Surface Defect Layer Research Articles

High-performance CIGS solar cells using a double active layers approach – SCAPS 1D optoelectronic modeling approach

One of the properties of the CIGS solar cell is that it can have an adjustable band gap energy. The band gap varies in the range from 1.01 to 1.7 eV as a function of materials content. Enhancing the bandgap profile of the active layer, which is where the majority of charge carrier photo-generation occurs, should significantly improve cell performance. Superimposing absorber layers with different electrical characteristics is one way of refining the bandgap profile and achieving these results. It is possible to analyze the optoelectronic output properties and simulate this active multilayer approach using a reference cell thanks to the SCAPS numerical modeling tool. Considering this, we have successfully simulated the following structure: CIGS2/CIGS1/SDL/ZnS/ZnO. The SDL which stands for Surface Defect Layer, has been considered for the property discontinuity interface, mainly characterized by the formation of defect states. That enabled to achieve realistic-like device with an improvement of power conversion efficiency (PCE) up to 11.98 %, i.e. 29.22 % and a fill factor (FF) of 82 % employing a total thickness of active layer of 800 nm. All simulations were performed considering experimental environment parameters, an external temperature of 300 K, light illumination of AM1.5G and defects states were assumed in both the bulk and at interfaces.

Multi-dimensional carbon modification strategy for lithium-ion battery anodes: Carbon-covered TiP2O7 supported by 3D carbon skeleton

Carbon coating is a beneficial method for improving surface capacitive behavior, electron transfer kinetics and cyclic stability of three-dimensional lattice lithium-embedded anode materials. Herein, we adopt one-step pyrolysis to achieve carbon-covered TiP2O7 supported by a three-dimensional carbon skeleton utilizing phytic acid and glucose as carbon sources. The two-dimensional amorphous carbon layer on TiP2O7 surface improves the initial Coulombic efficiency and rate capacity by inhibiting the irreversible embedding of lithium ions and reducing the interfacial charge transfer impedance. The three-dimensional carbon skeleton not only forms a conductive pathway between the carbon-covered TiP2O7, but also its large specific surface area, randomly oriented and defective carbon layer provide extra lithium storage sites and capacitive contribution. In addition, the specific capacity of the TiP2O7/C composite is still as high as 314.5 mA h g−1 after 1000 cycles at 1 A g−1. A TiP2O7/C//LiFePO4 full cell delivers a high energy density of 273.96 Wh kg−1 at 0.153 kW kg−1, and retains 114.43 Wh kg−1 even at the power density of 4.086 kW kg−1. The multi-dimensional carbon modification strategy has improved the electrochemical performance of TiP2O7-based anode materials, providing a model for synthesizing other high-performance anode materials.

Toward High‐Efficiency CIGS‐based Thin‐film Solar Cells Incorporating Surface Defects Layer, through a Comparative Study of Electrical Characteristics—SCAPS 1D Modeling

This research contribution investigates a way of improving performance of CIGSe‐based second‐generation thin‐film solar cells by analyzing output parameters of two reference cells using cadmium sulfide and zinc sulfide as buffer layers. The performances are improved by acknowledging both the exceptional properties of ZnS as a buffer layer, and the beneficial contributions of an indium‐enrich layer, which form a surface defect layer at the ZnS/CIGSe heterojunction. SCAPS‐1D numerical modeling software is used to conduct calculations, and the structure using ZnS enables achieving an efficiency of 24.31%. Deeper investigation on the effects of variation of functional layers properties such as bandgap, electron affinity, doping level, and thickness enables retaining an optimized structure, and results show an improved efficiency of 25.22% and a fill factor of 80.26%, indicating of a fluid flow of charge carriers, thus a more stable device. All simulations are performed considering experimental environment parameters, an external temperature of 300 K, light illumination of AM1.5G, and defects states are assumed in both the bulk and at interfaces.

Analysis of the magnetization reversal mechanism of heterogenous grain boundary diffused Nd-Fe-B sintered magnets

The grain boundary diffusion (GBD) method could effectively improve the coercivity of Nd-Fe-B sintered magnets, but the uneven distribution of heave rare earth (HRE) elements would lead to the decrease of squareness factor of the demagnetization curve of the magnets, which limited the application of this method. In this paper, three typical-structure regions were summarized based on microstructure characterization, and the magnetic properties and magnetization reversal mechanism were analyzed. The differences in nucleation positions and magnetization reversal processes of the three regions were discussed, and it found that the remarkable differences among them resulted in the low squareness factor of GBD Nd-Fe-B sintered magnets. In addition, the efficiency of Tb elements could be further improved to enhance the coercivity of Nd-Fe-B sintered magnets by forming homogeneous and complete core-shell structure grains, which could strengthen the nucleation field and even transfer the nucleation position from the grain surface defect layer to the grain interior region. Our results could provide guidance and reference for further improving the permanent magnetic properties of Nd-Fe-B sintered magnets by optimized GBD method.

One-dimensional photonic crystal magnetic sensors based on incomplete surface defect patterns

We propose and study an innovative magnetic sensor of incomplete surface defect one-dimensional (1D) photonic crystal composed of magnetic fluid, SiO2, and TiO2 as defect layers. The magnetic fluid film covers the surface of the 1D photonic crystal, whereas the magnetic fluid penetrates into the array of circular holes with period ∧ inscribed on the dielectric layers of SiO2 and TiO2 to form the incomplete surface defect layer. The sensing characteristics of a 1D photonic crystal magnetic sensor (1D-PCMS) were analyzed using the theory of rigorous coupled wave analysis. The innovative use of the angular interrogation method in magnetic field detection has investigated the effect of defect layer structure parameters, optical dielectric loss on magnetic sensor sensitivity and quality factor at a fixed wavelength. This incomplete surface defect mode 1D-PCMS structure demonstrates the feasibility of scanning angular measurements of magnetic fields and provides a reference for future research on 1D-PCMS based on angular interrogation.

РЕПРОФИЛИРОВАНИЕ ЖЕЛЕЗНОДОРОЖНЫХ РЕЛЬСОВ НА РЕЛЬСОФРЕЗЕРНЫХ СТАНКАХ

The study objective is to increase the productivity of restoring rail profiles. The paper is devoted to the solution of the problem to determine thermal force, vibro-acoustic and energy parameters of milling machining of rail steel in various conditions. The computational and analytical method of research, express diagnostics are used. The novelty is in the proposed improved technology of rail reprofiling. The following results are obtained: it is found that the most productive and effective method of rail reprofiling in stationary conditions is milling on special rail milling machines; the main directions of increasing the machinability of rail steel are determined, which allows the development of induction heating technology for softening the surface defective metal layer of the rail head. Conclusion: the range of rational cutting modes of rail steel with thermal annealing are found.

Sellotape Exfoliated Layered Quasi‐2D Perovskite Thin Film for Efficient Light‐Emitting Diodes

AbstractIn 2004, K. S. Novoselov and A. K. Geim et al. have used sellotape to peel off the layered 2D graphite, and successfully obtained few‐layer thin graphene. Inspired by this, herein, the sellotape is initially used to exfoliate the layered Ruddlesden–Popper (RP) quasi‐2D perovskite film for efficient light‐emitting diodes application. The top surface layer of quasi‐2D perovskite film is mechanically peeled off by the sellotape without damaging the crystalline region below, which minimizes the poor conductivity issue of quasi‐2D perovskite film owing to the decreased defect density. Moreover, the exfoliated quasi‐2D film exhibits low charge traps density and enhanced energy transfer from low‐dimensional to high‐dimensional domains due to the elimination of surface defective layer and the recrystallization of quasi‐2D perovskite crystal, leading to high photoluminescence quantum yield (PLQY) up to 83.2%. Subsequently, an efficient perovskite light‐emitting diode based on the exfoliated quasi‐2D perovskite thin film is achieved with high current efficiency of 46.0 cd m−2 and excellent external quantum efficiency (EQE) up to 14.8%.

Surface-sensitive magnetism of mesoscopic hollow CeO2 spheres

This study demonstrates magnetism of mesoscopic hollow ceria spheres (H─CeO2) with different defect distribution characteristics. The content and distribution of defect of micro-scale hollow spheres are controlled by varying the reaction with HNO3 and the annealing process. The obtained spheres are divided into three groups according to the surface structure, defect content and defect distribution of the shell. Group I is characterized by rough sphere surface and with large ceria clusters. Group II has relatively continuous surface defective layers and reduced surface roughness of the sphere. Group III has a continuous and smooth surface defective layer, and a decreasing gradient of Ce3+ concentration inside this layer. All spheres were ferromagnetic at room temperature. Saturation magnetization from high to low is in the sequence: group III, group II, and group I. The strongest magnetism is obtained for the samples subjected to the reaction with 1 M HNO3 for 60 min and then annealed, in which defects are distributed homogeneously within the surface thin layer and the sphere surface is smooth. We thus conclude that the surface plays the major role in the magnetic behavior of micro-scale hollow sphere.

Processing of a Diamond Blend in Supercritical Isopropanol

Abstract—Samples of a diamond blend (DB) are processed in supercritical isopropanol using a specially designed unit, and the IR spectra, Raman spectra, and X-ray diffraction data before and after processing are analyzed. It is shown that a noticeable decrease in the intensity of the IR absorption bands of the oxygen-containing bonds is observed as a result of this process, which is indicative of the effective etching of the shell of diamond crystallites during processing. A noticeable increase is found in the half-width of the diamond line in the Raman spectra of the samples subjected to processing, which is determined by the decrease in the dimensions of diamond nanocrystallites due to the etching of the surface defect layer. The proposed method has significant advantages over a traditional acid-based technology of purification of a diamond blend and indicates the prospect of practical application for this process.

The quantitative analysis of silicon carbide surface smoothing by Ar and Xe cluster ions

Abstract The gas cluster ion beam technique was used for the silicon carbide crystal surface smoothing. The effect of processing by two inert cluster ions, argon and xenon, was quantitatively compared. While argon is a standard element for GCIB, results for xenon clusters were not reported yet. Scanning probe microscopy and high resolution transmission electron microscopy techniques were used for the analysis of the surface roughness and surface crystal layer quality. The gas cluster ion beam processing results in surface relief smoothing down to average roughness about 1 nm for both elements. It was shown that xenon as the working gas is more effective: sputtering rate for xenon clusters is 2.5 times higher than for argon at the same beam energy. High resolution transmission electron microscopy analysis of the surface defect layer gives values of 7 ± 2 nm and 8 ± 2 nm for treatment with argon and xenon clusters.

Slow-muon study of quaternary solar-cell materials: Single layers and p−n junctions

Thin films and $p\ensuremath{-}n$ junctions for solar cells based on the absorber materials $\mathrm{Cu}(\mathrm{In},\mathrm{G}\mathrm{a}){\mathrm{Se}}_{2}$ and ${\mathrm{Cu}}_{2}{\mathrm{ZnSnS}}_{4}$ were investigated as a function of depth using implanted low energy muons. The most significant result is a clear decrease of the formation probability of the ${\mathrm{Mu}}^{+}$ state at the heterojunction interface as well as at the surface of the $\mathrm{Cu}(\mathrm{In},\mathrm{G}\mathrm{a}){\mathrm{Se}}_{2}$ film. This reduction is attributed to a reduced bonding reaction of the muon in the absorber defect layer at its surface. In addition, the activation energies for the conversion from a muon in an atomiclike configuration to a anion-bound position are determined from temperature-dependence measurements. It is concluded that the muon probe provides a measurement of the effective surface defect layer width, both at the heterojunctions and at the films. The CIGS surface defect layer is crucial for solar-cell electrical performance and additional information can be used for further optimizations of the surface.

A study on the prediction of tool wear in drilling the carbon fibre reinforced plastic

Carbon fibre reinforced plastics has a lot of merit such as mechanical characteristic, lightweight, and thermal resistance. For using carbon fibre reinforced plastics, the cutting and drilling process is necessary, and the study of optimal cutting conditions is very necessary, too. Generally, CFRP needs the processes of lathe turning, drilling, milling and cutting after moulding. However, these processes cause such problems as sudden abrasion of the tools, heavy surface roughness and defective layer by crack and delamination. Therefore, the study to examine the conditions for the high precision products by minimising these problems is very important. In this study, a sample was made with a CFRP plate to take a drilling test under a set condition with a high speed steel drill. This dissertation is a study on the optimal drilling conditions of CFRP with various drilling condition. The drilling of these various specimens with different machining condition is performed.

Negative photoconductivity of InAs nanowires

Negative photoconductivity is observed in InAs nanowires (NWs) without a surface defective layer. The negative photoconductivity is strongly dependent on the wavelength and intensity of the light, and is also sensitive to the environmental atmosphere. Two kinds of mechanisms are discerned to work together. One is related to gas adsorption, which is photodesorption of water molecules and photo-assisted chemisorption of O2 molecules. The other one can be attributed to the photogating effect introduced by the native oxide layer outside the NWs.

Thin Film Limit Correction Method to the Surface Defective Layer in Low Absorption Spectroscopy

Thin Film Limit Correction Method to the Surface Defective Layer in Low Absorption Spectroscopy

Thin-film limit formalism applied to surface defect absorption.

The thin-film limit is derived by a nonconventional approach and equations for transmittance, reflectance and absorptance are presented in highly versatile and accurate form. In the thin-film limit the optical properties do not depend on the absorption coefficient, thickness and refractive index individually, but only on their product. We show that this formalism is applicable to the problem of ultrathin defective layer e.g. on a top of a layer of amorphous silicon. We develop a new method of direct evaluation of the surface defective layer and the bulk defects. Applying this method to amorphous silicon on glass, we show that the surface defective layer differs from bulk amorphous silicon in terms of light soaking.

Computational analysis of the effect of the surface defect layer (SDL) properties on Cu(In,Ga)Se2-based solar cell performances

In this article, the performances of Cu(In,Ga)Se2 (CIGS) solar cells have been modelled and numerically simulated using the one-dimensional simulation program Solar Cell Capacitance Simulator in 1 Dimension (SCAPS-1D), and a detailed analysis of the effect of surface defect layer (SDL) thickness, band gap and carrier mobility with Fermi level pinning is presented. Furthermore, donor-type defect state density in the SDL has been investigated, and their effect on device performances has been presented. Based on the simulation results, optimal properties of the SDL for the CIGS solar cell are proposed. The simulated results show that the optimal thickness of the SDL to optimise the solar cells is in the range of 100–200nm. The increase in the band gap of the SDL >1.3eV improves the device performance by enhancing the open-circuit voltage (Voc), fill factor (FF) and conversion efficiency due to the larger quasi-Fermi energy-level splitting, and optimal band offset between the SDL and the buffer layer (CdS). The simulation results suggest that the SDL defect density as well as carrier mobilities are the critical parameters for the limitation of the performances for the CIGS solar cells. All these results show that the SDL plays an important role in designing high-efficiency and high-performance CIGS-based solar cells.

Energy-loss mechanism of single-crystal silicon microcantilever due to surface defects generated during plasma processing

The mechanism behind the degradation of the mechanical properties of silicon (Si) microcantilevers caused by plasma-induced surface defects was investigated. The resonant frequency (f) and quality factor (Q factor) were deteriorated by defects generated after irradiating Ar plasma. We found that Young's modulus in the surface region was decreased after the plasma irradiation, but this does not explain the drastic change to the resonant frequency. The decrease could be explained by using a model in which a surface defect layer causes energy dissipation. Hydrogen annealing at 450 °C and rapid thermal annealing at 1000 °C could not repair the mechanical properties degraded by the plasma irradiation. After annealing, Young's modulus was not recovered while the dangling bonds were diminished, because the annealing could not restore the crystalline structure of the silicon. These results indicate that extensive defects such as dislocations or amorphous phases may be generated during plasma irradiation, causing energy dissipation. Since the degraded mechanical property in the plasma processes cannot be restored by annealing, it is important to prevent any damage from occurring at any stage of the processes.

Electrical modeling of Cu(In,Ga)Se2 cells with ALD-Zn1−xMgxO buffer layers

Electrical modeling of Cu(In,Ga)Se2 solar cells with Zn1−xMgxO buffer layers is performed. A number of different device models are implemented and tested by comparing simulation results and measurement data. Room temperature light-soaking and dark-light cross-over behavior as well as low-temperature characteristics of these cells are studied. The light-soaking improvements in the solar cell parameters are attributed to an increase in buffer donor density, due to persistent photo conductivity, that counteracts charged acceptors in the absorber-buffer region. Dark-light JV-curve cross-over is explained by deep acceptor defects with small electron capture cross-section, in the buffer. Best correspondence to measurements on ZnO and Zn0.83Mg0.17O cells is obtained with models including absorber-buffer interface acceptor states. No wideband-gap surface defect layer is needed to reproduce measurement data.

Baseline model of graded-absorber Cu(In,Ga)Se 2 solar cells applied to cells with Zn 1 − xMg xO buffer layers

A baseline parameter set for electrical modelling of Cu(In,Ga)Se 2 solar cells with compositionally graded absorber and CdS buffer layer is established. The cases with and without Fermi level pinning as well as with and without a surface defect layer are considered. Simulations with a defect layer are observed to give the best correspondence to measurements. Zn 1 − x Mg x O buffer layers are introduced and initial modelling of the light soaking behaviour is performed. Simulation results are compared with experimental data.

Frequency dependent steering with backward leaky waves via photonic crystal interface layer

A Photonic Crystal (PC) with a surface defect layer (made of dimers) is studied in the microwave regime. The dispersion diagram is obtained with the Plane Wave Expansion Method. The dispersion diagram reveals that the dimer-layer supports a surface mode with negative slope. Two facts are noted: First, a guided (bounded) wave is present, propagating along the surface of the dimer-layer. Second, above the light line, the fast traveling mode couple to the propagating spectra and as a result a directive (narrow beam) radiation with backward characteristics is observed and measured. In this leaky mode regime, symmetrical radiation patterns with respect to the normal to the PC surface are attained. Beam steering is observed and measured in a 70 degrees angular range when frequency ranges in the 11.88-13.69 GHz interval. Thus, a PC based surface wave structure that acts as a frequency dependent leaky wave antenna is presented. Angular radiation pattern measurements are in agreement with those obtained via numerical simulations that employ the Finite Difference Time Domain Method (FDTD). Finally, the backward radiation characteristics that in turn suggest the existence of a backward leaky mode in the dimer-layer are experimentally verified using a halved dimer-layer structure.