CommuniCation
1805409 (1 of 9)
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2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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Organic–Inorganic Hybrid Passivation Enables Perovskite
QLEDs with an EQE of 16.48%
Jizhong Song,* Tao Fang, Jianhai Li, Leimeng Xu, Fengjuan Zhang, Boning Han,
Qingsong Shan, and Haibo Zeng*
Prof. J. Song, Dr. T. Fang, Dr. J. Li, Dr. L. Xu, 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.201805409.
DOI: 10.1002/adma.201805409
Highly efficient perovskite QLEDs can
be realized when QD films possess two
crucial synergistic parameters: highly
luminescent features and effective electric
transport properties. Regarding the emis-
sive properties of QD films, although long
organic ligands perfectly passivated the
QD’s surface and endowed ink with the
near-unity luminescent properties with a
PLQY approaching 100%,
[11,12]
the films
generally exhibited a relatively low PLQY
of about 40% due to the formation of
nonradiative recombination centers. This
phenomenon results from the dynamic
characteristic of the bonding between the
QD’s surface and organic capping ligands,
leading to the mismatched ligands during
the film-forming process.
[13,14]
Meanwhile,
these ligands act as electrically insulating
layers on the QD’s surface resulting in
inefficient carrier injection and transporta-
tion,
[15,16]
which are detrimental to device
performance. To enhance the electric properties of QD films,
much attention
[17,18]
has been devoted to the development of
ligand strategies that minimize the interparticle spacing. For
example, Li et al. demonstrated an effective enhancement in
electrical properties and EQE of CsPbBr
3
QLEDs through the
control of surface ligand density.
[9]
Through ligand-exchange
strategies,
[8,19]
a relatively short (C12) ligand, didodecyl dime-
thyl ammonium bromide (DDAB), was used to enhance device
performance, obtaining an EQE of 8.73% under an effective
washing process. Unfortunately, these methods are still based
on long organic ligands, which cannot render the QD solid
with ideal carrier injection and transportation features. Thus, it
is significantly crucial to find an effective and feasible strategy
to control the surface state of perovskite QDs, which could
guarantee the high exciton recombination and carrier injec-
tion in constructing high-performance electroluminescent (EL)
devices.
Inorganic ligands with less space separation among particles
could effectively enhance the electrical properties of QD
films.
[20,21]
Meanwhile, they also improved the PL features
through the reduce of the defect-related nonradiative recom-
bination, which has been proven in traditional QDs.
[22–25]
For
example, the halide-related ligands have improved the lumi-
nescent feature and radiative recombination in Cd-based QDs,
which was realized by the ligand-exchange process.
[20,26,27]
But
such a strategy is not feasible for perovskite QDs because they
Perovskite quantum dots (QDs) with high photoluminescence quantum yields
(PLQYs) and narrow emission peak hold promise for next-generation flexible and
high-definition displays. However, perovskite QD films often suffer from low
PLQYs due to the dynamic characteristics between the QD’s surface and organic
ligands and inefficient electrical transportation resulting from long hydrocarbon
organic ligands as highly insulating barrier, which impair the ensuing device
performance. Here, a general organic–inorganic hybrid ligand (OIHL) strategy
is reported on to passivate perovskite QDs for highly efficient electrolumines-
cent devices. Films based on QDs through OIHLs exhibit enhanced radiative
recombination and effective electrical transportation properties compared to
the primal QDs. After the OIHL passivation, QD-based light-emitting diodes
(QLEDs) exhibit a maximum peak external quantum efficiency (EQE) of 16.48%,
which is the most efficient electroluminescent device in the field of perovskite-
based LEDs up to date. The proposed OIHL passivation strategy positions
perovskite QDs as an extremely promising prospect in future applications of
high-definition displays, high-quality lightings, as well as solar cells.
Perovskite QLEDs
Perovskite quantum dots (QDs) possess unique size, compo-
sition, and shape tunable optical and electrical properties and
are considered building blocks for various low-cost, solution-
processable electronic and optoelectronic devices,
[1–5]
including
solar cells, light-emitting diodes (LEDs), and photodetectors.
High photoluminescence quantum yields (PLQYs) of up to
95% and narrow light-emitting peak with full width at half
maximum (FWHM) of about 20 nm make them a particularly
attractive option for next-generation flexible and high-definition
displays.
[6,7]
Perovskite-QD-based light-emitting diodes (QLEDs)
have presently demonstrated an external quantum efficiency
(EQE) of up to 9%.
[8,9]
Yet in contrast to perovskite film–based
LEDs with an EQE of 14.35%,
[10]
QLED performance remains
comparatively poor.
Adv. Mater. 2018, 30, 1805409