Abstract

In this research, we investigated the potential of the hybrid organic-inorganic material (CH₃NH₃)₂CuCl₄ as an absorber in perovskite solar cells (PSCs). Perovskite solar cells are becoming more popular as a potential boost to the efficiency of traditional photovoltaic cells. The advantages of this cell over commercial silicon or other organic and inorganic solar cells are its high efficiency and eco-friendliness. In this study, we used the SCAPS-1D software to improve device performance parameters, employing ZnSe as the electron transport layer and SrCu₂O₂, a promising hole-transport material identified in (CH₃NH₃)₂CuCl₄ -based perovskite solar cells (PSCs). To further enhance device performance, we have analyzed the effects of absorber and buffer layer thickness, acceptor density, absorber defect density, and interfacial defect densities at the ETL/Absorber and Absorber/HTL interfaces. In addition, we analyzed the effects of operating temperature, series resistance, and shunt resistance on the quantum efficiency, back contact materials, current density-voltage, and overall optimum device performance. Gold is utilized for the back contact. The efficient perovskite solar cell achieved an exceptionally high efficiency of 28.5% with a 0.05 μm buffer layer and a 0.6 μm absorber layer. The proposed solar cell structure may enable high-performance perovskite solar cells.

Keywords

Solar Energy, Perovskite Solar Cell, Thin Film, SCAPS-1D, SrCu₂O₂

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1. Introduction

Scientists have been studying alternative energies for decades, since fossil fuels are dirty and finite. We will inevitably look for other energy sources. Fossil fuel sources are becoming harder to find. Consequently, the focus of scientific inquiry has shifted to sustainable energy, with solar energy remaining the primary source. Directly converting solar radiation into electrical power is a form of harnessing solar energy [1] [2]. The development of third-generation thin-film photovoltaic (PV) technology has led to perovskite solar cells (PSCs). Perovskite solar cells have mechanical, optical, and physical characteristics that make them appropriate for photovoltaic systems. Scholars have examined some of these attributes through density functional theory and first-principles computation [3]-[6].

Double- or stacked-perovskite materials are the most promising approach for creating lead-free PSCs. This technique substitutes one monovalent M⁺ cation and one divalent M²⁺ cation for the traditional two divalent Pb cations inside the perovskite structure. Consequently, these double perovskites have the following chemical structure: A₂M⁺M²⁺X₆, where A can be CH(NH₂) or CH₃NH³⁺ [7]. With its creative structural design, ecologically friendly PSCs could be produced without sacrificing functionality, providing a more sustainable and clean method of solar energy harvesting. We used ZnSe as a buffer layer because it is low-cost and highly transparent, which improves overall device efficiency [8]. With a broad 2.7 eV bandgap, ZnSe is a significant technical optoelectronic semiconductor. ZnSe is a suitable replacement for solar photovoltaic cells. It is regarded as a crucial technical material because of its potential uses in various optical and electrical devices, as well as in buffer and window materials for thin-film heterojunction solar cells [9]. This study used SrCu₂O₂ as an HTL layer because oxides are more chemically stable and less moisture-sensitive than many organic or halide materials. Using SrCu₂O₂ may improve device stability, particularly in operational/ambient exposure. For SCAPS modeling, this supports selecting buffer parameters with less drift (stable defect densities and lifetimes) and exploring stability under temperature variation [10]. It has been discovered that inorganic p-type transparent conductive oxides (TCOs), such as SrCu₂O₂, are excellent hole conductors for solar cells with suitable valence and conduction band positions [11]-[14].

The proposed perovskite solar cell used (CH₃NH₃)₂CuCl₄ as an absorber layer for Lead-free, lower toxicity, replacing Pb with Cu makes (CH₃NH₃)₂CuCl₄ an attractive, environmentally friendlier absorber for lead-free perovskite device concepts, which is an important design consideration in simulation studies to explore non-toxic alternatives [15]. And also used ITO as an ETL layer because it has a realistic bandgap of ITO (~3.5 - 4.0 eV), so it doesn’t absorb visible light significantly [16]. In this simulation, we introduce an ITO/ZnSe/(CH₃NH₃)₂CuCl₄ /SrCu₂O₂/Au perovskite solar cell. During this simulation, a total efficiency of 28.5% was gained. This proposed perovskite solar cell can be used for its high-efficiency application.

2. Numerical Simulation and Parameters of Materials

The computational model’s framework provides an understanding of the fundamentals of solar cells and the key parameters influencing their performance. Crucial one-dimensional semiconductor equations can be solved directly through the SCAPS-1D software [17]. The continuity equations for electrons and holes are as follows:

$-\left(\frac{1}{q}\right)\frac{d_{jn}}{dx}-Un+G=\frac{d_n}{dt}$ (1)

$-\left(\frac{1}{q}\right)\frac{d_{jp}}{dx}-Up+G=\frac{d_p}{dt}$ (2)

where Jn and Jp are electron and hole current densities, and G is the generation rate. The Poisson equation is

$\frac{d^2}{d{x}^2}\psi \left(x\right)=\frac{e}{{\epsilon }_o\cdot {\epsilon }_r}\left[\rho \left(x\right)-n\left(x\right)+N_D-N_A+{\rho }_P-{\rho }_n\right]$ (3)

The electrostatic potential is represented by ψ, the electrical charge is represented by e, the relative and vacuum permittivity by ε_r and ε₀, the concentrations of holes and electrons are represented by p and n, respectively, the charge impurities of the acceptor and donor types are represented by N_A and N_D, and the distributions of holes and electrons are represented by ρ_p and ρ_n [18]. The literature and the user manual for SCAPS, a very potent program for solar cell performance, provide descriptions of the program and the algorithms it employs [19]-[22]. For this (CH₃NH₃)₂CuCl₄-based Perovskite solar cell, Figure 1 displays the schematic diagram. Figure 2 presents the energy band alignment for various materials utilized in the proposed perovskite solar cell. Table 1 shows the simulation of the material parameters used in the proposed solar cell.

Figure 1. Schematic diagram of a proposed perovskite solar cell.

Figure 2. Energy band alignment for various materials utilized in the proposed perovskite solar cell.

Table 1. For the simulation, the material parameters were used in the proposed solar cell.

3. Results and Discussions

3.1. Effect of Absorber Layer Thickness

The thickness of the absorber layer is a significant factor in establishing the device’s specifications. The absorber layer thickness on the perovskite solar cell (PSC) is depicted in Figure 3. The thickness of the absorber layer varies from 0.2 µm to 2 µm. Figure 3 shows that all solar cell performance parameters, such as Open Circuit Voltage (Voc), Short Circuit Current (Isc), Fill Factor (FF), and efficiency, have improved. Efficiency increases from 22.8% to 28.5%, Isc from 24.62 mA/cm² to 34.76 mA/cm², and FF from 85.05% to 85.5%. From 0.97 V to 0.94 V, Voc falls. Due to enhanced light absorption, the Power Conversion Efficiency (PCE) increases from 22.8% to 28.5%. By increasing the thickness of the absorber layer, the absorber layer improves light absorption and carrier generation, thereby increasing the short-circuit current density [23].

Figure 3. Effect of absorber layer thickness on the solar cell parameters.

3.2. Effect of Buffer Layer Thickness

Figure 4 shows the effect of the Electron Transport Layer (ETL) layer on the perovskite solar cell. ETL thickness varies from 0.01 µm to 0.05 µm. It shows that all the PV parameters are slightly increased, but the values are almost constant.

The change is negligible; in this simulation, 0.05 µm was the optimized ETL thickness, with an Open Circuit Voltage (Voc) of 0.95 V, a Short Circuit Current Density (Jsc) of 34.75 mA/cm², a Fill Factor (FF) of 85.54%, and an efficiency of 28.5%. This suggests that there is not much impact of ETL thickness on the perovskite solar cells (PSC’s) electrical properties [24].

3.3. Effect of Series & Shunt Resistance

Figure 5(a)-(b) illustrates how series and shunt resistance affect the solar cell.

Figure 4. Effect of buffer layer thickness on the solar cell parameters.

Figure 5. (a): Effect of series resistance on the solar cell parameters. (b): Effect of shunt resistance on the solar cell parameters.

The series resistance is changed in Figure 5(a) from 0.5 Ω cm⁻² to 4 Ω cm⁻². It has been noted that, apart from Jsc, all solar cell properties decrease as series resistance rises. Fill Factor (FF) diminishes as the series resistance increases. At higher resistance values, the short-circuit current decreases [25]. Here, equations 4 and 5 illustrate how series resistance affects the performance metrics.

$I_{SG}=I_o\left(e\frac{Vocq}{nkT}-1\right)$ (4)

$I_{SG}=I_l-I_o\left(e\frac{Vocq}{nkT}-1\right)-\frac{V_{OC}+I_{SCRS}}{rsh}$ (5)

where R_sh represents shunt resistance, and I_L represents light-induced current. The math above shows that when R_S rises, the Short Circuit Current (I_SC) decreases [26] [27]. Figure 5(b) demonstrates the effect of shunt resistance on the proposed perovskite solar cell (PSC). The shunt resistance is varied from 1E1 Ωcm⁻² to 1E7 Ωcm⁻². As seen, all the parameters improve with variation. It’s noticeable that there isn’t much effect on the short circuit current. Shunt resistance losses predominantly originate from defect-state recombination; hence, higher shunt resistance indicates fewer defect states [28].

3.4. Effect of Temperature

Figure 6 shows the effect of temperature on the solar cell, with temperature ranging from 275 K to 400 K. All the metrics, except short-circuit current, decrease gradually. This may result from a decline in efficiency brought on by the defect density in the layers rising with temperature. Temperature-related increases in deformation stress may lead to a decrease in the device’s efficiency [29]. Here, Open Circuit Voltage (Voc) decreases from 0.987 V to 0.83 V, Fill Factor (FF) 86.5% to 80.2%, and Power

Figure 6. Effect of temperature on the solar cell parameters.

Conversion Efficiency (PCE) 29.3% to 23%. Because temperature alters the diffusion length, which raises the series resistance, the device’s FF and efficiency are reduced [30]. For this device simulation, an optimized temperature of 300 K was used.

3.5. Effect of Defect Density

The impact of absorber-layer defect density on the solar cell is shown in Figure 7. In this case, the defect varies between 1E12 cm⁻³ and 1E18 cm⁻³. This variation affects every parameter in this case. Power Conversion Efficiency (PCE) decreases from 36% to 5%. Short Circuit Current (Isc) ranges from 35.6 mA/cm² to 11 mA/cm², Fill Factor decreases (FF) from 87.6% to 65%, and Open Circuit Voltage (Voc) from 1.1 V to 0.62 V. An increase in defect density reduces carrier lifetimes because more recombination and traps are present, making paths more accessible. This lowers effective carrier mobility [31]. Defects must occur in all materials to achieve high efficiency at low defect concentrations [32]. For this reason, we selected an absorber layer defect density of 1E15 cm⁻³.

Figure 7. Effect of defect density of absorber layer on the solar cell parameters.

3.6. Quantum Efficiency

Figure 8 shows the quantum efficiency vs wavelength characteristics curve. It shows the highest absorption in the visible wavelength range. There is a noticeable decline in quantum efficiency in the infrared. In this case, the absorber layer ranges from 0.2 to 2 µm. An optimal thickness of 0.6 µm was obtained for this simulation. Figure 8 shows that as the absorber layer thickness increases, the quantum efficiency rises at longer wavelengths. This is because there aren’t enough photons in the absorber layer to generate sufficient electron-hole pairs [33].

Figure 8. Quantum efficiency characteristics of the PSC solar cell.

3.7. Current Density-Voltage Characteristics

Figure 9 displays the solar cell’s J-V properties. In this simulation, the thickness of the absorber layer is adjusted from 0.2 µm to 2 µm.

Figure 9. Current-voltage characteristics of the PSC solar cell.

Here, 0.6 µm was the ideal thickness for the absorber layer, resulting in an Open Circuit Voltage (Voc) of 0.95 V, Short Circuit Current (Isc) of 34.75 mA/cm², Fill Factor (FF) of 85.54%, and efficiency of 28.5%. When the absorber is thickened, the electron-hole pair is added, which raises the voltage and current [34].

3.8. Interface Defect

Table 2 shows the interface defect density for the device.

Table 2. The interface defect density for the device.

3.9. Effect of ETL/Absorber and Absorber/HTL Interface Defect Density

The impact of interface defect density on the suggested perovskite solar cell is depicted in Figure 10. This simulation changes the Electron Transport Layer (ETL)/Absorber layer and the Absorber/Hole Transport Layer (HTL) interface from 1E10 cm⁻³ to 1E14 cm⁻³.

Figure 10. (a): Effect of ETL/Absorber on the solar cell parameters. (b): Absorber/HTL defect density on the solar cell parameters.

Through simulation, it is found that interface fault densities significantly impact all the parameters. Low photocurrent generation and overall efficiency are caused by high defect density because it creates mid-gap trap states that serve as recombination without radiation focal points, restricting diffusion length and carrier lifetime [35]. Figure 10(b) shows the Absorber/Hole Transport Layer (HTL) defect density on the proposed perovskite solar cell. High interface defect density causes efficiency to drop quickly. Defects cause recombination centers for charging carriers, which lowers efficiency and current density [36]. Because of this, an interface defect density of less than 1E11 cm⁻³ [37] and a thickness of 0.6 µm are required for the maximum efficiency.

3.10. Effect of Back Contact Material

Table 3 presents the Metal work function for different materials.

Table 3. Metal work functions for different materials.

The metal’s quantity of energy is known as the work function or the number of photons necessary to eliminate a single electron from its surface [38]. Improved solar cell efficiencies have been associated with higher work function values [39] [40]. Au and Pt are expensive metals frequently employed as back contacts in solar cells. In this work, simulations were conducted to identify an appropriate, commercially available metal for the back contact of the proposed device configuration. Figure 11 shows the impact of various materials used for the back contact on the PCE. The maximum efficiency achieved in this instance was 28.5%.

Figure 11. Different back contact materials’ effects on solar cells.

4. Conclusion

A novel copper-based perovskite solar cell was studied using SCAPS 1D simulation software in this research. This study analyzes the effects of absorber layer thickness, buffer layer thickness, absorber layer defect density, series resistance, and shunt resistance to determine the optimized values. Furthermore, the quantum efficiency and current-voltage characteristics were investigated for the proposed perovskite solar cell. After simulation, the optimum values of the absorber layer thickness (0.6 µm) and the total defect density (N_t = 1E15 cm⁻³) were obtained. It’s observed that at 300K, the device performs at its highest level. After simulation, Voc 0.95 V, Jsc 34.75 mA/cm², FF 85.54%, and efficiency 28.5% were obtained as the optimized values. Overall, this proposed perovskite solar cell is observed as a high-efficiency, green, and stable heterojunction cell.

Acknowledgements

The authors would like to thank Dr. Marc Burgelman and his colleagues at the Department of Electronics and Information Systems (ELIS), University of Gent, Belgium, for providing the SCAPS simulation package.

Data Availability Statement

The data that support the findings of this study are available from the corresponding author upon reasonable request.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

References