Interface Defect Density Research Articles

Defect and doping concentration study with series and shunt resistance influence on graphene modified perovskite solar cell: A numerical investigation in SCAPS-1D framework

Perovskite solar cells (PSCs) have the potential to be highly efficient, low-cost next-generation solar cells. By raising open circuit voltage (Voc), the interfacial recombination kinetics can further improve device performance. In this study, we used simulation concept to elucidate the influence of using graphene as a surface passivation material in perovskite solar cells. Graphene works well as an interlayer to promote hole extraction and reduce interfacial recombination. In order to evaluate the effect of graphene in PSCs, the simulation was done in the SCAPS-1D framework to compare the performance of a device with and without graphene. Three interface layers were included to the model: TiO2/MAPbI3, MAPbI3/Graphene, and Graphene/Spiro-OMeTAD, in order to account for the impacts of interface defect density on device performance. The impacts of absorber doping concentration, absorber defect density, ETL doping concentration, HTL doping concentration, series resistance, and shunt resistance were also evaluated for the modelled PSC. Without any optimization, the control device with power conversion efficiency (PCE) of 20.677% was outperformed by the graphene-modified device with PCE of 20.911%. This difference is mostly due to the lower recombination losses and more effective suppression of interfacial non-radiative recombination. With optimization, the modified graphene-based device has a PCE of 26.667%. This result shows an enhancement of ∼1.28 times over that of the pristine graphene-based device. The outcomes have opened the way for the development of cost-effective and comparable state-of-the-art, high-efficiency perovskite solar cells with graphene interlayer by eliminating defects and managing non-radiative recombination.

Numerical analysis of Al/Gr/ETL/MoS2/Sb2S3/Ni solar cell using non-toxic In2S3/SnS2/ZnSe electron transport layer

In this study, Molybdenum disulfide (MoS2) based thin film solar cells (TFSCs) of the structure Al/Gr/ETL/MoS2/Sb2S3/Ni have been simulated using SCAPS-1D software. Due to their remarkable properties, three Cd-free and non-toxic (In2S3, SnS2, and ZnSe) electron transport layer (ETL) materials were suggested for MoS2-based TFSCs. The effect of various layer parameters on the performance of the cells was investigated for various ETL materials. The considered parameters are the MoS2 absorber layer thickness, the carrier density and thickness of the ETL, and the ETL/MoS2 interface defect density, as well as the impact of the working temperature, series resistance, and shunt resistance. The simulation results show that the highest power conversion efficiency is achieved for the MoS2 absorber layer thickness of 1.0 µm, and the thickness and carrier density of different ETLs of 0.05 µm and 1016 cm-3, respectively. We found that the defect density of the ETL/MoS2 interface should be controlled under 1012 cm-2. The optimized power conversion efficiencies of MoS2-based TFSCs are found by simulation 27.88%, 28.22%, and 28.29% for the cell with In2S3, SnS2, and ZnSe ETL, respectively. Among the three ETL materials used, zinc selenide (ZnSe) shows the best results due to its wider band gap. We have found that the cells with the FTO window layer show slightly better performance than those with the graphene. Maximum photovoltaic efficiency of 28.54% has been achieved for the solar cell of the structure Al/FTO/ZnSe/MoS2/Sb2S3/Ni. The results of simulations reveal that high-efficiency MoS2 solar cells with non-toxic (In2S3, SnS2, and ZnSe) ETLs can be obtained. Overall, the numerical simulation conducted in this study could contribute to the manufacture of Cd-free non-toxic and highly efficient MoS2-based solar cells.

Hydrogen-induced degradation dynamics in silicon heterojunction solar cells via machine learning

Among silicon-based solar cells, heterojunction cells hold the world efficiency record. However, their market acceptance is hindered by an initial 0.5% per year degradation of their open circuit voltage which doubles the overall cell degradation rate. Here, we study the performance degradation of crystalline-Si/amorphous-Si:H heterojunction stacks. First, we experimentally measure the interface defect density over a year, the primary driver of the degradation. Second, we develop SolDeg, a multiscale, hierarchical simulator to analyze this degradation by combining Machine Learning, Molecular Dynamics, Density Functional Theory, and Nudged Elastic Band methods with analytical modeling. We discover that the chemical potential for mobile hydrogen develops a gradient, forcing the hydrogen to drift from the interface, leaving behind recombination-active defects. We find quantitative correspondence between the calculated and experimentally determined defect generation dynamics. Finally, we propose a reversed Si-density gradient architecture for the amorphous-Si:H layer that promises to reduce the initial open circuit voltage degradation from 0.5% per year to 0.1% per year.

Sub‐Stochiometric Nickel Oxide Hole‐Selective Contacts in Solar Cells: Comparison of Simulations and Experiments with Sputtered Films

Sub‐stochiometric nickel oxide (NiOx) films were investigated as a hole selective contact option in silicon (Si) heterojunction solar cells. Numerical simulations were carried out to evaluate the impacts of the NiOx electronic properties variations and the NiOx/Si interface defect density (Dit) on device performance. Simulation data suggest that the best performance is achievable for wide bandgaps (Eg) and corresponding high valence band edge (EVB) positions in the NiOx films. Overall, in simulations, the performance remains practically unchanged for the nickel vacancy concentrations [VNi] = 1017–1021 cm−3, assuming high EVB and low Dit. The experimental data measured using NiOx films prepared by radio‐frequency magnetron sputtering reveal that the increase in [VNi] lifts the conductivity, concurrently decreasing Eg and EVB. As a result, we concluded that the performance of the fabricated sputtered NiOx/Si heterojunction solar cell is limited by high Dit as well as narrow Eg and low EVB.

Design and numerical analysis of CIGS-based solar cell with V2O5 as the BSF layer to enhance photovoltaic performance

Copper indium gallium selenide (CIGS)-based solar cells have exhibited greater performance than the ones utilizing cadmium telluride (CdTe) or hydrogenated amorphous silicon (a-Si: H) as the absorber. CIGS-based devices are more efficient, considering their device performance, environmentally benign nature, and reduced cost. In this article, we proposed a potential CIGS-absorber-based solar cell with an FTO/ZnSe/CIGS/V2O5/Cu heterostructure, with a V2O5 back-surface field (BSF) layer, SnO2:F (FTO) window layer, and ZnSe buffer layer. Using the solar cell capacitance simulator one-dimensional simulation software, the effects of the presence of the BSF layer, the thickness, bulk defect density, and acceptor density of the absorber layer, buffer layer thickness, interfacial defect density, device resistance, and operating temperature on the open-circuit voltage, short-circuit current, fill factor, and efficiency, as well as on the quantum efficiency and recombination and generation rate, of the device have been explored in detail. The simulation results revealed that only a 1 μm-thick-CIGS absorber layer with V2O5 BSF and ZnSe buffer layers in this structure offers an outstanding efficiency of 31.86% with a VOC of ∼0.9 V. Thus, these outcomes of the CIGS-based proposed heterostructure provide an insightful pathway for fabricating high-efficiency solar cells with performance more promising than the previously reported conventional designs.

Design and Performance Exploration of a Lead‐Free All‐Inorganic Hydrogenated Cs2AgBiBr6‐Based Double Perovskite Solar Cell: A Numerical Modeling Study

Lead‐free double perovskite Cs2AgBiBr6 has attracted wide attention owing to its nontoxic and stable properties. Recently, hydrogenated Cs2AgBiBr6 (HCABB) films have been shown to possess superior optoelectronic properties than pristine Cs2AgBiBr6, and the double perovskite solar cell (DPSC) based on the films broke the efficiency record of DPSCs as soon as it was proposed. However, its poor energy band alignment and thin absorber layer thickness prevent HCABB from realizing its full photovoltaic potential. In this article, we design a lead‐free all‐inorganic HCABB‐based DPSC for application purposes. To explore its photovoltaic potential, we numerically optimize the transport layer materials, the thickness and bulk defect density of the absorber layer, the interface defect densities, the back contact material, and the parasitic series and shunt resistances step by step for the HCABB‐based DPSC. We predict the HCABB‐based DPSC with the structure of FTO/Nb2O5/HCABB/CuI/Cu can achieve an open‐circuit voltage of 1.139 V, short‐circuit current density of 22.40 mA cm−2, fill factor of 83.35%, and power conversion efficiency of 21.28%. Overall, our work explores the photovoltaic potential of HCABB and provides guidance for fabricating more efficient HCABB‐based DPSCs.

Simulation study of CsPbIxBr1-x and MAPbI3 heterojunction solar cell using SCAPS-1D

The perovskite solar cells are attaining maximum efficiency but lagging in stability as compared with other solar cells. The consistent use of hybrid organic–inorganic materials in PSC poses greatest hurdle in the path of stability. To overcome this problem the attention of research community, is diverted from methyl ammonium based perovskite solar cells to cesium (Cs) based perovskite solar cell. To enhance the efficiency of PSCs further, effective absorption of solar-spectrum by the multi-layer will allow the maximum utilization of spectrum and in turn it will increase the efficiency of the resulting Perovskite Solar Cell (PSC). Here, we have analyzed the efficiencies of single, double and triple absorber layers PSCs. Initially we have simulated and studied the performance of two CsPbI2Br and CsPbIBr2 based single-junction perovskite solar cell. Then we have simulated a PSC with CsPbI2Br and CsPbIBr2 as the two absorber layers and have optimized the performance of bilayer solar cell. Finally, we simulated a triple layer PSC have used the combination of CsPbI2Br, CsPbIBr2 and MAPbI3 as absorber layers. The bilayer and triple layer PSCs are optimized with respect to different variables i.e., absorber layer thickness, defect density and interface defect density in all three PSCs. In this study we achieved a remarkable efficiency of 29.92%, 20.62% and 7% efficiency in case of triple layer solar cell, in case of bilayer solar cell and in case of single-junction PSC respectively. Thus, well aligned multiple absorber layers in PSC will provide the future pathways for highly efficient PSCs.

Titanium oxide nanomaterials as an electron-selective contact in silicon solar cells for photovoltaic devices

To obtain high conversion efficiency, various carrier-selective contact structures are being applied to the silicon solar cell, and many related studies are being conducted. We conducted research on TiO2 to create an electron-selective contact structure that does not require a high-temperature process. Titanium metal was deposited using a thermal evaporator, and an additional oxidation process was conducted to form titanium oxide. The chemical compositions and phases of the titanium dioxide layers were analyzed by X-ray diffraction. The passivation effects of each titanium oxide layer were measured using the quasi-steady-state photoconductance. In this study, the layer properties were analyzed when TiO2 had a passivation effect on the silicon surface. The charge and interface defect densities of the layer were analyzed through CV measurements, and the passivation characteristics according to the TiO2 phase change were investigated. As a result, by applying optimized TiO2 layer thickness and annealing temperature conditions through the experiment for passivation to the cell-like structure, which is the structure before metal and electrode formation, an implied open-circuit voltage (iVoc) of 630 mV and an emitter saturation current density (J0) value of 60.4 fA/cm2 were confirmed.

Lead-Free Perovskite Homojunction-Based HTM-Free Perovskite Solar Cells: Theoretical and Experimental Viewpoints.

Simplifying the design of lead-free perovskite solar cells (PSCs) has drawn a lot of interest due to their low manufacturing cost and relative non-toxic nature. Focus has been placed mostly on reducing the toxic lead element and eliminating the requirement for expensive hole transport materials (HTMs). However, in terms of power conversion efficiency (PCE), the PSCs using all charge transport materials surpass the environmentally beneficial HTM-free PSCs. The low PCEs of the lead-free HTM-free PSCs could be linked to poorer hole transport and extraction as well as lower light harvesting. In this context, a lead-free perovskite homojunction-based HTM-free PSC was investigated, and the performance was then assessed using a Solar Cell Capacitance Simulator (SCAPS). A two-step method was employed to fabricate lead-free perovskite homojunction-based HTM-free PSCs in order to validate the simulation results. The simulation results show that high hole mobility and a narrow band gap of cesium tin iodide (CsSnI3) boosted the hole collection and absorption spectrum, respectively. Additionally, the homojunction's built-in electric field, which was identified using SCAPS simulations, promoted the directed transport of the photo-induced charges, lowering carrier recombination losses. Homojunction-based HTM-free PSCs having a CsSnI3 layer with a thickness of 100 nm, defect density of 1015 cm-3, and interface defect density of 1018 cm-3 were found to be capable of delivering high PCEs under a working temperature of 300 K. When compared to formamidinium tin iodide (FASnI3)-based devices, the open-circuit voltage (Voc), short-circuit density (Jsc), fill factor (FF), and PCE of FASnI3/CsSnI3 homojunction-based HTM-free PSCs were all improved from 0.66 to 0.78 V, 26.07 to 27.65 mA cm-2, 76.37 to 79.74%, and 14.62 to 19.03%, respectively. In comparison to a FASnI3-based device (PCE = 8.94%), an experimentally fabricated device using homojunction of FASnI3/CsSnI3 performs better with Voc of 0.84 V, Jsc of 22.06 mA cm-2, FF of 63.50%, and PCE of 11.77%. Moreover, FASnI3/CsSnI3-based PSC is more stable over time than its FASnI3-based counterpart, preserving 89% of its initial PCE. These findings provide promising guidelines for developing highly efficient and environmentally friendly HTM-free PSCs based on perovskite homojunction.

Numerical assessment and optimization of highly efficient lead-free hybrid double perovskite solar cell

In this work, a performance assessment of a double perovskite Cs2BiCuI6 solar cell with the typical lead-based perovskite CH3NH3PbI3 as an active layer is presented using SCAPS-1D software. The theoretical analysis depicts the improvement in power conversion efficiency (PCE) for Cs2BiCuI6-based solar cells. This shows that in the coming future, the hybrid double perovskite Cs2BiCuI6 possess the capability to replace toxic CH3NH3PbI3-based solar cell which would help to create lead-free harmless solar cells. Detailed structural parameters optimization such as the absorbing layer thickness, and charge carrier mobility, and variation in interface defect density is carried out to enhance the device efficiency. This gives a PCE of 24.84 % for a hybrid double perovskite-based solar cell. The optimized values are 1013 cm−3, and 5 cm2 V−1 s−1 for interface defect density and carrier mobility respectively which also enhances the fill factor to 82 % with open circuit voltage of 1.28 V and 24.54 mA/cm2 short circuit current density Jsc.

Atomic Imaging of Interface Defects in an Insulating Film on Diamond.

The insulator/semiconductor interface structure is the key to electric device performance, and much interest has been focused on understanding the origin of interfacial defects. However, with conventional techniques, it is difficult to analyze the interfacial atomic structure buried in the insulating film. Here, we reveal the atomic structure at the interface between an amorphous aluminum oxide and diamond using a developed electron energy analyzer for photoelectron holography. We find that the three-dimensional atomic structure of a C-O-Al-O-C bridge between two dimer rows of the hydrogen-terminated diamond surface. Our results demonstrate that photoelectron holography can be used to reveal the three-dimensional atomic structure of the interface between a crystal and an amorphous film. We also find that the photoelectron intensity originating from the C-O bonds is strongly related to the interfacial defect density. We anticipate significant progress in the study of amorphous/crystalline interfaces based on their three-dimensional atomic structures analysis.

Optimization of lead-free CsSnI3-based perovskite solar cell structure

Abstract Perovskites are considered the most promising material for the latest generation of solar cells. However, due to the presence of lead in their composition, the development of non-toxic Perovskite cells has become an essential goal to enable their large-scale production. In this work, we have simulated, modeled and optimized the structure of a single solar cell that consists of a non-toxic cesium–tin–iodine CsSnI3 Perovskite absorber with a low band gap energy value of 1.3 eV, between TiO2 and PTAA materials as ETL and HTL layers, respectively. A simulation model describing the charge carrier processes and the effect of interface defect density is presented. Several structures based on alternative ETL and HTL materials are proposed. An optimal device structure is proposed based on the results obtained. An efficiency of 19.92% is obtained with V oc = 0.829 V, J sc = 30.68 mA/cm2 and FF = 73.33% using SnO2 and Spiro-OMeTAD as ETL and HTL materials. However, 29.22% is achieved using the optimal structure as the bottom cell in a tandem configuration.

Defect control for high-efficiency all-inorganic CsPbBr3 perovskite solar cells via hydrophobic polymer interface passivation

All-inorganic CsPbBr3-based perovskite solar cells (PSCs) have been proved to possess upgraded humidity and thermal stability. However, the CsPbBr3-based PSCs with a typical device configuration without hole transport layer (HTL) suffer from serious carrier recombination as a result of high interfacial defect density, which limits the enhancement of photoelectric conversion efficiency (PCE). To settle this issue, an interfacial engineering methodology is imported by utilizing polymethyl methacrylate (PMMA) as a passivation layer between the CsPbBr3 film and the carbon electrode. Through the interaction within the uncoordinated Pb2+ ions and oxygen atoms of carbonyl (CO) in the PMMA molecule chains, the trap sites existed in the modified CsPbBr3 interface can be greatly suppressed, beneficial for a faster extraction and transportation of photogenerated carriers. Besides, the PMMA interlayer can raise the valence band of the CsPbBr3 surface for a better energy level alignment, and simultaneously portray as a protective layer against moisture owing to the hydrophobic nature of long-chain polymers. Ultimately, the PMMA modified device exhibited a champion PCE of 9.60 % with a high open-circuit voltage (VOC) of 1.58 V, as well as showcasing ignorable PCE loss enduring over 400 h of aging.

Novel dual-modification strategy using Ce-containing compounds toward high-performance flexible perovskite solar cells

The carrier non-radiative recombination loss caused by numerous interfacial defects existing between perovskite and neighboring charge transport layers, such as SnO2/perovskite and perovskite/spiro-OMeTAD, which greatly restricts the performance improvement of flexible perovskite solar cells (PSCs). Herein, we devised a novel dual-modification strategy using Ce-containing compounds (Ce2(SO4)3 and Ce(SO4)2) to minimize interfacial defect density at the interface of SnO2/perovskite and perovskite/spiro-OMeTAD respectively, thus enhancing the performance and stability of flexible PSCs. It was revealed that the introduction of Ce2(SO4)3 interface layer was conducive to ameliorating the electrical properties of SnO2 and significantly reducing the SnO2/perovskite interface defects. Moreover, the Ce(SO4)2 was adopted as a novel oxidant to achieve the rapid oxidation of spiro-OMeTAD, thus enhancing the hole mobility of bulk spiro-OMeTAD and suppressing perovskite/spiro-OMeTAD interface defects. Therefore, reduced non-radiative recombination losses near the two interfaces of the perovskite layer could be achieved by such a novel and comprehensive modification strategy. In consequence, the Ce-modified flexible and rigid PSCs achieved excellent photoelectric conversion efficiency (PCE) of 19.34 % and 22.62 %, respectively. Notably, the optimized flexible PSCs exhibited outstanding mechanical durability, and 83.2 % of the initial PCE was maintained after 3000 bending cycles.

Non-leaded, KSnI3 based perovskite solar cell: A DFT study along with SCAPS simulation

The commercialization of perovskite solar cells raises serious environmental concerns due to the presence of toxic lead. In the present work, we have studied a non-leaded perovskite, KSnI3 through density functional theory (DFT). The structural properties such as tolerance factor, octahedral factor, and formation energy of the orthorhombic structure of KSnI3 have been obtained to highlight its thermodynamic stability. The elastic constants and mechanical properties such as young's modulus, Poisson's ratio, and Pugh's ratio have been obtained to show its mechanical stability and ductility, which are desirable properties for the fabrication of thin films of the absorber layer. The optical properties of orthorhombic KSnI3 such as refractive index, absorption coefficient, dielectric function, optical loss factor, and reflectivity have been calculated to show its potential as an absorber material in perovskite solar cells (PSC). The density of states and band structure of orthorhombic KSnI3 have been calculated. The band structure has been utilized to obtain the effective masses of charge carriers, and a bandgap of 1.841 eV. The parameters of orthorhombic KSnI3 obtained through DFT have been used to simulate the performance of PSC. The performance of the perovskite solar cell has been optimized with respect to(w.r.t) its interface defect density, doping concentration, thickness, and defect concentration. The effect of series and shunt resistance on the performance of PSC has been studied. Finally, tungsten has been proposed as a budget-friendly replacement for gold as the back contact, and an efficiency of 9.776% is obtained. This study demonstrates the potential of a low-toxicity, lead-free, KSnI3 as an absorber material in perovskite solar cells.

Tuning Surface Oxidation States of Nickel Oxide for Efficient Inverted Perovskite Solar Cells

Nickel oxide (NiOx), as an inorganic p-type semiconductor, has been widely adopted as hole-transporting layers in perovskite solar cells. Despite its superior material stability, the poor charge extraction and multi-vacancies greatly restrict the photovoltages and efficiencies. Here, we propose a facile method to tune the surface oxidation states of NiOx films by a lithium salt treatment for photovoltage enhancement. X-ray photoelectron spectroscopy measurement indicates that the lithium treatment only reduces the Ni3+ sites at the top region rather than in the bulk of NiOx films. This graded distribution allows more efficient charge extraction at the NiOx/perovskite interface as revealed by photoluminescence studies. Through a combination of capacitance–voltage and drive-level capacitance profiling measurements, we confirm enhanced built-in potentials and decreased interface defect densities in lithium-modified devices. Further modifying the interface with a self-assembly monolayer, the energy offsets at the interface can be largely reduced. Based on these enhanced properties, the modified devices achieve a high-power conversion efficiency of 22.4% (0.07 cm2) with a 120 mV enhancement in photovoltage in comparison with the untreated devices.

Theoretical study of highly efficient all-inorganic Sb2S3-on-Si monolithically integrated (2-T) and mechanically stacked (4-T) tandem solar cells using SCAPS-1D.

The power conversion efficiency of all-inorganic Sb2S3-on-Si two-terminal (2-T)monolithically integrated and four-terminal (4-T)mechanically stacked tandem solar cells are investigated. A one-dimensional solar cell capacitance simulator (SCAPS-1D) has been used to simulate the stand-alone antimony trisulfide (Sb2S3) top sub-cell, silicon (Si) bottom sub-cell, 2-T monolithic, and 4-T mechanically stacked tandem solar cells. The stand-alone sub-cells are optimized by extensive studies, including interface defects density, bulk defects density, absorber layer thickness, and series resistance. The power conversion efficiency (PCE) of simulated stand-alone sub-cells is compared and verified with the existing literature. A current matching condition is established to characterize the 2-T monolithic Sb2S3-on-Si tandem cell. A filtered spectrum has been utilized for bottom sub-cell measurement in the tandem solar cells. The best-simulated PCE of Sb2S3-on-Si 2-T monolithic and 4-T tandem cells is 30.22% and 29.30%, respectively. The simulation results presented in this paper open an opportunity for the scientific community to consider Sb2S3 as a potential top sub-cell material in Sb2S3-on-Si tandem solar cells with high PCE.

Performance enhancement in MA0.7FA0.3PbI3 based perovskite solar cell by gradient doping

The mixed organic cation-based perovskite solar cells have attracted researcher attention due to their stability as compared to other perovskite material-based cells. The present manuscript has investigated the cell structures, i.e., FTO/SnO2/MA0.7FA0.3PbI3/HTL free/Au and FTO/SnO2/ MA0.7FA0.3PbI3 /CuInSe2 (HTL)/Au using SCAPS software. The performance of both the structures is studied using uniform doping and gradient doping method. The effect of absorber thickness and uniform doping in the absorber layer resulted in an efficiency of 13.21% for HTL free structure and 19.78% with HTL structure. Furthermore, the effect of doping gradient, average doping gradient, defect density in the absorber and interface defect density are studied in both the structures. After optimization of these parameters, an improved performance is obtained, i.e., efficiency of 18.08% for HTL free and 23.97% with HTL. The present study simplifies the manufacturing techniques by diving the absorber layer into four sublayers of equal thickness with the optimised value of the doping gradient. It is suggested that by considering two sublayers, one can achieve the highest cell performance using gradient doping method. Our results provide an effective technique to the experimentalist for fabricating the highly efficient device.

MAPbI3-on-CuInSe2 two-terminal monolithically integrated and four-terminal mechanically stacked tandem solar cells: A Theoretical Investigation Using SCAPS-1D

Two-terminal (2-T) and four-terminal (4-T) tandem solar cells with wide bandgap perovskite (MAPbI3) as the top sub-cell and low bandgap copper indium diselenide (CuInSe2, CIS) as the bottom sub-cell have potential to outperform the single-junction power conversion efficiency. The proper consideration of native defects density and interface defects density in tandem solar cell (TSC) is required to achieve the full ability. The present paper examines a MAPbI3-on-CuInSe2 (MAPbI3-on-CIS) TSC. The bottom sub-cell of CIS has a bandgap of 1.04 eV, while the top sub-cell of MAPbI3 has a bandgap of 1.61 eV. The performance of the independent top and bottom sub-cells is explored by considering the physical parameters such as interface defects density, bulk defects density, and absorber layer thickness. The filtered spectra have been used to investigate the performance of 2-T monolithically integrated and 4-T mechanically stacked TSCs. When measuring the short-circuit current density (JSC) in a 2-T monolithic TSC, the top sub-cell's absorber layer thickness is changed to determine the exact thickness for the current matching condition. The proposed 2-T monolithic TSC satisfies the current matching requirement at a thickness of 0.346 μm of the top sub-cell’s absorber layer, resulting in a power conversion efficiency (PCE) of 30.21%. The best simulated PCE of 4-T mechanically stacked TSC is 31.07%.

Numerical simulation of PbS quantum dot solar cell and optimisation of absorber layer

A Quantum dot Solar Cell (QDSC) can be defined as a photovoltaic cell which utilises quantum dot as the captivating photovoltaic device. It is used as a substitute to the bulk material for example silicon or copper indium gallium selenide. Researchers have proven that nanotechnology may considerably increase the amount of electricity generated by solar cells. On altering the size of the quantum dots, a wide variety of energy levels can be observed with different bandgaps. Further, in CQD devices, the electron transport layer-ETL and hole transport layer-HTL plays a vital role in enhancing the performance. Maximum power conversion efficiency is achieved in this work by treating the HTL (PbS-EDT) with the absorber layer (PbS-TBAI) and ETL(TiO2). In the initial simulation, efficiency obtained is 9.88%. After altering the thickness of the absorber layer from 200 to 600 nm, the optimum result is obtained at 600 nm. Acceptor doping (NA) of HTL layer and Donor doping (ND) of ETL layer is optimised at 1x1019 cm−3 where Interface Defect Density (IDD) is kept constant at 1x1013 cm -2. The maximum power conversion efficiency (PCE) achieved is 22.35% using 1D SCAPS Simulator.