Device Modeling Simulations Research Articles

Parametric extraction and internal analysis of fullerene-based polymer bulk heterojunction solar cell

This paper present device model simulation describing the current-voltage characteristics of polymer/fullerene bulk heterojunction solar cell. In the research paper an organic photovoltaic device with PPV/PCBM [poly (2-methoxy-5-{3’,7’-dimethyloctyloxy}-p-phenylene vinylene) and {6,6}- phenyl C61-butyric acid methyl ester] was simulated via Silvaco TCAD 2-D simulation tool. PCBM acts as acceptor and PPV is donor. The models used to simulate the device were Langevin for recombination, s.binding and a.singlet. Simulation of these type of devices is an vital approach to project and predict the cell performance. Under the illumination of one sun (AM 1.5) the simulated organic cell showed a short circuit current density (JSC) of 28 A/m2, open circuit voltage (VOC) of 0.84 Volt and a fill factor (FF) of 52.51%, the resulting maximum efficiency of the PPV/PCBM organic solar cell is 1.22%.

Achieving adjustable digital-to-analog conversion in memristors with embedded Cs2AgSbBr6 nanoparticles.

In this work, the proportions of Cs2AgSbBr6 nanoparticles (NPs) mixed in a PMMA film are adjusted to the digital and analog types of resistive switching (RS) behaviors in Ag/PMMA&Cs2AgSbBr6-NPs/ITO memristor devices. It is confirmed that when the concentration of NPs doped in the PMMA film is about 5 wt%, the memristor devices demonstrate bipolar digital RS behaviors with excellent electrical characteristics such as low operating voltage, high ON/OFF ratio (>500), good endurance (>800 cycles), and stable retention ability (>104 s). However, the devices showed a transition to analog-type memristive behavior when the concentration of NPs doped in the PMMA film is around 10 wt%, and several artificial synapse behaviors are successfully simulated. The device model simulation is also used to explore the effect of the NPs on the local electric field and growing filaments. Our work provides an opportunity to explore next-generation artificial synapse devices based on lead-free halide perovskites.

Validating the Reliability Simulation Using Bohlamp Circuit with Accelerated Life Test Method

Learning media is very importance tools to achieved the learning outcome like capable to design reliability engineering system (RES). The students should be understanding with basic theory of reliability and also have technical skill based on need analysis. Unfortunately, the RES learning media are still not available specially to implement of several type of reliability system. Objective of the study is introducing reliability device model simulation with choice option series, parallel and combine series-parallel system. Method of the study are using accelerated life testing method (ALT) which has been analyzed with statistical method to estimate life-time at normal condition. Validating value of each reliability system are have similarity between experimental test (Re) and theoretical (Rt) i.e.: series (Rt=0.329; Re=0.359); parallel (Rt=0.976; Re=0.972.), and combined of series-parallel (Rt=0. 651; Re=0.686). The conclusion is the parallel have high-fidelity on application of reliability simulation with error 0.000409.

Toward the core-edge coupling of delta-f and total-f gyrokinetic models

The coupling of core reduced delta-f and edge total-f gyrokinetic models could enable a significant speed-up of the whole device modeling simulations. It is thus interesting to compare these models in the core where they will be coupled. The main difference between these models is the presence of the zeroth order term on the right-hand side of the total-f gyrokinetic equation. This term is responsible for driving a radial electric field that is also associated with Geodesic acoustic mode-like oscillations. To investigate the coupling between these models, the subsequent large-scale gyrokinetic 3D turbulence simulations have been performed starting from an already saturated gyrokinetic axisymmetric equilibria (collisions are not included). This work has also been extended to couple different axisymmetric and turbulent models available in XGC. It is shown that the radial electric field and its drive have to be taken care of consistently while coupling different models together.

Modeling Thin Film Solar Cells: From Organic to Perovskite.

Device model simulation is one of the primary tools for modeling thin film solar cells from organic materials to organic–inorganic perovskite materials. By directly connecting the current density–voltage (J–V) curves to the underlying device physics, it is helpful in revealing the working mechanism of the heatedly discussed organic–inorganic hybrid perovskite solar cells. Some distinctive optoelectronic features need more phenomenological models and accurate simulations. Herein, the application of the device model method in the simulation of organic and organic–inorganic perovskite solar cells is reviewed. To this end, the ways of the device model are elucidated by discussing the metal–insulator–metal picture and the equations describing the physics. Next, the simulations on J–V curves of organic solar cells are given in the presence of the space charge, interface, charge injection, traps, or exciton. In the perovskite section, the effects of trap states, direct band recombination, surface recombination, and ion migration on the device performance are systematically discussed from the perspective of the device model simulation. Suggestions for designing perovskite devices with better performance are also given.

Computational Approaches to Photoelectrode Design through Molecular Functionalization for Enhanced Photoelectrochemical Water Splitting.

Photoelectrochemical water splitting is a promising carbon-free approach to produce hydrogen from water. A photoelectrochemical cell consists of a semiconductor photoelectrode in contact with an aqueous electrolyte. Its performance is sensitive to properties of the photoelectrode/electrolyte interface, which may be tuned through functionalization of the photoelectrode surface with organic molecules. This can lead to improvements in the photoelectrode's properties. This Minireview summarizes key computational investigations on using molecular functionalization to modify photoelectrode stability, barrier height, and catalytic activity. It is discussed how first-principles density functional theory, first-principles molecular dynamics, and device modeling simulations can provide predictive insights and complement experimental investigations of functionalized photoelectrodes. Challenges and future directions in the computational modeling of functionalized photoelectrode/electrolyte interfaces within the context of experimental studies are also highlighted.

Self-consistent core-pedestal transport simulations with neural network accelerated models

Fusion whole device modeling simulations require comprehensive models that are simultaneously physically accurate, fast, robust, and predictive. In this paper we describe the development of two neural-network (NN) based models as a means to perform a snon-linear multivariate regression of theory-based models for the core turbulent transport fluxes, and the pedestal structure. Specifically, we find that a NN-based approach can be used to consistently reproduce the results of the TGLF and EPED1 theory-based models over a broad range of plasma regimes, and with a computational speedup of several orders of magnitudes. These models are then integrated into a predictive workflow that allows prediction with self-consistent core-pedestal coupling of the kinetic profiles within the last closed flux surface of the plasma. The NN paradigm is capable of breaking the speed-accuracy trade-off that is expected of traditional numerical physics models, and can provide the missing link towards self-consistent coupled core-pedestal whole device modeling simulations that are physically accurate and yet take only seconds to run.

Origin of the high open circuit voltage in planar heterojunction perovskite solar cells: Role of the reduced bimolecular recombination

The high open circuit voltage is an attractive feature for the currently popular organic-inorganic hybrid perovskite solar cells. In this paper, by employing the macroscopic device model simulation, we investigate its origin for the planar heterojunction perovskite solar cells. Based on the calculated current density-voltage characteristics, it is revealed that compared to the excitonic solar cells, the fast thermal-activated exciton dissociation in the bulk due to the small exciton binding energy may improve the short circuit current and the fill factor, but its beneficial role on the open circuit voltage is marginal. The most significant contribution for the open circuit voltage comes from the reduced bimolecular recombination. In the perovskites, with the recombination prefactor many orders of magnitude smaller than that based on the Langevin's theory, the internal charge density level is significantly enhanced and the density gradient is removed, leading to the high quasi-Fermi level splitting and thus the small open circuit voltage loss. For the nonradiative recombination pathway due to the deep trap states, it may induce significant loss of open circuit voltage as the trap density is high, while for the moderately low density its effect on the open circuit voltage is small and negligible.

Mechanisms of device degradation in organic solar cells: Influence of charge injection at the metal/organic contacts

Organic solar cells suffer from device degradation under various undesirable ambient conditions, which limits their efficiencies and applications a lot. The frequently appeared S-shaped current density–voltage (J–V) characteristics just reflect this effect and make its underlying mechanisms even obscurer for experimentalists. By performing device model simulation, we investigate the J–V curves of a organic bulk heterojunction solar cell for different interfacial charge injection conditions. We find the S-shaped kinks appear when both electron and hole injection barriers exceed 0.3eV, which is attributed to the shortage of dark injection carriers. For the nearly Ohmic contacts, the open circuit voltage is significantly reduced. The quantitative study suggests it arising from the majority carrier accumulation and the induced local field variation at the vicinity of the contacts. S-shaped kink is gradually eliminated with increasing carrier mobilities. Finally, we find the decreasing of fill factor under enhanced light absorption, which results from the drastic bimolecular recombination and thus signifies remarkable internal losses.

Effects of Gate-Recess Structure on High-Frequency Characteristics of 0.1 μm Metamorphic HEMTs

We investigate effects of the gate-recess structure on the high-frequency characteristics of the depletion-mode metamorphic high electron mobility transistors (HEMTs). We characterize the dc and radio frequency performances of two different gate-recess structures and perform a comparative study using the hydrodynamic device model simulation and small-signal parameter analysis. The narrow gate-recess structure shows significantly higher dc performances than the wide gate-recess structure, and this phenomenon is due to the presence of the negatively charged surface states on the Schottky barrier layer surface in the wide gate-recess structure. Despite the superior dc characteristics, the narrow gate-recess structure shows more degraded maximum frequency of oscillation of than that of the wide gate-recess structure and almost the same cutoff frequency of . The degraded of the narrow gate-recess structure is attributed to a higher gate-to-drain capacitance . The significant increase of is caused by the reduction of effective gate-to-drain spacing due to the nonlinear electric potential distribution in the gate-to-drain region.

Monte Carlo formulation of velocity-field characteristics and expressions for AlxGa1-xAs

Steady-state velocity-field characteristics in AlxGa1-x As are calculated for a wide range of composition, doping, and temperature variations, using Monte Carlo techniques. The results are related to the scattering mechanisms which are responsible for the observed transport parameters. A single empirical expression is formulated to fit all the Monte Carlo data. This expression incorporates all the nonlinear transport effects and would be useful for numerical simulation of device models. A general methodology is also presented for formulating such expressions, and the results are applicable to modelling field-dependent mobility in AlxGa1-x As devices.