Tuning the energy levels and photophysical properties of triphenylamine-
featured iridium(
III) complexes: application in high performance polymer
light-emitting diodes
Minrong Zhu,
a
Yanhu Li,
b
Chen’ge Li,
a
Cheng Zhong,
a
Chuluo Yang,
*
a
Hongbin Wu,
*
b
Jingui Qin
a
and Yong Cao
b
Received 15th February 2012, Accepted 28th March 2012
DOI: 10.1039/c2jm30928a
A new triphenylamine-based homoleptic iridium(
III) complex is designed and synthesized by simply
altering the ligation positions of the triphenylamine units. The theoretical calculations reveal that the
difference in the ligation position has a significant influence on the optical and electronic properties of
the complexes. Through dispersing the green phosphor G-Ir into PVK in the presence of an electron-
transport material, 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD), the green phosphorescent
device achieves maximum current/power/external quantum efficiencies of 43.8 cd A
1
/20.5 lm
W
1
/15.1%. The new green phosphor and its counterparts O-Ir and R-Ir have been demonstrated as
active components for white polymer light-emitting diodes (WPLEDs). A single-layer white light-
emitting device is fabricated by doping the sky-blue emitter iridium(
III) bis(2-(4,6-difluorophenyl)-
pyridinato-N,C
2
)picolinate (FIrpic), G-Ir, O-Ir and R-Ir into a general polymer matrix, with the
maximum current/power/external quantum efficiencies of 23.5 cd A
1
/12.0 lm W
1
/8.6%, which are
comparable with the best results obtained from the conventional RGB primary color system under
the same device structure.
Introduction
White organic light-emitting devices (WOLEDs) have attracted
great attention due to their revolutionizing applications in next
generation flat-panel displays and solid-state illumination sour-
ces.
1–4
Among the approaches towards realizing WOLEDs, white
polymer light-emitting devices (WPLEDs) offer particular
advantages such as screen printing and ink-jet deposition, large
area coverage and low power consumption.
5
Of critical interest
are phosphorescent emitters of heavy metal complexes which can
harvest both singlet and triplet exciton emissions and elevate the
internal quantum efficiency of the devices up to 100% theoreti-
cally.
6–8
Generally, the mixtures of three primary (red, green and
blue, RGB) or complementary colors (blue and orange) are
required to generate white emission.
9
Hence, developing highly
efficient phosphors covering the entire visible light spectrum is
very crucial for the marketing of WOLEDs as solid-state lighting
sources.
Among the phosphorescent dyes, cyclometallated iridium
complexes with high quantum yields and short excited-state
lifetimes have been extensively studied.
10
The main issues for high
efficiency in phosphorescent devices are charge balance and the
triplet–triplet annihilation in the emission layer. Several groups
have been interested in the integration of functional units pos-
sessing charge injection and transporting characters into organic
ligands to generate multifunctional Ir(
III) complexes.
11–18
Recently, we have reported multifunctional Ir(III) phosphors
with cyclometalated ligands bearing a carbazole framework. In
addition to the hole-injection/transporting properties endowed
by the carbazole units, remarkable color tuning could be realized
by linkage isomers in which iridium ligates with carbon at the
2- or 3-position of the carbazole unit.
17
Like carbazole, triphenylamine units possess good hole-
transporting ability and sufficiently high triplet energy (ca.
2.9 eV). In contrast, most triphenylamine compounds have
a higher HOMO level (ca. 5.2 eV) than carbazole derivatives, and
thus allow efficient hole injection. Therefore, we have developed
a series of triphenylamine-based Ir(
III) complexes. High perfor-
mance orange single-layer PLEDs are acquired through
dispersing the fac-tris[2,4-bis(4-(N,N-diphenylamino)phenyl)
pyridine]iridium(
III)(O-Ir) into a poly(N-vinylcarbazole)
(PVK) host in the presence of an electron-transport material,
2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD), with
maximum current/power/external quantum efficiencies of 47.4 cd
a
Department of Chemistry, Hubei Key Lab on Organic and Polymeric
Optoelectronic Materials, Wuhan University, Wuhan 430072, People’s
Republic of China. E-mail: clyang@whu.edu.cn
b
Institute of Polymer Optoelectronic Materials and Devices, State Key
Laboratory of Luminescent Materials and Devices, South China
University of Technology, Guangzhou 510640, People’s Republic of
China. E-mail: hbwu@scut.edu.cn
11128 | J. Mater. Chem., 2012, 22, 11128–11133 This journal is ª The Royal Society of Chemistry 2012
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