Ionic Charge Accumulation Research Articles

Phase transformation and plasmonic damping study for semi-solid ionic polymeric hydrogel system at higher temperature and low radio frequency

This article represents the findings regarding the phase transitions exhibited by a polymeric hydrogel material composed of sodium polyphosphate-polyethylene glycol. These transitions play a crucial role in the generation of ionic plasmons and the manifestation of surface plasmon resonance (SPR) with dielectric permittivity damping within the polymer electrolyte system of the hydrogel. Usually, SPR has been observed in electron-conducting systems within an optical frequency range. However, here SPR is observed in an ionic system within a lower radio frequency range of 104-10 (Parwati et al., 2024) 77 Hz for temperatures exceeding 80 °C. The mechanism responsible for permittivity damping can be elucidated by considering the accumulation of ionic charges at the interface between the electrode and the electrolyte, coupled with a high degree of charge absorption following the Drude model. A power law has been used to describe the resonance that occurs between the applied DC frequency and the motion of charge carrier ions, thus confirming the presence of free ionic motion within the hydrogel matrix. tan δ shows significant energy absorption further substantiating permittivity damping, which transitions from positive to negative values.

Capacitive and Inductive Effects in Perovskite Solar Cells: The Different Roles of Ionic Current and Ionic Charge Accumulation

Dynamic hysteresis effects have been long known to occur in the current density-voltage characteristics of perovskite solar cells, with the ionic migration being identified as the primary factor. The hysteretic effects impacted early studies by the uncertainty in the evaluation of the power conversion efficiency, while currently, potential links to degradation mechanisms are the focus. Therefore, understanding ion migration is a central goal, typically addressed by performing a combined large and small signal analysis. The reported large capacitive and inductive effects created controversies with respect to the underlying mechanisms, yielding essentially two classes of models, one based on the large accumulation capacitances and the other based on the ionic modulation of the collected current. We introduce here an equivalent circuit model and interpret these phenomena in terms of recombination current modulation, identifying the distinct contributions from ion current and ionic charge accumulations. These contributions to the recombination current are associated with capacitive and inductive effects, respectively, and we corroborate the numerical simulations with electrochemical impedance spectroscopy measurements. These show the role of the recombination currents of photogenerated carriers in producing both capacitive and inductive effects as the illumination is varied. Moreover, we provide a bridging point between the two classes of models and suggest a framework of investigation of defect states based on the observed inductive behavior, which would further aid the mitigation of the degradation effects.

Effect of Ion Vacancy Migration on Open‐Circuit Voltage of Perovskite Solar Cells

Herein, the influence of ion vacancy migration on the open‐circuit voltage (Voc) of perovskite solar cells (PSCs) by computer simulation is explored. It is found that for PSCs, Voc is determined not only by the carrier recombination process, but also dominantly by the space charge effect of the ion vacancy stored within the Debye layers of the perovskite absorber layer. The migration of ion vacancy affects the ionic charge accumulation within the Debye layers, which affects the screen voltage via the space charge effect and thus determines Vocr and Vocf (open‐circuit voltage for reverse sweep and forward sweep, respectively). By tuning the parameters that determine ion vacancy mobility, the effects of ion vacancy mobility on Vocr and Vocf is investigated.

Hole injection in perovskite light-emitting device with PEDOT:PSS/perovskite interface via MS contact

The hole-injection mechanism of FAPbBr3-based lead halide perovskite light-emitting diodes with PEDOT:PSS as the hole injection layer is revealed as the metal-semiconductor contact at the PEDOT:PSS/perovskite interface. The accumulation of ionic charges at the interface at the external voltage is responsible for the enhancement of hole injection. It is discovered that the strong binding between the positively charged PEDOT chain and the negatively charged Br− gives rise to the slowest charge relaxation. Moreover, the charge concentration of FAPbBr3 perovskite is estimated to be around 3.0 × 1018 cm−3 by saturating the relaxation current.

Role of Ionic Charge Accumulation in Perovskite Solar Cell: Carrier Transfer in Bulk and Extraction at Interface

By combining a simplified drift-diffusion model with the density functional theory, we quantitatively explore the contributing effects of the mobile defects in perovskites on the hysteresis of perovskite solar cells from aspects of both carrier transfer in the perovskite and extraction at the interface. Based on the solution of the one-dimensional Poisson equation, we demonstrate that at a positive biasing voltage applied to the hole contact layer that is larger than the presetting voltage, the carriers in perovskite need to overcome an energy barrier to transfer toward their selective contacts. The dependence of the energy barrier on the scanning voltage is determined by properties of both perovskite and contacts. By using the first-principles calculations, we further find that the perovskite/TiO2 band offsets are larger at a higher positive presetting voltage. The results reveal that the contributions of the defect migration to the hysteresis depend not only on the structural properties of perovskite but also on the choice of the contact materials via both carrier transfer in the bulk perovskite and carrier extraction at the interface between the perovskite and the contact materials.

Heterointerface effects in the electrointercalation of van der Waals heterostructures.

Molecular-scale manipulation of electronic and ionic charge accumulation in materials is the backbone of electrochemical energy storage1-4. Layered van der Waals (vdW) crystals are a diverse family of materials into which mobile ions can electrochemically intercalate into the interlamellar gaps of the host atomic lattice5,6. The structural diversity of such materials enables the interfacial properties of composites to be optimized to improve ion intercalation for energy storage and electronic devices7-12. However, the ability of heterolayers to modify intercalation reactions, and their role at the atomic level, are yet to be elucidated. Here we demonstrate the electrointercalation of lithium at the level of individual atomic interfaces of dissimilar vdW layers. Electrochemical devices based on vdW heterostructures 13 of stacked hexagonal boron nitride, graphene and molybdenum dichalcogenide (MoX2; X = S, Se) layers are constructed. We use transmission electron microscopy, in situ magnetoresistance and optical spectroscopy techniques, as well as low-temperature quantum magneto-oscillation measurements and ab initio calculations, to resolve the intermediate stages of lithium intercalation at heterointerfaces. The formation of vdW heterointerfaces between graphene and MoX2 results in a more than tenfold greater accumulation of charge in MoX2 when compared to MoX2/MoX2 homointerfaces, while enforcing a more negative intercalation potential than that of bulk MoX2 by at least 0.5 V. Beyond energy storage, our combined experimental and computational methodology for manipulating and characterizing the electrochemical behaviour of layered systems opens new pathways to control the charge density in two-dimensional electronic and optoelectronic devices.

Inductive Loop in the Impedance Response of Perovskite Solar Cells Explained by Surface Polarization Model.

The analysis of perovskite solar cells by impedance spectroscopy has provided a rich variety of behaviors that demand adequate interpretation. Two main features have been reported: First, different impedance spectral arcs vary in combination; second, inductive loops and negative capacitance characteristics appear as an intrinsic property of the current configuration of perovskite solar cells. Here we adopt a previously developed surface polarization model based on the assumption of large electric and ionic charge accumulation at the external contact interface. Just from the equations of the model, the impedance spectroscopy response is calculated and explains the mentioned general features. The inductance element in the equivalent circuit is the result of the delay of the surface voltage and depends on the kinetic relaxation time. The model is therefore able to quantitatively describe exotic features of the perovskite solar cell and provides insight into the operation mechanisms of the device.

63-3: The Novel FFS Structure to Improve Image-Sticking in Liquid Crystal Displays

Image-Sticking in Liquid Crystal Displays (LCDs) was found to be dependent on the accumulation of ionic charges at interface between liquid crystal (LC) and alignment layer through the residual voltage bias after the driving waveforms. In the case of the Fringe Field Switching (FFS) structure, it can be weaker to Image-Sticking because the only one polarity electrode is located on the top of TFT glass. In this paper, we investigate the novel FFS structure to improve Image-Sticking. The proposed structure of FFS has a form of exposing the pixel electrode and common electrode at the same time, can be made by applying the dry etch process without additional patterning process. As a result, two electrodes are in contact with organic material Poly-Imide (PI) film. Moving path of the accumulated charge by one polarity electrode is formed through PI film and the Image-Sticking level has been reduced.

Analyte Concentration at the Tip of a Nanopipette

Concentration of molecules within the tips of nanopipettes when applying a DC voltage is herein investigated using finite-element simulations. The ion concentrations and fluxes due to diffusion, electro-migration, and electro-osmotic flow, and the electric potential are determined by the simultaneous solution of the Nernst-Planck, Poisson, and Navier-Stokes equations within the water solution containing sodium and chloride ions and negatively charged molecules. The electric potential within the pipette glass wall is at the same time determined by the Poisson equation together with appropriate boundary conditions and accounts for a field effect through the wall. Fixed negative surface charge on both the internal and external glass surfaces of the nanopipette is included together with the field effect through the glass wall to account for the electric double layer and the electro-osmosis. The inclusion of the field effect through the pipette wall is new compared to previous modeling of similar structures and is shown to be crucial for the behavior at the tip. It is demonstrated that the concentration of molecules is a consequence of ionic charge accumulation at the tip screening the electric field, thereby slowing down the electrophoretic motion of the molecules, which is further slowed down or stopped by the oppositely directed electro-osmosis. It is also shown that the trapping is very sensitive to the properties of the molecule, that is, its electrophoretic mobility and diffusion coefficient, the properties of the pipette, the ionic strength of the solution, and the applied electric field.

An analytical approach to space charge distortions for time projection chambers

In a time projection chamber (TPC), the possible ion feedback and also the primary ionization of high multiplicity events result in accumulation of ionic charges inside the gas volume (space charge). This charge introduces electrical field distortions and modifies the cluster trajectory along the drift path, affecting the tracking performance of the detector. In order to calculate the track distortions due to an arbitrary space charge distribution in the TPC, novel representations of the Green's function for a TPC geometry were worked out. This analytical approach finally permits accurate predictions of track distortions due to an arbitrary space charge distribution by solving the Langevin equation.

Study of the mechanism of crystallization electromotive force during growth of congruent LiNbO 3 using a micro-pulling-down method

We have investigated the crystallization electromotive force (EMF) during the growth of congruent LiNbO 3 (LN) by exploiting the features of a micro-pulling-down ( μ-PD) method. The electric potential distribution around the growth interface that was measured in the μ-PD system was attributed to the Seebeck effect and several mV of crystallization EMF. The mechanism of the crystallization EMF during the growth of congruent LN from the melt was explained using a model wherein segregation of the ionic species in the melt formed a net ionic charge at the growth interface resulting in the development of an EMF. Redistribution of the net ionic charge, which was analyzed on the basis of a one-dimensional differential equation that included electric-field-driven transport in the melt, well reproduced the experimental data of the nonlinear dependence of crystallization EMF on the growth rate. We concluded that the crystallization EMF occurred during crystal growth of the congruent LN owing to the ionic-charge accumulation at the growth interface.

Direct Measurement of Ion Accumulation at the Electrode Electrolyte Interface under an Oscillatory Electric Field

The ionic charge accumulation at the metal-electrolyte interface is directly measured by using differential interferometry as a function of magnitude and frequency (2-50 kHz) of external electric field. The technique developed probes the ion dynamics confined to the electrical double layer. The amplitude of modulation of the ions is linearly proportional to the amplitude of applied potential. The linearity is observed up to high electrode potentials and salt concentrations. The frequency response of the ion dynamics at the interface is interpreted in terms of the classical RC model.

Time-resolved photoacoustic calorimetry of aqueous peroxodisulfate photolysis in the presence of nitrite anions

The photodissociation of aqueous peroxodisulfate in the presence of nitrite anions was studied between 282 and 292 K by time-resolved photoacoustic calorimetry at 266 nm. Aqueous peroxodisulfate was chosen as the calorimetric reference, thus enabling the measurement of the enthalpy and volume changes associated with the reaction of the photoproduced sulfate radicals with nitrite anions to form SO4−2 and NO2 in the submicrosecond time range. The enthalpy change obtained (−192 ± 19 kJ mol−1) is consistent with available thermochemical data for related species. The interpretation of the measured reaction volume (−13.8 ± 0.7 mL mol−1) points to the ionic charge accumulation on the sulfate anion as the dominating change causing the contraction of the solvent. The comparative analysis of our experimental result and data for partial molar volumes and electrostriction volumes of electrolytes, reinforces the concept that particularly in the case of water, more realistic models for the solvent are needed involving structure rather than continuous features.

Effect of Lithium Perchlorate Doping and Prebiasing on Electrical Conduction of Molecularly Doped Poly (N-vinylcarbazole) Light Emitting Diode

The effect of lithium perchlorate (LiClO4) doping on the electrical properties of light emitting diodes prepared by spin coating from the mixtures of Alq3 and Coumarin 6 and poly (N-vinylcarbazole) was investigated in this study. We compared the current density–voltage (I–V) and the luminance–voltage (L–V) characteristics of the devices with and without LiClO4. It was found that the charge injection and the efficiency of the luminance were enhanced by doping a small amount of LiClO4. We also investigated the effect of prebiasing on the current flows and the time response of current flows (I–t curves) during the prebiasing. The current flow in the film with LiClO4 decreased in the first several 10 s, and then gradually increased and reached a constant value, whereas the current flow in the film without LiClO4 decreased monotonously during the prebiasing. The charge injection was improved by the prebiasing, and it was ascribed to the field enhancement effect due to the accumulation of ionic charges at the electrode/film interface.