High-quality CsPbBr3 perovskite nanocrystals for quantum dot light-emitting diodes

Article abstract of DOI:10.1039/c6ra27665b

Metal halide perovskites, such as CsPbX₃ (X = Cl, Br, and I), have gained extensive attention due to their increasing demand in optoelectronic applications such as solar cells and lighting-emitting devices. Herein, we report a versatile approach to synthesize high-quality CsPbBr₃ perovskite nanocrystals (sized 5-15 nm) by ligand-assisted reprecipitation at room temperature. The monodispersed CsPbBr₃ nanocube perovskites displayed relatively high photoluminescence quantum yields of 50-80%. By virtue of the quantum size effects, the bandgap energies were manipulated from blue to green spectral regions (410-530 nm). In addition, through compositional modulations of the anion exchange technique, the bright photoluminescence could be almost tuned over the entire visible spectral region (450-650 nm). Furthermore, the photoluminescence of the CsPbBr₃ nanocrystals was characterized by narrow emission line widths of 15-50 nm and radiative lifetimes of 5-15 ns. Finally, by taking advantage of these outstanding merits, the CsPbBr₃ perovskites were successfully utilized in the application of highly fluorescent patterning and color-purity light-emitting diodes.

Full text of DOI:10.1039/c6ra27665b

RSC Advances
View Article Online
View Journal | View Issue
PAPER
High-quality CsPbBr perovskite nanocrystals for
3
quantum dot light-emitting diodes†
Cite this: RSC Adv., 2017, 7, 10391
a
a
a
a
a
a
Xiafang Du,‡ Guan Wu,‡ Jian Cheng, Hui Dang, Kangzhe Ma, Ya-Wen Zhang,
a
ab
Peng-Feng Tan and Su Chen*
Metal halide perovskites, such as CsPbX
3
(X ¼ Cl, Br, and I), have gained extensive attention due to their
increasing demand in optoelectronic applications such as solar cells and lighting-emitting devices.
3
Herein, we report a versatile approach to synthesize high-quality CsPbBr perovskite nanocrystals (sized
5–15 nm) by ligand-assisted reprecipitation at room temperature. The monodispersed CsPbBr
3
nanocube perovskites displayed relatively high photoluminescence quantum yields of 50–80%. By virtue
of the quantum size effects, the bandgap energies were manipulated from blue to green spectral regions
(
410–530 nm). In addition, through compositional modulations of the anion exchange technique, the
bright photoluminescence could be almost tuned over the entire visible spectral region (450–650 nm).
Furthermore, the photoluminescence of the CsPbBr nanocrystals was characterized by narrow emission
line widths of 15–50 nm and radiative lifetimes of 5–15 ns. Finally, by taking advantage of these
outstanding merits, the CsPbBr perovskites were successfully utilized in the application of highly
fluorescent patterning and color-purity light-emitting diodes.
Received 2nd December 2016
Accepted 26th December 2016
3
DOI: 10.1039/c6ra27665b
3
rsc.li/rsc-advances
severely discourage their further development and potential
application.
3
Recently, all-inorganic halide perovskites (such as CsPbX ,
Introduction
Halide perovskites have attracted signicant interests in
a variety of optoelectronic applications, including solar cells,
light-emitting diodes (LEDs), photodetectors, and lasers,
1
,2
X ¼ Cl, Br, and I), which can present relatively higher PLQYs
3,4
5,6
7,8
17,18
compared with organic–inorganic hybrid perovskites,
are
9
10
due to their high photoluminescence, excellent stability, and emerging in perovskites family. In this respect, Protesescu et al.
11
low-threshold lasing. Halide perovskites mainly contain two reported a facile colloidal synthesis of monodispersed CsPbX
categories: organic–inorganic hybrid perovskites (APbX
, where nanocubes at high temperature, which displayed a high PLQY
3
3
A stands for the small molecular organic amine, such as of upto 90%, as well as a bright emission with a wide color
+
CH
3
NH
3
3
, and X represents a halide, such as Br, I, and Cl) and gamut. The PL emission spectra of CsPbX perovskites could be
19
all-inorganic halide perovskites (CsPbX ). For the organic– tuned over the entire visible spectral region (410–700 nm). In
inorganic hybrid perovskites,
aration process can be utilized to yield high-quality perovskite dots (QDs) through a hot injection method and rst developed
3
12–14
3
the facile and low-cost prep- addition, Song et al. synthesized high-quality CsPbX quantum
20
nanocrystals (NCs). Wong et al. reported a versatile strategy to the quantum dots-based QLEDs with sharp emissions. To
prepare color-tunable CH NH PbBX
perovskite nanorod arrays further achieve the high-quality CsPbX perovskites at low
temperature, Li et al. developed a supersaturated recrystalliza-
tion method for the synthesis of CsPbX perovskites in the
3
3
3
3
15
through an anion exchange technique at low temperature.
Zhang et al. fabricated brightly luminescent colloidal CH
3
-
3
NH
quantum yield (QY) of upto 70% at room temperature via white LEDs with tunable color temperature, and a wide color
3 3
PbX
NCs with an absolute photoluminescence (PL) application of white LEDs. Excellent PL with high QY upto 95%,
16
21
a ligand-assisted reprecipitation (LARP) strategy. However, the gamut were obtained. It is because of the high PLQY that
relatively low PLQYs of organic–inorganic hybrid perovskites CsPbX perovskites are widely used in optoelectronic
3
applications.
Herein, we report a high-quality colloidal CsPbBr3 perov-
skites NCs (sized 5–15 nm) synthesized at room temperature
using a new precursor: cesium bromide (CsBr). The mono-
a
State Key Laboratory of Materials-Oriented Chemical Engineering, College of
Chemistry and Chemical Engineering, Nanjing Tech University (former: Nanjing
University of Technology), Nanjing 210009, P. R. China. E-mail: chensu@njtech.edu.
cn; Fax: +86-25-83172258; Tel: +86-25-83172258
dispersed CsPbBr
3
nanocube perovskites exhibited relatively
b
Jiangsu Key Lab of Fine Chemical & Functional Polymer Materials, P. R. China
high PLQY (50–80%) and size-tunability of their bandgap
†
1
‡
Electronic supplementary information (ESI) available. See DOI: energies that were manipulated from the blue to green spectral
0.1039/c6ra27665b
3
regions (410–530 nm). The PL of CsPbBr NCs also possessed
Contributed equally to this work.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 10391–10396 | 10391

View Article Online
RSC Advances
Paper
narrow emission line widths of 15–50 nm and radiative life- Device fabrication
times of 5–15 ns. In addition, via utilizing the anion exchange
Solutions of ZnO nanocrystals were spin-coated on the ITO-
coated glass substrates at 4000 rpm for 50 s and annealed in
air at 200 C. Perovskite solutions were spin-coated on the ZnO
reaction technique, the bright PL could nearly be tuned over the
entire visible spectral region (450–650 nm). Moreover, when
ꢀ
+
+
considering cation exchange (MA and Cs ), the hybrid perov-
skites exhibited a high QY and narrow emission. Finally, we
successfully designed highly luminescent patterning and color-

lms to prepare a perovskite lm (in the range of 125–150 nm).
Then, a 25 nm thin layer of TFB was spin-coated using a m-
ꢁ1
xylene solution (10 mg mL ) at 2500 rpm. Finally, the MoO
x
/Au
3
purity LEDs using CsPbBr perovskite NCs, where the LED
maintained the low turn-on voltages and narrow full-width at
half maxima (FWHM) emission.
electrodes were deposited using a thermal evaporation system.
Characterization
Ultraviolet-visible (UV-vis) absorption spectra were obtained
using a Perkin-Elmer Lambda 950 spectrometer. Photo-
luminescence (PL) measurements were carried out using a Var-
Experimental
Materials
2 3 2
Lead(II) bromide (PbBr , 99%), methylamine (CH NH
, 33 wt% ian Cary Eclipse spectrophotometer. The photoluminescence
in absolute ethanol), n-octylamine (99%), dodecylamine (98%), quantum yield (PLQY) was estimated according to a standard
oleylamine (90%), hydrochloric acid (HCl, 37 wt%), hydro- procedure using appropriate dye molecules for the blue, green,
bromic acid (HBr, 48 wt%), hydriodic acid (HI, 57 wt%), and and red spectral regions (coumarin 343, uorescein, and
oleic acid (90%) were purchased from Aladdin Chemistry Co., rhodamine 6G). X-ray diffraction (XRD) was performed via
Ltd. N,N-Dimethylformamide (DMF), cesium bromide (CsBr), a Rigaku Corporation D/max-rC rotating anode X-ray powder
toluene, cyclohexane, dichloromethane, and chloroform were diffractometer using a copper target. Transmission electron
purchased from Sinopharm Chemical Reagent Co., Ltd microscopy (TEM) images were obtained using a Tecnai G2 F30
(
Shanghai, China). All reagents were used without further S-TWIN transmission electron microscope. X-ray photoelectron
purication.
(XPS) spectra were acquired using an ES-CAIAB250 XPS system
with an Al/Ka source, and the energy step size was set at
0.100 eV. Energy dispersive X-ray (EDX) analysis was performed
using two scanning electron microscopes (Zeiss Gemini 1530
and Hitachi, S-4800). TCSPC data were performed using an
Edinburgh FL 900 photo counting system. LED devices were
measured using a Keithley 2400 source meter and a ber inte-
gration sphere (FOIS-1) coupled with a QE-6500 spectrometer
was used for room temperature measurements under ambient
conditions.
3
Fabrication of the colloidal perovskite CsPbBr NCs
Colloidal perovskite CsPbBr
technique, which has been described as follows. In a typical
synthesis, a mixture of 0.1 mmol CsBr and 0.2 mmol PbBr was
dissolved in 5 mL of DMF via ultrasonication, and then 20 mL of
n-octylamine and 0.5 mL of oleic acid were added to form
a precursor solution. A 250 mL of precursor solution was added
to 10 mL of toluene under vigorous stirring. A bright green
solution could be immediately observed. Aer centrifugation at
3
NCs were fabricated by the LARP
2
1
2 000 rpm for 10 min to discard the precipitates, a bright blue- Results and discussion
3
green colloidal solution was obtained. Other CsPbBr NCs were
fabricated using different solvents, precursors, and ligands
based on a similar LARP strategy.
3
The colloidal CsPbBr NCs were synthesized via a simple and
versatile LARP technique and a schematic of the detailed
operation is shown in Fig. 1. A mixture of CsBr, PbBr , oleic
2
acid, and the assisted-ligand of n-octylamine was dissolved in N-
Synthesis of CH
CH NH
described in the literature. First, methylamine was dissolved
in absolute ethanol under stirring at 0 C for 2 h. Then, the
corresponding acid was added to the abovementioned solution
and it was le to react for 2 h at 0 C under continuous stirring.
Aer this, the solvent was removed by rotary evaporation with
a pressure of 0.1 MPa at 50 C. Aer rotary evaporation, the
3
NH
3
X (MAX, X ¼ Cl and I)
dimethylformamide (DMF), ultrasonicated, and a uniform free-
3
3
X (X ¼ Cl and I) was prepared using an approach
23
standing layered precursor solution was formed (Fig. 1a).
22
Then, the precursor solution was gradually added into a vigor-
ously stirred non-polar solvent (toluene, dichloromethane, etc.).
Aer this, a blue-green colloidal solution was formed, implying
ꢀ
ꢀ
22
an aggregation process of the precursor into nanoparticles. It
was also revealed that the crystallization process was controlled
by supersaturation, which was initially induced by the solubility
ꢀ
precipitate powders were collected and washed three times
18
change with solvent mixing. Finally, a high-quality colloidal
ꢀ
(diethylether) and dried in a vacuum oven (60 C, 5 h).
solution was achieved, which is clearly seen from the optical
image shown in Fig. 1b. Via utilizing the high PL properties of
Ion-exchange reactions
CsPbX
Ion-exchange with solid methylamine halide salts (MAX, X ¼ Cl (Fig. 1d) with saturated color-purity were obtained.
and I) were performed by adding different quantities (normally The morphology, phase structure, and composition features
ranging from 1 to 2 mmol) of MAX solid salt to a rapidly stirred are shown in Fig. 2. TEM image of the CsPbBr NCs is illustrated
3
perovskites, a “taiji” patterning (Fig. 1c) and LEDs
3
crude colloidal perovskite CsPbBr
toluene).
3
NCs solution (10 mL in Fig. 2a, which displays the cube shape and an average
diameter of 7.45 nm with a size deviation of ꢂ0.5 nm (Fig. 2b).
10392 | RSC Adv., 2017, 7, 10391–10396
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
analysis was carried out via XPS (Fig. S1a†). As described in
Fig. S1b–d,† the XPS showed the Cs 3d peaks at 726 eV and
740 eV, Pb 4f peaks at 141 eV and 146 eV, and the tted two
peaks of Br 3d at 69 eV and 71 eV.
3
The optical properties of the colloidal CsPbBr perovskite
NCs were further investigated utilizing UV-vis absorption and
PL spectroscopies. As described in Fig. 3a, the colloidal CsPbBr
3
NCs present the absorption (red) and emission (black) spectra.
A band edge at about 500 nm could be clearly observed in the
UV-vis absorption spectrum. The CsPbBr3 NCs displayed
a sharp emission peak position centered at 518 nm with
a narrow FWHM value of only 18 nm from the PL spectrum,
suggesting superior color saturation of the NCs (see the inset of
Fig. 3a). The PLQY of the colloidal CsPbBr
3
NCs was estimated
to be 50–80%, which could be compared to the coated chalco-
Fig. 1 (a) Schematic of the prepared process for colloidal CsPbBr
3
25,26
perovskite NCs, and the precursor solution and assembly into NCs. (b) genide NCs.
We further investigated the time-resolved PL
NCs (Fig. 3b). The PL decay curve was tted
The optical image of the colloidal nanocrystal solution. (c) The highly
decay of the CsPbBr
3
3
luminescent CsPbBr NCs-PMMA polymer patterning, and (d) LEDs
to the biexponential decay functions, and the radiative lifetimes
were in the range of 5–20 ns.
using CsPbBr NCs.
3
The LARP method is a versatile technique to fabricate NCs
via a solvent mixing approach and it is also a useful strategy to
manipulate the size and morphology of the NCs via introducing
capped ligands on the nanoparticles surface. It was reported
that long-chain ligands could control the NCs size and the
solvent polarity had a role in restraining the aggregation effects.
Hence, we comprehensively investigated the solvent polarity,
long-chain ligands (alkylamine with long chains), and the
amount of ligands and precursor to affect the uorescence
properties (Fig. S2†). As illustrated in Fig. S2a,† PL showed a red
shi effect with the increasing solvent polarity. Additionally, the
red shi effect was obviously seen by increasing the alkyl chains
of the capping ligand, as shown in Fig. S2b.† Furthermore, with
the increasing amount of precursor, the red shi effect of PL
was seriously decreased (Fig. S2c†). However, the blue shi
effect of the PL intensity was increased aer increasing the
amount of ligand (Fig. S2d†). Thus, the added solvent polarity,
ligand, and the amount of ligands and precursor could signif-
icantly inuence the PL properties.
To further tune the wide spectra of the NCs PL, we adopted
NCs. (b) Size distribution ion-exchange to realize the color of NCs by mixing the as-
Fig. 2 (a) TEM image of the colloidal CsPbBr
3
analysis for the sample. (c) High-resolution TEM image of the colloidal
CsPbBr NCs. (d) XRD patterns of the colloidal CsPbBr NCs. (e)
Molecular structure model, and (f) EDX spectrum of the colloidal
CsPbBr NCs.
prepared CsPbBr
neously investigated the effects of anion-exchange (halide
source) and cation-exchange (MA and Cs ). The size and shape
characteristics of the CsPbX NCs by ion-exchange manipula-
3
NCs and MAX (X ¼ Cl and I). We simulta-
3
3
+
+
3
3
tion can be clearly seen in Fig. 4. It is superior to those directly
The phase structure of the as-synthesized samples was further
characterized by HRTEM and XRD patterns. It was observed
that the lattice fringes of the NCs were 0.55 nm (Fig. 2c), cor-
19
responding to the (100) crystal faces. From the XRD patterns
(
Fig. 2d), the (100), (110), and (200) peaks demonstrated the
9,24
cubic crystal structure of CsPbBr
3
NCs.
Fig. 2e shows the
molecular structural model of CsPbBr NCs, which claried that
3
the ideal Cs : Pb : Br atomic ratio was close to 1 : 1 : 3 for the
perovskite NCs. The detailed EDX result, as shown in Fig. 2f,
reveals that the atomic ratio of the NCs was 1 : 1 : 3.2 (see Table
Fig. 3 (a) UV-vis absorption and PL emission spectra (inset: image (lex
¼
365 nm) CsPbX
3
NCs). (b) Time-resolved PL decay and fitting curve
NCs sample.
S1†), which was close to the theoretical value. The elemental for the colloidal CsPbBr
3
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 10391–10396 | 10393

View Article Online
RSC Advances
Paper
3
Fig. 4 TEM images of the CsPbBr NCs after treatment with various
quantities of MAI (up) and MACl (down). The insets show the evolution
of emission colors (under a UV lamp, lex ¼ 365 nm) from crude
Fig. 5 (a) An overview of the PL spectra of the samples obtained by
CsPbBr
3
NCs to composited perovskite NCs. Scale bars correspond to
mixing CsPbBr
365 nm for all). (b) Evolution of the optical absorption (solid lines)
and PL (dashed lines) spectra of CsPbBr NCs with the increasing
3
NCs with either MACl or MAI NCs in various ratios (lex
5
0 nm.
¼
3
quantities of MAX (X ¼ Cl and I), added as ion-exchange sources. (c)
Evolution of the time-resolved PL decay spectra of CsPbBr
mixing with either MACl or MAI NCs at various ratios.
3
NCs and
synthesized with mixed-halides CsPbX3 at low temperature,
which obtained either bulk or poorly polydispersed non-
luminescent crystallites. It was also suggested that our ion-
exchanged samples could even be comparable to the directly
+
XRD patterns, we could infer the replacement of Cs ions with
3
synthesized mixed-halides CsPbX sample at high temperature.
+
MA ions. However, the ion-exchange reactions almost had no
+
+
The molar ratios between MA ions and Cs ions were further
determined by EDX measurements (Table S2†). Therefore, we
considered that the reaction between MAX and CsPbBr3 in
a non-stoichiometric ratio resulted in the formation of
inuence on the shape and cubic structure of the starting
CsPbBr3 sample under low temperature of the ion-exchange
reaction.
29
Light-emission applications generally demand compati-
bility of the NC-emitters with matrix materials. To demonstrate
(
Cs) (MA) Pb(Cl/Br)3 or (Cs) (MA) Pb(Br/I)3 intermediate
x 1ꢁx x 1ꢁx
complex.
this miscibility, the CsPbBr
3
NCs were embedded into poly-
The bright PL of perovskite NCs (Fig. S3a†) could be tuned
over almost the entire visible spectral region (450–650 nm). As
observed from the PL spectra, as shown in Fig. 5a and b, the
resulting composition of the ion-exchanged NCs were Stokes-
shied with respect to the optical absorption spectra and the
NCs possessed a narrow FWHM of 10–40 nm, as previously re-
(methylmethacrylate) (PMMA) forming well dispersed compos-
ites where the composites yielded excellent optical clarity and
bright emission. Concomitantly, the versatile uorescent
patterns were further achieved by silk screen printing, which is
30
a widely used and effective technique. As shown in Fig. 6a,
a mixture of PMMA and CsPbBr NCs acting as printing ink was
19
3
ported. The PLQY of the samples generally dropped from the
starting value of 82% aer mixing the as-prepared CsPbBr NCs
cast onto a mask (160 meshes screen), and the ink was inl-
trated through the patterned mask onto the substrate by
scraping the ink. Fig. 6b–d show the designed patterns of
3
with either MACl or MAI (Fig. S3b†). Time-resolved photo-
luminescence decays of the resulting composition indicated the
radiative lifetimes in the range of 1–20 ns. In general, the life-
times of the resulting composition were increased with an
increase of I-ions and decreased with an increase of Cl-ions
“
NJTU” and “taiji”. The pattern was invisible under daylight
Fig. 6c), whereas it was remarkably visible under UV light (Fig.
d). It was revealed that the patterns possessed both “vis-
(
6
(Fig. 5c).
It is well-known that the high speed of anion-exchange in the
2
7
perovskite NCs is rooted in the ionic conductivity of halides.
+
However, aer using MAX (X ¼ Cl and I), the cation (MA ) could
be also engaged in ion-exchange reactions and raised a further
+
˚
complication, resulting in the replacement of Cs (1.81 A) ions
with the larger MA (2.70 A) ions. According to the Fourier
+
˚
transform infrared spectroscopy (FTIR) analysis, we could
obviously see the peaks intensity signicantly strengthened at
ꢁ
1
2
800 and 2900 cm , corresponding to stretching vibration of
28
+
+
N–H (Fig. S4†). It was revealed that Cs ions replaced MA ions.
Fig. 6 (a) The schematic of patterning by screen printing. (b), (d)
Images (lex ¼ 365 nm) and (c) (under daylight) of the patterning ob-
To further demonstrate the ion-replacement, XRD was per-
formed (Fig. S5†). From the lattice parameters change of the tained using the mixture of CsPbBr NC-PMMA.
3
10394 | RSC Adv., 2017, 7, 10391–10396
This journal is © The Royal Society of Chemistry 2017

View Article Online
Paper
RSC Advances
PL spectrum (450–650 nm), and the PL is also affected by both
the cation and anion exchange processes. Furthermore, we have
constructed high color-purity LED using CsPbBr3 perovskite
nanocrystals, which maintains the low turn-on voltages and
narrow full-width at half maxima (FWHM) emission. We believe
our results will guide the development of perovskites and open
an avenue towards the design of high-performance optoelec-
tronic devices.
Acknowledgements
This work was supported by National Natural Science Founda-
tion of China (21474052) and Priority Academic Program
Development of Jiangsu Higher Education Institutions (PAPD).
3
Fig. 7 (a) Device structure of the CsPbBr perovskite LEDs. Schematic
and the cross-sectional TEM image of the device: ITO/ZnO/perov- This work was supported by the National Key Research and
skite/TFB/MoO /Au. (b) Normalized EL spectrum of the CsPbBr
Development Program of China (project No. 2016YFB0401700).
perovskite thin film-based LEDs at the applied voltage of 4 V. (c)
Current density and luminance for the CsPbBr perovskite LED
x
3
3
measured at room temperature. (d) The external quantum efficiency Notes and references
(
EQE) versus current density curves of this LED.
1
2
3
N. J. Jeon, J. H. Noh, Y. C. Kim, W. S. Yang, S. Ryu and
S. I. Seok, Nat. Mater., 2014, 13, 897–903.
D. Li, P. Liao, X. Shai, W. Huang, S. Liu, H. Li, Y. Shen and
M. Wang, RSC Adv., 2016, 6, 89356–89366.
Z. K. Tan, R. S. Moghaddam, M. L. Lai, P. Docampo,
R. Higler, F. Deschler, M. Price, A. Sadhanala, L. M. Pazos,
D. Credgington, F. Hanusch, T. Bein, H. J. Snaith and
R. H. Friend, Nat. Nanotechnol., 2014, 9, 687–692.
Y. Ling, Z. Yuan, Y. Tian, X. Wang, J. C. Wang, Y. Xin,
K. Hanson, B. Ma and H. Gao, Adv. Mater., 2016, 28, 305–311.
L. Dou, Y. M. Yang, J. You, Z. Hong, W. H. Chang, G. Li and
Y. Yang, Nat. Commun., 2014, 5, 5404.
invisible” and “UV-visible” properties, which has potential
application in the anti-counterfeit and labelling elds.
To design the practical application of the as-synthesized
CsPbBr
electroluminescence (EL) LEDs were fabricated. The LED device
consisted of multiple layers of ITO/ZnO/CsPbBr /TFB/MoO /Au
Fig. 7a): indium tin oxide (ITO) was coated on the glass
3
perovskite in optoelectronic devices, bright green
3
x
4
5
6
7
(
substrate, 40 nm ZnO NCs were employed as electron-
transporting and hole-blocking layers, the 25 nm poly(9,9-
dioctyl-uorene-co-N-(4-butylphenyl)diphenylamine)
(TFB)
L. Su, Z. X. Zhao, H. Y. Li, J. Yuan, Z. L. Wang, G. Z. Cao and
G. Zhu, ACS Nano, 2015, 9, 11310–11316.
G. Xing, N. Mathews, S. S. Lim, N. Yantara, X. Liu, D. Sabba,
M. Gratzel, S. Mhaisalkar and T. C. Sum, Nat. Mater., 2014,
served as the hole-transporting and electron-blocking inter-
layers, 10 nm molybdenum trioxide, and 100 nm gold (Au)
electrode acted as a hole selective contact. Fig. 7b shows the EL
spectra of the device under a bias of 4 V. The EL emission peak
at 510 nm with a narrow FWHM of 20 nm and the shape of the
EL spectrum did not change, indicating that the carriers were
well conned within the perovskite layers. Fig. 7c presents the
current density and luminescence versus driving voltage. The
device displayed a turn on voltage of 3 V at room temperature.
The current density and luminance rapidly increased aer
turning on the voltage, suggesting a very low series resistance
13, 476–480.
8
9
Y. Fu, H. Zhu, C. C. Stoumpos, Q. Ding, J. Wang,
M. G. Kanatzidis, X. Zhu and S. Jin, ACS Nano, 2016, 10,
7963–7972.
A. Swarnkar, R. Chulliyil, V. K. Ravi, M. Irfanullah,
A. Chowdhury and A. Nag, Angew. Chem., Int. Ed., 2015, 54,
15424–15428.
1
1
1
1
0 S. Huang, Z. Li, L. Kong, N. Zhu, A. Shan and L. Li, J. Am.
and efficient operation of the LED device. The CsPbBr
skite LEDs device presented a peak external quantum efficiency
(
3
perov-
Chem. Soc., 2016, 138, 5749–5752.
1 Y. Wang, X. Li, X. Zhao, L. Xiao, H. Zeng and H. Sun, Nano
Lett., 2016, 16, 448–453.
2 Y. S. Zhao, H. Fu, A. Peng, Y. Ma, D. Xiao and J. Yao, Adv.
Mater., 2008, 20, 2859–2876.
3 F. Zhu, L. Men, Y. Guo, Q. Zhu, U. Bhattacharjee,
P. M. Goodwin, J. W. Petrich, E. A. Smith and J. Vela, ACS
Nano, 2015, 9, 2948–2959.
EQE) at around 0.06% at ꢃ4 V (Fig. 7d), which is comparable to
4,31
the previously reported studies.
Conclusions
In summary, we synthesized highly luminescent colloidal
CsPbBr
blue and green emission (410–530 nm) using a simple and
versatile LARP technique. Additionally, the post synthetic 15 A. B. Wong, M. Lai, S. W. Eaton, Y. Yu, E. Lin, L. Dou, A. Fu
chemical transformations (ion-exchange, (MAX, X ¼ Cl, I)) and P. Yang, Nano Lett., 2015, 15, 5519–5524.
approach was utilized to achieve a wide variety of complex 16 F. Zhang, H. Zhong, C. Chen, X.-g. Wu, X. Hu, H. Huang,
3
NCs with high QY (QY ¼ 50–80%) and highly bright 14 C. Lee, J. Hong, A. Stroppa, M.-H. Whangbo and J. H. Shim,
RSC Adv., 2015, 5, 78701–78707.
perovskite NCs, which displayed a visible spectral region of the
J. Han, B. Zou and Y. Dong, ACS Nano, 2015, 9, 4533–4542.
This journal is © The Royal Society of Chemistry 2017
RSC Adv., 2017, 7, 10391–10396 | 10395

View Article Online
RSC Advances
Paper
1
1
7 J. Li, X. Yuan, P. Jing, J. Li, M. Wei, J. Hua, J. Zhao and
L. Tian, RSC Adv., 2016, 6, 78311–78316.
8 G. Nedelcu, L. Protesescu, S. Yakunin, M. I. Bodnarchuk, 25 P. Maity, T. Debnath and H. N. Ghosh, J. Phys. Chem. C, 2015,
D. Y. Chung, A. J. Freeman, B. W. Wessels and
M. G. Kanatzidis, Cryst. Growth Des., 2013, 13, 2722–2727.
M. J. Grotevent and M. V. Kovalenko, Nano Lett., 2015, 15,
635–5640.
9 L. Protesescu, S. Yakunin, M. I. Bodnarchuk, F. Krieg,
119, 26202–26211.
26 K. W. Song, R. Costi and V. Bulovi ´c , Adv. Mater., 2013, 25,
1420–1423.
5
1
R. Caputo, C. H. Hendon, R. X. Yang, A. Walsh and 27 J. Mizusaki, K. Arai and K. Fueki, Solid State Ionics, 1983, 11,
M. V. Kovalenko, Nano Lett., 2015, 15, 3692–3696. 203–211.
0 J. Song, J. Li, X. Li, L. Xu, Y. Dong and H. Zeng, Adv. Mater., 28 S. Zhu, Q. Meng, L. Wang, J. Zhang, Y. Song, H. Jin, K. Zhang,
2
2
2
2
2
2
015, 27, 7162–7167.
H. Sun, H. Wang and B. Yang, Angew. Chem., Int. Ed. Engl.,
2013, 52, 3953–3957.
29 F. Meinardi, A. Colombo, K. A. Velizhanin, R. Simonutti,
M. Lorenzon, L. Beverina, R. Viswanatha, V. I. Klimov and
S. Brovelli, Nat. Photonics, 2014, 8, 392–399.
1 X. Li, Y. Wu, S. Zhang, B. Cai, Y. Gu, J. Song and H. Zeng, Adv.
Funct. Mater., 2016, 26, 2435–2445.
2 S. Sun, D. Yuan, Y. Xu, A. Wang and Z. Deng, ACS Nano, 2016,
10, 3648–3657.
3 Y. Niu, F. Zhang, Z. Bai, Y. Dong, J. Yang, R. Liu, B. Zou, J. Li 30 S.-S. Liu, C.-F. Wang, C.-X. Li, J. Wang, L.-H. Mao and
and H. Zhong, Adv. Opt. Mater., 2015, 3, 112–119. S. Chen, J. Phys. Chem. C, 2014, 2, 6477.
4 C. C. Stoumpos, C. D. Malliakas, J. A. Peters, Z. Liu, 31 N. Yantara, S. Bhaumik, F. Yan, D. Sabba, H. A. Dewi,
M. Sebastian, J. Im, T. C. Chasapis, A. C. Wibowo,
N. Mathews, P. P. Boix, H. V. Demir and S. Mhaisalkar, J.
Phys. Chem. Lett., 2015, 6, 4360–4364.
10396 | RSC Adv., 2017, 7, 10391–10396
This journal is © The Royal Society of Chemistry 2017