Search Results (9)

CuIn₅Se₈ is reported as a remarkable copper-deficient layer that contains ordered vacancy compounds (OVCs) for high-efficiency chalcopyrite-based solar cells; however, the understanding of its carrier characteristics has remained limited. OVCs could naturally form on the surface of chalcopyrite absorber. In this study, the carrier dynamics characteristics of OVCs were investigated by constructing a junction consisting of chalcopyrite absorber and CdS buffer layer. At first, the band structure of CuIn₅Se₈ was studied to determine the bandgap properties. Then, thermodynamic stability, defect formation energy, defects and carrier concentration, defect transition energy level of CuIn₅Se₈ and its Cd doping state (caused by CdS) were comparatively studied. The results suggest that Cd doping has different effects on the defect and carrier characteristics of OVCs with various chemical potentials. However, the OVC always remains n-type under the whole thermodynamically stable region, with contribution from the hallow-level In_Cu donor defect. Finally, the OVC’s carrier dynamics characteristics were assessed using the collected defect and carrier data. It is indicated that the OVC layer may contribute to the formation of a p-n homojunction in solar cells. Under selenium-rich conditions, the OVC layer increases the carrier density on the n-type side of p-n junction nearly 30-fold, which helps reduce the difference in carrier density and minority current density between two sides of the p-n junction. The conversion efficiency of the solar cell with OVC shows a 7.25% improvement when compared to the control. The distinct behavior of OVCs may serve as a valuable reference for the creation or improvement of a related functional film layer or device. Full article

ZnO and ZnO:5%B nanoparticles produced by sol–gel synthesis exhibit a single-phase wurtzite structure. X-ray diffraction (XRD) investigation reveals crystallite sizes in the range of $32.37–39.63$ nm and microstrain values on the order of $(1.98–8.03)\times {10}^{-4}$, despite the Uniform Stress Deformation Model (USDM) indicating the presence of considerable tensile stress. Significant band-tail states are introduced via boron doping, resulting in Urbach energies ranging from $110$ to $193$ meV and a narrowed optical band gap of $3.216$ eV. With a refractive index range of $2.05–2.71$, the material exhibits tunable optical characteristics. Violet and blue emissions originating predominantly from zinc interstitials (Znᵢ) and zinc vacancies (V_Zn) dominate the photoluminescence spectra, while oxygen interstitial-related contributions remain relatively weak. A high spin density is confirmed by electron spin resonance measurements, which reveal a strong defect-related signal at $g\approx 2.294$. The formation of Znᵢ/V_Zn defect centers due to charge compensation and ionic size mismatch induced by B³⁺ substitution for Zn²⁺ significantly modifies the band-edge states and optical constants. These defect-engineered properties render the material promising for applications in ultraviolet (UV) photodetectors, transparent conducting oxides, and electron transport layers in organic photovoltaic devices. Full article

Interactions of ZnO nanoplates with water are crucial in determining its structure and performance of the catalyst, yet the details for these processes remain missing due to the lack of an effective detection method that provides resolution at the atomic level. Here, ¹⁷O solid-state NMR spectroscopy is applied to investigate the interactions and the associated stabilization mechanisms for the polar surface of ZnO nanoplates. It shows that the specific O sites (around Zn vacancy) on the polar surface also contribute to the ¹⁷O NMR signal at −18.8 ppm. The observed trends in both ¹⁷O and ¹H spectra after exposing to water vapor further support the assignment of this ¹⁷O high-frequency signal (−18.8 ppm). In addition, the dissociation of water at defective sites of polar surfaces is evidenced, which leads to the generation of OH groups on both (000$\overline{1}$)-O and (0001)-Zn surfaces. The generated OH species obviously improves the dispersity of ZnO nanocrystals, as well as the stability of polar facets by significant electrostatic repulsion interactions. This study will provide insight into the adsorption properties of water on polar facets and the related stabilization mechanisms of the polar surface in nanocrystals. Full article

Two−dimensional halide perovskites have emerged as promising optoelectronic materials, yet the uncontrolled defect formation during synthesis remains a critical challenge for their practical applications. In this work, we systematically investigate the structural, electronic, and optical properties of monolayer CsPb₂Br₅ in two representative configurations: ds−CsPb₂Br₅ and ss−CsPb₂Br₅. By introducing four types of vacancy defects—V_Br−c, V_Br−b, V_Cs, and V_Pb, we analyze their structural distortions, formation energies, and their impact on band structure and optical response using first−principles calculations. Our results reveal that Br−related vacancies are energetically most favorable and induce shallow defect levels and absorption edge redshifts in the ds−CsPb₂Br₅ structure, while in the ss−CsPb₂Br₅ configuration, only V_Br−b forms a defect state. V_Pb and V_Cs lead to significant sub−bandgap absorption enhancement and dielectric response due to band−edge reorganization, despite not introducing in−gap states. Notably, V_Br−c exhibits distinct infrared absorption in the ss−CsPb₂Br₅ model without electronic trap formation. These findings underscore the critical influence of defect type and slab asymmetry on the optoelectronic behavior of CsPb₂Br₅, providing guidance for defect engineering in perovskite−based optoelectronic applications. Full article

The objective of the proposed work was to investigate the electrical performance of a 250 µm-thick 4H-SiC p-n junction detector after irradiation with DT neutrons (14.1 MeV energy) at high temperature (500 °C). The results showed that the current–voltage (I-V) characteristics of the unirradiated SiC detector were ideal, with an ideality factor close to 1.5. A high electron mobility (µ_n) and built-in voltage (V_bi) were also observed. Additionally, the leakage current remained very low in the temperature range of 298–523 K. High-temperature irradiation caused a deviation from ideal behaviour, leading to an increase in the ideality factor, decreases in the µ_n and V_bi values, and a significant rise in the leakage current. Studying the capacitance–voltage (C-V) characteristics, it was observed that neutron irradiation induced reductions in both Al-doped (p⁺-type) and N-doped (n⁻-type) 4H-SiC carrier concentrations. A comprehensive investigation of the deep defect states and impurities was carried out using deep-level transient spectroscopy (DLTS) in the temperature range of 85–750 K. In particular, high-temperature neutron irradiation influenced the behaviours of both the Z_1/2 and EH_6/7 traps, which were related to carbon interstitials, silicon vacancies, or anti-site pairs. Full article

Quantum dot light-emitting diodes (QLEDs) based on high-color-purity blue quantum dots (QDs) are crucial for the development of next-generation displays. I-III-VI type QDs have been recognized as eco-friendly luminescent materials for QLED applications due to their tunable band gap and high-stable properties. However, efficient blue-emitting I-III-VI QDs remain rare owing to the high densities of the intrinsic defects and the surface defects. Herein, narrow-band blue-emissive CuAlSe₂/Ga₂S₃/ZnS QDs is synthesized via a facile strategy. The resulting QDs exhibit a sharp blue emission peak at 450 nm with a full width at half maximum (FWHM) of 35 nm, achieved by coating a double-shell structure of Ga₂S₃ and ZnS, which is associated with the near-complete passivation of Cu-related defects (e.g., Cu vacancies) that enhances the band-edge emission, accompanied by an improvment in photoluminescence quantum yield up to 69%. QLEDs based on CuAlSe₂/Ga₂S₃/ZnS QDs are fabricated, exhibiting an electroluminescence peak at 453 nm with a FWHM of 39 nm, a current efficiency of 3.16 cd A⁻¹, and an external quantum efficiency of 0.35%. This research paves the way for the development of high-efficiency eco-friendly blue QLEDs. Full article

Nitrogen-doped graphene has been increasingly utilized in a variety of energy-related applications, serving as a catalyst or support material for fuel cells, and as an anode material for lithium-ion batteries, among others. The thermal reduction of graphene oxide (GO) in nitrogenous sources to incorporate nitrogen, producing nitrogen-doped reduced graphene oxide (NRGO), is the most favored method. Controlling atomic configurations of nitrogen-doped sites is the key factor for tailoring the physico-chemical properties of NRGO, but major challenges remain in identifying detailed atomic arrangements at nitrogen binding sites on highly defective and chemically functionalized GO surfaces. In this paper, we present atomistic-scale modeling of the nitrogen doping process of GO with different types of vacancy defects. Molecular dynamics simulations using a reactive force field indicate that the edge carbon atoms on defect sites are the dominant initiation location for nitrogen doping. Further, first-principles calculations using density functional theory present energetically favorable chemical transition pathways for nitrogen doping. The significance of this work lies in providing important chemical insights for the effective control of the desired properties of NRGO by suggesting a detailed mechanism of the nitrogen doping process of GO. Full article

Nanorods of erbium-doped zinc oxide (ZnO:Er) were fabricated using a hydrothermal method. One batch was prepared with and another one without constant ultraviolet (UV) irradiation applied during the growth. The nanorods were free-standing (FS) as well as deposited onto a fused silica glass substrate (GS). The goal was to study the atomistic aspects influencing the charge transport of ZnO nanoparticles, especially considering the differences between the FS and GS samples. We focused on the excitons; the intrinsic defects, such as zinc interstitials, zinc vacancies, and related shallow donors; and the conduction electrons. UV irradiation was applied for the first time during the ZnO:Er nanorod growth. This led to almost total exciton and zinc vacancy luminescence reduction, and the number of shallow donors was strongly suppressed in the GS samples. The effect was much less pronounced in the FS rods. Moreover, the exciton emission remained unchanged there. At the same time, the Er³⁺ content was decreased in the FS particles grown under constant UV irradiation while Er³⁺ was not detected in the GS particles at all. These phenomena are explained. Full article

Space particle irradiation produces ionization damage and displacement damage in semiconductor devices. The enhanced low dose rate sensitivity (ELDRS) effect caused by ionization damage has attracted wide attention. However, the enhanced low-particle-flux sensitivity effect and its induction mechanism by displacement damage are controversial. In this paper, the enhanced low-neutron-flux sensitivity (ELNFS) effect in Boron-doped silicon and the relationship between the ELNFS effect and doping concentration are further explored. Boron-doped silicon is sensitive to neutron flux and ELNFS effect could be greatly reduced by increasing the doping concentration in the flux range of 5 × 10⁹–5 × 10¹⁰ n cm⁻² s⁻¹. The simulation based on the theory of diffusion-limited reactions indicated that the ELNFS in boron-doped silicon might be caused by the difference in the concentration of remaining vacancy-related defects (V_r) under different neutron fluxes. The ELNFS effect in silicon becomes obvious when the (V_r) is close to the boron doping concentration and decreased with the increase in boron doping concentration due to the remaining vacancy-related defects being covered. These conclusions are confirmed by the p⁺-n-p Si-based bipolar transistors since the ELNFS effect in the low doping silicon increased the reverse leakage of the bipolar transistors and the common-emitter current gain (β) dominated by highly doped silicon remained unchanged with the decrease in the neutron flux. Our work demonstrates that the ELNFS effect in boron-doped silicon can be well explained by noise diagnostic analysis together with electrical methods and simulation, which thus provide the basis for detecting the enhanced low-particle-flux damage effect in other semiconductor materials. Full article