Current-voltage Characteristic Curves Research Articles

Fault-tolerant power extraction strategy for photovoltaic energy systems

Photovoltaic (PV) arrays are subject to various types of environmental disturbances and component-related faults that affect their normal operation and result in a considerable energy loss. The nonlinear current-voltage (I-V) characteristic curve of the PV array prevents the detection and isolation of the faults and also makes the tracking of the maximum power operating point (MPP) more difficult. Fault detection and identification (FDI) techniques methods have been proposed to detect the presence of faults and isolate them. Many maximum power point tracking (MPPT) methods have been proposed to find the best operating point in the presence of disturbed environmental conditions. However, existing FDI methods do not consider the tracking of the MPP in faulted operating conditions, and available MPP tracking methods do not consider the occurrence of faults in the PV system. The objective of this study is to propose a fault-tolerant control (FTC) strategy to detect the presence of abnormal operating conditions and reconfigure the MPPT procedure to search for the new suboptimal operating point. The FDI method is based on monitoring the PV panel generated power for the presence of abrupt changes; the MPPT reconfiguration is based on a combination between Incremental Conductance (IncCond) Algorithm and an Improved Current-based Particle Swarm Optimization (ICPSO) tracking technique. Simulation and experimental results show an excellent performance of the proposed FTC method in the presence of various types of faults.

Development of a generalised PV model in MATLAB/Simulink using datasheet values

This study proposes an improved single-diode modelling approach for photovoltaic (PV) modules suitable for a broad range of the PV technologies available today, including modules based on tandem cell structures. After establishing the model (which has an overall of seven parameters), this study devises a methodology to estimate its parameters using Standard Test Conditions (STC) data, Nominal Operating Cell Temperature (NOCT) data, and temperature coefficient values as provided in most manufacturers’ datasheets. Simulation results and their comparison with a previous work show a very accurate prediction of critical points in the current-voltage characteristics curve. The precise prediction happens for both STC and NOCT conditions and the error in predicting maximum power point (MPP) lies within 1% limit, and the error in its corresponding voltage and current is almost always within 2% limit. Further, for both MPP and open-circuit voltage, the statistical variance around manufacturer measurements due to temperature changes is demonstrated to be low for five various module technologies.

New bipyridine ruthenium dye complexes with amide based ancillary ligands as sensitizers in semitransparent quasi-solid-state dye sensitized solar cells

Abstract A series of three heteroleptic ruthenium complexes containing 2,2′-bipyridine-4,4′-dicarboxamide ligands with different substituents (propyl, benzyl or 2-phenylethyl) was synthesized as possible sensitizers for dye sensitized solar cells (DSSCs). Their structure was characterized with 1H NMR and FTIR while their optical and electrochemical properties were also investigated. The observed optical differences were associated to structural properties of the three complexes and different electron donor strength of the ancillary ligands. In particular, ruthenium complex with propyl based ligand showed higher molar extinction coefficient succeeding better light harvesting. Semitransparent dye sensitized solar cells employing quasi-solid-state electrolyte and the three ruthenium complexes were constructed under the same fabrication conditions and electrically characterized under standard conditions of light irradiance (100 mW/cm2, AM 1.5). Their behavior was compared with that of commercially available ruthenium complex D907 with increased conjugation length of the ancillary ligand, in terms of current–voltage characteristic curves under simulated solar light and in the dark while electrochemical impedance spectroscopy was also used for local resistance to charge transfer across the TiO2-dye/electrolyte interface. The influence of ancillary ligands into ruthenium complexes was discussed in terms of the cells’ efficiency. A maximum overall performance of 5.0% was monitored for ruthenium complex with propyl substituent in comparison to 5.1% that was measured for semitransparent quasi-solid state devices with commercial D907.

Evaluation of the limiting factors affecting large-sized, flexible, platinum-free dye-sensitized solar cells performance: a combined experimental and equivalent circuit analysis

Reducing further the cost, increasing the application range, and scaling up of dye-sensitized solar cells (DSSCs) are important issues for their wide commercialization. The present paper constitutes a comprehensive analysis of the limiting factors affecting large-sized, flexible, platinum-free DSSCs performance. The results are interpreted using a series of materials characterization techniques, including scanning electron microscopy, atomic force microscopy, X-ray diffraction, Brunauer–Emmett–Teller analysis, ultraviolet–visible spectroscopy, diffuse reflectance spectroscopy, photoluminescence analysis, and cyclic voltammetry. Equivalent circuit analysis of DSSCs was applied, in all cases, to derive the key electrical circuit elements values, determining solar cells performance. Α satisfactory energy conversion efficiency was achieved by the implementation of the novel fabricated carbon-based counter electrodes to DSSCs, equal to the corresponding obtained by the photo-electrochemical cells employing commercially available platinum-based counter electrodes. The flexible, platinum-free DSSCs demonstrated a decreased photo-generated current and electron transport kinetics, while the charge recombination rate at TiO2/electrolyte and conductive substrate/electrolyte interfaces was increased, compared to the rigid ones. The scaling up effect was intense in the flexible devices, while the area-specific total series parasitic resistance increased, at high rates, by the solar cell active area. Equivalent circuit model successfully reproduced all experimental current–voltage characteristic curves of DSSCs, revealing that it is a powerful tool for routine analysis when designing novel photo-electrochemical cells.

Unraveling the mechanism of ultraviolet-induced optical gating in Zn1−xMgxO nanocrystal solid solution field effect transistors

We report ultraviolet (UV)-induced optical gating in a Zn1−xMgxO nanocrystal solid solution (NCSS) field effect transistor (FET) through a systematic study in which UV-induced charge transport properties are probed as a function of Mg composition. Change in the electrical properties of Zn1−xMgxO NCSS associated with electronic traps is investigated by field effect-modulated current–voltage characteristic curves in the dark and under illumination. Under UV illumination, significant threshold voltage shift to a more negative value in an n-channel Zn1−xMgxO NCSS FET is observed. Importantly, as the Mg composition increases, the effect of UV illumination on the threshold voltage shift is alleviated. We found that threshold voltage shift as a function of Mg composition in the dark and under illumination is due to difference in the deep trap density in the Zn1−xMgxO NCSS. This is supported by Mg composition dependent photoluminescence intensity in the visible range and reduced FET mobility with Mg addition. The presence of the deep traps and the corresponding trap energy levels in the Zn1−xMgxO NCSS are ensured by photoelectron spectroscopy in air.

Photothermal‐Induced Nanowelding of Metal–Semiconductor Heterojunction in Integrated Nanowire Units

AbstractAn improvised and comparatively inexpensive method for welding semiconductors and metal nanowires (NWs) utilizing a plasmon‐enhanced photothermal effect is presented in this article. Different types of heterojunction‐based (single Schottky junction and back‐to‐back Schottky junctions) electronic nanodevices are fabricated by welding various combinations of silver and ZnO NWs on two gold electrodes using continuous wave laser (λ = 532 nm) shots. It is inferred from the current–voltage characteristic curves of these devices that the junction formed between the ZnO nanowire (NW) and the gold electrode demonstrates Schottky barrier‐like behavior, whereas the junctions between silver‐and‐gold and silver‐and‐ZnO behave like ohmic contacts. The maximum currents obtained for a single Schottky junction and back‐to‐back Schottky junctions corresponding to the applied bias voltage 40 V are 42 µA and 7 µA, respectively. This plasmon‐enhanced nanowelding technique extends the range of applications of nanowelding in fabrication of electronic nanodevices.

Tailoring of electroluminescence from n-ZnO/p-GaN heterojunctions

In this study, electroluminescence (EL) from n-ZnO/p-GaN heterojunctions is investigated and tailored. The heterojunctions were obtained by depositing high-quality ZnO films on the p-GaN substrate through pulsed laser deposition (PLD), and the characteristics were analyzed by X-ray diffraction (XRD), photoluminescence (PL) spectra at room-temperature (RT, 300 K), current-voltage (I-V) characteristics curves, and the EL spectra. By means of the band energy theory, a simple and effective way to tailor the luminescent properties of the heterojunction was discussed. The ultra-violet (UV) emission from the n-ZnO was obtained through the improvement of the electrical properties of the films and the substrates. The visible light emissions were tailored through the transition of different defect caused color emissions. Besides, an unexpected yellow light (YL) emission caused by Ga-O interlayer was also studied.

Multiprobe characterization of plasma flows for space propulsion

Plasma engines for space propulsion generate plasma jets (also denominated plasma plumes) having supersonic ion groups with typical speeds in the order of tens of kilometers per second, which lies between electron and ion thermal speeds. Studies of the stationary plasma expansion process using a four-grid retarding field energy analyzer (RFEA), an emissive probe (EP) and a Langmuir probe (LP), all mounted on a three dimensionally (3D) displaced multiprobe structure are discussed. Specifically, the determination of plasma beam properties from the RFEA current-voltage (IV) characteristic curves is presented. The experimental results show the ion energy spectra to be essentially unchanged over 300 mm along the plasma-jet expansion axis of symmetry. The measured ion velocity distribution function (IVDF) results from the superposition of different ion groups and has two dominant populations: A low-energy group constituted of ions from the background plasma is produced by the interaction of the plasma jet with the walls of the vacuum chamber. The fast-ion population is composed of ions from the plasma beam moving at supersonic speeds with respect to the low-energy ions. The decreasing spatial profiles of the plasma-jet current density are compared with those of the low-energy ion group, which are not uniform along the axis of symmetry because of the small contributions from other ion populations with intermediate speeds.

Enhanced radioluminescent nuclear battery by optimizing structural design of the phosphor layer

Radioluminescent nuclear battery is a type of energy conversion device that can be miniaturized, which has the ability to convert nuclear energy into light energy, and again into electrical energy. To explore the response relationship between the phosphor layer structure and the electrical performance of radioluminescent nuclear battery, the physical model was established to research the deposition energy distribution by using Monte Carlo method. The radioluminescence spectra and current-voltage characteristic curves were used to investigate the optical and electrical properties. Through a comprehensive comparison of single plane layer, double plane layer, and V groove layer structures, the simulated results are consistent with experimental results. The results indicate that the Monte Carlo simulation is applicable to analysis of the phosphor layer structure of radioluminescent nuclear battery. Additionally, the results also show that the structure type and physical parameters of the phosphor layer have great influence on the energy deposition. A suitable phosphor layer structure can provide a new route to exhibit higher energy conversion efficiency as well as improving the matching degree between the range of radioactive particles and the thickness of the phosphor layer.

Characteristic features of the magnetoresistance in the ferrimagnetic (Sr2FeMoO6-δ) – dielectric (SrMoO4) nanocomposite

Magnetic metal-oxide compounds with high values of magnetoresistance (MR) have attracted huge interest for spintronic applications, among which Sr2FeMoO6-δ (SFMO) has been relatively less known compared to the cobaltites and manganites, despite 100% electrons spin-polarization degree and a high Curie temperature. Here, stable fabrication and systematic analysis of nanocomposites based on SFMO with SrMoO4 dielectric sheaths are presented. SFMO-SrMoO4 nanocomposites were fabricated as follows: synthesis of the SFMO single-phase nanopowders by the modified citrate-gel technique; compaction under high pressure; thermal treatment for sheaths formation around grains. The nanocomposite is observed to exhibit a transitional behavior of conductivity from metallic, which is characteristic for the SFMO to semiconductor one in the temperature range 4 – 300K under magnetic fields up to 10T. A negative MR is observed due to the spin-polarized charge carriers tunneling through dielectric sheaths. MR value reaches 43% under 8T at 10κ. The dielectric sheaths thickness was determined to be about 10 nm by electric breakdown voltage value at current-voltage characteristics curves. The breakdown is found to be a reversible process determined by collisional ionization of dielectric atoms in strong electric field depending on knocked-out electrons from the SrMoO4. It was found that MR changes sign in electric breakdown region, revealing the giant magnetoresistive properties.

Conductivity switching of labyrinth metal films at the percolation threshold

Electrical properties of silver, gold and copper films at the percolation threshold were investigated experimentally. A convenient method to obtain films at the percolation threshold that consists of two phases: deposition of metal in vacuum on a dielectric substrate and subsequent thermal annealing has been developed. The metallic films produced in this way exist in two different states: a low-conductivity state and a high-conductivity state. The films can be switched between these states by the applied voltage with hysteresis of current-voltage characteristic curves. The conductivity difference between the states reaches seven orders of magnitude. The switching threshold voltage depends on the annealing time. The switching times differ considerably for different metals. They were 200 ns for silver, 2 µs for gold, and 60 µs for copper. A plausible explanation of the switching mechanism based on the voltage induced fine mechanical deformations is suggested and discussed.

Enhancing the efficiency of low-temperature planar perovskite solar cells by modifying the interface between perovskite and hole transport layer with polymers

In this work, planar perovskite solar cells (PSCs) based on CH3NH3PbI3 perovskite layer and low-temperature processed TiO2 have been fabricated. Polymers including poly(methylmethacrylate) (PMMA), poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-pheny- lenevinylene] (MEH-PPV) and polyethylene glycol (PEG) in chlorobenzene solution have been selected to modify the interface between perovskite and hole transport layer (HTL), respectively. The concentrations of the three polymer solutions have been optimized. The effect of interfacial modification by different polymer solutions on the photoelectric properties of perovskite layer and the performance of PSCs has been systematically investigated. The microstructure and photoelectric properties of the modified perovskite films has been systematically studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), conducting force microscopy (CFM) and Kelvin probe force microscopy (KPFM). The results reveal that the modified perovskite films with tetrahedral perovskite structure have lager grain size, lower roughness and better photoelectric properties compared with the reference sample. The electron trap state density (Dtrap), charge extraction, carrier transfer and recombination process in the PSCs have been investigated by current-voltage (I-V) characteristic curves, steady-state photoluminescence (PL), photo-voltage decay and electrochemical impedance spectroscopy (EIS). The results indicate that the polymeric interface modification at the optimum concentration can reduce the Dtrap, promote the charge transfer and suppress carrier recombination, resulting in the improved performance of PSCs. All of the modified PSCs at an optimum concentration exhibit the improved fill factor (FF) and open circuit voltage (Voc), thus the power conversion efficiency (PCE) is enhanced to over 17% from 15.49%.

Influence of the deGennes extrapolation parameter on the resistive state of a superconducting strip

We studied the resistive state of a mesoscopic superconducting strip (bridge) at zero external applied magnetic field under a transport electric current, Ja, subjected to different types of boundary conditions. The current is applied through a metallic contact (electrode) and the boundary conditions are simulated via the deGennes extrapolation length b. It will be shown that the characteristic current–voltage curve follows a scaling law for different values of b. We also show that the value of Ja at which the first vortex–antivortex (V–Av) pair penetrates the sample, as well as their average velocities and dynamics, strongly depend on the b values. Our investigation was carried out by solving the two-dimensional generalized time dependent Ginzburg–Landau (GTDGL) equation.

STRUCTURAL, ELECTRICAL AND OPTICAL PROPERTIES OF TiO2THIN FILM DEPOSITED ON THE NANO POROUS SILICON TEMPLATE

The porous silicon (PSi), which is produced by the electrochemical etching, has been used as a substrate for the growth of the titanium oxide (TiO2) thin films. By using the EBPVD method, TiO2thin films have been deposited on the surface of the PSi substrate. TiO2/PSi layers were annealed at the temperature of 400[Formula: see text]C, 500[Formula: see text]C and 600[Formula: see text]C for different tests. The morphology and structures of layers were investigated by the scanning electron microscopy (SEM) and X-ray diffraction (XRD). The current–voltage characteristic curves of samples and the ideality factor of heterojunction were studied. The results showed that the electrical properties of the samples change with increase in the annealing temperature. The optical properties of the prepared samples were investigated by using UV–Vis and photoluminescence (PL) spectroscopy. Green light emission of the PSi combined with the blue light and violet–blue emission obtained from the TiO2/PSi PL spectra. The results showed that the optical band gap energy of the PSi has increased from 1.86[Formula: see text]eV to 2.93[Formula: see text]eV due to the deposition of TiO2thin film.

Simplex simplified swarm optimisation for the efficient optimisation of parameter identification for solar cell models

The development and application of photovoltaic (PV) systems are becoming increasingly more important as the global need for energy resources expands and environmental protection becomes more highly valued. Parameters of PV models can be identified by measuring their current-voltage ( I - V ) characteristic curves. Identifying these parameters quickly, accurately and reliably is critical in determining the operating status of in situ PV arrays and, in turn, optimising solar energy conversions. To achieve both fast and accurate parameter identification with high reliability, a new algorithm called algorithm based on SSO and Nelder-Mead simplex (NMS) (SSSO) based on the simplified swarm optimisation (SSO) and the NMS is proposed in this study. To demonstrate the performance of SSSO in identifying solar cell system parameters, its performance on the single diode model and the double diode model was compared with existing algorithms in terms of both fitness value and run time. The experiment results indicate that SSSO outperformed the compared algorithms in both run time and standard deviation of fitness value.

Study of Scanning Micro-arc Oxidation and Coating Development

Micro-arc oxidation (MAO) continues to be the focus of numerous investigations, whereas relatively few studies have considered scanning micro-arc oxidation (SMAO). In the present work, an experimental study was performed using stationary and moving electrodes to investigate coating development in SMAO and discern the effect of key process parameters. Examination of oxide deposits made on A356 aluminum show that coating thickness and growth rate are inversely related to inter-electrode spacing and travel speed. An evaluation of SMAO deposits made by stationary and moving nozzles revealed that coating thickness profiles follow a Gaussian distribution due to the electrolyte flow field in the impingement zone. Hardness surveys and scanning electron microscope analysis of SMAO coatings revealed that micro-hardness distributions and cross-sectional morphology are similar to MAO for a stationary nozzle but that a denser outer layer develops when a moving nozzle is used. This is attributed to a high density of discharge occurring in micropores of the oxide film and remelting which results from the moving electrolyte column. Analysis of voltage–current characteristic curves shows that the resistance of the electrolyte column is essentially linear over the range considered and results indicate that it can be modeled as a variable length resistor. While further testing is needed, results confirm that SMAO is suitable for coating large, planar parts and for repairing worn surfaces.

Characteristics of Soil Ionization around a Ground Rod under Impulse Voltages

The study described the results of experiment on electrical and physical characteristics related to soil ionization around a ground electrode to which impulse voltages were applied to coaxial circular electrode system, simulated by the ground rod or the horizontally buried ground electrode. Ground resistance was significantly reduced by soil ionization caused by impulse voltage in which the voltage-current characteristic curve ( curve) appeared as ∞-shape of a cross-closed loop. According to the increase of impulse current through a ground electrode, the equivalent soil resistivity was reduced, but the delayed time to the maximum of the equivalent radius of the ground electrode was increased. As soil ionization progressed, average progress speed increased proportionally, according to the increase of peak current.

Parameters identification of photovoltaic models using an improved JAYA optimization algorithm

Parameters identification of photovoltaic (PV) models based on measured current-voltage characteristic curves is significant for the simulation, evaluation, and control of PV systems. To accurately and reliably identify the parameters of different PV models, an improved JAYA (IJAYA) optimization algorithm is proposed in the paper. In IJAYA, a self-adaptive weight is introduced to adjust the tendency of approaching the best solution and avoiding the worst solution at different search stages, which enables the algorithm to approach the promising area at the early stage and implement the local search at the later stage. Furthermore, an experience-based learning strategy is developed and employed randomly to maintain the population diversity and enhance the exploration ability. A chaotic elite learning method is proposed to refine the quality of the best solution in each generation. The proposed IJAYA is used to solve the parameters identification problems of different PV models, i.e., single diode, double diode, and PV module. Comprehensive experiment results and analyses indicate that IJAYA can obtain a highly competitive performance compared with other state-of-the-state algorithms, especially in terms of accuracy and reliability.

Insulating NiO enhanced MgZnO-based single-barrier 340 nm photodetector

Combining pulsed laser deposition and thermal oxidation techniques, an enhanced MgZnO-based photodetector was achieved by inserting an insulating NiO layer between Au electrode and the Mg0.21Zn0.79O active layer. Bias voltage dependent spectral response of the Au/NiO/MgZnO/In photodetector was investigated systematically and it exhibited a peak response of 340 nm with a cutoff wavelength at 355 nm. Under reverse bias, a negative differential resistance feature was observed in the dark and light current-voltage characteristic curves.

Transition characteristics of low-pressure discharges in a hollow cathode

Based on a two-dimensional (2-D) fluid model, the transition processes of discharges in a hollow cathode at low pressure are observed by changing three parameters, i.e., applied voltage U0, gas pressure p, and external circuit ballast resistance Rb. The voltage-current characteristic curves, electron density distributions, and electric potential distributions of different discharge operating points in a hollow cathode are obtained. The transition processes are characterized by the voltage-current characteristic curves, the electron density distributions, and the electrical potential distributions. The transition modes observed from the voltage-current characteristics include the low-current abnormal mode, normal mode, and high-current abnormal mode. Increasing the applied voltage U0 can have a similar effect on the discharge transition processes to decreasing the ballast resistance. By increasing U0 from 200 V to 500 V and decreasing Rb from 5000 kΩ to 100 kΩ independently, it is observed that the discharge transfers from the outside to the inside of the hollow cavity, thus forming the virtual anode potential. By increasing the gas pressure p from 50 Pa to 5 kPa, the discharge also moves into the hollow cavity from the outside; however, a further increase in the gas pressure leads to the discharge escaping from the hollow cavity. Simulation results and characterizations for different parameters are presented for the transition properties of low-pressure discharges in a hollow cathode. It is verified that the hollow cathode discharge only exists under certain ranges of the above parameters.