Numerical Investigation of Power Conversion Efficiency of Sustainable Perovskite Solar Cells

Abstract

Perovskite solar cells have been researched for high efficiency only in the last few years. These cells could offer an efficiency increase of about 3% to more than 15%. However, lead-based perovskite materials are very harmful to the environment. So, it is imperative to find lead-free materials and use them in designing solar cells. This research investigates the potential for using a lead-free double-perovskite material, La₂NiMnO₆, as an absorbing layer in perovskite solar cells to enhance power conversion efficiency (PCE). Given the urgent need for environmentally friendly energy sources, the study addresses the problem of developing alternative materials to replace lead-based perovskite materials. Compared to single-perovskite materials, double perovskites offer several advantages, such as improved stability, higher efficiency, and broader absorption spectra. In this research work, we have simulated and analyzed a double-perovskite La₂NiMnO₆ as an absorbing material in a variety of electron transport layers (ETLs) and hole transport layers (HTLs) to maximize the capacity for high-efficiency power conversion (PCE). It has been observed that for a perovskite solar cells with La₂NiMnO₆ absorbing layer, C₆₀ and Cu₂O provide good ETLs and HTLs, respectively. Therefore, the achieved power conversion efficiency (PCE) is improved. The study demonstrates that La₂NiMnO₆, as a lead-free double-perovskite material can serve as an effective absorbing layer in perovskite solar cells. The findings of this study contribute to the growing body of research on developing high-efficiency, eco-friendly perovskite solar cell technologies and have important implications for the advancement of renewable energy production.

1. Introduction

Solar power has received a significant amount of attention from researchers in recent years because it is one of the most important renewable energy sources that have the potential to satisfy the growing energy demands on the planet. A high absorption coefficient, low excitation–binding energy, an adjustable optical bankgap, comprehensive charge carrier mobility, and low-temperature manufacturing technology are the primary requirements for an excellent solar cell [1]. Recent research has shown that perovskite materials have made significant advancements and become a crucial component in developing efficient solar cell technology [2]. The research for perovskite materials began with the investigation of calcium titanium oxide, the mineral of primary interest. The term “perovskite” refers to any chemical substance with the same crystalline structure as calcium titanium oxide. The crystalline structure of perovskite is depicted in Figure 1. The Perovskite compounds have the chemical formula ABX3, where A and B both represent cations and X represents an anion that binds to both cations. According to research conducted in the past [3], the power conversion efficiency (PCE) of solar cell devices constructed from lead-based perovskite materials has the potential to reach as high as 25.2%. Perovskite solar cells are highly toxic and pose a serious health risk [4]. The challenge of lead poisoning must be overcome before commercializing these cells. In addition, device stability and efficient and cost-effective production methods are critical factors. Investigations into the effects of rain on PSC modules have raised concerns about lead and tin contamination and human health. These studies have shown that rainwater can contaminate photovoltaic solar cell modules with lead and tin.

Long-term exposure to lead can cause anemia, paralysis, and kidney and brain damage. Even low levels of lead exposure can be fatal at high concentrations, making it a significant risk especially for pregnant women and developing fetuses. Lead can cross the placental barrier, putting the growing fetus at risk. In addition, infants exposed to lead may experience harm to their mental development. Lead exposure also increases the risk of cardiovascular disease, hypertension, and kidney disease and lowers fertility in lead-exposed individuals.

Based on the material characteristics, the solar cell developments can be categorized in three generations as depicted in Figure 2. The Perovskite solar cells have entered their third generation since their introduction, representing a type of thin-film photovoltaic technology. Depending on the context, PSCs can be developed as single-junction cells or tandem cells with multiple junctions. Perovskites possess advantageous physical, mechanical, and optoelectronic properties, making them well suited for photovoltaic (PV) applications. Researchers have combined first-principles calculation and density functional theory to investigate these properties. However, the active component in traditional perovskite solar cells, which combines organic and inorganic halides, suffers from two significant drawbacks. First, the element lead (Pb) is harmful to the environment. Second, the organic cations in these materials lead to instability, shortening the shelf life of the perovskite molecule.

To provide the increased power conversion efficiency and various photovoltaic properties necessary for solar cell devices, lead-free materials have been the subject of a variety of theoretical and experimental studies. In order to replace lead, perovskite solar cells based on inorganic halide perovskites (such as silver, tin, bismuth, and copper) are investigated, but these devices have a bankgap greater than 2 eV, which makes them unsuitable for use in photovoltaic applications. Recent research have demonstrated that hybrid coupling can provide better performance in terms of output power and sensitivity in comparison to the linear summing of the performances of individual components. Additionally, hybridization enables the device as a whole to be adapted to various working situations, free from the limits that would otherwise be imposed by the individual functioning processes. The term “hybrid bio-nanogenerators” will henceforth refer to hybrid systems that rely on piezoelectric and triboelectric devices, are based on biocompatible materials, and are intended for the collection of clean energy from the surrounding environment and for use in biomedical applications (HBNGs). There are three types of nanogenerators—energy harvesting, wearable bioelectronics, and implantable bioelectronics—in terms of their flexibility, output voltage, output current, output power density, lifetime and reliability, ease of miniaturization, low-frequency operation, high-frequency operation, and biocompatibility [6,7,8]. Several research studies have examined the properties of perovskite materials, including low open-circuit voltage for Sn2+ cation, instability upon oxidation of Ge2+ cation, poor charge transport capability for bismuth, low open-circuit voltage for Sb, and weak photovoltaic qualities for Cu, among others [9]. In addition, recent research has focused on a particular class of perovskite materials known as double perovskites, which have received significant attention due to their unique properties and potential applications.

Following the universal formula ABO₃, double-perovskite structures can be produced, each of which possesses a unique combination of magnetic properties. A double-perovskite structure is produced when one B’ cation replaces half of the other cations at the B site, and rock salt (NaCl) ordering is achieved. The substitution of one B for B’ in the formula for A₂B₂O₆ increases the perovskite structure’s original unit by a factor of 2. In addition to the flexibility and degrees of freedom offered by simple perovskite structures with one A cation site and one B cation site, a great deal of research has been done on double-perovskite compounds with two different transition metal (TM) elements at B sites (B, B’) and even two different rare earth and alkaline earth elements at A sites. These compounds have been the subject of much attention in recent years. The A site can also be occupied by two different types of cations at the A site, resulting in a perovskite with the formula AA’BB’O₆, referred to as both doubly ordered perovskite and double-double perovskite. Approximately 1000 different double-perovskite compounds have been synthesized, with the A site being occupied by divalent cations such as Sr, Ca, or Ba (and occasionally Pb or Cd) [10].

Double-perovskite structures offer a significant degree of flexibility in the cations that can be accommodated at the B site owing to the typical oxidation states of the B site, which are 4+ and 3+ for divalent and trivalent A cations, respectively. Practically all cations listed in the periodic table can occupy the B site of a double-perovskite structure [11]. LNMO is a ferromagnetic semiconductor composed of Ni2+ and Mn4+ ions, which exhibits two ferromagnetic transitions at 150 K and 280 K around its transition temperature Tc of 280 K, depending on its synthesis and heating conditions. Numerous studies have been carried out on the structural, magnetic, and optical properties of LNMO-based nanoparticles [12]. However, the greatest challenge is their practical application in devices. Recent studies have explored the medical applications of magnetic nanoparticles such as CoFe₂O₄, MnFe₂O₄, Fe₂O₃, Fe₃O₄, and Fe [13], but to the best of our knowledge there have been no reports on the use of double-perovskite La₂NiMnO₆ nanoparticles in medicine. La₂NiMnO₆ is a fascinating double-perovskite material with ferromagnetic properties, but its monodispersed nanoparticles are required for use in biological and medical applications due to their ability to bind and interact with biomolecules, which concentrate near the liquid–solid interface [14]. The adsorption capacity of bovine serum albumin is affected by the temperature at which the annealing process is performed. This paper employs the SCAPS-1D modelling technique to examine the absorptive properties of LNMO as an absorbing material in a heterostructure device and compares the results obtained by varying the ETLs and the work function of the front electrode. The magnetic properties of double-perovskite nanoparticles have been studied using various techniques, but their application in the biomedical field has yet to be reported. The ability of proteins to bind to surfaces has important applications in biomedical engineering, biotechnology, and environmental science.

2. Background Works

In the 1950s, a new class of materials known as double perovskites was discovered. Their usual formulas are A2BB’O6, where A represents an alkaline rare earth metal divalent ion and B and B’ represent a transition, alkali, or alkaline earth metal [15]. Using various doping or composite forms makes it feasible to fine-tune the exotic features of double perovskites [16].

Moreover, aggressive light absorption, longer diffusion lengths, and low-temperature processing have proved very helpful in solar cell technology [17]. Perovskite solar cells provide a far better alternative to conventional solar cells as well as solar cells containing toxic lead for these and other reasons.

A few years ago, the efficiency of certain perovskite solar cells was just 3.8% [18], but it has since improved to as high as 22.7%. La₂NiMnO₆, a prominent member of the double-perovskite family, is researched more often due to its unusual magneto-dielectric behaviour and near proximity to room temperature [19]. Previous work using density functional approximation reveals that the band structure of La₂NiMnO₆ allows for semiconductivity [20]. In addition, when La₂NiMnO₆ is oxidized, ferromagnetic and antiferromagnetic LaMnO₃ and LaNiO₂ are generated [21]. The amazing qualities of this material have garnered considerable attention and curiosity in recent years.

In contrast, the structure of La₂NiMnO₆ deviates somewhat from the ideal structure, with the degree of deviation varying with temperature [22]. The monoclinic phase of La₂NiMnO₆ occurs at room temperature, whereas the rhombohedral phase occurs at higher temperatures [23]. The environment and temperature effects on the characteristics and crystal structure of La₂NiMnO₆ during mixing phase have been established [24].

Double perovskites exhibit unique properties that can be fine-tuned by doping or composite forms [25]. The physical characteristics of double perovskites change when the A site is swapped due to differences in B-O-B bond angles. Calcium doping, for instance, induces a mild ferromagnetic first-order phase transition that enhances long-range ferromagnetic order. On the other hand, gadolinium doping may be utilized to improve the performance of insulating material. DFT doping has been used to improve the performance of various materials, including perovskites, carbon nanotubes, and oxides [26]. However, replicating laboratory findings via simulation can be challenging. In addition, double perovskites pose their own distinct challenges in terms of stability, performance, and efficiency when applied in various sectors. For instance, primary concerns are the pricing and potential toxicity of light-harvesting materials such as silicon solar cells and lead–halide perovskite cells. To address these limitations, extensive research has been focused on identifying suitable materials. The applicability of LMNO’s monoclinic phase system in solar cells was studied by the authors of this work. Substitution doping was used to further increase light responses, and the optical examination of doped materials showed good conductivity in the visible spectrum, indicating that the system may be used in solar and energy-storage applications.

The double-perovskite material A2BB’O6, where A represents rare earth elements and B, B′ represents transition metal elements, was recently found to satisfy the need for a lead-free light-absorbing layer while maintaining the typical perovskite crystal structure [27]. Due to its useful bandgap, many double-perovskite materials have been studied for application in photovoltaics [28]. These components consist of [KNbO₃]1 × [BaNi₁/2Nb₁/2O₃-d], Bi₂CrFeO₆, Dy₂NiMnO₆ (DNMO), Lu₂NiMnO₆ (LNMO), and La₂NiMnO₆ (LNMO). LNMO has turned to chemical processing, the simplest form of material synthesis [29] in order to produce a double-perovskite layer. By comparing the optical spectra of LNMO epitaxial films to those of CH₃NH₃PbI₃ with a 1.5 eV bandgap [30], Golubev et al. [31] showed the sol-gel method for polycrystalline LNMO deposition. Experiments demonstrated that LNMO crystallizes at room temperature of either a orthorhombic or a monoclinic structure and depends on the disorder or order of the sample [32]. Tai et al. [33] revealed the first experimental and theoretical analysis of the double-perovskite material LNMO and its potential usage in solar cells. They utilized both monoclinic and rhombohedral structures of LNMO together that had corresponding bandgaps of 1.4 eV and 1.2 eV, respectively. Double-perovskite LNMO with a monoclinic structure is preferred over rhombohedral structures for solar applications, according to the results [34]. Multiple investigations demonstrate that the double-perovskite LNMO possesses two ferroelectric Curie transition temperatures at temperatures of 60 K and 285 K, respectively. This material’s high dielectric constant aids in the dielectric screening of photo-generated charge carriers, which is significant given that it lacks ferroelectric characteristics at ambient temperature [35]. Wang et al. [36] showed La₂NiMnO₆ for photovoltaic applications in order to further the development of lead-free inorganic double-perovskite materials, where Ln represents La, Eu, Dy, and Lu. This unique material has a longer carrier lifetime than previously known halide perovskite materials, which are comparable to silicon solar cells. The constructed device demonstrated a PCE of 0.17%, an open-circuit voltage of 336 mV, a fill factor of 0.27, and a current density of 0.27. Research on a similar double-perovskite Cs₂TiBr₆ can be found in [37,38].

The contribution of this project is the exploration and analysis of La₂NiMnO₆ as a potential absorbing material in perovskite solar cells as well as the optimization of the electron transport layers (ETLs) and hole transport layers (HTLs) to improve the power conversion efficiency (PCE) of the cells. The project also investigated the impact of varying the thickness and defect density fluctuations of the absorbing layer on PCE [39]. The motivation for this project is to develop a more efficient and cost-effective alternative to traditional silicon-based solar cells. By exploring new materials and optimizing the structure and composition of the cells, the researchers aim to improve the efficiency of solar cells and potentially lower their cost, which could contribute to the wider adoption of solar energy as a clean and sustainable energy source. Additionally, the research could provide insights into the use of double perovskites, such as La₂NiMnO₆, in other optoelectronic applications.

3. Material and Methods

The use of numerical modelling has become more important in recent years in order to improve the understanding of physical characteristics and facilitate the construction of solar cells based on crystalline, polycrystalline, and amorphous materials. In order to achieve an advanced level of knowledge, construction, and optimization of cell structures, the use of numerical simulation is essential. It is difficult to conduct measurement analysis in the absence of a trustworthy model. The SCAPS simulator is used in this investigation to carry out a quantitative analysis of the functioning of the DPSC that is being suggested. The graphical solar cell modelling tool known as SCAPS was developed by Professor Marc Burgelman of the Electronics and Information Systems (ELIS) department at the Catholic University of Gent in Gent, Belgium. He did so by making use of National Instruments Lab Windows/CVI.

The Poisson equation, the hole continuity equation, and the electron continuity equation all contribute to the foundation of this simulation technique. Doping concentration, defect density, electron affinity, and other properties of the absorbing layer in addition to ETLs and HTLs may all influence the efficiency of power conversion. The primary objective of this research is to determine how to improve the performance of PSCs.

Table 1. Parameters of different materials.

Material Properties	TiO2	LMNO	C60	ZnO	Cu2O	FTO	CuI
Layer thickness (nm)	30	350	30	30	200	500	200
Optical bandgap(eV)	3.2	1.05	1.7	3.3	2.17	3.5	3.1
Affinity of electron (eV)	3.9	3.52	3.9	4	3.2	4	2.1
Relative permittivity	32	3.5	4.2	9	7.11	9	6.5
Effective DOS in the conduction band (cm−3)	1 × 1019	1 × 1018	8 × 1019	2 × 1018	2.2 × 1018	2.2 × 1018	2.2 × 1018
Effective DOS in the valance band (cm−3)	1 × 1019	1 × 1018	8 × 1019	1.8 × 1019	1.9 × 1019	1.8 × 1019	1.8 × 1019
Thermal velocity of electron (cm/s)	107	107	107	107	107	107	107
Thermal velocity of hole (cm/s)	107	107	107	107	107	107	107
Mobility of electron (cm2/Vs)	20	22	1 × 10−2	100	3 × 102	20	100
Hole mobility (cm2/Vs)	10	22	3.5 × 10−3	25	8 × 101	10	47.9
Donor density (cm−3)	1 × 1017	-	2.6 × 1018	1 × 1018	-	1 × 1019	-
Acceptor density (cm−3)	-	7 × 1016	-	-	1 × 1018	-	1 × 1018
Defect density	1014	1014	1014	1014	1014	1014	1014

provides a summary of the many simulation parameters. According to previously published studies, experimental and theoretical study determines the parameters.

This study aims to determine how various ETLs (C₆₀, ZnO, and TiO₂) impact the device of a double-perovskite solar cell based on La₂NiMnO₆. The analysis has been applied to the optical absorption constant from absorption submodels sqrt (h-Eg) law (SCAPS conventional). The defect density has been set to 1 × 10¹⁴ cm³ across all layers, while the electron and hole thermal velocities have been determined based on the structures. Interaction between 2 levels at a device’s interface significantly impacts its performance. Two interfacial flaws were considered in this device configuration, including LNMO/TiO₂ and LNMO/CuI as the displayed structures in the Figure 3.

The parameters of different materials are shown in Table 1. These parameters were used during simulation in SCAPS software.

4. Results and Discussion

This section presents the investigated characteristics of LMNO double perovskite. The bandgap is a fundamental characteristic of photovoltaic solar cell technologies. We determined that a bankgap of 1.5 eV is optimal for perovskite solar cells; thus, we adopted this value in our research. LMNO models Electron Transport Layers (ETLs) and Hole Transport Layers (HTLs) to determine the efficiency of power conversion between the two. C60/LMNO/Cu₂O solar cells offer the best power conversion efficiency. This solar cell has an energy conversion efficiency of 0.43%. Cu₂O as a HTL has not been extensively studied in the past. ZnO/LMNO/Cu₂O demonstrates the lowest performance. Figure 4 shows the current densities for the different proposed structures, and it is observed that the maximum current density was observed for the C60/LMNO/Cu₂O structure. Figure 5 shows the quantum efficiency of all the simulated structures, which is the function of the wavelength. It demonstrates how the quantum efficiency is varying s a function of incident wavelength in all the proposed structures. The performance parameters of simulated devices are shown in

Table 2. Extracted results from the proposed structure.

Structure	JSC	VOC	FF	Efficiency (%)
C60/LMNO/Cu2O	3.71	0.202	56.83	0.43
TiO2/LMNO/CuI	1.92	0.1919	49.5	0.18
C60/LMNO/CuI	1.91	0.1838	48.44	0.17
ZnO/LMNO/Cu2O	0.003	0.1873	52.11	0.01

. At all interfaces and surfaces of each layer of the simulated device, the optical reflectance is set to zero.

4.1. Effect of Thickness

Table 3. Effect on efficiency and Voc with thickness.

Thickness	Efficiency	Voc(V)
1.00 × 10−1	4.20 × 10−1	0.2009
1.00 × 100	4.30 × 10−1	0.2018
1.50 × 100	4.30 × 10−1	0.202
2.00 × 100	4.30 × 10−1	0.2021

indicates how perovskite thickness affects the efficiency and open-circuit voltage. It is essential to have a sufficiently thick absorber layer for efficient light absorption. Photon-generated electrons and holes must be able to reach the outer contact with little recombination, necessitating optimal thickness. This implies that up to a particular thickness, the power conversion efficiency increases but thereafter decreases. The greatest results are achieved using the geometry C60/LMNO/Cu₂O (efficiency 0.43). Figure 6 shows the efficiency as a function of thickness variation by adjusting the thickness of perovskite from 0.1 to 1 mm in batch simulations. It is observed that optimal performance is achieved with a thickness of 0.22 mm. As seen in Figure 7, the open-circuit voltage rises with increasing perovskite thickness.

4.2. Effect of Defect Density

A change in defect density occurred at 10(e) cm³. It was determined that the Jsc saturates at a fault density of 10⁹ cm³ and that below this threshold, the parameters fluctuate relatively minimally.

Table 4. Effect on efficiency and Voc with defect density.

Defect Density	Efficiency	Voc
1.00 × 1010	4.20 × 10−1	0.199
2.50 × 1015	4.20 × 10−1	0.199
5.50 × 1015	4.20 × 10−1	0.198
7.50 × 1015	4.20 × 10−1	0.198
1.00 × 1016	4.20 × 10−1	0.198

illustrates the results collected. As seen in Figure 8 and Figure 9, defect number has a negligible impact on solar cell properties. The energy-level diagram of the corresponding structures using C60/LMNO/Cu₂O and TiO₂/LMNO/CuI is shown in Figure 10 and Figure 11, respectively.

5. Conclusions

The aim of the present study was to investigate the structural, optoelectronic, and photovoltaic properties of La₂NiMnO₆ using first principles and SCAPS-1D simulations. La₂NiMnO₆ has been shown to possess high potential as a photovoltaic material, as demonstrated by the results obtained in this work. For example, the maximum power conversion efficiency (PCE) obtained for the FTO/C60/La₂NiMnO₆/Cu₂O heterojunction in the photovoltaic investigation was 0.435%, which is significantly higher than the recently predicted value for the solar cell based on La₂NiMnO₆ (0.18%), as shown in

Table 5. Performance comparison.

Structure	VOC	JSC	FF	PCE	Parameters Optimized
C60/LMNO/Cu2O (Proposed)	0.1919	1.92	49.5	0.43	ETL, HTL, thickness of absorbing layer, defect density
C60/Perovskite/CuI [40]	0.1982	1.9110	47.82	0.18	ETL and work function

.

The thickness and defect density fluctuations of the absorbing layer were found to be the critical factors influencing PCE. However, research in La₂NiMnO₆-based PSCs is still limited, and further investigation is necessary to optimize their performance. In future studies, we plan to explore the effect of doping concentration, electron affinity, different back-metal contacts, and varied hole transport layer materials of the absorber, ETLs, and HTLs on the PCE of La₂NiMnO₆-based perovskite solar cells.

In summary, the present work sheds light on the high potential of La₂NiMnO₆ as a photovoltaic material and provides insights into the critical factors that influence its PCE. The findings of this study could help pave the way for the development of efficient and cost-effective perovskite solar cells based on La₂NiMnO₆.