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Superior light harnessing and charge injection kinetics utilizing mirror-like nano cuboidal ceria coupled with reduced graphene oxide in zinc oxide nanoparticle based photovoltaics
摘要： Efficiency in nanoparticle based photovoltaics is limited by optical transparency, light absorption as well as detrimental back transfer of electron at the hetero-interfaces. Three dimensional (3D) micro/nanostructures with excellent light scattering properties play pivotal role in light harvesting efficiency in DSSCs. Present study deals with the design and development of ternary hybrid photoanode utilizing high quality mirror like nano-cuboidal ceria (CeO2 NC) and 2D- reduced graphene oxide (RGO) sheets in conjunction with ZnO nanoparticle. A ～6% power conversion efficiency has been achieved for photoanode with optimized CeO2 NC loaded with 1 wt% RGO into ZnO NP. CeO2 NC owing to its size and high quality mirror like facets provides a better light harvesting by multiple interactions of incident photon with the absorber as revealed by UV–Vis diffused reflectance and IPCE analysis. 2D- RGO is proposed to act as an electron sink and provides faster electron transport pathway. Inclusion of 2D- RGO sheets yields a better charge injection kinetics (keinj ～ 2.3 × 108 s?1 for ternary, 1.1 × 108 s?1 for reference device) and collection at FTO as well as elevated recombination resistance (Rrec) and photo-induced electron life time (τe), unveiled by Electrochemical Impedance Spectroscopic (EIS) analysis corroborates a reduced reverse tunneling of photo-injected electron at ZnO/sensitizer/redox couple interface.
关键词： Diffusion,Mirror-like,Light scattering material,Reduced graphene oxide,Electrochemical impedance spectroscopy,Nano cuboidal
更新于2025-11-21 11:01:37
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Diffusion Behavior of Differently Charged Molecules in Self-Assembled Organic Nanotubes Studied Using Imaging Fluorescence Correlation Spectroscopy
摘要： The diffusion behavior of fluorescent molecules within bolaamphiphile-based organic nanotubes (ONTs) was systematically investigated using imaging fluorescence correlation spectroscopy (imaging FCS). Anionic sulforhodamine B (SRB), zwitterionic/cationic rhodamine B (RB) or cationic rhodamine 123 (R123) was loaded into ONTs having cylindrical hollow structures (ca. 10 nm in inner diameter) with amine and glucose groups on the inner and outer surfaces, respectively. Wide-field fluorescence video microscopy was used to acquire imaging FCS data for dye-doped ONTs in aqueous solutions of different ionic strengths (1 – 500 mM) at different pH (3.4 – 8.4). The diffusion behavior of these dyes was discussed on the basis of their apparent diffusion coefficients (D) that were determined by autocorrelating the time transient of fluorescence intensity at each pixel on an ONT. Molecular diffusion in the ONTs was significantly slowed by molecule-nanotube interactions, as shown by the very small D (10-1 – 10-2 μm2/s). The pH-dependence of D revealed that dye diffusion was basically controlled by electrostatic interactions associated with the protonation of the amine groups on the ONT inner surface. The pH-dependent change in D was observed over a wide pH range, possibly due to electrostatically induced variations in the pKa of the densely packed ammonium ions on the ONT inner surface. On the other hand, the influence of ionic strength on D was relatively unclear, suggesting the involvement of non-coulombic interactions with the ONTs in molecular diffusion. Importantly, individual ONTs of different lengths (1 – 5 μm) afforded similar diffusion coefficients for each type of dye at each solution condition, implying that the properties of ONTs were uniform in terms of solute loading and release. These results highlight the characteristics of molecular diffusion behavior within the ONTs, and will help in the design of organic nanotubes better suited for use as drug vehicles and contaminant adsorbents.
关键词： Electrostatic Interactions,Diffusion Behavior,Ionic Strength,pH-dependence,Imaging Fluorescence Correlation Spectroscopy,Organic Nanotubes
更新于2025-11-19 16:56:42
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Controllable preparation of phase-separated Pb/Zn heterogeneous nanoparticles by laser ablation and their application in the growth of PbS tipped ZnS nanorods heterostructures
摘要： Phase-separated Pb/Zn heterogeneous nanoparticles (Pb/Zn HNPs) with a controllable phase ratio were firstly prepared by long-pulse-width millisecond laser ablation of Pb/Zn binary metal target immersed in anhydrous ethanol under room conditions. The phase ratio in the as-ablated Pb/Zn HNPs was mainly determined by the molar ratio of Pb/Zn in the initial binary metal target and the structure of Pb/Zn HNPs was partly influenced by the pulse laser width. Then the PBS tipped ZnS nanorods heterostructures (PbS/ZnS heterostructures) were grown by simply heating the mixture of the as-ablated Pb/Zn HNPs and thioacetamide (TAA) at 450 (cid:1)C in a tube furnace. The size and morphology of Pbs/ZnS heterostructures were decided by the original absolute size and relative size between phase-separated Pb and Zn nanoparticle. The formation of Pbs/ZnS heterostructures was the result of the diffusion-limited of S atoms in the Pb/Zn HNPs. This study not only provides a new strategy for the controllable preparation of phase-separated bimetallic nanoparticles that can be used for the growth of specific heterostructures but a new view on the fundamental physical and chemical aspects of nanocrystal formation after laser ablation of solids in liquids.
关键词： Heterostructure,Phase-separated,Heterogeneous nanoparticles,Laser ablation,Binary metal target,Diffusion-limited
更新于2025-11-14 17:04:02
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Luminescent Composites Based on Tetrafluoroethylene Copolymer Porous Films Produced by the Diffusion Embedding of Semiconductor Nanoparticles in a Supercritical Medium
摘要： A method for creating film composites based on a new material—a fibrous copolymer of tetrafluoroethylene and vinylidene fluoride—using the diffusion embedding of ready-made nanoparticles into a porous matrix in a supercritical (SC) carbon dioxide medium is developed. The method of cold or hot pressing of impregnated porous films was used at the final stage of creation of such composites. The peculiarities of the effect of the supercritical fluid treatment of porous copolymer films on the surface structure of pressed films are discussed. Luminescent composites with semiconductor nanoparticles of cadmium selenide and nanocrystalline silicon are obtained; their radiation covers a range of 500–1000 nm. The change in the luminescence properties of the resulting nanocomposites under the action of excitation laser radiation at 405 nm is demonstrated.
关键词： cadmium selenide,film composite,fibrous matrix,luminescent properties,diffusion embedding,nanocrystalline silicon
更新于2025-11-14 15:30:11
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Effect of exciton diffusion on the triplet-triplet annihilation rate in organic semiconductor host-guest systems
摘要： We study the contribution of triplet exciton diffusion to the efficiency loss resulting from F?rster-type triplet-triplet annihilation (TTA) in organic phosphorescent semiconductor host-guest systems, using kinetic Monte Carlo (KMC) simulations. Our study focusses on diffusion due to F?rster-type guest-guest transfer, but includes also a comparison with simulation results for the case of Dexter-type guest-guest transfer. The simulations are carried out for a wide range of F?rster radii, and for guest concentrations up to 100 mol%, with the purpose to support analyses of time-resolved photoluminescence experiments probing TTA. We find that the relative contribution of diffusion to the TTA-induced efficiency loss may be deduced quite accurately from a quantitative experimental measure for the shape of the time-dependent photoluminescence intensity, the so-called r ratio. For small guest concentrations and F?rster radii that are most relevant to organic light-emitting diodes (OLEDs), the diffusion contribution is in general quite small. Under these weak-diffusion conditions, the absolute diffusion contribution to the TTA-induced efficiency loss can be understood quantitatively using a capture radius formalism. The effective guest-guest diffusion coefficient that follows from the TTA simulations, using the capture radius formalism, agrees well with the diffusion coefficient that follows from direct KMC diffusion simulations. The simulations reveal that the diffusion coefficient is strongly affected by the randomness of the distribution of guest molecule locations.
关键词： OLEDs,photoluminescence,kinetic Monte Carlo simulations,Dexter transfer,organic semiconductors,triplet-triplet annihilation,exciton diffusion,host-guest systems,F?rster transfer
更新于2025-09-23 15:23:52
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Tailoring metal film texture by use of high atomic mobility at metal-semiconductor interfaces
摘要： The difference in the microstructural and texture evolution of Al films grown on amorphous SiO2 (a-SiO2) and amorphous Ge (a-Ge) substrates have been investigated. Surprisingly, the a-Ge substrate was found to change the preferred orientation of Al grains from the conventional (1 1 1) to the unconventional (1 1 0). The effect of the high mobility of Ge atoms at the metal-semiconductor interface on the microstructural and texture evolution of the metal thin film was studied. The diffusion of the Al adatoms on the a-Ge substrate was suppressed owing to the segregation of Ge atoms at the film surface. The mobility of Al grain boundaries was also suppressed because of grain-boundary wetting by the Ge atoms. It is concluded that the a-Ge substrate could tailor the Al grain orientation from (1 1 1) to (1 1 0) owing to the change in the film-growth mode from three-dimensional to two-dimensional nucleation. The concept of interaction-induced island-growth model, which is based on the Volmer–Weber growth model, is also discussed here. This work thus demonstrates how the atomic mobility at the interface of the metal thin film and the semiconductor substrate controls the film microstructure and texture during deposition.
关键词： Substrate,Microstructure,Surface diffusion,Texture,Metal thin film,Grain-boundary wetting
更新于2025-09-23 15:23:52
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Diffusion of Ar atoms implanted in a TiO2 matrix studied with Temperature Programmed Out-Diffusion?
摘要： The diffusion of noble gas argon in the near-surface region of rutile TiO2 has been explored with the Temperature Programmed Out-Diffusion (TPOD) method. The Ar atoms were deposited in a several-nanometer-deep layer of the single-crystal TiO2(110) surface by bombardment with 1–5 keV energy Ar ions. Subsequently, in the TPOD experiments this sample was heated at a linear rate and the out-diffusion of argon was monitored with a mass-spectrometer. Surface conditions were probed with Auger Electron Spectroscopy (AES) and Low-Energy Electron Diffraction (LEED). The experimental results were analyzed with the aid of numerical simulations. The measurements showed a dependence of the Ar diffusion rates on the concentration of buried argon and composition of the surface layer. The kinetic parameters of Ar diffusion in pristine rutile TiO2 were estimated as Ea = 104 kJ/mol and D0 = 6 ? 10?9 m2/s. A distinctive diffusion regime, related to the rock salt TiO phase formation, were identified.
关键词： Sputtering,TiO2,Low-energy ion implantation,Solid diffusion,Ar
更新于2025-09-23 15:23:52
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Uniform-in-time bounds for approximate solutions of the drift–diffusion system
摘要： In this paper, we consider a numerical approximation of the Van Roosbroeck’s drift–diffusion system given by a backward Euler in time and finite volume in space discretization, with Scharfetter–Gummel fluxes. We first propose a proof of existence of a solution to the scheme which does not require any assumption on the time step. The result relies on the application of a topological degree argument which is based on the positivity and on uniform-in-time upper bounds of the approximate densities. Secondly, we establish uniform-in-time lower bounds satisfied by the approximate densities. These uniform-in-time upper and lower bounds ensure the exponential decay of the scheme towards the thermal equilibrium as shown in Bessemoulin-Chatard (Numer Math 25(3):147–168, 2016).
关键词： Finite volume method,Uniform-in-time bounds,Scharfetter–Gummel scheme,Drift–diffusion system,Numerical analysis
更新于2025-09-23 15:23:52
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Optical-property coefficient estimation of bulky medium in experiments with a succinctly analytical calculation
摘要： Diffuse optical imaging enables to reconstruct distribution of optical properties, absorption and scattering coefficients, in tissue for breast cancer detection based on diffusion equation with the help of the initial guess obtained from measured data. To estimate the initial guess of the optical-property coefficients, an analytical solution of diffusion equation can be used and compared with the measured data. The analytical solution for a homogeneous infinite medium can be obtained in the frequency domain, expressing that the photon intensity and the phase lag relative to the distance between source and detector in a linear relationship. In this study, a succinct calculation using the trigonometric relation is proposed to estimate the optical-property coefficients. A tank-type and a cylinder Lipovenoes phantoms with two concentrations of 1.25% and 2.5% are employed and measured for verification. It is found that the method proposed here shows better results and results in estimation errors of 0–14.81% for μa and 20–42% for μs′.
关键词： Diffusion equation,Photo-density wave experiment,Optical-property coefficients
更新于2025-09-23 15:23:52
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Effect of monatomic and molecular ion irradiation on time resolved photoluminescence decay in GaN
摘要： Optical effects induced in silicon-doped wurtzite (0001) GaN epilayers by keV monatomic and molecular ion irradiation were experimentally investigated. Results were analyzed together with data on structure defect formation. In all the cases under consideration, an increase in the collision cascade density (the cases of molecular and heavy atomic ion bombardment) enhances the stable damage accumulation rate and, accordingly, intensifies quenching of luminescence. The processes of PL suppression were theoretically considered as an increase of surface recombination rate of nonequilibrium photo-excited charge carriers due to production of stable damage at the irradiated subsurface layer. It is shown that carrier diffusion determines PL decay time shortening in the shallow implantation cases studied.
关键词： Radiation damage,Photoluminescence,Collision cascade density,Time-resolved PL,Charge carrier diffusion,Ion implantation,GaN
更新于2025-09-23 15:23:52