Voltage Scan Research Articles

Redox-Active Polyaniline Covalently grafted Black Phosphorus Nanosheets for Integrated Digital-Analogue Memristors.

Surface covalent modification of black phosphorus (BP) with organic polymers represents a promising strategy to enhance its stability and tailor its electronic properties. Despite this potential, developing memristive materials through suitable polymer structures, grafting pathways, and polymerization techniques remains challenging. In this study, polyaniline (PANI)-covalently grafted black phosphorus nanosheets (BPNS) are successfully prepared with redox functionalities via the in situ polymerization of aniline on the surface of 4-aminobenzene-modified BPNS. The PANI coating protects the BP from direct exposure to oxygen and water, and it endows the material with analog memristive properties, characterized by a continuously adjustable resistance within a limited voltage scan range. When subjected to a broader voltage scan, the Al/PANI-g-BPNS/ITO device demonstrates a typical bistable digital memristive behavior. The integration of both digital and analog memristive functionalities in a single device paves the way for the development of high-density, multifunctional electronic components.

Observation of voltage dependent negative differential resistance (NDR) in SnS2-GO nanocomposites

This study investigates the structural, optical, and electrical properties of tin disulfide (SnS2) and SnS2-graphene oxide (GO) nanosheets synthesized via chemical bath deposition method (CBD). Structural characterization confirms the formation of hexagonal crystal phases with nanosheet morphology. It shows a well distribution of nanosheet average square sizes of 10 nm for SnS2 and 6 nm for SnS2-GO. Optical analysis shows blue shifts in absorption edges compared to bulk SnS2, attributed to quantum confinement effects. Photoluminescence emission peaks exhibit different energy levels in SnS2-GO originated to native defects. The composites show a sharp reduced of PL intensity due to enhanced charge carrier separation. Electrical measurements on SnS2-GO thin films demonstrate negative differential resistance (NDR) behavior in both planar and sandwich contact configurations, suggesting electron injection/extraction mechanisms. The NDR phenomenon exhibits a dependence on voltage scan rate, indicating the involvement of electronic and ionic elements in charge transport mechanisms. Overall, this study provides insights into the NDR properties of SnS2-GO nanocomposite, laying the groundwork for their potential applications in optoelectronics and nanoelectronics.

On the reconstruction of LEIS spectra after distortion by an electrostatic energy analyzer

The study attempts to reveal the influence of the transmission function of electrostatic deflector analyzers with linear voltage scan on the shape of the LEIS energy spectra and the arising error in surface elemental composition and film thickness analysis. The practical applicability of several analytical and numerical approaches for reconstructing true energy distributions of particles is studied using examples of simulated LEIS spectra. The presented methodology can be extended to a wider range of applications involving electrostatic or magnetic analyzers of charged particles. The study proposesa freely available and ready-to-use tool for simulating distortions of spectra caused by the transmission function of spectrometers and for reconstructing true distributions of arbitrary spectra.

Molecular-Potential and Redox Coregulated Cathodic Electrosynthesis toward Ionic Azulene-Based Thin Films for Organic Memristors.

Organic memristors as promising electronic units are attracting significant attention owing to their simplicity of molecular structure design. However, fabricating high-quality organic films via novel synthetic technologies and exploring unprecedented chemical structures to achieve excellent memory performance in organic memristor devices are highly challenging. In this work, we report a cathodic electropolymerization to synthesize an ionic azulene-based memristive film (PPMAz-Py+Br-) under the molecular-potential and redox coregulation. During the cathodic electropolymerization process, electropositive pyridinium salts migrate to the cathode under an electric field, undergo a reduction-coupling deprotonation reaction, and polymerize into a uniform film with a controllable thickness on the electrode surface. The prepared Al/PPMAz-Py+Br-/ITO devices not only exhibit a high ON/OFF ratio of 1.8 × 103, high stability, long memory retention, and endurance under a wide range of voltage scans, but also achieve excellent multilevel storage and history-dependent memristive performance. In addition, the devices can mimic important biosynaptic functions, such as learning/forgetting function, synaptic enhancement/inhibition, paired-pulse facilitation/depression, and spiking-rate-dependent plasticity. The tunable memristive performances are attributed to the capture of free electrons on pyridinium cations, the migration of the aluminum ions (Al3+), and the form of Al conductive filaments under voltage scans.

Hysteresis in memristors produces conduction inductance and conduction capacitance effects.

Memristors are devices in which the conductance state can be alternately switched between a high and a low value by means of a voltage scan. In general, systems involving a chemical inductor mechanism as solar cells, asymmetric nanopores in electrochemical cells, transistors, and solid state memristive devices, exhibit a current increase and decrease over time that generates hysteresis. By performing small signal ac impedance spectroscopy, we show that memristors, or any other system with hysteresis relying on the conductance modulation effect, display intrinsic dynamic inductor-like and capacitance-like behaviours in specific input voltage ranges. Both the conduction inductance and the conduction capacitance originate in the same delayed conduction process linked to the memristor dynamics and not in electromagnetic or polarization effects. A simple memristor model reproduces the main features of the transition from capacitive to inductive impedance spectroscopy spectra, which causes a nonzero crossing of current-voltage curves.

Determination of Electrochemical Pretreatment Voltage Limits, Scan Rate and Cycle Number

Electrochemical characterisation analyses are performed to determine the electrochemical behaviour of the electrode and electrolyte of vanadium redox battery components. A 3-electrode system which consisted of counter electrode, working electrode and reference electrode is used for electrochemical testing. It is important for the consistency of the proposed idea that the results obtained from the analyses are comparable and repeatable under the same conditions. In order to prepare the working electrode surface for electrochemical reactions, an electrochemical treatment procedure is applied in addition to the polishing procedure [1,2]. In this study, it is aimed to determine the optimum pretreatment conditions of the working electrode. For this purpose, a 3-electrode system consisting of a reference electrode (Saturated KCl, ALS RE-1CP), a working electrode (ALS GCE 3 mm) and a counter electrode (platinum wire) was established. All pretreatment procedure experiments were carried out using 2 M H2SO4. After each pretreatment step, cyclic voltammetry analyses were carried out with 1.6 M VOSO4 + 2 M H2SO4 solution. CV analyses were performed in the range of 0 V - 1.2 V at a scan rate of 20 mV/s. The upper voltage was chanced between 1.5 V and 2.3 V with 0.1 V steps at the constant lower voltage limit. In contrast, the establishment of the lower voltage limit encompassed incremental increases by 0.3 V steps from -0.7 V to 1.4 V at a constant upper voltage limit. Different scan rates (10 mV/s, 20 mV/s, 50 mV/s, 100 mV/s, and 200 mV/s) were explored to identify the optimal scan rate for the pretreatment process. Additionally, experiments were performed across varying cycle numbers (1, 2, 4, 6, 8, 10) under predefined pretreatment conditions.The results of the pretreatment procedure and CV analysis are graphically presented in Figure 1. The upper voltage limit determination and CV analysis results under a lower voltage limit are displayed in Figure 1.a and 1.b. Redox reactions did not occur when the upper voltage limit was 1.5 V-1.8 V. While redox reactions started to occur after 1.9 V, the highest anodic and cathodic peaks values were obtained in the 0-2 V range. Lower limit pretreatment results and CV analysis under constant upper voltage are shown in Figures 1.c and 1.d, respectively. These experiments indicated minimal distinctions between -0.7 V and 0 V CV results, leading to the selection of 0 V as the lower limit. In cases where the lower limit is greater than 0 V, redox reactions were negatively affected by the pretreatment process. There was no significant difference was observed between the CV results of 10 mV/s and 20 mV/s. However, redox reactions were negatively affected at scanning rates of 50 mV/s and higher. The scan rate of the pretreatment process was determined as 20 mV/s. Figures 1.g and 1.h show the results of pretreatment cycle number and CV analysis results at the 0 V-2 V voltage limits and 20 mV/s scan rate. Redox reactions did not occur when pretreatment was applied in 1 and 2 cycles while 4 and higher cycle numbers were obtained. The highest anodic and cathodic peaks were obtained when the cycle numbers were 6 and 8, and these results are very close to each other. The cycle number of the pretreatment process was determined as 6 cycle.It has been shown that the conditions of the pretreatment process have a significant influence on the reaction behaviour of the working electrode. It conclusively establishes the optimum pretreatment process conditions as a voltage range 0 V-2 V, scan rate 20 mV/s and number of cycles 6. Acknowledgements This work supported by the Scientific Research Projects Unit of Erciyes University under contract no: FDK-2020-10376. The first named author MT thanks to The Scientific and Technological Research Council of Turkey (TÜBİTAK) for their scholarships under “2211-C Priority Areas PhD Scholarship Program with the grant number 1649B032000390” and “2214-A International Research Fellowship Program for PhD Students with the grant number 1059B142200567”. References J. Noack et al., J. Energy Chem., 27, 1341–1352 (2018).N. Roznyatovskaya et al., Batteries, 5, 1–16 (2019). Figure 1

Monitoring levodopa oxidation and reduction reactions using surface plasmon resonance on a nanohole array electrode

The traditional method of monitoring the oxidation and reduction of biomedical materials usually relies on electrochemical (EC) measurement techniques. Here, we demonstrate a surface plasmon resonance (SPR) method to monitor the oxidation process. Using levodopa L-dopa as the target analyte, a nanohole sensing plate is embedded in the EC electrode to enhance the oxidation signal and generate SPR. Cyclic voltammetry (CV) measurement was first conducted to understand the baseline of EC response of L-Dopa. Then, the redox reactions were simultaneously monitored through SPR measurements during the CV voltage scan. The results showed that the limit of detection using traditional CV reached 1.47 μM while using EC-SPR, the limit of detection improved to 1.23 μM. Most importantly, we found a strong correlation between CV current profiles and the SPR reflection spectra. Our results facilitate detecting electrochemical reactions using an optical probing method.

Improved resistive switching performance of amorphous InGaZnO-based memristor with the TiO2 insertion layer

A stable I–V repeatability memristor based on amorphous InGaZnO (a-IGZO) with a TiO2 insertion layer was investigated. Two memristive structures composed of Pt/a-IGZO/Pt and Pt/TiO2/a-IGZO/Pt were manufactured on SiO2/Si substrate by the magnetron sputtering method. The crystallization of IGZO thin films was analyzed by the XRD process under different annealing temperatures, and the results show that the thin films remain in a stable amorphous state. The resistive switching performance of the two structures was tested by the semiconductor parameter analyzer 4200-SCS at room temperature. After 30 cyclic scans, the Pt/a-IGZO/Pt structure shows signs of degeneration in its I–V cyclic characteristics. However, in the Pt/TiO2/a-IGZO/Pt structure, the cyclic characteristics of I–V are highly stable (cycles >105 sweeps) with a limiting operating current of 0.01 A. Its rectification ratio is approximately 20 at low operating voltages (±1.0 V), and conductance increases (or decreases) progressively with continuous positive (or negative) voltage scans. Further analysis of the experimental energy band diagram was measured by UV–vis spectra and ultraviolet photoemission spectroscopy (UPS). The results demonstrate that the operational mechanism is the modulation of the barrier at the TiO2/a-IGZO interface, which is conducive to the stable I–V cyclic characteristic of Pt/TiO2/a-IGZO/Pt memristor.

Effectiveness of low tube voltage scan in the exposure dose for lenses during paediatric thoracic CT examination: anthropomorphic phantoms study.

To determine whether using lower-tube voltage reduces the scattered dose for the lens during paediatric thoracic computed tomography (CT). Two paediatric anthropomorphic phantoms (ATOM Phantom, CIRS, Norfolk, Virginia, USA) representing a newborn and 5-year-old were placed on the gantry of CT scanner, and optically stimulated luminescence dosemeters were placed on the left and right lenses, in front of the left and right thyroid glands, in front of the left and right mammary glands, and in front of and behind the mammary gland level and we measured scattered dose of the optically stimulated luminescence dosemeter was compared for each phantom between 80 and 120kVp. Significant differences were observed in the scatter doses for the lens between 80 and 120kVp (p<0.01). Compared with the 120kVp scan, the scatter doses for the lens were ~15-40% lower in newborn and 5-year-olds using the 80kVp scan during paediatric CT.

Synthesis of NiBTC metal-organic framework thin layers on nickel foam by different electrochemical methods: A comparative study for hydrogen evolution reaction

In this study, for the first time two electrochemical synthesis techniques including cyclic voltammetry (CV) and linear sweep voltammetry (LSV) were used for MOF synthesis. The Ni3(BTC)2 electrocatalyst was synthesized and deposited without any binder, for a short time and at ambient temperature on the nickel foam substrate. Morphology studies showed that the LSV method leads to preserving the 3D structure of nickel foam which promotes the catalytic activity. It should be noted that two parameters, such as voltage range and scan rate, were optimized during the LSV method. Moreover, X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to confirm the MOF's structural integrity. Furthermore, the Brunauer-Emmett-Teller (BET) method verified the porous structure of NiBTC MOF. Additionally, the performance of bare and modified nickel foams was also examined for the hydrogen evolution reaction (HER) which demonstrated the tremendous potential of NiBTC/Ni foam in HER catalytic activity.

Resistive switching properties of CdTe/CdSe core–shell quantum dots incorporated organic cow milk for memory application

Our study focuses on the resistive switching memory characteristics of devices containing active layers of CdTe/CdSe core–shell quantum dots (QDs) dispersed in organic cow milk. We fabricated devices containing CdTe/CdSe particles per volume of milk using a direct-dipping method, with particle concentrations of 2.4 × 10[Formula: see text] (S1), 4.8 × 10[Formula: see text](S2), and 7.2 × 10[Formula: see text](S3). This method was cost-free. Distinct memory characteristics were observed among devices featuring these concentrations. S1- and S2-based devices exhibited memory behavior with ‘S-type’ and ‘O-type’ hysteresis, respectively. The device based on S3 exhibited an initial asymmetric ‘N-type’ behavior with a large ON/OFF ratio ([Formula: see text]104). The memory attribute of the aforementioned device disappeared after the initial three cycles but was subsequently restored by modifying the scan voltage step from 10 mV to 1 mV. The observed results indicate typical symmetric ‘N-type’ behavior of the device, accompanied by threshold switching under positive voltage bias. Additionally, the switching was observed to be as low as 0.04 V. The S1- and S2-based devices were found to exhibit hopping conduction and Schottky emission in the OFF- and ON-state, respectively, while the S3-based device showed conductive bridge resistive switching as the conduction mechanism. The findings indicate that it is possible to produce biodegradable and disposable memory devices using full cream cow milk and CdTe/CdSe core–shell QDs. The device’s switching and memory functions can be manipulated by regulating the quantity of CdTe/CdSe particles present in the milk. Finally, we have demonstrated that the switching behavior of ReRAMs based on milk can be influenced by the voltage steps used during scanning.

Extraction, chemical, and dual-functional memory and threshold resistive switching characteristics of Elaeodendron buchananii extract

This work presents a study on the electrical properties of plant materials, which is a fascinating area of research. These materials show promising potential in mitigating the exponential increase in electronic waste by enabling the development of eco-friendly electronic devices that can biodegrade. This research article showcases findings on the extraction, chemical analysis, and dual-functional memory and threshold resistive switching of extracts from the Elaeodendron buchananii plant. We report threshold switching with impressive ON/OFF ratio of >103, a retention time of ≥103, and endurance of 20 cycles, for the sandwich type device consisting of Elaeodendron buchananii plant extract-based film positioned between silver and indium-doped tin oxide electrodes. After modifying the experimental parameters, specifically by reducing the voltage scan increments to 1mV and increasing the compliance current to 150μA, transition from threshold switching to bipolar memory mode was detected. This particular memory mode exhibited an ON/OFF ratio of 10 and demonstrated very low switching voltages of −0.37V and +0.22V, although for only a limited number of write/erase cycles. The switching mechanism for both the threshold and memory mode can be attributed to the formation of conductive filaments caused by the migration of oxygen vacancies.

Plant-inspired rearrangement of liquid in a porous structure for controlled swelling

Soft robots can adapt to dynamic environments without prior knowledge of their properties. Plants inspire mechanisms for counterbalancing dynamic loads by locally modulating compliance through anisotropic humidity-responsive materials and structures. In addition to well-known passive bilayers, plants may also actively control swelling. The combination of robust hygroscopic material-level response and simple electrical control makes active swelling particularly attractive for technological implementation. However, dynamic swelling demands the development and optimisation of congruent pumping solutions. This work suggests electrohydrodynamic pumping, enabled by highly reversible ion immobilisation at capacitive electrodes, as a particularly suitable low-pressure, high-area liquid displacement solution for active swelling. Local pore fill ratio (PFR) modulation is used as a measure for dynamic liquid displacement and swelling. A method for highly localised (10 μm membrane thickness) assessment of the dynamic variation of PFR in a 400 μm laminate undergoing cross-plane electrokinetic liquid displacement is developed. Two modes for transient PFR modulation were identified: electrokinetic ion transfer and diffusive solvent redistribution, pronounced at high and low voltage scan rates, respectively. The strategic combination of these modes enables various compliance-modulation scenarios. The system contains (within a cycle) a constant amount of liquid in an open network of liquid-filled pores. 30%–75% PFR yielded the highest dynamic PFR modulation: a high amount of empty pores is beneficial, yet a too-low PFR compromises the continuous liquid pathway necessary for electrokinetic pumping. The dynamic nature of internal liquid rearrangement was characterised by relatively fast electrokinetics-driven fluxes (6.3% PFR change in 80 s), followed by a slow equilibration of concentration and PFR. At high scan rates, PFR decreased at positive polarisation, while both positive and negative polarity yielded a similar decrease at low scan rates (5 mV s−1). Localised control over the swelling gradient enables the design of systems that morphologically adapt to complex dynamic loading conditions.

3D-graphene hydrogel and tungsten trioxide-MnO2 composite for ultra-high-capacity asymmetric supercapacitors: A comparative study

Researchers worldwide use graphene extensively in its powder form for various applications such as supercapacitors, solar cells, drug delivery, and polymer composites, owing to its considerably valuable properties. However, relatively few studies have been made on the 3D-hydrogel form of graphene for these applications. Here we report a simple and fresh method to prepare 3D graphene hydrogel (3DGH) and its bimetal composite with tungsten trioxide (WO3) and manganese dioxide (MnO2). The structure of 3DGH and its composite is confirmed by advanced characterization techniques viz. Raman Spectroscopy, X-Ray diffraction (XRD), Fourier-transformed infrared spectroscopy (FT-IR), scanning electron microscope (SEM), and tunneling electron microscope (TEM). Further, two symmetric devices using 3DGH, 3DGH-metal composite (3DGHMC), and one asymmetric 3DGHMC-3DGH device are comparatively studied using two electrode systems. The effects of scan rates, current densities, voltage window, and frequency were examined for each device by cyclic voltammetry (CV), galvanic charge-discharge (GCD), and Electron impedance spectroscopy (EIS). The asymmetric device showed a high specific capacitance of 657 F g−1 with an excellent energy density of 48.25 W h kg−1 and a high-power density of 596.06 W kg−1 at the current density of 1 A g−1. Also, the asymmetric device retains 100 % of its initial capacitance after 1000 charging-discharging cycles, also extends its stability after 1000 cycling test. Moreover, the quantitative analysis of the device is also made by Dunn's method to evaluate the percentage contribution from surface and diffusion capacitance.

Utility of lower tube voltage scans in reducing exposure of healthcare workers within computed tomography room to scattered radiation.

The aim of this study was to estimate the effect of tube voltage on the scattered dose in a computed tomography (CT) room. To this end, we conducted experiments using anthropomorphic phantoms and a CT scanner at different tube voltages during CT. The scattered dose was measured using an electronic pocket dosemeter at 50-cm intervals from the centre of the gantry. The structure of the CT room was measured at 57 points (28 points in the front of the gantry (on the bed side), 6 points on the side of the gantry and 23 points behind the gantry) to be up to 200cm. We compared the scattered dose distributions between 80 and 120 kVp at heights of 50, 100 and 150cm above the floor surface. The scattered dose was reduced by ~30% when the tube voltage was reduced from 120 to 80 kVp.

Nano-Memory Based on MoS2 Embedded in Al2O3 on Bulk Ge

MoS2 captured a lot of attention in the past decade due to its intrinsic stability at nanoscale dimensions promising low power, high density, and CMOS-compatible devices [1-6]. The claimed improvements in MoS2-based devices can be related to their capacity to change the material interface properties and it’s not limited by the absence of a band gab. Despite this, such devices are still in the early stages of development due to several issues, including growth scalability, passivation, doping, and metal junctions [7, 8]. Almost no work conducted on MoS2/Ge-based systems which can be promising for various photonics applications, especially in the infrared regime.Nanoscale resolution electrical characterizations utilizing conductive atomic force microscopy (cAFM) provide a useful method to study electronic transport and conduction in MoS2 structures. In this work, we demonstrate a nano-memory structure utilizing MoS2 flakes embedded in high-k ALD oxide on bulk Ge. The process of charge injection in the MoS2 flake was explored utilizing the fabricated structure along with a control structure with no embedded MoS2.The cleaning and fabrication are conducted in a cleanroom of 100 level. A Ge bulk wafer is diced into 1×1 cm2 pieces and then ultrasonic cleaned in DI water, acetone, and IPA for native oxide removal and cleaning. The first 3 nm Al2O3 layer is grown using plasma-enhanced atomic layer deposition (PE-ALD) at 200⁰C. Immediately followed by spin coating 20µL of MoS2 solution on the Al2O3/Ge substrates at 1000 RPM for 30 seconds. The MoS2 solution concentration is 18 mg/L with flakes between 1-8 monolayers thick and 100-400 nm lateral size. The structure is finalized by depositing another 3 nm Al2O3 layer, capping the MoS2 flakes.We performed the following 2.5×2.5 µm2 current scans using the cAFM, operating in contact mode, respectively: Read scan at 0.5 volts, write scan at 5 volts, read scan at 0.5 volts, erase scan -8 volts then read scan at 0.5 volts. Under the low read voltage (0.5V), no currents were observed in their pristine form. However, currents were spotted under higher write voltage (5V). The current readings, produced by the write scan, can also be seen under the following low read voltage scan (0.5V). The same currents are rarely visible after any erase scan (-8V) and during the subsequent read scan (0.5V). The results of cAFM demonstrate a MoS2-based structure that may be promising for future nano-memory applications.

Abnormal Dynamic Reverse Bias Behavior and Variable Reverse Breakdown Voltage of ETL‐free Perovskite Solar Cells

Perovskite solar cells (PSCs) have shown an impressive power conversion efficiency of 26.1%, while their upcoming commercialization urgently needs to solve the stability problem. Among numerous stability issues of PSCs, little attention is paid to reverse bias stability. When some cells of the module are shaded by irresistible factors, this will cause the current of the illuminated part to flow through the shaded cells as a reverse current and force them to be under reverse bias. Herein, the breakdown mechanism dominated by different reverse bias regions of a prototype electron transport layer free PSCs is distinguished. And, it is confirmed that PSCs present a thought‐provoking dynamic reverse bias (DRB) behavior and variable reverse breakdown voltage (VRB), which is essentially distinct from classic solar cells. Specifically, VRB is significantly affected by voltage scan rate, range and direction, and illumination. The underlying mechanism is explained by drift‐diffusion modeling taking into account the electric field generated by directional ion migration. The latter can hinder the movement of charge carriers and cause the observed variable VRB and DRB behavior. Predictably, the understanding of the dynamic process is crucial to establish a standard VRB measurement procedure and further promote the commercialization of PSCs.

Impact of Scan Rate and Mobile Ion Concentration on the Anomalous J-V Curves of Metal Halide Perovskite-Based Memristors

Bias voltage scan rate and mobile ion concentration have a strong influence in <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J-V</i> curves of metal halide perovskite-based memristors. In addition to hysteresis, in some cases <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J-V</i> curves also show an anomalous drop in current known as negative differential resistance. This feature is usually related to electrochemical reactions between the reactive metal and I <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-</sup> ions, and to air exposure. However, in devices with low-reactive electrodes, its origin is still under debate. In this work, we propose a theoretical model based on ionic-electronic drift-diffusion. This model sheds light into the ionic-electronic processes that shape hysteresis, and it helps to explain the appearance and evolution of a negative resistance in memristors with low-reactive contacts and capacitive hysteresis. Finally, experimental <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">J-V</i> curves are presented to validate the proposed model.

Impact of Interface Energetic Alignment and Mobile Ions on Charge Carrier Accumulation and Extraction in p‐i‐n Perovskite Solar Cells

AbstractUnderstanding the kinetic competition between charge extraction and recombination, and how this is impacted by mobile ions, remains a key challenge in perovskite solar cells (PSCs). Here, this issue is addressed by combining operando photoluminescence (PL) measurements, which allow the measurement of real‐time PL spectra during current–voltage (J–V) scans under 1‐sun equivalent illumination, with the results of drift‐diffusion simulations. This operando PL analysis allows direct comparison between the internal performance (recombination currents and quasi‐Fermi‐level‐splitting (QFLS)) and the external performance (J–V) of a PSC during operation. Analyses of four PSCs with different electron transport materials (ETMs) quantify how a deeper ETM LUMO induces greater interfacial recombination, while a shallower LUMO impedes charge extraction. Furthermore, it is found that a low ETM mobility leads to charge accumulation in the perovskite under short‐circuit conditions. However, thisalone cannot explain the remarkably high short‐circuit QFLS of over 1 eV which is observed in all devices. Instead, drift‐diffusion simulations allow this effect to be assigned to the presence of mobile ions which screen the internal electric field at short‐circuit and lead to a reduction in the short‐circuit current density by over 2 mA cm−2 in the best device.

Corn stover‐derived porous carbon for asymmetric supercapacitors

AbstractIn this investigation, hydrothermal liquefaction‐derived hydrochar from pulverized corn stover (avg. particle size 1.12 mm and ash content 6.75 wt%) is chemically activated with aqueous KOH in the presence of Pluronic F127 surfactant and thermally treated further up to 800°C to generate porous carbon (POC) with higher specific surface area and porosity. POC obtained under different processing conditions is thoroughly characterized by Brunauer‐Emmett‐Teller surface area analyzer, Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. Metallic impurity present in POC is characterized by inductively coupled plasma mass spectrometry. Higher specific surface area POC is observed with the use of the surfactant during the activation process. Fully characterized POC is used with (Mn, Ti)‐mixed oxide electrode to fabricate asymmetric supercapacitor (ASC). Specific capacitance of ASC is measured by cyclic voltammetry (CV) technique using Gamry G‐300 potentiostat/galvanostat/ZRA. CV plots are obtained with different voltage scan rates whereas galvanostatic charge‐discharge plots are studied by varying the current density. Renewable corn stover‐derived POC prepared using Pluronic F127/KOH activation method is found to be highly suitable as an electrode material because of higher capacitance and electrochemical stability over 100 charging‐discharging cycles.