Interface Defect Density Research Articles

Numerical simulation of lead-free vacancy ordered Cs2PtI6 based perovskite solar cell using SCAPS-1D.

In recent years, vacancy-ordered halide double perovskites have emerged as promising non-toxic and stable alternatives for their lead-based counterparts in optoelectronic applications. In particular, vacancy ordered Cs2PtI6 has emerged as a star material because of its high absorption coefficient, band gap of 1.37 eV, and long minority carrier lifetime. Despite substantial experimental research on this new class of material, theoretical simulations of their device properties remain scarce. In this work, a novel n-i-p device architecture (FTO/SnO2/Cs2PtI6/MoO3/C) is theoretically investigated using a solar cell capacitance simulator (SCAPS-1D). Theoretical investigations are carried out in order to optimize the device performance structure by varying the perovskite and selective charge transport layer thickness, absorber and interface defect density, operating temperature, back contact, series and shunt resistance, respectively. The optimized device showed an impressive power conversion efficiency (PCE) of 23.52% at 300 K, which is higher than the previously reported values. Subsequent analysis of the device's spectral response indicated that it possessed 98.9% quantum efficiency (QE) and was visibly active. These findings will provide theoretical guidelines for enhancing the performance of Cs2PtI6-based photovoltaic solar cells (PSCs) and pave the way for the widespread implementation of environmentally benign and stable perovskites.

Back contact optimization for Sb<sub>2</sub>Se<sub>3</sub> solar cells

Antimony selenide (Sb<sub>2</sub>Se<sub>3</sub>) has advantages of low-toxicity, abundant and excellent photoelectric properties. It is widely considered as one of the most promising light-harvesting materials for thin-film solar cells. However, the power conversion efficiency of the Sb<sub>2</sub>Se<sub>3</sub> thin-film solar cell is still far inferior to that of cadmium telluride, copper indium gallium selenium and perovskite solar cells. As is well known, the Sb<sub>2</sub>Se<sub>3</sub> solar cell performance is closely related to the light absorber layer (crystallinity, composition, bulk defect density, etc.), PN heterojunction quality (charge carrier concertation, energy band alignment, interface defect density, etc.) and back-contact barrier formation, which determines the process of carrier generation, excitation, relaxation, transfer and recombination. The low fill factor is one of the core problems that limit further efficiency improvement of Sb<sub>2</sub>Se<sub>3</sub> solar cells, which can be attributed to the high potential barrier at the back contact between the Mo electrode and Sb<sub>2</sub>Se<sub>3</sub> absorption layer. In this work, a heat treatment is applied to the Mo electrode to generate a MoO<sub>2</sub> buffer layer. It can be found that this buffer layer can inhibit MoSe<sub>2</sub> film growth, exhibiting better Ohmic contact with Sb<sub>2</sub>Se<sub>3</sub>, and reducing the back contact barrier of the solar cell. The Sb<sub>2</sub>Se<sub>3</sub> thin film is prepared by an effective combination reaction involving sputtered and selenized Sb precursor. After introducing the MoO<sub>2</sub> buffer layer, it can also promote the formation of (<i>hk</i>1) (including (211), (221), (002), etc.) preferentially oriented Sb<sub>2</sub>Se<sub>3</sub> thin films with average grain size over 1 μm. And the ratio of Sb to Se is optimized from 0.57 to 0.62, approaching to the stoichiometric ratio of Sb<sub>2</sub>Se<sub>3</sub> thin film and inhibiting the formation of V<sub>se</sub> and Sb<sub>Se</sub> defects. Finally, it enhances the open-circuit voltage (<i>V</i><sub>OC</sub>) of solar cells from 0.473 to 0.502 V, the short-circuit current density (<i>J</i><sub>SC</sub>) from 22.71 to 24.98 mA/cm<sup>2</sup>, and the fill factor (FF) from 46.90% to 56.18%, thereby increasing the power conversion efficiency (PCE) from 5.04% to 7.05%. This work proposes a facile strategy for interfacial treatment and elucidates the related carrier transport enhancement mechanism, thus paving a bright avenue to breaking through the efficiency bottleneck of Sb<sub>2</sub>Se<sub>3</sub> thin film solar cells.

Harnessing the potential of CsPbBr3-based perovskite solar cells using efficient charge transport materials and global optimization.

Perovskite solar cells (PSCs) have become a possible alternative to traditional photovoltaic devices for their high performance, low cost, and ease of fabrication. Here in this study, the SCAPS-1D simulator numerically simulates and optimizes CsPbBr3-based PSCs under the optimum illumination situation. We explore the impact of different back metal contacts (BMCs), including Cu, Ag, Fe, C, Au, W, Pt, Se, Ni, and Pd combined with the TiO2 electron transport layer (ETL) and CFTS hole transport layer (HTL), on the performance of the devices. After optimization, the ITO/TiO2/CsPbBr3/CFTS/Ni structure showed a maximum power conversion efficiency (PCE or η) of 13.86%, with Ni as a more cost-effective alternative to Au. After the optimization of the BMC the rest of the investigation is conducted both with and without HTL mode. We investigate the impact of changing the thickness and the comparison with acceptor and defect densities (with and without HTL) of the CsPbBr3 perovskite absorber layer on the PSC performance. Finally, we optimized the thickness, charge carrier densities, and defect densities of the absorber, ETL, and HTL, along with the interfacial defect densities at HTL/absorber and absorber/ETL interfaces to improve the PCE of the device; and the effect of variation of these parameters is also investigated both with and without HTL connected. The final optimized configuration achieved a VOC of 0.87 V, JSC of 27.57 mA cm-2, FF of 85.93%, and PCE of 20.73%. To further investigate the performance of the optimized device, we explore the impact of the temperature, shunt resistance, series resistance, capacitance, generation rate, recombination rate, Mott-Schottky, JV, and QE features of both with and without HTL connected. The optimized device offers the best thermal stability at a temperature of 300 K. Our study highlights the potential of CsPbBr3-based PSCs and provides valuable insights for their optimization and future development.

Designing an efficient lead-free perovskite solar cell with green-synthesized CuCrO2 and CeO2 as carrier transport materials.

With increased efficiency, simplicity in manufacturing, adaptability, and flexibility, solar cells constructed from organic metal halide perovskite (PVK) have recently attained great eminence. Lead, a poisonous substance, present in a conventional PVK impacts the environment and prevents commercialization. To deal with this issue, a number of toxicity-free PVK-constructed solar cells have been suggested. Nevertheless, inherent losses mean the efficiency conversion accomplished from these devices is inadequate. Therefore, a thorough theoretical investigation is indispensable for comprehending the losses to improve efficiency. The findings of a unique modelling method for organic lead-free solar cells, namely methylammonium tin iodide (MASnI3), are investigated to reach the maximum practical efficiencies. The layer pertinent to MASnI3 was constructed as a sandwich between a bio-synthesized electron transport layer (ETL) of CeO2 and a hole transport layer (HTL) of CuCrO2 in the designed perovskite solar cells (PSCs). In this study, the use of algae-synthesized Au in the back contacts has been proposed. To obtain the maximum performance, the devices are further analyzed and optimized for active layer thickness, working temperature, total and interface defect density analysis, impedance analysis (Z'-Z), and capacitance-voltage (C-V), respectively. An optimal conversion efficiency of 26.60% has been attained for an MASnI3-constructed PSC. The study findings may open the door to a lead-free PSC through improved conversion efficiencies.

Comparison of SiNx‐Based Surface Passivation Between Germanium and Silicon

Germanium (Ge) has attracted much attention as a promising channel material in nanoscale metal–oxide–semiconductor devices and near‐infrared sensing because of its high carrier mobilities and narrow bandgap, respectively. However, efficient passivation of Ge surfaces has remained challenging. Herein, silicon nitride (SiNx)‐based passivation schemes on Ge surfaces are studied and the observations are compared to Si counterparts. These results show that instead of a high positive charge density (Qtot) that is found in SiNx‐passivated Si samples, similar Ge samples contain a high amount of negative Qtot (in the range of 1012 cm−2). The maximum surface recombination velocity of the samples is shown to reduce by a factor of three in both Si and Ge samples by a post‐deposition anneal at 400 °C. The SiNx‐coated samples are capped with an atomic‐layer‐deposited aluminum oxide (Al2O3) layer, which reduces the midgap interface defect density (Dit) after annealing to 7 × 1010 and 4 × 1011 cm−2 eV−1 in Si and Ge, respectively. Interestingly, while the Al2O3 capping seems to have no impact on Qtot of the Si samples, it turns the stack virtually neutral (∼−1.6 × 1011 cm−2) on Ge. The presented SiNx‐based passivation schemes are promising for optoelectronic devices, where a low Dit and/or a low charge are favored.

Performance Analysis of Ultrathin Cu(In,Ga)Se2 Solar Cells with Backwall Superstrate Configuration Using AMPS-1D

This study used AMPS-1D to peform numerical simulations and model the behavior of back-wall superstrate solar cells based on Cu(In,Ga)Se2 (CIGS) thin films to investigate optimal conditions and obtain maximum efficiency. The effects of absorber thickness and density of interface defects were examined along with the work function of the transparent conductive oxide (WTCO) to investigate their influence on the output parameters. Measurements of device performance (J-V) and Quantum Efficiency (QE) showed that the performance of the cell improved as the thickness of the CIGS layer decreased because photons were absorbed near the junction. The device achieved an efficiency of 16.4% using an optimal thickness for the CIGS layer on the order of 0.3µm, defect densities in the range of 1013-1015cm-3, doping concentration of the n-TCO back contact on the order of 1019cm-3, and WTCO in the range of 4.5-5.2eV. These results show that the generated electron-hole pairs had a high probability of separation and demonstrate the potential of this device structure.

Creating tougher interfaces via suture morphology in 3D-printed multi-material polymer composites by fused filament fabrication

This study presents a facile strategy for architecting the interface morphology to create tougher and stronger interfaces in additively manufactured multi-material polymer composites. A sutural interfacial morphology between two dissimilar polymer phases PLA (hard) and TPU (soft) is designed and fabricated by the fused filament fabrication technique. The proposed strategy utilizes one of the process parameters (i.e., overlap distance) to create sutural interfaces with soft protrusions. The microscopic inspections of the interface suggest that the proposed strategy can control the protrusion amplitude, which indirectly influences the interfacial defect density. A positive correlation between the overlap distance and resulting protrusion amplitude is obtained. The interfacial toughness measurements by the double cantilever beam test reveal a linear correlation between the interfacial toughness and protrusion amplitude. The proposed interfacial architecture can result in up to a 16–18-fold increase in the interfacial toughness in comparison with the baseline interface. Three distinct toughening mechanisms associated with the fracture of the proposed interfaces are identified: (1) geometric toughening associated with the interface roughness, (2) enhancement of the intrinsic interfacial toughness due to the reduced interfacial defect density between the PLA and TPU, and (3) additional plastic (or inelastic) energy dissipation within the TPU layer. The results reported in this study are anticipated to provide guidelines to produce multi-material polymer composites with stronger and tougher interfaces via additive manufacturing.

Concurrent investigation of antimony chalcogenide (Sb2Se3 and Sb2S3)-based solar cells with a potential WS2 electron transport layer

Antimony (Sb) chalcogenides such as antimony selenide (Sb2Se3) and antimony sulfide (Sb2S3) have distinct properties to be used as absorber semiconductors for harnessing solar energy including high absorption coefficient, tunable bandgap, low toxicity, phase stability. The potentiality of Sb2Se3 and Sb2S3 as absorber material in Al/FTO/Sb2Se3(or Sb2S3)/Au heterojunction solar cells (HJSCs) with 2D tungsten disulfide (WS2) electron transport layer (ETL) layer has been investigated numerically using SCAPS-1D solar simulator. A systematic investigation of the impact of physical properties of each active material of Sb2Se3, Sb2S3, and WS2 on photovoltaic parameters including layer thickness, carrier doping concentration, bulk defect density, interface defect density, carrier generation, and recombination. This study emphasizes the exploration of causes of low performance of actual devices and demonstrates the individual variation in the open-circuit voltage (VOC), short-circuit current density (JSC), fill factor (FF), power conversion efficiency (PCE) and quantum efficiency (QE). Thereby, highly potential heterostructures of Al/FTO/WS2/absorber (Sb2Se3 or Sb2S3)/Au proposed, in which, the PCE over 28.20 and 26.60% obtained with VOC of 850 and 1230 mV, Jsc of 38.0 and 24.0 mA/cm2, and FF of 86.0 and 89.0% for Sb2Se3 and Sb2S3 absorber, respectively. These detailed findings revealed that the Sb-chalcogenide heterostructure with potential WS2 ETL can be used to realize the fabrication of feasible thin film solar cells and thus the design of high-efficiency high-current (HEHC) and high-efficiency high-voltage (HEHV) solar panels.

Performance analysis of n-TiO2/p-Cu2O, n-TiO2/p-WS2/p-Cu2O, and n-TiO2/p-WS2 heterojunction solar cells through numerical modelling.

A new hetero-structure of n-TiO2/p-WS2/p-Cu2O is proposed as a potential candidate for solar energy generation using tungsten disulfide (WS2) as an absorber layer. The proposed device performance is simulated by employing a one-dimensional solar cell capacitance simulator (SCAPS-1D). The numerical simulation studies compared the performances of n-TiO2/p-Cu2O, n-TiO2/p-WS2/p-Cu2O, and n-TiO2/p-WS2 hetero-structures based on various physical parameters like interface defects density, bulk defects density, absorber layer thickness, series resistance, shunt resistance, and operating temperature. In our simulation investigations, we found that interface defects pose a formidable impact on heterojunction devices. Interface defects closer to the front surface severely deteriorate the performances than the back surface. The bandgap of the absorber layer influences the performances of the solar cells. A closer comparison between n-TiO2/p-Cu2O and n-TiO2/p-WS2 heterojunction solar cells (HJSCs) revealed that the latter (n-TiO2/p-WS2) has nearly 182% better performance than the former (n-TiO2/p-Cu2O) devices. Additionally, the performance of the n-TiO2/p-WS2 solar cell is further boosted by ~ 139% in the presence of a hole transport layer of p-Cu2O. The best-simulated efficiency of the proposed new hetero-structure (n-TiO2/p-WS2/p-Cu2O) solar cell is 28.86%. Moreover, these optimized physical parameters may shed light on "easy to apply" new path for fabrication of a non-toxic, environment-friendly, and highly efficient novel thin-film heterojunction (n-TiO2/p-WS2/p-Cu2O) solar cell.

Modeling and Simulation of Tin Sulfide (SnS)-Based Solar Cell Using ZnO as Transparent Conductive Oxide (TCO) and NiO as Hole Transport Layer (HTL).

This paper describes the simulation by Solar Cell Capacitance Simulator-1D (SCAPS-1D) software of ZnO/CdS/SnS/NiO/Au solar cells, in which zinc oxide (ZnO) is used as transparent conductive oxide (TCO) and nickel oxide (NiO) is used as a hole transport layer (HTL). The effects of absorber layer (SnS) thickness, carrier concentration, SnS defect density, NiO HTL, ZnO TCO, electron affinity and work function on cell performance have been evaluated. The effect of interface defect density of SnS/CdS on the performance of the heterojunction solar cell is also analysed. As the results indicate, a maximum power conversion efficiency of 26.92% was obtained.

Dielectric Front Passivation for Cu(In,Ga)Se2Solar Cells: Status and Prospect

Cu(In,Ga)Se2(CIGSe) solar cells are among the most efficient thin‐film solar cells on lab scale. However, this thin‐film technology has relatively large upscaling losses for commercial technology. To tackle this, paradigm shifts are proposed that allow for simpler, cost‐effective, and efficient CIGSe solar cells. Front passivation using dielectric layers is one of the options being investigated as this is widely used in Si technology. Research on front passivation for CIGSe is in an early stage and no improvements are made yet. A close comparison with silicon technology is made to understand why it seems to be more difficult for CIGSe solar cells. In general, chemical passivation is less effective, resulting in higher interface defect densities than seen for Si. Also, field‐effect passivation requires positive charges, which have not been implemented yet on the CIGSe front surface. Finally, for Si passivation, often a high‐temperature annealing step is applied, which is not possible for CIGSe. It is proposed to apply a dielectric tunneling layer with positive fixed charges in combination with an electron transport layer to move forward. A list of potential dielectric layers that could be suitable for CIGSe is provided.

Structural, Morphological, Optical Properties and Modelling of Ag Doped CuO/ZnO/AZO Solar Cell

Copper (II) oxide (CuO) has attained significant attention from researchers because of its unique chemical and physical properties. Ag-doped CuO thin films have been produced on the soda glass substrate (SLG) by spin coating technique at different doping ratios. Structural, morphological, and optical properties of thin films produced depending on altered silver ratios have been examined through X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), and UV-vis absorption spectroscopy, respectively. Band gaps of prepared undoped and 1% Ag-doped CuO thin films have been measured as 1.90eV and 1.63eV, respectively. Ag/undoped CuO and Ag-doped CuO/ZnO/AZO solar cells have been modelled, and their photovoltaic parameters have also been calculated using the SCAPS-1D simulation program. This work aims to investigate the photovoltaic parameters that would improve the efficiency of a solar cell. The effect of Ag atoms on the efficiency of CuO solar cells has been investigated depending on the acceptor density (Na), the interface defect density (Nt), and the operating temperature. Ag-doped CuO solar cells have shown the highest efficiency for Nt=1010 cm-3 and Na=6, 5x1016 cm-3 values. It has been well observed that as the operating temperature increases, the solar cells’ power conversion efficiency decreases. The highest charge generation rates in the undoped and Ag-doped solar cells have been determined as 1.49×1022 1/cm3.s and 1.51×1025 1/cm3.s, respectively. All the results, either theoretical or experimental, have been presented in this work and have been compared for a conclusion that has been made in detail.

Numerical simulation and optimization of physical properties for high efficiency CuSbS2 thin film solar cells

Here we present numerical modeling of copper antimony sulfide (CuSbS2) solar cells to analyze the impact of several interrelated physical parameters of the absorber layer and absorber/buffer interface such as bulk vs interface defect density, energy band gap vs electron affinity of CuSbS2, absorber thickness vs acceptor density together with device shunt vs series resistance on the device efficiency. A benchmark simulation of the experimental CuSbS2 solar cell is initially performed in SCAPS-1D (Solar Cell Capacitance Simulator in one dimension) environment considering a suitable defect model, which gave an efficiency of 3.19 % comparable to the experimental value. After the systematic optimization of different materials properties and interface defect density, the power conversion efficiency is increased up to 10.71 % with a remarkable upgrade in open circuit voltage, photocurrent, and fill factor. A detailed analysis of heterojunction features such as built-in potential, depletion width, diffusion length, and carrier recombination was performed to understand the impact of the aforementioned physical parameters on the performance of this solar cell. The present results give an important guideline to find out the shortcomings of CuSbS2 solar cells, which in turn help the researchers for designing and feasible fabrication of more efficient CAS solar cells.

Influence of absorption, energy band alignment, electric field, recombination, layer thickness, doping concentration, temperature, reflection and defect densities on MAGeI3 perovskite solar cells with Kesterite HTLs

Over the past decade, perovskite materials have emerged as a promising absorber layer in photo voltaic (PV) cells. Germanium (Ge) based perovskite layers have attracted the attention of scientists because of its excellent photovoltaic properties and nontoxic nature. Selecting the right material for charge transport layers (CTL) can further enhance the performance and stability of the cell. Kesterite materials are chalcogenides quaternary compound with high conductivity and tunable bandgap. They have exhibited excellent performance when employed in thin film PV cells as the active material and hence emerged as an option to be used as hole transport layer (HTL) in perovskite solar cells. In this work the Ge based perovskite solar cell (PSC) of methyl ammonium germanium tri-iodide (MAGeI3) is numerically modelled with 6 kesterite quaternary compounds as HTLs and 4 oxide/sulphide materials as electron transport layers (ETL). Henceforth, a total of 24 unique structures are numerically modelled and optimized using SCAPS-1D. A systematic methodology is adopted to analyze the effect of the charge transport materials on the absorption, quantum efficiency, energy band alignment, electric field intensity, recombination rate, carrier density, thickness, doping concentration, temperature, reflection and interface defect densities of the PSC in detail. The optimization of the PSC structures enhanced the performance of the cells up to 7% more. Based on the simulation results the best performing perovskite structures were TiO2/Per/CZTS and SnO2/Per/CZTS with PCE of 24.57% and 24.87%, Jsc of 16.13 mA cm−2 and 16.32 mA cm−2, Voc of 1.730 V and 1.733 V and F.F of 88.10% and 88.101% respectively.

Computational analysis of mixed cation mixed halide-based perovskite solar cell using SCAPS-1D software

Standard MAPbI3 (MAPI) perovskite suffers from stability and toxicity problems. In this numerical simulation study using SCAPS-1D software, we propose a hybrid perovskite (MA1−xFAxPb1−ySryI3) to reduce these effects; thus, the influence of the mixture of formamidinium (NH2CHNH2+ (FA+)), strontium (Sr), methylammonium (CH3NH2+ (MA+)) and lead (Pb) on the electrical parameters of a hybrid perovskite-based solar cell is studied. This simulation was performed through modeling the perovskite absorber band gap depending on x and y proportions. This mixture leads to increase the crystallinity or stability by decreasing MA+ proportion by FA+, while the toxicity is reduced by decreasing Pb2+ proportion by Sr2+. We show that the substitution of 90% MA and 15% Pb (MA0.1FA0.9Pb0.85Sr0.15I3) to the standard MAPI radically changes the electrical parameters of the material and the performance of the solar cell. A maximum efficiency of 29% (Jsc=24.2 mA/cm2, Voc=1.37 V, FF=87.49%) is obtained in this simulation of the hybrid perovskite-based solar cell. These results are obtained after optimizing the hybrid perovskite band gap (Eg = 1.60 eV), layer thicknesses (0.400 μm for hybrid perovskite, 0.250 μm for TiO2 ETL, and 0.150 μm for Cu2O HTL), absorber bulk defect density (1013 cm−3), and perovskite/TiO2 interface defects density (1012 cm−2). Our results show that the composition of MA, FA, Pb, and Sr in the MA1−xFAxPb1−ySryI3 hybrid perovskite may be a way to obtain new perovskites with interesting physical properties for application in solar cells.

Voltage Deficit in Wide Bandgap Perovskite Solar Cells: The Role of Traps, Band Energies, and Effective Density of States

Wide‐bandgap (1.7 eV) perovskite solar cells (PSCs) are plagued by relatively low open‐circuit voltages. This is problematic as they are key to achieving perovskite silicon tandems, which can boost the potential of silicon solar cells. Performance in PSCs is widely considered to be limited by recombination at the interface between the perovskite and the transport layer (TL). Here, a number of design rules to increase the open‐circuit voltage of wide‐bandgap PSCs are introduced. A numerical device model that includes a detailed description of the interfacial recombination processes is presented. The combined effects of interface traps, ions, band alignment, and transport properties are introduced to identify the critical parameters for improving the open‐circuit voltage. A large number of devices are simulated by picking random combinations of parameters and are looked for trends. It is shown that interface recombination can be suppressed by reducing the minority carrier density close to the interface with the TLs. It is demonstrated that the alignment of energy levels is only part of the story; the effective densities of states are of equal importance. The results pave the way to achieving high open‐circuit voltages, despite a significant density of interface defects.

A Codoping Strategy for Efficient Planar Heterojunction Sb2S3 Solar Cells

AbstractAntimony sulfide is a promising wide bandgap light‐harvesting material owing to its high absorption coefficient, nontoxicity, superior stability, and low cost. However, the reported Sb2S3 absorber suffers from complicated defect characteristics due to its quasi‐1D structure. Herein, a codoping technique from chlorine and selenium is developed in hydrothermal method to regulate the film defect properties and promote the device efficiency. The theoretical calculation and experimental results demonstrate that the Cl&Se codoping plays a synergistic role in absorber film quality improvement. Se doping could efficiently fill the intrinsic deep defect level VS and Cl is a benign n‐type dopant and favor [hk1] oriented deposition. Systematic device physical characterizations verify the codoped device superior heterojunction quality and much lower interface and bulk defect density comparing with control one. The optimal codoping device delivers a certified power conversion efficiency of 7.15% (5.9% for control one), the highest certified value in planar Sb2S3 solar cells. This study develops an effective doping strategy with multi‐element synergistic incorporation which sheds new light on high‐efficiency Sb2S3 solar cells.

Density functional theory calculations for investigation of atomic structures of 4H-SiC/SiO2 interface after NO annealing

We propose the atomic structures of the 4H-SiC/SiO2 interface for a face (11¯00), m face (112¯0), the C face (0001¯), and Si face (0001) after NO annealing using the OH-terminated SiC surface models. Our proposed structures preferentially form at the topmost layers of the SiC side of the interface, which agrees with the experimental finding of secondary-ion mass spectrometry; that is, the N atoms accumulate at the interface. In addition, the areal N-atom density is of the order of 1015atom/cm2 for each plane, which is also consistent with the experimental result. Moreover, the electronic structure on the interface after NO annealing in which the CO bonds are removed and the nitride layer only at the interface is inserted, is free from gap states, although some interface models before NO annealing include the gap states arising from the CO bonds near the valence band edge of the bandgap. Our results imply that NO annealing can contribute to the reduction in the density of interface defects by forming the nitride layer.

Numerical Study on the Effect of Graphene Oxide As Hole Transporting Layer in Caesium Based Perovskite Solar Cell – Scaps 1D Approach

Perovskite solar cells (PSCs) have emerged as a promising candidate for addressing the energy crisis due to their rapid efficiency improvement up to 24.2% within 10 years. One of the most challenging obstacles to commercialization of PSCs is their instability toward environmental conditions. Lead-free, halide-based perovskites are drawing appreciable attention for solar cell applications due to the non-toxic nature and stable performance in ambient environment. With the aim of improving reproducibility and spectral properties of the devices, in the last three years the scientific community strongly focused on Caesium-doping for hybrid (typically, organolead) perovskites. In parallel, in order to further contrast hygroscopicity and reach thermal stability, research has also been carried out to achieve the development of all-inorganic perovskites based on Caesium, the performances of which are actually rapidly increasing. This article represents the study of physical, optical, and electrical properties Caesium Titanium (IV) based single halide Perovskite absorbing material for the optimum photovoltaic application. Also in recently developed high-efficiency metal organometal halide PSCs, electron and hole transporting materials have shown key roles in determining the growth of perovskite crystals, as well as the performance and stability of the device. The utilization of polymer materials has been studied as both HTM’s and ETM’s but with little effectiveness, typically resulting in a lower conversion efficiency. But some other materials such as Spiro-OMeTAD requires comparable dopants and additives, which is a source of perovskite instability and also it requires very high design costs ; which all leads to the idea of alternate transport materials. In this study, a numerical simulation analysis on the PSCs performance with Graphene Oxide (GO) as HTM is conducted. We investigated GO/Cs2TiBr6/ TiO2 structure (Figure 1) and studied the change in various photovoltaic parameters with the change in different input factors. The deep understanding of operation mechanism of PSCs is essential and required to furtherly improve device performance. Therefore, Solar Cell Capacitance Simulator (SCAPS-1D), a device simulator widely using in inorganic solar cells, was employed to controllably design PSCs. This simulator package basically uses the poisons equation, the drift and diffusion carrier equation and the continuity equation to solve for various input parameters. It has numerous advantages than any other simulators available in the market like incorporating the interface defect densities, simulation of devices with up to 7 layers in a single run etc. The influence of thickness of the absorber layer, the hole transport layer, defect density of two interfaces ( perovskite/ETL and HTL/perovskite), band gap of absorber layer, electron affinity of both absorber and ETL , finally the temperature and parasitic resistance ( series and shunt ) of the lead-free device is studied. The main objective of the study was the exploration of the effect and efficiency of Graphene Oxide (GO) and the Hole transport layer (HTL) on the performance of the proposed Caesium based heterojunction solar cell.The simulation was carried out in the standard operation conditions for SCAPS-1D. The optimized thickness values for maximum PCE value are observed to be 1 μm for absorber, 0.1 μm for HTL. The performance of the device deteriorated when the defect density value increases for both interfaces and was found that that the front interface density should be less than 1E16 and the back interface density less than 1E10 for optimum performance. It can be attributed due to larger number of recombinations at these interfaces. The performance decreased with the increase in operating temperature range and also with the increase in parasitic resistances as expected. Finally the electron affinity of the absorber seems to be not much involved with the inner working of the device as the parameters almost remained constant with a change in it.The elicited results suggest that Cs2TiBr6 can play a momentous role as an absorbing perovskite towards the highly efficient lead-free all-inorganic perovskite solar cell technology .The findings also reveal that the GO could be a promising HTL for the fabrication of low cost, high efficiency Caesium based heterojunction solar cell. In the future, this efficiency may offer prominent potential as a substitute in a highly efficient green solar absorber material for photovoltaic applications after confirmation in the laboratory. Figure 1

POx/Al2O3 stacks for surface passivation of Si and InP

Passivation of semiconductor surfaces is crucial to reduce carrier recombination losses and thereby enhance the device performance of solar cells and other semiconductor devices. Thin-film stacks of phosphorus oxide (PO x ) and aluminum oxide (Al 2 O 3 ) have recently been shown to provide excellent passivation of semiconductor surfaces, including crystalline silicon and indium phosphide, and can also be highly interesting for passivation of other semiconductor materials such as Ge and III-V semiconductors. On silicon, the excellent passivation is attributed to the combination of a high positive fixed charge and a very low interface defect density. On InP nanowires, application of the PO x /Al 2 O 3 stacks improves charge carrier lifetime threefold as compared to unpassivated nanowires. In this work, we review and summarize recent results obtained on PO x /Al 2 O 3 stacks for semiconductor surface passivation. Several topics are discussed, including the passivation performance on various semiconductor surfaces, the processing of the PO x and Al 2 O 3 layers, the role of the capping layer, and aspects related to device integration. The PO x /Al 2 O 3 stacks feature some unique properties, including an unusually high positive fixed charge density, a low interface defect density, and can be prepared over a wide deposition temperature range. These unique properties arise in part from the mixing process that occurs between the PO x and Al 2 O 3 layers, which upon post-deposition annealing leads to the formation of AlPO 4 . The surface passivation provided by PO x /Al 2 O 3 stacks is highly stable and the stack can be used to conformally coat high-aspect-ratio structures such as nanowires, showing their promise for use in semiconductor devices. • PO x /Al 2 O 3 stacks provide excellent surface passivation on Si and InP. • PO x /Al 2 O 3 has a unique high positive fixed charge density (10 12 -10 13 cm −2 ) on Si. • PO x /Al 2 O 3 has low interface defect density down to 10 10 -10 11 eV −1 cm −2 on Si. • The Al 2 O 3 layer mixes with PO x during deposition, leading to AlPO 4 upon annealing. • The surface passivation quality provided by PO x /Al 2 O 3 is stable for over 1000 days.