ПРОЦЕСИ ФАЗОУТВОРЕННЯ ОРГАНО-НЕОРГАНІЧНИХ ПЕРОВСКИТІВ CH3NH3PbI3 ПРИ ВИКОРИСТАННІ РОЗЧИННИКА ДМФА
The organic-inorganic perovskite films CH3NH3PbI3 were synthesized from solutions with different ratios (1:1, 1:2 and 1:3) of initial reagents (PbI2 and CH3NH3I) in a DMF solvent. XRD and Raman spectroscopy shows that the perovskites are formed according to different schemes depending on the ratio o...
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| Дата: | 2021 |
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| Автори: | , , , , , |
| Формат: | Стаття |
| Мова: | Англійська |
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V.I.Vernadsky Institute of General and Inorganic Chemistry
2021
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Репозитарії
Ukrainian Chemistry Journal| _version_ | 1871465734239944704 |
|---|---|
| author | Torchyniuk, Pavlo V'yunov, Oleg Yukhymchuk, Volodymyr Hreshchuk, Oleksandr Vakarov, Serhii Belous, Anatolii |
| author_facet | Torchyniuk, Pavlo V'yunov, Oleg Yukhymchuk, Volodymyr Hreshchuk, Oleksandr Vakarov, Serhii Belous, Anatolii |
| author_institution_txt_mv | [
{
"author": "Pavlo Torchyniuk",
"institution": "V. I. Vernadsky Institute of General and Inorganic Chemistry"
},
{
"author": "Oleg V'yunov",
"institution": "V. I. Vernadsky Institute of General and Inorganic Chemistry"
},
{
"author": "Volodymyr Yukhymchuk",
"institution": null
},
{
"author": "Oleksandr Hreshchuk",
"institution": "V. I. Vernadsky Institute of General and Inorganic Chemistry"
},
{
"author": "Serhii Vakarov",
"institution": null
},
{
"author": "Anatolii Belous",
"institution": "V. I. Vernadsky Institute of General and Inorganic Chemistry"
}
] |
| author_sort | Torchyniuk, Pavlo |
| baseUrl_str | https://ucj.org.ua/index.php/journal/oai |
| collection | OJS |
| datestamp_date | 2026-07-22T08:23:47Z |
| description | The organic-inorganic perovskite films CH3NH3PbI3 were synthesized from solutions with different ratios (1:1, 1:2 and 1:3) of initial reagents (PbI2 and CH3NH3I) in a DMF solvent. XRD and Raman spectroscopy shows that the perovskites are formed according to different schemes depending on the ratio of PbI2 and CH3NH3I. At the ratio 1:1 of initial reagents, three intermediate compounds are formed: (CH3NH3)2(DMF)xPbI4, (CH3NH3)2(DMF)2Pb3I8, (CH3NH3)3(DMF)PbI5. At the ratio 1:2 of initial reagents four intermediate compounds are formed: in addition to the above phases, the phase (CH3NH3)2(DMF)2Pb2I6 is found. And at the ratio 1:3 of initial reagents, only two intermediate phases, (CH3NH3)2(DMF)xPbI4 and (CH3NH3)3(DMF)PbI5, are observed. The morphology of the perovskite films was established to depend primarily on the ratio of the initial reagents. The temperature of heat treatment changes only the grain size of films. |
| doi_str_mv | 10.33609/2708-129X.87.08.2021.63-81 |
| first_indexed | 2025-09-24T17:43:40Z |
| format | Article |
| fulltext |
UDC: 544.344.015.4:621.3.016.35:539.216:548.736.442.5 doi: 10.33609/2708-129X.87.08.2021.63-81
PHASE FORMATION PROCESSES OF ORGANIC-INORGANIC CH3NH3PbI3
PEROVSKITES USING A DMF SOLVENT
P.V. Torchyniuk1, O.I. V’yunov1*, V.O. Yukhymchuk2, O.M. Hreshchuk2,
S.V. Vakarov1, A.G. Belous1
1V. I. Vernadsky Institute of General and Inorganic Chemistry of the NAS of Ukraine, 32/34
Aсademiс Palladin Avenue, Kyiv 03142, Ukraine
2V. E. Lashkaryov Institute of Semiconductor Physics of the NAS of Ukraine, Nauky Avenue, Kyiv
03028, Ukraine
*e-mail: vyunov@ionc.kiev.ua
The organic-inorganic perovskite films CH3NH3PbI3 were synthesized from solutions with
different ratios (1:1, 1:2 and 1:3) of initial reagents (PbI2 and CH3NH3I) in a DMF solvent.
XRD and Raman spectroscopy shows that the perovskites are formed according to different
schemes depending on the ratio of PbI2 and CH3NH3I. At the ratio 1:1 of initial reagents,
three intermediate compounds are formed: (CH3NH3)2(DMF)xPbI4, (CH3NH3)2(DMF)2Pb3I8,
(CH3NH3)3(DMF)PbI5. At the ratio 1:2 of initial reagents four intermediate compounds are
formed: in addition to the above phases, the phase (CH3NH3)2(DMF)2Pb2I6 is found. And at
the ratio 1:3 of initial reagents, only two intermediate phases, (CH3NH3)2(DMF)xPbI4 and
(CH3NH3)3(DMF)PbI5, are observed. The morphology of the perovskite films was established
to depend primarily on the ratio of the initial reagents. The temperature of heat treatment
changes only the grain size of films.
Keywords: organic-inorganic perovskite, X-ray diffraction analysis, Raman spectroscopy,
intermediate compounds, stability.
INTRODUCTION. Nowadays, much of the
energy comes from hydrocarbons, coal and
other fossil fuels. Their usage in electricity ge
neration leads to significant CO2 emissions in
the atmosphere, increases the greenhouse ef-
fect and changes the climate across the globe in
disastrous proportions. The increase of energy
produced by photovoltaic elements contributes
to solving the problem of global warming [1].
Today, most solar panels are manufactured
based on indirect band gap silicon.The active
layers of these materials are relatively thick
(∼200 μm) for the complete absorption of solar
radiation in the visible and near-infrared ran
ges. This increases their cost and holds back
the growth of solar power plants. Therefore,
the direct band gap semiconductors with a
high absorption coefficient in the visible spec-
tral range based on environmentally friendly
and economically attractive materials are of
interest. They are characterized by a high level
of properties, which allows them to be consi
dered as promising materials for next-gene
ration PV technologies: high electron mobility
PHASE FORMATION PROCESSES OF ORGANIC-INORGANIC CH3NH3PbI3 PEROVSKITES USING A DMF SOLVENT
64 ISSN 2708-129X. Укр. хім. журн., 2021
INORGANIC CHEMISTRY
(800 cm2 / Vs) [2], long carrier diffusion length
(over 1 μm) [3, 4], ambipolar nature of moving
charges [5], high absorption coefficient (great-
er than 105 cm−1) [3], etc. The search for such
materials is going in several directions. In par-
ticular, the following materials are investigated
as an active layer of solar cells: multicompo-
nent metal chalcogenides Cu2ZnSnS4 [6], orga-
nic semiconductors [7], semiconductor quan-
tum dots [8], and organic-inorganic halides
CH3NH3PbI3-yXy with perovskite structure [9].
In recent years, the efficiency of perovskite
solar cells based on CH3NH3PbI3 has dynam-
ically increased [9-11]. Indeed, they are quite
promising materials for producing solar cells.
The organic-inorganic perovskite films are re
latively easy to synthesize, they have high light
absorption coefficients in the visible spectral
range and a large diffusion length of charge
carriers [10]. Over the last 10 years, the effi-
ciency of solar-to-electrical conversion of
perovskite-based photoelectric elements has
grown from 3% [11] to 25.2% [12].
However, organic-inorganic perovskites
have some drawbacks. In particular, their struc-
ture degrades due to atmospheric humidity. To
overcome the above problems, the processes in
the formation of CH3NH3PbI3 perovskite films
have to be clearly described.
The ratio of starting reagents and the chem-
istry of precursors are the main factors affect-
ing the structural and, as a result, physical
and chemical properties of CH3NH3PbI3 per-
ovskites [13–18]. The complex chemical inter-
action of an organic cation, a coordinating sol-
vent, and an inorganic component determines
the processes of crystal nucleation and forma-
tion [19] and consequently affects the proper-
ties of crystalline films. However, practically
no data is published about the phase transfor-
mations during the synthesis of samples in dif-
ferent synthesis conditions (ratios of initial re-
agents, solvents, heat-treatment temperatures).
The aim of this work was to study in a wide
temperature range (from 20 to 175 °C) the
processes in the synthesis of organic-inorganic
CH3NH3PbI3 perovskite films using the initial
reagents CH3NH3I and PbI2 in different ratios,
which are dissolved in dimethylformamide
(DMF).
EXPERIMENT AND DISCUSSION OF
THE RESULTS. Materials. Lead iodide (PbI2),
methylammonium chloride (CH3NH3Cl) and
pre-synthesized methylammonium iodide
(CH3NH3I) were used as starting materials.
To stabilize the perovskite structure, iodine
was partially substituted with chlorine by
the addition of methylammonium chloride
(CH3NH3Cl) [19]. In this paper, for simplici-
ty, the solid solution CH3NH3PbI2.98Cl0.02 will
be further written as CH3NH3PbI3. Dried di-
methylformamide (DMF) was used as the sol-
vent.
Synthesis of methylammonium iodide and
organic-inorganic perovskites. Methylammo-
nium iodide (CH3NH3I) was synthesized by
the dropwise addition of aqueous HI (Sigma
Aldrich, 57%, 1.0eq) into methylamine (Sigma
Aldrich, aqueous, 40%, 1.05eq) under stirring
at 10 °C. The solution was stirred for two hours,
then the solvent was removed by rotary evapo-
ration. The yellow-white crystals were washed
three times with methyl tert-butyl ether, fil-
tered, and dried overnight under vacuum to
yield white crystals of CH3NH3I.
For the deposition of CH3NH3PbI3 films,
the initial reagents, PbI2 and CH3NH3I with
molar ratios of 1:1; 1:2; 1:3 were dissolved in
DMF and stirred at 70 °C for 1 hour. The crys-
talline CH3NH3PbI3 films were formed in a dry
P.V. Torchyniuk, O.I. V’yunov, V.O. Yukhymchuk, O.M. Hreshchuk, S.V. Vakarov, A.G. Belous
65https://ucj.org.ua
UCJ № 8 / Vol. 87
box. The previously prepared clear solution
was deposited on to a purified glass substrate
by spin-coating with a speed of 2400 rpm for
30 seconds. The films were thermally treated
on a preheated hot plate at temperatures from
20 to 180 °C for 15 min.
The microstructure and the elemental com-
position of organic-inorganic perovskites were
controlled using a scanning electron micro-
scope SEC miniSEM SNE 4500MB equipped
with EDAX Element PV6500/00 F spectro
meter.
The phase composition of films was iden-
tified by X-ray diffractometry (XRD) using a
DRON-4-07 diffractometer (CuKα-radiation,
40 kW, 20 mА) at 2Θ = 5–50º, a step of 0.04º
and a count time of 4 s.
Experimental Raman scattering spectra were
studied at room temperature in the back-scat-
tering geometry with an MDR-23 single-stage
spectrometer equipped with a CCD detector
(Andor) using λexc = 457 nm (diode-pumped
solid-state laser, CNILaser). The laser excitation
power was kept as low as possible, to avoid the
damage of molecules under investigation either
due to heating or photochemical reactions.
Figure 1 shows SEM images of the surface
of the synthesized films obtained on glass sub-
strates at different ratios of the initial PbI2 and
CH3NH3I reagents and heat treatment temper-
atures of 25 °C (a, b, c) and 75 °C (d, e, f). The
ratio of the starting reagents PbI2 and CH3NH3I
has a decisive influence on the morphology of
the synthesized films. The ratio of the initial
components significantly affects the formation
of CH3NH3PbI3 precursors and, accordingly,
the subsequent growth of perovskite crystals
and their shape [19, 20]. The heat treatment
of films at different temperatures also affects
their morphology. As the temperature of the
heat treatment of films increases, the shape of
the characteristic structures (grains) on their
surface remains similar, although their dimen-
sions are significantly reduced.
Fig. 1. SEM image of the surface of CH3NH3PbI3 perovskite films deposited on glass substrates at
different ratios of the initial reagents: PbI2 : CH3NH3I = 1:1 (a, d); 1:2 (b, e); 1:3 (c, f), and at the tempe
ratures: 25 °C (a, b, c) and 75 °C (d, e, f).
PHASE FORMATION PROCESSES OF ORGANIC-INORGANIC CH3NH3PbI3 PEROVSKITES USING A DMF SOLVENT
66 ISSN 2708-129X. Укр. хім. журн., 2021
INORGANIC CHEMISTRY
Table 1
Unit cell parameters at room temperature of the initial reagents, probable intermediate
and terminal compounds in the synthesis of organic-inorganic perovskite films.
Compound Symmetry and
space group Unit cell parameters References
(CH3NH3)2(DMF)2Pb2I6 Monoclinic P21/c
(№ 14)
a = 4.5647(9) Å
b = 25.446(5) Å
c = 12.119(2) Å
α = γ = 90 °
β = 96.75(3) °
Z = 4
V=1397.9(5) Å3
[21]
(CH3NH3)2(DMF)2Pb3I8 Orthorhombic
Pnnm
(№ 58)
a = 17.165(9) Å
b = 21.955(4) Å
c = 4.5549(9) Å
α = β = γ = 90 °
Z = 2
V =1716.6(6) Å3
[21]
(CH3NH3)3(DMF)PbI5 Triclinic
P-1
(№ 2)
a = 10.1714(15) Å
b = 11.335(3) Å
c =12.394(2) Å
α = 111.18(3) °
β = 101.11(3) °
γ = 109.80(3) °
Z = 2
V = 1170.0(7) Å3
[21]
(CH3NH3)2(DMF)xPbI4 - - [22]
(CH3NH3)4PbI6
.2H2O Monoclinic P21/n
(№ 14)
a = 10.421(3) Å
b = 11.334(2) Å
c = 10.668(2) Å
α = β = 90°
γ = 91.73(2)
Z = 2
V=1259.4(5) Å3
[23]
Table 1 shows literature data [21–28] on
the unit cell parameters of the initial reagents,
probable intermediate and terminal com-
pounds in the films formed in a DMF solvent
at different ratios of the initial reagents PbI2
and CH3NH3I.
P.V. Torchyniuk, O.I. V’yunov, V.O. Yukhymchuk, O.M. Hreshchuk, S.V. Vakarov, A.G. Belous
67https://ucj.org.ua
UCJ № 8 / Vol. 87
Compound Symmetry and
space group Unit cell parameters References
CH3NH3PbI3
.H2O Monoclinic P21/m
(№ 11)
a = 10.46 Å
b = 4.63 Å
c = 11.10 Å
α = β = 90°
γ = 101.50°
Z = 2
V=536.05(19)
[24,25]
CH3NH3PbI3 Tetragonal
I4/mcm
(№ 140)
а = 8.870(2) Å
с = 12.669(8) Å
V = 996.8(7) Å3
[26]
PbI2 Trigonal
P-3m1
(№ 164)
a = 4.558 Å
c = 6.986 Å
V = 125.69 Å3
[27]
CH3NH3I Tetragonal
P4/nmm (№ 129)
a = 5.12729(1) Å
c = 9.01794(2) Å
V = 237.074(1) Å3
[28]
Table 1
Fig. 2. X-ray diffraction pattern of films pre-
pared with the ratio 1:1 of the initial reagents PbI2
and CH3NH3I with heat treatment at different
temperatures. The second phases are denoted by
“□” – (CH3NH3)2(DMF)xPbI4; “*” – (CH3NH3)2
(DMF)2Pb3I8; “●” (CH3NH3)3(DMF)PbI5; “o” –
PbI2; and “◊” – CH3NH3PbI3.
Figure 2 shows the results of an XRD analy-
sis of CH3NH3PbI3 perovskite films prepared at
a ratio of the initial reagents PbI2 and CH3NH3I
of 1:1 and at different temperatures of heat
treatment.
The X-ray diffraction patterns of the films
show the peaks corresponding to CH3NH3PbI3
(14.1 °) and second phases. In particular, the
peaks at 2Θ = 6.53 °, 8.04 °, 9.5 °, 10.03 °, 6.53 °,
11.06 °, 13.08 °, 16.13 °, 17.46 °, 19.18 ° and
19.68 ° (denoted in Fig. 1 as “*”) correspond
to the phase (CH3NH3)2(DMF)2Pb3I8 [21]. The
X-ray peaks at 2Θ = 7.71 ° and 11.48 ° (denoted
in Fig. 2 as “□”) correspond to the compound
(CH3NH3)2(DMF)xPbI4 [22], the peaks at
2Θ = 9.15 °, 16.94 ° and 18.36 ° (denoted in
Fig. 2 as “●”) correspond to the compound
- (CH3NH3)3(DMF)PbI5 [21], and the peaks
PHASE FORMATION PROCESSES OF ORGANIC-INORGANIC CH3NH3PbI3 PEROVSKITES USING A DMF SOLVENT
68 ISSN 2708-129X. Укр. хім. журн., 2021
INORGANIC CHEMISTRY
at 2Θ = 12.7° (denoted in Fig. 2 as “o”) corre-
spond to the PbI2. Thus, depending on the tem-
perature of heat treatment, the CH3NH3PbI3
films prepared with the ratio 1:1 of the initial
reagents PbI2 and CH3NH3I contain three in-
termediate phases.
Figure 3 shows the results of an XRD analy-
sis of CH3NH3PbI3 perovskite films obtained at
a ratio of the initial reagents PbI2 and CH3NH3I
1:2 after heat treatment in the temperature
range from 20 to 170 °C.
Fig. 3. X-ray diffraction pattern of films pre-
pared with the ratio 1:2 of the initial reagents PbI2
and CH3NH3I with heat treatment at different
temperatures. The second phases are denoted by
“□” – (CH3NH3)2(DMF)xPbI4; “*” – (CH3NH3)2
(DMF)2Pb3I8; “●” – (CH3NH3)3(DMF)PbI5; “∆“ –
(CH3NH3)2(DMF)2Pb2I6; and “◊” – CH3NH3PbI3.
The analysis of the X-ray diffraction pattern
of films shows that in addition to the peaks of
the perovskite phase (14.1°), the peaks of other
intermediate compounds are present. In par-
ticular, the peaks at 7.71 °, 11.35 °, 11.48 °,
12 °, and 15.59 ° indicate the formation of an
intermediate compound (CH3NH3)2PbI4 or
(CH3NH2)2(DMF)xPbI4. The peaks at 2Θ =
9.16 °, 16.94 °, 17.75 °, and 18.66 ° indicate the
formation of the compound (CH3NH3)3(DMF)
PbI5; at 2Θ = 6.94° and 10.1° for the formation
of (CH3NH3)2(DMF)2Pb2I6 and at 2Θ = 6.53°
and 8.04° for the formation of ((CH3NH3)2
(DMF)2Pb3I8 compounds.
Figure 4 shows the results of an XRD anal-
ysis of CH3NH3PbI3 perovskite films prepared
at the ratio 1:3 of the initial reagents PbI2 and
CH3NH3I at different temperatures of heat
treatment.
Fig. 4. X-ray diffraction pattern of films pre-
pared with the ratio 1:3 of the starting reagents PbI2
and CH3NH3I with heat treatment at different tem-
peratures. The second phases are denoted by “□” –
(CH3NH3)2(DMF)xPbI4; “●” – (CH3NH3)3(DMF)
PbI5; and “◊” – CH3NH3PbI3.
Intense peaks of the perovskite phase (14.1°)
and peaks from other intermediate phases are
observed. In particular, the peaks at 2Θ angles
of 11.35 °, 11.48 °, 11.64 °, 12 °, and 15.59 °
can be attributed to the intermediate phase
(CH3NH3)2(DMF)xPbI4, at 2Θ angles of 9.16 °,
10.1 °, 16.94 °, 17.75 °, 18.36 °, and 18.66 ° to
(CH3NH3)3(DMF)PbI5.
To determine the temperature ranges of
the formation of the intermediate compounds
in the synthesized films, Raman spectroscopy
was used. It should be noted that the interac-
P.V. Torchyniuk, O.I. V’yunov, V.O. Yukhymchuk, O.M. Hreshchuk, S.V. Vakarov, A.G. Belous
69https://ucj.org.ua
UCJ № 8 / Vol. 87
tion of laser excitation with the sample results
in several types of radiation: inelastic (Ra-
man) scattering, elastic (Rayleigh) scattering,
and photoluminescence (PL). The intensity of
Rayleigh scattering depends significantly on
the morphology of films, which, like PL, in-
terferes with the recording of Raman spectra
of perovskite films [29,30]. In the presence of
intense PL, it is not possible at all to recordr the
Raman spectrum of these films. The PL band
of perovskites is quite wide (675–850 nm), so
to excite Raman spectra, the laser radiation
in the spectral regions before and after the PL
band should be used [31,32]. However, if the
film consists of several compounds, it is dif-
ficult to consider all of these factors. That is
why a change in the film composition may not
result in the appearance/disappearance of Ra-
man bands of a particular compound. In this
case, the spectrum changes as a whole due to
the overlapping of the contribution of Raman
and Rayleigh scattering, and PL. The analysis
of such changes allows us to evaluate the phase,
component and morphological changes that
occurred during the formation of the film at
different ratios of the initial reagents and tem-
perature of heat treatment.
Fig. 5. Raman spectra of a film obtained at a
ratio of the starting reagents PbI2 and CH3NH3I of
1:1 at a temperature of 90 оC with intensive laser
treatment (laser radiation density ∼1.5⋅104 W/cm)
and varying the irradiation time from 1 to 60 mi-
nutes.
Fig. 6. Raman spectra of films prepared at the ratio 1:1 of initial reagents PbI2 and CH3NH3I and with
heat treatment at different temperatures. (a) Raman spectra in the low-frequency range, (b) Raman spec-
tra in the high-frequency range.
PHASE FORMATION PROCESSES OF ORGANIC-INORGANIC CH3NH3PbI3 PEROVSKITES USING A DMF SOLVENT
70 ISSN 2708-129X. Укр. хім. журн., 2021
INORGANIC CHEMISTRY
Figure 5 shows that in the spectrum of the
original film (curve 1) there is a low-intensi-
ty band in the region of 58 cm-1, which corre-
sponds to I-Pb-I vibrations [33]. As the irra-
diation time increases, perovskite decomposes
into CH3NH3I and PbI2, as evidenced by an
increase in the intensity of the bands of the
latter compound over time. Subsequently, to
record the Raman spectra of perovskite films,
the intensity of laser excitation radiation was
chosen such that it did not lead to degradation
of the film under investigation, even prolonged
action.
Figure 6 shows Raman spectra of the syn-
thesized films prepared at the ratio 1:1 of the
initial reagents PbI2 and CH3NH3I after heat
treatment at different temperatures.
The Raman spectrum of a film formed at 20
to 30 °C contains intense bands of Pb-I vibra-
tions (59 and 110 cm-1), CH3NH3 vibrations (110
and 138 cm-1) corresponding to CH3NH3PbI3
perovskite and intermediate compounds, and
bands of the DMF solvent (864, 982, 1103 cm-1,
etc.). Increasing the temperature of the film
heat treatment to 30 °C leads to the disappea
rance of the bands at 59 and 110 cm-1 and the
emergence of a low-frequency band with a
maximum of 51 cm-1 and intense photolumi-
nescence (PL)
The emergence of intensive PL is most like-
ly associated with the compound (CH3NH3)2
(DMF)2Pb3I8. According to X-ray diffraction
data at temperatures above 30 °C, the content of
the compound in the film increases due to the
decomposition of the compounds (CH3NH3)3
(DMF)PbI5 and (CH3NH3)2(DMF)xPbI4.
At temperatures of 50–100 °C, in the spec-
tra there appear bands at 51, 250, 752, 838 cm-1,
which can be assigned to the compound
(CH3NH3)2(DMF)2Pb3I8. When the tempera
ture rises to 100 °C, the intensity of PL de-
creases, which is associated with a decrease
in the content of (CH3NH3)2(DMF)2Pb3I8 in
the film of organic-inorganic perovskite. At
temperatures of 50–100 °C, the CH3NH3PbI3
perovskite content increases. During the for-
mation of films at a temperature of 100 °C,
bands with frequencies of 110 and 96 cm‑1,
which are characteristic of PbI2, appear in the
Raman spectrum. According to X-ray diffrac-
tion at a temperature of 100 °C, in addition
to perovskite, phases of PbI2 and (CH3NH3)2
(DMF)2Pb3I8 are present in the film. At 115 °C,
a single-phase film of organic-inorganic CH3N-
H3PbI3 perovskite is formed. At temperatures
above 120 ° C, PbI2 bands (51, 59 and 110 cm-1)
have appeared, and their intensity increases.
When using starting reagents with a ratio of
PbI2 and CH3NH3I of 1:1 for the synthesis of
perovskite film, the single-phase perovskite is
formed at 115 °C, which degrades at tempera-
tures above 115 °C with the formation of PbI2.
Figure 7 shows Raman spectra of films pre-
pared at a ratio of 1:2 of the initial reagents
PbI2 and CH3NH3I and heat-treated at differ-
ent temperatures. As for the films obtained at
a ratio of PbI2 and CH3NH3I of 1:1, bands of
Pb-I vibrations (∼65–106 cm-1) correspond-
ing to perovskite, intermediate compounds,
and the DMF solvent (864, 982, 1103 cm-1) are
present in the Raman spectra of films obtained
at temperatures from 20 to 30 °C. At higher
temperatures, bands of DMF do not appear in
the spectra. Instead, in the temperature range
of 40 to 90 °C in the low-frequency region of
the Raman spectra, bands appear with maxi-
ma in the region of 80 and 106 cm-1, which are
characteristic of perovskites and other phases.
At the same time, in the high-frequency part
of the spectrum for films formed in the tem-
P.V. Torchyniuk, O.I. V’yunov, V.O. Yukhymchuk, O.M. Hreshchuk, S.V. Vakarov, A.G. Belous
71https://ucj.org.ua
UCJ № 8 / Vol. 87
perature range from 50 to 120 °C, bands with
a frequency of ∼1207 cm-1 appear, which most
likely correspond to the phases (CH3NH3)3
(DMF)PbI5 and (CH3NH3)2(DMF)xPbI4.
According to X-ray data, these phases are
present in the perovskite film in this tem-
perature range. Heating such films even to
175 °C does not lead to their decomposition
into CH3NH3I and PbI2. The presence of the
(CH3NH3)2(DMF)xPbI4 phase in the film may
lead to greater stability of perovskite.
Fig. 7. Raman spectra of films prepared at the ratio 1:2 of the initial reagents PbI2 and CH3NH3I and
heat-treated at different temperatures. (a) Raman spectra in the low-frequency range, (b) Raman spectra
in the high-frequency range.
Fig. 8. Raman spectra of films prepared at the ratio 1:3 of the initial reagents PbI2 and CH3NH3I and
heat-treated at different temperatures. (a) Raman spectra in the low-frequency range, (b) Raman spectra
in the high-frequency range.
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72 ISSN 2708-129X. Укр. хім. журн., 2021
INORGANIC CHEMISTRY
Figure 8 shows Raman spectra of films
prepared at the ratio 1:3 of the initial rea-
gents PbI2 and CH3NH3I and the variation
of the heat treatment temperature from 20 to
175 °C. In the temperature range from 20 to
30 °C, bands characteristic of DMF (861, 982,
1103 cm-1) appear in the spectra. At tempe-
ratures above 30 °C, DMF bands in the spec-
tra are no longer visible. For films formed at
temperatures in the range from 20 to 100 °C,
bands characteristic of perovskite and other
phases appear in the Raman spectra. Indeed,
when the film formation temperature chan-
ges, the intensity of the bands is redistribu-
ted in the range from 80 to 110 cm-1, which
is characteristic of the vibrations of different
phases, both CH3NH3PbI3 and (CH3NH3)3
(DMF)PbI5 and (CH3NH3)2(DMF)xPbI4. At
temperatures above 120 °C, bands character-
istic of perovskite with a maximum of 106 cm-1
appear in the spectra and, as in the case of
film synthesis using the starting components
in a ratio of 1:2, degradation of the perov-
skite phase to PbI2 and CH3NH3I is not ob-
served. The band at 980 cm -1 can be assigned
to the compounds (CH3NH3)3(DMF)PbI5 and
(CH3NH3)2(DMF)xPbI4. At a temperature
of 175 °C, this band is not observed, which
indicates the decomposition of compounds
and the formation of a single-phase film of
CH3NH3PbI3 perovskite.
XRD and Raman spectroscopy data al-
lows the reaction schemes of the formation
of CH3NH3PbI3 perovskite and intermediate
compounds at different ratios of the initial rea-
gents PbI2 and CH3NH3I to be recorded.
Figure 9 shows the scheme of the formation
reaction of perovskite and intermediate phases
at the ratio 1:1 of the initial reagents PbI2 and
CH3NH3I and using the DMF solvent.
Fig. 9. The scheme of the formation of pe
rovskite and intermediate compounds at the ratio
1:1 of the initial reagents PbI2 and CH3NH3I and
using DMF.
In this case, the intermediate phases are
(CH3NH3)2(DMF)2Pb3I8, (CH3NH3)2(DMF)xPbI4
and (CH3NH3)3(DMF)PbI5.
Figure 10 shows the scheme of the forma-
tion reaction of perovskite and intermediate
phases at the ratio 1:2 of the initial reagents
PbI2 and CH3NH3I and using the DMF solvent.
Fig. 10. The scheme of the formation of pe
rovskite and intermediate compounds at the ratio
1:2 of the initial reagents PbI2 and CH3NH3I and
using DMF.
In this case, among the intermediate phases,
besides (CH3NH3)2(DMF)2Pb3I8, (CH3NH3)2
(DMF)xPbI4 and (CH3NH3)3(DMF)PbI5, the
phase (CH3NH3)2(DMF)2Pb2I6 is additionally
observed.
Figure 11 shows the scheme of the forma-
tion reaction of perovskite and intermediate
phases at the ratio 1:3 of the initial reagents
PbI2 and CH3NH3I and using the DMF solvent.
P.V. Torchyniuk, O.I. V’yunov, V.O. Yukhymchuk, O.M. Hreshchuk, S.V. Vakarov, A.G. Belous
73https://ucj.org.ua
UCJ № 8 / Vol. 87
Fig. 11. The scheme of the formation of pe
rovskite and intermediate compounds at the ratio
1:3 of the initial reagents PbI2 and CH3NH3I and
using DMF.
In this case, the intermediate phases are only
(CH3NH3)2(DMF)xPbI4 and (CH3NH3)3(DMF)
PbI5.
At the first glance, the schemes presented
above are contradictory, while they show that
the same intermediate phases may exist at dif-
ferent temperatures depending on the initial
reaction conditions. However, XRD proves this
fact. Indeed, the stability of the intermediate
compounds and the sequence of their conver-
sion to perovskite depend on their properties.
The difference in temperature stability can be
shown based on the enthalpies of intermedi-
ate compounds formation (Table 2). The com-
pound (CH3NH3)2(DMF)2Pb3I8 is the most
stable at the ratio 1:1 of the initial components
PbI2 and CH3NH3I. Increasing the ratio of the
initial reagents decreases the temperature of
interval of the existence of this compound. In
contrast to (CH3NH3)2(DMF)2Pb3I8, the tem-
perature interval of existence of the unstable
compound (CH3NH3)3(DMF)PbI5 increased
with an increase in CH3NH3I amount (Table 2).
XRD shows that CH3NH3PbI3 films pre-
pared on glass substrates at different ratios of
the initial reagents PbI2 and CH3NH3I may
contain other intermediate compounds after
heat treatment at different temperatures. The
phase composition of the film depends on the
ratio of the initial reagents and the tempera-
ture of heat treatment. The presence of other
compounds in the film, on the one hand, re-
duces the proportion of perovskite and, on the
other hand, can contribute to its stability in the
surrounding atmosphere.
Table 2
Enthalpy of formation [14] and temperature interval of existence of intermediate
compounds at different ratios of starting reagents.
Compound
Enthalpy of
formation
(kcal/mol)
Temperature interval of existence
1:1 1:2 1:3
(CH3NH3)2(DMF)2Pb3I8 -180.1 20-110 °С 20-25 °С –
(CH3NH3)2(DMF)2Pb2I6 -177.6 – 20-25 °С –
(CH3NH3)3(DMF)PbI5 -133.8 20-50 °С 20-130 °С 20-150 °С
(CH3NH3)2(DMF)xPbI4 – 20-55 °С 20-160 °С 20-170 °С
The influence of moisture on the stability of
organic-inorganic perovskite has been studied.
The stability of organic-inorganic perovskite
films was determined by X-ray diffractometry.
The stability of the films was evaluated from
the content of the PbI2 phase, which is formed
as a result of the degradation of the organic-in-
organic perovskite film. The diffractometry
PHASE FORMATION PROCESSES OF ORGANIC-INORGANIC CH3NH3PbI3 PEROVSKITES USING A DMF SOLVENT
74 ISSN 2708-129X. Укр. хім. журн., 2021
INORGANIC CHEMISTRY
results are analyzed and presented as the de-
pendence of the PbI2 phase content on the time
of exposure to moisture (Fig. 12.).
Fig. 12. The dependence of the PbI2 phase con-
tent in the decomposition of perovskite prepared
with different ratios of starting reagents: (1) 1:1;
(2) 1:2; (3) 1:3.
It was established that moisture signifi-
cantly affects the stability of organic-inorganic
perovskite films.The films obtained at a ratio
of starting reagents of 1:3 are the most stable.
The formation of these films of CH3NH3PbI3
perovskite occurs through the formation of 2
intermediate compounds. The films obtained
at a ratio of starting reagents of 1:2 show the
least resistance to moisture, they are charac-
terized by the formation of 4 intermediate
compounds. The formation of CH3NH3PbI3
perovskite at a ratio of 1:1 occurs through the
formation of 3 intermediate compounds, and
these films show better stability to moisture
than the films obtained at a ratio of starting re-
agents of 1:2, but lower stability than for films
at a ratio of 1:3. Thus, the presence of a certain
number of intermediate compounds affects the
properties of organic-inorganic perovskite.
Raman spectroscopy confirms the forma-
tion of the intermediate compounds and de-
termines the temperature intervals of their
existence. The ratio of initial reagents and the
temperature of heat treatment should be con-
trolled at the synthesis of perovskite films since
it affects the presence of intermediate phases
and, as a result, the morphology of films and
the processes of their degradation.
CONCLUSIONS. The formation of CH3NH3
PbI3 perovskite films at different ratios (1:1,
1:2 and 1:3) of the initial reagents PbI2 and
CH3NH3I dissolved in the DMF and after heat
treatment at different temperatures from 20 to
175 °C has beeninvestigated. SEM established
that the morphology of the films mainly de-
pends on the ratio of the initial reagents. The
temperature of heat treatment changes only
the dimensions of the characteristic structures
of films. The presence of other compounds in
the film influences the morphology of the film
and, as a result, the reflection and absorption
of solar radiation.
XRD and Raman spectroscopy show that
depending on the ratio of the initial reagents
and the heat treatment temperature of films,
the formation of organic-inorganic perovskite
occurs according to different schemes: through
the formation of 3, 4 or 2 intermediate com-
pounds at the ratio of the initial reagents of 1:1,
1:2 or 1:3, respectively. The intermediate pha-
ses (CH3NH3)2(DMF)xPbI4, (CH3NH3)3(DMF)
PbI5, (CH3NH3)2(DMF)2Pb2I6 and (CH3NH3)2
(DMF)2Pb3I8 in the films were found. The pres-
ence of intermediate compounds can signi-
ficantly affect the degradation of films. It has
been established that moisture significantly
affects the stability of organic-inorganic pe
rovskite films.The films obtained at a ratio of
starting reagents of 1:3 are the most stable.
P.V. Torchyniuk, O.I. V’yunov, V.O. Yukhymchuk, O.M. Hreshchuk, S.V. Vakarov, A.G. Belous
75https://ucj.org.ua
UCJ № 8 / Vol. 87
Acknowledgements
The authors acknowledge the support
from the Targeted Program of Basic
Research of the National Academy of
Sciences of Ukraine “Advanced fundamen-
tal research and innovative development of
nanomaterials and nanotechnologies for the
needs of industry, healthcare, and agricul-
ture” (State registration № 0120U102242).
ПРОЦЕСИ ФАЗОУТВОРЕННЯ ОРГАНО-НЕОР-
ГАНІЧНИХ ПЕРОВСКИТІВ CH3NH3PbI3 ПРИ ВИ-
КОРИСТАННІ РОЗЧИННИКА ДМФА
П. В. Торчинюк1, О. І. В’юнов1*,
В. О. Юхимчук2, О. М. Грещук2,
С. В. Вакаров1, А. Г. Білоус1
1Інститут загальної та неорганічної хі-
мії імені В. І. Вернадського НАН України,
просп. Академіка Палладіна, 32/34, Київ
03142, Україна
2Інститут фізики напівпровідників імені
В. Є. Лашкарьова НАН України, просп. Нау-
ки, 41, Київ 03028, Україна
* e-mail: vyunov@ionc.kiev.ua
Плівки органо-неорганічних перовски-
тів CH3NH3PbI3 було синтезовано з розчи-
нів із різним співвідношенням (1:1, 1:2 та
1:3) вихідних реагентів (PbI2 та CH3NH3I) у
розчиннику ДМФА. Методами рентгенофа-
зового аналізу та раманівської спектроско-
пії було показано, що органо-неорганічні
перовскити утворюються за різними схе-
мами залежно від співвідношення PbI2 та
CH3NH3I.
При співвідношенні вихідних реаген-
тів 1:1, крім органо-неорганічного перов
скиту CH3NH3PbI3, утворюються три про-
міжні сполуки: (CH3NH3)2(DMF)xPbI4,
(CH3NH3)2(DMF)2Pb3I8, (CH3NH3)3(DMF)
PbI5. При співвідношенні вихідних реа-
гентів 1:2 утворюються чотири проміжні
сполуки: крім зазначених фаз, виявляється
фаза (CH3NH3)2(DMF)2Pb2I6. При збільшен-
ні співвідношення вихідних реагентів до
1:3 спостерігають лише дві проміжні фази
(CH3NH3)2(DMF)xPbI4 та (CH3NH3)3(DMF)
PbI5. Встановлено, що морфологія плівок
перовскитів залежить, перш за все, від
співвідношення вихідних реагентів. Тем-
пература оброблення змінює лише розміри
зерен плівок.
Наявність проміжних сполук при синте-
зі органо-неорганічних перовскитів може
суттєво впливати на властивості плівок.
Методом РФА було досліджено вплив во-
логи на стійкість плівок органо-неорганіч-
них перовскитів CH3NH3PbI3, отриманих
при співвідношенні PbI2:CH3NH3I – 1:1, 1:2,
1:3. Стійкість плівок оцінювали за вмістом
фази PbI2, яка утворюється в результаті де-
градації плівки органо-неорганічного пе-
ровскиту. Показано, що стійкість плівок
залежить від кількості проміжних сполук,
які утворюються при синтезі перовскиту.
Плівки перовскиту, які утворюються при
співвідношенні 1:3 через формування та
розпад двох проміжних сполук, є найстій-
кішими до дії вологи. Плівки перовскиту,
отримані при співвідношенні 1:2 і в яких
утворення перовскиту відбувається через
утворення чотирьох проміжних сполук, є
найменш стійкими до дії вологи.
Для синтезу плівок органо-неорганіч-
них перовскитів необхідно контролювати
PHASE FORMATION PROCESSES OF ORGANIC-INORGANIC CH3NH3PbI3 PEROVSKITES USING A DMF SOLVENT
76 ISSN 2708-129X. Укр. хім. журн., 2021
INORGANIC CHEMISTRY
співвідношення вихідних реагентів і тем-
пературу оброблення плівки, оскільки це
впливає на кількість проміжних фаз і, як
результат, морфологію плівок, процеси їх-
ньої деградації.
Ключові слова: органо-неорганічний
перовскит, рентгенофазовий аналіз, рама-
нівська спектроскопія, проміжні сполуки,
стабільність.
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per-resolution luminescence microspec-
troscopy reveals the mechanism of pho-
toinduced degradation in CH3NH3PbI3
perovskite nanocrystals. The Journal of
Physical Chemistry C, 2016, 120 (19).
P. 10711–10719.
33. Barugkin C., Cong J., Duong T., Rahman S.,
Nguyen H. T., Macdonald D., White T. P.,
Catchpole K. R., Ultralow absorption co-
efficient and temperature dependence of
radiative recombination of CH3NH3PbI3
perovskite from photoluminescence. The
journal of physical chemistry letters, 2015,
6 (5). P. 767–772.
34. Niemann R. G., Kontos A. G., Palles D.,
Kamitsos E. I., Kaltzoglou A., Brivio F.,
Falaras P., Cameron P. J., Halogen effects
on ordering and bonding of CH3NH3
+ in
CH3NH3PbX3 (X = Cl, Br, I) hybrid pe
rovskites: a vibrational spectroscopic
study. The Journal of Physical Chemistry C,
2016, 120 (5). P. 2509–2519.
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Стаття надійшла 23.07.2021.
|
| id | oai:ojs2.1444248.nisspano.web.hosting-test.net:article-341 |
| institution | Ukrainian Chemistry Journal |
| keywords_txt_mv | keywords |
| language | English |
| last_indexed | 2026-07-23T01:06:44Z |
| publishDate | 2021 |
| publisher | V.I.Vernadsky Institute of General and Inorganic Chemistry |
| record_format | ojs |
| resource_txt_mv | ucjorgua/1b/62465977fb870c9089fced001680a01b.pdf |
| spelling | oai:ojs2.1444248.nisspano.web.hosting-test.net:article-3412026-07-22T08:23:47Z PHASE FORMATION PROCESSES OF ORGANIC-INORGANIC CH3NH3PbI3 PEROVSKITES USING A DMF SOLVENT ПРОЦЕСИ ФАЗОУТВОРЕННЯ ОРГАНО-НЕОРГАНІЧНИХ ПЕРОВСКИТІВ CH3NH3PbI3 ПРИ ВИКОРИСТАННІ РОЗЧИННИКА ДМФА Torchyniuk, Pavlo V'yunov, Oleg Yukhymchuk, Volodymyr Hreshchuk, Oleksandr Vakarov, Serhii Belous, Anatolii organic-inorganic perovskite, X-ray diffraction analysis, Raman spectroscopy, intermediate compounds, stability. The organic-inorganic perovskite films CH3NH3PbI3 were synthesized from solutions with different ratios (1:1, 1:2 and 1:3) of initial reagents (PbI2 and CH3NH3I) in a DMF solvent. XRD and Raman spectroscopy shows that the perovskites are formed according to different schemes depending on the ratio of PbI2 and CH3NH3I. At the ratio 1:1 of initial reagents, three intermediate compounds are formed: (CH3NH3)2(DMF)xPbI4, (CH3NH3)2(DMF)2Pb3I8, (CH3NH3)3(DMF)PbI5. At the ratio 1:2 of initial reagents four intermediate compounds are formed: in addition to the above phases, the phase (CH3NH3)2(DMF)2Pb2I6 is found. And at the ratio 1:3 of initial reagents, only two intermediate phases, (CH3NH3)2(DMF)xPbI4 and (CH3NH3)3(DMF)PbI5, are observed. The morphology of the perovskite films was established to depend primarily on the ratio of the initial reagents. The temperature of heat treatment changes only the grain size of films. V.I.Vernadsky Institute of General and Inorganic Chemistry 2021-09-24 Article Article Inorganic Chemistry Неорганическая химия Неорганічна хімія application/pdf https://ucj.org.ua/index.php/journal/article/view/341 10.33609/2708-129X.87.08.2021.63-81 Ukrainian Chemistry Journal; Vol. 87 No. 8 (2021): Ukrainian Chemistry Journal; 63-81 Украинский химический журнал; ##issue.vol## 87 ##issue.no## 8 (2021): Ukrainian Chemistry Journal; 63-81 Український хімічний журнал; Том 87 № 8 (2021): Український хімічний журнал; 63-81 2708-129X 2708-1281 en https://ucj.org.ua/index.php/journal/article/view/341/180 Copyright (c) 2021 Pavlo Torchyniuk, Oleg V'yunov, Volodymyr Yukhymchuk, Oleksandr Hreshchuk, Serhii Vakarov, Anatolii Belous https://creativecommons.org/licenses/by-nc/4.0 |
| spellingShingle | Torchyniuk, Pavlo V'yunov, Oleg Yukhymchuk, Volodymyr Hreshchuk, Oleksandr Vakarov, Serhii Belous, Anatolii ПРОЦЕСИ ФАЗОУТВОРЕННЯ ОРГАНО-НЕОРГАНІЧНИХ ПЕРОВСКИТІВ CH3NH3PbI3 ПРИ ВИКОРИСТАННІ РОЗЧИННИКА ДМФА |
| title | ПРОЦЕСИ ФАЗОУТВОРЕННЯ ОРГАНО-НЕОРГАНІЧНИХ ПЕРОВСКИТІВ CH3NH3PbI3 ПРИ ВИКОРИСТАННІ РОЗЧИННИКА ДМФА |
| title_alt | PHASE FORMATION PROCESSES OF ORGANIC-INORGANIC CH3NH3PbI3 PEROVSKITES USING A DMF SOLVENT |
| title_full | ПРОЦЕСИ ФАЗОУТВОРЕННЯ ОРГАНО-НЕОРГАНІЧНИХ ПЕРОВСКИТІВ CH3NH3PbI3 ПРИ ВИКОРИСТАННІ РОЗЧИННИКА ДМФА |
| title_fullStr | ПРОЦЕСИ ФАЗОУТВОРЕННЯ ОРГАНО-НЕОРГАНІЧНИХ ПЕРОВСКИТІВ CH3NH3PbI3 ПРИ ВИКОРИСТАННІ РОЗЧИННИКА ДМФА |
| title_full_unstemmed | ПРОЦЕСИ ФАЗОУТВОРЕННЯ ОРГАНО-НЕОРГАНІЧНИХ ПЕРОВСКИТІВ CH3NH3PbI3 ПРИ ВИКОРИСТАННІ РОЗЧИННИКА ДМФА |
| title_short | ПРОЦЕСИ ФАЗОУТВОРЕННЯ ОРГАНО-НЕОРГАНІЧНИХ ПЕРОВСКИТІВ CH3NH3PbI3 ПРИ ВИКОРИСТАННІ РОЗЧИННИКА ДМФА |
| title_sort | процеси фазоутворення органо-неорганічних перовскитів ch3nh3pbi3 при використанні розчинника дмфа |
| topic_facet | organic-inorganic perovskite X-ray diffraction analysis Raman spectroscopy intermediate compounds stability. |
| url | https://ucj.org.ua/index.php/journal/article/view/341 |
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