Supplementary Information
Role of the Crystallization Substrate on the Photoluminescence
Properties of Organo-Lead mixed Halides Perovskites
Michele De Bastiani1,2†, Valerio D’Innocenzo1,3†, Samuel D. Stranks4, Henry J. Snaith4 and
Annamaria Petrozza1,*.
1
Center for Nano Science and Technology @Polimi, Istituto Italiano di Tecnologia, via Giovanni Pascoli
70/3, 20133, Milan, Italy
2
Dipartimento di Scienze Chimiche, Università degli Studi di Padova, via Marzolo 1, 35131 Padova, Italy.
3
Dipartimento di Fisica, Politecnico di Milano, Piazza L. da Vinci, 32, 20133 Milano, Italy.
4
University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, United Kingdom
*
Correspondence to: annamaria.petrozza@iit.it;
†
these authors equally contributed
Figure S1. Structure of perovksite fibrils growth on ZnO scaffold made of 20 nm diameter
nanoparticles. Scale bar: 1µm.
Table S1. SFE has been determined by Contact Angle (CA) measurements using the OwensWendt-Rabel-Kaelble (OWRK) model. This model splits the SFE in two part: the dispersion forces
on one hand and all the polar components on the other, in the approximation of negligible spreading
pressure. This model uses a linear equation of different measures of CA obtained from different
solvents whose both polar and disperse components of surface tension are well known. The slope
and the intercept of the linear fitting are the square roots of the polar and disperse components of
the SFE of the material under study.
The SFE of the different ZnO scaffolds are reported in Table S1 together with the SFE of the Meso
Al2O3 scaffold. The liquids used for the CA measurements are water, ethylene glicole and mixing of
both in different ratios.
np size
SFE
Polar
Disperse
ZnO 70 nm
48.38
28.8
19.6
ZnO 50 nm
34.32
10.2
24.13
ZnO 20 nm
25.9
17.2
8.63
Al2O3 50 nm
63.75
58.13
5.62
Figure S2. Photolominescence emission spectra of CH3NH3PbI3-xClx deposited either on 70 nm
(red circles), 50 nm (green circles), 20 nm (blue circles) ZnO nanoparticles’ mesoporous substrates
or on 50 nm Al2O3 nanoparticles’ mesoporous substrate. The spectra collected from the 50 nm Zn
np, 20 nm ZnO np and 50 nm Al2O3 np substrates were multiplied by a factor 5, 20 and 30
respectively. Excitation wavelength λ = 480 nm.
Figure S3. Photoluminecence (PL) decay of CH3NH3PbI3-xClx deposited on ZnO mesoporous
scaffold substrates obtained from 70 nm nanoparticles exciting the capping layer side is compared
to PL decay of CH3NH3PbI3-xClx deposited on compact TiO2. Moreover, PL decay of CH3NH3PbI3xClx
deposited on ZnO mesoporous scaffold substrates obtained from 20 nm exciting from the
substrate side is compared to PL decay of CH3NH3PbI3-xClx deposited on TiO2 mesoporous scaffold
substrates obtained also from 20 nm nanoparticles.
Figure S4. Cross-sectional SEM of Structure of perovksite polycrystalline film grown in a ZnO
scaffold made of 20 nm diameter nanoparticles. Scale bar: 200 nm.
Methods
Sample preparation. The precursor solution of perovskite has been prepared following the well
established method reported in literature. Methylamine (CH3NH2) solution 33 wt% in absolute
ethanol was reacted with hydroiodic acid (HI) 57 wt % in water with excess methylamine under
nitrogen atmosphere in ethanol at room temperature. Crystallization of methylammonium iodide
(CH3NH3I) was achieved using a rotary evaporator; a white colored powder was formed indicating
successful crystallization.
Methylammonium iodide (CH3NH3I) and lead (II) chloride (PbCl2) was dissolved in anhydrous
N,N-Dimethylformamide at a 3:1 molar ratio of CH3NH3I to PbCl2, to produce a mixed halide
perovskite precursor solution. The solution has been deposited on different samples by spin-coating
followed by an heating treatment of 1 minute at 100 °C.
ZnO nanoparticles scaffolds have been prepared using different commercial solutions containing
20, 50 or 70 nm diameter nanoparticles purchased from Alfa-Aesar and deposited by spin coating
on pre cleaned glass substrate. A thermal annealing at 130 °C for 1h 30 min has been processed in
order to remove the solvents inside the scaffolds.
Alumina sample has been prepared diluting commercial solution (purchased from Sigma
Aldrich)1:2 in IPA and spin coated on glass substrate followed by a thermal treatment at 150° for
1h.
SEM. SEM pictures have been collected using an high vacuum tungsten filament commercial Jeol
6010-LV, with a working bias of 15 kV.
Contact Angle. SFE has been determined using OWRK model extrapolated from Contact Angle
measurements (Dataphysic OCA) using water, ethylene glycol and a mixture of them (80% 50%
20% water dilution respectively) for each sample.
UV-Vis Absorption. Absorption measurements were performed using a spectrophotometer (Perkin
Elmer Lambda 1050) together with an integrating sphere module. The total transmittance (T%) and
total reflectance (R%) were . Subsequently the Optical Density was evaluated according to the
subsequent equation:
𝐼𝑇 = (𝐼0 − 𝐼𝑅 )10−𝑂𝐷∗𝑑
where IT, I0 and IR are the transmitted, impinging and reflected light respectively, while d is the
sample thickness.
We extracted an approximated penetration depth at λ = 480 nm inverting the beer-lambert law (
𝐼𝑇 = (𝐼0 − 𝐼𝑅 )𝑒 −𝛼∗𝑑 ) in order to obtain the absorption coefficient α. The penetration depth τ is then
the inverse of the absorption coefficient at the chosen wavelength, according to the following:
𝜏=
1
𝐼𝑇 (𝜆)
= − ln (
)
𝛼(𝜆)
(𝐼0 (𝜆) − 𝐼𝑅 (𝜆))
Photoluminescence Spectra. The spectra were collected using a spectrofluorimeter (Horiba Jobin
Yvon), exciting the sample with a monochromated Xenon lamp source (central wavelength λexc =
480 nm). On the collection line a long pass filter cutting at 695 nm was used in order to filter the
excitation light.
Time Resolved Photoluminescence. Time-resolved fluorescence measurements were performed
using a femtosecond laser source and streak camera detection system (Hamamatsu C5680). An
unamplified Ti:Sapphire laser (Coherent Chameleon Ultra II) operating at 80MHz was tuned to
provide pulses with central wavelengths of 960 nm, energies of ~50 nJ, and temporal and spectral
bandwidths of ~140fs and ~5 nm, respectively. A b-barium borate crystal was used for type I
phase-matched second harmonic generation, leading to pulses with central wavelengths of 480 nm.
Measurements used a linear voltage sweep module with 1 MHz repetition rate excitation, achieved
through the use of an acousto-optical modulating pulse picker (APE Pulse Select), yielding a
maximum temporal resolution of ~50 ps.