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Thickness-dependent photoelectric properties of MoS2/Si heterostructure solar cells
摘要： In order to obtain the optimal photoelectric properties of vertical stacked MoS2/Si heterostructure solar cells, we propose a theoretical model to address the relationship among film thickness, atomic bond identities and related physical quantities in terms of bond relaxation mechanism and detailed balance principle. We find that the vertical stacked MoS2/Si can form type ii band alignment, and its photoelectric conversion efficiency (PCE) enhances with increasing MoS2 thickness. Moreover, the optimal pce in MoS2/Si can reach 24.76%, inferring that a possible design way can be achieved based on the layered transition metal dichalcogenides and silicon.
关键词： detailed balance principle,photoelectric properties,bond relaxation mechanism,solar cells,MoS2/Si heterostructure
更新于2025-09-11 14:15:04
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Transport in armchair graphene nanoribbons and in ordinary waveguides
摘要： We study dc and ac transport along armchair graphene nanoribbons using the k (cid:1) p spectrum and eigenfunctions and general linear-response expressions for the conductivities. Then, we contrast the results with those for transport along ordinary waveguides. In all cases, we assess the influence of elastic scattering by impurities, describe it quantitatively with a Drude-type contribution to the current previously not reported, and evaluate the corresponding relaxation time for long- and short-range impurity potentials. We show that this contribution dominates the response at very low frequencies. In both cases, the conductivities increase with the electron density and show cusps when new subbands start being occupied. As functions of the frequency, the conductivities in armchair graphene nanoribbons exhibit a much richer peak structure than in ordinary waveguides: in the former, intraband and interband transitions are allowed, whereas in the latter, only the intraband ones occur. This difference can be traced to that between the corresponding spectra and eigenfunctions.
关键词： transport,elastic scattering,armchair graphene nanoribbons,intraband and interband transitions,conductivities,relaxation time,Drude-type contribution
更新于2025-09-11 14:15:04
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Fast Electron and Slow Hole Relaxation in InP-Based Colloidal Quantum Dots
摘要： Colloidal InP-based quantum dots are a promising material for light-emitting applications as an environment friendly alternative to their Cd-containing counterparts. Especially for their use in optoelectronic devices, it is essential to understand how charge carriers relax to the emitting state after injection with excess energy and if all of them arrive at this desired state. Herein, we report on time-resolved differential transmission measurements on colloidal InP/ZnS and InP/ZnSe core/shell quantum dots. By optically exciting and probing individual transitions, we are able to distinguish between electron and hole relaxation. This in turn allows us to determine how the initial excess energy of the charge carriers affects the relaxation processes. According to the electronic level scheme, one expects a strong phonon bottleneck for electrons, while holes should relax easier as their energy levels are more closely spaced. On the contrary, we find that electrons relax faster than holes. The fast electron relaxation occurs via an efficient Auger-like electron-hole scattering mechanism. On the other hand, a small wave function overlap between core and shell states slows the hole relaxation down. Additionally, holes can be trapped at the core/shell interface leading to either slow detrapping or nonradiative recombination. Overall, these results demonstrate that it is crucial to construct devices enabling the injection of charge carriers energetically close to their emitting states in order to maximize the radiative efficiency of the system.
关键词： InP,differential transmission spectroscopy,phonon bottleneck,charge carrier relaxation,trap states,electron-hole scattering,colloidal quantum dots
更新于2025-09-11 14:15:04
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Spontaneous Enhancement of the Stable Power Conversion Efficiency in Perovskite Solar Cells
摘要： The power conversion efficiency (PCE) of lead-halide perovskite solar cells (PSCs) is reported to increase over a period of days after their fabrication while they are stored in dark. Thus far, effects underlying this spontaneous enhancement are not understood. This work investigates the phenomenon for a variety of multi-cation-halide PSCs with different perovskite compositions and architectures. The observations reveal that spontaneous enhancement is not restricted to specific charge-transport layers or perovskite compositions. The highest PCE observed in this study is the enhanced stable PCE of 19% (increased by 4% absolute). An increased open-circuit voltage is the primary contributor to the improved efficiency. Using time-resolved photoluminescence measurements, initially-present low-energy states are identified that disappear over a storage period of a few days. Furthermore, trap states probed by thermally stimulated current technique exist in pristine PSCs and strikingly decrease for stored devices. In addition, ideality factor approaches unity and X-ray diffraction analyses show a lattice strain relaxation over the same period of time. These observations indicate that spontaneous enhancement of the PSCs is based on a reduction in trap-assisted non-radiative recombination possibly due to strain relaxation. Considering the demonstrated generality of spontaneous enhancement for different compositions of multi-cation-halide PSCs, our results highlight the importance of determining absolute PCE increase initiated by spontaneous enhancement for developing high-efficiency PSCs.
关键词： spontaneous enhancement,perovskite solar cells,power conversion efficiency,trap states,strain relaxation
更新于2025-09-11 14:15:04
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[IEEE 2018 IEEE 8th International Conference Nanomaterials: Application & Properties (NAP) - Zatoka, Ukraine (2018.9.9-2018.9.14)] 2018 IEEE 8th International Conference Nanomaterials: Application & Properties (NAP) - Theoretical Model of the Processes of Nanostructuring the Material Surface under the Influence of Laser Radiation
摘要： The transition between different structural states of a surface of a solid after influence of laser radiation can be presented by the self-consistent behavior of three parameters: the relaxation field, the fields of stress and the concentration of relaxation zones. Within the framework of the Lorentz system, the transition between stable states of formations on the surface of a solid was presented. The dependence of the stationary value of the order parameter, at which the formation of relaxation zones is possible, was obtained. The intermittent version of the formation of relaxation zones was examined using the mechanism of first order phase transition.
关键词： phase transition,nanostructure,residual deformation,relaxation parameter
更新于2025-09-11 14:15:04
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AIP Conference Proceedings [AIP Publishing PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS: ICAM 2019 - Kerala, India (12–14 June 2019)] PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON ADVANCED MATERIALS: ICAM 2019 - Insulator to semiconductor transition in graphene quantum dots
摘要： Zero dimensional graphene quantum dots (GQDs) exhibit interesting physical and chemical properties due to the edge effect and quantum confinement. As the number of carbon atoms in edge is more than on basal plane, GQDs are more reactive. Room temperature XRD pattern confirms the formation of the GQDs. UV-Visible spectra confirm that GQDs show optical absorption in the visible region. The emission peaks in the photoluminescence spectra are red shifted with the increase of excitation wavelength. Dynamic light scattering (DLS) analysis shows that the average size of the particles is found to be ~65 nm. The frequency dependent electrical transport properties of the GQDs are investigated in a temperature range from 300 to 500 K. Most interestingly, for the first time, the insulator to semiconductor transition of GQD is observed near 400K. The transition mechanism of GQD is discussed with detailed dielectric analysis. The effects of intercalated water on temperature dependent conductivity are clearly discussed. The dielectric relaxation mechanism is explained in the framework of permittivity, conductivity and impedance formalisms. The frequency dependent ac conductivity spectra follows the Jonscher's universal power law. Cole-Cole model is used to investigate the dielectric relaxation mechanism in the sample.
关键词： Graphene Quantum Dots,Insulator to Semiconductor Transition,Dynamic Light Scattering,Dielectric Relaxation,Photoluminescence
更新于2025-09-11 14:15:04
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Effect of High Pressure in the Luminescence of Pr <sup>3+</sup> Doped Ge <sub/>2</sub> O- PbO Glass Containing Au Nanoparticles
摘要： In this paper it was investigated the combined effect of gold nanoparticles and high-pressure densification on the luminescence of Pr3+ doped heavy metal GeO2-PbO photonic glass. Localized states related to ion-trapped exciton defects, S1 and S2, were observed at 342 and 412 nm before densification. After densification under 7.7 GPa the structure of the glass host changed irreversibly, as indicated by the infrared spectrum, refractive index and density measurements. TEM analyses indicated that the high-pressure densification induced the formation of clusters of gold nanoparticles. The modifications observed in the absorption and luminescence spectra of Pr3+ ions in the VIS-NIR range were associated to the changes in the local field surrounding the Pr3+ ions in the host glass induced by high-pressure. For excitation at 445 nm (luminescence from 3P2) and 593 nm (luminescence from 1D2), the combined effect of densification and gold nanoparticles induced an increase in the emission band at 1050 cm-1. For excitation at 488 nm (luminescence from 3P0), the combined effect resulted in a strong decrease in the emission intensities in the VIS, revealing the emergence of non-radiative processes in resonance with 3P0 state. The observed behavior was probably due to energy transfer, ion trapped exciton defects and cross-relaxation processes among the Pr3+ ions and gold nanoparticles.
关键词： cross-relaxation processes,gold nanoparticles,Pr3+ doped,high-pressure densification,energy transfer,GeO2-PbO glass,luminescence
更新于2025-09-11 14:15:04
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Photoexcitation Dynamics of Thiocyanate-Bound Heme Proteins Using Femtosecond Infrared Spectroscopy
摘要： Myoglobin (Mb) and hemoglobin (Hb) have been used as model systems to understand the relationships between protein function, structure, and dynamics. These studies have primarily been carried out by observing the (re)binding between ferrous heme proteins and neutral ligands. Ferric heme proteins also bind to various anionic ligands, such as CN?, N3?, OCN?, and SCN?. Only a few anion-bound ferric heme proteins have been investigated for ligand-binding dynamics.1–4 Although CN?-bound Mb (MbCN) was reported to be photostable, i.e., not photodeligated by a visible photon, recent study using Raman spectroscopy claimed a photodeligation quantum yield for MbCN of 0.75.5 Thus, the photostability of ?-bound MbCN is still in question. At room temperature, N3?-bound Mb (MbN3) exists in both high spin (HS) and low spin (LS) complexes. When MbN3 absorbs a visible photon, the ligand is not dissociated; instead the excited MbN3 undergoes a thermal relaxation process involving a spin transition.3 Recently, we have shown that photoexcited OCN?-bound Mb and OCN?-bound Hb are also photostable, losing their excess energy via thermal relaxation after rapid electronic relaxation.4 Here, to determine the general excitation properties of anion-bound heme proteins after absorption of a visible photon, we have extended our study of photoexcitation dynamics to SCN?-bound ferric Mb (MbNCS) and Hb (HbNCS).
关键词： Femtosecond vibrational spectroscopy,Thiocyanate-bound myoglobin,Electronic relaxation,Ferric heme proteins,Thermal relaxation
更新于2025-09-10 09:29:36
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[IEEE IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Valencia, Spain (2018.7.22-2018.7.27)] IGARSS 2018 - 2018 IEEE International Geoscience and Remote Sensing Symposium - Non-Convex Low-Rank Approximation for Hyperspectral Image Recovery with Weighted Total Varaition Regularization
摘要： Low-rank representation has been widely used as a powerful tool in hyperspectral image (HSI) recovery. The existing studies involving low-rank problems are commonly under the nuclear norm penalization. However, nuclear norm minimization tends to over-shrink the components of rank, which leads to modeling bias. In this paper, a new non-convex penalty is introduced to obtain an unbiased low-rank approximation. In Addition, local spatial neighborhood weighted spectral-spatial total variation (TV) regularization is introduced to preserve spatial structural information. And sparse 1l-norm is used as a constraint to sparse noise. Finally, a novel HSI non-convex low-rank relaxation restoration model is proposed. A number of experiments show that the proposed method can effectively remove the mixed-noise, and result in an unbiased estimate with better robustness.
关键词： Hyperspectral image(HSI),total variation(TV),low-rank representation,non-convex relaxation
更新于2025-09-10 09:29:36
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Investigations of dual-frequency nematic liquid crystals doped with dichroic dye
摘要： In this work, we studied and analysed a particular variety of liquid crystals, the so-called dual-frequency nematic liquid crystals (DFNLCs). The interest was to perform dielectric spectroscopy and optical characterisation with two pure and doped mixtures of DFNLCs. By means the dielectric spectroscopy we observed a low value of crossover frequency at room temperature for one dye doped mixture. Additionally, in the spectra studies, a scattering of light at cross-frequency, and a stable and unstable focal conical state was observed, respectively, for the investigated mixtures.
关键词： relaxation frequency,crossover frequency,dielectric spectroscopy,optical characterisation,Dual-frequency liquid crystal
更新于2025-09-10 09:29:36