Supporting information for
Harnessing Defect-Tolerance at the Nanoscale:
Highly Luminescent Lead Halide Perovskite
Nanocrystals in Mesoporous Silica Matrixes
Dmitry N. Dirin†,§, Loredana Protesescu†,§, David Trummer†, Sergii Yakunin†,§, Frank
Krumeich†, Maksym V. Kovalenko*,†,§
† Institute of Inorganic Chemistry, Department of Chemistry and Applied Bioscience, ETH
Zürich, CH-8093 Zürich, Switzerland
§ Laboratory for Thin Films and Photovoltaics, Empa − Swiss Federal Laboratories for Materials
Science and Technology, CH-8600 Dübendorf, Switzerland
Synthetic methods
Chemicals
Lead iodide (PbI2, 99%, Aldrich), lead bromide (PbBr2, 98+%, Acros), cesium iodide (CsI, 99.999%,
ABCR), cesium bromide (CsBr, 99.999%, ABCR), methylamine solution in ethanol (33 wt%, Aldrich),
formamidinium acetate (FAAc, 99%, Aldrich), hydroiodic acid (HI, 55-58 wt%, ABCR), hydrobromic
acid (HBr, 48 wt%, Aldrich), N-methylformamide (MFA, 99+%, TCI), propylene carbonate (PC
anhydrous, 99+%, Merk), N,N-dimethylformamide (DMF, 99.8%, Aldrich), dimethylsulfoxide (DMSO,
99.5%, Aldrich), formamide (FA, 99+%, Aldrich), glycol sulphite (EGS, 99%, Acros), gammabutyrolactone (GBL, 99+%, Acros), octadecylsilane (ODS, 95%, ABCR), octadecyltrimethoxysilane
(OTMS, 97%, ABCR), docusate sodium (AOT, 98%, Aldrich) ,ethanol (EtOH, 99.8+%, Fluka), toluene
(99.8+%, Fischer), and diethyl ether (Et2O, 99.8+%, Aldrich) were used as received.
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Mesoporous silica (meso-SiO2) matrices
All mesoporous silica materials used as template matrixes were purchased from commercial vendors, and
were used as received. Their properties and identification information are given in Table S1. .
Table S 1. Properties and identification information of meso-SiO2 matrixes. Information is taken
from the commercial vendors.
Pore size, nm
Pore shape
2.5nm-SiO2
4nm-SiO2
7nm-SiO2
2.5-3
cylindrical
channels
hexagonal,
4.6-4.8
4 nm
cylindrical
channels
hexagonal
Figure S8
7.1 nm
cylindrical
channels
hexagonal,
~11.6
SBA-15
MSU-H
Pore ordering
and unit cell,
nm
aluminosilicate
Common
MCM-41
name
1.0
Pore volume,
3
cm /g
940-1000
Surface area,
m2/g
0.2-0.5
Particle size,
µm
variable
Particle shape
Manufacturer
and catalog
number
Aldrich,
643653
15nmSiO2
15 nm
variable
30nm-SiO2
30 nm
variable
50nmSiO2
50 nm
variable
disordered
disordered
disordered
0.91
1.15
0.9
750
300
100
0.2
0.5-1
35-70
20
0.5-2
spherical
nanoparticles
Aldrich,
748161
variable
variable
variable
Aldrich,
643637
Aldrich,
236810
spherical
microparticles
Alfa Aesar,
44101
Grace,
SP54110309,
ID7765
Synthesis of methylammonium (MA) and formamidinium (FA) halides
CH3NH3I (MAI) and CH3NH3Br (MABr) were synthesized according to Ref.1 24 mL of a 33 wt%
methylamine solution in absolute ethanol were added to 100 mL of ethanol (pre-cooled to 0 °C). Then 10
mL (8.6 mL) hydroiodic (hydrobromic) acid were added and the resulting mixture was stirred under inert
atmosphere for 1 hour. Water and ethanol were then removed by rotary evaporation at 40 °C. The product
was dissolved in ethanol, recrystallized in diethyl ether, and dried under vacuum at 40 °C for 14 hours.
The composition and phase purity were confirmed by powder XRD.
The formamidinium bromide (FABr) precursor was prepared in a similar manner to FAI, as reported
elsewhere.2
Template-assisted synthesis of lead halide perovskite nanocrystals (NCs)
Typical template-assisted synthesis was conducted as outlined in Figure S1. The templates were dried at
150° C for 12 h under vacuum, reaching a final pressure of 5·10-5 mbar, before use. Then, 2.0 mg of
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mesoporous silica were impregnated with 10 µL of 0.3 M solution of methylammonium lead iodide
(MAPbI3, 186 mg mL-1) or with similarly concentrated CsPbI3, formamidinium lead bromide (FAPbBr3)
or MAPbBr3 in MFA. For the synthesis of CsPbBr3 NCs, a lower concentration (0.1 M) solution in MFA
was used due to the lower solubility of CsPbBr3. After impregnation, the excess solution was removed by
damping with filter paper. The as-obtained powder was sandwiched between two glass slides and heated
up to 120°C (for MA and FA salts) or 150°C (for Cs salts) in a vacuum oven for 40 minutes. Afterwards,
the powder was allowed to cool to 80 °C under vacuum and then to room temperature in air. Larger-scale
syntheses (for >50 mg of silica powder) were performed in an analogous way except for in one step:
excess solution was removed by vacuum on a glass filter (porosity class 2) instead of by damping with
filter paper.
Preparation of dispersions and films of mesoporous silica microparticles impregnated with lead
halide perovskite NCs
Glass substrates were washed with acetone, isopropanol, and deionized water in an ultrasonic bath, then
treated with reduced air plasma (100W for 5 minutes) and dipped into a 5% OTMS solution in toluene for
10 minutes, as described elsewhere.3 These hydrophobized substrates were then carefully rinsed with
toluene and dried at 70 °C for 2 minutes.
To prepare films, a mixture of 2 mg of silica 4nm-SiO2 impregnated with CsPbBr3 NCs, 2 mg AOT and 2
mg polystyrene was dispersed in 200 µL toluene and sonicated. This mixture was drop-cast onto freshly
hydrophobized substrates and allowed to dry naturally.
Synthesis of colloidal CsPbBr3 NCs
Colloidal CsPbBr3 NCs were prepared as described elsewhere.4
Estimation of the MAPbI3 solubility in organic solvents
MAPbI3 solubility was measured near the reaction temperature, 100 °C, in order to check the possible
effect of perovskite solubility on the growth of the NCs (such a solubility evaluation at 120 °C is
complicated due to iodide oxidation to iodine on a similar time scale as that of the experiment). In order
to avoid potential problems with impurities or stoichiometry uncertainty, we have used only single
crystals which have been prepared as reported elsewhere.5 Small single crystals were added to 0.2 mL of
the solvent at 100 °C until no more could be dissolved. Then 50 µL of the obtained saturated solution was
drop-cast on a glass substrate, dried, and weighed.
Characterization techniques
Scanning Transmission Electron Microscopy (STEM)
STEM investigations were performed on the aberration-corrected HD-2700CS (Hitachi; cold-field
emitter), operated at an acceleration potential of 200 kV. A probe corrector (CEOS) is incorporated in the
microscope column between the condenser lens and the probe-forming objective lens providing excellent
high-resolution capability (minimum beam diameter ~0.1 nm). Images were recorded using a high-angle
annular dark field (HAADF) detector leading to atomic number (Z) contrast. Furthermore, a secondary
electron (SE) detector was installed inside the column of the HD-2700CS microscope above the sample
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allowing studies of sample morphology. The images (1024 x 1024 pixels) were recorded with frame times
of 20 s. Energy-dispersive X-ray spectra (EDXS) of selected areas were recorded with an EDAX detector
(Gemini system, EDAX).
Powder X-ray diffraction (XRD)
Powder XRD was performed using a STOE STADI P diffractometer, operating in transmission mode. A
germanium monochromator, Cu Kα1 irradiation and a silicon strip detector (Dectris Mythen) were used.
Photoluminescence (PL) spectroscopy
A Fluoromax-4 Horiba spectrofluorimeter equipped with a PMT detector was used to acquire the steady
state PL spectra of the silica microparticles impregnated with perovskite NCs. Samples were sandwiched
between 2 cover slips. All spectra were corrected for the detector sensitivity.
Photoluminescence quantum yield (PL QY) measurements
The absolute value of the PL QY was measured by methods similar to those described elsewhere.6 Use of
an integrating sphere with a short-pass filter allowed us to simultaneously measure absorbance corrected
to reflectance and scattering losses. As the excitation source, a CW Laser Diode Module was used at a
wavelength of 405 nm with a power of 0.3 W modulated at 30 Hz. For spatial averaging, an integrating
sphere (IS200-4, Thorlabs) was applied. The absorbed and emitted light was measured using short-pass
and long-pass filters (FES450 and FEL450, Thorlabs). This light was measured by a broadband (0.1-20
µm) UM9B-BL-DA pyroelectric photodetector (Gentec-EO). The modulated signal from the detector was
recovered by a lock-in amplifier (SR 850, Stanford Research). The ratio between the emitted and
absorbed light gives an energy yield. This value was then transformed into the PL QY taking into account
the difference in photon energies for the laser and PL band (the PL band was used as the average energy).
The PL QY was corrected by transmission of applied edge-pass filters.
Time-resolved photoluminescence (TR PL) spectroscopy
PL lifetime measurements were performed using a time-correlated single photon counting (TCSPC)
setup, equipped with SPC-130-EM counting module (Becker & Hickl GmbH) and an IDQ-ID-100-20ULN avalanche photodiode (Quantique) for recording the decay traces. The emission of the perovskite
NCs was excited by a BDL-488-SMN laser (Becker & Hickl) with a pulse duration of 50 ps and a
wavelength of 488 nm, equivalent to a CW power of ~0.5 mW, externally triggered at a 1 MHz repetition
rate or with 10 ps pulses of frequency-tripled (355 nm) irradiation by a Duetto laser (Time-Bandwidth)
triggered at 200 kHz. The intensity of the pumping laser beam was varied over 2 orders of magnitude by a
neutral density optical attenuator (NDC-100C-2M, Thorlabs). PL emission from the samples passed
through a long-pass optical filter with an edge at 500 nm in order to reject the excitation laser line. The
PL emission was attenuated with optical density filters in order to prevent saturation effects at the
avalanche detector.
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Figure S1. Scheme showing the synthesis procedure when a large (>50 mg) or small (<50 mg) amount of
mesoporous silica is impregnated with lead halide perovskites.
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Figure S2. High-angle annular dark field scanning transmission electron microscopy (HAADF STEM)
image of 4nm-SiO2 impregnated with CsPbI3, showing a large CsPbI3 crystal impurity and energydispersive X-ray spectroscopy (EDXS) of the corresponding area (inset).
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Figure S3. HAADF STEM image of 2.5nm-SiO2 impregnated with CsPbI3. Bright spots represent pores
filled with CsPbI3 NCs.
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Figure S4. Photoluminescence (PL) wavelength dependence on solvent surface tension for MAPbI3 NCs
synthesized in 7nn-SiO2. GBL – gamma-butyrolactone, DMF – N,N-dimethylformamide, MFA – Nmethylformamide, PC – propylene carbonate, DMSO – dimethylsulfoxide, EGS – glycol sulfite, FA –
formamide.
Figure S5. PL wavelength dependence on MAPbI3 solubility in a given solvent for MAPbI3 NCs
synthesized in 7nn-SiO2. GBL – gamma-butyrolactone, DMF – N,N-dimethylformamide, MFA – Nmethylformamide, PC – propylene carbonate, DMSO – dimethylsulfoxide, EGS – glycol sulfite, FA –
formamide.
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Figure S6. Time-resolved (TR) PL traces of colloidal CsPbBr3 NCs in solution. The arrow denotes the
direction of increasing fluency intensity.
Figure S7. Stability of the PL decay rate for CsPbBr3 NCs synthesized in 7nm-SiO2. Between the
collection of the two traces, the NCs were exposed to pulsed irradiation for 30 minutes, which
corresponds to 1010 laser shots with an intensity of 2 µJ/cm2.
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Figure S8. TEM image of 4nm-SiO2 microparticles (as received).
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