Defect States Research Articles

Investigating the Performance of FASnI3‐Based Perovskite Solar Cells with Various Electron and Hole Transport Layers: Machine Learning Approach and SCAPS‐1D Analysis

AbstractIn this study, tungsten disulfide (WS2) as an electron transport layer (ETL) and zinc phosphide (Zn3P2) as a hole transport layer (HTL) are incorporated to improve the performance of the FASnI3‐based perovskite solar cell (PSC). The solar cell capacitance simulator in one dimension (SCAPS‐1D) is used to investigate the photovoltaic (PV) performances of the heterojunction Al/FTO/WS2/FASnI3/Zn3P2/Ni solar structure. The performance metrics of proposed device with numerous ETLs and HTLs are discussed. The suggested device provides appropriate band structures, which in turn potentially reduce minority electron recombination, thereby enhancing overall performances. Influences of various physical parameters such as thickness, doping concentration, bulk defect, interface defect states, work function, and back surface recombination velocity (BSRV) on the device performances have also been analyzed. An efficiency of 29.81% is achieved at the optimum thicknesses of 0.05 µm for WS2 ETL, 1.0 µm for FASnI3 absorber, and 0.1 µm for Zn3P2 HTL. Furthermore, a machine learning algorithm is used to assess the impact of multiple semiconductor parameters, and found that defect density influences the most. This model, which has an approximate correlation coefficient (R2) of 0.937, can predict the data with precision. Therefore, these numerical outcomes will help researchers further design and manufacture a low‐cost and highly efficient FASnI3‐based PSC.

Condition‐based maintenance management for two‐stage continuous deterioration with two‐dimensional inspection errors

AbstractInspections often perform imperfect outcomes during maintenance processes owing to human errors, management issues and other limitations. In particular, such imperfection affects the maintenance management of multistage deterioration significantly due to both false state identification and measurement errors, whose quantitative analysis, however, is seldom reported in the literature. To fill these gaps, this paper devises a condition‐based maintenance management strategy oriented to two‐stage continuous degradation under two‐dimensional inspection imperfection. Specifically, a threshold‐based replacement is executed under the normal‐working state if the detected degradation value exceeds the preset limit; additionally, preventive replacement is immediately performed once the defective state is identified. Notably, the detection outcome rather than the actual working condition decides how preventive maintenance operates. The long‐run cost rate is minimized via the optimization of the inspection cycle and replacement limit. Besides, numerical experiments conducted on train bogie bearing are provided, showing substantial superiorities over cost‐effectiveness promotion and performance improvement.

Insight into the damage mechanism of KH2PO4 crystals with BaK-SiP by hybrid density functional theory

The laser-induced damage threshold (LIDT) of potassium dihydrogen phosphate (KDP) crystals is one of the key factors affecting the application of KDP crystals for Inertial confinement fusion (ICF). Previous studies have found that Ba, Si impurities can form BaK-SiP defect complexes in KDP crystals. However, the microscopic nature of the defect complexes is still unclear. We precisely calculate defect formation energy (DFE) in various charge states (-1, 0, +1), configuration coordinate diagram (CCD) and optical spectra by hybrid density functional theory. We found BaK-SiP introduce two defect states in the band gap. In the transitions (BaK-SiP)✕+h∙→(BaK-SiP)∙ and (BaK-SiP)✕+e-→(BaK-SiP)′, excited state and ground state have an intersection point in the Marcus inverted region and the activation energies are nearly 0 eV. The results showed that the defect complexes could capture holes and electrons through lattice relaxation, causing significant heat deposition and resulting in crystal damage. This implies a new damage mechanism of KDP crystals is discovered.

Gas Molecule Assisted All-Inorganic Dual-Interface Passivation Strategy for High-Performance Perovskite Solar Cells.

The trap states at both the upper and bottom interfaces of perovskite layers significantly impact non-radiative carrier recombination. The widely used solvent-based passivation methods result in the disordered distribution of surface components, posing challenges for the commercial application of large-area perovskite solar cells (PSCs). To address this issue, a novel NH3 gas-assisted all-inorganic dual-interfaces passivation strategy is proposed. Through the gas treatment of the perovskite surface, NH3 molecules significantly enhanced the iodine vacancy formation energy (1.54eV) and bonded with uncoordinated Pb2+ to achieve non-destructive passivation. Meanwhile, the reduction of the film defect states is accompanied by a decrease in the work function, which promotes carrier transport between the interface. Further, a stable passivation layer is constructed to manage the bottom interfacial defects using inorganic potassium tripolyphosphate (PT), whose ─P═O group effectively mitigated the charged defects and lowered the carrier transport barriers and nucleation barriers of PVK, while the gradient distribution of K+ improved the crystalline quality of PVK film. Based on the dual-interface synergistic effect, the optimal MA-contained PSCs with an effective area of 0.1 cm2 achieved an efficiency of 24.51% and can maintain 90% of the initial value after aging (10-20% RH and 20°C) for 2000h.

Temperature Dependence of the Defect States in LWIR (100) and (111)B HgCdTe Epilayers for IR HOT Detectors

HgCdTe epilayers grown by chemical vapor deposition (MOCVD) on GaAs substrates operating in the long-wave infrared range were characterized by the photoluminescence (PL) method. Photodiode and photoconductor designs, both (100) and (111)B crystallographic, were analyzed. Spectral current responsivity (RI) and a PL signal approximated by a theoretical expression being the product of the density of states and the Fermi–Dirac distribution were used to determine the fundamental transition (energy gap, Eg). For all the samples, an additional deep-level-related transition associated with mercury vacancies (VHg) were observed. The energy distance of about 80 meV above the valence band edge was observed for all the samples. Moreover, measurements at low temperature showed shallow acceptor-level (AsTe and VHg as acceptors) transitions. In HgCdTe(100), due to the higher arsenic activation, AsTe was the dominant acceptor dopant, while, in HgCdTe(111)B, the main acceptor level was formed by the neutral VHg. The determined activation energies for AsTe and VHg dopants were of about 5 meV and 10 meV, respectively.

Statistical and sensitivity analysis of ultrasound signals for effective condition monitoring of electro-motors using industrial approach

This paper researches the importance of ultrasound methodology for swiftly detecting faults in electric motors and rotating machines. The primary focus of this research is on the intricate signal processing of ultrasound signals from both faulty and fault-free electro-motors. The principal goal is to conduct a comprehensive statistical investigation into signal factors, examining the effects of defect progression on the factors associated with continuously operating faulty electro-motors. In addition to the statistical analysis, this study explores the envelope-frequency spectrum of the signal under both healthy and defective conditions, employing the envelope method alongside Hilbert transformation. The objective is to thoroughly scrutinize the dynamic changes in ultrasound waveform and envelope spectrum of defective states, considering diverse degrees of defect severity over an extended time span. Moreover, the paper meticulously tracks the trajectory of factor changes over a 40-day operational period of a defective electro-motor. Additionally, the study delves into the sensitivity of the ultrasound method to impulse-wise shocks, which are recurrently observed in ultrasound signals, leading to deviations in certain signal factors from their established healthy thresholds. In response to this challenge, this paper conducts a particular analysis of signal factor sensitivity to impulse-wise noises, identifying robust factors that serve as reliable tools for firm condition monitoring. These identified factors are then presented as invaluable contributors to ensuring the precision and reliability of condition monitoring, especially in the presence of disruptive impulse-wise noises.

Prospects of silicide contacts for silicon quantum electronic devices

Metal contacts in semiconductor quantum electronic devices can offer advantages over doped contacts, primarily due to their reduced fabrication complexity and lower temperature requirements during processing. Some metals can also facilitate ambipolar device operation or form superconducting contacts. Furthermore, a sharp metal–semiconductor interface allows for contact placement in close proximity to the active device area avoiding damage caused by dopant implantation. However, in the case of gate-defined quantum dots in intrinsic silicon, the formation of a Schottky barrier at the silicon–metal interface can lead to large, nonlinear contact resistances at cryogenic temperatures. We investigate this issue by examining hole transport through metal oxide-semiconductor transistors with platinum silicide contacts on intrinsic silicon substrates. We extract the contact and channel resistances as a function of temperature and improve the cryogenic conductance of the device by more than an order of magnitude by implementing meander-shaped contacts. In addition, we observe signatures of enhanced transport through localized defect states, which we attribute to platinum clusters in the depletion region of the Schottky contacts that form during the silicidation process. These results showcase the prospects of silicide contacts in the context of cryogenic quantum devices and address associated challenges.

Research on the Method and Device for Judging the Position and Status of GIS Disconnectors

Abstract When there is a mechanical defect in the isolation switch, its action process must be different from the normal state, and this difference will inevitably lead to changes in the working condition of the power source. Therefore, the mechanical state of the isolation switch can be determined by detecting the state quantity of the power source. This paper compares the power curves of the defect state and the normal mechanical state through simulation testing, and judges the mechanical state of the isolation switch based on the trend of power curve changes in different motion stages. Based on this technical route, an online monitoring device for the mechanical status of isolation switches has been developed, which can intelligently judge the mechanical status and opening/closing status of the tested isolation switch based on online monitoring data, quantitatively diagnose existing mechanical defects, and provide corresponding maintenance opinions, providing strong support for the installation, operation, maintenance, and quality judgment of high-voltage isolation switches.

UV and X-ray induced photochromic material based on defect state exchanges

Inorganic photochromic (PC) materials are gaining increasing recognition as promising candidates for applications in optical storage and information display. However, conventional photochromic materials exhibit sluggish coding rates and a deficiency in intelligent response for writing and erasing under multiple excitation sources. This deficiency contributes to suboptimal readout/decoding efficiency and storage security. Here, we show a Ba2NaNb5O15:Er3+ photochromic material with photoluminescence reversible modulation that can fast respond to both ultraviolet light and 532 nm laser within about 1 s, which accompanied by thermal bleaching. The PC mechanism which is based on defect state exchanges between oxygen vacancy defects and color centers is attributed to the structural flexibility of Nb-O systems and oxygen vacancy increased under irradiation. More importantly, it shows differential PC decay behavior in response to X-ray and UV light due to the difference in the number of trapped carriers. Therefore, a simple strategy based on different self-recovery levels induced by double excitation is constructed to develop an encrypted optical memory model. This fast and differential excitation source response behavior hopefully stimulates the development of new encrypted optical memory.

Unraveling the Presence and Positions of Nitrogen Defects in Defective g‐C3N4 for Improved Organic Photocatalytic Degradation: Insights from Experiments and Theoretical Calculations

AbstractIn this work, nitrogen‐defective g‐C3N4 with different nitrogen defect densities is synthesized for ciprofloxacin photocatalytic degradation. Compared with pristine g‐C3N4, g‐C3N4 etched with NaBH4 for 1 h exhibits an approximately ten‐fold increase in the rate constant of ciprofloxacin (CIP) degradation. The combined experimental analysis and theoretical calculations reveal that nitrogen defects can be incorporated into g‐C3N4 in all nitrogen sites and that C─N═C is the most susceptible site. By incorporating nitrogen defects to induce defect states between the conduction band (CB) and valence band (VB), the electronic and band structures are tuned. The induced defect states can be downshifted to approach the valance band, reaching increased nitrogen defect density within optimum ranges to accommodate excited electrons to narrow the bandgap, extend the light absorption capability, and enhance the charge carrier separation and transfer efficiency. The g‐C3N4 etched by NaBH4 for 2 h with over‐introduced nitrogen defects exhibits a declined performance due to a deteriorated structure, and the over‐downshifted defect states turn out to be a new recombination center for charge carriers.

Carrier dynamics of excited state absorption in germanium using Mid-IR probe pulses

Semiconductors play a crucial role in various industries, and the study of carrier dynamics is essential in understanding their behavior. This manuscript presents the transient dynamics of Germanium in the transmission geometry, probed with low-energy mid-IR pulses ranging from 0.154 eV to 0.774 eV. The system is pumped with 0.953 eV, an energy greater than the band gap in the near-infrared region. Results elucidate the temporal evolution of excited state absorption (ESA) of the pump-created carrier dynamics. Excitation from the defect states to various energy levels of the band curvatures is observed with varying probe energy from the above band gap to the below band gap probing energies. For each probe energy, we extracted the pump photon flux-dependent ESA variation. In all the cases, this ESA is linearly increasing with pump power. However, the rate of increase of optical density with pump power (d(ESA)/dP) varies. This new parameter, d(ESA)/dP, is monitored for different probe energies and pump-probe delay. Interestingly, this parameter is maximum at the band gap. We believe these new experiments pave the way to understanding the intricate band structure of the excited systems.

Achieving Precise Control of Defect States and Residual Strain in Perovskite Solar Cells Using π-Conjugated Dual-Anchor Molecules

Achieving Precise Control of Defect States and Residual Strain in Perovskite Solar Cells Using π-Conjugated Dual-Anchor Molecules

Controlling the Orientation‐Dependent Second Harmonic Generation in Hybrid Germanium Perovskites

AbstractManipulating the crystal orientation plays a crucial role in the conversion efficiency during second harmonic generation (SHG). Here, we provide a new strategy in controlling the surface‐dependent anisotropic SHG with the precise design of (101) and (2 0) MAGeI3 facets. Based on the SHG measurement, the (101) MAGeI3 single crystal exhibits larger SHG (1.3×(2 0) MAGeI3). Kelvin probe force microscopy imaging shows a smaller work function for the (101) MAGeI3 compared with the (2 0), which indirectly demonstrates the stronger intrinsic polarization on the (101) surface. X‐ray photoelectron spectroscopy confirms the band bending within the (101) facet. Temperature‐dependent steady‐state and time‐resolved photoluminescence spectroscopy show shorter lifetime and wider emission band in the (101) MAGeI3 single crystal, revealing the higher defect states. Additionally, powder X‐ray diffraction patterns show the (101) MAGeI3 possesses larger in‐plane polar units [GeI3]− density, which could directly enhance the spontaneous polarization in the (101) facet. Density functional theory (DFT) calculation further demonstrates the higher intrinsic polarization in the (101) facet compared with the (2 0) facet, and the larger built‐in electric field in the (101) facet facilitates surface vacancy defect accumulation. Our work provides a new angle in tuning and optimizing hybrid perovskite‐based nonlinear optical materials.

Controlling the Orientation-Dependent Second Harmonic Generation in Hybrid Germanium Perovskites.

Manipulating the crystal orientation plays a crucial role in the conversion efficiency during second harmonic generation (SHG). Here, we provide a new strategy in controlling the surface-dependent anisotropic SHG with the precise design of (101) and (2 0) MAGeI3 facets. Based on the SHG measurement, the (101) MAGeI3 single crystal exhibits larger SHG (1.3×(2 0) MAGeI3). Kelvin probe force microscopy imaging shows a smaller work function for the (101) MAGeI3 compared with the (2 0), which indirectly demonstrates the stronger intrinsic polarization on the (101) surface. X-ray photoelectron spectroscopy confirms the band bending within the (101) facet. Temperature-dependent steady-state and time-resolved photoluminescence spectroscopy show shorter lifetime and wider emission band in the (101) MAGeI3 single crystal, revealing the higher defect states. Additionally, powder X-ray diffraction patterns show the (101) MAGeI3 possesses larger in-plane polar units [GeI3]- density, which could directly enhance the spontaneous polarization in the (101) facet. Density functional theory (DFT) calculation further demonstrates the higher intrinsic polarization in the (101) facet compared with the (2 0) facet, and the larger built-in electric field in the (101) facet facilitates surface vacancy defect accumulation. Our work provides a new angle in tuning and optimizing hybrid perovskite-based nonlinear optical materials.

Optically Active Defect Engineering via Plasma Treatment in a MIS‐Type 2D Heterostructure

AbstractAt the interface of 2D heterostructures, the presence of defects and their manipulation play a crucial role in the interfacial charge transfer behavior, further influencing the device functionality and performance. In this study, the impact of deliberately introduced photo‐active defects in the h‐BN layer on the interfacial charge transfer and photoresponse performance of a metal‐insulator‐semiconductor type heterostructure device is explored. The formation and concentration of defects are qualitatively controlled using an inductive coupled plasma treatment method, as evidenced by enhanced h‐BN defect emission and more efficient optically induced doping of graphene at the graphene/h‐BN interface. Besides, the use of the h‐BN layer between graphene and WS2 not only suppresses charge carriers in the dark state, but also promotes the separation of photo‐generated electron‐hole pairs and interfacial charge transfer due to the existence of defect levels, leading to orders of magnitude improvement in the light on/off ratio and self‐driving performance of the heterostructure photodetector. This strategy of controlling defect states in the insulating layer provides a new approach to optimize the charge transfer processes at the 2D interfaces, so as to expand its potential applications in the fields of electronic and optoelectronic devices.

Thermodynamical stability of carbon-based defects in α boron from first principles

We report an exhaustive study of the formation enthalpy and charge states of carbon-based defects in rhombohedral α boron within the density functional theory (DFT) that enables us to derive rules about the formation of complex carbon defects. We have accounted for one and two interstitial carbon atoms, eventually combined with one substitutional carbon atom and/or one interstitial boron atom and varied several geometric parameters. We find that when positioned in the plane perpendicular to the [111] rhombohedral axis, two carbon atoms turn out to preferentially form a graphite-like hexagon with four boron atoms. When positioned instead along the [111] axis, the distance between them strongly affects the defect thermodynamic stability, and we find in particular that additional negative charges strongly stabilize the diatomic carbon–carbon chains.

Effect of Ferromagnet/Organic Semiconductor Interface Defect States on Tunnel Magnetoresistance of Hybrid Magnetic Tunnel Junctions

Herein, analytical modeling of Fe3O4/x(≈1.1 nm)/Co (x = rubrene, C60, and bathocuproine (BCP)) magnetic tunnel junctions (MTJs) has been performed using rubrene, C60, and BCP as organic spacer layers. The simulation is considered as nonequilibrium Green's function assuming spin precession at ferromagnet/organic semiconductor (FM/OSC) interface defect states. The voltage‐dependent resistances for both parallel (RP) and antiparallel (RAP) orientations have been observed to be dependent on spin injection from FM/OSC defect states. Pinning well‐dependent defect state depths have been associated with band misalignment‐induced lattice distortion at FM/OSC interface of the devices. The large tunnel magnetoresistance (TMR) response for rubrene‐based MTJ device has been attributed to a higher change of FM/OSC defect state depths with voltage. High TMR may have reduced spin torque‐dependent spin precession, leading to lower spin transfer torque for the rubrene device. Hence, engineering of defect states at the FM/OSC interface may lead to the successful realization of enhanced TMR in organic spacer MTJs for high‐performance spintronic memory applications.

Optical properties of NiO films: Effect of nitrogen-doping, substrate temperature and band gap estimation using machine learning

In this study, nickel oxide (NiO) thin films were synthesized on glass substrates using RF magnetron sputtering with varying nitrogen (N) doping ratio and substrate temperatures to explore modifications in their structural, morphological, and optical properties. The films were prepared using a high-purity NiO target under controlled sputtering conditions. Structural analysis by X-ray diffraction revealed an improvement in crystallinity in the (200) direction with increasing N ratio. In contrast, higher N ratio led to the suppression of (111) and (220) peaks, indicating a significant influence of N on the crystal structure and orientation. The films’ thickness and morphology, examined using scanning electron microscopy and energy-dispersive X-ray spectroscopy, showed uniform and homogeneous growth with smooth surface topologies. Optical properties, assessed by UV–Vis-NIR spectrophotometry, demonstrated a decrease in transmittance and a redshift in the absorption edge with increased N doping, corresponding to a narrowing of the energy bandgap from 3.7 eV to 3.45 eV. This bandgap reduction is attributed to N incorporation substituting oxygen sites, introducing defect states within the band structure. Additionally, the impact of substrate temperature on film growth enhanced crystallinity and orientation along the (111) plane at higher temperatures, with a simultaneous reduction in film thickness due to increased adatom mobility and potential thermal decomposition. The evaluation of Kernel Ridge Regression (KRR) and Ridge Regression (RR) models revealed their effectiveness in predicting band gap values for thin films at varying substrate temperatures and thicknesses. While RR excelled in predicting a band gap of 3.6 eV for a film with a substrate temperature of 24 °C and a thickness of 112.7 nm, KRR outperformed in predicting a band gap of 3.65 eV for a film with a substrate temperature of 24 °C and a thickness of 107 nm. These findings elucidate the dual influence of N doping and substrate temperature on enhancing the functional properties of NiO thin films, promising for applications in optoelectronic devices and gas sensors.

Terahertz Spin-Conductance Spectroscopy: Probing Coherent and Incoherent Ultrafast Spin Tunneling.

Thin-film stacks | consisting of a ferromagnetic-metal layer and a heavy-metal layer are spintronic model systems. Here, we present a method to measure the ultrabroadband spin conductance across a layer between and at terahertz frequencies, which are the natural frequencies of spin-transport dynamics. We apply our approach to MgO tunneling barriers with thickness d = 0-6 Å. In the time domain, the spin conductance Gs has two components. An instantaneous feature arises from processes like coherent spin tunneling. Remarkably, a longer-lived component is a hallmark of incoherent resonant spin tunneling mediated by MgO defect states, because its relaxation time grows monotonically with d to as much as 270 fs at d = 6.0 Å. Our results are in full agreement with an analytical model. They indicate that terahertz spin-conductance spectroscopy will yield new and relevant insights into ultrafast spin transport in a wide range of spintronic nanostructures.

Efficient and stable CsPbBr3/Cs4PbBr6 composite powders passivated and encapsulated with a novel silicon-based ligand

The metal halide perovskite have garnered significant attention for their exceptional photoelectric properties. However, their inherent instability and the sharp decrease of photoluminescence quantum yield (PLQY) in the solid-state significantly limit their practical applications. Appropriate heterojunction structures or matrix encapsulation can efficiently improve the PLQY and stability of the metal halide perovskite. Herein, we report a new silicon-based ligand hydrolysis condensation encapsulation to synthesize CsPbBr3/Cs4PbBr6/BTESPA-x (CPB–Si-x) composite powders with improved luminescence properties and enhanced thermal stability. With the increase of BTESPA (from 0 to 150 μL), the efficient hydrolysis condensation process occurs on the surface of CsPbBr3/Cs4PbBr6. Finally, the abundant amino-silane groups in BTESPA bind to undercoordinated Pb2+, thereby suppressing the surface defect states and enhancing the PLQY from 34.3 % for CsPbBr3/Cs4PbBr6 (CPB) to 82.1 % for CPB-Si-5. Simultaneously, the thermal stability of CPB-Si-5 exhibits a 13 % improvement over that of CPB after undergoing thermal cycling. Furthermore, tricolor white light-emitting-diode (WLEDs) with high color rendering index were fabricated using on-chip blue LED with bright green-emissive CPB-Si-5 composite powder and red-emissive K2SiF6:Mn4+ phosphor, demonstrating the potential applicability of these powders in WLED backlight systems.