Hybrid Advances 7 (2024) 100301

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Hybrid Advances
journal homepage: www.journals.elsevier.com/hybrid-advances

Research Article

Performance optimization of FASnI3 based perovskite solar cell through

SCAPS-1D simulation
Ateeq ul Rehman a , Shahbaz Afzal b,c,*, Iqra Naeem a , Dilawaiz Bibi a , Sakhi Ghulam Sarwar c,d ,
Faran Nabeel e, Raphael M. Obodo c,f
a
Institute of Physics, Baghdad ul Jadeed Campus, The Islamia University of Bahawalpur, Bahawalpur, 63100, Pakistan
b
Department of Physics, University of Education Lahore, DG Khan Campus, 32200, Pakistan
c
National Centre for Physics, Quaid-i-Azam University Campus, Islamabad, 44000, Pakistan
d
School of Materials Science and Engineering, Beijing Institute of Technology, Beijing, 100081, China
e
Department of Chemistry, Materials Chemistry Laboratory, Government College University, 54000, Lahore, Pakistan
f
Department of Physics and Astronomy, University of Nigeria, Nsukka, 410001, Nigeria

A R T I C L E I N F O A B S T R A C T

Keywords: The article provides a detailed look at the fabrication of a high-performance structure for FASnI3-based perov­
Solar cell skite solar cells (PSCs). The FTO/CeO2/FASnI3/CuI/Au structure is designed using the Solar Cell Capacitance
SCAPS simulation Simulator in One Dimension (SCAPS-1D) to investigate the fabricated PSC’s performance. This investigation’s
Efficiency
main objective is to improve PSCs performance by using non-traditional Hole transport layer (HTL) and Electron
Fill factor
transport layer (ETL) materials, such as CeO2 and CuI, which have both been the subject of limited research.
Current density
Moreover, the investigation seeks to determine the impact of several perovskite layer characteristics, including
bandgap (Eg), electron affinity (χ), acceptor density (NA), thickness (t), and defect density (Nt). Additionally, this
study also investigates the effect of various back contact work functions. Significant improvements in solar cell
parameters, such as power conversion efficiency (PCE) from 22.06% to 24.87% and current density (Jsc) from
26.0274 to 30.675 mA/cm2, were observed by optimizing the device’s parameters. In contrast, the fill factor (FF)
and open circuit voltage (Voc) decreased their values from 86.13% to 87.10% and 0.9843 to 0.9308 V,
respectively. These findings show that our designed solar cell structure performs better than those with
conventionally used HTLs and ETLs. Consequently, this study highlights the potential benefits of lead-free PSCs
and presents fresh opportunities for their development and use in various solar applications.

1. Introduction formula, ABX3. In this structure, ‘A’ indicates a sizable cation, ‘B’ de­
notes a tinier cation, and ‘X’ symbolizes a halide anion. However,
Solar cell technology represents a sustainable and environmentally various challenges must be overcome to facilitate their widespread
friendly energy solution that does not produce greenhouse gas emissions commercial utilization. Nonetheless, their high absorption coefficients,
[1]. Given the growing hesitation regarding climate change and the need long carrier diffusion lengths, and flexible, lightweight, and ultra-thin
to decrease carbon emissions, adopting solar cell energy is becoming PSCs possess unique characteristics that distinguish them from tradi­
increasingly crucial in reducing our reliance on fossil fuels [2]. This form tional silicon-based solar cells, make them a imperative alternative.
of energy offers a sense of security by reducing the dependence on im­ PSCs have diverse applications, including integration into calculators,
ported fossil fuels, thereby establishing itself as the third most vital building structures, wearable electronics, and even space applications in
source of renewable energy after wind and hydropower [3]. Perovskites situations where conventional solar cells would not be practical [5]. This
are an exciting class of materials that have captured the attention of indicates that PSCs have the potential to transform solar cell technology.
scientists and researchers globally, primarily because of their remark­ From the first to the fourth generation, PSCs have emerged as a leading
able performance and perhaps inexpensive production expenses [4]. energy source, with reported PCE reaching 25.7%, approaching the
Perovskites represent a category of materials characterized by a specific levels of silicon-based solar cells [6]. Even after the significant attraction

* Corresponding author. National Centre for Physics, Quaid-i-Azam University Campus, Islamabad, 44000, Pakistan.
E-mail address: shahbazafzal2216@gmail.com (S. Afzal).

https://doi.org/10.1016/j.hybadv.2024.100301
Received 29 May 2024; Received in revised form 2 October 2024; Accepted 2 October 2024
Available online 3 October 2024
2773-207X/© 2024 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC license (http://creativecommons.org/licenses/by-
nc/4.0/).
A. Rehman et al. Hybrid Advances 7 (2024) 100301

by the researchers, the PSCs face problems in commercialization, and cell performance [18]. Within this particular investigation, SCAPS-1D
their performance is affected by ecological effects such as extremes of numerical simulation software, which was formulated by the Univer­
temperature and humidity, circuit hyperventilation, fault creation, sity of Gent, was employed. This software is utilized for the modeling of
interface non-uniformity, and substance toxicity [7]. Notably, compared electronic and optical characteristics essential to solar cells, facilitating
to methyl ammonium (MA)- based PSCs, formamidinium (FA)-based the evaluation of various parameters, including FF, Jsc, Voc, and PCE,
lead-free PSCs are efficient, more stable, and less toxic. Furthermore, through the Poisson and continuity equations solutions which are
due to their identical qualities with lower levels of toxicity and better written below [19]. The outcomes of this simulation tool are illustrated
performance, tin (Sn)-based PSCs are becoming more and more popular using diverse diagrams and data outputs, including the I–V curve, QE,
compared to their lead (Pb)-based replacements [8]. Numerous in­ C–V, and C–f.
vestigations have been conducted in recent years on lead-free PSCs by ( )
d dψ [ ]
utilizing various ETL, HTL, and Absorber layers. Taking this into ac­ ε(χ ) = q p(x) − n(x) + ND+ (x) − N−A (x) + pt (x) − nt (x) eq.1
dx dx
count, Ahmad et al., used the SCAPS simulation methodology to opti­
mize the design of solar cells based on FASnI3, resulting in notable /
1
improvements; Jsc: 31.20 mA/cm2, Voc: 1.81 V, FF: 33.72%, and PCE: ∂Jp ∂x + Rp (x) − G(x) = 0 eq. 2
J
19.08%, surpassing the initial efficiencies of 1.75% and 1.66% [9].
Furthermore, Nalianya et al., reported a PCE of 18.79% for the device 1
/
structure FTO/PCBM/CsSn0.5Ge0.5I3/Spiro-OMeTAD/Au by optimizing − ∂Jn ∂x + Rn (x) − G(x) = 0 eq. 3
J
the parameters of the absorber layer [10]. Regarding HTL-free compo­
nents, Sajid et al., observed a PCE percentage of 19.03% with CsSnI3, Table 1 summarizes the fundamental parameters essential for the cell
whose thickness was 100 nm, contact defected density, and defective computation, derived from previous theoretical research, while Table 2
density of 1018 cm− 3 and 1015 cm− 3, accordingly [11]. The research demonstrates interfacial defects in the HTL, absorber, ETL, and FTO
delves into the inverted p-i-n structure of FASnI3 PSC using simulation contacts. Fig. 1(a) indicates the energy band structure of FTO/CeO2/
tools, focusing on parameters like εr, carrier lifetime (τ), and thickness FASnI3/CuI/Au. The visualized configuration of the solar cell comprises
effects. The highest efficiency (17.33 %) depends on a high τ (>50 ns) an n-i-p hetero-junction, where the FASnl3 perovskite layer is interposed
and low εr, where SRH recombination is identified as a crucial perfor­ between CeO2 as the ETL and CuI as the HTL, depicted in Fig. 1(b).
mance constraint, providing valuable insights for enhancing lead-free Transparent front and back contacts are established using fluorine-
PSCs [12]. During optimizing, Jan et al. obtained a PCE of 17.74% doped tin oxide (FTO) and Au, respectively, with work functions of
utilizing CH3NH3GeI3 as the active layer and Spiro-OMeTAD as the 4.4 eV for FTO and 5.1 eV for Au [20].
power source HTL [13]. In another study, the authors used the FASnI3 By employing the conventional AM 1.5 spectrum and 300K tem­
photovoltaic by substituting toxic Pb with Sn, controlling Sn oxidation perature [21], the solar cell performance is observed by changing the
with innovative HTLs. CuSbS2 emerges as the most effective HTL, different parameters of the device like perovskite layer band gap, elec­
achieving an efficiency of 16.05% and addressing significant obstacles in tron affinity, acceptor density, thickness and different Back contact. The
lead-free perovskite solar cell technology [14]. Employing CsGeI3 as the comparison of the past and current work is displayed in Table 3. We
active layer’s substrate and adjusting the defect concentrations of the report the structure and performance of the FASnI3-based solar cell. Our
active layer, charge transport layers, and ETL/active layer interface, literature indicates that different scientists configure their solar cells
Chabri et al., demonstrated a PCE coefficient of 15.68% using simula­ with the FASnI3 perovskite layer using different HTLs and ETLs. Finally,
tions in the year 2023 [15]. In a recent study, FTO/ZnO/FASnI3/­ we discussed how well our produced solar cell structure performed
Cu2O/Au-based study gave an efficiency of 7.83 % [16]. following various parameter optimizations.
We outlined a few studies previously, and these studies on solar
energy make use of several ETL and HTL kinds. Nevertheless, our work
presents a new strategy that has not been investigated in earlier simu­
lations: we use CeO2 as the Electron Transport Layer (ETL) in conjunc­
tion with FASnI3 as the perovskite layer. This choice is driven by CeO2’s
unique properties, such as its wide band gap, high dielectric constant, Table 1
and excellent thermal and chemical stability, making it a promising Parameters used in the present study [28,29].
alternative to traditionally used ETLs [17]. By integrating CeO2, we aim Electrical Parameter CuI FASnI3 CeO2 FTO
to address the limitations observed in earlier PSC designs, particularly
Bandgap (eV) 3.1 1.45 3.5 3.5
regarding stability and efficiency under varying environmental condi­
Dielectric permittivity (eV) 6.5 8.2 9 9
tions. Additionally, our work emphasizes using tin (Sn) as a more sus­ Thickness (μm) 0.1 0.45 0.45 0.4
tainable and less toxic alternative to lead (Pb), further contributing to CB effective density of states 2.8 × 1019 1.0 × 1.0 × 2.2 ×
developing eco-friendly PSCs. In our current work, we employed CuI as (cm− 3) 1018 1020 1018
the HTL, FASnI3 as the perovskite layer, and CeO2 as ETL within the VB effective density of states 1.0 × 1019 1.0 × 2.0 × 1.8 ×
(cm− 3) 1018 1021 1019
device structure FTO/CeO2/FASnI3/CuI/Au for simulation purposes Electron affinity (ev) 2.1 4 4.6 4.3
using SCAPS-1D software. To evaluate their impact on device perfor­ Electron mobility (cm2/Vs) 1 × 102 2.2 × 101 1.0 × 2.0 ×
mance, we systematically modified various parameters of the perovskite 102 101
layer, including the band gap, electron affinity, acceptor density, Hole mobility (cm2/Vs) 4.390 × 2.2 × 101 2.5 × 1.0 ×
101 101 101
thickness, defect density, and back contact work functions. This study
Uniform donor density ND 0 0 1.0 × 1.0 ×
significantly contributes to advancing PSC technology by highlighting (cm− 3) 1021 1018
the potential of CeO2 as an effective ETL and FASnI3 as a lead-free Uniform acceptor density NA 1.0 × 1018 7.0 × 0 0
perovskite material, thereby enhancing the sustainability and effec­ (cm− 3) 1016
7
tiveness of PSCs. Electron thermal velocity 1.0 × 10 1.0 × 107 1.0 × 1.0 ×
(cm/s) 107 107
7 7
Hole thermal velocity (cm/s) 1.0 × 10 1.0 × 10 1.0 × 1.0 ×
2. Methodology 107 107
Defect density Nt 1.0 × 1015 1.0 × 1.0 × ​
Several computational tools, such as SILVACO, COMSOL, SETFOS, 1015 1015
References [28] [29] [28] [29]
and SCAPS-1D, are accessible for the numerical investigation of solar

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A. Rehman et al. Hybrid Advances 7 (2024) 100301

Table 2 then a greater number of electronic states develop near the band edges,
Interface parameters of layers. thereby enhancing carrier production and resulting in an elevation of Jsc
Parameters HTL/PL/ETL [25]. Additionally, absorption in the visible spectrum increases, which is
evident from the reduced reflection and transmission losses. In parallel,
Defect Type Neutral
Capture cross section for electrons/hole (cm2) 1.0 × 1019 a decline in band gap typically leads to a decrease in Voc from 0.9843V
Energetic distribution Single to 0.9073V due to a smaller quantity of photons possessing energies
Energy concerning Reference (eV) 0.6 surpassing the band gap that can initiate electron-hole pairs, conse­
Characteristic energy/Ev 0.1 quently yielding a reduced Voc. The fill factor values drop from 86.12%
Total density (integrated over all energies) (1/cm2) 1.0 × 1010
to 85.47% with the decrease in band gap since the reduction in charge
transfer efficiency surpasses any associated losses. However, at signifi­
3. Results and discussion cantly low band gaps, escalated trap-assisted recombination may induce
a decline in the fill factor [26]. Thus, the overall efficiency exhibits an
3.1. Impact of perovskite layer bandgap initial increase due to intensified light absorption, reduced reflection
and transmission, and charge creation, followed by a subsequent
The main benefit associated with inorganic halide perovskites is the decrease owing to heightened recombination losses at exceedingly low
adjustability of their bandgap [22]. By changing the bandgap of PSCs,
the Light absorption capacity, charge separation, effectiveness, and
optical performance-encompassing reflection, transmission, and
absorption-are all affected, impacting the solar cell’s performance. In
general, a smaller bandgap in the PL enhances the solar cell’s capacity to
absorb the region of visible light, thereby increasing the absorption and
reducing reflection losses. The excitation of electrons in the conduction
band occurs when photons are absorbed, while holes are retained in the
valence band. However, if the layer has a large band gap value, then
holes and the electrons weekly interact with each other [23], potentially
increasing refection and transmission losses, which diminish the overall
light absorption efficiency. Conversely, a too-small bandgap of FASnI3
could result in the recombination of electron-hole pairs, thus weakening
the effectiveness of charge separation. Consequently, careful consider­
ation is required to determine the appropriate size of the PL bandgap to
attain the maximum PCE of the device.
We adjusted the bandgap of the PL within the range from 1.45 to
1.37 eV, and their outcomes are depicted in Fig. 2, which indicates by
decreasing the bandgap value of the PL, Jsc experiences a rise, whereas
the PCE and FF display an initial rise then decline, and Voc consistently
drop [24]. As the value of the band gap decreases from 1.45 to 1.37 eV, Fig. 2. Impact of perovskite layer band gap on key solar cell parameters.

Fig. 1. (a) Energy band structure (b) Presented solar cell Structure.

Table 3
Comparative analysis of Previous and presented work.
Solar Cell Structure Voc (V) Jsc (mA/cm2) FF (%) PCE (%) References

FTO/TiO2/FASnI3/Spiro-OMeTAD 1.81 31.20 33.72 19.08 [38]

ITO/C60/FASnI3/PEDOT:PSS 0.806 25.2 83.62 17.33 [12]
FTO/C60/FASnI3/Spiro-OMeTAD 0.65 26.93 58.79 10.25 [14]
FTO/ZnO/FASnI3/Cu2O/Au 0.76 12.26 64.91 7.83 [16]
FTO/ZnO/FASnI3/Spiro- OMeTAD 1.06 16.71 85.85 19.80 [39]
FTO/ZnO0.25S0.75/FASnI3/Mg–CuCrO2 0.7725 25.5612 76.50 15.11 [40]
FTO/PCBM/FAPbI3/CuI 1.14 21.64 70.93 17.61 [24]
FTO/CeO2/Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3/CuI/Au (experimental) 1.015 21.05 64.0 13.69 [17]
FTO/CeO2/FASnI3/CuI/Au 0.9308 30.675 87.10 24.87 This Work

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A. Rehman et al. Hybrid Advances 7 (2024) 100301

band gaps [27].

At 1.41 eV, the PCE is close to its peak at 22.25%. This indicates that
1.41 eV is nearly optimal for balancing the trade-offs between Voc, Jsc,
and FF. The Jsc is high at this bandgap, but the slightly lower Voc and FF
prevent the PCE from reaching its absolute maximum, which occurs at
1.39 eV. This shows that while 1.41 eV is very efficient, a small further
reduction in bandgap could yield slightly higher efficiency. The above-
mentioned trends highlight the intricate balance among light absorp­
tion, charge transport, recombination mechanisms, and optical perfor­
mance in influencing the overall efficiency of solar cells as the band gap
undergoes variations. Hence, the optimal bandgap value for FASnI3 is
determined to be 1.39 eV, yielding Jsc = 29.047 mA/cm2, PCE =
22.57%. Voc = 0.9073 V and FF = 85.62 %. Fig. 3 represents the effect of
different energy band gap values on the J-V curve.

3.2. Impact of perovskite layer electron affinity

The electron affinity is the amount of energy required for obtaining a Fig. 4. Impact of perovskite layer electron affinity on key solar cell parameters.
released electron from the perovskite layer’s maximum occupied mo­
lecular orbiting (HOMO) to the lowest unoccupied molecular orbital
(LUMO) [30]. On the contrary, a reduced electron affinity signifies a
decreased energy demand for electron removal, facilitating the injection
of electrons into the solar cell and consequently leading to an elevated
Jsc value. By changing electron affinity values changes from 4.0 eV to
3.6 eV. Keeping the other parameters of the same and different layers
constant, it has been determined that FF, Voc, and PCE exhibit a
decreasing trend in their values from 86.12 to 82.02%, 0.9843 to 0.6684
V, and 22.06 to 14.46%, respectively except the Jsc, which increases
from 26.0274 to 26.3794 mA/cm2 as shown in Fig. 4.
The trends in FF, Voc, and PCE can be attributed to the reduction in
electron affinity, influencing the energy level alignment and resulting in
heightened recombination losses, diminished potential difference for
charge separation, and ultimately decreased device performance, as
shown in Fig. 5. The marginal rise in Jsc indicates a potential
enhancement in charge carrier generation or collection efficiency,
although insufficient to counterbalance the adverse effects on Voc and
FF. Additionally, the performance is critically affected by these changes
in electron affinity. Reducing electron affinity may result in modified
optical characteristics, including enhanced reflection and transmission
at specific wavelengths, which could diminish the effective absorption of
incident light within the perovskite layer. This decline in absorption can
adversely affect the generation of photogenerated carriers, consequently Fig. 5. Total recombination for different electron affinity of the perov­
impacting the overall efficiency of the device. As electron affinity skite layer.

decreases, the absorption coefficient and light-harvesting efficiency may

diminish, thus contributing to the observed reduction in PCE.
Moreover, the modifications emphasize the complex equilibrium
required to enhance material properties to achieve superior photovoltaic
efficacy. Improved reflection and transmission, in conjunction with
reduced absorption, may additionally lead to heightened parasitic los­
ses, thereby further diminishing overall efficiency [31]. Whereas, in
Fig. 5, the curve at 3.7 eV shows minimal recombination current at low
voltages, followed by a sharp increase around 0.7 V, indicating that at
this voltage, the energy becomes sufficient to overcome potential bar­
riers, leading to a significant rise in electron-hole recombination. Fig. 6
illustrates the photovoltaic response concerning the electron affinity of
the perovskite layer. In this fig, the current density remains steady at low
voltages. Then it decreases sharply after the same threshold, reflecting
the onset of dominant recombination processes that reduce the net
current flow. Consequently, a peak PCE of 22.06% is attained when the
electron affinity is established at 4.0eV [32].

3.3. Impact of perovskite layer doping NA

Fig. 3. Impact of perovskite layer band gap on J-V curve. The electrical features of the PSC are significantly influenced by the

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A. Rehman et al. Hybrid Advances 7 (2024) 100301

decreased number of ionized dopants that contribute to the electric field

spanning the junction [34]. Consequently, this reduced built-in potential
correlates with a decrease in Voc [35]. Additionally, the FF values also
experience a decline as the doping concentration decreases because of
the rise in trap-assisted recombination. Traps serve as recombination
sites for charge carriers, thereby impeding the overall efficiency of the
solar cell by restricting the charge carrier collection efficiency [36]. The
minimal rise in Jsc could be attributed to decreased recombination rates
at lower doping levels. A decrease in dopants leads to a lower occurrence
of recombination centers, which are often located at dopant atoms, thus
potentially enabling a higher participation of photogenerated carriers in
the current [37]. Hence, the optimal NA value for FASnI3 is determined
to be 7 × 1016, yielding, Jsc = 26.02 mA/cm2, PCE = 22.06%. Voc =
0.9843 V and FF = 86.12%. Fig. 8 indicates the impact of NA concen­
trations on the J-V curve.
Higher doping levels can enhance the absorption of incident light
due to increased free carrier absorption and reduced reflection losses.
However, excessive doping may increase reflection losses if the perov­
skite layer becomes too optically thick or if the doping induces signifi­
cant scattering. As doping concentration decreases, there might be an
Fig. 6. J-V curves for different electron affinity of the perovskite layer. increase in transmission through the perovskite layer, but a decrease in
absorption efficiency often accompanies this.
perovskite acceptor concentration. A greater number of doping results in
a denser pack of charge carriers inside the perovskite, which may 3.4. Impact of perovskite layer thickness
improve PSC effectiveness and raise PCE% [24]. This phenomenon can
be thoroughly investigated by changing the concentration of doping When undertaking the optimization of the perovskite absorber
rates in the perovskite from 7 × 1016 to 7 × 1012 cm− 3. Fig. 7 shows the layer’s thickness in a photovoltaic cell, the quarter-wavelength (λ/4)
PSC’s functionality in response to absorber doping and provides principle assumes a pivotal significance. This theoretical framework is
important information about the relationship between doping concen­ predicated upon the notion that the thickness of the absorber layer
trations and the total PSC effectiveness. The findings indicate that should optimally represent an odd multiple of one-quarter of the
adjusting the doping from 7 × 1016 to 7 × 1012 cm− 3 shows the PCF, wavelength of the incident electromagnetic radiation. At such thick­
Voc, and FF decrease from 22.06 to 19.80%, 0.9843 to 0.9708V, and nesses, constructive interference is realized between the light waves that
86.12 to 77.10%, while the Jsc increasing slightly from 26.02 to 26.45 are reflected from the anterior and posterior surfaces of the layer,
mA/cm2 during all the variations. Higher doping levels can enhance the culminating in a heightened absorption of light within the material. This
absorption of incident light due to increased free carrier absorption and enhanced absorption consequently elevates the generation of charge
reduced reflection losses. However, excessive doping may increase carriers, which subsequently augments both the photocurrent and the
reflection losses if the perovskite layer becomes too optically thick or if overall PCE of the photovoltaic cell. Furthermore, the quarter-
the doping induces significant scattering. As doping concentration de­ wavelength thickness serves to minimize reflection losses at the in­
creases, there might be an increase in transmission through the perov­ terfaces by facilitating a match in optical impedance between the
skite layer, but this is often accompanied by a decrease in absorption various layers, thereby permitting a greater proportion of light to be
efficiency. absorbed rather than being reflected away from the cell [41]. Further­
The Voc is ascertained through the gap in the quasi-Fermi levels of more, the variation in photovoltaic parameters with changes in perov­
both electrons and holes [33]. Elevated levels of NA lead to a corre­ skite thickness is depicted in Fig. 9. The Fig shows that by increasing the
sponding increase in the built-in potential, thereby resulting in a rise of
Voc. The reduction in the NA diminishes the built-in potential owing to a

Fig. 7. Impact of acceptor density of perovskite layer on key solar

cell parameters. Fig. 8. Impact of varying NA (cm− 3) on J-V characteristics.

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A. Rehman et al. Hybrid Advances 7 (2024) 100301

thickness of the perovskite layer the Voc, Jsc and PCE values increase
from 0.9843 to 0.9855V, 26.027–27.577 mA/cm2 and 22.06–23.36%
respectively. It can be realized that higher absorber thicknesses
contribute to decreased recombination and result in an improvement in
various photovoltaic parameters of the cell [42]. The
quarter-wavelength principle aids in attaining a judicious equilibrium,
ensuring that the thickness is fine-tuned to optimize light absorption
without incurring substantial recombination losses or exacerbating
resistance. Notably, it is also observed that the FF values decrease by
changing the thickness of the layer. The performance of an absorber
layer is influenced by various factors during thickness variation. For
instance, higher thicknesses may lead to decreased charge recombina­
tion, improved light absorption within the layer and also facilitate
charge transportation. Fig. 10 shows the chances of the presence of
recombination within the layer by changing the thickness [43]. In the
context of our investigation, the selected thickness of 650 nm likely
corresponds to an optimized scenario that closely aligns with the
quarter-wavelength for a specified segment of the solar spectrum,
resulting in enhanced efficiency and minimized recombination, thereby
bolstering the overall performance of the photovoltaic cell. Fig. 10 il­
lustrates the total recombination current density as a function of voltage
for different thicknesses of the perovskite layer (denoted by different Fig. 10. Total recombination for varying thickness of perovskite layer.
markers). The recombination current remains low and stable across all
thicknesses up to about 0.8 V. Beyond this voltage, there is a sharp in­ the absorber FASnI3 layers [44]. Besides that, several reports have
crease in recombination current. Thicker perovskite layers (corre­ revealed that the existence of defects within the FASnI3 layer leads to the
sponding to different markers) tend to show slightly higher recombination of charge carriers via trap states. In this work, the defect
recombination currents at higher voltages, indicating that thicker layers density of the absorber layer was modified within the range of 1015 to
may lead to more significant recombination losses, particularly under 1011 cm-3, which is placed 0.6 eV above the valence band edge (Ev)
high voltage conditions. while maintaining all other parameters constant. As the density of de­
fects diminishes, the optical efficacy of the absorber layer exhibits
considerable enhancement, particularly concerning augmented light
3.5. Impact of perovskite layer defect density (Nt) absorption and diminished losses associated with reflection and trans­
mission. This phenomenon can be attributed to the improved capacity of
The parameter Nt denotes the number of imperfections found within the material to effectively capture and utilize incident photons, thereby
the absorber layer of PSCs, including impurities, interstitials, and va­ reducing the loss of light that would otherwise be subject to reflection or
cancies. The existence of defects holds the potential to substantially transmission. Consequently, a notable rise in overall all the parameters
impact the efficiency of the photovoltaic device. Furthermore, the of the solar cell, such as PCE, Voc, FF, and Jsc, is from 22.06 % to
research tries to analyze the impact of Nt on the PCE of PSCs featuring

Fig. 9. Impact of Perovskite layer thickness on Voc, Jsc, FF, and PCE%.

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A. Rehman et al. Hybrid Advances 7 (2024) 100301

22.87%, 0.9843–0.9865 V, 86.12–87.62% and 26.02–26.45 mA/cm2 as parameters of the device structure. This study simulated the FASnI3
shown in Fig. 11. This increase is attributed to consequently higher light based solar device and optimized the different PL parameters and back
absorption and lowering the rate of trap-assisted recombination [45]. It contact. It is assumed that reducing the Nt to 1 × 1011 cm− 3 and band
is observed that the device performance shows significant enhancement gap 1.39 eV, increasing the thickness to 650 nm, enhances the perfor­
below 1015 cm− 3. Therefore, the optimal defect density is identified as mance of the PSCs to 24.87% with a fill factor of 87.10%. The results of
1011 cm− 3. solar cell devices before and after optimization are shown in Table 4. At
the same time, the difference in the J-V curve between them is illustrated
3.6. Varying back contacts in Fig. 14. Furthermore, through specific fabrication methods, high-
performance lead-free perovskite devices are composed to meet mar­
The performance of the solar has been influenced by changing the ket demands and address concerns regarding lead toxicity. These
back contact work function. Fig. 12 illustrates the variation in the solar simulated parameters are fundamental in directing experimental efforts
cell parameters as influenced by different back metal contacts possessing in PSCs by offering insights, calculations, enhancements, and device
work functions ranging from 5.1 to 4.7 eV [46]. When we are employing efficiency. This study contributes to better comprehending the chal­
Au, Ag, W and Cu then Ag shows low performance in the overall pa­ lenges associated with experimental findings.
rameters of solar cells as compared to other Back contact such as Au, W,
and Cu. The Voc and Jsc of Au, W and Cu almost remain the same but 3.8. Energy band alignment of solar cell before and after optimization
there is variation in PCE and FF values. Throughout these alterations,
the enhanced performance observed in all configurations with high The interface configuration between the ETL and the absorber, as
work function rear metal contacts can be attributed to the reduction in well as the absorber and the HTL, can significantly affect the efficiency
reverse saturation current facilitated by the intensified field effect and of a solar cell. Fig. 15 shows the difference between the energy levels
extraction mechanisms enabled [47]. Furthermore, the optical efficacy before and after the optimization of the device. In the fig, it is illustrated
of photovoltaic cells is profoundly influenced by the material composi­ that, before the optimization of the cell, there is a notable drop in the
tion of the back contact. High-work-function substances such as gold conduction band energy (EC) at the ETL/absorber interface, indicating a
(Au) and platinum (Pt) not only enhance electrical performance but also cliff configuration. This could lead to increased recombination at this
exert a significant impact on optical attributes including reflection, interface, reducing cell performance. Similarly, the valence band (EV)
transmission, and absorption. These materials are adept at minimizing shows a drop at the absorber/HTL interface, suggesting another cliff
reflection losses and augmenting light absorption within the active configuration. This configuration might allow more holes to recombine,
layers of the photovoltaic cell, consequently leading to an enhancement negatively affecting the solar cell’s efficiency. Fig also be illustrated
in overall efficiency. Conversely, materials characterized by lower work that, after the optimization of the cell the optimized of cell, the con­
functions may induce heightened reflection and diminished absorption, duction band (EC) at the ETL/absorber interface shows a reduced or
thereby contributing to suboptimal optical performance and, as a result, eliminated cliff, potentially forming a spike configuration instead. This
a reduction in overall efficiency. Fig. 13 indicates higher work function suggests that the optimization has reduced recombination by creating a
values show low recombination even after high voltage. When the value barrier that blocks holes from reaching the ETL, thereby improving ef­
of the work function is low, then high recombination occurs. ficiency. The valence band (EV) at the absorber/HTL interface shows
Furthermore, the migration of holes towards the hole transport less of a cliff and may form a slight spike configuration. This change
material (HTM) to the rear contact leads to a decrease in the reverse would reduce electron recombination at the HTL, allowing for better
saturation current [48]. Moreover, the high-work function materials of hole transport and thus better cell performance.
the rear contacts do not undergo chemical reactions with the CuI and
perovskite layers. Through optimization, we achieved peak performance 4. Conclusion
of the PSC by utilizing rear metal contacts with a work function
exceeding 5.1 eV. Employing various rear metal contacts including Pd, Numerous Simulations and experimental investigations have been
Se, Ni and Pt is possible. conducted concerning FASnI3-based solar cells with different types of
HTL and ETL layers; nonetheless, the highest PCE has persisted below
20 %. Within this study, a solar cell configuration has been proposed
3.7. Device optimization FTO/CeO2/FASnI3/CuI/Au, incorporating CeO2, FASnI3, and CuI as
ETL, perovskite material and HTL, respectively, which was simulated
The optimal device performance is achieved through optimized through SCAPS-1D. The impact of different parameters of PL and back
contact has been analyzed. The findings have indicated that enhancing
the thickness and lowering the band gap and Nt of the PL enhances the
device’s performance. The final optimizations were found to be PCE of
24.87%, FF of 87.10%, Jsc of 30.675 mA/cm2, and Voc of 0.9308 V.
According to the results, it was determined that lead-free tin-based PSCs
may achieve a higher level of PCE than those using conventional ETL
layers by using CeO2 as the ETL surface. This study illuminates the po­
tential of diverse material combinations and charts a clear pathway for
future research endeavors. In synthesizing the knowledge acquired, re­
searchers are composed to refine and further optimize the next gener­
ation of photovoltaic devices, indicating a brighter, more sustainable
future.

Disclosure statement

The authors affirm no financial or interpersonal conflicts affected the

research in this study.

Fig. 11. Impact of varying Nt on key solar cell parameters.

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A. Rehman et al. Hybrid Advances 7 (2024) 100301

Fig. 12. Impact of different back contact work functions on Voc, Jsc, FF, and PCE%.

Fig. 13. Total recombination for different back contacts. Fig. 14. J-V curves before and after optimization.

Data availability statement

Table 4
Simulation results before and after optimization. Data can be given upon request.
Parameters Before Optimization After Optimization

Jsc (mA/cm2) 26.027 30.675 CRediT authorship contribution statement

Voc (V) 0.9843 0.9308
FF (%) 86.12 87.10 Ateeq ul Rehman: Methodology, Conceptualization. Shahbaz
PCE (%) 22.06 24.87
Afzal: Writing – original draft. Iqra Naeem: Methodology. Dilawaiz
Bibi: Writing – review & editing, Software. Sakhi Ghulam Sarwar:
Visualization, Validation, Investigation. Faran Nabeel: Investigation,
Validation, Visualization. Raphael M. Obodo: Writing – review &
editing, Visualization, Validation, Supervision.

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A. Rehman et al. Hybrid Advances 7 (2024) 100301

Fig. 15. Energy band alignment of solar cell before and after optimization.

Declaration of competing interest [17] J. Dong, X. Feng, J. Jia, B. Shi, Y. Wu, B. Cao, Annealing free CeO2 electron
transport layer for efficient perovskite solar cells, J. Solid State Chem. 317 (2023),
https://doi.org/10.1016/j.jssc.2022.123661.
The authors declare that they have no known competing financial [18] R. Vakulchuk, I. Overland, D. Scholten, Renewable energy and geopolitics: a
interests or personal relationships that could have appeared to influence review, Renew. Sustain. Energy Rev. 122 (2020), https://doi.org/10.1016/j.
the work reported in this paper. rser.2019.109547.
[19] K. Bhavsar, P.B. Lapsiwala, Numerical simulation of perovskite solar cell with
different material as electron transport layer using SCAPS-1D software, Semicond.
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