Improving performance of perovskites solar cells using solvent engineering, via Lewis adduct of MAI-DMSO-PbI2 and incorporation of imidazolium cation

Article abstract of DOI:10.1016/j.jallcom.2019.153076

Perovskite solar cells (PSCs) are a great promise to solve the problem of energy demand. However, one of the most important factors to obtain higher yields of high efficiency photovoltaic devices is to produce high quality methyl ammonium lead iodide (MAPbI₃) films. In this work, strategies such as solvent engineering, Lewis adduction formation and the incorporation of Imidazolium cation (Im⁺) were implemented to improve the microstructural quality of the films. The mixed MA₉₉ImI₁ film displayed a more homogeneous microstructure compared to the original MAPbI₃ film, as well as an improved power conversion efficiency, with a value of 17%.

Full text of DOI:10.1016/j.jallcom.2019.153076

Journal Pre-proof
Improving performance of perovskites solar cells using solvent engineering, via Lewis
adduct of MAI-DMSO-PbI and incorporation of imidazolium cation
2
Edgar González-Juárez, Diego González-Quijano, Diana F. Garcia-Gutierrez,
Domingo I. Garcia-Gutierrez, Jorge Ibarra-Rodríguez, Eduardo Sanchez
PII:
S0925-8388(19)34322-1
DOI:
https://doi.org/10.1016/j.jallcom.2019.153076
JALCOM 153076
Reference:
To appear in: Journal of Alloys and Compounds
Received Date: 7 August 2019
Revised Date: 16 November 2019
Accepted Date: 17 November 2019
Please cite this article as: E. González-Juárez, D. González-Quijano, D.F. Garcia-Gutierrez, D.I. Garcia-
Gutierrez, J. Ibarra-Rodríguez, E. Sanchez, Improving performance of perovskites solar cells using
solvent engineering, via Lewis adduct of MAI-DMSO-PbI and incorporation of imidazolium cation,
2
Journal of Alloys and Compounds (2019), doi: https://doi.org/10.1016/j.jallcom.2019.153076.
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Author Contributions section
For the development of this manuscript it was necessary to form a work team in
such a way that each one contributes with their experience, in this sense the
authors and their contribution are listed:
Dr. Edgar González performed the MAPbI3 synthesis for its application in
photovoltaic devices.
Dr. Diego González conducted the first studies to obtain the ImIPbI3 phase through
chemical synthesis and analysis of SEM and XRD.
Dr. Domingo I. Gutierrez and Dra. Diana F. Gutierrez conducted studies of the
morphology of each of the films manufactured by spin-coating and which were
characterized by scanning electron microscopy (SEM).
Dr. Jorge Ibarra conducted XRD studies and Rietveld analysis
Dr. Eduardo Sánchez is the leader of the group and in addition to supporting
experimentation, he is responsible for managing resources for the purchase of
reagents and infrastructure.

Improving performance of perovskites solar cells using solvent
engineering, via Lewis adduct of MAI-DMSO-PbI and incorporation of
2
imidazolium cation.
1
2
3
Edgar González-Juárez , Diego González-Quijano , Diana F. Garcia-Gutierrez ,
3
1*
Domingo I., Garcia-Gutierrez , Jorge Ibarra-Rodríguez, Eduardo Sanchez .
1
Universidad Autónoma de Nuevo León, UANL, Facultad de Ciencias Químicas, FCQ, Av.
Universidad S/N, Cd. Universitaria, San Nicolás de los Garza, Nuevo León, C.P. 66450,
México.
2
Universidad Autónoma de Aguascalientes Campus sur. Centro de Ciencias de la
Ingeniería. Av. Prolongación Mahatma Ghandi 6601, Colonia el Gigante,
Aguascalientes, Aguascalientes, México
3
Universidad Autónoma de Nuevo León, UANL, Facultad de Ingeniería Mecánica y
Eléctrica, FIME, Av. Universidad S/N, Cd. Universitaria, San Nicolás de los Garza, Nuevo
León, C.P. 66450, México

Abstract
Perovskite solar cells (PSCs) are a great promise to solve the problem of energy
demand. However, one of the most important factors to obtain higher yields of high
efficiency photovoltaic devices is to produce high quality methyl ammonium lead iodide
(
MAPbI ) films. In this work, strategies such as solvent engineering, Lewis adduction
3
+
formation and the incorporation of Imidazolium cation (Im ) were implemented to
improve the microstructural quality of the films. The mixed MA ImI film displayed a
99
1
more homogeneous microstructure compared to the original MAPbI
3
film, as well as an
improved power conversion efficiency, with a value of 17%.
Keywords: Perovskite solar cell, Imidazolium iodide, Thin film enhancement, solvent
engineering.
Highlights
●
The quality of the film is a very important factor determining the power
conversion efficiency (PCE), and it can be optimized by solvent engineering
methods and incorporation of alternative MA cations.
+
+
1
●
●
ImI has a cyclic structure of five members with two nitrogen atoms that can
provide a stronger Lewis basicity to passivate sub-coordinated Pb atoms and
associated defects.
A stable 3D perovskite structure is important to improve the PCE.
Introduction
Photovoltaic devices are one of the most promising technologies to produce
electricity from sunlight. Sunlight has great potential as an alternative and renewable

14
energy source, with an irradiation of 1.8 × 10 kW on the surface of the earth [1].
Renewable energy has a variety of sources such as solar, wind, biomass, hydraulic and
geothermal [2]. Photovoltaic panels, based on silicon, show commercial efficiencies
between 15-20 % [3,4] with a record efficiency of 24.4 % [5]. However, the
manufacturing of these devices uses harmful chemicals and complex purification
processes, as well as high cost production methodologies [6]. Recently, perovskite solar
cells (PSCs) have been attracting enormous interest owing to their excellent
advantages, including lower production cost, ease of fabrication, and high efficiency [7-
10]; as well as unique features displayed by lead halide perovskite, such as broad and
strong light absorption [11], longer charge carrier lifetime and diffusion length [12,13]
and low exciton binding energy [14]. Furthermore, several research groups have
achieved great success in recent years with a demonstrated power conversion efficiency
(PCE) increasing rapidly from 3.8 % to 22% [15-17] in less than 5 years. However,
drawbacks for a wider deployment of PSCs, despite its promising PCE, is that lead (Pb)
still plays a very important role in the photovoltaic cells based on perovskites with
highest efficiencies to date. Pb is known to be toxic [18,19] and efforts are ongoing to
replace the Pb component of the organo-metallic halide.
However PSCs, due to its low-temperature solution processing attribute, have
been fabricated on rigid or flexible substrates of small dimensions with remarkable
performance, allowing greater portability, bendability, light weight, conformability,
wearability and potential for integration in self powered consumer electronics, military
applications for on-demand supply of electricity in missions, solar lantern, backpacks,
self-powered electric cars among others.[20, 21
]

Many reasons contribute to this improvement, particularly the enhanced quality of
the perovskite film due to modifications on the deposition method. Various
methodologies such as one-step deposition [22,23] two-step sequential deposition [24-
26], solvent engineering [27], vapor-assisted deposition [28,29], additive engineering
[
30], and vacuum evaporation [31] can now produce high-quality films of MAPbI with flat
3
surfaces and complete surface coverage. Controlling the crystallization speed in the
MAPbI thin films has led to substantial improvements in the PCE of MAPbI based
3
3
PSCs. In other hand, hybrid organic-inorganic perovskites have been recently
investigated for optimizing their thin films’ crystal quality and to enhance the photovoltaic
performance of hybrid PSCs by substitution of inorganic anions [32], metal cations [33]
and organic ligands [34,35]. For instance, partially replacing methyl ammonium (MA)
+
+
2+
and formamidinium (FA) with inorganic cation Cs [36] and Rb [37]; replacing Pb with
2+
2+
−
−
−
−
Sn and Ge ; and replacing I with Cl , Br [38] and SCN [39]. Different investigations
show that the size of the ionic radius (IR) of the organic cation has a great influence on
the structure-property of the perovskites, which can be determined by its tolerance
factor, t. If t = 1 a perfectly packed structure is expected, for t > 1 the perovskite tends to
distort towards a tetragonal structure, finally if t < 1 there is a tendency to deform
towards twisted octahedrons. Interestingly, perovskite cells mixed with cations such as
Cs/MA [40], Cs/FA [41] and Cs/MA/FA [42] showed better stability than MAPbI -based
3
+
2
devices. Qiand et. al., found that Mn , (IR=67 pm) doping can decrease the bandgap of
CsPbIBr and simultaneously enhance its crystallinity as well as its morphology. The
2
PSCs constructed with CsPbIBr reached an outstanding PCE of 7.36% [43]. Baillie et
2
+
2
+2
al. confirmed that partially replacing Pb with Ca (IR=100 pm) or Sr , (IR=118 pm) in

3
CsPbX can optimize the morphology and passivate the surface states of the
perovskites [44].
+
+
Imidazolium cation (Im ) has a calculated effective radius of 258 pm [45], which is
+
very close the calculated size of the FA cation (253 pm), therefore it could be possible
+
+
to crystallize a 3D perovskite structure with Im replacing FA . However, Weller [46],
recently published that lead imidazolium iodide crystalizes in a 1D face-sharing infinity
-
chains of [PbI
3
] in hexagonal space group P6
3
/m (see Figure 1).
Figure 1. ImPbI structure P6 /m
3
3
Low dimensional organo-metal halide perovskites remain relatively unfamiliar [47] and
the understanding of their properties, beyond solar cells, is incomplete. Recently Jen et
+
al. (2018) [48], had published on the incorporation of Im to (MA)PbI in an inverted
3
perovskite solar cell configuration (NiO /MA Im PbI /PCBM/Bis-C /Ag) with interesting
x
1-x
x
3
60

+
results, reporting a 2% increase on efficiency at 5% of Im incorporation. Results on
+
further incorporation of Im cation into MAPbI
3
on a perovskite solar cell have been
recently published [49], adding an extra step in which the PSC is exposed to an
atmosphere rich in methylamine. Also, an increment in the efficiency, has been related
+
to the deprotonation of Im cation, which improved the quality of the thin film.
In this sense, the current work describes alternative strategies that were carried out
+
+
to improve the quality of the MAPbI thin film using the simple mixture of Im and MA
3
cations through solvent engineering. In the first stage, the synthesis and characterization
of imidazolium iodide was carried out, using different stoichiometries. In the second
stage, a cell reported in the literature was reproduced to validate the results derived
from the strategies carried out to improve the quality of the MAPbI thin films. In the third
3
stage chlorobenzene was used as antisolvent, and the formation of the adduct CH NH I-
3
3
PbI -DMSO to reduce the growth rate of the crystal using a mixture of dimethylsulfoxide
2
(DMSO) and N, N,-dimethylformamide (DMF); and finally, the incorporation of
imidazolium iodide was carried out in different weight percents.
2
. Experimental
.1 Materials.
2
All the chemicals were used as received, including titanium diisopropoxide
bis(acetylacetonate) (75 wt % in isopropanol, Sigma-Aldrich), 1-butanol (99.8%, Sigma-
Aldrich), titanium oxide (TiO ) paste (Dyesol 18NR-T), PbI (99.9983%,Sigma-Aldrich),
2
2
N,N-dimethylformamide (DMF, anhydrous 99.5 %, Sigma-Aldrich), lithium
bis(trifluoromethylsulfonyl)imide (Li-TFSI, Sigma-Aldrich), spiro-MeOTAD (99 %,
Shenzhen Feiming), chlorobenzene (SigmaAldrich), acetone, ethanol, acetonitrile.

The morphological characteristics of the thin films were observed by scanning
electron microscopy (SEM) in a JEOL JCM-6000 and a Hitachi SU-8020. X-ray
diffraction (XRD) was employed to characterize the crystallinity of the films using an
XRD Bruker D2 phaser. The UV–Vis transmission spectra were characterized by using a
scientific evolution 300 Spectrometer.
2.2. Perovskite standard solar cell device construction
Fluorine doped Tin Oxide (FTO) glass was patterned by chemical etching with Zinc (Zn)
powder and chloride acid (HCl) solution. The etched substrate was then cleaned with
hellamanex 2 % and ultrasonically cleaned with 2-propanol and deionized water in
sequence for 15 min, respectively. Afterward, the substrates were further cleaned using
O plasma cleanning for 15 min. A dense layer of TiO was then coated on the
2
2
substrates by spin coating of titanium diisopropoxide bis(acetylacetone) (75 wt% in
isopropanol, Aldrich) diluted in absolute ethanol (v/v, 1/20) at 3000 rpm for 1 min. The
substrates were then heated at 180 ºC by 5 min followed by annealing at 450 °C for 1 h.
A mesoporous layer of TiO was then deposited by spin-coating TiO paste (Dyesol
2
2
18NR-T) diluted in absolute ethanol at 1:12 weight ratio at 5000 rpm for 30 s. The
substrates were then heated at 180 °C for 5 min, followed by annealing at 450 °C for 1h.
For the fabrication of the standard cell, the methodology proposed by Sutanto et al.,
2017 [50], was followed, using DMF as solvent. Previously prepared solution 1.25 M of
PbI : MAI with a 1: 1 molar ratio and left at 70° C for 12 h. MAPbI solution was
2
3
deposited by spin-coating on the mesoporous layer of TiO at 5000 rpm for 30 s. After 4
2
s of having started the centrifugation technique, 400 µL of chlorobenzene were rapidly
added to the substrate. Furthermore, a hole transport material (HTM) of Spiro-OMeTAD
was spin-coated at 3000 r.p.m. for 30 s from a chlorobenzene solution (79.1 mg in 690

µl,) that contained 22 µL of 4-tert-butylpiridine and 15 µl of Li-TFSI
Bis(trifluoromethane)sulfonimide lithium salt ) from a 500 mg/ml stock solution in
acetonitrile as dopants.
(
Figure 2. Configuration of the standard cell based on perovskite
+
1
To study the effect of Im on MAPbI on the performance of the photovoltaic
3
+
1
device, Im was incorporated in a different stoichiometric ratio. The perovskite film was
deposited also by spin coating a previously prepared solution 1.15 M of MAI:PbI with a
2
1:1 molar relation in a solvent mixture of DMF/DMSO (80:20 v/v) by a one-step process
at 3000 r.p.m. for 30 s. After a 6 s delay time of the spin coating process, a 650 µL of
anhydrous chlorobenzene were added on top of the substrate. Additionally, perovskite
thin films were sintered at 100 ºC for 10 min. HTM was spin coated at 3000 rpm for 30 s.
Finally, an 80 nm thick silver counter electrode was deposited under high vacuum by
physical vapor deposition.
2.3. Photovoltaic characterization

The J-V curves were measured using a solar simulator (Newport, Oriel
Instruments, 91160A) with a source meter (Keithley 2400). In addition, a Xenon lamp
was used as a light source and the illumination source was calibrated using a silicon
2
reference solar cell (enlitech) to calibrate the output power of the lamp to 1000 W/m .
The measurements were performed inside the glove box in order to protect the stability
of the cells. The cell area was limited using a metal mask (2.54mm x 2.54mm). The
2
active area of device is 0.65 mm .
2.4 Synthesis of Imidazolium iodide
Initially a purification of the HI (Iodhydric acid) solution was carried out; a 0.36 M
solution of tributyl phosphate in chloroform was prepared, and a liquid-liquid extraction
was carried out in a separating funnel. For crystallization, 10 ml of HI solution was used,
and 0.9412 g of imidazole was dissolved, the mixture was poured into a crystallizer and
slow evaporation was prevented. The iodine crystals were recrystallized with ethanol
and anhydrous diethyl ether.
3.0 Results and Discussion
3.1 Characterization of hybrid compounds; Imidazolium iodide and PbI
2
In a first stage, the synthesis of the perovskite type ImPbI was carried out by
3
means of the ImI and PbI precursors to be evaluated in the active layer of the
2
photovoltaic cell. The precursors were heated at 120° C for two hours and characterized
by SEM, FT-IR, UV-Vis. Furthermore, the stoichiometry of the hybrid system ImI-PbI2
was varied, 1:1 and 2:1. The absorption spectra in solution are shown in figure 3a,
where two absorption peaks are observed, located in λmax=268 and 354 nm, these

absorption peaks are attributed to the energy transitions of n- π * and π-π*, respectively.
FT-IR analysis of the hybrid system was carried out. Figure 3b shows the FTIR spectra
acquired. In general, the same bands are observed in both spectra, since in both
systems the same functional groups are present, the difference in intensity was related
to the stoichiometry (Table 1).
Figure 3. Characterization of the hybrid ImI-PbI systems. 3a) Absorption; 3b) spectrum
2
FT-IR.
X-ray diffraction analysis initially shows the absence of precursor materials,
indicating the formation of another phase for both systems. ImPbI -P6 /m was used as
3
3
reference and it is observed that the hybrid 1:1 system synthesized shows the same
pattern of peaks at 11.3º, 25.2º, 27º, 30.5º, 31.95º, 37.88º and 40º. However, studies of
single crystals of Imidazolium iodide show that the peak that appears in 11.3º
corresponds to the plane (110) of a one-dimensional structural arrangement [51-53].
+
1
This one-dimensional arrangement is attributed to the size of the ImI cation that does

not allow the formation of a stable 3D structure, despite complying with the Goldsmith
law previously mentioned.
On the other hand, the hybrid system 2:1 shows a different pattern, with peaks at
42.6º, 21.4º, and the 11.3º peak can still be observed. This suggests that the excess of
Imidazolium iodide generates the combination of different phases, indicating the
necessity to perform more thorough studies in order to confirm it.
Figure 4. XRD patterns of precursors, pattern and hybrid system 1:1 and 2:1
Moreover, films were prepared for both systems by mixing the Imidazolium iodide and
2
PbI in DMF and heated at 90 ° C for 2 h. The solutions were deposited by spin-coating
with a centrifuge ramp at different times with a heat treatment of 120 ° C for 1 h.

The films manufactured were pale yellow and in general both systems show
irregularities that limit their application in photovoltaic devices. SEM images of the
fabricated thin films are shown in figure 5. The hybrid system (2:1) shows the formation
of agglomerates due to the excess of imidazolium, while the film of the system (1:1)
shows many spaces that generate a non-homogeneous morphology. Clearly, the quality
of the films offers an opportunity to perform optimization through solvent engineering
that has recently been implemented for the optimization of thin film quality.
F
igure 5. SEM Micrographics the hybrid system 1:1 and 2:1.
3.2 Optimization and performance of standard perovskite solar cell

The manufacture of the devices by this methodology produced solar cells with PCE of
approximately 16% (Figure 6a). However, problems associated with the humidity of one
of the precursors, in this case MAI, produced that the films that were subsequently
manufactured became opaque and resulted in a significant drop in the photovoltaic
performance, down to a PCE of approximately 5 % (figure 6b).
Figure 6. Current voltage (J-V); a) Standard cell; b) Cell with wet precursor (MAI)
MAI was recrystallized using ethanol and diethyl ether as solvents, left in a
vacuum oven at 0.5 atm at 60° C overnight. On the other hand, it has been reported that
PbI
2
contains a certain percentage of humidity, and in this sense, it was also put in the
films again
oven for drying. Despite the treatment given to both precursors, the MAPbI
3
became opaque. In order to improve the quality of MAPbI films, the methodology
3
proposed by Yinhke et. al., 2017 [54] was followed, modifying both the MAPbI3
concentration from 1.25 M to 1.15 M and other parameters. A mixture of DMF / DMSO
solvents (80:20) was used to dissolve the precursors at 65°C for 45 minutes. The

purpose of using this mixture of solvents is to control the rapid nucleation and the rate of
crystallization to optimize the morphology of the films.
3
Obtained MAPbI thin films displayed an improved quality, this may be attributed to
the formation of adducts between DMF and DMSO with the precursors, specifically MAI-
PbI -DMF and MAI-PbI -DMSO [55]. Although the mechanisms of formation of these
2
2
adducts have not been fully studied, their interaction with the anti-solvent
chlorobenzene) improves the quality of the MAPbI thin films in two respects: (1)
(
3
washed away the excess solvent, which is harmful for high-quality film formation; (2)
promoted the formation of intermediate phases, and thus retarded the crystallization of
MAI and PbI
2
[54]. Subsequently, the solution was deposited on the substrate
chlorobenzene as antisolvent. The use of chlorobenzene or toluene during the spin
coating process generates a dense and uniform layer of MAPbI [54]. Afterward, MAPbI3
3
films were subjected to a heat treatment to remove the volatile DMSO from the adduct.
A post annealing process is always indispensable to achieve good crystallinity. In the
early research of perovskite solar cells, simple annealing processes at 70–100 °C for
10– 45 min were often employed to achieve an adequate PCE for the resulting devices.
Although the PCE of 16 % was not achieved, it was improved significantly from 5 % to
13%.
3.3 Integration of imidazolium cations into the structure of the MAPbI3
The next stage included the incorporation of imidazolium iodide within the structure
of the perovskite. Imidazolium iodide was incorporated in different percentages by
weight in order to analyze the effect on the structure-property of the perovskite, its effect
on photovoltaic performance and stability. Four different percentages were prepared

(
MA:ImI; 0.95:0.5, 99:1, 97:3, 95:5) and labeled as follows MA0.95ImI0.5PbI
3 1
, MA99ImI ,
MA ImI , MA ImI ). As control, a film of pure MAPbI was prepared as well. The
97
3
95
5
3
manufacturing of the devices is described in section 2.2 and the J-V curves showing
their performance are displayed in figure 7, and Table 2 shows the photovoltaics
parameters.
Figure 7. Figure. J-V curves of the best efficiencies obtained in this study.
Table 2. Photovoltaic parameters for a batch of 18 cells for each mixture and a standard
deviation of 1.1 on average.
-
2
Perovskite
Jsc [mA cm ] Voc [V]
FF
ᶯ[%]
13
9
MAPbI3
23.90
21.57
29.33
26.7
0.91
0.90
0.93
0.90
0.88
58.4
47.6
63.6
46.1
42.6
MA99.5ImI . PbI3
0 5
MA ImI PbI
17
11
7
99
1
3
3
3
MA97ImI
3
PbI
MA ImI PbI
18.92
95
5

3
XRD results for the MAImIPbI systems are shown in figure 8. The diffractograms
show the same peaks of greater intensity at 14 °, 28 ° and 31.7 °, corresponding to the
planes (110), (220) and (310), respectively (figure 8a); these peaks correspond to those
previously reported by Jen et. al. [48] for an inverted cell; ITO /NiO / MA A PbI / [6,6]
X
1-xI
X
3
-
phenyl-C -butyric acid methyl (PCBM) / bis-C /Ag. In this study a correlation was
61 60
found between the efficiency of the photovoltaic device and the presence of PbI2,
indicated by peak at approximately 12.55° for each of the mixtures (figure 8b). In this
sense, the diffractograms of MA95ImI
5
PbI
3
5
and MA95. ImI
0 5 3
. PbI show a more intense
peak at ~12.55°, associated to the presence of PbI
2
. It is well known that the presence
of PbI significantly affects the photovoltaic performance for this type of devices. The
2
efficiencies achieved using these compositions were 9% and 7%, respectively. On the
other hand, in the MA ImI PbI and MA ImI PbI mixtures, this peak shows a lower
99
1
3
97
3
3
intensity, and consequently these samples displayed higher efficiencies of 17% and
1%, respectively.
1
Figure 8a. XRD patterns of MA1-xIA
0º-14º
x 3
PbI films; 8b) highlighted diffraction profiles in the range from 2θ
1

In the analysis by SEM (figure 9) very similar microstructures can be observed.
These differences are associated with the Marangoni effect, discussed by Sautanto et.
al. [50], they explain that the roughness of the perovskite film results from the mass
transfer of two solvents, the sudden turbulence of a second injection causes, to a large
extent, liquid-solid phase separations and non-homogeneous concentrations to form
gradient differences of tension on the perovskite surface before evaporation of the
solvents. The surface tension gradient causes a random crystallization of the perovskite
and a rougher surface is obtained. In general, MAPbI
PbI present a random crystallization, that is, a greater roughness that
influences the efficiencies, whereas MA ImI PbI shows a more homogenous
3 3 3 3
, MA95.5ImI0.5PbI , MA97ImI PbI ,
MA95ImI
5
3
99
1
3
morphology and resulted in a higher efficiency of 17 %. It is important to highlight the
+
1
absence of pinhole on the surface the film. This is attributed to the incorporation of ImI
that has a cyclic structure of five members with two N atoms that can provide a stronger
Lewis basicity to passivate sub-coordinated Pb atoms and associated defects. In
addition, it can form hydrogen bonds with iodide atoms at two different angles, which
can form a molecular block at the grain boundaries to harden the MAPbI
improve overall robustness and device performance [48].
3
domains and
a)
b)
c)

d)
e)
Figure 9. Scanning Electron Microscopy (SEM) images for the MAPbI perovskite layers; a)
3
MAPbI , b) MA ImI PbI , c) MA ImI PbI , d) MA ImI PbI , e) MA ImI PbI
3
3
95.5
0.5
3
99
1
3
97
3
3
95
5
It has been studied that the under-coordinated iodides in perovskite thin-flms tend to act
as hole-trapping sites to create charge accumulation and cause undesirable charge
recombination. These defects can be passivated by the incorporation of systems that
behave as bases of Lewis such as thiophene, pyridine [56].
On the other hand, it is well-known that perovskite films tend to degrade into other
chemical species in humid environments, due to the reaction of perovskite materials with
water in air. Other factors found are thermal effects, ultraviolet radiation and processing
solutions. Different studies have suggested that water is the catalyst for the irreversible

degradation reaction of perovskite and its degradation mechanism has also been
extensively studied.
In this study, moisture stability of the as-prepared perovskite films was tested
under approximately 50 % RH (relative humidity) in ambient conditions without any
encapsulation. In this sense, the diffractograms show a significant increase of the
characteristic peak of PbI at 12.5º as the time of exposure to humidity increases. This
2
same behavior was presented by the other systems (figure 10).
x 3
Figure 10. XRD patterns of stability of MA1-xIA PbI

At the same time a stability analysis was carried out for the manufactured cells.
The results show that during the first 8 h there is a gradual loss of efficiency, however,
after 48 h they begin to suffer the effect of humidity that is reflected in the decrease in
the performance of the photovoltaic devices. MA ImI PbI film showed greater stability
99
1
3
during this time retaining 59 % of its initial PCE, attributed to a better crystallinity, since
the grain boundaries of the film retard the diffusion of moisture and oxygen. On the other
3 5 3 3 3 5 3
hand, MAPbI , MA95. ImI0.5PbI , MA97ImI PbI and MA95ImI PbI could only retain 15%,
22%, 18% and 12.5%, respectively.
Figure 11. MA IA PbI PCE vs degradation time
1
-x
x
3

4. Conclusions
The films ImIPbI
3
were pale yellow and the analysis by XRD revealed a 1-dimensional
structure(1D), so its use in photovoltaic devices is limited-
Different strategies were explored to optimize the MAPbI film and its photovoltaic
3
performance. Solvent engineering favored the formation of good film quality by
increasing the conversion efficiency from 5 to 13%.
A method of site-A engineering was used to improve the quality of the perovskite film.
+
The incorporation of ImI favored the photovoltaic performance observing different
morphologies. The best PCE obtained was 17%, through the combination of
-
2
1
MA99ImI PbI3, with Voc= 0.93V and Jsc=29.33 mA cm . At the same time, it presented
greater stability, attributed to better crystallinity, since the grain boundaries of the film
retard the diffusion of moisture and oxygen.
5.0 References
[
1] Panwar NL, Kaushik SC, Kothari S, Role of renewable energy sources in
environmental protection: a review, Renew Sustain Energy Rev 2011;15(3):1513.
[
2] BP Statistical Review of World Energy 2017; 2017. Available from:
bp.com/content/dam/bp/en/corporate/pdf/energy-economics/statistical-review 2017 /bp-
statistical-review-of-world-energy-2017-full-report.pdf
〈https://www.
〉
.
[
[
3] SunPower; 2017.
〈www.us.sunpower.com〉.
4] Fraunhofer – photovoltaics report; 2017. Available from:
〈
https://www.ise. fraunhofer.
de/content/dam/ise/de/documents/publications/studies/ Photovoltaics-Report.pdf〉.
[
5] Green MA, Hishikawa Y, Warta W, Dunlop ED, Levi DH, Hohl-Ebinger J, et al. Solar
cell efficiency tables (version 50). Progress Photovolt: Res Appl 2017;25(7):668–76.

[
6] Mulvaney D. Hazardous materials used in silicon PV cell production: a primer. Sol
Ind 2013.
[
7] H. Zhou, Q. Chen, G. Li, S. Luo, T. Song, H. Duan, Z. Hong, J. You, Y. Liu, Y. Yang,
Interface engineering of highly efficient perovskite solar cells, Science 345 (2014) 542–
46. https:/doi.org/10.1126/science.1254050
5
[
8] F. Bella, G. Griffi ni, J. Correa-Baena, G. Saracco, M. Gratzel, A. Hagfeldt, S. Turri, C.
Gerbaldi, Improving efficiency and stability of perovskite solar cells with photocurable
fluoropolymers, Science 354 (2016) 203–206. https:/doi.org 10.1126/science.aah4046.
[
9] J. Wu, Z. Lan, J. Lin, M. Huang, Y. Huang, L. Fan, G. Luo, Y. Lin, Y. Xie, Y. Wei,
Counter electrodes in dye-sensitized solar cells, Chem. Soc. Rev. 46 (2017) 5975–6023.
https:/10.1039/c6cs00752j.
[
10] J. H. Noh, S. H. Im, J. H. Heo, T. N. Mandal and S. I. Seok, Chemical Management
for Colorful, Efficient, and Stable Inorganic–Organic Hybrid Nanostructured Solar Cells,
Nano Lett., 2013, 13, 1764–1769. https://doi.org/10.1021/nl400349b.
[
11] J.P. Correa-Baena, M. Anaya, G. Lozano, W. Tress, K. Domanski, M. Saliba, T.
Matsui, T.J. Jacobsson, M.E. Calvo, A. Abate, Unbroken Perovskite: Interplay of
Morphology, Electro-optical Properties, and Ionic Movement, Adv. Mater. 28 (2016)
5031-5037. https://doi.org/10.1002/adma.201600624.
[
14] X. Liu, J. Wu, Y. Yang, T. Wu, Q. Guo, Pyridine solvent engineering for high quality
anion-cation-mixed hybrid and high performance of perovskite solar cells, Journal of
Power Sources 399, (2018) 144-150.
[
15] X. Li, D. Bi, C. Yi, J.-D. Decoppet, J. Luo, S.M. Zakeeruddin, A. Hagfeldt, M.
Gratzel, A vacuum flash-assisted solution process for high-efficiency large-area
perovskite solar cells, Science 353 (2016) 58-62.
https://doi.org/10.1126/science.aaf8060.
[
16] J.-W. Lee, H.-S. Kim, N.-G. Park, Lewis Acid–Base Adduct Approach for High
Efficiency Perovskite Solar Cells, Accounts Chem. Res. 49 (2016) 311-319.
https://doi.org/10.1021/acs.accounts.5b00440.
[
17] T. Todorov, O. Gunawan, S. Guha, A road towards 25% efficiency and beyond:
perovskite tandem solar cells, Mol. Syst. Des. Eng. 1 (4) (2016) 370-376. https://doi:
0.1039/C6ME00041J.
1

[
18] M. Grätzel, The light and shade of perovskite solar cells, Nature Materials
volume13, 838–842 (2014) https://doi.org/10.1038/nmat4065.
[
19] Idris K. Popoola Mohammed A. Gondal Talal F. Qahtan, Recent progress inflexible
perovskite solar cells: Materials, mechanical tolerance and stability. Renewable and
Sustainable Energy Reviews. https://doi.org/10.1016/j.rser.2017.10.028.
[
20] S.S. Shin, W.S Yang, J.H. Noh, J.H. Suk, N. J. Jeon, J.H Park, High-performance
flexible perovskite solar cells exploiting Zn SnO prepared in solution below 100 °C. Nat
Commun. 6 (2015) 1–8. http://dx.doi.org/10.1038/ncomms8410.
2
4
[
21] M. Ye, X. Hong, X. Y Liu, Recent Advancements in Perovskite Solar Cells:
Flexibility, Stability and Large Scale. J Mater Chem A 4 (2016) 6755–71.
http://dx.doi.org/10. 1039/C5TA09661H.
[
22] A. Mei, X. Li, L. Liu, Z. Ku, T. Liu, Y. Rong, M. Xu, M. Hu, J. Chen, Y. Yang, H. Han,
A hole-conductor–free, fully printable mesoscopic perovskite solar cell with high stability,
45 (2014) 295. https://doi.org/10.1126/science.1254763.
3
[
23] N.J. Jeon, J.H. Noh, W.S. Yang, Y.C. Kim, S. Ryu, J. Seo, S.I. Seok, Compositional
engineering of perovskite materials for high-performance solar cells, Nature 517 (2015)
76-480. https://doi.org/10.1038/nature14133.
4
[
24] J. Burschka, N. Pellet, S. Moon, R. Humphry-Baker, P. Gao, M. Nazeeruddin, M.
Gratzel, Compositional engineering of perovskite materials for high-performance solar
cells, Nature 499 (2013) 316. https://doi.org/10.1038/nature14133.
[
25] Z. Xiao, C. Bi, Y. Shao, Q. Dong, Q. Wang, Y. Yuan, C. Wang, Y. Gao, J. Huang,
Efficient, high yield perovskite photovoltaic devices grown by interdiffusion of solution-
processed precursor stacking layers, Energy Environ. Sci. 8 (2014) 2619-2623.
https://doi.org/ 10.1039/C4EE01138D.
[
26] Z. Xiao, Q. Dong, C. Bi, Y. Shao, Y. Yuan, J. Huang, Solvent Annealing of
Perovskite Induced Crystal Growth for Photovoltaic Device Efficiency Enhancement,
Adv. Mater. 26 (2014) 6503-6509. https://doi.org/10.1002/adma.201401685.
‐
‐
[
27] N. Jeon, J. Noh, Y. Kim, W. Yang, S. Ryu, S. Seol, Solvent engineering for high-
performance inorganic-organic hybrid perovskite solar cells, Nat. Mater. 13 (2014) 897.
https://doi.org/ 10.1038/nmat4014.

[
28] D. Liu, T.L. Kelly, Perovskite solar cells with a planar heterojunction structure
prepared using room-temperature solution processing techniques, Nat. Photonics 8
2014) 133-138. https://doi.org/10.1038/nphoton.2013.342.
(
[
29] M. Liu, M.B. Johnston, H.J. Snaith, Efficient planar heterojunction perovskite solar
cells by vapour deposition. Nature 501 (2013) 395-398.
https://doi.org/10.1038/nature12509.
[
30] Y. Jeon, S. Lee, R. Kang, J. Kim, J. Yeo, S. Lee, S. Kim, J. Yun, D. Kim, Planar
heterojunction perovskite solar cells with superior reproducibility. Sci. Rep. 4 (2014)
953. https://doi.org/10.1038/srep06953.
6
[
31] M. Liu, M. Johnston, H. Snaith, Efficient planar heterojunction perovskite solar cells
by vapour deposition, Nature 501 (2013) 395. https://doi.org/10.1038/nature12509.
[
32] A. Kojima, K. Teshima, Y. Shirai, T. Miyasaka, Organometal halide perovskites as
visible light sensitizers for photovoltaic cells, J. Am. Chem. Soc. 131 (2009) 6050-6051.
https://doi.org/10.1021/ja809598r.
[
33] J.Y. Jeng, Y.F. Chiang, M.H. Lee, S.R. Peng, T.-F. Guo, P. Chen, T.-C. Wen,
CH NH PbI perovskite/fullerene planar-heterojunction hybrid solar cells, Adv. Mater. 25
2013) 3727-3732. https://doi.org/10.1002/adma.201301327.
3
3
3
(
[
34] M.Z. Liu, M.B. Johnston, H.J. Snaith, Efficient planar heterojunction perovskite solar
cells by vapour deposition, Nature 501 (2013) 395-398.
https://doi.org/10.1038/nature12509.
[
35] M. Xiao, F. Huang, W.C. Huang, Y. Dkhissi, Y. Zhu, J. Etheridge, A. Gray-Weale, U.
Bach, Y.B. Cheng, L. Spicca, A fast deposition-crystallization procedure for highly
efficient lead iodide perovskite thin-film solar cells. A fast deposition-crystallization
procedure for highly efficient lead iodide perovskite thin-film solar cells, Angew. Chem.
Int. Ed. 126 (2014) 10056-10061. https://doi.org/10.1002/anie.201405334.
[
36] M. Saliba, T. Matsui, J. Seo, K. Domanski, J. Correa-Baena, M. Nazeeruddin, S.
Zakeeruddin, W. Tress, A. Abate, A. Hagfeldt, Cesium-containing triple cation perovskite
solar cells: improved stability, reproducibility and high efficiency. Energy Environ. Sci. 9
(2016) 1989. https://doi.org/10.1039/C5EE03874J.
[
37] M. Saliba, T. Matsui, K. Domanski, J. Seo, A. Ummadisingu, S. Zakeeruddin, J.
Correa-Baena, W. Tress, A. Abate, A. Hagfeldt, Incorporation of rubidium cations into

perovskite solar cells improves photovoltaic performance. Science 354 (2016) 206.
https://doi.org/10.1126/science.aah5557.
[
38] T. Wu, J. Wu, Y. Tu, X. He, Z. Lan, M. Huang, J. Lin, J, Solvent engineering for
high-quality perovskite solar cell with an efficiency approaching 20%. Power Sources
65 (2017) 1–6. https://doi.org/10.1016/j.jpowsour.2017.08.074.
3
[
39] A. Abate, J. Correa-Baena, M. Saliba, M. Su'ait, F. Bella, Frontispiece: Perovskite
Solar Cells: From the Laboratory to the Assembly Line, Chem. Eur J. 24 (2018) 3083–
100. https://doi.org/10.1002/chem.201704507.
3
[
40] H. Choi, J. Jeong, H. Kim, S. Kim, B. Walker, G. Kim, J. Kim, Cesium-doped
methylammonium lead iodide perovskite light absorber for hybrid solar cells Nano
Energy 7 (2014) 80. https://doi.org/10.1016/j.nanoen.2014.04.017.
[
41] J. Lee, D. Kim, H. Kim, S. Seo, S. Cho, N. Park, Formamidinium and cesium
hybridization for photo-and moisture-stable perovskite solar cell Adv. Energy Mater 5
2015) 201501310. https://doi.org/10.1002/aenm.201501310.
(
[
42] J. Burschka, N. Pellet, S. Moon, R. Humphry-Baker, P. Gao, M. Nazeeruddin, M.
Gratzel, Sequential deposition as a route to high-performance perovskite-sensitized
solar cells, Nature, 499 (2013) 316. https://doi.org/10.1038/nature12340.
[
43] J. Liang, Z. Liu, L. Qiu, Z. Hawash, L. Meng, Z. Wu, Y. Jiang, L.K. Ono, Y. Qi,
Enhancing Optical, electronic, crystalline, and morphological properties of cesium lead
halide by Mn substitution for high-stability all-inorganic perovskite solar cells with carbon
electrodes, Adv. Energy Mater. 8 (2018) 1800504.
[
44] C.F.J. Lau, X. Deng, J. Zheng, J. Kim, Z. Zhang, M. Zhang, J. Bing, B. Wilkinson, L.
Hu, R. Patterson, S. Huang, A. Ho-Baillie, Enhanced performance via partial lead
replacement with calcium for a CsPbI3 perovskite solar cell exceeding 13% power
conversion effi ciency, J. Mater. Chem. A 6 (2018) 5580–5586
[
45] G. Kieslich, S. Sun, K. Cheetham, Solid-state principles applied to organic–
inorganic perovskites: new tricks for an old dog, Chem. Sci., 2014, 5, 4712.
https://doi.org/10.1039/C4SC02211D.
[
46] O. J. Weber, K. L. Marshall, L. M. Dyson, M. T. Weller. Structural diversity in hybrid
organic–inorganic lead iodide materials Acta Cryst. (2015) B71, 668–678.
https://doi.org/10.1107/S2052520615019885.

[
47] H. Lin, C. Zhou, Y. Tian, T. Siegrist, T. B. Ma, Low-Dimensional Organometal Halide
Perovskites. Energy Lett. 2018, 3, 54−62.
https://doi.org/10.1021/acsenergylett.7b00926.
[
48] Q. Wang, F. Lina, Chu-Chen C, T. Zhaoa, M. Eslamian, A. K.Y. Jen, Enhancing
efficiency of perovskite solar cells by reducing defects through imidazolium cation
incorporation Materials Today Energy, 7, 2018, 161-168.
http://doi.org./10.1016/j.mtener.2017.09.007.
[
49] Yi. Z., Giulia G., Zhafu F., Erfan Shirzadi., Xuehui L., Emad Oveise., Farzaneh.,
Rosario S., Yaquing F., Mohammad K. N., Paul.J. D. Nano Energy 58 (2019) 105–111].
[
50] A. Sutanto, S. Lan, C. Cheng, S. B. Mane, H-P. Wu, M. Leonardus, M-Y. Xie, S-C.
Yeh, C-W. Tseng, C-T. Chen, E. W-G. Diau, C-H. Hung, Solar Energy Materials and
Solar Cells 172 (2017) 270–276. https://doi.org/10.1016/j.solmat.2017.07.043.
[
51] C. C. Stoumpos, C. D. Malliakas, M. G. Kanatzidis, Semiconducting Tin and Lead
Iodide Perovskites with Organic Cations: Phase Transitions, High Mobilities, and Near-
Infrared Photoluminescent Properties Inorg. Chem. 52 (2013) 9019–9038.
https://doi.org/10.1021/ic401215x.
[
52] N. Pellet, P. Gao, G. Gregori, T. Y. Yang, M. K. Nazeeruddin, J. Maier, M. Grätzel,
Mixed-organic-cation perovskite photovoltaics for enhanced solar-light harvesting.
Angew. Chem. Int. Ed. 53 (2014) 3151–3157. https://doi.org/10.1002/anie.201309361.
[
53] Y. Huang,L.Li,Z.Liu,H.Jiao,Y.He,X.Wang,R.Zhu,D.Wang,J.Sun,Q.Chen, H.Zhou, J.
The intrinsic properties of FA(1−x)MA PbI perovskite single crystals, Mater. Chem. A 5
x
3
(2017) 8537–8544. https://doi.org/ 10.1039/C7TA01441D.
[
54] R. Yinhke, D. Bin D, X. Yafeng, H. Yang, L. Zhaoquian, H. Linhua, H. Tasawar, W.
Hongxia, Z. Jun, D. Songyuan. Scince China Materials 2017, 60(5): 392-398.
[
55] N. J. Jeon, J. H. Noh, Y.C. Kim, W.S. Yang, S. Ryu, S.I. Seok, Solvent engineering
for high-performance inorganic-organic hybrid perovskite solar cells, Nat. Mater. 13
2014) 897-903.
(
[
56] N. K. Noel, A. Abate, S. D. Stranks, E. S. Parrott, V. M. Burlakov, A. Goriely and H.
J. Snaith, ACS Nano, 2014, 8, 9815–9821.

-
1
Table 1. IR absorption bands (cm ) and their assignments for the synthesized
compounds.
Hybrid system
υ
N-H st
υ
C- H st
υ
C-Nst
υ
C=Cst
υ
C-H oop
υ
C-H ring
ImI-PbI -1:1
3263
3476
3121
3121
1428
1397
1621
1633
1030
1030
735
746
2
ImI-PbI -2:1
2

Declaration of interest statement
The authors declare there is no conflict of interests