Series Circuit Model Research Articles

Mathematical expressions for simulation of supercapacitor voltammetry curves and capacitance dependence on scan rate

A straightforward RC series circuit model was proposed to fit the cyclic voltammetry experimental data of various symmetrical electrochemical supercapacitors. The model simulated the experimental behavior for exponential dependence of capacitance on the scan rate. In this model, the zero-scan rate capacitance was considered as a constant, and the equivalent serial resistance depended on the scan rate. Neither the equivalent parallel resistance nor a possible intrinsic dependence of capacitance on applied voltage was considered in the modelling.

The influence of electrode geometry on the electrochemical performance of fabric-based screen-printed coplanar supercapacitors

Coplanar supercapacitors are promising flexible energy storage systems due to the excellent flexibility and tailored shapes and sizes of electrodes. However, the influence mechanism of electrode’ geometry parameter on the electrochemical performance of the flexible coplanar supercapacitors needs to be elucidated to realize the performance enhancement. Herein, the flexible coplanar supercapacitors with different thicknesses, widths and lengths of screen-printed electrodes were constructed on the cotton fabric substrates utilizing multi-walled carbon nanotubes ink and polymer gel electrolytes. The relationship between electrodes' geometry and overall electrochemical performance of flexible coplanar supercapacitors was detailed analyzed and demonstrated by employing equivalent series circuit model and electrode kinetic theory. Furthermore, due to the favorable aspect ratio and relatively low electrode and electrolyte resistance, the fabric-based coplanar supercapacitor with electrode size of 4 × 10 mm shows optimal electrochemical performance with areal capacitance of 3.08 mF cm−2 at 20 mV s−1, fast electrode response and effective kinetic process. Most importantly, the fabric-based supercapacitor exhibits excellent flexibility and cycling performance with capacitance retention rate over 79.6 % after 4000 charge and discharge cycles, indicating application potential in wearable electronic devices. The analysis and assessments of electrodes' geometry provides theoretical reference for the electrode design and optimization of flexible coplanar supercapacitors.

An in-depth analysis on the switching response and impedance curves of n-si/In2O3 NW/Ag NPs/In based devices by a double-step glancing angle deposition technique

Silver (Ag) nanoparticles (NPs) were coated upon indium oxide (In2O3) nanowires (NW) by a double-step glancing angle deposition (GLAD) technique. The study focuses on the experimental analysis of current (I) versus voltage (V), current (I) versus time (t), as well as impedance (Zexp) versus voltage (V) curves for n-Si/In2O3 NW/Ag NPs/In based devices with a sweeping voltage of ±10 V at room temperature in different frequency responses varying from 100 Hz to 2 MHz. The n-Si/In2O3 NW/Ag NPs/In based device showed faster rise and fall time of 0.13 s and 0.12 s than the other devices due to oxygen-related defect states. The presence of Ag NPs also improved oxygen related defect states, resulting in high impedance value for n-Si/In2O3 NW/Ag NPs/In based device. The series circuit model (SCM) was used to derive the theoretical investigations of impedances, indicating the n-Si/In2O3 NW/Ag NPs/In based device can be used in nanoelectronics applications.

Synthesis and detailed characterizations of Ag nanoparticles coated In2O3 nanostructured devices: An analytical and experimental approach

The impact of a high-performance nanostructured device using metal nanoparticle (NP) deposition is studied in this paper. Two devices, namely, a silver (Ag) NP coated indium oxide (In2O3) nanostructured device and a bare In2O3 nanostructured device, were fabricated by glancing angle deposition aided electron beam vacuum coating system to study the impact of Ag NPs over In2O3 nanostructures. The morphology of Ag NPs, as-fabricated nanostructures, and growth regions was analyzed using field emission scanning electron microscopy. The formation of Ag3O4 monoclinic crystal structures was confirmed by high-resolution x-ray diffraction profiles. The current density (J)-voltage (V) plot shows the modulating performances of an Ag NP coated In2O3 nanostructured device due to the occurrence of trap states originated from the incorporation of Ag NPs. For in-depth analyses of the impact of Ag NPs, frequency-dependent capacitance (C)-V, conductance (G)-V, and impedance (Z)-V characteristics were analyzed. A free charge carrier concentration (Nd) of ∼8.23 × 1016/cm3, a trap concentration (NT) of ∼1.48 × 1017/cm3, and a significant increment in conductance were observed for an Ag NP coated In2O3 nanostructured device (∼23.36 μS) than the bare In2O3 nanostructured device (∼13.05 μS) at a high frequency of 2 MHz. The delta-depletion model was implemented to obtain the C-V plots to match the experimental data adequately. The Ag NP coated In2O3 nanostructured device was further investigated by an analytical series circuit model, which manifests that the device can be used as catalysts, medical devices, etc.

Toward Current Matching in Tandem Dye-Sensitized Solar Cells.

The tandem pn-type dye-sensitized solar cells (pn-DSCs) have received much attention in the field of photovoltaic technologies because of their great potential to overcome the Shockley-Queisser efficiency limitation that applies to single junction photovoltaic devices. However, factors governing the short-circuit current densities (Jsc) of pn-DSC remain unclear. It is typically believed that Jsc of the pn-DSC is limited to the highest one that the two independent photoelectrodes can achieve. In this paper, however, we found that the available Jsc of pn-DSC is always determined by the larger Jsc that the photoanode can achieve but not by the smaller one in the photocathode. Such experimental findings were verified by a simplified series circuit model, which shows that a breakdown will occur on the photocathode when the photocurrent goes considerably beyond its threshold voltage, thus leading to an abrupt increase in Jsc of the circuit. The simulation results also suggest that a higher photoconversion efficiency of the pn-DSCs can be only achieved when an almost equivalent photocurrent is achieved for the two photoelectrodes.

Modeling and practical realization of thin film silicon‐based integrated solar water splitting devices

An integrated solar water splitting device based on thin film silicon multijunction photocathodes is presented. A graphical representation of the photovoltaic current–voltage data is introduced which allows for an estimation of the maximum achievable solar‐to‐hydrogen efficiency of the integrated device. Furthermore, a simple yet very useful series circuit model is used to predict the photoelectrochemical performance of the integrated device in a more elaborate way when the j–V characteristics of the individual components are known. Within the model, the j–V characteristics of each component can be either modeled with parameters from the literature or measured. The photocathode, the electrolyte concentration, and the hydrogen and oxygen evolving catalysts were varied exemplarily and the impact of each component on the integrated device performance was evaluated. A maximum solar‐to‐hydrogen efficiency of 9.5% was found using a triple junction solar cell functionalized with a Pt catalyst for the hydrogen evolution and a RuO2 catalyst for the oxygen evolution reaction in a 1 M KOH electrolyte. This result was confirmed experimentally and is compared to efficiencies reported in the literature.

Influence of the operating temperature on the performance of silicon based photoelectrochemical devices for water splitting

This paper highlights the effect of the operation temperature on the performance of a photovoltaic-biased electrosynthetic cell (PV-EC) device for solar hydrogen production based on a triple junction thin film silicon solar cell. The influence of the temperature in the range from 25°C to 60°C was studied individually for all components of the device: the solar cell, the hydrogen evolving cathode, the oxygen evolving anode, and the electrolyte. Based on the experimental data, the overall temperature-dependent current–voltage characteristics of the complete PV-EC device was modeled by merging the current–voltage characteristics of the individual components in an empirical series circuit model. We found that a decrease in the photovoltage of the solar cells with increasing temperature can be compensated by an improved electrochemical kinetics with temperature. This lead to a slight improvement in the performance of the integrated PV-EC device. Under an assumption of 100% faradaic efficiency, a maximum solar-to-hydrogen efficiency of 9.5% was found in 1M KOH at an operation temperature of 50°C.

Resistive switching characteristics of Ti/ZrO2/Pt RRAM device

In this paper, the bipolar resistive switching characteristic is reported in Ti/ZrO2/Pt resistive switching memory devices. The dominant mechanism of resistive switching is the formation and rupture of the conductive filament composed of oxygen vacancies. The conduction mechanisms for low and high resistance states are dominated by the ohmic conduction and the trap-controlled space charge limited current (SCLC) mechanism, respectively. The effect of a set compliance current on the switching parameters is also studied: the low resistance and reset current are linearly dependent on the set compliance current in the log—log scale coordinate; and the set and reset voltage increase slightly with the increase of the set compliance current. A series circuit model is proposed to explain the effect of the set compliance current on the resistive switching behaviors.

GaN垒层厚度渐变的双蓝光波长发光二极管

Due to low color rendering index of white light-emitting diodes based on packing of single-blue wavelength chip and Y3Al5O12∶Ce3+yellow phosphors,using dual-blue wavelength chip,Y3Al5O12∶Ce3+yellow phoshpor is proposed to realize high color rendering index white emission,and feasibility of the method is analyzed.Dual-blue wavelength light-emitting diodes based on two pairs of In0.18Ga0.82N/GaN quantum-well and two pairs of In0.12Ga0.88N/GaN quantum-well structure were grown sequentially on the same sapphire substrate by metal-organic chemical vapor deposition.Optoelectronic properties of dual-wavelength light-emitting diodes with different GaN barrier thicknesses were also studied.The experimental results indicate that efficient dual-blue-wavelength emission and higher luminescent efficiency are realized from lightemitting diodes by reducing GaN barrier thickness from n-GaN to p-GaN.The a.c.impedance spectroscopy can be explained in terms of the equivalent series circuit model of a set of parallel resistor-capacitor RpCpand a resistor Rsfor the dual-blue wavelength light-emitting diodes.Varied GaN barrier thickness can tune parallel resistor and capacitor while it has no effect on series resistor.In addition,Y3Al5O12∶Ce3+phosphor-converted white light emission with high color rendering index is achieved by use of dual-blue emitting active regions from reducing barrier thickness.

Design of metamaterial surfaces with broadband absorbance

A simple design paradigm for making broadband ultrathin plasmonic absorbers is introduced. The absorber's unit cell is composed of subunits of various sizes, resulting in nearly 100% absorbance at multiple adjacent frequencies and high absorbance over a broad frequency range. A simple theoretical model for designing broadband absorbers is presented. It uses a single-resonance model to describe the optical response of each subunit and employs the series circuit model to predict the overall response. Validity of the circuit model relies on short propagation lengths of the surface plasmons.

Simple method of determining plasma impedance of streamer discharge in atmospheric air

For atmospheric streamer discharges using a lightning impulse generator, we demonstrate a method of determining the plasma impedance in a streamer region by analyzing the periodic attenuated discharge waveforms having high-frequency components. When the streamer region in the plasma can be treated as an equivalent series circuit model including resistance and inductance elements, the regression waveforms obtained by reducing and smoothing the discharge waveforms are analyzed in the equivalent circuit. We found that the streamer resistance increased exponentially with time after the discharge, whereas the streamer inductance and series impedance were constant at 4.0 Ω for longer than the first period of the discharge waveforms. Moreover, the slope of the regression curve increases more rapidly for the positive streamer resistance than for the negative resistance. Finally, the absolute values of the streamer impedance versus time were 3.3-19 Ω and 3.5-9.0 Ω for positive and negative discharges, respectively.

Dissipation-factor-based criterion for the validity of carrier-type identification by capacitance-voltage measurements

High series resistance and parasitic parallel conductance—typical problems in electronic materials at early stages of development—can lead to serious artifacts in capacitance-voltage measurements. Depending on the assumed equivalent circuit model, these artifacts can even lead to an incorrect carrier type identification. Based on an analytical model we show that a dissipation factor of less than unity indicates that the correct carrier type is obtained in the series circuit model. In the context of Schottky diodes, we also show how the characteristics of the measured conductance-voltage curves from the parallel circuit model can be used to infer the carrier type. We demonstrate these effects with the example of an n-type ZnO sample for which the measured capacitance-voltage dependence seemingly shows the presence of p-type conductivity.

Simulation on the relation of distribution of overall critical transport current to that of local one in bent-damaged Bi2223 superconducting composite tape

The superconducting Bi2223/Ag/Ag alloy composite tape specimens with a length 6 cm, composed of a series circuit of six local elements with a length 1 cm, were bent by 0.37% and 1.0% for measurement of distributions of the overall (6 cm) and local (1 cm) critical transport current and n-value. When the damage amount was small (0.37% bending strain), the distributions of the measured local and overall critical currents were described by the three parameter Weibull distribution function, while when the damage amount was large (1.0% bending strain), those were described by the bimodal Weibull distribution function. The distributions of n-value in the diagram of n-value versus critical current for both local elements and overall specimens were expressed by the regression curve of n-value as a function of critical current and the normal distribution function for the deviation of the measured n-values from the regression curve. The experimentally measured critical current distribution and the diagram of the n-value versus critical current of the overall specimens were reproduced successfully in the computer by inputting the formulated distribution functions for the critical current and n-value of the local elements into the proposed simulation method, which used a Monte Carlo simulation method and a one-dimensional series circuit model for the generated voltage near the transition of superconducting to normal state.

Sample-length dependence of the critical current of slightly and significantly bent-damagedBi2223 superconducting composite tape

The local critical current along a sample length is different from position to position in along sample, especially when the sample is damaged by externally applied strain. In thepresent work, we attempted to reveal the relation of the distribution of the localcritical current to overall critical current and the sample-length dependence ofcritical current for slightly and significantly damaged Bi2223 composite tapesamples. In the experiment, 48 cm long Bi2223 composite tape samples, composedof 48 local elements with a length of 1 cm and 8 parts with a length 6 cm, werebent by 0.37 and 1.0% to cause slight and significant damage, respectively. TheV–I curve, criticalcurrent (1 µV cm−1 criterion) and n value were measured for the overall sample as well as for the local elements and parts. Itwas found that the critical current distributions of the 1 cm elements at 0.37 and 1.0%bending strains are described by the three-parameter- and bimodal Weibull distributionfunctions, respectively. The critical current of a long sample at both bendingstrains could be described well by substituting the distributed critical current andn value of the short elements into the series circuit model for voltage generation. Also themeasured relation of average critical current to sample length could be reproduced well in thecomputer by a Monte Carlo simulation method. It was shown that the critical current andn value decrease with increasing sample length at both bending strains. The extent ofthe decrease in critical current with sample length is dependent on the criterionof the critical current; the critical current decreases only slightly under the1 µV cm−1 criterion which is not damage-sensitive, while it decreases greatly withincreasing sample length under damage-sensitive criteria such as the1 µV one.

曲げ変形により損傷を受けたBi2223超伝導複合テープにおける局所臨界電流の分布と試料全体の臨界電流との関係

The damage extent and therefore the critical current are different from position to position in a long sample especially when the sample is deformed severely. In the present work, a 48 cm long Bi2223 composite tape bent by 0.7%, being composed of 48 elements with a length of 1 cm and of 8 parts with a length of 6 cm, was used as the test sample. The V-I curve, critical current and n-value were measured for the 48 elements, 8 parts and overall sample, and the relation of the distribution of the critical current of the elements to the critical current of the parts and overall sample and the sample length dependence of critical current were discussed. It was found that the critical current and n-value of parts and overall sample are described well by the voltage summation model which regards the parts and overall sample to be composed of a series circuit of elements. The critical current distribution of the elements was described by the bi-modal Weibull distribution function. Applying the simulation method, in which the estimated Weibull distribution function for the critical current of elements, the empirical relation between the critical current and n-value, the series circuit model for voltage generation and the Monte Carlo method were combined, the relation of average critical current to sample length could be described well. From these results and the features of the V-I curve of the damaged part, it was shown that the critical current and n-value decrease with increasing sample length and the extent of the decrease in critical current with sample length is dependent on the criterion for the definition of critical current.

Predictions of Specific Energies and Specific Powers of Double‐Layer Capacitors Using a Simplified Model

A model based on dilute‐solution porous‐electrode theory is proposed to describe electrochemical devices that store energy in the double layer (double‐layer capacitors). Various assumptions, such as neglecting concentration polarization, potential‐dependent capacitance, and micropore effects, are made in the model. For constant‐current discharges, the model reduces to a resistance capacitance (RC) series circuit model after the initial discharging transients. The RC series circuit model is seen to fit existing experimental data for the discharge times available. The specific energy for constant‐current and constant‐power discharges is maximized over a range of discharge times by optimizing the electrode thickness, electrode porosity, and the final voltage constrained by the cutoff voltage. This maximization allows predictions of the attainable specific energies and powers for these devices and shows the influence of the various cell properties. Energy efficiencies are found for cycles when the capacitor is discharged in a given time and then charged infinitely slowly, and when the capacitor is discharged and charged in the same amount of time. Limitations to the model are discussed. © 2000 The Electrochemical Society. All rights reserved.