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ZnSe/ZnS Core/shell Quantum Dots with Superior Optical Properties through Thermodynamic Shell Growth
摘要： Epitaxial growth of a protective semiconductor shell on a colloidal quantum dot (QD) core is the key strategy for achieving high fluorescence quantum efficiency and essential stability for optoelectronic applications and bio-tagging with emissive QDs. Herein we investigate the effect of shell growth rate on the structure and optical properties in blue-emitting ZnSe/ZnS QDs with narrow emission linewidth. Tuning the precursor reactivity modifies the growth mode of ZnS shells on ZnSe cores transforming from kinetic (fast) to thermodynamic (slow) growth regimes. In the thermodynamic growth regime, enhanced fluorescence quantum yields and reduced on-off blinking are achieved. This high performance is ascribed to the effective avoidance of traps at the interface between the core and the shell, which are detrimental to the emission properties. Our study points to a general strategy to obtain high-quality core/shell QDs with enhanced optical properties through controlled reactivity yielding shell growth in the thermodynamic limit.
关键词： thermodynamic,core/shell QDs,heavy-metal-free,ZnSe/ZnS,kinetic
更新于2025-09-19 17:13:59
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Triplet-triplet annihilation effects in rubrene/C60 OLEDs with electroluminescence turn-on breaking the thermodynamic limit
摘要： Recently, Engmann et al. experimentally and theoretically examined the higher-order effects in rubrene/C60 organic light-emitting diodes (OLEDs), claiming that triplet-triplet annihilation (TTA) is not responsible for the electroluminescence (EL) with extremely-low turn-on voltage (Voc). Instead, the evidence from the equivalent circuit fitting suggest that the direct band-to-band recombination can interpret the low voltage phenomena. However, at applied bias of about 1.0 V, the excitons prefer to form on the charge-transfer state between rubrene/C60 interface. Direct singlet formation on rubrene and direct band-to-band recombination seems impossible to be accountable for such low Voc.
关键词： thermodynamic limit,electroluminescence,rubrene/C60 OLEDs,triplet-triplet annihilation
更新于2025-09-19 17:13:59
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Comparative study of electron temperature in cascaded arc Ar/N <sub/>2</sub> plasma using laser Thomson scattering combined optical emission spectroscopy approach
摘要： The expanding cascaded arc Ar/N2 plasma has been investigated by both the active and passive optical diagnostic technologies. In the investigation, the laser Thomson scattering (LTS) and optical emission spectroscopy (OES) have been adopted to measure electron temperature (Te) and electron excitation temperature (Texc), respectively. The LTS measurements show that a remarkable nonlinear behavior of Te as a function of the N2/(Ar + N2) ratio is found, which is caused by the collective interaction between the superelastic collision and the electron-impact excitation. The superelastic collisions by the highly excited vibrational nitrogen molecules can effectively heat the free electrons, while the electron kinetic energy can be transferred to N2 molecular internal energy via the electron impact with N2 in the ground state. The difference between Texc and Te demonstrates that the cascaded arc Ar/N2 plasma significantly deviates from the local thermodynamic equilibrium. This would be useful for improving our further understanding of nonequilibrium plasma and extending applications of the cascaded arc Ar/N2 plasma.
关键词： cascaded arc Ar/N2 plasma,local thermodynamic equilibrium,laser Thomson scattering,electron temperature,optical emission spectroscopy
更新于2025-09-19 17:13:59
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: Why Sn substitution should be preferred to Pb vacancy for optimum solar cell efficiency
摘要： Methylammonium lead halide (MAPbI3) perovskite has emerged as one of the frontier optoelectronic semiconductors. To avoid lead toxicity, the role of Sn substitution and Pb vacancy (Pb-(cid:2)) are addressed in regulating stability and solar cell ef?ciency of MAPb1?X ?Y SnX (cid:2)Y I3 perovskite using hybrid density functional theory (DFT). The role of spin-orbit coupling (SOC) and the electron’s self-interaction error are examined carefully. We ?nd to reduce the Pb content from pristine MAPbI3, Sn substitution has a more favorable thermodynamic stability than creating Pb-(cid:2). Moreover, on substituting Sn, due to strong s-p and p-p couplings, the lower parts of the conduction band gets shifted downwards, which results in the reduction of the band gap (direct). This further helps us to get a high optical absorption coef?cient (redshifted) and maximum solar cell ef?ciency in MAPb1?X SnX I3 for 0 < X (cid:2) 0.5.
关键词： spin-orbit coupling,MAPbI3,solar cell efficiency,Pb vacancy,thermodynamic stability,Sn substitution,Methylammonium lead halide,hybrid density functional theory,optical absorption coefficient
更新于2025-09-19 17:13:59
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Chalcogenide Materials and Derivatives for Photovoltaic Applications
摘要： Chalcogenide AB(S,Se)3 materials have recently attracted increased attention as they could simultaneously solve both the stability and toxicity issues faced by conventional perovskite solar cells. Computer-aided design of metal chalcogenide semiconductors has experienced important progress over the past few years, leading to the discovery of very promising AB(S,Se)3 compounds and derivatives for application as absorbers in thin-film photovoltaic devices. Experimental evidence demonstrates that the synthesis of such compounds is possible, confirming the theoretical predictions, although more research work needs to be done to further investigate the optoelectrical properties of the corresponding thin films. With the aim to provide an exhaustive starting point to further develop chalcogenide absorbers and related devices, this Review presents both an overview of the predicted chalcogenide materials and interesting derivatives for thin-film solar cells applications, as well as a summary of the synthesis techniques developed so far to prepare such materials. The possible challenges that can be encountered during the development of chalcogenide-based solar cells are also discussed.
关键词： lead-free perovskites,chalcogenides,solar cells,computational materials designs,thermodynamic stabilities
更新于2025-09-19 17:13:59
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THE TEMPORARY CHARACTERISTICS OF VACUUM DISCHARGE WITH LASER IGNITION
摘要： A study was made of the switching process of a vacuum discharger ignited by a pulsed solid-state laser operating in the Q-switched mode. The dependence of the response time on the energy of the igniting pulse of laser radiation and the thermodynamic characteristics of the target material has been demonstrated. On the basis of the experimental data, it was suggested that under the action of a laser pulse in the erosion products of the electrodes an initial glow discharge is ignited, which, as a result of the development of ionization-superheating instability, undergoes a contraction of the current channel and turns into an arc channel.
关键词： vacuum discharge,laser ignition,switching process,Q-switched mode,glow discharge,arc channel,solid-state laser,thermodynamic characteristics
更新于2025-09-16 10:30:52
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Numerical Study on Thermodynamic Behavior during Selective Laser Melting of 24CrNiMo Alloy Steel
摘要： In this paper, a multi-layer and multi-track ?nite element model of 24CrNiMo alloy steel by selective laser melting (SLM) is established by using the ABAQUS software. The distribution and evolution of temperature ?eld and stress ?eld and the in?uence of process parameters on them are systematically studied. The results show that the peak temperature increases from 2153 C and the residual stress increases from 335 MPa to 364 MPa with increasing laser power from 200 W to 300 W; the peak temperature decreases from 2905 C and the residual stress increases from 327 MPa to 363 MPa with increasing scanning speed from 150 mm/s to 250 mm/s; the peak C and the residual stress decreases from 354 MPa to 300 temperature increases from 2621 MPa with increasing preheating temperature from 25 C. Far away from scanning area, far away from starting point, and the adjacent areas with vertical scanning direction, resulting in a uniform temperature distribution, help to reduce the residual stress. Due to the remelting e?ect, the interlayer scanning angle changing helps to release the residual stress of the former layer causing a smaller residual stress after redistribution.
关键词： substrate preheating,?nite element analysis,thermodynamic behavior,selective laser melting,scanning strategy,24CrNiMo alloy steel
更新于2025-09-16 10:30:52
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A Simulation Study on Performance Improvement of Solar Assisted Heat Pump Hot Water System by Novel Controllable Crystallisation of Supercooled PCMs
摘要： Domestic hot water (DHW) has a significant share in building’s energy consumption. In order to reduce this consumption, various solutions have been proposed such as controlling the system in an efficient way, using renewable sources and using phase change materials (PCM) in the system to increase heat capacity. However, this study is not only offering heat capacity improvement of the DHW storage unit but also proposing that energy efficiency can be improved by controlling the heat releasing time of the PCM. In this study, supercooled PCM tubes are placed in a water tank and charged with a solar assisted heat pump unit, these supercooled PCM tubes can then be discharged anytime when the hot water is required. In this paper, a transient thermodynamic model is built for the whole system including solar collector, heat pump, water tank with PCM and DHW demand profile. System components are modelled and a 24 hours of demand profile is used in simulation for a UK home for summer and spring weather conditions. The results show that the PCM tubes effectively compensate the morning peak hot water demand and reduce daily energy consumption around 12.1% and 13.5% by shifting heating provision from immersion heater to solar heat pump.
关键词： Transient thermodynamic simulation,DHW,Supercooled PCM,Solar assisted heat pump
更新于2025-09-16 10:30:52
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Microstructure evolution in yttria stabilized zirconia during laser hybrid induction modification
摘要： To minimize crack susceptibility, a laser hybrid induction modification (LHIM) technique, involving the lowest laser energy required for continuously remelting at a preset inducting heating temperature, was used to partially remelt atmospheric plasma spraying (APS) yttria stabilized zirconia (YSZ) coating. Computational fluid dynamics (CFD) simulations indicate that a combination of elevated preheating temperature and low laser energy is essential to lower the cooling rate and temperature gradient and increase the solidification rate of melt pool. This is consistent with the experimental results obtained by eliminating the undesirable monoclinic phase and achieving the desired columnar and equiaxed grains. More importantly, the intersplat pores are healed to a higher degree, and the APS coatings become denser. These obvious structural changes decrease the differential shrinkage rate, mainly responsible for the initiation of cracks existing between the remelted layer and residual APS coatings during laser thermal shock. The healing of intersplat pores is also helpful for achieving less interfacial imperfections in the expansion of molten pool, thus developing a well-bonded remelted layer. Thus, a significantly decreased mismatch strain resulting from the lower thermal gradient and reduced differential shrinkage rate produces an acceptably low stress level for the crack susceptibility of remelted coating. Instead, the stress relief related to splat sliding is beneficial to achieve enlarged intercolumn gaps with high strain tolerance.
关键词： Computer simulations,Microstructure,Thermodynamic properties,Coating materials,Laser processing
更新于2025-09-16 10:30:52
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Novel thermodynamic efficiency indices for choosing an optimal location for large-scale photovoltaic power generation
摘要： Sustainable energy is a current key priority across the globe. Hence, renewable energy sources have been widely accepted as potential substitutes for fossil fuels in the existing energy infrastructures. A recent report showed that photovoltaic power generation constituted around 100 GW out of 2378 GW of the global renewable power capacity installed in 2018. Consequently, various researchers are investigating how the increasing utilisation of photovoltaics can be handled in order to reduce future environmental impacts; whilst leveraging their operational zero-emission. From a circular economic paradigm, recycling, reuse and reduction strategies are often adopted to improve the sustainability of systems. This study proposes novel thermodynamic ef?ciency indices as a resources reduction strategy. By selecting an optimal location for large-scale photovoltaic power generation (LSPPG), the same amount of resources (such as land space, materials, energy) will achieve higher utilisation ef?ciency. In this study, actual two-year solar radiation and temperature data were sourced from Nigerian Meteorological Agency, Abuja. A probability distribution modeling was used to generate statistical mean values for solar radiation and temperature based on the classical almost sure central limit theory. Then, Photovoltaic modeling and simulation code was used to simulate the power generation characteristics of the LSPPG. Comparative analyses of the results for a 5 MW (MW) LSPPG showed that statistical mean value of power generation, energy ef?ciency index and exergy ef?ciency index range from 0.76 to 0.99 MW, 1.315 to1.254 and 1.298 to1.237, respectively, across the locations studied. Overall, the thermodynamic ef?ciency indices can complement the current laboratory-based rating of the photovoltaic modules in order to establish the environmental, economic and policy rationales for sitting a LSPPG. This would ultimately improve the cradle-to-cradle management of LSPPG installations based on resources reduction strategy.
关键词： Solar energy,Thermodynamic ef?ciency indices,Nigeria,Photovoltaic modules,Modeling and simulation
更新于2025-09-12 10:27:22