Nanoscale
PAPER
Cite this: Nanoscale, 2015, 7, 2951
Received 8th November 2014,
Accepted 4th January 2015
DOI: 10.1039/c4nr06593j
www.rsc.o rg/nanoscale
Bright, efficient, and color-stable violet
ZnSe-based quantum dot light-emitting diodes†
Aqiang Wang,
a
Huaibin Shen,*
a,b
Shuaipu Zang,
a
Qingli Lin,
a
Hongzhe Wang,
a,b
Lei Qian,
a
Jinzhong Niu
a
and Lin Song Li*
a,b
In this paper, highly stable violet-blue emitting ZnSe/ZnS core/shell QDs have been synthesized by a
novel “low temperature injection and high temperature growth” method. The resulting nearly monodis-
perse ZnSe/ZnS core/shell QDs exhibit excellent characteristics such as a high color saturation (typical
spectral full width at half-maximum between 12 and 20 nm), good emission tunability in the violet-blue
range of wavelengths from 400 to 455 nm, a high absolute PL quantum yield (up to 83%), and superior
chemical and photochemical stability. By employing ZnSe/ZnS core/shell quantum dots (QDs) as emitters
with a fully solution processable method, bright, efficient, and color-stable violet Cd-free quantum dot-
based light-emitting diodes (QD-LEDs) with maximum luminance up to 2632 cd m
−2
and a peak EQE of
7.83% have been demonstrated successfully. Considering the factors of the photopic luminosity function,
the brightness and efficiency results of such violet QD-LEDs not only represent a 12-fold increase in
device efficiency and an extraordinary 100 times increase in luminance compared with previous Cd-free
QD-LEDs but also can be much superior to the best performance (1.7%) of their Cd-based violet counter-
parts. These results demonstrate significant progress in short-wavelength QD-LEDs and shed light on
the acceleration of commercial application of environmentally-friendly violet QD-based displays and
lighting.
Introduction
Colloidal semiconductor quantum dots (QDs) have attracted
much attention due to their unique size-dependent optical
properties which can achieve excellent spectral purity at high
optical flux. Their excellent optical properties make them
potential superstars in light-emitting diodes (LEDs) and
displays.
1–7
To fully exploit the potential of QDs in these appli-
cations, researchers need to synthesize materials that
simultaneously meet the following five criteria: narrow and
symmetric emission spectra, high photoluminescence (PL)
quantum yields (QYs), high optical stability, eco-friendly
materials, and low-cost methods for mass production. Most of
the previous studies on highly emissive and color-tunable QDs
have mainly concentrated on materials containing toxic
cadmium, mercury, or lead.
8–16
For example, red light emitters
of CdSe/CdS QDs with QYs up to 90%,
14
green region emitters
of CdSe/ZnS/CdSZnS QDs with the best QYs of 100% and
improved photo- and chemical-stabilities,
15
and the QYs of
Zn
x
Cd
1−x
S/ZnS QDs also reached almost unity even in the
violet-blue region.
16
However, there are increasing concerns that
these toxic materials such as cadmium, lead, and mercury
would pose serious threats to human health and the environ-
ment, and the European Union’s Restriction of Hazardous
Substances (RoHS) rules ban any consumer electronics con-
taining more than trace amounts of these materials.
17
The
likelihood of commercial success for quantum dot-based light-
emitting diodes (QD-LEDs) and displays will therefore be
greatly improved if the devices can be fabricated using
eco-friendly and heavy-metal-free QDs.
Most of the syntheses of non-toxic or low toxicity QDs are
now focused on I–III–VI semiconductors (such as CuInS
2
),
18–22
III–V semiconductors (such as InP),
23–26
and II–VI semi-
conductors (such as ZnSe and rela ted Cu-, Mn-doped ZnSe),
27–31
which have low-toxicity, tunable emissions in the visible-to-
near-infrared region. The current QYs for the CuInS
2
core/shell
QDs is up to 60%, but the emission tunability is mainly con-
fined between 540 and 650 nm.
20,21
The obtained III–V heavy-
metal-free QDs typically possess emissions from 480 to
600 nm with the highest QYs up to 70%.
24,25
Most recently, the
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c4nr06593j
a
Key Laboratory for Special Functional Materials of Ministry of Education,
Henan University, Kaifeng 475004, China. E-mail: shenhuaibin@henu.edu.cn,
lsli@henu.edu.cn
b
Collaborative Innovation Center of Nano Functional Materials and Applications,
Henan Province, P. R. China
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