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Enhanced optical efficiency and color purity for organic light-emitting diodes by finely optimizing parameters of nanoscale low-refractive index grid
摘要： To extract the confined waveguided light in organic light-emitting diodes (OLEDs), inserting a low refractive index (RI) periodic structure between the anode and organic layer has been widely investigated as a promising technology. However, the periodic-structure-based light extraction applied inside devices has been shown to severely distort spectrum and affect EL characteristics. In this study, a simple light extraction technology using periodic low-RI nanodot array (NDA) as internal light extraction layer has been demonstrated. The NDA was fabricated simply via laser interference lithography (LIL). The structural parameters of periodic pattern, distance, and height were easily controlled by the LIL process. From computational analysis using finite-difference time-domain (FDTD) method, the NDA with 300 nm pitch and 0.3 coverage ratio per unit cell with 60 nm height showed the highest enhancement with spectral-distortion-minimized characteristics. Through both computational and experimental systematic analysis on the structural parameters of low-RI NDA-embedded OLEDs, highly efficient OLEDs have been fabricated. Finally, as representative indicators, hexagonal and rectangular positioned NDA-embedded OLEDs showed highly improved external quantum efficiencies of 2.44 (+29.55%) and 2.77 (+57.38%), respectively. Furthermore, the disadvantage originating from the nanoscale surface roughness on the transparent conductive oxide was minimized.
关键词： organic light-emitting diodes,nanodot array,FDTD simulation,laser interference lithography,light extraction,low refractive index
更新于2025-09-23 15:21:01
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Atomic simulation of irradiation of Cu film using femtosecond laser with different pulse durations
摘要： It is necessary to understand the light-matter interaction for application of femtosecond laser micro/nanoprocessing. In this work, the authors investigated the melting and disintegration behavior of a Cu film irradiated by a femtosecond laser with different pulse durations in the range of 35–500 fs by using a combined two temperature model (TTM) and molecular dynamics (MD) method. On the basis of TTM-MD, the temperature and stress evolution of the Cu film were analyzed. The result indicated that the Cu film disintegrates when the pulse duration is shorter than 100 fs but melts at a pulse duration of 200 fs. The photomechanical and thermomechanical evolutions induced by the femtosecond laser were also analyzed. The stress wave and increasing temperature were the main reasons for film disintegration and vibration. The snapshots of the Cu film indicate the melting and disintegration processes on an atomic scale. It shows that the melting occurs homogeneously, whereas the disintegration occurs at the center of the film. These results are helpful to understand the mechanism of femtosecond laser materials ablation.
关键词： TTM-MD simulation,Cu film,pulse durations,femtosecond laser,irradiation
更新于2025-09-23 15:21:01
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Impact of high resistivity transparent (HRT) layer in cadmium telluride solar cells from numerical simulation
摘要： In this study, Solar Cell Capacitance Simulator (SCAPS-1D) is utilized to examine the properties of cadmium telluride (CdTe) based solar cell. The key aim of this study is to explore the prospects of enhancing the ef?ciency of CdTe solar cells by adding a high resistivity transparent (HRT) layer to the conventional cell structure. For that purpose, novel HRT layer structures are suggested in CdTe solar cells between a cadmium sul?de (CdS) window layer and transparent conductive oxide (TCO) layer. Simulation results presented in this paper are from four proposed structures with three different HRT materials compared to the conventional design. The optimal parameters that offer the optimum functionality of the conventional design (SnO2/CdS/CdTe/MoTe2), with and without the HRT layer, are determined. Obtained results validate an enhancement in ef?ciency of the solar cell with Zn2SO4 as the HRT layer due to lower recombination loss and barrier height at the back contact region. The suggested cell with Zn2SO4 demonstrates an ef?ciency of 17.61% (Voc ? 0.92 V, Jsc ? 25.41 mA/cm2, FF ? 75.35), with only 20 nm HRT layer and 25 nm CdS as a window layer. In the meantime, the reference cell (no HRT layer) depicts an ef?ciency of 17.01% with 4000 nm thick CdTe as an absorber layer. However, the normalized ef?ciency of the suggested cells decreases linearly with increased temperature.
关键词： SCAPS-1D,solar cells,cadmium telluride,high resistivity transparent layer,numerical simulation
更新于2025-09-23 15:21:01
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A detailed comparison of measured and simulated optical properties of a short-period GaAs/Al <sub/><i>x</i> </sub> Ga <sub/> 1a?? <i>x</i> </sub> As distributed Bragg reflector
摘要： A 6-period GaAs/Al0.9Ga0.1As distributed Bragg re?ector (DBR) has been grown and its optical properties have been both measured and simulated. Incremental improvements were made to the simulation, allowing it to account for internal consistency error, incorrect layer thicknesses, and absorption due to substrate doping to improve simulation accuracy. A compositional depth pro?le using secondary-ion mass spectrometry (SIMS) has been taken and shows that the Al fraction averages 88.0% ± 0.3%. It is found that the amplitude of the transmission is signi?cantly affected by absorption in the n-doped GaAs substrate, even though the energy of the transmitted light is well below the GaAs band gap. The wavelength of the features in the transmission spectrum are mostly affected by DBR layer thicknesses. On the other hand, the transmission spectrum is found to be relatively tolerant to changes to Al fraction.
关键词： optical simulation,AlGaAs,distributed Bragg re?ector,SIMS,cross section,telecoms,vertical cavity
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE 7th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Raleigh, NC, USA (2019.10.29-2019.10.31)] 2019 IEEE 7th Workshop on Wide Bandgap Power Devices and Applications (WiPDA) - Detailed Study of Breakdown Voltage and Critical Field in Wide Bandgap Semiconductors
摘要： We systematically study the analysis and simulation of ac-biased superconductor transition-edge sensor (TES) circuits. In these ac-biased circuits, the current and voltage of the TES experience large swings in both directions, and small-signal analysis around a dc steady state does not apply. To understand their electrical and thermal behavior, we rely on concepts and techniques from radio-frequency circuit simulation and introduce the periodic steady state and perform periodic ac analysis. We also construct TES device models based on a comprehensive two-fluid physical model and investigate the behavior of ac-biased TES circuits using advanced circuit simulators. By relating our findings to results for the analysis of dc-biased TES circuits, we give appropriate definitions for the current and temperature sensitivity of the TES in ac-biased circuits. Our work not only builds a rigorous foundation for theoretical analysis of ac-biased TES circuits but also introduces powerful simulation techniques valuable for their design and research.
关键词： Circuit analysis,computer simulation,superconducting devices
更新于2025-09-23 15:21:01
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The influence of the solar radiation database and the photovoltaic simulator on the sizing and economics of photovoltaic-diesel generators
摘要： This study evaluated the outcome differences when adopting five different solar irradiation databases on the sizing of hybrid solar photovoltaic-diesel generators designed to supply electricity to isolated minigrids. To do this, the two most widely adopted photovoltaic (PV) simulation packages in the market, namely PVsyst? and HOMER Energy? were used. The different origins, data timespan, space and time resolution, of the five most relevant solar irradiation databases available for the region were compared. A case study was presented to illustrate the influences of the solar irradiation database and the solar simulation tool on the resulting PV generator. Furthermore, the hourly behavior of the energy supply to an existing load in a minigrid in the Brazilian Amazon was evaluated, together with the savings in diesel obtained with the resulting PV generator. Evaluating the five options of solar radiation databases, for the same PV plant configuration, variations of up to 19.7% were found in the expectation of PV generation. When the simulation software package was varied, the combined effect (radiation database X PV system sizing tool) showed differences of up to 20.6%. This demonstrates that despite having different algorithms, computational tools have a small influence (less than 1%) on results. These combined differences, taking into account the load curve behavior and the total diesel generation capacity installed at the site, resulted in over 100% differences in the optimum PV generator size in the case study. The total savings in diesel fuel, over a 15-years period, ranged from $ 6.5 million to over $ 16 million (> 2.5 times) for the smallest PV system. This demonstrates the importance of the correct choice of database. These evaluations can be extended to minigrids of any size elsewhere. The novelty and originality of this study is to demonstrate and quantify for the first time the influence of the solar radiation database and the PV simulator package on the sizing of PV-diesel generators. The consequences of this study are not only of scientific and academic importance, but of economic and commercial interest as well.
关键词： Photovoltaic simulation tool,Hybrid photovoltaic-diesel power plant,Solar database,Minigrids,Solar irradiation
更新于2025-09-23 15:21:01
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[IEEE 2019 Compound Semiconductor Week (CSW) - Nara, Japan (2019.5.19-2019.5.23)] 2019 Compound Semiconductor Week (CSW) - Regional band-gap tailoring of 1550nm-band InAs quantum dot Intermixing by controlling ion implantation depth
摘要： This paper studies the electric vehicle (EV) charging scheduling problem to match the stochastic wind power. Besides considering the optimality of the expected charging cost, the proposed model innovatively incorporates the matching degree between wind power and EV charging load into the objective function. Fully taking into account the uncertainty and dynamics in wind energy supply and EV charging demand, this stochastic and multistage matching is formulated as a Markov decision process. In order to enhance the computational efficiency, the effort is made in two aspects. Firstly, the problem size is reduced by aggregating EVs according to their remaining parking time. The charging scheduling is carried out on the level of aggregators and the optimality of the original problem is proved to be preserved. Secondly, the simulation-based policy improvement method is developed to obtain an improved charging policy from the base policy. The validation of the proposed model, scalability, and computational efficiency of the proposed methods are systematically investigated via numerical experiments.
关键词： smart grid,simulation-based policy improvement (SBPI),renewable energy,Electric vehicle (EV)
更新于2025-09-23 15:21:01
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Stages of the Excitation Relaxation in a Superconductor after the Impact of a Femtosecond Laser Pulse Taking into Account the Momentum Distribution of Quasiparticles
摘要： A theoretical model is formulated for the description of the nonequilibrium state of a superconductor on the basis of the nonequilibrium distribution function of phonons and quasiparticles on a finite momentum lattice convenient for numerical simulation. The simulation is performed under conditions of pulsed optical impact demonstrating the role of excess quasiparticles in suppressing the order parameter and the main stages of the relaxation process in the absence of electric current.
关键词： superconductivity,kinetics simulation,nonequilibrium processes,ultrashort laser pulse
更新于2025-09-23 15:21:01
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[IEEE 2019 Chinese Automation Congress (CAC) - Hangzhou, China (2019.11.22-2019.11.24)] 2019 Chinese Automation Congress (CAC) - Design of a Distributed Multi-missile Simulation System Based on Optical Fiber Reflective Memory Network
摘要： The simulation system is one of the important means to develop the weapon system. The distributed real-time simulation system can greatly accelerate the weapon research process. Distributed real-time simulation systems based on UDP and fiber-optic reflective memory networks enhance system computing, resource scheduling, and network communications. Based on the reflective memory network and Ethernet, the simulation system uses dual network transmission. Finally, the experimental results show that the system is real-time, communication is stable, high-speed, reliable, and the simulation system meets the requirements of multi-missile simulation.
关键词： reflective memory,multi-missile,UDP,distributed real-time simulation
更新于2025-09-23 15:21:01
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Fluorinated graphene nanoparticles with 1-3 nm electrically active graphene quantum dots
摘要： A new perspective approach to how to create a new and locally nanostructured graphene-based material is reported on. We studied the electric and structural properties for the partially fluorinated graphene (FG) films obtained from a FG-suspension and nanostructured by high-energy Xe ions. Local shock heating in ion tracks is suggested to be the main driving force of the changes. It was found that ion irradiation leads to the formation of locally thermal expanded FG and its cracking into nanosized nanoparticles with embedded small (~1.5-3 nm) graphene quantum dots, which band gap was estimated as 1-1.5 eV, into them. A further developed approach was applied to correction of the functional properties of the printed FG-based crossbar memristors. Dielectric FG films with small quantum dots may offer prospects in graphene-based electronics due to their stability and promising properties.
关键词： memristor,molecular dynamics simulation,nanostructuring,swift ion irradiation,fluorinated graphene,graphene quantum dots
更新于2025-09-23 15:21:01