Optimization and Performance Evaluation of Cs2CuBiCl6 Double Perovskite Solar Cell for

Lead-Free Photovoltaic Applications

1
Syeda Anber Urooj Wasti1, Sundus Naz1, Ammara Sattar2, Asad Yaqoob3, Ateeq ul Rehman4,
Fawad Ali5*, Shahbaz Afzal6*
1
Department of Physics, University of Agriculture Faisalabad.
2
Department of Physics, Faculty of Engineering and Applied Sciences (FEAS), Riphah
International University, Islamabad, 44000, Pakistan.
3
Department of Physics, Abbottabad University, Pakistan.
4
Institute of Physics, Baghdad ul Jadeed Campus, The Islamia University of Bahawalpur,
Bahawalpur, 63100, Pakistan.
5
Department of Physics, University of Education Lahore, DG Khan Campus, Punjab, Pakistan.
6
Nanophotonics Research Centre, Shenzhen University and Key Laboratory of Optoelectronic
Devices and Systems of Ministry of Education and Guangdong Province, College of
Optoelectronics Engineering, Shenzhen University, Shenzhen 518060, China.

Corresponding author(s): Fawad Ali, Email: fawadali2022@163.com; Shahbaz Afzal, Email:

shahbazafzal2216@gmail.com.

Abstract

In the previous decade, there has been a significant advancement in the performance of
perovskite solar cells (PSCs), characterized by a notable increase in efficiency from 3.8% to
25%. Nonetheless, PSCs face many problems when we commercialize them because of their
toxicity and stability. Consequently, lead-PSCs need an alternative solar cell with high
performance and low processing cost; lead-free inorganic perovskites have been explored.
Recent research showcased Cs2CuBiCl6, a lead-free inorganic double perovskite material with
remarkable photoelectric characteristics and exceptional environmental robustness. To
investigate the potential of Cs2CuBiCl6 material, the solar cell structure
FTO/ETL/Cs2CuBiCl6/HTL/Au was used and analyzed through a solar cell capacitance
simulator (SCAPS-1D). CeO2 is used as the Electron transport layer (ETL), and CuI is the Hole
transport layer (HTL). Furthermore, the research examined the optimization of different
parameters of the absorber layer (AL), such as thickness, defect density, electron affinity, band
gap, and operational temperature. In the end, it has been noticed that by setting the temperature
at 300 K and an electron affinity of 4.3 eV of the absorber layer, the PSCs achieve the highest
efficiency of 24.51 %, FF of 43.01 %, Voc of 1.73V, and Jsc of 32.82mA/cm2. This is the highest
Cs2CuBiCl6 double PSCs efficiency we've reached yet. In theoretical studies, 17.03% of PCE
was achieved using Cs2CuBiCl6 as an active layer. The analysis underscores the significant
potential of Cs2CuBiCl6 as an absorbing layer in developing highly efficient lead-free all-
inorganic PSCs.

Keyword: lead-free inorganic perovskites, Cs2CuBiCl6, ETL (CeO2), HTL (CuI), Optimization,
SCAPS-1D
 1. Introduction
Energy consumption is currently at its highest levels, with demand projected to rise further due
to the ever-increasing global population. This situation underscores the urgent need to identify
alternative energy sources beyond fossil fuels. Such efforts are essential for sustaining a healthy
society and environment and meeting global energy requirements. Among the various solutions,
renewable energy-based solar cell technologies have emerged as one of the most promising
approaches to address the ongoing energy crisis [1, 2]. Since the 1950s, silicon- as the primary
material in first-generation solar cells- has been widely used in photovoltaic applications due to
its high efficiency. However, its extraction and production costs remain prohibitively expensive
[1]. A first-generation solar cell offers superior efficiency but comes with higher production
costs. Second-generation solar cells, also known as thin-film solar cells, were introduced in
response to these challenges. These are fabricated using amorphous silicon, cadmium telluride
(CdTe), and copper indium gallium Selenide (CIGS). While second-generation solar cells are
lighter, more flexible, and cheaper to produce than first-generation silicon-based solar cells, they
generally exhibit lower efficiencies, shorter lifespans, and pose potential environmental and
health risks due to using toxic materials during production and disposal [2]. The third generation
of perovskite solar cells (PSCs) was developed to overcome these limitations. PSCs have
garnered significant attention over the past two decades due to their rapid efficiency
improvements and potential for low-cost production [3]. Several unique physic-chemical
properties contribute to the popularity of PSCs: i) an adjustable energy band gap, ii) efficient
utilization of incident light utilization, iii) cost-effective and versatile preparation techniques, and
iv) rapid progress in research and development. Remarkably, PSCs achieved a dramatic
enhancement in power conversion efficiency (PCE), increasing from 3.8% to 25.7% within a
short time period [4, 5]. Structurally, PSCs typically comprise a transparent conducting oxide
TCO (e.g., FTO and ITO), an electron transport layer ETL, a hole transport layer HTL, and a
perovskite layer (i.e., perovskite layer positioned between the ETL and HTL layer. Perovskites
are materials characterized by the general formula ABX3, where 'A' represents a large cation, 'B'
denotes a smaller Cation, and 'X' is a halide anion. By introducing new elements through doping,
novel perovskite structures with enhanced optoelectronic properties can be engineered. Bismuth-
based double perovskite is a particularly intriguing class of perovskite with researchers’
attention. These materials offer significant potential for solar energy applications due to their
high stability, efficient generation of electron-hole pairs, and tunable optoelectronic properties
[6, 7]. Double perovskite (DP), also known as an elpasolite, is derived by replacing one
monovalent B+ and one trivalent B3+ ion with a Pb2+ ion in the traditional perovskite structure,
resulting in the formula A2B+B3+X6(Cs2CuBiCl6) [8]. In Double perovskite solar cells, the
absorber layer- a thin film of double perovskite material- is crucial for absorbing light and
generating electron-hole pairs. These absorber layers are central to distinct characteristics and
enhanced performance of double perovskite solar cells. Compared to conventional perovskites,
double perovskites offer notable advantages, including higher stability, superior electron-hole
pair production, and customizable optoelectronic properties, making them a promising
alternative for next-generation photovoltaic technologies.

Cs2CuBiCl6 is a promising lead-free double perovskite due to its optimal 1.1 eV band gap,
facilitating efficient light absorption and conversion into electricity while exhibiting impressive
stability for sustained performance. This exceptional stability enhances the material's suitability
for solar cell applications [9]. Moreover, its remarkable optical properties further augment its
ability to effectively capture and convert solar energy [10]. Double perovskites offer a
sustainable alternative by replacing the lead with a combination of other metals. For instance,
one of the most researched double perovskites is Cs2AgBiBr6, where silver (Ag) and bismuth
(Bi) substitute lead, resulting in a lead-free material with promising photovoltaic properties [11].
Over the past few years, extensive research has focused on developing double perovskite to
improve overall stability and efficiency while maintaining a low-cost and lead-free solar cell
system. Recent studies have demonstrated the potential of double perovskite in photovoltaic
applications. For example, Kale et al. reported a power conversion efficiency (PCE) of 17.03%
using TiO2 as ETL Cu2O as HTL and Cs2CuBiCl6 as absorber layer [12]. Mohandas et al.
utilized Cs2AgBiBr6, as the active layer and reported a PCE efficiency of 1.44% by using
SCAPS-1D. Furthermore, Ferdous et al. simulated Cs2TiI2Br4-based double PSCs and gained an
impressive efficiency of 23.41% [13]. In this research, Cs2CuBiCl6 was selected as the absorber
layer due to its superior material capabilities and the scarcity of comparative studies on this
compound. According to the literature, only one study has been conducted using Cs2CuBiCl6 as a
double perovskite layer [12].

This work aims to address this gap by systematically exploring the photovoltaic performance of
lead-free double perovskite solar cells employing FTO/CeO2/Cs2CuBiCl6/CuI/Au configuration
using SCAPS-1D simulation software. In the proposed structure, Cs2CuBiCl6 serves as double
perovskite layer (DPL), CeO2 as the electron transport layer (ETL), CuI as the hole transport
layer (HTL), FTO as the transparent conductive substrate, and Au as the back-contact material.
The significance of this work lies in the detailed investigation of factors influencing the
performance of Cs2CuBiCl6-based PSCs. Key parameters of the absorber layer, including
thickness, defect density; electron affinity and operating temperature were systematically
analyzed to optimized device performance. The impacts of these parameters on power
conversion efficiency (PCE), fill factor (FF), open-circuit voltage (Voc), and short-circuit current
density (Jsc) were comprehensively evaluated [14]. In the presented
FTO/CeO₂/Cs₂CuBiCl₆/CuI/Au solar cell structure, CeO₂ and CuI are chosen as the electron
transport layer (ETL) and hole transport layer (HTL), respectively, due to their unique properties
that enhance device performance. CeO₂, an n-type semiconductor with a wide band gap of 3.2
eV, ensures minimal parasitic absorption and efficient light transmission to the absorber layer. Its
high electron mobility facilitates rapid extraction and transport of photogenerated electrons,
reducing recombination losses and improving efficiency. Additionally, CeO₂ is thermally and
chemically stable, making it suitable for long-term operational stability in solar cells. Similarly,
CuI, as a p-type semiconductor, provides excellent hole mobility (up to 44 cm²/V·s), ensuring
efficient hole extraction and transport. Its wide band gap (3.1 eV) minimizes optical losses, while
its low cost and easy fabrication makes it suitable for scalable applications. The energy level
alignment of CuI with Cs₂CuBiCl₆ enables efficient hole transfer and suppresses electron
backflow, enhancing power conversion efficiency. Together, CeO₂ and CuI create a synergistic
charge transport framework that reduces recombination, optimizes carrier collection, and ensures
high stability, making them ideal for sustainable, high-performance solar cells. However,
through the optimization of critical parameters such as absorber layer thickness, electron affinity,
band gap, defect density, electron affinity, this research demonstrates and able to obtained the
PCE of 20.43% which is greater than theoretical work (17.03%) performed by A.J. Kale et al
with same double perovskite layer [12]. Table 3 presents previously reported work on different
double perovskite layers and present work. By focusing on modeling and optimizing these
factors, this study contributes to developing more efficient, stable, and sustainable photovoltaic
technologies. The findings provide valuable insights into the design and optimization of lead-free
double perovskite solar cells, addressing the global demand for renewable energy solutions while
advancing the frontiers of perovskite solar cell technology.

2. Device Simulation
Simulation provides an effective and reliable approach to analyzing the intrinsic physical
properties of a solar cell, eliminating the need for complex and resource-intensive laboratory
fabrication. Through simulation, the physical characteristics of solar cells can be accurately
assessed while significantly reducing material while significantly reducing materials
consumption, financial cost, and time [15]. To evaluate the performance of PCS, various
modeling software tools, including GPVDM, SILVACO, AMPS, ATLAS, COMSOL, and
SCAPS, are widely used [16]. SCAPS-1D was employed to simulate and analyze the
performance of the FTO/CeO2/Cs2CuBiCl6/CuI/Au solar cell configuration. SCAPS-1D is
particularly advantageous due to its user-friendly interface and capability to perform simulations
under light and dark conditions. It enables the evaluation of key solar cell properties, including
current-voltage (I-V) characteristics, capacitance-voltage (C-V) profile, capacitance-frequency
(C-f) behavior, and quantum efficiency (QE). Simulations were conducted under standard AM
1.5G illumination and at a temperature of 300 Kelvin. The software allows for comprehensive
AC and DC electrical calculations in varying temperature and illumination conditions, providing
flexibility and precision in solar cell modeling [21]. Voltage readings were calibrated to a zero-
volt reference, and the frequency for AC calculations was fixed at 1 MHz [21]. Figure 1 (a)
illustrates the presented solar cell configuration, which includes a layered configuration of
FTO/CeO2/Cs2CuBiCl6/CuI/Au, where Cs2CuBiCl6 serves as the absorber layer, CeO2 acts as the
electron transport layer (ETL), and CuI is employed as the hole transport layer (HTL). The
absorber layer is positioned at the top of the cell, with the p-type CuI and n-type CeO2 layers
placed beneath it [17]. Tables 1 and 2 detail the simulation parameters, carefully selected based
on experimental data and previous simulation studies [12, 18, 19]. The simulation incorporated
physical properties such as carrier transport processes, electromagnetic field distribution,
recombination characteristics, and specific current densities. SCAPS-1D operates by solving
Poisson’s equation alongside the coupled continuity equations for electrons and holes, providing
a robust framework for modeling the physical and electrical behavior of the device as shown in
equations 1, 2, and 3 [20, 21].

𝑑 𝑑𝜓
(𝜀(𝜒) ) = 𝑞[𝑝(𝑥) − 𝑛(𝑥) + 𝑁𝐷+ (𝑥) − 𝑁𝐴− (𝑥) + 𝑝𝑡 (𝑥) − 𝑛𝑡 (𝑥)] (1)
𝑑𝑥 𝑑𝑥
1
𝐽 𝜕𝐽𝑝
+ 𝑅𝑝 (𝑥) − 𝐺(𝑥) = 0 (2)
𝜕𝑥
1
− 𝐽 𝜕𝐽𝑛 /𝜕𝑥 + 𝑅𝑛 (𝑥) − 𝐺(𝑥) = 0 (3)
Figure 1. (a) Schematic Diagram of the Presented Solar Cell.

Table 1. Numerical Parameters for the device designed in this study.

Thickness (µm) 0.1 0.45 0.45 0.4
Electron affinity (eV) 2.1 4 4.6 4.3
Band gap (eV) 3.1 1.21 3.5 3.5
CB effective density of
2.80×1019 1.00×1018 1.00×1020 2.20E×1018
states (cm-3)
VB effective density of
1.00×1019 1.00×1018 2.00×1021 1.80×1019
states (cm-3)
Dielectric permittivity
6.5 3.72 9 9
(eV)
Electron mobility, µn
1.00×102 2.00×100 1.00×102 2.00×101
(cm2/Vs)
Hole mobility, µh
4.39×101 2.00×100 2.50×101 1.00×101
(cm2/Vs)
Uniform donor density
0 1.00×1013 1.00×1021 1.00×1018
ND (cm-3)
Uniform acceptor
1.00×1018 1.00×1017 0 0
density NA (cm-3)
Electron thermal
1.00×107 2.00×100 1.00×107 1.00×107
velocity (cm/s)
Hole thermal velocity
1.00×107 2.00×100 1.00×107 1.00×107
(cm/s)
Defect density Nt (cm-3) 1.00×1015 1.00×1015 1.00×1015 1.00×1015
References [18] [12] [18] [22]

Table 2. Electrical parameters of interface defects layer

Parameters CuI/Cs2CuBiCl6/CeO2

Defect Type Neutral

Capture cross section for electrons/ hole (cm 2) 1.00×1015

Energetic distribution Single

 Energy with respect to Reference (eV) 0.6 Above the highest Ev

Characteristic energy /Ev 0.1

Total density (integrated over all energies) (cm -2) 1.00×1015

Table 3. Previous and present work on different double perovskite layers

Solar Cell Structures Voc (V) Jsc (mA/cm2) FF (%) PCE (%) References

FTO/TiO2 /Cs2CuBiCl6 /Cu2O 0.91 21.66 85.99 17.03% [12]

ITO/SnO2/Cs2AgBiBr6/MoO3 1.419 9.4741 72.61 11.41%

FTO/ETL/Cs2AgBiBr6/HTLs/Cu 7.2 8.02 6.45 3.75 % [24]

FTO/SnO2/Cs2AgBiBr6/Cu2O/Au 1.09 1.73 0.76 1.44% [25]

FTO/ZnOS/Cs2AgBi0.75Sb0.25Br6 /Cu2O 1.39 16.04 78.34 18.8%

FTO/ TiO2 / Cs2TiBr6 /Cu2O 1.10 25.82 51.74 14.68% [26]

FTO/ZnO/ Cs2 AgBiBr6/ NiO/Au 1.29 20.69 81.72 21.88%

FTO/CeO2/ Cs2CuBiCl6/CuI/Au 0.897 33.639 67.65 20.43% Before optimization

FTO/CeO2/ Cs2CuBiCl6/CuI/Au 1.7359 32.829760 43.01 24.51% Final results

3. Results and Discussion

This research aims to explore the photovoltaic performance of Cs2CuBiCl6 (CCBIC) and also
changes some parameters of the absorber layer (AL), which affect its efficiency. This work studies several
factors that influence solar cell performance, including thickness, defect density (Nt), Electron
affinity, band gap (Eg), and the system's temperature. By changing these factors, we also studied
their impact on FF, Voc, PCE, and Jsc. During all parameter changes, the optimized parameter
remains unchanged throughout the optimization process.

3.1.Influence of the double perovskite layer (DPL) thicknesses

The absorber layer's thickness plays a crucial role in determining the performance of PSCs.
When light falls on solar cells, electron-hole pairs are generated, leading to electricity
production. An optimized PL thickness is crucial for maximizing the device's generation of
charge carriers (electrons and holes). In this study, the PL thickness was varied from 0.450 to
2.000 µm while maintaining the other parameters of different layers, as presented in Tables 1 and
2. It was observed that increasing the PL thickness negatively impacted the key solar cell
parameters, including the Voc, Jsc, FF, and PCE, as illustrated in Figure 2 (a, b). This decline in
performance can be attributed to increased charge recombination and light transmittance losses
within the device at greater thickness. The absorber layer's thickness significantly affects the
solar cell performance since both the saturation current density (Jo) and the device's short circuit
current (Jsc) are close to open-circuit voltage (VOC). According to the equation 4:

𝐾𝑇 𝑗𝑠𝑐
𝑉𝑜𝑐 = ln ( + 1) 4
𝑞 𝑗𝑜

Where K is the Boltzmann constant, T is the temperature, and Q is the electronic charge, it is
evident that any changes in Jo or Jsc due to absorber layer thickness directly influence Voc.
Thus, optimizing the PL thickness is essential to achieving balanced charge generation and
transport, minimizing recombination losses, and maximizing the overall device performance.

Figure 2. Impact of thickness on (a) FF and Efficiency (b) Voc and Jsc.

3.2.Influence of the DPL defect density (Nt)

In this study, the defect density (Nt) within the absorber layer (AL) was systematically varied
over a range from 1E15 cm−3 to 1E19 cm−3 to evaluate its impact on the device performance of
the solar cell. Optimizing the defect density is critical for enhancing device performance, as Nt
directly influences the quality of the absorber film. An increase in defect density deteriorates the film
quality, leading to a higher rate of charge carrier recombination, adversely affecting the solar cell's
overall efficiency. A high defect density in the AL has been identified as a primary cause of reduced
PCE due to the abundance of recombination centers [27, 28]. Figure 3(a, b) illustrates the trend in
key performance parameters, including PCE, Jsc, and FF as a function of Nt. The results show
that increasing Nt leads to a significant reduction in these parameters. However, variations in Nt
did not result in noticeable fluctuations in the Voc. One possible reason for this reduction in
performance is the increased likelihood of charge carriers (electrons and holes) being trapped by
defects in the material at higher Nt values. Consequently, at high defect densities, all key output
metrics of the solar cell- PCE, Jsc, FF and Voc experience significant degradation. From the
analysis, it was established that optimal device performance was achieved at a defect density of
1E15 cm−3, which yielding notable values: PCE of 20.43%, Voc of 0.8978V, Jsc of
33.639722mA/cm2, and FF of 67.65% [34, 35]. The result underscores the critical role of
minimizing defect density to achieve high-performance solar cells. Elevated defect densities
introduce numerous recombination centers and traps, which impede charge carrier transport and
significantly reduce device functionality. It is evident that superior device performance can only
be attained by maintaining a low defect density in the absorber layer.

Figure 3. Impact of defect density on (a) FF and Efficiency (b) Voc and Jsc.

3.3.Influence of the DPL electron affinity

The electron affinity of the perovskite material (PM) is a critical factor that significantly impacts
the performance of PSCs. In this study, the electron affinity of the absorber layer was optimized
using SCAPS-1D simulations to evaluate its effect on the device’s performance. The electron
affinity of the PM determines the energy-level alignments between the absorber and the ETL and
between the absorber and the HTL. Proper alignment is essential for ensuring efficient charge
carrier transport and minimizing energy losses, directly affecting the overall device performance.
To analyze the effect of electron affinity, the value of the absorber layer’s electron affinity was
systematically varied from 4.1 eV to 4.7 eV while keeping the Nt of the perovskite layer constant
at 1E15 cm−3. Figure 4(a, b) presents the trends in all solar cell performance parameters as a
function of the absorber’s electron affinity. The results indicate that increasing the electron
affinity initially enhances the device's performance. Specifically, the PCE improved from
20.43% at 4.1 eV to a maximum of 24.51% at 4.3 eV, marking a substantial enhancement in
efficiency, as shown in Figure 4 (a). This improvement can be attributed to optimized energy-
level alignment, which facilitates efficient charge carrier transport and minimizes recombination
losses at the interfaces between absorber and transport layers. While the initial increase in
electron affinity enhances charge transport efficiency, excessively high electron affinity values
likely result in excessive electron transport from the ETL to the absorber, destabilizing the
charge separation process. This destabilization negatively impacts overall device performance
and leads to a notable reduction in PCE.
Figure 4. Impact of electron affinity on (a) FF and Efficiency (b) Voc and Jsc.

The Voc, Jsc, and FF show a random fluctuation as the electron affinity increases, as shown in
Figure 4 (a, b). While the initial increase in electron affinity enhances charge transport
efficiency, excessively high electron affinity values likely result in excessive electron transport
from the ETL to the absorber, destabilizing the charge separation process. This destabilization
negatively impacts overall device performance and leads to a notable reduction in PCE. The
results demonstrated that optimizing the electron affinity of the perovskite absorber layer is
critical for achieving high device performance. An electron affinity value of approximately 4.3
eV is identified as an optimal condition, yielding the highest PCE of 24.51%. Beyond these
values, the misalignment of energy levels between absorber and transport layers compromises
charge carrier dynamics, reducing device efficiency. These findings highlight the importance of
fine-tuning the electronic properties of the absorber layer to achieve the best possible
performance in PSCs.

3.4.Influence of band gap (Eg) of the absorber layer

Numerous factors influence the efficiency and productivity of the photovoltaic cell performance.
[29, 30]. Among these, the band gap of the absorber layer is a critical parameter. The band gap
represents the energy difference between the valance band maximum and the conduction band
minimum, directly impacting the light absorption, charge carrier generation, and overall
performance of photovoltaic devices. This study systematically investigated the impact of
varying the band gap of the absorber layer on the performance of PSCs. To evaluate this effect,
the band gap of the absorber layer was varied from 1.12eV to 1.45 eV. Figure 5 (a,b) displays the
I-V curve of the PSC with the configuration of CeO2/Cs2CuBiCl6 /CuI as a function of the
absorber layer band gap. The analysis reveals a clear trend; as the band gap of the perovskite
layer increases, the PCE also increases, reaching a peak before declining at higher band gap
values. The maximum PCE of 20.086% was achieved at an optimal band gap of 1.4 eV,
corresponding to Voc of 1.26%, Jsc = 54.74 mA/cm2, and FF = 54.74%. This enhancement in the
PCE up to a band gap of 1.41 eV can be attributed to improved light absorption in the visible
spectrum and better alignment of energy levels, which enhance charge carrier separation and
transport. As the band gap increases beyond 1.41 eV, a noticeable decline in PCE is observed. At
a band gap of 1.45 eV, both Jsc and FF significantly decrease, while Voc exhibits moderate
increases. This reduction in Jsc is likely due to decreased light absorption, as a higher band gap
limits the range of the solar spectrum that the absorber layer can effectively absorb. Similarly,
the decline in FF can be attributed to increased recombination, adversely affecting charge carrier
collection efficiency. The moderate increase in Voc with the band gap can be explained by the
reduced radiative recombination rate and better separation of quasi-Fermi levels. However, the
trade-off between Voc and improvement and Jsc reduction beyond the optimal gap results in an
overall decline in device performance. This highlights the decline balance required in band gap
optimization to achieve maximum efficiency. The results emphasize the critical role of the
absorber layer's band gap in determining PSC performance

Figure 5. Impact of band gap on (a) FF and Efficiency (b) Voc and Jsc.

3.5.Influence of Operating Temperature

The operating temperature of PSCs has a significant impact on their efficiency and
stability. Understanding these temperature-related effects is crucial for optimizing both the
performance and durability of PSCs, particularly in outdoor applications where
temperature fluctuations are frequent. This study's influence on temperature range varied
from 300 k to 320 k [31]. Figure 6(a, b) illustrates the variation in key performance
parameters, including Voc, Jsc, FF, and PCE as a function of temperature. The simulation
results reveal that as the operating temperature increases, Jsc, PCE, and FF exhibit an
increasing trend [32]. Specifically, the PCE enhancement with rising temperature can be
attributed to factors such as alternations in material properties, including band gap, carrier
transport concentration, and electron and hole mobilities. These temperature-induced
changes align with analytical predictions and highlight the dynamic nature of PSC
performance under varying thermal conditions. Interestingly, the decline in Voc with
increasing temperature contrasts with the improvements observed in other parameters. This
reduced Voc can be attributed to an increased density of interfacial defects, leading to
higher series resistance and a decrease in carrier diffusion length. Elevated temperature
tends to enhance thermal excitation, increasing interface recombination losses and
adversely affecting the voltage output. The simulation also demonstrated that PSCs based
on the CS2CuBiCl6 (CCBC) absorber layer exhibit promising performance at elevated
temperatures. At 320 K, the PSC achieves a high PCE of 20.51%, Voc of 0.892 V, Jsc of
33.71 mA/cm2, and FF of 68.18%. These results underscore the potential of CCBC-based
PSCs for application in environments with moderate temperature variations, as their
performance parameters remain robust under such conditions. The findings highlight the
critical importance of thermal stability and temperature optimization in PSC design.

Figure 6. Impact of temperature on (a) FF and Efficiency (b) Voc and Jsc

4. Conclusion
This research presents a comprehensive investigation of Cs2CuBiCl6-based PSCs with an
FTO/CeO2/Cs2CuBiCl6/CuI/Au structure, focusing on the optimization of critical absorber layer
parameters using SCAPS-1D simulations. Key parameters were systematically analyzed to
enhance device performance, including thickness, defect density (Nt), electron affinity, band gap,
and operating temperature. The findings demonstrated that optimizing the absorber layer’s
thickness enhances electron-hole pair generation and reduces recombination losses. Defect
density emerged as a crucial determinant of film quality, with lower Nt 1E15 cm−3 achieving a
PCE of 20.43%. The electron affinity of the perovskite absorber was identified as a significant
factor influencing energy-level alignment and charge transport. Band gap tuning revealed that an
energy gap of 1.41 eV provided the highest efficiency of 20.86%. Furthermore, operating
temperature was found to top impact device performance, with a PCE of 20.51% achieved at 320
K, Voc to 0.892 V, Jsc to 33.71 mA/cm2, and FF to 68.18%. The optimized cell performance,
characterized by a maximum efficiency of 24.51%, highlights the potential of Cs 2CuBiCl6 as a
viable lead-free alternative in PSC applications. This work provides critical insight into the role
of absorber layer parameters in device performance. It establishes a foundation for further
experimental and theoretical advancements in lead-free photovoltaic materials.

Data availability statement

Data is available upon request.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.

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