Novel synthesis process of methyl ammonium bromide and effect of particle size on structural, optical and thermodynamic behavior of CH3NH3PbBr3 organometallic perovskite light harvester

Article abstract of DOI:10.1016/j.jallcom.2018.01.355

A simple, cost effective production approach having high stability is pertinent to any organic-inorganic perovskite solar cells. The main focus of the present work has been to formulate and estimate the stability of CH₃NH₃PbBr₃ micro-cubes and nanoparticles based perovskite solar cells. Firstly, novel synthesis route has been introduced for the preparation of CH₃NH₃Br (MABr) electrolyte salt which is less time consuming, as well as cost effective than pristine methods. We also reported a facile single solution process to grow large scale CH₃NH₃PbBr₃ (MAPbBr₃) hybrid perovskite micro-cubes and nano-particles. The effect of different size (micro-cube & nano-particles) of perovskite material on structural, optical, thermal stability and degradation kinetics has been examined. X-ray diffraction spectra of MAPbBr₃ perovskite reflect high crystallinity and cubic structure of the material at the room temperature. The surface morphology of micro-cubes and nano-particle MAPbBr₃ has been obtained from scanning electron microscope (SEM). Broad absorption spectrum has found in the visible region with high absorption coefficient and PL spectra show the green emission which is in good agreement with the optical band gap of MAPbBr₃ from absorption measurements. With decreasing the size of perovskite materials, band gap and emission spectra tuned towards the blue region. The simultaneous thermal analysis (STA) study indicates towards the more thermal stability of micro-cubes structures than nanoparticles material while the change in enthalpy (ΔH) and specific heat capacity (ΔCp) of nano particle have increased by reducing the particle size of perovskite due to modification of endothermic peaks.

Full text of DOI:10.1016/j.jallcom.2018.01.355

Accepted Manuscript
Novel synthesis process of methyl ammonium bromide and effect of particle size on
structural, optical and thermodynamic behavior of CH NH PbBr organometallic
3
3
3
perovskite light harvester
Rajan Kumar Singh, Ranveer Kumar, Amit Kumar, Neha Jain, Rajiv Kr. Singh, Jai
Singh
PII:
S0925-8388(18)30373-6
10.1016/j.jallcom.2018.01.355
JALCOM 44819
DOI:
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 29 August 2017
Revised Date: 12 January 2018
Accepted Date: 27 January 2018
Please cite this article as: R.K. Singh, R. Kumar, A. Kumar, N. Jain, R.K. Singh, J. Singh, Novel
synthesis process of methyl ammonium bromide and effect of particle size on structural, optical and
thermodynamic behavior of CH NH PbBr organometallic perovskite light harvester, Journal of Alloys
3
3
3
and Compounds (2018), doi: 10.1016/j.jallcom.2018.01.355.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

ACCEPTED MANUSCRIPT
Novel synthesis process of methyl ammonium bromide and effect of particle size on structural,
optical and thermodynamic behavior of CH3NH3PbBr3 organometallic perovskite light harvester
Rajan Kumar Singh1, Ranveer Kumar1*,Amit Kumar2, Neha Jain1, Rajiv Kr. Singh2, and Jai Singh1
1Department of Physics, Dr. Harisingh Gour Central University, Sagar – 470003, M. P. India
2Advanced Material & Devices Division, CSIR, National Physical Laboratory, New Delhi – India
* Corresponding author:ranveerssi@yahoo.com
Abstract:
A simple, cost effective production approach having high stability is pertinent to any organic-inorganic
perovskite solar cells. The main focus of the present work has been to formulate and estimate the stability
of CH3NH3PbBr3 micro-cubes and nanoparticles based perovskite solar cells. Firstly, novel synthesis route
has been introduced for the preparation of CH3NH3Br (MABr) electrolyte salt which is less time
consuming, as well as cost effective than pristine methods. We also reported a facile single solution process
to grow large scale CH3NH3PbBr3 (MAPbBr3) hybrid perovskite micro-cubes and nano-particles. The
effect of different size (micro-cube & nano-particles) of perovskite material on structural, optical, thermal
stability and degradation kinetics has been examined. X-ray diffraction spectra of MAPbBr3 perovskite
reflect high crystallinity and cubic structure of the material at the room temperature. The surface
morphology of micro-cubes and nano-particle MAPbBr3 has been obtained from scanning electron
microscope (SEM). Broad absorption spectrum has found in the visible region with high absorption
coefficient and PL spectra show the green emission which is in good agreement with the optical band gap
of MAPbBr3 from absorption measurements. With decreasing the size of perovskite materials, band gap
and emission spectra tuned towards the blue region. The simultaneous thermal analysis (STA) study
indicates towards the more thermal stability of micro-cubes structures than nanoparticles material while the
change in enthalpy (∆H) and specific heat capacity (∆Cp) of nano particle have increased by reducing the
particle size of perovskite due to modification of endothermic peaks.
1

ACCEPTED MANUSCRIPT
Keywords: Perovskite, Chemical Synthesis, Microstructure, Nanostructure, Optical Properties, Enthalp
Graphical Abstract:
Highlights:
ꢀ Solution processed methyl ammonium lead bromide was highly cubic crystalline at room
temperature.
ꢀ MAPbBr3, micro-cubes was more thermally stable than nano-particles.
ꢀ High absorbance and luminescence property show the light harvesting nature of the materials.
ꢀ Change in enthalpy and specific heat capacity of perovskite particle was increased by reducing the
particle size.

ACCEPTED MANUSCRIPT
1. Introduction
Recent development in nanoscience and nanotechnology has not only brought potential building block for
nanoelectronics, optoelectronics, but also offer a breakthrough in photovoltaic performance in devices1,
2.Hybrid perovskites have attracted attention in recent years due to their excellent potential as light
harvesting material for application in solar cells and light emitting diodes3,4. Furthermore, the extraordinary
properties of color tunability/optical absorption, high absorption coefficient, excellentphotoluminescence
efficiency and low non-radiative recombination rates, extends their applications into various optoelectronic
devices such as solar cell, light emitting diodes, photo detectors, light emitting cables and optical memory
etc5-9.
In 2009 Miyasaka group have used OIHP absorber layer for photovoltaic devices first time with 3.8% power
conversion efficiency (PCE)10. After this discovery many groups have fabricated different types of OIHP
materials tuning with the A, B and X sites of the perovskite materials11-15. Recently, national renewable
energy laboratory (NREL) has certified the maximum 22.7% PCE of the perovskite solar cell16. Weber et al.
successfully studied the various composition of the 3-dimensional (3-D) CH3NH3PbX3 perovskite material
by tuning their crystal structure and phases17,18. They have reported that MAPbBr3 (MA=CH3NH3)
perovskite material shows the cubic phase I (Pm3m), tetragonal phase II (I4mcm) and orthorhombic phase
IV (Pnma, z = 4) for different temperature.OIHP compounds have wide direct band gap and this direct band
gap of the materials can be tuned by either changing the Agroup,B group or the X group. MAPbBr3 material
is a p-type semiconductor with a direct band gap of 1.93-2.3eV that corresponds to an absorption onset of
≤550nm19,20. This excellent optical property of the material stands it in the first row of the light harvesting
materials. Optical properties of perovskite material very interestingly changes with particle size of the
material. Effect of particle size recently have been reported, with reducing size of particle, blue shifting in
absorption edge and increase in photoluminescence obtained5,6. Gao et al has synthesized CH3NH3PbBr3
perovskite of the micro-plates and micro-rods. They have studied the three-photon process in single crystal
3

ACCEPTED MANUSCRIPT
CH3NH3PbBr3 microstructures9. They have observed a three-photon excited whispering-gallery-mode laser
experimentally in both of perovskite micro-plate and micro-rod micro-structures. Wenger et al has been
synthesized single crystals of methylammonium lead bromide (CH3NH PbBr3) using the rapid growth
3
route5. The as synthesized material has been characterised via optical absorption and photoluminescence and
show that the optical properties have found almost the same to that of polycrystalline CH3NH3PbBr3 films.
Additionally, absorption coefficients of the OIHP materials are greater than traditional
semiconducting materials such as silicon, gallium arsenide, N719 conventional dye molecules etc21. The
photoluminescence property of MAPbBr3 perovskite material is of great interest due to its emissive
property. Perez-Prieo group first achieved this type of perovskite nanoparticles with a bright
photoluminescence (PL) peak at around 530nm wavelength22. Thermal properties of different hybrid
perovskite materials containing pure halide and mixed halide have been reported by different research
groups23. Liu et al. reported that by changing the halide composition of perovskite materials, thermal
stability of materials changes due to different decomposition behavior of precursors. Mixed halide
perovskites are more thermally stable than pure halide compounds. That’s why for thin filmpreparation,
mixed halide perovskite films are required slightly higher temperature and more time24. In our recent work,
we also found that, precursor ratio of the compound play an important roal for thermal stability and
crystallization25. For pure halide perovskite equal molar ratio was found perfect but in case of mixed halide,
precursor ratio can be tuned by suitable stability and capability of structure of the materials. As revealed
from the above literature, elaborative work has been carried out on the effect on thermal behavior of
different synthesis rout, precursor ratio and halide effect on perovskite materials but joint studies on the
effect of particle size on the thermal and optical properties have not been fully available.
Here, we have synthesized the MABr and MAPbBr3 micro-cubes and nano-particles by low cost,
solution method without using any legends, additives or purifying agents. We have also investigated the
thermal behavior of micro-cubes and nano-particles of prepared perovskite material in ambient conditions.
4

ACCEPTED MANUSCRIPT
To prove, MAPbBr3 as a light harvesting material, we have studied the UV-Visible absorption and
photoluminescence study with the help of different spectroscopy techniques.Recently,optical and electrical
properties of quantum dots, nano-particles and crystalline MAPbBr3 perovskite material have been reported
buttheir thermalbehavior is still not reported26. The investigation of the effect of particle size of hybrid
perovskite on optical and thermal properties will helps to tuning of band gap and thermodynamics behavior
of the material.
2. Experimental Section
2.1 Chemicals
Methylamine (40% in methanol, Sigma Aldrich, USA), hydrobromic acid (53% in water) (Merck,
India), Lead bromide (PbBr2) (99.99% Sigma Aldrich, USA), N, N’- dimethyleformamide (DMF) (99.8%
Sigma Aldrich, USA).
2.2 Synthesis of MAPbBr3
For the preparation of CH3NH3Br, methylamine and hydrobromic acid are mixed into 250ml of three
necked round bottom flask with continuous stirring at 0°C for 2hrs, homogeneous transparent CH3NH3Br
solution obtained. CH3NH3Br solution isevaporated at 60°C in vacuum oven for 24hrs. White precipitate is
obtained after 24hrs vacuum heating and this is grinded with agate mortar pestle and stored in the dry place.
The schematic representation of synthesis process is shown in Fig. (S1).In this synthesis rout, there is no
need of purification with diethyl ether for long time. Diethyl ether is a hazarded chemical and rapidly
vaporized at room temperature. This is used for the purification of electrolyte salt if yellowish MABr is
obtained. But in our care, we obtained white and crystalline salt. Therefore there is no need of further
purification of material.
For the synthesis of MAPbBr3, prepared MABr and commercial PbBr2 powder are mixed with 1:1
molar ratio in DMF organic solvent. After continuous stirring at 60°C over night, transparent solution is
5

ACCEPTED MANUSCRIPT
obtained. This perovskite precursor can be stored for thin film study in glove box. To obtain powder form of
perovskite material, precursor is evaporated at 120°C for half an hour in the ambient condition in the Petri
dish which gives the cubic orange crystals. To obtain the nano-particle ofMAPbBr3, large cubic perovskite
crystalshavebeen grinded with agate mortar pestle for 30minutesand store in glove box or vacuum
desiccators.
For micro-cube characterization, thin film formed on indium doped tin oxide (ITO) glass substrate. Before
the thin perovskite thin film fabrication, ITO glass substrate was sonicated with DI water for 15 minutes and
cleaned with soap solution. After soap solution cleaning, substrate was again sonicated with DI water for
15minutes and cleans with acetone & isopropenol treatment respectively. Then prepared, MAPbBr3
perovskite precursor was spin coated on the substrate at a rotation speed of 3000rpm for 30seconds and a
uniformed orange film was obtained by annealing at 100˚C for 10minutes.Synthesis Process of MAPbBr3,
micro-particles and nano-particles are summarized below:
2.3 Characterizations:
Crystal structure was examined by Bruker, Model D8 Discover X-ray Diffractometer using a Cu X-
ray tube at voltage of 35kV and 35mA with a step size of 0.02 in ambient conditions.Crystalline phase was
6

ACCEPTED MANUSCRIPT
also confirmed by high resolution transmission electron microscope (HRTEM) [TEMTECNAI G2] and by
corresponding selected area electron beam diffraction. Micrograph of materials was captured by scanning
electron microscope FESEM, Model- Quanta 200 FEI. Ultraviolet- visible (UV-Vis) absorption and
photoluminescence spectrum was measured by UV-2401PC UV-Visrecording spectrometer and
photoluminescence spectrometer respectively.For thermal behavior analysis (TG/DTG, DSC), simultaneous
thermal analyzer (NETZCH STA 449 F1 Jupiter)was used. The samples were heated from room temperature
to 700˚C with at a constant rate of 10˚C/min under a nitrogen flow of 60ml/min.
3. Results and Discussion:
Fig.(1a) XRD patterns of MAPbBr3 micro-cubes and nano-particles respectively, (1b) typical cubic crystal
structure of MAPbBr3 by VesTA- software and (1c) Plot for sinθ/λ Vs β cosθ/λ of MAPbBr3 micro cubes
and nano-particles
Figure 1(a) shows the X-ray diffraction pattern of the MAPbBr3 nano-particles and micro-cubes in the
ambient conditions, which indicate the cubic phase of the perovskite material22. The typical peaks at 2θ with
7

ACCEPTED MANUSCRIPT
14.95, 21.1, 30.07, 33.69, 37.13, 43.03, 45.91 and 48.55 corresponding to (100), (110), (111), (200), (211),
(220), (300), (310), (222), (320) and (321) planes, which indicate the cubic phase of the perovskite
material27. In addition sharp XRD peaks also demonstrate the phase purity of the cubic MAPbBr3 perovskite
structure and with reducing the particle size of perovskite material, broadness of XRD peaks increases and
intensity decreases. The polyhedral representation of cubic MAPbBr3 is illustrated by VesTA software as
shown in figure 1(b).
From crystal structure, it can be observed that each MA (CH3NH3) ion is present on corner of crystal
and Pb is present on center of crystal unit. Each bromine is bonded to Pb ion and present on surface of cube.
The change in particle size causes change in alignment which affects strain into crystal. In present report,
strain is calculated by Williamson Hall plot28. The equation from which strain is calculated is
= +
Where, θ is Bragg’s diffraction angles, β is FWHM (full width at half maximum), D is the effective
crystalline site and ε is the micro-strain.
Figure 2: Micrographs of Perovskite materials, (a) TEM image (b) Selected area diffraction pattern and (c)
HRTEM image ofnano-particles of the MAPbBr3 Perovskite Material
Figure 1c shows plot between sinθ/λ and β cosθ/λ which estimate micro-strain by slope of graph. It is
0.00511 and 0.01182 for micro and nano-particles. Since micro-strain is increases which decreasing particle
8

ACCEPTED MANUSCRIPT
size because of decrease in crystallanity. Fig 2a shows the TEM image of nano-particles of MAPbBr3which
was prepared by grinding the micro cubes and deposited on carbon coated copper grid for the TEM
analysis.High resolution TEM (HRTEM) image of nano -particle MAPbBr3 hybrid perovskite had shown in
fig 2c with lattice fringes spaced by 3.14 and 2.14Å in different regions. This fringe spacing corresponds to
the (310) and (211) plane spacing, respectively for the cubic perovskite material. A selected area diffraction
patterns (SADP) of the MAPbBr3 (Fig. 2(b) also confirms the (310) and (211) plane present in the perovskite
material that indicates the cubic phase of the material at room temperature.
Fig 3,Physical appearance and SEM Micrographs of Perovskite materials, (a) digital image of as prepared
perovskite ink (b) digital image of dried MAPbBr3 perovskite at 120˚C (c) digital image of separated cubic
crystals from 3b (d) SEM image of cubic crystals (inset figure, single cubic microstructure ) &(e)
nanoparticles of the MAPbBr3 Perovskite Material
The physical appearance of MAPbBr3 perovskite precursor solution was transparent as shown in fig
3a. In general this perovskite precursor is used for thin film preparation for different device fabrications.
9

ACCEPTED MANUSCRIPT
Perovskite precursor was dried at 120˚C which gave orange cubes crystal growth of the material (fig 3b) and
these perovskite cubes were separated by sharp twizer (as shown in fig 3c). Further surface morphology of
MAPbBr3 had examined by SEM analysis. The SEM images in fig 3(d) and (e) shows the overall
morphology of the MAPbBr3 cube crystals and nano-particles. As prepared MAPbBr3 perovskite was large
cubes of orange color as shown in digital image in fig 3 b & c and on the other hand when the same
precursor solution was deposited on ITO substrate for thin film formation of MAPbBr3, also confirmed the
micro cubes like structure (as shown in figure 3d) of the perovskite material22. In addition cubic morphology
of MAPbBr3 perovskite interestingly converted into spherical particle due to reducing the particle size of the
materials which shown in figure 3e and TEM image of fig 2a also confirmed the nano-particle formation of
the perovskite materials by grinding of micro cubes.
For the UV - Visible absorption and photoluminescence study, we prepare a thin film of the
perovskite material deposited upon ITOsubstrate for bulk perovskite and nanopowder perovskite dispersed
in toluene. (Fig. 4) shows the strong and broad absorption spectra is obtained in the visible range between
400 to 700nm which indicates, the light harvesting property of MAPbBr3 perovskite material. Additionally,
nanoparticleMAPbBr3 perovskite absorption onset occurs at nearly 521nm, consistent with previous reported
works29, 30.With decreasing the particle size of the same perovskite, absorption onset of UV-visible spectra is
shifted towards blue region. The band gap of the material is calculated by using formula, Eg = 1237.5/
λ,where Eg, is band gap of the material and λ is the wavelength of absorption onset curve. The band gap of
micro cubes and nano-particles MAPbBr3 is found, 2.15 and 2.22 eV, respectively31. Here nanoparticles of
perovskite has slightly higher band gap than bulk perovskite because in bulk materials ground state and first
excited state levels are very broadened and this broadening leads to narrowing of the band gap. On the other
hand broadening in nano materials is less than bulk materials which causes the more energy band gap and
blue shift from bulk to nanomaterials32.
10

ACCEPTED MANUSCRIPT
Figure 4:(a) UV-Visible absorption spectraof MAPbBr3micro cubes and nano-particles, (b)
Photoluminescence spectra& inset CIE spectrum with 390nm excitation wavelengths of MAPbBr3 micro-
cubes and nano-particles.
Figure (4b) shows the photoluminescence (PL) emissionspectra andCIE spectrum of micro cubes and
nano-particle of MAPbBr3 perovskite. Similar to UV-Visible onset absorption spectra, PL emission of
nanoparticles perovskite indicates blue shift from bulk to nanoparticle which is in good agreement with
absorption study of the material. Additionally, CIE spectrum is also confirmed the blue shift with bulk to
nanomaterials.From photoluminescence and CIE spectra, it hasalso confirmed that MAPbBr3 material has
excellent PL performance and high color purity because no sub spectra or sub-band gap emission is present
in PL and CIE spectra33. We, we have also found that, the excitation and emission bands of MAPbBr3
organic inorganic halide perovskite offer a larger stokes shift than the typical natural and organic dyes34, 35
.
Thermal stability behavior (TG/DTG) of MAPbBr3 micro cubes and nano particles are shown in
figure 5 (a & b). TGA analysis of both particles show, thermal stability of materials up to 200˚C, then it
starts losing weight. The extension starting decomposition temperature was determined to be 182°C and the
mass loss process ended at around 607°C for micro-particles and 588°C for nano-particles. In 1st step, there
11

ACCEPTED MANUSCRIPT
was 18.11% mass loss occurred between 182-300°C due to the decomposition of HBr and next 33.25%mass
loss wasoccurred due to decomposition of organic part methylamine up to 400°C. These results also indicate
amine group is bounded into the hybrid perovskite matrix more tightly than HBr23, 36. But from TGA study
of MABr, it is noted that this type of decomposition, by sequential loss of HBr followed by the amine group,
has not detected in MABr organic electrolyte salt. MABr was decomposed in one step between 250- 350˚C
with sublimation temperature of 250˚C (Fig. S2). this sublimation of mass loss in one step shows the highly
purity of MABr. In 3rd stage of mass decomposition 48.13% mass loss occurred between 587-603˚C due to
decomposition of PbBr2 within these temperature region (Fig S3).First differential thermogrametry analysis
of MAPbBr3, clarify that this perovskite material was decomposed into three steps in which maximum mass
loss occurred at 588˚C and minimum mass loss occurred at 278˚C (Fig 5b TGA).
Fig 5 Thermal behavior of TGA (green) and DTG (violet) of (a) MAPbBr3 micro cubes and (b) MAPbBr3
nano-powder
12

ACCEPTED MANUSCRIPT
In addition, micro-cubes we have also found that there are differences in thermal stability of
MAPbBr3 nanoparticles and cubic crystals. The trend in cubic perovskite crystals was quite similar but the
temperature of decomposition and first derivative peaks shifted towards lower values for first degradation
step and higher value (360 and 607˚C) for next two decomposition steps suggesting a slightly higher
stability of the perovskite micro cubes as shown in fig. (5). From TG/DTG study of both micro and nano-
particle of perovskite, it is clear that thermal stability of material also depends on particle size and thermal
stability decreases by reducing the particle size of the materials because micro-crystals is formed by bulk
amount of materials and it is required more heat for breaking the bonding of materials while in nano-
particles there are more surface area available and required less heat to break the bonding in the materials.
Thus in both of the cases, perovskite decomposed into three steps which can be understood by given
chemical reaction:
CH3NH3PbBr3 ↔ HBr + CH3NH2 + PbBr2
Thermal degradation parameters of TG/DTG of both micro cubes and nano particle MAPbBr3 perovskite are
summarized in table 1.
Differential scanning Calorimetry (DSC) analysis of the both types of MAPbBr3 perovskites are shown in
figure 6 (a and b). The DSC was used to investigate the melting behavior and nature
(endothermic/exothermic) of different particle sized perovskite material. DSC graphs show the endothermic
nature of both micro and nano particle of perovskites but due to variation of size of MAPbBr3, endothermic
peaks are modified. With reducing the particle size, the sharpness and area of endothermic peaks are
enhanced. The increased peak area of the endotherm of MAPbBr3 nanoparticle in DSC may be due to the
fine size and the greater the rate of diffusion of Nanomaterials. These properties causing the reaction to
occur over a much shorter endothermic reactions for the hybrid perovskite materials. Enthalpy change of the
micro crystals and nanoparticles of perovskite also have been calculated by DSC analysis (figure 5a and b).
Enthalpy change (∆H) is the amount of heat released or absorbed at constant pressure. Nature of ∆H depends
13

ACCEPTED MANUSCRIPT
upon the exothermic and endothermic behavior of the materials. For the endothermic reactions, ∆H is
always positive while for exothermic reactions, it is negative37. As we discussed above section that different
particle size of MAPbBr3 perovskites are endothermic in nature with different peak area.
Table 1: TG/DTG parameters of cubic micro crystals and nano particle of MAPbBr3 perovskite
Decomposition Onset
Mass loss in different steps in
TGA peaks for Residual
Materials
Steps
&
%
diff. steps (˚C)
Mass
Ended
point
(˚C)
(B/wtem.)
200-
300-
400-
300˚C
400˚C
620˚C
61.84%
Cubic
3
3
170
13.14% 21.52%
268 360 607
0.15%
0.51%
Micro
Crystals
Nano
& 607
182
18.11% 33.25%
48.13%
278 326 588
Particle
& 588
∆H is directly proportional to the peak area of the endothermic reactions. That’s why for nano
particles perovskite, the value of ∆H is also increased due to increasing the area of endothermic peak. From
figure 6, it was concluded that, for larger particle has three small endothermic peaks with ∆H of 5.218,
27.38 & 9.55 J/g up to 300°C while in nanoparticles perovskite two instance endothermic peaks are
absorbed with ∆H of 26.62 & 111.3J/g. Additionally two large endothermic peaks were detected near 358 &
610°C (∆H = 265 & 155.1J/g) in macro size perovskite and in nano particle these peaks are slightly shifted
towards lower temperature at 350 & 593°C (∆H = 349 & 187J/g). Different thermodynamic kinetics (Nature
of materials, ∆H and Specific heat capacity i.e. ∆Cp) of DSC of large and nanoparticles perovskite is also
14

ACCEPTED MANUSCRIPT
summarizes in table 2. For overall system, enthalpy change for macro particle and Nanomaterials were
found 462.25J/g and 574.2J/g respectively.
Figure 6: DSC curve with different enthalpy change of (a) micro cubes& (b) nano particle of MAPbBr3
Specific heat capacity (∆Cp) of the different particle sized perovskite materials were anlysized with the help
of DSC curve as given in figure 7 a & b. The specific heat capacity is the amount of heat needed to increase
the temperature of one gram of substance by one degree. It can be calculated by ∆Cp = ∆H / ∆T, here ∆T is
the temperature difference between two endothermic peaks. The heat transfer for different state of matter
(solid, liquid & gas) can be stored in various forms of energy such as potential (vibrational mode),
translational & rotational kinetic energy. In solid, thermal energy is stored in only vibrational mode and this
storage capacity can be measured by calculating ∆Cp. From analysis of ∆Cp of both particles of MAPbBr3, it
was concluded that nanoparticles perovskite has mare specific heat capacity compared to the larger
perovskite crystals. ∆Cp for different endothermic peaks of the particles also summarized in table 2.
15

ACCEPTED MANUSCRIPT
Table 2: DSC kinetics of cubic macro and nanoparticles MAPbBr3 perovskite
Nature of
Materials
(Endo/Exo.)
No. of
Positions of
∆H
∆Cp
MAPbBr3 Perovskite
Materials
Endothermic Endothermic
(J/g)
(J/g.K)
peaks
peaks (˚C)
Cubic Micro Crystals
Endothermic
5
4
202.50
255.20
297.60
358.80
610.30
204.80
280.70
350.00
593.20
5.22
27.38
9.55
0.76
0.81
1.01
6.14
3.25
3.69
4.80
7.41
3.25
265.00
155.10
28.62
111.30
349.00
187.70
Nano Particle
Endothermic
Fig 7: DSC curve with different Specific Heat capacity (∆Cp) of micro cubes (green line) & (b) nano particle
(orange line) of MAPbBr3 perovskite
16

ACCEPTED MANUSCRIPT
We have alreadyshowed that nanoparticles display a blue shift due to more surface area and higher energy
structure. Nanoparticles have a greater proportion of exposed atoms than bulk particles that increases the
surface area of nanomaterials because, by reducing the size of crystals, the number of atoms at the surface of
the crystal compared to the number of atoms in the crystal itself increases. This increased surface area
increases the enthalpy change and specific heat capacity of the materials which would be stored through an
increased vibrational energy38, 39.Quantitative comparative analysis of enthalpy change and specific heat
capacity fordifferent particle size of hybrid perovskite is shown in figure 8 a and b respectively. The value of
∆H and ∆Cp for nanoparticles perovskite are found more than micro crystal perovskite due to enhancement
of endothermic peak of nanomaterials. Therefore particlesize of perovskite materials playsa very important
role in energy storing devices.
Figure 8: Quantitative analysis of (a) Enthalpy change, ∆H & (b) Specific heat capacity, ∆Cp of micro and
nano particles of MAPbBr3 hybrid perovskite
17

ACCEPTED MANUSCRIPT
4 CONCLUSION
In this study, we reported here the preparation of MABr and MAPbBr3 perovskite material with cost
effective synthesis approach in the ambient conditions without using legands and capping agents. MAPbBr3
has high purity, high crystallinity and cubic phase at ambient condition and room temperature and with
decreasing the particle size FWHM peaks increases and intensity of peaks decreases of XRD. Optical
properties of materials also have been tuned by tuning the size of the materials (micro-cubes to nano-
particles) . This size controlled energy band gap and tunable PL emission of MAPbBr3 perovskite opens up
the possibility to develop the low-cost light emitting diodes, photodetectors, stable perovskite solar cells,
perovskite batteries, and other energy storing devices. From the thermal analysis (DSC/TG) of the micro-
cubes and nano-particles of hybrid perovskite, it is clear that thermal stability and thermal kinetics (enthalpy
change and specific heat capacity) of perovskite materials affected by reducing the size of the material.
Nanoparticles perovskite has broader endothermic peaks with shifting towards lower melting points than
micro-cubes which enhanced the ∆H and ∆Cp value of nanomaterials. The thermal reactions occurring in the
different halide containing perovskite may be more complicated than usually assumed and that further study
is required for a better understanding of the thermodynamic reaction and stability study. In addition, the
stability and toxicity due to the presence of lead in organic inorganic halide perovskite is a big issue for
commercialization of the type of the materials. So, we need more study regarding stability and lead-free
perovskite material.
ACKNOWLEDGEMENT
Rajan acknowledges the National Junior Research Fellowship provided by University Grants Commission
(UGC), Govt. of India. Jai Singh would like to acknowledge UGC-India and DST for providing project
under UGC Start-up Grant and DST Fast track.
18

ACCEPTED MANUSCRIPT
References:
1. Y. Zhang, G. Grancini, Y. Feng, A. M. Asini and M. K. Nazeeruddin, Optimization of Stable Quasi-
Cubic FAxMA1-xPbI3 Perovskite Structure for Solar Cells with Efficiencybeyond 20%, ACS Energy
Lett. 2(4)(2017) 802-806.
2. T. Singh, J. Singh and T. Miyasaka, Role of Metal Oxide Electron-Transport Layer Modification on
the Stability of High Performing Perovskite Solar Cells, ChemSusChem 9 (2016) 1-9.
3. R. Sheng,M. T. Hörantner,Z. Wang,Y. Jiang,W. Zhang, A. Agosti,S. Huang,X. Hao,A. Ho-
Baillie,M. Green,and H. J. Snaith, Monolithic Wide Band Gap Perovskite/Perovskite Tandem Solar
Cells with Organic Recombination Layers, J. Phys. Chem. C 121 (2017) 27256−27262.
4. S. Demchyshyn, J. M. Roemer, H. Groiß, H. Heilbrunner, C. Ulbricht, D. Apaydin, A. Böhm, U.
Rütt, F. Bertram, G. Hesser, M. C. Scharber, N. S. Sariciftci, B. Nickel, S. Bauer, E. D. Głowacki,
M. Kaltenbrunner, Confining metal-halide perovskites in nano porous thin films, Sci. Adv. 3 (2017)
e1700738.
5. B. Wenger, P. K. Nayak, X. Wen, S. V. Kesava, N. K. Noel & H. J. Snaith, Consolidation of the
optoelectronic properties of CH3NH3PbBr3 perovskite single crystals, Nat. Commun. 8(1) (2017)
590.
6. Y. Zhao and K. Zhu, Organic–inorganic hybrid lead halide perovskites for optoelectronic and
electronic applications, Chem. Soc. Rev. 45 (2016) 655.
7. S. A. Veldhuis, P. P. Boix, N. Yantara, M. Li, T. C. Sum, N. Mathews & G. Mhaisalkar, Perovskite
Materials for Light-Emitting Diodes and Lasers, Adv. Mater. 28 (2016) 6804-6834.
8. X. Tan, B. Zhang, and G. Zou, Electrochemistry and Electrochemiluminescence of Organometal
Halide Perovskite Nanocrystals in Aqueous Medium, J. Am. Chem. Soc. 139 (2017) 8772−8776.
9. Y. Gao, S. Wang, C. Huang, N. Yi, K. Wang, S. Xiao & Q. Song, Room temperature three-photon
pumped CH3NH3PbBr3 perovskite microlasers, Sci Rep. 7 (2017) 45391.
19

ACCEPTED MANUSCRIPT
10. A. Kojima K.Teshima, Y. Shirai, T. Miyasaka, Organometal halide perovskite as visible light
sensitizers for photovoltaic cells, J. Am. Chem. Soc. 131 (2009) 6050.
11. T. Singh, Y. Udagawa, M. Ikegami, H. Kunugita,K. Ema, and T. Miyasaka, Tuning of perovskite
solar cell performancevia low-temperature brookite scaffoldssurface modifications, APL Materials 5,
(2017) 016103.
12. R. J. Sutton, G. E. Eperon, L. Miranda, E. S. Parrott, B. A. Kamino, J. B. Patel, M. T Hörantner, M.
B. Johnston, A. A. Haghighirad, D. T Moore, H. J. Snaith, Bandgap tunable cesium lead halide
perovskites with high thermal stability for efficient solar cells, 6 (2016) 1502458.
13. H. Rao, W. Sun, S. Yen, W. Yan, Y. Li, H. Peng, Z. Liu, Z. Bin, C. Huang, Solution-Processed CuS
NPs as an Inorganic Hole-Selective Contact Material for Inverted Planar Perovskite Solar Cells ACS
Appl. Mater. Interfaces 8 (2016) 7800-7805.
14. Y. Liu, L. A. Renna, M. Bag, Z. A. Page, P. Kim, J. Choi, T. Emrick, D. Venkataraman, and T. P.
Russell, High Efficiency Tandem Thin-Perovskite/Polymer Solar Cells with a Graded
Recombination Layer,ACS Appl. Mater. Interfaces 8 (2016) 7070-7076.
15. T. Singh and T. Miyasaka, Stabilizing the Efficiency Beyond 20% with a Mixed CationPerovskite Solar
Cell Fabricated in Ambient Air under Controlled HumidityAdv. Energy Mater. 2017, 1700677, DOI:
10.1002/aenm.201700677A.
16. NREL chart, http://www.nrel.gov/ncpv/images/efficiency_chart.jpg (accessed: December, 2017).
17. A. Poglitsch and D. Weber, Disorder in Methylammonium trihalogen oplumbates (II) Observed by
Millimeter-wave Spectroscopy, J. Chem. Phys. 87 (1987) 6373–6378.
18. B. Suarez, , V. Gonzalez-Pedro, T. S. Ripolles, R. S.Sanchez, L. Otero and I. Mora-
Sero,Recombination Study of Combined Halides (Cl, Br, I) Perovskite Solar Cells, J. Phys.Chem.
Lett. 5 (2014) 1628–1635.
20

ACCEPTED MANUSCRIPT
19. S. Mali, C. S. S,him and C. K. Hong, Highly stable and efficient solid-state solar cells based on
methylammonium lead bromide (CH3NH3PbBr3) perovskite quantum dots,NPG Asia Materials 7
(2015) e208.
20. D. M. Jang, K. Park, , D. H. Kim, J. Park, F. Shojaei, J. Lee, Reversible Halide Exchange Reaction
of Organometal Trihalide Perovskite Colloidal Nanocrystals for Full-Range Band Gap Tuning, Nano
Letter,15 (8) (2015) 5191–5199.
21. W. J. Yin, J. H. Yang, J. Kang, Y. Yan, S. H. Wei,Reversible Halide Exchange Reaction of
Organometal Trihalide Perovskite Colloidal Nanocrystal for Full-Range Band Gap Tuning,J. Mater
Chem. A3 (2015) 8926-8942.
22. S. Gonalez, R. E. Galian, J. Perez-Prieto, maximizing the emissive properties of CH3NH3PbBr3
perovskite nanoparticles, J. Mater. Chem. A 3 (2015) 9187-9193.
23. Y. Zhou, T. Zhang, C. Li., Z. Liang, L. Gong, J. Chen, W. Xie, J. Xie, P. Liu, Rapid growth of high
quality perovskite crystal by solvent mixing,CrystEngComm.18 (2016) 1184-1189.
24. Y. Liu, Z. Yang, D. Cui, X. Ren, J. Sun, X. Liu, J. Zhang, Q. Wei, H. Fan, F. Yu, X. Zhang, C. Zhao,
S. Liu,Two-Inch-Sized Perovskite CH3NH3PbX3 (X = Cl, Br, I) Crystals: Growth and
Characterization, Adv Mater. 27 (2015) 5176-5183.
25. R. K. Singh, R. Kumar, J. Singh, Effect of precursor ratio on crystallanity and thermal stability of
CH3NH3PbI3, AIP Conference Proceeding 1832 (2017) 050056.
26. J. S. Manser, J. A. Cristians, P. V. Kamat, Intriguing Optoelectronic Properties of Metal Halide
Perovskites, Chem. Rev. 116 (21) (2016) 12956-13008.
27. D. Priante, I. Dursun, M. S. Alias, D. Shi, V. A. Melnikov, T. K. Ng, O. F. Mohammed, O. M .Bakr,
B. S. Ooi, The recombination mechanisms leading to amplified spontaneous emission at the true-
green wavelength in CH3NH3PbBr3 perovskites, Appled Physics Letters 106(2015) 081902.
21

ACCEPTED MANUSCRIPT
28. G. K. Willamson, W. H. Hall, X-ray line broadening from filed aluminium and wolfram Die
verbreiterung der roentgeninterferenzlinien von aluminium- und wolframspaenen A.cta Mettall.
1(1953) 22.
29. L. C. Schmidt, A. Petegas, S. G. Carrero, O. Malinkiewicz, S. Agoura, G. M. Espallargas, H. J.
Bolink, R. E. Galian, J. Perez-Prieto, Nontemplate synthesis of CH3NH3PbBr3 perovskite
nanoparticles, J. Am. Chem. Soc. 136 (2014) 850-853.
30. A. Kojima, M. Ikegami, K. Teshima, T. Miyasaka, Highly Luminescent Lead Bromide Perovskite
Nanoparticles Synthesized with Porous Alumina Media, Chem. Let. 41 (2012) 397-399.
31. S. Mireshadi, S. Ahmadi—Kandjani, Efficient thin luminescent solar concentrator based on
Organometal halide perovskite, Dye and Pigments 26 (2015) 15-21.
32. P. Kumar, C. Moth, V. C. Nair and K. S. Narayan,Quantum Confinement Effects in Organic Lead
Tribromide Perovskite Nanoparticles, J. Phys. Chem. C, 120 (2016) 18333-18339.
33. Y. Yamada, T. Nakamura, T. Nakamura, M. Endo, A. Wakamiya, Y. Kanemitsu, Photo carrier
Recombination Dynamics in Perovskite CH3NH3PbI3 for Solar Cell Applications,J. Am. Chem.
Soc.136(2014) 11610-11613.
34. H. R. Xia, W. T. Sun, L. M. Peng, Hydrothermal synthesis of Organometal halide perovskites for Li-
ion batteries, Chem. Commun. 51 (2015) 13787-13790.
35. M. F. Aygler, M. D. Weber, B. M. D. Puscher, D. D. Medina, P. Docampo, R. D. Costa, , Light-
Emitting Electrochemical Cells Based on Hybrid Lead Halide Perovskite Nanoparticles, J. Phys.
Chem. C 119 (2015) 12047.
36. R. K. Singh, N. Jain, J. Singh, R. Kumar, Stability behaviour of chemically synthesized organic
electrolyte salts and Methylammonium lead halide perovskite light harvester, Advanced Materials
Letters 8 (6) (2017) 707-711.
22

ACCEPTED MANUSCRIPT
37. E. Martine, The effect of particle size on the thermal properties of serpentine minerals, The
American Mineralogist 46 (1961) 901-912.
38. L. Wang, Z. Tan, S. Meng, D. Liang, G. Li, Enhancement of molar heat capacity of nanostructured
Al2O3. J. Nanoparticle Res. 3 (2001) 483-487.
39. B. X. Wang, L. P. Zhou, X. F. Peng,Surface and Size Effects on the Specific Heat Capacity of
Nanoparticles, International Journal of Thermophysics 27 (1) (2006) 139-151.
23

ACCEPTED MANUSCRIPT
Highlights:
ꢀ Solution processed methyl ammonium lead bromide was highly cubic crystalline at room
temperature.
ꢀ MAPbBr3, micro-cubes was more thermally stable than nano-particles.
ꢀ High absorbance and luminescence property show the light harvesting nature of the
materials.
ꢀ Change in enthalpy and specific heat capacity of perovskite particle was increased by
reducing the particle size.