Saman Thesis: Simulation of Sn-Pb Mixed Perovskite Solar Cells PDF
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Hazara University, Mansehra
2024
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Summary
This thesis investigates the performance of Sn-Pb mixed halide perovskite solar cells. The author used SCAPS-1D to simulate the devices and analyze key parameters such as J-V characteristics, quantum efficiency, and the impact of various parameters. The thesis was written in 2024 at Hazara University, Mansehra, Pakistan.
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SIMULATION OF Sn-Pb MIXED PEROVSKITE SOLAR CELLS TO STUDY ITS PERFORMANCE PARAMETERS BY USING SCAPS-1D By SAMAN 4012-221009 DEPARTMENT OF PHYSICS HAZARA UNIVERSITY, MANSEHRA...
SIMULATION OF Sn-Pb MIXED PEROVSKITE SOLAR CELLS TO STUDY ITS PERFORMANCE PARAMETERS BY USING SCAPS-1D By SAMAN 4012-221009 DEPARTMENT OF PHYSICS HAZARA UNIVERSITY, MANSEHRA 2024 SIMULATION OF Sn-Pb MIXED PEROVSKITE SOLAR CELLS TO STUDY ITS PERFORMANCE PARAMETERS BY USING SCAPS-1D By SAMAN 4012-221009 DEPARTMENT OF PHYSICS FACULTY OF COMPUTATIONAL AND NATURAL SCIENCE HAZARA UNIVERSITY, MANSEHRA 2024 This copy of the thesis has been supplied on the condition that any one consulting it is understood to recognize that the copy right rest with the another and that neither quotation from the thesis, nor any information may be published without the authors prior written consent. ii DECLARATION The work presented in this thesis was carried out by me under the supervision of Dr. Muhammad Abrar, Assistant Professor, Department of Physics, Faculty of Computational and Natural Science, Hazara University Mansehra, and Dr. Irfan Ahmed, Assistant Professor, Department of Physics, Govt. College, Balakot. The conclusions are my own research after numerous discussions with my supervisor and co-supervisor. I have not presented any part of this work for any other degree. Research Scholar: ___________________ Saman We certified that to the best of our knowledge above statement is correct. Research Supervisor: ___________________ Dr. Muhammad Abrar Research Co-supervisor: _______________________ Dr. Irfan Ahmed iii CERTIFICATE It is certified that the dissertation entitled “SIMULATION OF Sn-Pb MIXED PEROVSKITE SOLAR CELLS TO STUDY ITS PERFORMANCE PARAMETERS BY USING SCAPS-1D” submitted by Ms. Saman for the award of Master of Philosophy in Physics, is based on the result of studies carried out by her in Hazara University, Mansehra under our guidance and supervision during the research. The dissertation or any part of it has not been previously submitted for any other degree. Internal Examiner/Supervisor ___________________ Internal Examiner/Co-Supervisor ___________________ External Examiner: ___________________ Chairman: ___________________ Date: ___________________ iv Dedication To Parents For their endless love, support and encouragement without them I am nothing. The one who always picked me up on time and encouraged me to get on every adventure, especially this on To Teachers For nursing me with affections and their dedicated partnership for success in my life v ACKNOWLEDGEMENTS Words are bound, and the knowledge is limited to praise the Allah. The most Beneficent, gracious, merciful, and whose generous exaltation and blessing has flourished our thoughts, and we have endeavored to preserve our humble efforts in the form of a manuscript, of the blossoming spring of prosperous knowledge. I sincerely appreciate the constructive suggestions and valuable guidance of Dr. Muhammad Abrar. Throughout my research work, an inspiring attitude and his guidance have helped me complete the research. This acknowledgment will be incomplete unless I give humble and heartiest thanks to Dr. Irfan Ahmed for their guidance and support throughout my research work and writing of this thesis. I sincerely thank my dear parents, for their endless support. vi Table of Contents Table of Contents..................................................................................................... vii LIST OF FIGURES.................................................................................................... ix LIST OF TABLES......................................................................................................... x ABSTRACT................................................................................................................. xi CHAPTER 1.................................................................................................................. 1 INTRODUCTION....................................................................................................... 1 1.1 Energy Demand.................................................................................................... 1 1.2 Solar Cells............................................................................................................... 2 1.2.1 First Generation Solar Cells........................................................................ 3 1.2.2 Second Generation Solar Cells................................................................... 4 1.2.3 Third Generation Solar Cells...................................................................... 5 1.3 Device Architecture of Perovskite Solar Cells.................................................. 6 1.3.1 Planner junction device (N-I-P)................................................................. 6 1.3.2 Inverted Junction Device (P-I-N)............................................................... 6 1.4 Perovskite Crystal Structure................................................................................ 7 1.5 Working and Configuration of Perovskite Solar Cell...................................... 8 1.6 Perovskite Photo Absorber.................................................................................. 9 1.7 Sn Based Photo Absorber................................................................................... 11 1.8 Challenges with Sn-Based Perovskite Solar Cell............................................ 12 1.9 Recent Implementation of Sn Based PSCs....................................................... 13 1.10.1 A-Site Modification.................................................................................. 14 1.10.2 B-Site Modification.................................................................................. 15 1.10.3 X-Site Modification.................................................................................. 16 1.11 Functional Additives........................................................................................ 16 1.12 Performance Parameters.................................................................................. 16 1.12.1 Open Circuit Voltage (Voc).................................................................... 16 1.12.2 Short Circuit Current (JSC)....................................................................... 17 1.12.3 Fill Factor (FF)........................................................................................... 17 1.12.4 Quantum Efficiency (QE)........................................................................ 17 1.13 SIMULATION OF PV SYSTEM...................................................................... 17 vii 1.14 OBJECTIVES...................................................................................................... 18 1.15 Thesis Outline.................................................................................................... 19 CHAPTER 2................................................................................................................ 20 LITERATURE REVIEW........................................................................................... 20 2.1 Experimental Review......................................................................................... 20 2.2 Literature Review of Simulated Perovskite Solar Cell.................................. 22 CHAPTER 3................................................................................................................ 30 METHODOLOGY..................................................................................................... 30 3.1 Introduction......................................................................................................... 30 3.2 System Design and Characteristic Parameters for Digital Simulation........ 30 CHAPTER 4................................................................................................................ 37 RESULTS AND DISCUSSION.............................................................................. 37 4.1 Introduction......................................................................................................... 37 4.2 J-V Analysis of MAPbI3...................................................................................... 37 4.3 J-V Analysis of MASnI3...................................................................................... 38 4.5 Mixed Perovskite Solar Cell.............................................................................. 41 4.5.1 Simulation 0f Mixed Perovskite Solar Cell............................................. 41 4.6 Effect of Different concentration of Sn and Pb content on the Efficiency of MASnPbI3........................................................................................................... 41 4.7 J-V Analysis of MASn0.7Pb0.3SnI3 Perovskite Solar Cell................................. 43 4.7.1 Comparative Analysis of All Three Devices:......................................... 43 4.8 Effect of Thickness on Performance Parameters of Sn-Pb Mixed Perovskite Solar Cell............................................................................................................. 45 4.9 Analysis of Quantum Efficiency (QE).............................................................. 47 4.10 Temperature Variation Analysis..................................................................... 47 CHAPTER 5................................................................................................................ 50 CONCLUSION.......................................................................................................... 50 REFERENCES............................................................................................................. 52 viii LIST OF FIGURES Figure 1.1: Diagrammatic representation of Solar cell generations and their types.................................................................................................... 3 Figure 1.2: Diagrammatic overlook of PSCs architecture: a) N-I-P-(regular..... 7 Figure 1.3: ABX3 crystal structure schematic illustration of 3D halide perovskite [7, 8]............................................................................................................. 8 Figure 1.5: Crystal compositions of a) MASnI3 b) FASnI3 c) CsSnI3........... 14 Figure 3.1: Device structure of required cell with tentative layers.................... 32 Figure 3.2: Energy band presentation of MASnI3 by TiO2 & Spiro-OMeTAD. 32 Figure 3.3: charge transfer presentation of MAPbI3 with TiO2 and Spiro- OMeTAD.................................................................................................. 34 Figure 3.4: Band depiction of MASn1-xPbxI3 by means of transporting material..................................................................................................................... 34 Figure 4.1. Current Voltage graph (J–V) for MAPbI3........................................... 38 Figure 4.2. Current Voltage curve (J–V) function for MASnI3............................ 39 Figure 4.3. Comparison of Current Voltage curve (J–V) for MAPbI3 and MASnI3...................................................................................................... 40 Figure 4.4. Current Voltage graph (J–V) directed MASn0.7Pb0.3I3...................... 43 Figure 4.5. Comparison of Current Voltage curve (J–V) function for MAPbI3 and MASnI3 and MASn0.7Pb0.3I3............................................................ 44 Figure 4.6. Response of thicker absorber layer on (a) VOC (b) JSC (c) FF and (d) PCE............................................................................................................ 46 Figure 4.7. QE of Sn-Pb mixed perovskite vs wavelength.................................. 47 Figure 4.8: Temperature-dependent changes (300 K-350 K) on performance parameters................................................................................................ 48 ix LIST OF TABLES Table 3.1: Key material properties for Titanium Dioxide, Methylammonium Lead Iodide, and Spiro-OMeTAD........................................................ 33 Table 3.2. Key material properties for different device layers............................. 35 Table 4.1: Comparison of electrical parameters of MAPbI3 and MASnI3........... 40 Table 4.2.Performance parameters of Sn-Pb mixed PSC with different composition.............................................................................................. 42 Table 4.3. Dependence of performance metrics on thickness of MASn 0.7Pb0.3I3..................................................................................................................... 45 x ABSTRACT Perovskite solar cells (PSCs) have demonstrated enormous promise for photovoltaic applications with high efficiency. From their development in 2009, PSCs have been the most rapidly developing technology. This study presents a comprehensive simulation analysis of Sn-Pb mixed perovskite solar cells, exploring the impact of varying composition ratios on device performance. Utilizing SCAPS-1D software, the effects of different percentage compositions are investigated for Sn and Pb on Efficiency of power conversion, voltage at open circuit, and current density at short circuit. Our results reveal a complex interplay between composition ratio and device performance, with optimal ratios yielding enhanced efficiency. Notably, a 70% Sn and 30% Pb composition achieves MASn0.7Pb0.3I3 a peak power conversion efficiency of 27.89%. Further analysis reveals that increasing Sn content up to 70% improves Voltage at open circuit and current density at short circuit, which is due to lower bandgap value that is 1.17 eV. In addition, QE analysis, thickness adjustment, and the influence of temperature variations on the MASn0.7Pb0.3I3 cells performance parameters are studied. According to the thermal stability analysis device arrangement is stable at 300 K. This simulation-driven study offers a useful foundation for experimental research and the development of new devices, as well as fresh insights into the optimization of Sn-Pb mixed perovskite solar cells. Key words: Sn-Pb mixed, perovskite solar cells, simulation analysis, composition ratio, device optimization. xi CHAPTER 1 INTRODUCTION 1.1 Energy Demand Since the start of the scientific and industrial revolutions, the world energy needs have been steadily rising. It is important to remember that the population has grown by two billion in just one generation, largely due to the efforts of developing nations [1-3]. A twenty-first-century society least critical problem is how to prevent an energy crisis. In order to keep up with the growing world population, there is a rapid increase in the energy requirement. Because of growing populations and expanding activities, there are less resources available. Thus, in order to meet the requirements of the global population, energy sources must be considered [5, 6]. A number of variables, such as a nation growth profile, population, economic status, and technological advancements, affect how easily individuals may obtain enough energy. The search for sustainable energy is being fueled by the depletion of fossil fuels and the increasing knowledge of the long-term effects of [CO2] emissions into the environment. Furthermore, if non-sustainable energy sources are continuously relied upon, global warming may ensue, posing serious environmental risks to the planet ecosystems [7, 8]. Environmentally sustainable energy sources are important to choose if we want to better the world future. It is crucial to consider sustainable energy sources that are environmentally beneficial, such as solar, hydrothermal, geothermal, and wind power. Energy harvesting is currently considered to be essential, especially when it comes to daylighting. The goal of solar cell technology is to produce more affordable, environmentally friendly solar panels with high efficiency and long lifespan. In order to fulfill future demand without causing harm, solar energy has advanced significantly and is currently the most thoroughly investigated option. 1 1.2 Solar Cells Solar cells are devices that use semiconductor materials to convert sunlight to electrical energy.. Sunlight particles (photons) are absorbed by the semiconductor, releasing electrons. These electrons move within the material, filling empty spaces (holes) left by other electrons. This movement of electrons generates an electric current. This phenomenon, Known as the photovoltaic effect, this phenomenon was initially reported by A. E. Becquerel in 1839. The first photovoltaic cell concept was invented by Charles Fritts in 1883. There are three methods in which a solar cell operates:. (i) Absorption of photons to create holes and electrons. (ii) Electrons and holes separation. (iii) Forming a potential difference across the p-n junction. Photovoltaic research and development have advanced dramatically, especially for satellite applications. silicon solar cells were developed in the 1980s and achieved an efficiency of more than 20%, there was a lot of hope. Over time, thin film and multi-junction solar cells keep attracting the interest of numerous research institutions. Solar power holds immense promise as a long-term energy solution. Solar cells are classified based on their composition, structure, and cost. Traditional solar cells use silicon crystals, while newer technologies employ thin-film materials. Ongoing research is focused on developing advanced Solar cells, such as perovskite, dye-sensitized, and quantum dot varieties. Figure 1.1 shows a diagrammatic depiction of the three generations together with their corresponding categories. 2 Figure 1.1: Diagrammatic representation of solar cell generations and their types. 1.2.1 First Generation Solar Cells The field of photovoltaics (PV) was launched in 1954 when Bell Labs in the United States developed the crystalline silicon solar cell, which has a PCE of 6%. The main component of materials used in first-generation solar cells is silicon. The advantages of these photovoltaic (PV) cells were evident in the readily available raw materials and the advanced, effective technology. Silicon is the fundamental component of the vast majority of solar energy harvesting systems, which account for over 90% of global sales. It is the second most common element on earth after oxygen and makes for the most efficient single- PV cells. It has 1.1 eV band gap energy which is suitable for solar technology. Silicon wafers are classified as mono-crystalline, polycrystalline, or amorphous silicon solar cells depending on the method used to create them in energy applications. The extremely expensive and energy-intensive Czochralski process is used to produce monocrystalline silicon. These solar cells are a well-established technology with a PCE of 26.6%. To create polycrystalline solar cells, several silicon crystals are employed. 3 Polycrystalline cells are more cost-effective to manufacture, but performance is sacrificed in the process; on the other hand, monocrystalline cells provide higher efficiency at a higher cost. Monocrystalline solar PV cell production is more costly, although being less pure than single-crystalline silicon, polycrystalline and amorphous silicon are more frequently employed because to their lower cost. Because of the first-generation PV cells shortcomings, researchers have been working hard to discover new materials that display the PV effect and reasonably priced device architectures. As a consequence, scientists successfully created next-generation solar cells, marking a significant advancement in the field. 1.2.2 Second Generation Solar Cells The second generation of solar technology introduced thin film technology. In contrast to crystalline silicon technology, they consist of layers that are only a few micrometers thick. Thin-film technology is the basis for second-generation solar cells having high recombination rate, a brief diffusional path, and absorption [14, 17]. These materials make advantage of more practical and affordable substrates, such as ceramic, quartz, or glass as they can hold a lot. The main components used in thin-film solar cells are Gallium arsenide, cadmium telluride and copper indium gallium diselenide (CIGS). Thin-film solar cells generally offer a lower cost per watt compared to traditional silicon cells since they require less material with a PCE of 29.1%. GaAs have the highest efficiency among the materials in this category. Two more remarkable mentions are CdTe and CIGS, which obtain efficiencies of 23.15% and 22.1%, respectively. Still every material exhibits challenges that will keep it from becoming widely commercialized, because of their expensive and difficult manufacturing process, GaAs are only useful at high efficiency. The ability of these incredibly thin layers to be easily rolled, folded, and molded, outperforming more conventional silicon-based materials, is a significant advancement in thin-film technology. They are lightweight and flexible, which 4 significantly lowers the chance of damage from handling or impact. This gives them a substantial advantage in terms of longevity. Nearly ninety five percent of the thin film PV market is currently supplied by cadmium telluride (CdTe), the most advanced and least expensive thin film technology today. Thin film solar cells were less expensive and more efficient, but they also have certain disadvantages. An increasing number of these cells are becoming more infrequent (like indium) and extremely toxic (like cadmium). A new type of solar cell has been developed as a outcome of these defects. 1.2.3 Third Generation Solar Cells The high cost and safety concerns associated with first-generation solar cells, along with the limited material availability in second-generation cells, created significant hurdles that needed to be addressed. In response, researchers pursued the development of next-generation solar cell technologies, aiming to overcome these challenges and unlock more efficient, sustainable, and cost- effective energy solutions. Even though research on third-generation solar cells is still ongoing, these cells have shown promise and are growing quickly. These materials are widely used because cells may be made utilizing low-energy techniques and cheap materials. The third generation of solar cells, known as emerging technologies, comprises perovskite solar cells, dye-sensitized solar cells (DSSCs), quantum dot cells, copper zinc tin sulfide (CZTS), organic photovoltaic technology. Due to their ability to produce solar cells in large quantities using low-energy manufacturing techniques, PSCs and OPV cells have become market leaders. In order to provide silicon solar cells with greater flexibility, organic or polymer solar cells were created. Planned photovoltaic systems are going to use quantum dot technology due to their extraordinary efficiency and capacity to overcome the thermodynamic boundaries of conventional cells. Quantum dot Solar cells have drawn great interest because of their promise for high efficiency and cheap cost. However, the most successful devices to date have relied on the use of hazardous heavy metals like cadmium or lead. 5 The long-term viability of dye-sensitized cells over time and the extreme temperature changes encountered outside create the biggest problems because halide perovskite is more affordable and efficient than other materials, it may be a novel material. The development of perovskite solar cells has progressively improved [19, 20]. Solar cell efficiency has seen a substantial improvement, with a remarkable 3.8% gain in 2009, resulting in a current efficiency rate of 25.8%, marking a notable milestone in the field. The research aims to make solar energy more accessible, safe, stable throughout a wider spectrum of sunlight and efficient by enhancing the solar cells that are currently on the market. 1.3 Device Architecture of Perovskite Solar Cells Perovskite solar cell (PSCs) are classified into the resulting groups established on which carrying component (an electron or a hole) on the perovskite exterior first comes into contact with light. The two basic PSC architectures are: Planner junction device (N-I-P) Inverted junction device (P-I-N) 1.3.1 Planner junction device (N-I-P) In the n-i-p configuration of perovskite solar cells, the electron transport layer (ETL) is deposited first, followed by the hole transport layer (HTL). The ETL is the initial layer to interact with sunlight in this type of cell. Figure 1.2(a) shows the n-i-p, a typical device architecture. 1.3.2 Inverted Junction Device (P-I-N) The hole transport layer is positioned first in PIN architecture and gets light before ETL. Figure 1.2(b) shows the p-i-n, an inverted device design. There are several varieties of PSC including those with conventional NIP and inverted PIN architecture. ETL free cell 6 HTL free cell Perovskite-heterojunction devices Figure 1.2: Diagrammatic overlook of PSCs architecture: a) N-I-P-(regular), b) P-I-N-(inverted). Every configuration of PSC has advantages and disadvantages. Although this, perovskite solar cells are still being investigated, and soon new, low-cost types with excellent conversion efficiency and extended lifespans free from degradation issues could surface. 1.4 Perovskite Crystal Structure An initial use of the term "perovskite" was to refer to a calcium titanate mineral known by its chemical formula, CaTiO3. Russian mineralogist L.A Perovski gave the mineral its name after it was initially discovered by Gustav Rose in the Ural Mountains of Russia in 1839. As demonstrated in Figure 1.3 perovskite materials typically exhibit a three-dimensional crystalline structure conforming to the chemical formula ABX3, resembling the structure of CaTiO3. Here, X represents a halide anion (Br- , Cl-, or I-) as illustrated in Figure 1.3. The B site is occupied by a divalent cation such as lead or tin, while the A site accommodates A monovalent metals cation such as Formamidinium (C(NH2)2⁺), methylammonium (CH3NH3⁺), cesium (Cs⁺), or rubidium (Rb⁺).. The crystal lattice arranges with B cations surrounded by six X anions in an octahedral 7 configuration, and the A cations are situated approximately at cubic units eight corners. Figure 1.3: ABX3 crystal structure schematic illustration of 3D halide perovskite [7, 8]. 1.5 Working and Configuration of Perovskite Solar Cell The most widely studied approach of meeting future requirements without harming the environment is The solar cell, a gadget that turns sunlight directly into power [7, 8]. The efficiency of solar cells is significantly improved by their structure. The two layers that comprise a PSC fundamental structure include the hole transport layer (HTL) and the electron transport layer (ETL), into which free electrons and holes are inserted. Usually, the cathodes of a PSC are made of metal and FTO glass and metal. The three primary functions of a photovoltaic system are charge extraction, charge transfer, and photon absorption. Light- emitting photons travel through the glass and transparent electrode and into the perovskite layer, at which point they are absorbed. If the energy of a photon above the material energy gap Incident sunlight is absorbed by the photoactive perovskite layer, generating an electron-hole pair. The difference in work function between the transparent and metallic electrodes creates an electrical field within them. This internal electric field 8 separates excitons into free electrons and holes, with electrons migrating to the ETL and holes to the hole transport HT. In accordance with the direction of the electrons, holes are moved to the counter electrode layer and the transparent electrode. The hole in the metallic electrode and the electrons recombine after the electrons have created a current by crossing the circuit between the two electrodes. For the PSC to function properly, the energy level for each layer needs to be carefully set. The cell achieves optimal energy output by minimizing total energy, which suppresses hole-electron recombination and maintains efficiency through energy-efficient charge carrier management. 1.6 Perovskite Photo Absorber Perovskite solar cells have drawn attention from researchers worldwide because to its exceptional photoelectric properties. Remarkable compounds called perovskites have revolutionized solar technology. Kojima et al. in 2009 proclaimed the efficiency of the first perovskite-based solar cell, which had a 3.8% efficiency. PSCs were first given little attention because to their poor stability and performance. However, Park and colleagues found an efficiency of more than 9% and stability of more than 500 hours after making their measurements in ambient settings. Perovskite solar cells have achieved the third-highest single-junction efficiency, rapidly increasing from 14.1% to 25.2% over the past six years. The commercialization of perovskite solar cells faces several challenges, including environmental and health hazards, concerns over long-term durability, and difficulties in scaling up production. The following issues need to be resolved before they may be successfully commercialized. Perovskite solar cells and silicon solar cells are competing technologies, vying for dominance in terms of energy conversion efficiency. Perovskite solar cells are a rapidly emerging and promising technology within the photovoltaic industry. PSCs have gradually increased in total PCE because of their flexible bandgap, higher carrier diffusion length, mild optical absorption coefficient, 9 and highly simple production process. Lead perovskite with halide substance, Formamidinium lead iodide (FAPbI3), cesium lead iodide (CsPbI3), and methylammonium lead iodide (MAPbI3) are the major active elements in several high- efficiency perovskite solar cells (PSCs). Lead-based PSCs have attained a power conversion efficiency (PCE) of 25.8%, making them equivalent to silicon-based solar cells. Perovskite materials have remarkable optoelectronic properties, such as low electron-hole binding energy (below 10 meV), enhanced carrier mobility (nearly 800 cm2/Vs), enhanced life-time (up to 300 ns), high absorption coefficient (outstripping 105 cm-1), optimized band gap, superior structural defect tolerance, and low surface recombination probability. The development of materials that are more successful at absorbing sunlight has been made possible by the synthesis of hybrid organic-inorganic perovskites. The tunable frequency characteristic of these solar cells enables them to absorb different light wavelengths more effectively. By using multiple layers, each optimized for specific wavelengths, they achieve higher efficiencies than conventional solar cells. Perovskite solar cells constitute a significant achievement in the domain of photovoltaics. Perovskite solar cells (PSCs) have experienced a constant growth in total photochemical efficiency (PCE) due to its adaptable bandgap, extended carrier diffusion length, low optical absorption coefficient, and straightforward manufacturing method. Perovskite compounds including lead halides, Examples include methylammonium lead triiodide (MAPbI3), cesium lead triiodide (CsPbI3), and formamidinium lead triiodide (FAPbI3).—are used actively in most high efficiency PSCs.. A power conversion efficiency of 25.8% has been attained by lead-based PSCs, which is on par with silicon-based solar cells. Perovskite materials have remarkable optoelectronic characteristics, such as low electron hole binding energy (below 10 mev), enhanced carrier mobility (nearly 800 cm2/vs), enhanced life-time (up to 300 ns), high absorption coefficient (outstripping 105 cm-1), optimized band 10 gap, superior structural defect tolerance, and low surface recombination probability. More efficient materials for absorbing sunlight have been developed as a result of the development of hybrid organic-inorganic perovskites. Because of their adjustable frequency characteristic, which may raise their efficiencies, these solar cells can absorb various light wavelengths via different layers much more effectively than conventional solar cells. Pb- based perovskites present numerous difficulties in this sense.: Instability, which is presently addressed by two-dimensional perovskites and improved design, encapsulation, and architecture of devices. Extreme toxicity, which is hazardous for the ecosystem. As a further option, lead-free, non-toxic perovskite materials are being explored. The fact that Lead (Pb) is toxic potential risks to humans and the environment cannot be overlooked, posing a significant barrier to the future commercialization of lead-based perovskite. Some of the methods developed to improve PSC stability and reduce emissions are device encapsulation, dimensional modeling, and substituting less-toxic elements. Furthermore, it has been proposed that the very harmful lead could be replaced with a less hazardous element. 1.7 Sn Based Photo Absorber Researchers have been looking into less poisonous perovskite materials, like copper (Cu), tin (Sn), antimony (Sb), germanium (Ge), bismuth (Bi), and tin (Sn), as potential replacements for lead (Pb). One of these Pb-free potential materials that is thought to be the most promising is Sn-based perovskite. Given their Equivalent ionic radiuses (135 pm for Sn2+ and 149 pm for Pb2+ ions) identical outer electron configurations (ns2 np2), Pb and Sn, both group IVA elements, can fully substitute for each other in perovskite materials without inducing phase separation. Additional, Sn-based Perovskite solar cells have high charge carrier mobility, low electron-hole pair binding energy, and a The band gap is adjustable within the range of 1.2 to 1.4 eV, which is very near to 1.34 eV, the optimal energy band gap 11 for the Shockley-Queisser limit in single-junction solar cell junctions. As a result, environmentally friendly and green Sn-based perovskite solar cells are likely to find potential claims in other solar and photonic devices. It is encouraging that Sn-based PSCs exhibit excellent durability with PCE greater than 14%. Its exceptional efficiency shows why it is the best choice for the next generation of PV panels. Figure 1.4 shows how the performance of Sn-based PSCs changed over a period of six years. Figure 1.4: Efficiency improvement of PCSs and crystalline Silicon solar cell 1.8 Challenges with Sn-Based Perovskite Solar Cell Tin-based PVs, or photovoltaic solar cells, have shown a power conversion efficiency of 14.81%, yet they still underperform compared to lead-based devices. Key challenges for tin-based PSCs include: 1. Tin (Sn) readily oxidized from Sn2+ to Sn4+ within the glovebox despite minimal oxygen and water levels, Resulting in fewer guarantees and less productivity 2. The occurrence of P-type self-doping is attributed to the low formation energy of tin vacancies, which leads to substantial charge 12 recombination and thus diminishes the precision and performance of electric devices. 3. The rapid interaction between organic cation salts and SnI2 causes the unpredictable crystallization of Sn-based perovskite, making it difficult to produce perovskite films with outstanding uniformity and broad surface coverage. 4. Improper energy band structure with charge-carrying layers can result in energy barriers at the interfaces, which is detrimental to carrier mobility. Due to these challenges, Sn-based PSCs have poor efficiency and instability. As such, using Sn-based perovskite in photovoltaics is a challenging undertaking. 1.9 Recent Implementation of Sn Based PSCs The finding of direct bandgaps of 1.41 eV, 1.3 eV, and 1.20 eV for formamidinium tin iodide (FASnI3), cesium tin iodide (CsSnI3), and methylammonium tin iodide (MASnI3), respectively, has been reported, has led to significant advancements in the development of non-toxic PSCs. MASnI3, FASnI3, and CsSnI3 crystal structures are shown in Figure 1.5. It is commonly recognized that MASnI3 exhibits improved photo-conductivity, a longer carrier-diffusion length, increased charge mobility, and a stable structure, but MASnI3 solar cells power conversion efficiency is not as good as that of Pb-based perovskite solar cells. It is found that although both MASnI 3 and FASnI3 are stable in an inert atmosphere, but FASnI3 is much more stable than MASnI3. Hence, FASnI3 rather than MASnI3 more frequently utilized in effective Sn-based PCSs. 13 Figure 1.5: Crystal composition of a) MASnI3 b) FASnI3 c) CsSnI3. 1.10 Compositional Engineering Practically, all effective PSCs based on tin use a combination of cations and anion construction. By modifying the chemical composition of Sn-based perovskites, researchers can optimize their properties, such as bandgap, crystalline structure, and durability, for enhanced performance under diverse environmental conditions. Furthermore, the s-p antibonding coupling/interaction in the Sn-I bond also contributes to the low Sn vacancy formation energy; Nevertheless, the compositional engineering of the material can decrease the concentration of self-doping trap states. 1.10.1 A-Site Modification Variations in the anion-cation ratio have a substantial effect on perovskite durability and effectiveness. A-site cations also have a major impact on the indirect tuning of the energy band structure. combination of different A-site metal ions can modify the structural stability (tolerance factor, lattice strain), shape, and crystalline nature of the film. There has been recent interest in investigating cesium (Cs) as a doping element for FASnI3. The incorporation of Cs into FASnI3 allows it to function as a reducing agent, thereby stabilizing Sn2+ and preventing its oxidation to Sn4+. 14 Moreover, the lattice experiences compression when formamidinium (FA) is replaced by cesium (Cs), as Cs possesses a smaller atomic radius compared to FA. This process decreases the energy required to maintain the crystal structure, improves overall stability, and protections against deviations from the ideal crystal arrangement. response range and trap phase density, along with outstanding thermal, atmospheric, and illumination stability. Moreover, the electron mobility of Cs- doped FASnI3 is increased threefold. With reference to the benefit discussed earlier, the FA1-xCsxSnI3 films superior quality led to an efficiency of 6.08%, which is 63% higher than that of a pure device (with a PCE of 3.74%). The same process applied to mixed (FA, MA) based perovskite, and the best FA0.75MA0.25 SnI3 film achieved a power conversion efficiency of approximately 8%. The smaller co-cation MA increased the device Voc by delaying carrier recombination and somewhat modified the crystal dimensions and structure FA-based tin perovskite. 1.10.2 B-Site Modification Mixed lead-tin halide perovskites have shown significantly better performance and stability compared to Sn based and Pb free. By adjusting the Pb concentration, Sn-Pb mixed PSCs band gap may also be readily controlled; in fact, it might be less than that of pure Pb and pure Sn-based perovskite materials. Mixed lead-tin perovskites, such as MAPb0.5Sn0.5I3, have a smaller bandgap compared to pure lead or tin perovskites. This property makes them promising candidates for both tandem solar cells and single-junction cells aiming to maximize solar energy conversion efficiency. These materials are getting more and more common, and their bandgaps can be adjusted to be between 1.1 and approximately 1.3 eV (i.e., 1.1–1.3 eV). In the last few years, Sn-Pb mixed perovskite has advanced significantly. Monolithic all-perovskite tandem solar cells have achieved impressive efficiency levels. Devices combining tin-lead mixed perovskites and single-junction narrow bandgap 15 perovskites have reached power conversion efficiencies (PCE) of 25.6% and 21.74%, respectively. Germanium (Ge) is an additional interesting alternative to lead (Pb). 1.10.3 X-Site Modification The positioning of anions at the vertices of the BX6 octahedra has a profound impact Regarding the bandgap, crystal structure, and charge transport properties of perovskites, the use of mixed halide tin-based perovskites has led to a considerable rise in the solar efficiency of PSCs. 1.11 Functional Additives A homogeneous, pinhole-free perovskite sheet is crucial for obtaining high efficiency in perovskite solar cells in order limit undesired carrier recombination but compared to Pb2+, Sn2+ appears to have a higher Lewis acidity, which causes uncontrollable crystallization and the development of pinholes on the perovskite layer. Consequently, developing innovative methods to produce Boosting device functionality depends on highly quality tin-based perovskite films. and durability. SnF2 is an essential component for tin based PSCs because it can increase the energy of tin vacancy generation, which lowers the concentrations of this kind of defect. The addition of SnCl2 to tin perovskite produced a similar result [32, 33]. 1.12 Performance Parameters Fill factor (FF), open-circuit voltage (VOC), and short-circuit current density (JSC) and general performance define three criteria influencing solar cell efficacy. Material bandgap and series/shunt resistance are the respective determinants of FF and VOC. JSC is influenced not only by the intrinsic properties of the material, but also by external factors like the amount of incoming light. 1.12.1 Open Circuit Voltage (Voc) Open-circuit voltage (Voc) is the maximum voltage a solar cell can produce when no current is flowing. This voltage arises from the built-up electrical 16 potential within the cell due to light-generated electron-hole pairs. Essentially, Voc reflects the cell ability to separate these charge carriers before they recombine, and it is influenced by factors like cell material, temperature, and light intensity. 1.12.2 Short Circuit Current (JSC) Short-circuit current is the maximum electrical current a solar cell can produce when its terminals are directly connected. This happens when sunlight generates electron-hole pairs within the cell, causing current to flow. The amount of this current depends on the cells size, how well it absorbs light, and the intensity of sunlight. In ideal conditions, the short-circuit current is equal to the total current generated by the solar cell. 1.12.3 Fill Factor (FF) A measure of the quality of photovoltaic material is the fill factor. The parameter "FF" collaborates with "Voc" and "JSC" to ascertain the maximum output power of a solar cell. By definition, the FF is the product of Voc and JSC divided by the highest power of the solar cell. Pmax FF = Voc×Jsc 1.1 1.12.4 Quantum Efficiency (QE) Quantum efficiency tells us how well a solar cell turns sunlight into electricity. It measures the number of electrons produced for every photon (particle of light) that hits the cell. To put it another way, QE is a crucial tool for measuring the performance and characterization of solar cells. Additionally, the QE measures a performance of a solar cell in terms of photon absorption, electron- hole pair production, carrier separation, and extraction at particular contacts. 1.13 SIMULATION OF PV SYSTEM Simulation is an excellent tool for modeling and studying various aspects of optoelectronic devices, while using little resources, effort, and money. To reduce time and money, several researchers are creating devices by adjusting 17 parameters using different modeling tools. Researchers can use computer programs to study how well perovskite solar cells work. Popular software tools for this include MATLAB, AMPS, COMSOL, and SCAPS-1D. Simulations under AM1.5G light are carried out using the SCAPS solar cell permeability simulators (ver.3.3.02). One-dimensional optoelectrical simulator SCAPS is designed for systems with several semiconductor layers. For it to work, the continuity and Poisson equations must be solved. Since many years ago, SCAPS-1D has been used to estimate solar cell performance under specific circumstances. It is feasible to build up to seven semiconducting input layers, and nearly every parameter, including bandgap, electron affinity, defects density, temperature, and spectrum, can be changed. The following are a few equations that control SCAPS operations [12, 35]. nKT I VOC = (ln I c + 1) 1.2 q o qT J = Jo [exp (nKT) − 1] − Jsc 1.3 The designations JSC, VOC, and Jo stand for Fill factor (FF), open-circuit voltage (VOC), and short-circuit current (JSC) saturation current (Jo), respectively. The following is the PCE (η) provided: Pout [FF×VOC ×Jsc ] η= = 1.4 Pin Pin Vmp Jmp FF = 1.5 VOC Jsc In which Vmp and Jmp Stand for voltage and current, respectively, at the maximum power supply.. 1.14 OBJECTIVES The Major aim of this project is: 1. To simulate a device based on Sn, Pb and Sn-Pb mixed PSCs and to study its performance parameters. 2. To obtain the best possible structures of all proposed materials to improve performance of PSCs. 18 3. To compare Sn-based and Pb based PSCs with Sn-Pb mixed perovskite solar cell. 1.15 Thesis Outline Chapter 1 presents a comprehensive study on perovskite solar cells (PSCs). Chapter 2 begins with an overview of solar cells and PSCs in general, followed by an in-depth literature review focusing on simulation and experimental research on PSCs. The subsequent chapter examines into the technical aspects of the study, including device structure, parameters, and simulation methodology. The core of the research, encompassing results and discussions, is detailed in chapter 4. Finally, in chapter 5 the thesis concludes by summarizing the key findings of the research. 19 CHAPTER 2 LITERATURE REVIEW Perovskite solar cells use a variety of designs and techniques to increase durability and effectiveness. Perovskite has become a well-known material because of its affordable flexibility. Perovskite is a versatile material with a crystal structure similar to calcium titanate (CaTiO3). Originally discovered in 1839 by Gustav Rose, it has gained significant attention in recent decades for its potential in various applications. A breakthrough came in 1978 when Weber synthesized the first organometallic lead halide perovskite. This compound exhibited exceptional electrical properties, making it a prime candidate for solar cell technology. As the active layer in solar cells, perovskite has demonstrated remarkable efficiency in converting sunlight into electricity. A long time ago, in 1990, some scientists named Mitzi and friends found out that perovskite was special. It can turn light into electricity and do other cool things with light. They realized that perovskite could be used to make solar panels, lights, and even the tiny parts inside computers and phones. 2.1 Experimental Review This section reviews the experimental studies on PSCs, focusing on the material properties and device architectures. Experimental studies have played a crucial role in advancing the understanding of perovskite solar cells, providing valuable insights into their photo physical properties, charge transport mechanisms, and device performance. A big step for solar panels happened in 2009. A group of scientists led by someone called Kojima used a special kind of perovskite to make solar cells better at turning sunlight into electricity. They tried two different types of perovskites: one made with bromine reached an efficiency of 3.2%, and the other made with iodine reached a better efficiency of 3.8%. However, there was a problem. These early solar cells did not last very long because they were kind of runny like a liquid state. 20 To overcome stability issues P. Cui et al. demonstrated that the interface significantly affects the stability of solar cells, influencing both degradation and overall stability. To address these issues, they introduced additional layers and designed interfacial engineering techniques. Their research indicated that optimizing the interfaces on either side of the perovskite active layer was crucial for improving the cells overall stability.. Later on, S. Shao et al. experimentally determined that charge transfer at the perovskite interfaces with hole and electron transport materials is hindered by recombination. Optimal energy levels at these junctions are crucial for efficient charge movement. The absence of a depletion region, combined with the perovskite absorber and an interfacial layer, promotes charge injection while suppressing electron-hole pair recombination. After that many studies and experiment were employed to overcome stability, degradation and toxicity issues of perovskite where on compositional techniques played a best part. By using this technique Y. Ogomi and his group designed a device having typical charge transporting layer MASn0.3Pb0.7I3 absorber material. The FF achieved by this device is 34, JSC is 15.00, VOC is 0.15 V and efficiency rate is 0.78. The device also has a band gap of 1.20 eV. These results highlight their success in optimizing solar cell performance through innovative engineering and material selection. In 2018, M. M. Tavakoli et al. designed a device using MAPb0.2Sn0.8I3 as the absorber layer, with TiO2 serving as the electron transport layer (ETL) and spiro-ometad as HTL. Au used as the back metal contact and ITO used front metal contact. The device featured a regular structure of ITO/TiO2/MAPb0.2Sn0.8I3/spiro-OMeTAD/Au. With a bandgap of 1.24 eV, the device achieved a VOC of 0.673 V, a JSC of 19.1 mA cm−2, a fill factor of 55.4%, and a power conversion efficiency of 7.07%. F. Zuo and his group in 2014 design inverted device with device structure ITO/PEDOT:PSS/MASn0.15Pb0.85I3/PCBM/Bis-salt/Ag. they achieved a VOC of 0.77 V, a JSC of 19.5mA cm−2, a fill factor of 67%, and a power conversion 21 efficiency of 10.1%, with a band gap of 1.40eV.They used MASn0.15Pb0.85I3 as absorber layer and ITO used as front metal contact and ag used as back metal contact. D. Zhao et al. in 2017 design inverted device with structure of ITO/PEDOT:PSS/(FASnI3)0.6(MAPbI3)0.4/C60/BCP/Ag. They used two absorber layer with the composition of FASNI3 600% and MAPBI3 40%.ITO used as front metal contact and ag used as back metal contact. , the device achieved a VOC of 0.854 V, a JSC of 28.7 mA cm−2, a fill factor of 71.4%, and a power conversion efficiency of 17.5% with bandgap of 1.25. X. Lain et al. in 2018 design an inverted device with achieved good performance parameters. Designed device structure is TO/PEDOT:PSS/FAPb0.7Sn0.3I3/PEAI/PC61BM/BCP/Ag. They used different composition for achieving best result. their achieved results are a VOC of 0.78 V, a JSC of 26.46mA cm−2, a fill factor of 79%, and a power conversion efficiency of 16.26%, with a band gap of 1.34eV. 2.2 Literature Review of Simulated Perovskite Solar Cell While experimental studies have provided valuable insights into the performance of perovskite solar cells, numerical simulations can further elucidate the underlying mechanisms and optimize device design. Specifically, SCAPS-1D simulations have been employed to model the behavior of perovskite solar cells, allowing for the investigation of various parameters and their impact on device performance. The use of SCAPS-1D simulations has enabled researchers to optimize device design, identify performance-limiting factors, and explore new materials and architectures in time and cost relaxing method. Here are some reported studies on different perovskites: Abdelaziz et al. employed the SCAPS-1D simulator to model FASnI3-based solar cells. They systematically varied absorber properties (thickness, doping, defects) and layer characteristics (conduction/valence band offsets, thickness, 22 doping of electron/hole transport layers) to assess their impact on cell performance. Their optimization endeavor was directed at augmenting cell efficiency, commencing from an initial experimental structure with 1.75% efficiency. Post-optimization, they attained a (Jsc) = 22.65 mA/cm², an (Voc) = 0.92 V, a fill factor (FF) = 67.74%, and a (PCE) of 14.03%. In 2021, K. Deepthi Jayan and V. Sebastian utilized SCAPS 1D software to investigate lead-free perovskite solar cells employing MASnI3 as the light- absorbing material. They explored various combinations of electron transport materials (ETMs) such as TiO2, with hole transport materials (HTMs) including Cu2O, , P3HT, CuSCN, CuSbS2 :PSS, NiO, CuI, and Spiro-MeOTAD, and back contact metals like Au, W, Pd, Ni, Ag , Pt, Se, Cu, Fe and C, to optimize cell performance. Their simulations predicted a highest efficiency of 25.05% for a Glass/FTO/PCBM/MASnI3/CuI/Au configuration, with a fill factor =69.24%, short-circuit current density = 34.26864 mA/cm², and open-circuit voltage =1.0558 V. The study revealed that maintaining the optimal absorber layer thickness is crucial for achieving maximum efficiency. In 2016, Hui-Jing Du and his team enhanced solar cell efficiency in adjusting the perovskite layer doping concentration and the hole transport layer's electron affinity. Their research showed that modifying these parameters improved cell performance. Additionally, reducing defects within the perovskite layer significantly improved cell functionality. Their efforts achieved a high efficiency of 23.36%, demonstrating that MASnI3 is an efficient and environmentally friendly solar cell. In 2020, Priyanka Roy and her team attained a high (PCE) of 23.35% for Sn- based (PSCs), comparable to Pb-based PSCs. They assessed performance using various electron transport materials (ETMs) such as TiO2, PCBM, and ZnO-NR at different temperatures. TiO2-based PSCs exhibited slightly better thermal stability compared to ZnO-NR-based counterparts. While the PSC using Phenyl C-61 Butyric Acid Methyl Ester as the ETL achieved a lower efficiency of 11.56%, it demonstrated superior thermal durability. 23 Mixed Sn-Pb perovskites offer narrower bandgaps and reduced toxicity, making them promising candidates for solar cells. However, perovskites offer narrower bandgaps and reduced toxicity, making them promising candidates for solar cells. However, their underlying mechanisms and the impact of band alignment remain largely unexplored. In 2021, A. Wang team employed SCAPS-1D to investigate the influence of valence band offset (VBO) and conduction band offset (CBO) on inverted FA0.5MA0.5Pb0.5Sn0.5I3-based PSCs. Their findings revealed that band offsets significantly affect interface recombination and the built-in potential within the perovskite absorber, providing valuable insights for designing efficient mixed Sn-Pb perovskite solar cells. In 2022, Wenjun Zhang and collaborators conducted numerical simulations to assess the influence of cell structure, charge transport layers, defect levels, and active layer thickness on narrow-bandgap Pb-Sn perovskite solar cells (PSCs). Their model predicted a peak power conversion efficiency (PCE) of 26.01% and outlined potential strategies for further optimizing the performance of these mixed PSCs. In 2022, Tripathi et al. optimized cesium tin germanium iodide (CsSn0.5Ge0.5I3)-based perovskite solar cells (PSCs) by experimenting with different organic and inorganic charge transport layers (CTLs). Through C-V and G-V analysis of simulated cells, they highlighted the critical role of CTLs in determining cell potential. Their research indicated that the thickness of the electron transport material (ETM), hole transport material (HTM), and absorber layer, as well as defect levels, significantly impact PSC performance. The researchers proposed an optimized device architecture consisting of ITO/SnO2/CH3NH3SnI3/Spiro-OMeTAD/Au, achieving a power conversion efficiency of 22.2% with a 600 nm thick absorber layer. Key performance metrics included a fill factor of 66.34%, a short-circuit current density of 33.86 mA/cm², and an open-circuit voltage of 0.98 V. 24 In 2021, Ayush Tara and his group designed a FASnI3 PSC using Zinc oxysulfide (Zn(O0.3, S0.7)) is the ETM, while CuSCN is the HTL, developed via SCAPS-1D. They varied parameters such as defect density and thickness to study their effects one fficiency. The enhanced device achieved a JSC=28.12 mA/cm², VOC= 1.0858 V, FF of 84.8%, and efficiency of 25.95%, paving the way for new, ecologically sound tin-based PSCs that compete with lead-based counterparts. Table 2.2 summarizes the performance of simulated perovskite solar cells with varying compositions. Sn-based perovskite solar cells (PSCs) show promise with impressive stability and power conversion efficiency (PCE) exceeding 14%. However, challenges persist in improving the stability, open-circuit voltage (Voc), and overall efficiency of these devices compared to their lead- based counterparts. D. Jayan and V. Sebastian did comparative theoretical study models perovskite solar cells (PSCs) with MAPbI3 and MAGeI3 as absorber layers using the SCAPS-1D tool. They achived best performance for MAPbI3 with the configuration glass/FTO/SnO2/MAPbI3/NiO/Au, showing a PCE of 20.58% and FF of 68.34%. For MAGeI3, the best configuration is glass/FTO/SnO2/MAGeI3/CuO/Pd, with a PCE of 13.12% and FF of 68.29%. They study and highlights that low-cost SnO2 is a better ETM substitute for TiO2, and NiO and CuO improve PCE for MAPbI3 and MAGeI3, respectively. Additionally, Pd enhances performance for MAGeI3-based PSCs, which are more thermally stable and suitable for commercial applications due to their non-toxicity and competitive quantum efficiency. S. Srivastava and colleagues conducted a comprehensive study to optimize the performance of perovskite solar cells (PSCs) by systematically varying active layer materials, hole and electron transport layer thicknesses, and doping concentrations. Among lead-free PSCs, their CsSnI3-based device achieved a remarkable power conversion efficiency (PCE) of 28.97%. These results highlight the potential for developing high-performance, lead-free PSCs that 25 can rival their lead-based counterparts. The research contributes significantly to the pursuit of environmentally friendly and efficient solar energy solutions. Eli et al. employed the SCAPS simulator to investigate the influence of various parameters on perovskite solar cells (PSCs) utilizing cuprous oxide (Cu2O) as the hole transport material (HTM). Their study encompassed parameters such as absorber layer doping concentration and thickness, ETM and HTM thicknesses, and electron affinities of both layers. Results indicate that these factors significantly impact solar cell performance. Notably, reducing the ETM electron affinity and thickness led to substantial performance improvements. Optimized parameters resulted in a power conversion efficiency of 20.42% with a current density of 22.26 mA/cm², voltage of 1.12 V, and fill factor of 82.20%. Compared to the initial cell, the optimized device exhibited remarkable enhancements: 58.80% in PCE, 2.25% in Jsc, 20.40% in FF, and 30.23% in Voc. I. M. De Los Santos et al. conducted a combined experimental and theoretical investigation of CH3NH3PbI3 perovskite solar cells. Their experimental results yielded an initial efficiency of 13.32%. Through optimization of spiro-OMeTAD and perovskite thicknesses to 100 nm and 400 nm, respectively, they achieved an improved efficiency of 15.50%. The study highlighted the critical role of absorber diffusion length in device performance. By theoretically reducing defect density from 10¹⁶ cm⁻³ (experimental value) to 10¹⁰ cm⁻³, the simulated efficiency was further enhanced to 20.26%. T. Ouslimane and colleagues conducted a computational modelling of a standard planar junction device (NIP) perovskite solar cell (PSC) with the structure Glass/FTO/ZnO/MAPbI3/Spiro-OMeTAD/Au operating the SCAPS-1D tool. ZnO was selected as the electron transport material (ETM) due to its comparable properties to TiO2 but with superior charge mobility. Absorption coefficients for all layers were calculated and incorporated into the simulation model. The researchers investigated the influence of MAPbI 3 layer thickness, absorber defect density, and operating temperature on cell 26 performance. Optimal cell performance was achieved with a MAPbI3 thickness of 0.5 micrometers, an absorber defect density of 10¹³ cm⁻³, and an operating temperature of 300 Kelvin. The best performance yielded an efficiency (η) of 21.42%, open-circuit voltage (Voc) of 1.16 V, short-circuit current density (Jsc) of 29.44 mA/cm², and fill factor (FF) of 62.67%. L. Hao and his research team investigated factors influencing the efficiency of PSCs by using the SACPS-1D simulator and reducing the thickness of the lead- based active layer. Through parameter optimization, they aimed to maximize device efficiency. Their numerical resulted in PCE of 17.58% for lead-based and 6.14% for tin-based single-junction PSCs, which align closely with experimental findings. Simulation results indicated that the thickness of the absorber layer significantly impacts device performance. Optimal thicknesses were determined to be 20nm for lead-based absorbers (LBA) and 150nm for tin-based absorbers (TBA). By optimizing acceptor and donor doping concentrations, the team achieved advanced PCE and VOC values, with optimal doping levels of 10¹⁵ cm⁻³ for LBA and 10¹⁶ cm⁻³ for TBA. Furthermore, simulations revealed that the layered absorber layer positioned closer to the energy cause is primarily responsible for device performance. Their optimizations resulted in VOC of 0.94V, JSC of 19.56 mA/cm², FF of 71.13%, and PCE of 12.88%, providing a reference for future improvements. R. Jani and K. Bhargava employed SCAPS-1D simulations to investigate the impact of absorber layer crystallinity and interfacial properties on the performance of both lead-based and tin-based perovskite solar cells. Crystallinity was modeled by varying charge carrier mobility and defect density within the perovskite layer, while interface characteristics were represented by adjusting defect densities at the electron transport material (ETM)/perovskite and perovskite/hole transport material (HTM) junctions. Their results show that tuning these parameters is crucial for efficiency improvement. Performance depends heavily on absorber layer crystallinity, with lead-based cells more influenced by the ETM/perovskite interface and tin- based cells by both interfaces. 27 A. Wang and his collaborators investigated the promising potential of mixed Sn-Pb perovskite solar cells. These materials garner interest due to their desirable combination of narrow bandgaps and reduced lead content, contributing to lower toxicity. However, a deeper understanding of their performance and the influence of band alignment is lacking. To address this gap, Wang et al. employed SCAPS-1D software to analyze the band offsets within FA₀.₅MA₀.₅Pb₀.₅Sn₀.₅I₃ perovskite solar cells featuring an inverted p-i-n planar architecture. Their study identified optimal ranges for the conduction band offset (CBO): 0-0.3 eV at the FA₀.₅MA₀.₅Pb₀.₅Sn₀.₅I₃/interface defect layer (IDL) junction and 0.15 eV to -0.15 eV at the IDL/PCBM interface. These findings provide valuable theoretical guidance for optimizing the design of mixed Pb-Sn perovskite solar cells, paving the way for further advancements in this field. Optimal VBO ranges were -0.3 to -0.1 eV at the FA₀.₅MA₀.₅Pb₀.₅Sn₀.₅I₃/IDL interface and 0.1 to -0.1 eV at the IDL/PEDOT:PSS interface. This study provides theoretical guidance for designing mixed Pb–Sn perovskite solar cells. H. Lee and colleagues have recently focused on developing lead-free or lead- reduced perovskite materials with a bandgap optimal for high-efficiency solar cells. Sn-Pb mixed perovskites, with a bandgap of approximately 1.25 eV, have emerged as a promising candidate due to their potential for both single- junction and tandem devices. Reducing lead content by 50-60% partially addresses toxicity concerns. However, incorporating tin into the perovskite structure presents challenges such as uneven film formation, tin oxidation, and surface instability. Researchers have been working to overcome these issues through material composition adjustments, structural refinements, precursor modifications, and surface treatments. This review comprehensively examines advancements in Sn-Pb mixed perovskite solar cells, analyzes key factors influencing performance, and outlines future research directions. While MASnI3 and MAPbI3 perovskite solar cells have achieved high efficiencies, they still face challenges related to stability, toxicity, and 28 scalability. MASnI3 suffers from low stability due to the oxidation of Sn2+ ions, while MAPbI3 faces concerns over lead toxicity and high sensitivity to moisture and temperature. Sn-Pb mixed perovskite solar cell, on the other hand, offers a promising alternative by combining the benefits of both materials. However, its potential remains underexplored due to limited research attention. This study aims to simulate Sn-Pb mixed perovskite in order to study its potential in solar technology and to study the its performance with different composition which is limited in literature. 29 CHAPTER 3 METHODOLOGY 3.1 Introduction The following section will explore the parametric values and device structure thoroughly for the numerical simulation. MASnI3 and MAPbI3 comparative modeling was investigated using Planner (N-I-P). Furthermore, computational device modeling is carried out to investigate how mixed cations affect absorption capacity, electron hole mobility, and recombination rate. The computational model is generated utilizing a specialized software tool. The study was carried out in carefully monitored laboratory conditions with a sun spectral irradiance of 1.5G, a radiant flux of 1000 W/m2 and an ambient temperature of 300 K. 3.2 System Design and Characteristic Parameters for Digital Simulation First, devices with typical structures, such as MASnI3 and MAPbI3, were used in this study to optimize performance with structure FTO/TiO2/Absorber/Spiro-OMeTAD/Au. In table 3.1. The laboratory research and published papers that provided the parametric values for every single layer of the device are listed. In this study, by using MASnI3 and MAPbI3 as an absorber layer, titanium dioxide and Spiro-OMeTAD as a charge transporting layer was used to determine Voc, Jsc, and FF and performance of both devices. In this configuration, gold (Au) acts as the back contact, with fluorine-doped tin oxide (FTO) serving as the front contact. In the next study the perovskite solar cells are arranged in a planner configuration, through MASn1-xPbxI3 absorber with keeping the same charge transporting material. An advanced computational simulator (SCAPS-1D) intended for modeling photovoltaic devices is utilized to investigate and evaluate solar cell properties. 30 The electric field equation (Poisson equation) and the charge conservation rules (continuity) for both the hole and electron populations are the two main mathematical models that are used by the tool. Open-circuit voltage, fill factor, short-circuit current density and power conversion efficiency are among the important performance metrics, are calculated using the following equations. d dψ (−ε (x) dx ) = q[p(x) − n(x) + ND+ (x) − NA− (x) − pt (x) − n t (x)] 3.1 dx dpn pn −pn0 dξ dp n d2 pn = GP − + pn μp + μp ξ + Dp 3.2 dt τp dx dx dx2 dn p np −np0 dξ dnp d2 np = Gn − + np μ n + μn ξ + Dp 3.3 dt τn dx dx d x2 G : generation-rate τ_n and τ_p: Charge carrier survival time (for electron and hole) D : diffusion co-efficient Q : electronic-charge Ψ : coulomb potential-energy μ_(n), μ_(p): mobility of (electron and hole) n(x), n_t (x): density of (free and trapped electrons) p(x), p_ (t)(x): concentration of (holes and trapped holes N_D^+ (x), N_A^- (x): ionized concentrations of acceptor and donor X : thickness. The apparatus structural layout is shown below, displaying each of the suggested tiers. 31 Figure 3.1: Device structure of required cell with tentative layers. The energy level representation is presented in Figure 3.2 along with the electron and hole flow caused through active material. Figure 3.2: Energy band presentation of MASnI3 by TiO2 & Spiro-OMeTAD. As seen in Figure 3.2 there are five potential layers in the perovskite structure: TiO2 transports electrons, MAPbI3 present a role of active material, and Spiro- OMeTAD work for hole transference. The front metal contact is FTO, and the back metal contact is Au. The FTO/ETL interface, ETL/Perovskite, and Perovskite/HTL are the three main interfacing layers of the Perovskite device. The experimental data and parametric values shown in Table 3.2 are drawn 32 from reputable academic publications and literature [1, 58]. These parameters are universally applicable across all layers of the apparatus. Table 3.1: Key material properties for Titanium Dioxide, Methylammonium Lead Iodide, and Spiro-OMeTAD. Light will pass to perovskite device from bottom through the absorber layer (N-I-P) because the device construction is planned. The absorber layer generates charge carriers (holes and electrons), which are then attracted to them by the matching HTL and ETL materials. The performance of a Sn-free and a Pb-free PSC is compared via simulating both of them with the same transporting material. As shown in Figure 3.3 band diagram, the transportation of charges created via main layer of device. 33 Figure 3.3: charge transfer presentation of MAPbI3 with TiO2 and Spiro- OMeTAD. In addition, J-V analysis and mixed cationic device computation using composition MASn1-xPbxI3 have been performed. The energy level representation is presented in Figure 3.4 along with the electron and hole flow caused through active material. Figure 3.4: Band depiction of MASn1-xPbxI3 by means of transporting material. 34 The five potential layers of the mixed perovskite structure are shown in Figure 3.4. Additionally, comparative analysis is performed of all three perovskites, MASnI3, MAPbI3 and MASn1-xPbxI3. Throughout simulation, firstly two planner single-junction solar cells with the same structure and different absorbent layers are simulated, and then the mixed structure consisting of Pb-Sn mixed absorbent layers is evaluated with different composition to find out the performance parameters. The parametric values for each layer of the device are listed in Tables 3.2 and 3.3, respectively. The data is sourced from theoretical framework, empirical studies and existing publication [1, 31, 54, 70]. Table 3.2. Key material properties for different device layers. 35 A temperature of 300 K, an irradiation of 1000 W/m2 and an atmospheric composition of 1.5G were the usual laboratory conditions used to generate all computer models and results. The primary aim of this study is to design and model a perovskite structure that demonstrates stability, affordability, environmental sustainability and excellent performance for potential uses. Table 3.2 lists the input parameters for all required device [31, 54]. 36 CHAPTER 4 RESULTS AND DISCUSSION 4.1 Introduction In current years, there were major research efforts focused on Lead-containing material, specifically methylammonium lead iodide (MAPbI3), aiming to enhance the functionality of PSCs, but the poisonous nature of lead has restricted frequent usage. Tin (Sn) may therefore be used as substitute for lead (Pb). as active material. Renewable energy technologies are advancing rapidly due to breakthroughs in tin-based research. These cells exhibit impressive performance, with PCE greater than 14%, which is positive, but there are still some problems with ineffective band gap alignment, low efficiency, and Voc losses is being performed to study the simulated performance of single junction and multi junction solar cell. 4.2 J-V Analysis of MAPbI3 The design and structure of the perovskite material have a key impression on the PV devices performance. In this simulation, a MAPbI3 device was simulated under AM1.5 light using SCAPS-1D. The device was simulated to find out the performance parameters such FF, efficiency, Jsc and Voc. This simulation uses Spiro-OMeTAD and TiO2 as a charge transporting layer in the device construction. The thickness of the perovskite layers kept fixed throughout the simulation while selecting all required parameters from Table 3.1. The un enhanced device shows a JSC of 32.31 and VOC of 0.91 V, having average FF of 87.82% and maximum PCE approaching 25.86%. The current density for MAPbI3 is represented Figure 4.1. 37 Figure 4.1. Current Voltage graph (J–V) for MAPbI3. It is evident that the devices current density increased steadily until the voltage reached 1.06 V, at which point it suddenly decreased as the voltage increased even further. This is because the perovskite materials' implantation generated a more efficient absorption. 4.3 J-V Analysis of MASnI3 To determine the MASnI3 Perovskite performance parameters, including PCE, FF, Voc, and Jsc, a second simulation shot was performed In this simulation, TiO2 and Spiro-OMeTAD served as charge transporting layers in the PSC architecture. The thickness of the perovskite layers kept fixed throughout the simulation while selecting all required parameters from Table 3.1. The un improved device shows a JSC of 24.96 and VOC of 1.17 V, by an average FF of 80.6% and maximum efficiency approaching 23.92%. Figure comprises the current density over a biased voltage curve (J–V) function for MASnI3 under AM 1.5 solar illumination. 38 Figure 4.2. Current Voltage curve (J–V) function for MASnI3. As can be observed, the devices current density increased steadily with voltage up to 0.77 V before suddenly declining with additional voltage increase. This is because the addition of the perovskite materials caused more extensive absorption. 4.4 Comparative J-V Parameter Analysis for MAPbI3 and MASnI3 Comparison of the Devices J-V Parameters Under AM1.5 sun irradiation, the current density for MAPbI3 and MASnI3 devices along a biased voltage curve (J–V) function is compared in the figure. As can be observed, the J-V for both devices hold steady as the voltage increased to 1.06 V and 0.77 V, respectively, before abruptly dropping as the voltage increased even more. This is why the presence of both perovskite materials resulted in a more thorough absorption. 39 Figure 4.3. Comparison of Current Voltage curve (J–V) for MAPbI3 and MASnI3. The higher value of VOC, 1.17 V was observed for device MASnI3 this is because of lower bandgap, whereas MAPbI3 obtained an improved value of VOC of 0.91 V. In addition, the square or rectangle that fits on the J-V curve indicates the FF parameter, indicating that FF also contributed to the higher PCE value. So, due to the steeper value of the J–V curve, we obtained a higher value of FF for MAPbI3 compared to the MASnI3-based PSC device. Which leads to a higher value of PCE, as shown in Table 4.1 Table 4.1: Comparison of electrical parameters of MAPbI3 and MASnI3. 40 4.5 Mixed Perovskite Solar Cell When compared to Sn and Pb-based PSCs, the functionality and stability of multi junction perovskites are suggestively superior. By controlling the Pb concentration, energy gap of tin-lead mixed perovskites could effortlessly tune and might even be less than that of lead and tin-based perovskite materials. The ideal band gap of Sn-Pb mixed perovskite (1.1 to 1.3 eV) is superior to value of 1.30 eV for MASnI3 and 1.53 eV for MAPbI3. Tin-lead mixed PSC are a good alternative for all-perovskite tandem PSCs as well as for the best narrow- bandgap light absorber for single-junction solar cells to achieve the SQ limit. These materials are more common and contain bandgaps that may be varied from around 1.1 eV to 1.3 eV. 4.5.1 Simulation 0f Mixed Perovskite Solar Cell A lead-free or reduced-lead perovskite material having optimal bandgap range of 1.1 to 1.3 eV is presently being studied by several research organizations in an effort to achieve a greater theoretical efficiency and possibly less toxicity than Pb-based perovskites. Crucially, out of all the alternatives, Sn–Pb mixed perovskite is the only one that has demonstrated potential performance that is comparable to that of Pb perovskite. A phenomenon known as bandgap bowing, in which the bandgap contracts when Sn and Pb are combined, allows Sn–Pb perovskites to reach a bandgap of 1.25 eV. The optimal energy gap range of 1.1-1.3 eV facilitates the creation of high- efficiency single-junction photovoltaic cells and perovskite-perovskite tandem solar cells, while Sn-Pb mixed perovskites offer a reduced Pb content of 50-60% compared to traditional Pb perovskites, mitigating toxicity concerns. 4.6 Effect of Different concentration of Sn and Pb content on the Efficiency of MASnPbI3 This section uses the SCAPS computation to investigate the bandgap engineering of a Sn-Pb (mixed) solar cell. Pure tin halide perovskite have been developed as extra environmentally acceptable replacements to lead-based cells, and this helped in the creation of low-bandgap mixed Sn-Pb PSCs. The 41 bandgaps of Sn-Pb mixed perovskite varies with the concentration of Sn and Pb content. The functionality of the lead-based PCS is greatly affected by the addition of Sn content. Because Sn has a smaller ionic radius than Pb, which results in a wider crystal lattice and a smaller energy gap, increased Sn content lowers bandgap energy. The SCAPS-1D is used to measure the efficiency of Sn-Pb mixed perovskite solar cells with varying compositions. The simulated device structures are MASn0.3Pb0.7I3, MASn0.5Pb0.5I3, MASn0.7Pb0.3I3, MASn0.25Pb0.75I3 and MASn0.75Pb0.25I3 with energy band gap of 1.20, 1.18, 1.17, 1.24 and 1.25 respectively. All these structural composition with bandgap energy is taken from published work. The simulated results of all these devices with required electrical parameters is presented in Table 4.2.below. Table 4.2. Performance parameters of Sn-Pb mixed PSC with different composition. The MASn0.7Pb0.3I3 perovskite solar cell shows a greater simulated efficiency in comparison to the other compositions. This is because of the lower bandgap, which causes greater spectral sensitivity and longer wavelength absorption. This device composition also achieves a greater FF than other devices, which results in lower voltage losses, better quantum efficiency, and the best possible power conversion efficiency. In addition, compared to other devices, this device composition achieves a larger FF, which leads to reduced voltage losses, 42 improved quantum efficiency, and the highest attainable power conversion efficiency. In short, mixed Sn-Pb perovskite device is environmentally friendly, efficient and more stable device compare to single junction Sn-based and Pb based perovskite solar cell. 4.7 J-V Analysis of MASn0.7Pb0.3SnI3 Perovskite Solar Cell This simulation image was taken to determine the MAPb0.7Sn0.3I3 Perovskite solar cells performance parameters, including PCE, FF, Voc, and Jsc. In the simulated PSC device, Spiro-OMeTAD functioned as the HTM while TiO2 functioned as the ETM. The thickness of the perovskite layers kept fixed throughout the simulation while selecting all required parameters from Table 3.1. The device structure has a VOC of 1.19 V, JSC of 26.91, FF of 85.65%, and a maximum efficiency of about 27.89%. Figure shows the current density for MASn0.7 Pb0.3I3 under AM1.5 solar light illumination. Figure 4.4. Current Voltage graph (J–V) directed MASn0.7Pb0.3I3. It is observed that the rate of current increased steadily until the voltage reached 0.99 V, at which point it abruptly decreased. This is because the implantation of absorber materials caused a more thorough absorption. 4.7.1 Comparative Analysis of All Three Devices: All three types of solar cells are perovskite-based. 43 They have the same crystal structure. They are used for the same purpose (solar energy harvesting). The MASnI3 has a bandgap of 1.30 eV, MAPbI3 has 1.53 eV and Sn-Pb mixed perovskite has optimal band gap 1.17 eV. The J-V analysis of all three devices is shown in Figure 4.5. Figure 4.5. Comparison of Current Voltage curve (J–V) function for MAPbI3 and MASnI3 and MASn0.7Pb0.3I3. PCSs comprised of Sn have a higher Voc than those based on Pb. This is because the lower bandgap of Sn-based perovskites leads to a larger Voc. However, Sn- based perovskites also have lower current densities (Jsc) and fill factors (FF) compared to Pb-based perovskites, which leads to infer energy conversion rate overall. Compared to all other configurations, the simulated performance of the MASn0.7Pb0.3I3 perovskite solar cell is higher. This is because of the lower bandgap, which causes greater spectral sensitivity and longer wavelength absorption. This device composition also achieves a greater FF than other devices, which results in lower voltage losses, better quantum efficiency, and the uppermost possible PCE. 44 4.8 Effect of Thickness on Performance Parameters of Sn-Pb Mixed Perovskite Solar Cell The design and content of the perovskite layer have a significant impact on the performance of Photovoltaic modules. To determine the impact of MASn0.7Pb0.3I3 thickness change on performance metrics, JSC, VOC, fill factor, and efficiency, a device was modeled in the present research. The thickness of absorber material was adjusted in stages of 100 nm, ranging from 400 to 900 nm and all necessary values were chosen from Table 3.1 and 3.2. The absorber layers thickness considerably enhances PSC functionality. It is important to avoid having an overly thick or thin main layer since this can alter the minority carrier transport length and the perovskite layer capability for being absorbed, accordingly. To investigate the impact of multi junction solar cell thickness on functionality of cell, the perovskite thickness was varied between 400 nm and 900 nm. The results of this study are presented in Table 4.2. Table 4.3. Dependence of performance metrics on thickness of MASn0.7Pb0.3I3. As can be seen from the Table 4.2 and graphical portrayal, 4.6 the outcomes of JSC and efficiency improved considerably with increasing thickness because of a rise in the rate of absorptivity. 45 Although the level of the charges recombination across the perovskite layer increased significantly due to the denser layer, the Voc value decreased as layer thickness increase. The thicker perovskite layer lead in more series resistivity for the device, and also reduction of FF with thicker perovskite layer followed the same trend. The power conversion rate grew from 400 nm to 700 nm, but then it begins to sharply decline. The lower PCE values at smaller thickness values were caused by the reduced transport diffusing distance, which improved substantially across the 400–700 nm range. Figure 4.6. Response of thicker absorber layer on (a) VOC (b) JSC (c) FF and (d) PCE. The same trend was responsible for the PCE degradation after 700 nm, as more thickness resulted into sharp decrease in charges diffusion distance and higher recoupling rates. 46 4.9 Analysis of Quantum Efficiency (QE) The percentage of incident sunlight that are effectively collected and transformed into electric charges is known as a solar cells quantum efficiency. The quantum efficiency of simulated solar cell was analyzed using SCAPs-1d. The results are presented in Figure 4.7. 110 100 QE 90 80 70 60 QE (%) 50 40 30 20 10 0 300 400 500 600 700 800 900 Wavelength (nm) Figure 4.7. QE of Sn-Pb mixed perovskite vs wavelength. It is evident that the QE falls off at longer wavelengths. Moreover, quantum efficiency decreases at wavelengths greater than 700 nm because fewer photons at a longer wavelength are absorbed. At longer wavelength the probability of recombination losses increases, reducing the number of charge carriers available for charge collection. The simulated solar cells exhibit a decline of QE at spectral range shorter than 350 nm. This is attributed to the fact that the FTO is the dominant absorber of light in this configuration. 4.10 Temperature Variation Analysis The functionality of a PSC is significantly impacted by its working temperature. According to reports, its average working temperature is 300 K. However, when it is operating, the temperature will be significantly greater. Therefore, 47 the temperature was increased from 290 K to 370 K with the goal to assess the device thermal endurance. Alterations in temperature have an impact on the electrical characteristics of the device, as Figure 4.8 illustrates. Figure 4.8: Temperature-dependent changes (300 K-350 K) on performance parameters In addition, it has been discovered that the Voc greatly declines and the JSC rises with temperature. The following equation describes the solar cells open- KT JSC circuit voltage (Voc): VOC = (ln + 1) (4.3) q Jo In this case, Jo is the reverse saturation current, T is the temperature, and K is the Boltzmann constant. This further shows that an increase in reverse saturation current is what causes the VOC to decrease as temperature rises. The JSC has been seen to very slightly increase with temperature due to the semiconductor's band-gap shrinking. The values show that at higher temperatures (300 K to 360 K), the performance characteristics vary as follows: 48 1. Temperature has a linearly negative impact on the open circuit voltage of Tin-containing perovskite, causing it to decrease. 2. The JSC is affected by the temperature rise. The reason for this is that when temperature rises, the perovskite materials bandgap narrows and requires less energy electron transition, increasing the JSC. The performance cannot be maintained at higher temperatures. 3. In addition, the operating voltage falls off due to possibility of carrier recombination between the lower energy level and higher energy level with narrow bandgap. The current rise has a very tiny amplitude in relation to the voltage decrease. As a result, both the FF and PCE overall decrease. Research has shown that the overall efficiency of MASn0.7Pb0.3I3 degrades as temperature rises. 49 CHAPTER 5 CONCLUSION In this work, we developed and enhanced a cost-efficient, high-performing, and environmentally benign Sn-Pb mixed PSC using SCAPs one-dimensional modelling software. As part of our investigation, we have carried out simulation assessments to create an approach towards efficient and green PSCs. Here, utilizing the SCAPs tool, we have created a moderately efficient and green Perovskite n-i-p structure comprised of MASnI3, MAPbI3, and MASn1-xPbxI3. The following are the main conclusions of study: The adjusted efficiencies at 650 nm of CH3NH3PbI3 and CH3NH3SnI3 with conventional Devices for transporting electrons (TiO2) and holes (Spiro- OMeTAD) are 25.86% and 23.92, accordingly. It is found that efficiency of tin-based PSC is lower than Pb based which is owning to the contribution of higher FF of MAPbI3. In second analysis Sn-Pb mixed perovskite solar cell was simulated with different percentage composition of Sn and Pb content. The FTO/TiO2/MASn0.7Pb0.3I3/Spiro-OMeTAD/Au design was found to be efficient at 27.89%. The simulated efficiency of MASn0.7Pb0.3I3 perovskite solar cell is higher than all other composition. This is due to smaller bandgap which leads to longer wavelength absorption, increased spectral response. 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