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Photovoltaic Effect Related to Methylammonium Cation Orientation and Carrier Transport Properties in High-Performance Perovskite Solar Cells
摘要： Solar cells based on organic-inorganic hybrid halide perovskites (OIHHP) have been widely studied due to their increasing power conversion efficiency (PCE). Extensive research has been conducted in electrical, optical properties and device fabrication. However, in terms of material science, the photovoltaic effects of OIHHP are still not well understood. Here, we theoretically investigate the photovoltaic phenomena of MAPbI3 (MA=CH3NH3+) under standard AM 1.5G sunlight illumination, considering the MA cation orientation, light incident angle, polarization and photon energy, using Keldysh non-equilibrium Green’s function formalism combined with density functional theory calculations. It is found that the short-circuit current density Jsc has a maximum value of 383.149 A/m2 when the MA orientation is parallel to the transport direction, whereas it is negligible when the MA orientation is orthogonal to the transport direction. In addition, full consideration is also given to the direction of incidence of sunlight and its polarization state. Nevertheless, of all factors considered, MA orientation plays the decisive role, for Jsc still has a respectable value of 364.112 A/m2 even for a 90-degree sunlight incident angle relative to the transport direction, so long as the MAs are aligned in the transport direction. The increase in the photocurrent is attributed to an increase in the transmission coefficient of low-energy holes, as well as improvement of the velocities and mobilities of electrons and holes in MAPbI3-based device with [001] MA orientation. The results suggest that the design of high-performance OIHHP-based solar cells and photoelectronic devices should carefully consider the crystal orientation and MA cation orientation relative to the transport direction as they directly affect carriers transport properties.
关键词： photon energy,polarization angle,cation orientation,transport properties,photocurrent,incident angle
更新于2025-09-12 10:27:22
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Single atom laser in normal-superconductor quantum dots
摘要： We study a single-level quantum dot strongly coupled to a superconducting lead and tunnel coupled to a normal electrode which can exchange energy with a single-mode resonator. We show that such a system implements a single atom laser. We employ both a semiclassical treatment and a quantum master-equation approach to characterize the properties of this laser. In particular, we ?nd that this system can be operated with ef?ciency approaching unity; that is, a single photon is emitted into the cavity for every Cooper pair participating in the charge current. We ?nd also that lasing in the proposed setup is clearly identi?able in the transport properties: in the lasing state, the electrical current through the quantum dot is pinned to the maximum value achievable in this hybrid nanostructure, and hence, the onset of lasing can be detected simply by a current measurement.
关键词： semiclassical treatment,quantum dot,Cooper pair,transport properties,superconducting lead,charge current,single atom laser,quantum master-equation approach,single-mode resonator,normal electrode
更新于2025-09-12 10:27:22
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Effect of confinement potential shape on the electronic, thermodynamic, magnetic and transport properties of a GaAs quantum dot at finite temperature
摘要： The effect of the shape of the confinement potential on the electronic, thermodynamic, magnetic and transport properties of a GaAs quantum dot is studied using the power-exponential potential model with steepness parameter p. The average energy, heat capacity, magnetic susceptibility and persistent current are calculated using the canonical ensemble approach at low temperature. It is shown that for soft confinement, the average energy depends strongly on p while it is almost independent of p for hard confinement. The heat capacity is found to be independent of the shape and depth of the confinement potential at low temperatures and for the magnetic field considered. It is shown that the system undergoes a paramagnetic-diamagnetic transition at a critical value of the magnetic field. It is furthermore shown that for low values of the potential depth, the system is always diamagnetic irrespective of the shape of the potential if the magnetic field exceeds a certain value. For a range of the magnetic field, there exists a window of p values in which a re-entrant behavior into the diamagnetic phase can occur. Finally, it is shown that the persistent current in the present quantum dot is diamagnetic in nature and its magnitude increases with the depth of the dot potential but is independent of p for the parameters considered.
关键词： transport properties,thermodynamic properties,canonical ensemble approach,electronic properties,quantum dot,GaAs,paramagnetic-diamagnetic transition,persistent current,magnetic properties,power-exponential potential model,confinement potential
更新于2025-09-11 14:15:04
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[IEEE 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Ottawa, ON, Canada (2019.7.8-2019.7.12)] 2019 International Conference on Numerical Simulation of Optoelectronic Devices (NUSOD) - Atomistic analysis of transport properties of InGaN/GaN multi-quantum well
摘要： We present an atomistic analysis of transport properties of an InGaN/GaN multi-quantum well system. Our study is carried out in the combined frame of tight-binding and Non-Equilibrium Green’s Function theories. In our fully three-dimensional treatment, special attention is paid to the impact of random alloy ?uctuations on the electron transmission probability. The calculations reveal that the alloy microstructure signi?cantly impacts the transmission at least for the energetically lowest bound states in the quantum wells.
关键词： InGaN,atomistic description,quantum wells,transport properties
更新于2025-09-11 14:15:04
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Development of solid polymer electrolytes based on sodium-carboxymethylcellulose (NaCMC)-polysulphide for quantum dot-sensitized solar cells (QDSSCs)
摘要： Sodium-carboxymethylcellulose (NaCMC) films have been developed by solution casting technique. The films were soaked into an optimized aqueous polysulphide electrolyte containing 4 M sodium sulphide (Na2S) and 1 M sulphur (S). The optimized aqueous polysulphide electrolyte has the ambient conductivity of (1.46 ± 0.02) × 10-1 S cm-1. The NaCMC films were soaked for different durations of 30, 60, 68 and 75 s. The highest room temperature ionic conductivity (RTIC) of (2.79 ± 0.09) × 10-5 S cm-1 is exhibited by NaCMC film soaked in polysulphide electrolyte for 68 s. The conductivity-temperature relationship of NaCMC-based polysulphide solid polymer electrolytes (SPEs) follows the Arrhenius rule. The highest conducting SPE exhibits the lowest activation energy (EA) value of 0.38 eV. Ionic coefficient of diffusion (D), ionic mobility (μ) and free ions concentration (n) of the SPEs were determined. The newly developed SPEs are used as electrolyte in quantum dot-sensitized solar cells (QDSSCs) application with the configuration FTO/TiO2/CdS/ZnS/SPE/Pt/FTO. Under 1000 W m-2 illumination, QDSSC with CMC-68 SPE exhibits the highest power conversion efficiency (PCE) of 0.90%. The values of short circuit current (JSC) and PCE are closely related to electron lifetime and recombination rate.
关键词： Solid polymer electrolyte,Sodium-carboxymethylcellulose,Quantum dot-sensitized solar cells,Transport properties,Polysulphide
更新于2025-09-11 14:15:04
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Kinking effects and transport properties of coaxial BN-C nanotubes as revealed by <i>in situ</i> transmission electron microscopy and theoretical analysis
摘要： The insights into transport behavior and the effects of bending on heterostructures constructed from boron nitride (BN) and carbon (C) nanotubes are important for their flexible device applications because the two systems have equally excellent mechanical but completely different electrical properties. In this work, coaxial BN–C nanotubes have been fabricated and their intrinsic transport properties, as well as structural and electrical response to bending deformation, are studied inside a high-resolution transmission electron microscope. Ballistic, diffusive, and hopping transports within different tube length ranges have been observed. When bending deformation was applied to the tubes, although severe kinking becomes apparent, their transport properties are not notably affected. Meanwhile, both theoretical and experimental analyses confirm that the kink positions depend on the ratio of tube diameter to its length. Possible formation of quantum dots, directly within the kink areas, was predicted through calculations of electron density redistribution between nanotube walls at bending.
关键词： bending deformation,transport properties,BN-C nanotubes,in situ TEM,quantum dots
更新于2025-09-11 14:15:04
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Influence of alkali substitution in La0.7Ca0.3Mn0.8Cr0.2O3 perovskite manganite on structural, magnetic, and transport properties
摘要： In order to study the effect of A-site cation mismatch on the structural, magnetic, and transport properties, a systematic investigation of La0.7Ca0.25A0.05Mn0.8Cr0.2O3 (A = Ca, Li, Na, K) has been undertaken. The XRD data of the materials, prepared by glycine-nitrate combustion method, have been analyzed by Rietveld refinement technique. The iodometric and EDX results show that except K doped sample, the desired stoichiometry of all the phases remains the same. The phases display a paramagnetic to ferromagnetic transition at low temperature with Tc found to decrease with decreasing ?rA?. It has been concluded that the conduction mechanism was dominated by small polaron hopping model in the high temperature paramagnetic semiconducting region.
关键词： Combustion method,Transport properties,Magnetic properties,Rietveld refinements
更新于2025-09-09 09:28:46
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Electronic transport properties of (Se80Te20)100?xZnx (2?≤?x?≤?6) chalcogenide alloys
摘要： The bulk chalcogenide (Se80Te20)100-xZnx (2≤x≤6) alloys are prepared using melt quenching technique and electronic transport properties are studied in the frequency range 50 Hz–500 KHz and temperature range 400-520 K. The sharp peaks observed in X-ray diffraction pattern indicate the polycrystalline nature of prepared compositions. The measured dielectric properties and a.c. conductivity reveal the significant influence of Zn doping on the properties of the Se-Te matrix. The a.c. conductivity obeys Jonscher power law as ~ w s (s<1). To describe the conduction mechanism, the experimental results are analyzed in the framework of various theoretical models. The correlated barrier hopping (CBH) model successfully describe the observed frequency, temperature and composition response of ac conductivity.
关键词： a.c. conductivity,electronic transport properties,Chalcogenide alloys,dielectric constant,dielectric loss,X-Ray diffraction
更新于2025-09-09 09:28:46
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Exploring the Gel State: Optical Determination of Gelation Times and Transport Properties of Gels with an Inexpensive 3D-Printed Spectrophotometer
摘要： The study of gels and their properties is a compelling topic both technologically and scienti?cally, and should therefore be emphasized in chemistry and material science syllabuses. In the present laboratory experiment, we propose two experiences, aimed at introducing gelation and gel transport properties using silica gels made from sodium silicate and sodium citrate bu?er. In particular, gelation times are used to teach kinetics and optical properties to ?rst and second year General Chemistry students. Gelation times are determined by measuring the increment in scattering intensity with a 3D-printed spectrophotometer. The gel transport properties are presented to further exemplify Fickian and non-Fickian behavior through ionic dyes di?using in gels. A qualitative description is obtained from charge interactions, and a quantitative description utilizing the di?usion coe?cient is achieved by analyzing absorbance pro?les. These tasks were designed to encourage students to work with unusual topics in a holistic way, approaching new materials, properties, and DIY equipment. Blueprints for the spectrophotometer, resources for instructors, and a detailed students’ guide are provided together with a short report model to promote critical discussion of the observations.
关键词： Transport Properties,Physical Chemistry,Materials Science,Second-Year Undergraduate,Hands-On Learning/Manipulatives,First-Year Undergraduate/General
更新于2025-09-09 09:28:46
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Strain engineering of chevron graphene nanoribbons
摘要： In this work, we theoretically investigate the material and transport properties of strained chevron graphene nanoribbons (CGNRs) which can be easily synthesized by the bottom-up fabrication technology. Because of the unique atomic structures, the energy and pressure of the CGNRs vary asymmetrically along compressive and tensile strains. Under the two strain directions, the CGNRs’ bandgaps and carrier effective masses in the conduction band minimum and the valence band maximum are all reduced. The transport properties are promoted accordingly, except some negative differential conductance behaviors caused by energy state localizations. When the tensile strains exceed a criterion value, the C–C bonds in the inner sides of the CGNR corners will be broken in sequence. Meanwhile, the CGNRs can restore their initial unstrained states rapidly when the strains are removed. However, if the broken bonds are saturated by foreign atoms, such as H, a novel kind of stable carbon structure will be obtained. The investigations suggest possible applications of strain engineered CGNRs in transport devices.
关键词： carrier effective masses,strain engineering,transport properties,chevron graphene nanoribbons,bandgap
更新于2025-09-04 15:30:14