Voltage Transition Research Articles

Unraveling trap distribution in perovskite films: A qualitative analysis via diffusion to drift transition voltage of current–voltage characteristics

Traps cause accumulation of space charge near injecting contacts, due to which there is band bending in the vicinity of contacts. This leads to a lowering of voltage at which there is change from diffusion to drift dominated current under steady state, termed as transition voltage (Vα). We propose a technique to qualitatively understand the trap distribution by analyzing the Vα of a two terminal perovskite device. The validity of the proposed technique has been verified from the numerical simulations carried out using Sentaurus TCAD. Both density (NT) and energetic depth (ET) of traps were varied to study their effect on Vα. Devices with deeper and higher NT have been found to exhibit stronger band bending and thus lower Vα. In addition, Vα has been found to be sensitive to NT even when band bending due to accumulated ions or uncompensated dopants near interfaces is significant. This dependence has been further illustrated for a perovskite solar cell device. It has been concluded that Vα can be advantageous over VOC in optimizing perovskite film for trap-free solar cell. The availability of different methods to extract Vα from current–voltage (J–V) characteristics, and the extra sensitivity of Vα to NT paves a way to study traps effectively.

Preparation of Hybrid Films Based in Aluminum 8-Hydroxyquinoline as Organic Semiconductor for Photoconductor Applications.

In the present work, we have investigated an organic semiconductor based on tris(8-hydroxyquinoline) aluminum (AlQ3) doped with tetracyanoquinodimethane (TCNQ), which can be used as an organic photoconductor. DFT calculations were carried out to optimize the structure of semiconductor species and to obtain related constants in order to compare experimental and theoretical results. Subsequently, AlQ3-TCNQ films with polypyrrole (Ppy) matrix were fabricated, and they were morphologically and mechanically characterized by Scanning Electron Microscopy, X-ray diffraction and Atomic Force Microscopy techniques. The maximum stress for the film is 8.66 MPa, and the Knoop hardness is 0.0311. The optical behavior of the film was also analyzed, and the optical properties were found to exhibit two indirect transitions at 2.58 and 3.06 eV. Additionally, photoluminescence measurements were carried out and the film showed an intense visible emission in the visible region. Finally, a photoconductor was fabricated and electrically characterized. Applying a cubic spline approximation to fit cubic polynomials to the J-V curves, the ohmic to SCLC transition voltage VON and the trap-filled-limit voltage VTFL for the device were obtained. Then, the free carrier density and trap density for the device were approximated to n0=4.4586×10191m3 and Nt=3.1333×10311m3, respectively.

Soft Switching for MOSFET and IGBT Based Hybrid DC-DC Boost Converter

In this study, a hybrid DC-DC boost converter was proposed for high voltage gain. The proposed converter was analyzed and designed. The active soft switching method was applied to proposed converter to reduce the losses due to hard switching. While the main switch of proposed converter is turning off, the main switch current is zero during voltage transition and in the opposite case, the main switch voltage is zero during current transition. Thus, power losses for both states of the main switch were minimized. The simulation for MOSFET and IGBT based hybrid DC-DC boost converter with active soft switching were obtained for different loads.

Complementary inverter and reward-modulated spike timing dependent plasticity circuit based on organic transistors

Organic materials are the key to the next generation of electric memory elements because of their low cost, high flexibility and high scalability. Solution-processed n-channel and p-channel organic field effect transistors (FETs) by spinning coating technique was demonstrated. We use based-poly (vinylcarbazole) (PVK) p-type transistor and based-6-phenyl-C61 butyric acid methyl ester (PCBM) n-type transistor as the channel of bottom gate structure FET, respectively, to fabricate the complementary inverter. The maximum voltage gain of the electrically isolated FET complementary inverter is up to 22, the power consumption is less than 3 μW, and the transition voltage is −4.2 V. In addition, our devices are able to implement “AND”, “NAND”, “OR”, and “NOT” gate logic well. But more than that, p-type transistor based on PVK and n-type transistor based on PCBM were combined with the memristor, reward-modulated spike timing dependent plasticity was implemented by introduced reward/punishment signals to guide synaptic weight updates. It shows great potential in the electronic application system with low cost and high energy efficiency.

A reconstructed LCC‐LCC compensated inductive power transfer system with inherent constant current to constant voltage transition capability

SummaryDue to the merits of convenience and flexibility, inductive power transfer (IPT) systems have become popular for energy storage devices, such as lithium‐ion batteries, which require constant current (CC) and constant voltage (CV) outputs. The conventional LCC‐LCC topology with high design freedom is widely used for battery charging. The conventional LCC‐LCC topology achieves the initial CC output and the subsequent CV output by reconfiguring its topology or hopping its operating frequency, which increases the control complexity. This paper proposes a reconstructed LCC‐LCC compensated IPT system, which can achieve the inherent CC‐to‐CV transition without extra components and control methods. Compared with the conventional LCC‐LCC topology having CC and CV outputs, the operating frequency and topology of the proposed IPT system are fixed. Besides, the battery state of charge (SOC) detection and wireless communication are not required. The analysis and parameters design of the proposed IPT system is performed. Finally, an experimental prototype of the proposed IPT system with 48 V input and 72 V/2 A output is built to validate the proposal.

A novel programming circuit for memristors

Memristor has attracted a lot of interest due to its high processing speed, low power consumption and high integration ability, which is critical for electronic systems and memory-centric computing. However, the memristor programming circuit and strategy are still inflexible and complex, since the signal generator/collector and stimulate pulse must be carefully matched and designed based on memristor intrinsic characteristics without reconfigurable. Here, a simple and effective circuit only consists a parallel reference-resistor-and-NMOS is designed to program memristor with a >99% memristance precision. And the amplitude and width of stimulate pulse are fixed to ±4 V and 5 ms, respectively. In order to cope with the device variation, such as ±10% tolerance of transition voltage, an optimized programming strategy was proposed and demonstrated great robustness. Additionally, a set of reference resistors and NMOSs have been added to facilitate multi-level memristance operation without requiring any changes to the circuit structure. This program circuit was also employed to program memristor crossbar remains 99% precision. In the end, a memristor-based convolutional neural network which controlled by our optimized programming circuit was used for image recognition, and 89.36% accuracy can be achieved even under 15.8% memristance tolerance. This novel circuit demonstrates a simple and flexible strategy in memristor programming, providing a new way to control memristor crossbar for practical application.

A Soft-Switching Bridgeless Buck-Boost Power Factor Correction Converter With Simple Auxiliary Circuit and Low Input Current THD

In this paper, a new bridgeless (BL) buck-boost power factor correction (PFC) converter using pulse width modulation (PWM) control is presented. The introduced structure operates in discontinuous conduction mode (DCM) to achieve the sinusoidal form of the input current inherently. The proposed converter utilizes a simple zero voltage transition (ZVT) circuit in which the auxiliary switch is turned ON and OFF under zero current switching (ZCS) condition, and the main switches turn ON and OFF under zero voltage switching (ZVS). Moreover, all diodes are turned OFF under ZCS condition, and the reverse recovery problem is solved. By reducing the number of semiconductor elements in the current flow path, conduction loss is minimized. Also, the proposed structure utilizes only one magnetic element. The above-mentioned advantages along with a low total harmonic distortion (THD) and high efficiency are the main benefits of the proposed structure compared to previous topologies. In addition, unlike the BL-buck converter, the input current dead angle is omitted without adding any extra components. Finally, a 500 W-100 kHz prototype at 90-265 Vrms input and 96 V output is implemented to verify the theoretical analysis and it illustrates the efficiency of 97.35 % and the input current THD is about 2.7 % at 220Vrms input voltage.

Design and Implementation of a Flyback-Assisted Wide-Range Fully Soft-Switched T-Type Inverter

A novel soft-switched three-level T-type inverter (3LT <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> I) is proposed in this paper. The proposed inverter provides turning-on by zero voltage transition (ZVT) and turning-off by zero voltage switching (ZVS) for main switches without any voltage or current stresses. The switching energies are transferred to the snubber capacitors, so the turning-off process of the main switches is improved by these snubber capacitors. Besides, the auxiliary switches are turned on by zero current switching (ZCS) and turned off by ZVS. Furthermore, all snubber diodes are operated by soft switching (SS), and the proposed SS snubber cell decreases the electromagnetic interference (EMI) noises. The novel snubber cell has a simple structure, ease of application, common-ground switches, and low-cost features. The theoretical analysis of the inverter is clarified, and the operating modes for steady-state analysis are presented in detail. The experimental results rated 1 kW output power and 100 kHz switching frequency are provided to justify the theoretical analysis. The proposed unique snubber cell can be easily implemented in other three-level inverters (3LIs), and the practice is demonstrated in the paper.

Microstructural and electrical investigation of polymorph stabilization and multistate transition in interface engineered epitaxial VO2 films

Modulation of metal to insulator transition (MIT) in vanadium dioxide (VO2) remains one of the most important cornerstones for its wide scale applications in electrical devices. Incorporating VO2 within and beyond room temperature ranges requires energy efficient systems with high device performance and low transition losses. To achieve this performance, we studied pulsed laser deposition (PLD) grown VO2 films on sapphire substrate, with and without titanium dioxide (TiO2) buffer layer. An insight into microstructural modification and MIT was provided using in-situ characterization techniques. We observed that misfit strain and external stimuli induces polymorphs and phases like VO2 (M2), VO2 (T) and V2O3 in the epitaxial films along with higher stabilization of intermediate M2 for the TiO2 system. To understand the effect of interface engineering on transition temperature and voltage, in-plane and out-of-plane device architectures were fabricated and characterized using electrical measurements. We discovered that TiO2 interface enables realization of two step electrical transition, Tc close to room temperature and lowering of transition voltage and work function. Also, using DFT calculation, we studied the effect of substrate misfit strain on structural and electronic properties of polymorphs. Since M1 and R have different structures, the strain experienced before and after transition on the same substrate will be different. Using the orientation relation of PLD grown films, we predict the MIT temperature, validating the Tc observed through experimental electrical measurements.

Secondary Structure-Dependent Charge Transport in iLOV Protein Junctions.

The composition and structure of proteins are crucial for charge migration in the solid-state charge transport (CTp). Despite much progress, it is still challenging to explore the relationship between conformational change and CTp in the complex protein system. Herein, we design three improved light-oxygen-voltage (iLOV) domains, and efficiently regulate the CTp of the iLOV self-assembled monolayers (SAMs) by pH induced conformation variation. The current density can be controlled in the range of one order of magnitude. Interestingly, the CTp of iLOV displays negative linear relations with the β-sheet contents. Single-level Landauer fitting and transition voltage spectroscopy analysis suggest that β-sheet-dependent CTp would be related to the coupling between iLOV and electrodes. This work proposes a new strategy to explore the CTp in complex molecular system. Our findings deepen the understanding on protein structure-CTp relationship, and provide predictive mode of protein CTp responses for the design of functional bioelectronics.

84‐1: Studies on Optical Performance and Driving Method of HTN Mode Dye‐Doped Liquid Crystal Smart Window

Transmittance, haze and texture performance of new high twisted nematic(HTN)mode dichroic dye‐doped liquid crystal device under different voltages when power on and power off were studied. According to the elastic free energy theory of liquid crystal, two key phase transition voltages VPH and VHP of HTN mode liquid crystal were calculated. From a theoretical perspect, it was verified that the liquid crystal transition state under different voltages could correspond to the actual dimming performance, which could provide technical driving reference for other similar HTN device. Finally, based on the above analysis results, driving methods of three light dimming modes which included anti‐glare, privacy protect and high transparent mode were studied to meet the needs of different application scenarios.

Common mode conductive noise cancellation for multiphase converter using auxiliary winding

AbstractA multiphase DC‐DC converter consisting of a coupled inductor and fast switching devices enables power electronics equipment to achieve a high‐power density. However, with such devices, the fast voltage transition generates substantial common mode (CM) noise. However, there are very few studies on CM noise reduction for multiphase converters using a coupled inductor. Therefore, in this paper, a CM noise reduction method is proposed for a multiphase DC‐DC converter that hardly lowers the power density.

An Asymmetrical Dual Quasi-Z-Source Based 7-Level Inverter for PV Applications

This paper presents a new single-stage quasi-z-source (qZS) based power converter for Photovoltaic (PV) applications. This seamless topology is obtained by the fusion of two quasi-z-source networks with a 7-level cascaded multilevel inverter (MLI). The proposed converter requires fewer passive components and power switching devices compared to the seven-level topologies with impedance and quasi-impedance sources, reported in the literature. The proposed modulation technique achieves the required level of voltage boosting using the qZS networks while synthesizing seven levels in the output voltage waveform. While the proposed power converter can regulate the output voltage in the standalone mode, it can inject active power into the grid at Unity power factor (UPF) in the grid-connected mode of operation. This paper also aims to mitigate the leakage current, which is one of the major issues in transformerless PV inverters, by reducing the magnitude of voltage transitions in the parasitic capacitor and the suppression of higher-order harmonics in the ground leakage current. The steady-state and the dynamic performances of the proposed power converter during grid-connected mode of operation is assessed with simulation studies and are validated with experimental results.

An improved auxiliary circuit for IPT systems to achieve inherent CC‐to‐CV transition and load fault‐tolerant operation

AbstractThree‐coil inductive power transfer (IPT) charging system can not only achieve inherent constant current (CC) to constant voltage (CV) transition but also tolerate load open‐circuit. However, due to the cross‐coupling between the auxiliary coil and the receiver coil, the output voltage in CV mode may deviate from the CV voltage significantly, which makes the design freedom of the three‐coil coupler low. By replacing the auxiliary coil with a transformer, an improved auxiliary circuit is proposed in this paper to address the cross‐coupling issue and to increase the design freedom of the loosely coupled transformer (LCT). The improved auxiliary circuit can achieve load short‐circuit and open‐circuit protection. Besides, the optimization design of LCT is easy to achieve by load impedance matching. The operating principle and parameters design of the improved auxiliary circuit are discussed. A 1 kW experimental prototype is built to verify the feasibility of the proposed method.

A multi‐criteria methodology with algebraic validation for the design of space vector switching sequences over a fundamental period horizon

AbstractThis paper presents a novel methodology for the design of the Space Vector (SV) switching sequences in order to reduce the output voltage distortion and the common‐mode voltage (CMV) without increasing the number of commutations in comparison to conventional and optimised techniques presented in the literature. Three spaces can be distinguished in a converter, referring to: line‐to‐line voltages, phase voltages and switching states. Consequently, three correspondent sequences of vectors in each space can be verified. The output voltage distortion, CMV and switching count are mainly affected, respectively, by the sequences in the line‐to‐line voltage, phase voltage and switching state spaces. However, the three spaces are interdependent, and the selection of a sequence in one space affects the ones in the other spaces. As a consequence, this paper presents a novel SV approach, where the line‐to‐line voltage sequences are selected over a fundamental period horizon considering the impact in the phase voltages through an algebraic analysis, assuring minimal phase voltage transitions while using VIKOR method to choose the best trade‐off between reduction of output voltage distortion and CMV. In order to validate the proposed strategy, experimental results are given to a three‐phase five‐level Packed U‐Cell (PUC5) converter.

Comparison of Lithium Diffusion Coefficient Measurements in Tellurium Electrodes via Different Electrochemical Techniques

Both thin (55 μm) composite and thick (350 μm) all active material battery porous electrodes were prepared for estimating the diffusion coefficient of Li+ ( in tellurium (Te) during electrochemical lithiation. Galvanostatic intermittent titration technique (GITT), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS) were applied to quantify the chemical lithium solid-state diffusion coefficient within the Te active material in the electrodes. Multiple methods of GITT and EIS were assessed. For the composite Te electrodes, the was on the order of 10−11 cm2 s−1 from both CV and GITT methods, but 10−9 cm2 s−1 from EIS. For the thick tellurium electrodes, both GITT and EIS resulted in lithium diffusion coefficient estimates in the range of 10−11–10−12 cm2 s−1. The general trend across all methods that quantified the diffusion coefficient as a function of lithiation of tellurium was that the decreased rapidly when the Te material was initially lithiated. The at the phase transition voltage plateau (∼1.7 V, vs Li/Li+, where both Te and Li2Te were expected) had the lowest while the both before and after the plateau was generally higher. Among all the electrochemical measurements of the modified GITT method with modelling the relaxation region resulted in relatively low scatter in the data, provided values as a function of lithiation, and was well suited to thick electrodes with a flat discharge plateau as was the case herein.

Design of an energy-efficient nonvolatile lookup table circuit using active-load-localized circuitry with self-terminated writing/reading

An energy-efficient nonvolatile lookup table (LUT) circuit, where both write and read currents are automatically terminated if desired write/read operations are completed, is proposed. The use of self-terminated writing makes it possible to cut off wasted write current by continuously monitoring voltage transitions owing to the resistance change in the storage element. In addition, wasted read current can be cut off by utilizing the voltage drop in active-load-localized circuitry as a read completion signal. In fact, the proposed 6-input LUT circuit reduces 59% of write energy and 47% read energy with only 5% of hardware overhead compared with those of a conventional circuit style under a 45 nm CMOS technology.

Common Mode Conductive Noise Cancellation for Multiphase Converter Using Auxiliary Winding

A multiphase DC-DC converter consisting of a coupled inductor and fast switching devices enables power electronics equipment to achieve a high power density. However, with such devices, the fast voltage transition generates substantial common mode (CM) noise. However, there are very few studies on CM noise reduction for multiphase converters using a coupled inductor. Therefore, in this paper, a CM noise reduction method is proposed for a multiphase DC-DC converter that hardly lowers the power density.

Effect of Working Current on C12A7 Hollow Cathode

The C12A7 hollow cathode is expected to usher in a new generation of hollow cathodes because of its low work function and chemical stability. In order to reduce the emission melting and degradation caused by the overheating of this new cathode, different working currents of the C12A7 hollow cathode were studied in this work. The working currents ranged from 1 A to 20 A. The results show that the C12A7 hollow cathode works well under the condition of a low current, but it is unstable under high current condition. A simulation with the COMSOL internal working environment showed that enlarging the cathode orifice size is beneficial to reduce the risk of overheating of the electride emitter. The C12A7 hollow cathode shows a voltage transition phenomenon under a high operating current. The plasma plume state at the cathode outlet gradually changes from bright violet to dark yellow. The emitter also melts at high temperatures under high-current conditions. Its short lifetime makes the C12A7 hollow cathode difficult to apply in practical application scenarios under high-current conditions.

Evidence of Lampert Triangle and Jonscher’s Double Power Law in Doped Poly(3,4-ethylenedioxythiophene) Devices

The Lampert triangle model can be an interesting method for investigating the conduction mechanism in semiconducting polymers. A complete Lampert triangle is observed in PF6− doped poly(3,4-ethylenedioxythiophene) [PEDOT:PF6] devices, fabricated in a stainless steel/PEDOT/Ag structure and synthesized by electro-polymerization at three different doping levels (high-S1, medium-S2, and low-S3). The temperature-dependent current–voltage characteristics show three distinct regimes limited within a triangular region called the Lampert triangle: Ohmic, trap-limited/filling space charge-limited conduction (TFL-SCLC), and trap-free/trap-filled space charge-limited conduction (TF-SCLC). The vertices of the Lampert triangle represents the transition voltages (VT) for different conduction mechanisms, and the carrier density (p0), carrier transit time (tt), and relaxation time (td) for different doping levels are estimated through the analysis of the triangle. The mobility of carriers shows significant temperature dependence (Arrhenius type). The Jonscher’s double power law fit to AC conductivity data shows that the exponent (in the range 0–1) varies with carrier density and has different trends in bulk and interface. The impedance data and Nyquist plots are analyzed with two parallel RQ circuits (R: resistance; Q: constant phase element) connected in series. The values of onset frequency (ωo) in the conductivity plot of the different samples (S1, S2, and S3) give insights into their relative disorder. Raman spectroscopy studies have attempted to corroborate the changes in bond deformation with carrier density in correlation with the structure and disorder.