viewing) of the Devicesa)
device
host
HBL/ETL
Von
[V]
CE
PE
EQE
[%]b)
CIE
[x, y]c)
[cd A−1 b)
]
[lm W−1 b)
]
F1
p-PySiTPA
p-POSiTPA
p-PySiTPA
p-POSiTPA
p-PySiTPA
p-POSiTPA
Tm3PyPB/TPBI
Tm3PyPB/TPBI
SiDPO
3.3
3.1
3.1
3.1
2.7
3.1
22.0, 19.9, 20.7
25.9, 24.0, 21.1
33.5, 30.2, 21.7
40.1, 38.9, 30.7
29.1, 24.7, 15.6
46.5, 40.9, 27.3
15.7, 15.2, 11.8
20.8, 20.4, 13.5
34.0, 23.1, 11.5
40.5, 31.3, 17.5
31.5, 22.2, 9.6
47.2, 32.9, 15.6
12.4, 11.2, 11.6
13.8, 12.9, 11.3
18.8, 16.9, 12.0
22.2, 21.5, 17.1
11.5, 9.8, 6.4
(0.15, 0.23)
(0.15, 0.24)
(0.15, 0.24)
(0.15, 0.24)
(0.45, 0.41)
(0.42, 0.42)
F2
T1
T2
W1
W2
SiDPO
SiDPO
SiDPO
18.7, 17.3, 11.3
a)Abbreviations: HBL, hole-blocking layer; ETL, electron-transporting layer; Von, turn-on voltage; CE, current efficiency; PE, power efficiency; EQE, external quantum effi-
;
ciency; CIE [x, y], Commission International de I’Eclairage coordinates; b)Order of measured value: maximum, then values at 100 and 1000 cd m−2 c)Measured at 7 V.
Table 3. EL Performance of Representative FIr6-Based PhOLEDs
CEmax [cd A−1
]
PEmax [lm W−1
]
reference
this work
ref. [13]
structure of organic layer
TAPC/p-POSiTPA:FIr6/SiDPO
layer number
three
three
three
four
Von [V]
3.1a)
3.6a)
-
EQEmax [%]
22.2
14
CIE [x, y]
(0.15, 0.24)
(0.16, 0.26)
–
40.1
40.5
19
TAPC/Ad-CzPd:FIr6/TmPyPB
-
-
ref. [9b]
TAPC/UGH2:FIr6/BCP
7
5.5
∼3.2a)
-
ref. [10a]
ref. [10b]
ref. [11a]
ref. [11b]
ref. [12a]
ref. [12b]
TAPC/mCP:UGH3:FIr6/Tm3PyPB/Tm3PyPB:Cs
TAPC/TcTa:SPPO1:FIr6/Tm3PyPB/Tm3PyPB:Cs
NPB/mCP/BCPO:FIr6/TAZ
39.5
-
39.2
43.5
33.1
25.7
33
22.9
20.5
19.8
25.0
19
(0.163, 0.287)
–
four
four
3.0a)
4.3a)
3.2b)
3.0b)
36.8
42.5
-
(0.14, 0.25)
(0.14, 0.23)
(0.16, 0.28)
(0.16, 0.28)
NPB/mCP/BCPO:FIr6/tOXD-mTP
TAPC/Ad-Cz:FIr6/Ad-Pd:FIr6/TPBI
four
four
MeO-TPD:F4-TCNQ/TAPC/mCP:FIr6/
six
41
36
20
UGH2:FIr6/3TPYMB/3TPYMB:Cs
a)Defined as the drive voltage at the luminance of 1 cd m−2 b)Defined as the drive voltage at the luminance of 0.1 cd m−2
; .
To determine the origin of the different device perfor-
mance, we fabricated the hole-only devices with the structure
of ITO/MoO3 (10 nm)/TAPC (60 nm)/p-PySiTPA or p-POSiTPA
(70 nm)/MoO3 (10 nm)/Al, and two types of electron-only devices
with the configurations of type A: Al/LiF (1 nm)/p-PySiTPA
or p-POSiTPA (70 nm)/Tm3PyPB (5 nm)/TPBI (30 nm)/LiF
(1 nm)/Al, and type B: Al/LiF (1 nm)/p-PySiTPA or p-POSiTPA
(70 nm)/SiDPO (35 nm)/LiF (1 nm)/Al, corresponding to the
control and simplified devices, respectively. MoO3 and LiF layers
are employed to prevent electron- and hole-injection from the
cathode and anode, respectively. As shown in Figure 7, one can
evaluate the electron/hole transporting balance for a compound
by comparing the current densities under the same voltage
between hole- and electron-only devices. Obviously, p-POSiTPA
shows more balanced electron/hole transporting property over
p-PySiTPA in both the control and simplified devices. On the
other hand, the simplified devices employing SiDPO as ETL
reveal more matched electron/hole transporting abilities than
the control devices using Tm3PyPB/TPBI. The electron/hole
transporting balance correlates well with the device efficiencies.
We note that electron- and hole-only devices for p-POSiTPA with
SiDPO as ETL show almost the same current densities under
the same voltage, which could account for the best performance
achieved by device T2 for the FIr6-based blue PhOLEDs.
PhOLEDs (devices W1 and W2) with the configuration of ITO/
MoO3 (10 nm)/TAPC (60 nm)/p-PySiTPA or p-POSiTPA: FIr6
(6 wt%, 7 nm)/p-PySiTPA or p-POSiTPA: (fbi)2Ir(acac) (8 wt%,
Figure 7. Current density versus voltage characteristics of the hole-only
and electron-only devices. Hole-only devices: ITO/MoO3 (10 nm)/TAPC
(60 nm)/p-PySiTPA or p-POSiTPA (70 nm)/MoO3 (10 nm)/Al. Electron-
only devices: Al/LiF (1 nm)/p-PySiTPA or p-POSiTPA (70 nm)/Tm3PyPB
(5 nm)/TPBI (30 nm)/LiF (1 nm)/Al (type A), and Al/LiF (1 nm)/p-
PySiTPA or p-POSiTPA (70 nm)/SiDPO (35 nm)/LiF (1 nm)/Al (type B).
In view of the success in the high-efficiency simple-structure
blue PhOLEDs, we demonstrated two-color all-phosphor white
©
6
wileyonlinelibrary.com
2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201400149

www.afm-journal.de
www.MaterialsViews.com
Figure 8. (a) Current density-voltage-luminance characteristics for devices W1 and W2. (b) External quantum efficiency and power efficiency versus
luminance curves for devices W1 and W2. (c) The normalized EL spectra of device W1 at various voltages. (d) The normalized EL spectra of device
W2 at various voltages.
10 nm)/SiDPO (35 nm)/LiF (1 nm)/Al (100 nm) through using
bis(2-(9,9-diethyl-9H-fluoren-2-yl)-1-phenyl-1H-benzoimidazol-
N,C3)iridium acetylacetonate [(fbi)2Ir(acac)] as an orange phos-
phor.[25] Figure 8 shows the J-V-L characteristics, efficiency
versus luminance curves, and the normalized EL spectra at
various voltages for devices W1 and W2. Similar to the behavior
of the blue devices, both white devices have relatively low Von
of 2.7 V for W1, and 3.1 V for W2. The p-PySiTPA-based device
W1 shows a forward-viewing CEmax of 29.1 cd A−1 (Supporting
Information Figure S4), PEmax of 31.5 lm W−1 and EQEmax of
11.5%. Furthermore, the p-POSiTPA-based device W2 exhibits
better performance than p-PySiTPA-based device W1, with
the CEmax of 46.5 cd A−1, PEmax of 47.2 lm W−1 and EQEmax of
18.7%, which can be rationalized by the more balanced elec-
tron/hole transporting property of p-POSiTPA over p-PySiTPA.
It is noteworthy that without any light outcoupling enhance-
ment, the peak power efficiency of 47.2 lm W−1 for device W2
is close to the highest values of 51.9 lm W−1 reported by our
group[18b] and 52.7 lm W−1 reported by Kido et al.[26] for two-
color white PhOLEDs. In addition, devices W1 and W2 show
good color stability (Figure 8c and 8d). When the voltage
increases from 5 to 8 V, the Commission International de
I’Eclairage (CIE) coordinates slightly vary from (0.45, 0.41) to
(0.45, 0.42) for device W1, and from (0.42, 0.42) to (0.43, 0.43)
for device W2. Affected by the two-color system, the color-
rendering index (CRI) of the white devices is not high (58 for
device W1 and 60 for device W2).
3. Conclusion
The incorporation of appropriate charge transporting units
into the tetraarylsilane skeleton has allowed the realization
of a series of wide-bandgap functional materials with high
triplet energies, proper HOMO levels and good charge trans-
porting feature. Employing these functional materials results
in a simple-structure blue PhOLED that exhibits the highest
forward-viewing EQE (up to 22.2%) to date for three-organic-
layer FIr6-based blue PhOLEDs. This value is also among the
highest for FIr6-based blue PhOLEDs even compared with the
four or more than four organic-layer devices. Furthermore, with
the introduction of (fbi)2Ir(acac) as an orange emitter, an all-
phosphor warm-white PhOLED has been realized with a peak
power efficiency of 47.2 lm W−1, which is close to the highest
values ever reported for two-color white PhOLEDs. This work
reveals that judicious molecular design of functional materials
©
wileyonlinelibrary.com
Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201400149
2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
7

www.afm-journal.de
www.MaterialsViews.com
and then concentrated under reduced pressure to provide 2 as a white
solid (3.95 g), which was directly used in the next step without further
purification.
is a viable option to realize high-efficiency simple-structure
blue and all-phosphor warm-white PhOLEDs, and consequently
paves way towards the application of PhOLEDs for displays and
lighting sources.
Synthesis of {4-[(4-Bromophenyl)(diphenyl) silyl]phenyl}diphenylamine
(3) : A mixture of 2 (3.95 g), diphenylamine (1.32 g, 7.80 mmol), CuI
(76 mg, 0.40 mmol), and tBuOK (1.08 g, 9.60 mmol) in 1,4-dioxane
(30 mL) was degassed twice with argon followed by the addition of
( )-trans-1,2-diamino-cyclohexane (0.2 mL, 1.60 mmol). After being
refluxed for 18 h under argon, the reaction mixture was diluted with brine
(60 mL) and extracted with dichloromethane. The combined organic layer
was washed with brine and dried over anhydrous Na2SO4. After removal
of the solvent, the crude product was purified by column chromatography
on silica gel using dichloromethane/petroleum (1:5 by vol.) as the eluent
4. Experimental Section
General Information: 1H NMR and 13C NMR spectra were recorded
on a MECUYR-VX300 spectrometer. Elemental analyses of carbon,
hydrogen, and nitrogen were obtained on a Vario EL III microanalyzer.
GC-Mass spectra were collected on a Thermo Trace DSQ II GC/MS.
UV-vis absorption spectra were obtained on a Shimadzu UV-2500
spectrophotometer. Photoluminescence (PL) and phosphorescence
1
to afford a white powder. Yield: 54%. H NMR (300 MHz, CDCl3, 25 °C,
TMS, δ): 7.57 (d, J = 6.9 Hz, 4H), 7.50–7.40 (m, 8H), 7.37–7.35 (m,
spectra were measured on
a
Hitachi F-4500 fluorescence
4H), 7.29–7.24 (m, 4H), 7.13 (d, J = 7.5 Hz, 4H), 7.07–7.01 (m, 4H). 13
C
spectrophotometer. A previously reported integrating sphere method
was used to determine the PL quantum yields (PLQYs) of the doped films
in an absolute PLQY measurement system (Hamamatsus-C10027).[19,27]
The films (∼50 nm) with 10 wt% FIr6 doped into the host molecules
were thermally deposited onto precleaned quartz substrates under high
vacuum. The literature value for Ir(ppy)3 [fac-tris(2-phenylpyridinato)
iridium(III)] doped into CBP (N,N′-dicarbazolyl-4,4′-biphenyl) film
was utilized to verify against the accuracy of the system.[27] Differential
scanning calorimetry (DSC) was carried out on a NETZSCH DSC 200
PC unit under argon with a heating rate of 10 °C min−1 from 20 to
300 °C. The glass transition temperature (Tg) was obtained from the
second heating scan. Thermogravimetric analysis (TGA) was carried
out on a NETZSCH STA 449C instrument under nitrogen with a 10 °C
min−1 heating rate from 25 to 800 °C. Cyclic voltammetry (CV) was
performed with a CHI voltammetric analyzer at room temperature by
using the conventional three-electrode configuration which is composed
of a platinum working electrode, a platinum wire auxiliary electrode,
and an Ag wire pseudoreference electrode. Cyclic voltammograms
were recorded at a scan rate of 100 mV s−1 with tetrabutylammonium
hexafluorophosphate (TBAPF6) (0.1 M) in dichloromethane,
tetrahydrofuran or dimethylformamide as the supporting electrolyte,
and ferrocenium-ferrocene (Fc+/Fc) as the internal standard. The onset
potential was obtained from the intersection of two tangents drawn at
the rising and background current of the cyclic voltammogram.
NMR (75 MHz, CDCl3, 25 °C, δ): 149.20, 147.21, 137.89, 137.14, 136.26,
133.98, 133.67, 131.00, 129.67, 129.31, 127.91, 125.15, 124.59, 123.49,
121.47. MS (EI): m/z 581.0 [M+]. Anal. Calcd for C36H28BrNSi (%): C
74.22, H 4.84, N 2.40. Found: C 74.43, H 4.72, N 2.40.
Synthesis of {4-[Diphenyl(4-pyridin-3-ylphenyl)silyl]phenyl}diphenylamine
(p-PySiTPA): A mixture of 3 (2.04 g, 3.50 mmol), pyridin-3-ylboronic acid
(0.49 g, 4.00 mmol), Pd(PPh3)4 (80 mg, 0.07 mmol), and 2 M K2CO3
(7 mL, 14.0 mmol) in a mixed solvent of toluene (35 mL) and ethanol
(8 mL) was stirred at 100 °C for 48 h under argon. After cooling, the
solvent was evaporated under reduced pressure and extracted with
dichloromethane. The combined organic phase was washed with brine
and dried over anhydrous Na2SO4. After removal of the solvent, the
crude product was purified by column chromatography on silica gel
using ethyl acetate/dichloromethane (1:10 by vol.) as the eluent to
1
provide a white powder. Yield: 54%. H NMR (300 MHz, CDCl3, 25 °C,
TMS, δ): 8.87 (s, 1H), 8.60 (d, J = 3.6 Hz, 1H), 7.89 (d, J = 8.1 Hz, 1H),
7.71–7.68 (m, 2H), 7.61–7.60 (m, 6H), 7.45–7.35 (m, 9H), 7.29–7.24 (m,
4H), 7.14 (d, J = 7.2 Hz, 4H), 7.06–7.04 (m, 4H). 13C NMR (75 MHz,
CDCl3, 25 °C, δ): 149.18, 148.63, 148.34, 147.28, 138.72, 137.27, 137.13,
136.38, 134.75, 134.43, 134.31, 129.68, 129.36, 127.96, 126.51, 125.49,
125.17, 123.65, 123.49, 121.56. MS (EI): m/z 580.4 [M+]. Anal. Calcd for
C41H32N2Si (%): C 84.79, H 5.55, N 4.82. Found: C 85.19, H 5.45, N
4.76.
Synthesis of {4-[[4-(Diphenylphosphoryl)phenyl](diphenyl)silyl]phenyl}
diphenylamine (p-POSiTPA): n-Butyllithium (1.8 mL, 4.03 mmol, 2.26 M in
hexane) was added dropwise to a stirred solution of 3 (1.96 g, 3.36 mmol)
in anhydrous THF (50 mL) at −78 °C under argon atmosphere.
After stirring at −78 °C for a further 3 h, chlorodiphenylphosphine
(0.86 mL, 4.70 mmol) was added to give a clear, pale-yellow solution.
After stirring at −78 °C for 2 h, the mixture was gradually warmed to
room temperature under strirring and further reacted overnight. The
reaction mixture was quenched with water and then extracted with Et2O.
The combined organic phase was dried over anhydrous Na2SO4 and
concentrated under reduced pressure. The crude product was dissolved
in dichloromethane (20 mL) and then 30% aqueous hydrogen peroxide
(8 mL) was added. The mixture was stirred at room temperature for 8 h
and then extracted with dichloromethane. The combined organic phase
was washed with brine and dried over anhydrous Na2SO4. After removal
of the solvent, the residue was purified by column chromatography on
silica gel using methanol/dichloromethane (1:30 by vol.) as the eluent
to afford a white powder. Yield: 32%. 1H NMR (300 MHz, CDCl3, 25 °C,
TMS, δ): 7.71–7.62 (m, 8H), 7.56–5.54 (m, 6H), 7.48–7.34 (m, 12H),
7.29–7.24 (m, 4H), 7.13 (d, J = 8.1 Hz, 4H), 7.07–7.01 (m, 4H). 13C
NMR (75 MHz, CDCl3, 25 °C, δ): 149.24, 147.14, 137.16, 136.26, 136.11,
133.64, 132.94, 132.12, 131.98, 131.07, 130.96, 129.71, 129.29, 128.54,
128.37, 127.90, 125.15, 124.65, 123.49, 121.37. MS (EI): m/z 703.4 [M+].
Anal. Calcd for C48H38NOPSi (%): C 81.91, H 5.44, N 1.99. Found: C
81.66, H 5.32, N 1.87.
Device Fabrication and Measurement: The hole-injection material
MoO3, hole-transporting material TAPC, hole/exciton-blocking material
Tm3PyPB and electron-transporting material TPBI were commercially
available. Commercial ITO (indium tin oxide) coated glass with sheet
resistance of 10 Ω per square was used as the starting substrates. Before
device fabrication, the ITO glass substrates were precleaned carefully
and treated by oxygen plasma for 2 min. All layers were sequentially
deposited onto the ITO substrate by vacuum deposition in the vacuum
of 10−6 Torr. The various device structures were described in the text.
J-V-L characteristics of the devices were measured with a Keithley 2400
Source meter and a Keithley 2000 Source multimeter equipped with a
calibrated silicon photodiode. The EL spectra were measured by JY SPEX
CCD3000 spectrometer. The EQE values were calculated according to
previously reported methods.[28] All measurements were carried out at
room temperature under ambient conditions.
Materials: Bis(4-bromophenyl)(diphenyl)silane (1) was prepared
according to the literature.[29] Standard procedures are used to dry the
solvents. Unless otherwise stated, all reagents were used as received.
Synthesis of (4-Bromophenyl)(4-iodophenyl)diphenylsilane (2) : n-Butyl-
lithium (3.4 mL, 7.90 mmol, 2.33 M in hexane) was added dropwise to
a stirred solution of 1 (3.96 g, 8.00 mmol) in anhydrous THF (80 mL)
at −78 °C under argon atmosphere. After stirring at −78 °C for a further
1.5 h, a solution of I2 (2.54 g, 10.00 mmol) in anhydrous THF (20 mL)
was added to give a dark solution. After stirring at −78 °C for 2 h, the
mixture was gradually warmed to room temperature under strirring and
further reacted overnight. The reaction mixture was quenched with water
and then extracted with Et2O. The combined extracts were washed with
5% aqueous Na2S2O4 solution and brine, dried over anhydrous Na2SO4,
Synthesis of [(Diphenylsilanediyl)bis(4,1-phenylene)]bis(diphenylphos-
phine) dioxide (SiDPO): Prepared according to the same procedure as
p-POSiTPA but using bis(4-bromophenyl)(diphenyl)silane (1). Yield:
38%. 1H NMR (300 MHz, CDCl3, 25 °C, TMS, δ): 7.71–7.67 (m, 6H),
©
8
wileyonlinelibrary.com
2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201400149

www.afm-journal.de
www.MaterialsViews.com
7.65–7.63 (m, 10H), 7.57–7.53 (m, 8H), 7.50–7.43 (m, 10H), 7.41–7.36
(m, 4H). 13C NMR (75 MHz, CDCl3, 25 °C, δ): 138.23, 135.88, 135.74,
134.44, 133.07, 132.36, 131.69, 130.88, 130.77, 129.77, 128.22, 127.76.
MS (EI): m/z 736.5 [M+]. Anal. Calcd for C48H38O2P2Si (%): C 78.24, H
5.20. Found: C 78.06, H 4.93.
[10] a) J. Lee, J.-I. Lee, J.-W. Lee, H. Y. Chu, Org. Electron. 2010, 11, 1159;
b) J. Lee, J.-I. Lee, J. Y. Lee, H. Y. Chu, Appl. Phys. Lett. 2009, 95,
253304.
[11] a) H.-H. Chou, C.-H. Cheng, Adv. Mater. 2010, 22, 2468;
b) C.-A. Wu, H.-H. Chou, C.-H. Shih, F.-I. Wu, C.-H. Cheng,
H.-L. Huang, T.-C. Chao, M.-R. Tseng, J. Mater. Chem. 2012, 22,
17792.
[12] a) H. Fukagawa, N. Yokoyama, S. Irisa, S. Tokito, Adv. Mater.
2010, 22, 4775; b) S.-H. Eom, Y. Zheng, E. Wrzesniewski, J. Lee,
N. Chopra, F. So, J. Xue, Org. Electron. 2009, 10, 686.
[13] H. Fukagawa, S. Irisa, H. Hanashima, T. Shimizu, S. Tokito,
N. Yokoyama, H. Fujikake, Org. Electron. 2011, 12, 1638.
[14] X. Ren, J. Li, R. J. Holmes, P. I. Djurovich, S. R. Forrest,
M. E. Thompson, Chem. Mater. 2004, 16, 4743.
[15] A. Chaskar, H.-F. Chen, K.-T. Wong, Adv. Mater. 2011, 23, 3876.
[16] K. Goushi, R. Kwong, J. J. Brown, H. Sasabe, C. Adachi, J. Appl.
Phys. 2004, 95, 7798.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
The authors are grateful to the National Basic Research Program
of China (973 Program 2013CB834805), the National Science Fund
for Distinguished Young Scholars of China (51125013) and the
Research Fund for the Doctoral Program of Higher Education of China
(20120141110029) for financial support.
[17] D. Tanaka, T. Takeda, T. Chiba, S. Watanabe, J. Kido, Chem. Lett.
2007, 36, 262.
[18] a) S. Gong, Y. Chen, C. Yang, C. Zhong, J. Qin, D. Ma, Adv. Mater.
2010, 22, 5370; b) S. Gong, Y. Chen, J. Luo, C. Yang, C. Zhong,
J. Qin, D. Ma, Adv. Funct. Mater. 2011, 21, 1168; c) S. Gong,
Y. Chen, X. Zhang, P. Cai, C. Zhong, D. Ma, J. Qin, C. Yang, J. Mater.
Chem. 2011, 21, 11197.
Received: January 16, 2014
Revised: March 24, 2014
Published online:
[19] A. Endo, K. Suzuki, T. Yoshihara, S. Tobita, M. Yahiro, C. Adachi,
Chem. Phys. Lett. 2008, 460, 155.
[1] B. W. D’Andrade, S. R. Forrest, Adv. Mater. 2004, 16, 1585.
[2] T.-H. Han, Y. Lee, M.-R. Choi, S.-H. Woo, S.-H. Bae, B. H. Hong,
J.-H. Ahn, T.-W. Lee, Nat. Photonics 2012, 6, 105.
[3] Z. B. Wang, M. G. Helander, J. Qiu, D. P. Puzzo, M. T. Greiner,
Z. M. Hudson, S. Wang, Z. W. Liu, Z. H. Lu, Nat. Photonics 2011,
5, 753.
[20] P.-I. Shih, C.-H. Chien, F.-I. Wu, C.-F. Shu, Adv. Funct. Mater. 2007,
17, 3514.
[21] J. Kalinowski, M. Cocchi, D. Virgili, V. Fattori, J. A. G. Williams, Adv.
Mater. 2007, 19, 4000.
[22] S.-J. Su, Y. Takahashi, T. Chiba, T. Takeda, J. Kido, Adv. Funct. Mater.
2009, 19, 1260.
[4] M. A. Baldo, D. F. O’Brien, Y. You, A. Shoustikov, S. Sibley,
M. E. Thompson, S. R. Forrest, Nature 1998, 395, 151.
[5] a) L. Xiao, Z. Chen, B. Qu, J. Luo, S. Kong, Q. Gong, J. Kido,
Adv. Mater. 2011, 23, 926; b) S. Gong, Q. Fu, Q. Wang, C. Yang,
C. Zhong, J. Qin, D. Ma, Adv. Mater. 2011, 23, 4956.
[6] a) Y. Tao, C. Yang, J. Qin, Chem. Soc. Rev. 2011, 40, 2943; b) Y. Tao,
Q. Wang, C. Yang, Q. Wang, Z. Zhang, T. Zou, J. Qin, D. Ma, Angew.
Chem., Int. Ed. 2008, 47, 8104; c) S. Gong, X. He, Y. Chen, Z. Jiang,
C. Zhong, D. Ma, J. Qin, C. Yang, J. Mater. Chem. 2012, 22, 2894.
[7] a) S.-J. Su, E. Gonmori, H. Sasabe, J. Kido, Adv. Mater. 2008, 20,
4189; b) S. Ye, Y. Liu, J. Chen, K. Lu, W. Wu, C. Du, T. Wu, Z. Shuai,
G . Y u , Adv. Mater. 2010, 22, 4167.
[23] S.-y. Takizawa, V. A. Montes, P. Anzenbacher, , Jr., Chem. Mater.
2009, 21, 2452.
[24] a) V. Sivasubramaniam, F. Brodkorb, S. Hanning, H. P. Loebl,
V. van Elsbergen, H. Boerner, U. Scherf, M. Kreyenschmidt, J. Fluo-
rine Chem. 2009, 130, 640; b) S. Schmidbauer, A. Hohenleutner,
B. König, Adv. Mater. 2013, 25, 2114.
[25] W.-S. Huang, J. T. Lin, C.-H. Chien, Y.-T. Tao, S.-S. Sun, Y.-S. Wen,
Chem. Mater. 2004, 16, 2480.
[26] H. Sasabe, J.-i. Takamatsu, T. Motoyama, S. Watanabe,
G. Wagenblast, N. Langer, O. Molt, E. Fuchs, C. Lennartz, J. Kido,
Adv. Mater. 2010, 22, 5003.
[27] Y. Kawamura, K. Goushi, J. Brooks, J. J. Brown, H. Sasabe,
C. Adachi, Appl. Phys. Lett. 2005, 86, 071104.
[8] K. S. Yook, J. Y. Lee, Adv. Mater. 2012, 24, 3169.
[9] a) R. J. Holmes, B. W. D’Andrade, S. R. Forrest, X. Ren, J. Li,
M. E. Thompson, Appl. Phys. Lett. 2003, 83, 3818; b) Y. Zheng,
S.-H. Eom, N. Chopra, J. Lee, F. So, J. Xue, Appl. Phys. Lett. 2008,
92, 223301.
[28] S. R. Forrest, D. D. C. Bradley, M. E. Thompson, Adv. Mater. 2003,
15, 1043.
[29] L.-H. Chan, R.-H. Lee, C.-F. Hsieh, H.-C. Yeh, C.-T. Chen, J. Am.
Chem. Soc. 2002, 124, 6469.
©
wileyonlinelibrary.com
Adv. Funct. Mater. 2014,
DOI: 10.1002/adfm.201400149
2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
9