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Electronic Supplementary Information
A Relationship Between Crystal Structures and
Spectroscopic Properties in Cesium Lead Bromide
(CsPbBr3) Perovskite Nanocrystals : Focusing on the
Photoluminescence Efficiency
Jumi Park,† Youngsik Kim,‡ Sujin Ham,† Ju Young Woo,§ Taehee Kim,† Sohee Jeong,‡,* and
Dongho Kim†,*
† Department of Chemistry, Yonsei University, 50 Yonsei-ro, Seodaemun-gu, Seoul 03722,
Republic of Korea.
‡ Department of Energy Science, Sungkyunkwan University, 2066 Seobu-Ro, Jangan-Gu,
Suwon, Gyeonggi-do 16419, Republic of Korea.
§ Micro/Nano Scale Manufacturing Group, Korea Institute of Industrial Technology, 143
Hanggaulro, Sangrok-gu, Ansan, Gyeonggi-do 15588, Republic of Korea.
Corresponding Author: [email protected] (D.Kim); [email protected] (S.Jeong)
Electronic Supplementary Material (ESI) for Nanoscale.This journal is © The Royal Society of Chemistry 2019
Table of Contents
Experimental
1. Synthesis of CsPbBr3 nanocrystals (NCs)
2. UV-Visible & Photoluminescence spectroscopy
3. Femtosecond transient absorption spectroscopy (fs-TA)
4. Single molecule confocal microscopy
5. Auger ionization efficiency
6. PL intensity-lifetime scaling
Supporting Figures
1. Basic optical parameters
2. Photoluminescence (PL) spectra
3. Photoluminescence (PL) intensity trace in single crystals
4. Transient absorption spectra
5. Emission frequency shift
6. Multi-exciton Auger lifetime
7. X-ray photoelectron spectroscopy analysis
8. Energy diagram
9. Photoluminescence (PL) scan image
Reference
Experimental Section
1. Synthesis of CsPbBr3 nanocrystals (CPB)
CsPbBr3 nanocrystals were prepared following previously reported procedures with
modifications1,2
1) Preparation of cesium oleate solution: Cs2CO3 (0.163 g, Aldrich, 99.9 %), 1-
octadecene (8 mL, Uniam, 99%) and oleic acid (0.5 mL, Uniam, 99%) were loaded
into 100 mL of 3-neck flask. And then the solution was dried under vacuum at 110 oC
for 2 h. After drying, the temperature of the solution was further raised to 150 oC under
N2 and kept until the injection.
2) Synthesis of pristine-CPB and ZnBr2-CPB: We note that the samples are denoted as
“pristine-CPB” or “ZnBr2-CPB” depending on the presence of ZnBr2 in the synthesis.
0.138 g of PbBr2 (Aldrich, ≥98%), 1 mL of oleic acid (degassed, Uniam, 99%), and 1
mL of oleylamine (degassed, Aldrich, 70%) were placed into 100 mL 3-neck flask
(0,095 g of ZnBr2 (Aldrich, 99.999%) was added for the synthesis of ZnBr2-CPB). The
flask containing precursor solution is dried under vacuum at 110 oC for 2 h. And then,
the solution was further heated to 170 oC under N2, and 0.8 mL of prepared Cs-oleate
solution (150 oC) was swiftly injected. Approximately 10 s from the injection, the flask
was rapidly cooled down in an ice bath.
3) Isolation of CsPbBr3 nanocrystals: Reaction crude solution was centrifuged for 12
min at 10000 rpm. And then the precipitates were redispersed in 3 mL of anhydrous
toluene with strong vortexing. When the NCs were completely redispersed, the NC
solution was centrifuged for 32 min at 13000 rpm (temperature was set to 18 oC during
centrifugation). After the centrifugation, the precipitates were redispersed in 4 mL of
anhydrous hexane, and again centrifuged for 10 min at 6000 rpm. Finally, supernatant
was collected and filtered with syringe filter (pore size 0.45 µm) while the precipitates
were discarded. We note that all isolation procedures were performed under inert
condition.
2. UV-Visible & Photoluminescence spectroscopy
Steady-state absorption spectra were measured on a UV/Vis spectrometer (Cary5000, Varian)
and photoluminescence spectra were recorded by using a fluorescence spectrophotometer (F-
2500, Hitachi). Photoluminescence spectra are spectrally corrected by using correction factor
of the fluorescence spectrophotometer. All steady-state measurements carried out by using a
quartz cuvette with a pathlength of 1 cm at ambient temperatures.
3. Femtosecond transient absorption spectroscopy
The femtosecond time-resolved transient absorption (fs-TA) spectrometer consists of an optical
parametric amplifier (OPA; Palitra, Quantronix) pumped by a Ti:sapphire regenerative
amplifier system (Integra-C, Quantronix) operating at 1 kHz repetition rate and an optical
detection system. The generated OPA pulses have a pulse width of ~ 100 fs in the range of 280-
2700 nm, which are used as pump pulses. White light continuum (WLC) probe pulses were
generated using a sapphire window (4 mm thick) by focusing a small portion of the
fundamental 800 nm pulses which was picked off by a quartz plate before entering the OPA.
The time delay between pump and probe beams was carefully controlled by making the pump
beam travel along a variable optical delay (ILS250, Newport). Intensities of the spectrally
dispersed WLC probe pulses are monitored by a High Speed Spectrometer (Ultrafast Systems)
for both visible and near-infrared measurements. To obtain the time-resolved transient
absorption difference signal (ΔA) at a specific time, the pump pulses were chopped at 500 Hz
and absorption spectra intensities were saved alternately with or without pump pulse. Typically,
4000 pulses excite the samples to obtain the fs-TA spectra at each delay time. The polarization
angle between pump and probe beam was set at the magic angle (54.7°) using a Glan-laser
polarizer with a half-wave retarder in order to prevent polarization-dependent signals. Cross-
correlation fwhm in pump-probe experiments was around 200 fs and chirp of WLC probe
pulses was measured to be 1.2 ps in the 450-800 nm region. To minimize chirp, all reflection
optics were used in the probe beam path. A quartz cell of 2 mm path length was employed.
After completing each set of TA experiments, the absorption spectra of all samples were
carefully checked to rule out the presence of artifacts or spurious signals arising from, for
example, degradation or photo-oxidation of the samples in question.
4. Single molecule confocal microscopy
Samples for single molecule confocal measurements were prepared by spin-coating NC
solutions on rigorously cleaned quartz coverslips at 3000 rpm for 30s. The NC solutions were
composed of NCs in hexane containing 20 mg∙mL-1 polystyrene (M.W. = 40000, Aldrich). The
confocal microscope (TE2000-U, Nikon) was equipped with a sample scanning stage at RT.
Circular polarized light from a picosecond pulsed diode laser (LDH-D-C-450, Picoquent, 1
MHz repetition rate, prepared using a Berek compensator (5540, New Focus)) excited the
samples. It was passed through a laser line filter (FF01-420/10-25, Semrock) and collimating
lens. Then, it subsequently focused on the sample via an oil immersion objective (Plan Fluor,
1.3 NA, 100×, Nikon) with a power density corresponding to an average number of excitons
per pulse, ⟨𝑁𝑥⟩ = 0.1. Fluorescent signals were passed through a dichroic mirror (T425lpxr,
Chroma Technology), spectrally filtered using a notch filter (HNPF-420.0AR-1.0, Kaiser
optical systems) and a band pass filter (FF-01-430/LP-25, Semrock), and then split by using a
non-polarizing 50:50 beam splitter. Half of the fluorescence was dispersed via a spectrograph
(SpectraPro 2150i, Princeton Instruments) and projected onto an EMCCD camera (PL
PROEM:512B EMCCD, Princeton Instruments). The other half was detected by an avalanche
photodiode (APD) module (SPCM-AQR-16-FC, EG&G). The fluorescent signal detected by
the APD was registered by a time-correlated single photon counting (TCSPC) PC (SPC 830,
Becker & Hickl). The TCSPC was operated in first-in-first-out regime in which the arrival time
after the beginning of acquisition and the time lag with respect to the excitation pulse were
stored for each detected photon. The full-width half maximum (FWHM) of the overall
instrumental response function approximately corresponded to 500–600 ps. The data were
processed by using a BIFL data analyzer software (Scientific Software Technologies Center)
to obtain fluorescence intensity trajectories and the time-resolved fluorescence decays.
5. Auger ionization efficiency
The probability (P) of creating multiple excitons within a given bin time should be considered
to understand the on-time kinetics using Auger ionization processes. The probabilities of
creating n excitons in a single pulse and multiexciton (MX, n ≥ 2) were calculated by Equation
1 and 2.3
P⟨Nx⟩(n) = e-⟨Nx⟩∙⟨Nx⟩n/n! (1): the probability of the average number of created exciton on <Nx>
PMX = 1‒ e-⟨Nx⟩‒ ⟨Nx⟩·e-⟨Nx⟩ (2): the probability of the multiexciton on <Nx>, PMX
Here, the average number of generated excitons ⟨Nx⟩ can calculated by multiplying the
absorption cross section (σ, cm-2) at the excitation wavelength and the intensity of laser (j,
photons/cm2∙pulse) (⟨Nx⟩=jσ).
The Auger ionization efficiency influences the fall-off time of on-time distribution since Pfall-
off is the probability of forming the multiexciton state (PMX) and the ionization probability
(Pionize).3,4
Pfall off = ΔTrep/τfall-off = PMX × Pionize (3)
Pionize = Pfall off/PMX (Auger ionization probability, Pionize), where ΔTrep is a repetition rate of the
pulsed laser.
6. PL intensity-lifetime scaling
Intensity-lifetime scaling or the ratio of radiative rates between two distinct intensity levels ()
β =𝜏𝑜𝑛𝐼𝑜𝑛
×𝐼𝑜𝑓𝑓
𝜏𝑜𝑓𝑓
where and I are the PL lifetime and intensity of the corresponding “on” and “off” states.
In Figure 4(a), the radiative lifetime ratio of the the brightest state and dark state is calculated
as
𝜏𝑟𝑜𝑛𝜏𝑟𝑜𝑓𝑓
=𝜏𝑜𝑛𝐼𝑜𝑛
𝐼𝑜𝑓𝑓
𝜏𝑜𝑓𝑓=
4.24
95.2 − 2(𝑏𝑎𝑐𝑘𝑔𝑟𝑜𝑢𝑛𝑑)×15.6 − 2(𝑏𝑎𝑐𝑘𝑔𝑟𝑜𝑢𝑛𝑑)
0.49≈ 1.3
Thus, the dark state emission arises from trion.
In Figure 4(d), the radiative lifetime ratio of the brightest state and dark state is calculated as
𝜏𝑟𝑜𝑛𝜏𝑟𝑜𝑓𝑓
=𝜏𝑜𝑛𝐼𝑜𝑛
𝐼𝑜𝑓𝑓
𝜏𝑜𝑓𝑓=
3.54
35.8 − 2(𝑏𝑎𝑐𝑘𝑔𝑟𝑜𝑢𝑛𝑑)×14.2 − 2(𝑏𝑎𝑐𝑘𝑔𝑟𝑜𝑢𝑛𝑑)
1.38≈ 0.9
Thus, the dark state emission results from the trapping of band-edge electrons and holes.
Supporting Figures
Table S1 Basic optical parameters of CsPbBr3 NCs.
a The band gap energy yielded from first excitonic absorption peak Abs. b The Stokes shift is
defined as the energy difference between the first minimum in the 2/2 spectrum and the
emission peak. c The transition line width. d Absorption cross section at 3.1 eV. e Biexciton
binding energy.
Fig. S1 PL spectra and PL quantum yield of fresh Pristine- and ZnBr2-CPB.
3.1 2.5 2.1 1.8
400 500 600 700
Wavelength (nm)
PL
In
tensity (
a.u
.)
Energy (eV)
Pristine-CPB
ZnBr2-CPB
37.6%
71.5%
CsPbBr3 Ega [eV] s
b [meV] c [meV] absd
[10-15 cm2] xxe [meV] QY [%]
Pristine 2.46 45 14 9.27 77 72
ZnBr2 2.47 56 67 8.50 81 38
Fig. S2 Representative blinking dynamics for individual NCs : (a) fresh Pristine-, (b) 7-days
Pristine-, (c) fresh ZnBr2- and (d) 7-days ZnBr2-CPB.
Fig. S3 Femtosecond transient absorption (fs-TA) spectra of (a) Pristine-CPB and (b)
ZnBr2-CPB at early time before aging.
0 20 40 60 80 1000
50
100
150
200
250
300
350
PL inte
nsity (
count/20m
s)
Time (s)0 10 20 30 40 50 60
0
20
40
60
80
100
120
140
160
180
PL inte
nsity (
count/20m
s)
Time (s)0 10 20 30 40 50 60
0
50
100
150
200
250
300
350
PL inte
nsity (
count/20m
s)
Time (s)0 10 20 30 40 50 60
0
20
40
60
80
100
120
140
Time (s)
PL inte
nsity (
count/20m
s)
(a)
(b)
(c)
0 10 20 30 40 50 600
50
100
150
200
250
PL inte
nsity (
count/20m
s)
Time (s)0 10 20 30 40 50 60
0
50
100
150
200
250
PL inte
nsity (
count/20m
s)
Time (s)0 10 20 30 40 50 60
0
20
40
60
80
100
120
140
160
180
Time (s)
PL inte
nsity (
count/20m
s)
0 10 20 30 40 50 60 700
50
100
150
200
250
300
PL inte
nsity (
count/20m
s)
Time (s)0 10 20 30 40 50 60
0
20
40
60
80
100
120
140
160
PL inte
nsity (
count/20m
s)
Time (s)
(d)
0 10 20 30 40 50 600
20
40
60
80
100
120
140
160
180
PL inte
nsity (
count/20m
s)
Time (s)0 10 20 30 40 50 60 70
0
20
40
60
80
100
120
140
160
180
PL inte
nsity (
count/20m
s)
Time (s)0 10 20 30 40 50
0
10
20
30
40
50
60
PL inte
nsity (
count/20m
s)
Time (s)0 5 10 15 20 25 30 35
0
10
20
30
40
50
60
70
80
PL inte
nsity (
count/20m
s)
Time (s)
0 10 20 30 40 50 600
20
40
60
80
100
120
140
PL inte
nsity (
count/20m
s)
Time (s)0 10 20 30 40 50
0
20
40
60
80
100
120
Time (s)
PL inte
nsity (
count/20m
s)
0 10 20 30 40 500
20
40
60
80
100
PL inte
nsity (
count/20m
s)
Time (s)0 10 20 30 40 50
0
10
20
30
40
50
60
70
Time (s)
PL inte
nsity (
count/20m
s)
0 20 40 60 800
20
40
60
80
100
120
PL inte
nsity (
count/20m
s)
Time (s)
0 10 20 30 40 50 600
50
100
150
200
250
300
PL inte
nsity (
count/20m
s)
Time (s)
0 20 40 60 80 1000
20
40
60
80
100
PL inte
nsity (
count/20m
s)
Time (s)
480 500 520 540 560
2.58 2.48 2.38 2.30 2.21
-80
-40
0
40
80
Energy (eV)
m
A
Wavelength (nm)
0 ps 0.15 ps
0.35 ps 0.55 ps
0.75 ps 0.9 ps
1.5 ps 2 ps
3 ps 4 ps
5 ps
480 500 520 540 560
2.58 2.48 2.38 2.30 2.21
-80
-40
0
40
80
Energy (eV)
m
A
Wavelength (nm)
0 ps 0.15 ps
0.35 ps 0.55 ps
0.75 ps 0.9 ps
1.5 ps 2 ps
3 ps 4 ps
5 ps
Pristine-CPB(a) (b) ZnBr2-CPB
Fig. S4 Histograms of the net spectral shifts of a single CsPbBr3 NCs for (a) fresh Pristine-
CPB (b) Pristine-CPB after aging (c) fresh ZnBr2-CPB and (d) ZnBr2-CPB after aging.
Fig. S5 The Auger lifetime obtained from fitting the multiexciton dynamics by mono-
exponential decay for (a) fresh Pristine-CPB (b) fresh ZnBr2-CPB (c) Pristine-CPB after
aging and (d) ZnBr2-CPB after aging.
-100 -50 0 50 1000
500
1000
1500
2000
2500
Count
Emission Frequency Shift (meV)
Model Gauss
Equation y=y0 + (A/(w*sqrt(PI/2)))*exp(-2*((x-xc)/w)^2)
Reduced Chi-Sqr
107.46567
Adj. R-Square 0.99836
Value Standard Error
B
y0 1.18472 0.65746
xc 1.30571E-4 1.4801E-5
w 0.00833 2.97482E-5
A 27.45813 0.08575
sigma 0.00417 1.48741E-5
FWHM 0.00981 3.50259E-5
Height 2629.95644 8.10687
-100 -50 0 50 1000
500
1000
1500
2000
2500
Count
Emission Frequency Shift (meV)
Model Gauss
Equation y=y0 + (A/(w*sqrt(PI/2)))*exp(-2*((x-xc)/w)^2)
Reduced Chi-Sqr
197.87171
Adj. R-Square 0.99647
Value Standard Error
B
y0 1.47948 0.97212
xc 9.02056E-5 2.12087E-5
w 0.00746 4.26445E-5
A 22.04829 0.11023
sigma 0.00373 2.13223E-5
FWHM 0.00879 5.02101E-5
Height 2357.23614 11.62373
FWHM 12
FWHM 12
FreshPristine-CPB
-100 -50 0 50 1000
200
400
600
800
1000
1200
Count
Emission Frequency Shift (meV)
-100 -50 0 50 1000
200
400
600
800
1000
1200
Count
Emission Frequency Shift (meV)
Model Gauss
Equationy=y0 + (A/(w*sqrt(PI/2)))*exp(-2*((x-xc)/w)^2)
Reduced Chi-Sqr
57.95302
Adj. R-Square 0.99578
Value Standard Error
B
y0 0.85218 0.46664
xc 1.03956E-4 3.35035E-5
w 0.01226 6.74613E-5
A 15.89984 0.07679
sigma 0.00613 3.37307E-5
FWHM 0.01443 7.94296E-5
Height 1034.96319 4.91078
FWHM 8
FWHM 7
(a) (b)
(c) (d)
7-daysPristine-CPB
FreshZnBr2-CPB
7-daysZnBr2-CPB
0 20 40 60
0.1
1 <Nx>
1.5
2.5
3.7
7.4
14.2
0 20 40 60
0.1
1 <Nx>
1.5
2.5
3.7
7.4
14.2
0 20 40 60
<Nx>
1.4
2.2
3.4
6.8
13.0
-A
Time (ps) Time (ps)
-A
0 20 40 60
<Nx>
1.4
2.2
3.4
6.8
13.0
(a) (b)
(c) (d)Time (ps) Time (ps)
31 ps28 ps
31 ps26 ps
Fig. S6 (a) Pb/Cs and (b) Br/(Cs+Pb) atomic ratios of Pristine- and ZnBr2-CPB from XPS
data.
Fig. S7 Energy diagrams of Pristine-CPB (left) and ZnBr2-CPB (right). The bandgap energy
is obtained from first excitonic absorption peak (Table S1). The subband gap energy is
measured as the difference between the first transition energy and the second transition
energy. The intraband gap energy changes depending on the type of ligands adsorbed on the
substrate surface.
1.0
1.1
1.2
1.3
1.4
1.5
1.2
1.3
1.4
1.5
1.6
1.7
1.8
Pristine-CPB ZnBr2-CPBPristine-CPB ZnBr2-CPB
Pb
/Cs
Br/
(Cs+
Pb
)
(a) (b)
0.0840.073
Pri
stin
e-
Cs
Pb
Br 3
Zn
Br 2
-
CsPb
Br 3
2.4
6
2.47
E (eV)
Cs-o
leat
e
Br-
ole
yla
mm
on
ium
Fig. S8 Typical PL scan images of CsPbBr3 NCs in single crystal measurements.
Fresh 7-days
Reference
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