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Quantum Dot-Plasmon Lasing with Controlled Polarization Patterns
摘要： The tailored spatial polarization of coherent light beams is important for applications ranging from microscopy to biophysics to quantum optics. Miniaturized light sources are needed for integrated, on-chip photonic devices with desired vector beams; however, this issue is unresolved because most lasers rely on bulky optical elements to achieve such polarization control. Here, we report on quantum dot-plasmon lasers with engineered polarization patterns controllable by near-field coupling of colloidal quantum dots to metal nanoparticles. Conformal coating of CdSe?CdS core?shell quantum dot films on Ag nanoparticle lattices enables the formation of hybrid waveguide-surface lattice resonance (W-SLR) modes. The sidebands of these hybrid modes at nonzero wavevectors facilitate directional lasing emission with either radial or azimuthal polarization depending on the thickness of the quantum dot film.
关键词： nanolaser,band structure engineering,radially and azimuthally polarization states,surface lattice resonances,colloidal quantum dots,lattice plasmons,waveguide
更新于2025-09-19 17:13:59
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Improving the photovoltaic performance of CdSe0.2S0.8 alloyed quantum dot sensitized solar cells using CdMnSe outer quantum dot
摘要： In this paper, by introducing the Mn-doped CdSe (CdMnSe) layer as outer quantum dot (QD) on ternary CdSe0.2S0.8 QDs surface, we developed an effective way to enhance the power conversion efficiency (PCE) of the CdSexS1-x alloyed quantum dot sensitized solar cells (QDSSCs) when the molar ratio of Se/Na2S·9H2O is 1:4. As a result, a cascade band structure and the midgap states which favorable for electron injection and the hole transport, are obtained when the concentration of Cd2+, Se2+ and Mn2+ ions are 0.5, 0.5 and 0.05 M, respectively, in the CdMnSe outer QD deposited by the successive ionic layer absorption and reaction (SILAR) method with three cycles. Hence, with using polysulfide electrolyte and Cu2S-brass as counter electrode, the measured PCE for the CdSe0.2S0.8/10%CdMnSe QDSSC is 5.420% (Voc = 0.70 V, Jsc = 16.834 mA.cm?2, and FF = 0.460) at AM 1.5G, which is higher than the PCE of 4.327% for the device with bare CdSe0.2S0.8 QDs or a ~25.5% increase. Our findings indicate that such improvement in PCE is caused by the increasing of light-absorption, decrease of the surface roughness, improvement of electrons transfer from QDs to TiO2 CB, reduction of electrons recombination and thereby, the increasing collection of electrons in TiO2 film.
关键词： CdMnSe outer QD,Ternary CdSe0.2S0.8 QDs,Quantum dot sensitized solar cells,Cascade band structure
更新于2025-09-19 17:13:59
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Room-Temperature-Processed Amorphous Sn-In-O Electron Transport Layer for Perovskite Solar Cells
摘要： We report amorphous tin-indium-oxide (TIO, Sn fraction: >50 atomic percentage (at%)) thin films as a new electron transport layer (ETL) of perovskite solar cells (PSCs). TIO thin films with Sn fraction of 52, 77, 83, 92, and 100 at% were grown on crystalline indium-tin-oxide (ITO, Sn fraction: ~10 at%) thin films, a common transparent conducting oxide, by co-sputtering In2O3 and SnO2 at room temperature. The energy band structures of the amorphous TIO thin films were determined from the optical absorbance and the ultraviolet photoelectron spectra. All the examined compositions are characterized by a conduction band edge lying between that of ITO and that of perovskite (here, methylammonium lead triiodide), indicating that TIO is a potentially viable ETL of PSCs. The photovoltaic characteristics of the TIO-based PSCs were evaluated. Owing mainly to the highest fill factor and open circuit voltage, the optimal power conversion efficiency was obtained for the 77 at%-Sn TIO ETL with TiCl4 treatment. The fill factor and the open circuit voltage changes with varying the Sn fraction, despite similar conduction band edges. We attribute these differences to the considerable changes in the electrical resistivity of the TIO ETL. This would have a significant effect on the shunt and/or the series resistances. The TIO ETL can be continuously grown on an ITO TCO in a chamber, as ITO and TIO are composed of identical elements, which would help to reduce production time and costs.
关键词： perovskite solar cell,electron transport layer,electrical property,tin-indium-oxide,band structure,room temperature
更新于2025-09-16 10:30:52
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Theoretical Study of GaN/BP van der Waals Nanocomposites with Strain-Enhanced Electronic and Optical Properties for Optoelectronic Applications
摘要： Construction of van der Waals (vdW) nanocomposites can advance two-dimensional (2D) materials with desired properties and significantly widen their applications. Based on first-principles calculations, we verify that a gallium nitride/boron phosphide (GaN/BP) vdW nanocomposite is a direct-gap semiconductor with type-I band alignment. The nanocomposite shows significant optical properties in the visible and near-ultraviolet regions. Additionally, the bandgap, band edge positions, and optical absorption of the GaN/BP nanocomposite can be tuned by in-plane biaxial strains. A biaxial tensile strain with a strength of 3% can induce the type-II band alignment in the GaN/BP nanocomposite, which results in effective separation of the photo-generated charge carriers. Meanwhile, the application of biaxial strain can also significantly enhance the optical absorption of the GaN/BP nanocomposite in the near-infrared and visible regions. Furthermore, we show that the adjustment of interlayer coupling is also an effective way to modulate the electronic and optical properties of the GaN/BP nanocomposite. Our studies reveal the potential application of the GaN/BP nanocomposite in optoelectronic devices.
关键词： first-principles calculations,optical absorption,strain engineering,band structure,GaN/BP nanocomposite
更新于2025-09-16 10:30:52
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Quantum-chemical calculations on graphitic carbon nitride (g-C3N4) single-layer nanostructures: polymeric slab vs. quantum dot
摘要： Graphitic carbon nitride (g-C3N4) has been the focus of enormous attention in recent years for its fantastic in-plane and surface properties. Several periodic and cluster models of g-C3N4 including a quantum dot have been investigated using density functional theory (DFT) at the HSE06/Def2-TZVP level. The quantum dot with side triazine rings in nearly perpendicular alignment to the central ring was (by 98.40 kcal/mol) more stable than any other cluster, including its planar analogue—a metastable phase of carbon nitride. The g-C3N4 quantum dot showed the largest deviation (3.27 eV, 7.9%) from the bandgap of the polymeric material. On the other hand, the unrelaxed symmetrical cluster had the smallest deviation (+ 0.03 eV, 1.0%) from the reference bandgap (and also in terms of global hardness), indicating that it could be taken as a replacement cluster for modeling of a polymeric surface in such explorations. The plots of the density of states (DOS) revealed the inherent instabilities of the planar models compared to the quantum dot. Furthermore, the g-C3N4 quantum dot showed the highest chemical hardness among the models investigated. The electronic band structures of the g-C3N4 quantum dot implied its relatively better photoabsorption ability referenced to the polymeric surface. However, the structural changes had significant effects on the orbital and charge distributions in the C3N4 models.
关键词： Semiconductor,Graphitic carbon nitride,Band structure,Sensor,DFT,Quantum dot
更新于2025-09-16 10:30:52
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Engineering Directionality in Quantum Dot Shell Lasing Using Plasmonic Lattices
摘要： We report how the direction of quantum dot (QD) lasing can be engineered by exploiting high-symmetry points in plasmonic nanoparticle (NP) lattices. The nanolaser architecture consists of CdSe?CdS core?shell QD layers conformally coated on two-dimensional square arrays of Ag NPs. Using waveguide-surface lattice resonances (W-SLRs) near the Δ point in the Brillouin zone as optical feedback, we achieved lasing from the gain in CdS shells at off-normal emission angles. Changing the periodicity of the plasmonic lattices enables other high-symmetry points (Γ or M) of the lattice to overlap with the QD shell emission, which facilitates tuning of the lasing direction. We also increased the thickness of the QD layer to introduce higher-order W-SLR modes with additional avoided crossings in the band structure, which expands the selection of cavity modes for any desired lasing emission angle.
关键词： band structure engineering,laser directionality,surface lattice resonances,colloidal quantum dots,lattice plasmons,waveguide
更新于2025-09-16 10:30:52
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Hot carrier dynamics in a dispersionless plasmonic system
摘要： Hot carrier dynamics in a broadband, dispersionless, plasmonic structure are studied using pump-probe measurements with 45 fs time resolution. The results obtained by simultaneous measurement of differential transmittance and reflectance show the influence of pump generated carriers on the probe generated plasmons. The dependence of decay time on the pump fluence is linear for the interband and intraband carrier excitation near the L-symmetry point in gold. However, 1.908 eV pump excitation, which allows both interband transition at the X-symmetry point and intraband excitation at the L-symmetry point, shows quadratic dependence of decay time on the pump fluence. Degenerate pump-probe measurements at 1.55 eV, which allow L-valley intraband excitations, highlight the difference in surface (reflection) and the bulk (transmission) mechanisms. Hot carrier relaxation time is in the 1–3 ps range for different excitation energies. Rise time, governed by the plasmon to hot carrier conversion and electron-electron scattering processes, is about 200 ± 35 fs for the hot carrier and hot plasmon excitation cases that increased to about 485 ± 35 fs when the pump is resonant with the interband transition at the X-symmetry point. Results show that the hot carrier dynamics are governed by the bulk metal band structure. The dipole matrix element for each of the transitions is estimated by density matrix calculations.
关键词： pump-probe measurements,gold band structure,differential transmittance,reflectance,plasmonic system,hot carrier dynamics
更新于2025-09-12 10:27:22
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Interfacial charge dynamics of cross-linked polyethylene/ethylene-propylene-diene dual dielectric polymer as revealed by energy band structure
摘要： The discontinuous charge relaxation time related to the electrical conductivity and permittivity, i.e., traditional Maxwell-Wagner relaxation, is the prevailing explanation for the interfacial charge behavior in multi-layered dielectrics. However, the unipolar/bipolar charge dynamics and the corresponding mechanisms from a microscopic viewpoint remain unclear. This work focuses on the dynamics of the interfacial charges in cross-linked polyethylene (XLPE)/ethylene-propylene-diene (EPDM) dual layers to reveal the interfacial charge mechanisms using the energy band structure. The interfacial charge accumulation behavior of the XLPE/EPDM dual- layered structures is clearly observed under electrical stress. Either unipolar or bipolar charges occur at the interface, accompanied by charge injection, and trapping then occurs. The positive charges prefer to accumulate and migrate on the XLPE side. The homo-charges at the interface always remain on the EPDM side. The number of negative charges is higher than the number of positive charges at the interface. The bipolar interfacial charges are ascribed to the charge transfer process that occurs at the interface because of the energy level alignment that is revealed by the electronic energy structures of XLPE and EPDM. The trapping sites, along with the charge injection and transport, contribute to the interfacial charge behavior.
关键词： energy level,interface,trapping site,space charge,energy band structure
更新于2025-09-12 10:27:22
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Complex- <i>k</i> modes of plasmonic chain waveguides
摘要： Nanoparticle chain waveguide based on negative-epsilon material is investigated through a generic 3D finite-element Bloch-mode solver which derives complex propagation constant (k). Our study starts from waveguides made of non-dispersive material, which not only singles out ‘waveguide dispersion’ but also motivates search of new materials to achieve guidance at unconventional wavelengths. Performances of gold or silver chain waveguides are then evaluated; a concise comparison of these two types of chain waveguides has been previously missing. Beyond these singly-plasmonic chain waveguides, we examine a hetero-plasmonic chain system with interlacing gold and silver particles, inspired by a recent proposal; the claimed enhanced energy transfer between gold particles appears to be a one-sided view of its hybridized waveguiding behavior—energy transfer between silver particles worsens. Enabled by the versatile numerical method, we also discuss effects of inter-particle spacing, background medium, and presence of a substrate. Our extensive analyses show that the general route for reducing propagation loss of e.g. a gold chain waveguide is to lower chain-mode frequency with a proper geometry (e.g. smaller particle spacing) and background material setting (e.g. high-permittivity background or even foreign nanoparticles). In addition, the possibility of building mid-infrared chain waveguides using doped silicon is commented based on numerical simulation.
关键词： plasmonics,periodic structure,computational electromagnetics,waveguide,photonic band structure,finite-element simulation
更新于2025-09-11 14:15:04
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Graphene Quantum Dots Band Structure Tuned by Size for Efficient Organic Solar Cells
摘要： The electronic states of graphene quantum dots (GQDs) can be tuned by varying the lateral size and edge structure, which further influence their optoelectronic properties and the applications. In the work, three kinds of GQDs with different lateral size were prepared by photon-Fenton reaction and separated through gel column chromatography, and their effects on the photovoltaic performances of inverted organic solar cells based on the poly(3-hexylthiophene) (P3HT) and poly(3-hexylthiophene)/(6,6)-phenyl-C61 butyric acid methylester (PCBM) blend films were studied systematically. In comparing with P3HT:PCBM cells, the power conversion efficiency of the P3HT:PCBM solar cells containing 0.8% of GQDs-blue, GQDs-green, and GQDs-orange can be increased from 3.06 to 3.54, 4.43, and 3.73 % with a short-circuit current density of 10.3, 13.34, and 11.19 mA cm-2. It is illustrated also that the band structures (electronic energy states) tuned mainly by their lateral size of GQDs are the crucial factor to dominate their photovoltaic preferences as additives in conventional P3HT:PCBM solar cells.
关键词： power conversion efficiency,band structure,organic solar cells,graphene quantum dots
更新于2025-09-11 14:15:04