CommuniCation
1800764 (1 of 7)
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2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Room-Temperature Triple-Ligand Surface Engineering
Synergistically Boosts Ink Stability, Recombination Dynamics,
and Charge Injection toward EQE-11.6% Perovskite QLEDs
Jizhong Song,* Jinhang Li, Leimeng Xu, Jianhai Li, Fengjuan Zhang, Boning Han,
Qingsong Shan, and Haibo Zeng*
Prof. J. Song, Dr. J. Li, Dr. L. Xu, Dr. J. Li, Dr. F. Zhang, Dr. B. Han,
Dr. Q. Shan, Prof. H. Zeng
MIIT Key Laboratory of Advanced Display Materials and Devices
Institute of Optoelectronics & Nanomaterials
School of Materials Science and Engineering
Nanjing University of Science and Technology
Nanjing 210094, China
E-mail: songjizhong@njust.edu.cn; zeng.haibo@njust.edu.cn
The ORCID identification number(s) for the author(s) of this article
can be found under https://doi.org/10.1002/adma.201800764.
DOI: 10.1002/adma.201800764
blue,
[7]
green,
[8]
and red
[9]
colored devices,
respectively, and have already managed to
meet practical application requirements.
However, the synthesis of Cd-based QDs
involves a highly complex core–shell
growth process, high synthesis tempera-
ture (≈300 °C), and long reaction time.
[10]
These harsh conditions limit their com-
mercial production. Similarly, the cur-
rently reported other QDs
[11,12]
(e.g., InP)
are also faced with the complex core–shell
synthesis. In addition, they exhibited low
peak EQE (≈3.46%) and poor color purity
due to large full width at half maximum
(FWHM). Therefore, the industrialization
of QLED displays is heavily limited by QD
materials.
Halide perovskites, which have enjoyed
significant success in the applications
of solar cells,
[13–15]
light-emitting diodes
(LEDs),
[16–21]
and photodetectors,
[22–25]
show great potential as a new generation
of emitter materials. In addition to their
composition-dependent optoelectronic
properties, these materials in the QD form
have high photoluminescence quantum
yields (PLQYs) of up to 95% and narrow
light-emitting peaks with an FWHM of about 20 nm, making
them particularly attractive for high-quality lightings and dis-
plays.
[26]
Among recently reported perovskite QDs synthesized
by wet-chemistry colloidal methods, inorganic perovskite
cesium lead halides (CsPbX
3
, X = Cl, Br, and I) are favorable for
practical applications given high thermal stability and low mois-
ture sensitivity
[27–29]
compared with organic–inorganic hybrid
counterparts. CsPbX
3
QDs exhibiting tunable and highly effi-
cient PL were first synthesized by Kovalenko and co-workers
[30]
in 2015. These multicolored LEDs were first reported from
Song et al.,
[31]
and the CsPbBr
3
green LEDs exhibited an EQE
of 0.12% and a brightness of 946 cd m
−2
. Presently, LEDs based
on CsPbX
3
QDs demonstrate EQEs of up to 8.73% and a peak
luminance of up to >15 000 cd m
−2
.
[2,32,33]
QD materials used
in these devices are synthesized through the hot-injection (HI)
method under the inert gas, which conflicts with low-cost con-
sumption.
[34]
Thus, a synthetic process, carried out at room
temperature (RT) without inert gas, was proposed to prepare
Developing low-cost and high-quality quantum dots (QDs) or nanocrystals
(NCs) and their corresponding efficient light-emitting diodes (LEDs) is crucial
for the next-generation ultra-high-definition flexible displays. Here, there is
a report on a room-temperature triple-ligand surface engineering strategy
to play the synergistic role of short ligands of tetraoctylammonium bromide
(TOAB), didodecyldimethylammonium bromide (DDAB), and octanoic acid
(OTAc) toward “ideal” perovskite QDs with a high photoluminescence
quantum yield (PLQY) of >90%, unity radiative decay in its intrinsic channel,
stable ink characteristics, and effective charge injection and transportation
in QD films, resulting in the highly efficient QD-based LEDs (QLEDs).
Furthermore, the QD films with less nonradiative recombination centers
exhibit improved PL properties with a PLQY of 61% through dopant
engineering in A-site. The robustness of such properties is demonstrated by
the fabrication of green electroluminescent LEDs based on CsPbBr
3
QDs with
the peak external quantum efficiency (EQE) of 11.6%, and the corresponding
peak internal quantum efficiency (IQE) and power efficiency are 52.2% and
44.65 lm W
−1
, respectively, which are the most-efficient perovskite QLEDs
with colloidal CsPbBr
3
QDs as emitters up to now. These results demonstrate
that the as-obtained QD inks have a wide range application in future high-
definition QD displays and high-quality lightings.
Perovskite QLEDs
Quantum-dot-based light-emitting diodes (QLEDs) with narrow
and finely tunable emission spectra, which show high purity
and real color, have been considered a promising candidate
for next-generation flexible and high-definition displays.
[1–5]
Among semiconductor colloidal quantum dots (QDs), Cd-based
LEDs first developed in 1994
[6]
provide a maximum external
quantum efficiency (EQE) of 19.8%, 15.45%, and 20.5% for
Adv. Mater. 2018, 30, 1800764