Series Resistance Research Articles

Eliminating Resistance-Capacitance Coupling Shielding for Depicting the Defect Landscape in Perovskite Solar Cells by Capacitance Spectroscopy.

Capacitance spectroscopy techniques have been widely utilized to evaluate the defect properties in perovskites, which contribute to the efficiency and operation stability development for perovskite solar cells (PSCs). Yet the interplay between the charge transporting layer (CTL) and the perovskite on the capacitance spectroscopy results is still unclear. Here, they show that a pseudo-trap-state capacitance signal is generated in thermal admittance spectroscopy (TAS) due to the enhanced resistance capacitance (RC) coupling caused by the carrier freeze-out of the CTL in PSCs, which could be discerned from the actual defect-induced trap state capacitance signal by tuning the series resistance of PSCs. By eliminating the RC coupling shielding effect on the defect-induced capacitance spectroscopy, it is obtain the actual defect density which is 4-folds lower than the pseudo-trap density, and the spatial distribution of defects in PSCs which reveals that the commonly adopted interface passivators can passivate the defects about 60 nm away from the decorated surface. It is further revealed that phenethylammonium ions (PEA+) possess a better passivation capability over octylammonium ions (OA+) due to the deeper passivation depth for PEA+ on the surface defects in perovskite films.

Versailles Santa Barbara-5 derived bifunctional one-dimensional electrocatalysts of hierarchical Ni3S2 nanoprism@nanosheets arrays for self-supporting and binder-free efficient supercapacitor and methanol oxidation reaction

We herein present a structure consisting of two-dimensional (2D) single-crystal Ni3S2 nanosheets designed on one-dimensional (1D) Ni3S2 nanoprism arrays (also known as Ni3S2 nanoprism@nanosheets). These arrays are directly synthesized over nickel foam, which is referred to as Ni3S2/NF. These structures can be used as binderless, self-supporting electrodes for bifunctional methanol oxidation reaction (MOR) applications and high energy density hybrid supercapacitors (HSC). Ni3S2/NF is synthesized through the two steps of hydrothermal processes. In step I, 1D hexagonal Versailles Santa Barbara-5 (VSB-5) nanorod arrays have been prepared onto the surface of NF (denoted as VSB-5/NF). The precursor for step II was 1D VSB-5 nanorod arrays, which were transformed into Ni3S2 using Na2S as a sulfur source via the Kirkendall effect. Electrochemical examination results show that as-synthesized Ni3S2/NF electrode exhibited a high specific capacitance (Cs) of 145.0 mA h g−1 at 5 A g−1, low series resistance (0.18 Ω) and charge-transfer resistance (0.05 Ω), small relaxation time constant (τ0 = 8 ms) and high frequency response at 125.8 Hz. Ni3S2/NF has a superior specific capacity of 145.0 mA h g−1 at 5 A g−1 as a SC electrode. The Ni3S2/NF//CNTs/NF HSC can be operated up to 1.6 V in a 3 M KOH electrolyte, delivering an impressive energy density of 256.35 W h kg−1 at a power density of 6400 W kg−1. The as-assembled Ni3S2/NF//CNTs/NF HSC device exhibited an impressive stability of 81 % even after undergoing 10,000 charge-discharge cycles. When compared to previously reported catalysts, Ni3S2/NF was proved to be an excellent electrocatalyst for MOR due to its ability to generate a current density of 215.0 mA cm−2 at 0.5 VSCE, while maintaining a superior and stable current density of 619.2 mA cm−2 at 0.8 VSCE.

Studying effect of temperature on the efficiency of solar cells through the interpolation method

The objective of this paper is to present a comparative study between the traditional least squares method 'LSM' and the new method of "Polynomial Interpolation at Different Orders" for extracting the electrical parameters of a silicon solar cell. The focus is on the advantages and disadvantages of each approach. The results indicate that fourth-order interpolation yields the best results, but it is challenging to implement because the J-V function is neither linear nor transcendental. Therefore, we opted for the first-order Piecewise Linear Interpolation 'PLI' in the range where the J-V characteristic is nearly flat, i.e., the interval where the voltage varies from 0 to Vmax. By utilizing the first-order derivative of the function f(J, V) with two variables and MATLAB fzero function, we were able to determine the five critical parameters for our solar cell: the series resistance RS, the shunt resistance RSh, the light-generated current density Jph, the reverse saturation current density J0, and the ideality factor n. We used the Bland-Altman technique to evaluate the comparability between the two methods. The results obtained using this technique show that all the data points lie within the confidence interval. This indicates that the piecewise interpolation method provides J-V characteristic values very similar to those found by the LSM method. The strength of the new method lies in its speed, practicality, and the fact that it does not require initial values for the solar cell parameters. Additionally, it avoids the need to determine the variation intervals for each parameter and the use of complex functions such as the Lambert W function, which is necessary in the LSM method. By applying this method, we examined how the electrical parameters behave when the temperature varies from a cold region (0 °C) to a hot region (50 °C). The analysis of the results obtained by both scientific methods, namely the LSM method and polynomial interpolation, reveals a decrease in cell efficiency from 19.63 to 13.73 %. Similarly, the open-circuit voltage decreases from 0.62 to 0.524 V, and the ideality factor also decreases from 2.2 to 1.54. The current decreases from 39.50 to 34.30 mA/cm2 as the temperature increases from 0 °C to 30 °C, then stabilizes at 34.30 mA/cm2 for temperatures ranging from 30 °C to 50 °C.

Phase-Field Model of Electronic Antidoping.

Charge carrier doping usually reduces the resistance of a semiconductor or insulator, but was recently found to dramatically enhance the resistance in certain series of materials. This remarkable antidoping effect has been leveraged to realize synaptic memory trees in nanoscale hydrogenated perovskite nickelates, opening a new direction for neuromorphic computing. To understand these phenomena, we formulate a physical phase-field model of the antidoping effect based on its microscopic mechanism and simulate the voltage-driven resistance change in the prototypical system of hydrogenated perovskite nickelates. Remarkably, the simulations using this model, containing only one adjustable parameter whose magnitude is justified by first-principles calculations, quantitatively reproduce the experimentally observed treelike resistance states, which are shown unambiguously to arise from proton redistribution-induced local band gap enhancement and carrier blockage. Our work lays the foundation for modeling the antidoping phenomenon in strongly correlated materials at the mesoscale, which can provide guidance to the design of novel antidoping-physics-based devices.

Growth rate effect on the dielectric properties of FeNbO4 fibres processed by the laser floating zone technique

Fe-based materials exhibiting high dielectric constants have been attracting great attention due to their potential for application in electronic devices. In this work, iron niobate (FeNbO4) fibres were produced by the Laser Floating Zone technique, applying three different growth speeds: 5, 10 and 25 mm/h. The XRD patterns showed the presence of two phases, being the FeNbO4 the major one in all the samples. The effect of the growth speed is well perceptible in the morphology of the fibres. The dielectric measurements revealed that all samples have at least one dielectric relaxation phenomenon that is thermally activated, with the activation energy, estimated through the Arrhenius law, presenting values between 0.057 and 0.072 eV. The Nyquist plots showed the presence of a single semicircle for each temperature, that could be modelled by an equivalent electrical circuit consisting of an offset resistance in series with a parallel combination of a grain resistance and a grain constant phase element. The grain resistance increased with the increasing growth speed, from 574 to 64497 Ω, with the constant phase element showing the opposite trend, decreasing from 0.40 to 0.17 nF.

Deep insights into the optoelectronic properties of AgCdF3-based perovskite solar cell using the combination of DFT and SCAPS-1D simulation

The main focus of this research is to explore the properties and photovoltaic application of AgCdF3, and hence, initially, the CASTEP software was used in this study to assess the structural, optical, mechanical, and electrical characteristics of the AgCdF3 perovskite absorber layer within the context of the density functional theory (DFT) method. AgCdF3 resulting from the structural research is confirmed to be chemically and thermodynamically stable by the estimated tolerance factor and formation enthalpy. According to the band structure analysis, AgCdF3 is an indirect band gap semiconductor with a band gap of 1.106 eV, where the electrons of Cd-4d and F-2s dominate the band edges of this semiconductor. Analysis of mechanical properties revealed that the AgCdF3 cubic perovskite has a stable structure and enhanced ductility, indicating superior machinability. After completing the DFT analysis, a one-dimensional solar cell capacitance simulator 1D (SCAPS-1D) was used with three popular electron transport layers (ETLs), including ZnO, PCBM, and C60, to examine the photovoltaic (PV) performance of various AgCdF3-based solar cell heterostructures. Based on simulation findings, the device design with ITO/ZnO/AgCdF3/CuI/Au showed the highest photoconversion efficiency compared to the other configurations. A detailed analysis was conducted for the aforementioned configurations to determine the impact of variations in the absorber and ETL thickness on PV performance. Moreover, the effects of the three designs were assessed in terms of function, generation and recombination rate, capacitance, operating temperature, series and shunt resistance, and Mott-Schottky. Thus, this comprehensive simulation with validation results demonstrated the true potential of AgCdF3 absorber with appropriate ETLs such as ZnO, PCBM, and C60; on the other hand, the CuI as hole transport layer (HTL), paving the way for promising studies to develop high-efficiency AgCdF3 PSCs for the photovoltaic industry.

Cobalt- and copper-doped NASICON-type LATP polymer composite electrolytes enabling lithium titania electrode for solid-state lithium batteries with high-rate capability and excellent cyclic performance

This study reports cobalt- and copper-doped NASICON-type Li1.5Al0.5Ti1.7(PO4)3 (LATP) polymer composite solid-state electrolytes (CSEs) enabling Li4Ti5O12 (LTO) electrode with high-rate capability and excellent cyclic performance for solid-state lithium batteries. The fast Li+ conductor of Co- and Cu-doped LATP powders was successfully synthesized through a modified sol-gel method followed by thermal calcination. The equivalent series resistance as the linear decreasing function of the dopant concentration can be viewed, whereas the ionic conductivity showed an increasing function of the dopant amount. This reveals that the dopant concentration plays a positive role in facilitating the ionic conduction, and the ionic conductivity achieves as high as 3.18 × 10−4 S cm−1 (Co-doping) and 2.99 × 10−4 S cm−1 (Cu-doping) at ambient temperature. The changes in lattice characteristics and microstructure that the Co and Cu doping rely on are responsible for the elevated conductivity. The solid-state cell equipped with LTO-supported CSEs demonstrated not only high-rate capability at 5C (with a capacity retention of 84.6 % compared to the original capacity at 0.2C), but also superior cyclic stability with excellent Coulombic efficiency (> 99.2 %) over 425 cycles using Co- and Cu-doped LATP ceramics. With the aid of fast Li+ NASICON-type ceramics, the CSEs establish a conductive ionic pathway that facilitates Li+ ionic transport within the electrolyte while reducing the interfacial electrolyte/electrode resistance in solid-state cells (Li||CSE||LTO).

Quaternary functional semiconductor devices

Al/(Zn:Cd:Ni:TiO2)/p-Si diodes with (4:2:2:2), (5:2:2:1) and (6:4:4:0) ratios were named as D1, D2, D3, and Al/(CdO:ZnO:NiO:Ti)/p-Si diodes with of (4:2:2:2), (5:2:2:1) and (6:4:4:0) ratios were named as D4, D5 and D6, respectively. The functional interlayer was deposited via sol-gel spin coating method to develop new diodes/structures. Whereas the Ln(I)–V plot shows two linear sections for D1, D2, D3, and D5 structures, D2 and D6 revealed only one linear section in the forward-bias voltages. Therefore, D1, D2, D3, and D5 structures were found to exhibit two-exponential or two-parallel diode behavior in literature. The main electric parameters such as zero-bias barrier height, BH, (Φbo), ideality factor (n), reverse saturation-current (Is or Io)), rectification ratio at ±4.5 V, series resistance (Rs) and shunt resistance (Rsh) were extracted from the current-voltage (I-V) measurements. The number of surface sates (Nss) and their energy distribution were obtained using forward-bias I-V data by considering the voltage dependence of n and Φbo for each diode. The capacitance/conductance-voltage (C/G–V) plots at 1 MHz were used for extracting some of the other basic electrical parameters. The comparison of all the experimental results suggests that D1 and D3 structures have good performance in terms of lower leakage current, Nss and higher RR and so could be successfully used instead of conventional metal/insulator/semiconductor (MIS) structures.

Impact of fast charging and low-temperature cycling on lithium-ion battery health: A comparative analysis

Fast charging and low temperatures create harsh conditions that promote lithium deposition on graphite anodes, which significantly accelerates the degradation of the battery's state of health (SoH) and eventually could result in safety concerns. In this work, commercial lithium-ion batteries are investigated under fast charging conditions and at low environmental temperatures. The findings are compared with lithium-ion battery cycled under ambient temperature conditions. The fast charging and low temperatures result in dead lithium formation, which is then characterized by electrochemical impedance spectroscopy (EIS) and scanning electron microscope (SEM). The low-temperature cycled battery exhibits significant growth of series resistance by an average of 73 %. In comparison, growth in charge transfer resistance is 16 %, and no significant change was observed in solid electrolyte interface (SEI) resistance due to the formation of dead lithium, compared to the battery cycled at ambient temperature. SEM images also confirm the dead lithium formation. The results provide insight into battery degradation in the case of high current due to low temperature and could lead to a better understanding of the degradation mechanism.

Performance analysis of LaFeO3 perovskite solar cells: A theoretical and experimental study

Lanthanum ferrite (LaFeO3) is a potential candidate for Perovskite Solar Cell (PSC) application. The transition metal oxide has strong electron-electron correlation which results in an increase in quantum efficiency (QE) of PSC. In this investigation, we reported synthesis of LaFeO3 perovskite material, simulation of LaFeO3-based PSC followed by experimental validation. The sol-gel method was employed to prepare nanoparticles of LaFeO3 for PSC application. The prepared perovskite material is analyzed by XRD, SEM, EDS, UV–Vis and FTIR. The photovoltaic (PV) application of synthesized LaFeO3 material is studied by SCAPS-1D. The LaFeO3-based PSC is simulated with various ETLs such as TiO2, PCBM, IGZO, In2O3, C60, ZnO, SnO2, WS2 and HTLs of Cu2O, CuInSe2, Spiro-OMeTAD, P3HT, D-PBTTT-14, V2O5, CFTS, CBTS. The simulation outcomes of 64 distinct configurations deduced the eight-best performing PSCs. For these eight PSCs, impact of thickness of perovskite absorber layer, operating temperature, defect density, series and shunt resistance, work function of back contact, J-V characteristics and QE curve has been studied. We have achieved theoretical maximum efficiency of 13.03 % for the configuration of FTO/WS2/LaFeO3/CBTS/Au. The optimized structure has experimentally obtained maximum efficiency of 0.79 %. This shows that it is promising material for future PV application.

Impact of device resistances in the performance of graphene-based terahertz photodetectors

In recent years, graphene field-effect-transistors (GFETs) have demonstrated an outstanding potential for terahertz (THz) photodetection due to their fast response and high-sensitivity. Such features are essential to enable emerging THz applications, including 6G wireless communications, quantum information, bioimaging and security. However, the overall performance of these photodetectors may be utterly compromised by the impact of internal resistances presented in the device, so-called access or parasitic resistances. In this work, we provide a detailed study of the influence of internal device resistances in the photoresponse of high-mobility dual-gate GFET detectors. Such dual-gate architectures allow us to fine tune (decrease) the internal resistance of the device by an order of magnitude and consequently demonstrate an improved responsivity and noise-equivalent-power values of the photodetector, respectively. Our results can be well understood by a series resistance model, as shown by the excellent agreement found between the experimental data and theoretical calculations. These findings are therefore relevant to understand and improve the overall performance of existing high-mobility graphene photodetectors.Graphical

Numerical simulation to optimize power conversion efficiency of an FTO/GO/Cs2AgBiBr6/Cu2O solar cell.

Efficient conversion of solar power to electrical power through the development of smart, reliable, and environmentally friendly materials is a key focus for the next-generation renewable energy sector. The involvement of degradable and toxic elements present in hybrid perovskites presents serious concerns regarding the commercial viability of these materials for the solar cell industry. In this study, a solar cell with a stable, nondegradable, and lead-free halide-based double perovskite Cs2AgBiBr6 as the absorber layer, Cu2O as a hole transport layer, and GO as the electron transport layer has been simulated using SCAPS 1D. The thickness of the absorber, electron transport, and hole transport layers are tuned to optimize the performance of the designed solar cell. Notably, perovskite solar cells functioned most efficiently with an electron affinity value of 4.0 eV for Cu2O. In addition, the effect of variation of series resistance and temperature on generation and recombination rates, current density, and quantum efficiency has been elaborated in detail. The findings of this study provide valuable insight and encouragement toward the realization of a non-toxic, inorganic perovskite solar device and will be a significant step forward in addressing environmental concerns associated with perovskite solar cell technology.

In Situ Electrochemical Cobalt Doping in Perovskite-Structured Lanthanum Nickelate Thin Film Toward Energy Conversion Enhancement of Polymer Solar Cells.

This study demonstrates that the electrochemical doping of lanthanum nickelate (LNO) with cobalt ions is a promising strategy for enhancing its physical and electrochemical properties, which are critical for energy storage and conversion devices. LNO emerges as a promising hole transport layer (HTL) in solar cells due to its stability, large band gap, and high transparency. Nevertheless, its low conductivity and improperly aligned band positions are persistent problems. Here, in a pioneering endeavor, Co-doped LNO thin films were synthesized electrochemically and applied as the HTL in polymer solar cells (PSCs). Characterization revealed the impact of Co doping on the electrochemical, structural, morphological, and optical properties of LNO thin films. Depending on the Co doping level, PSCs based on 10 mol % Co-doped LNO outperformed pure LNO, achieving a champion efficiency of 6.11% with enhanced short-circuit current density (12.84 mA cm-2), fill factor (68%), open-circuit voltage (0.70 V), and external quantum efficiency (82.6%). This enhancement resulted from decreased series resistance, refined surface morphology, minimized trap-assisted recombination, enhanced conductivity, increased charge carrier production, favorable energy level alignment, and improved current extraction facilitated by LNC0.10O HTL. Moreover, the unencapsulated PSC-LNC0.10O long-term stability notably improved and retained 86% of its initial PCE after 450 h storage in ambient air, 82% after being continuously heated to 85 °C for 300 h, and 80% after operating at maximum power point for 300 h. These findings offer a straightforward approach to enhancing PSC performance through Co doping of LNO, supported by density functional theory (DFT) calculations that validate the experimental results and confirm the improvement in optical properties and stability of PSCs as an HTL.

Reactive DC Sputtered TiO2 Electron Transport Layers for Cadmium‐Free Sb2Se3 Solar Cells

AbstractThe evolution of Sb2Se3 heterojunction devices away from CdS electron transport layers (ETL) to wide bandgap metal oxide alternatives is a critical target in the development of this emerging photovoltaic material. Metal oxide ETL/Sb2Se3 device performance has historically been limited by relatively low fill factors, despite offering clear advantages with regards to photocurrent collection. In this study, TiO2 ETLs are fabricated via direct current reactive sputtering and tested in complete Sb2Se3 devices. A strong correlation between TiO2 ETL processing conditions and the Sb2Se3 solar cell device response under forward bias conditions is observed and optimized. Numerical device models support experimental evidence of a spike‐like conduction band offset, which can be mediated, provided a sufficiently high conductivity and low interfacial defect density can be achieved in the TiO2 ETL. Ultimately, a SnO2:F/TiO2/Sb2Se3/P3HT/Au device with the reactively sputtered TiO2 ETL delivers an 8.12% power conversion efficiency (η), the highest TiO2/Sb2Se3 device reported to‐date. This is achieved by a substantial reduction in series resistance, driven by improved crystallinity of the reactively sputtered anatase‐TiO2 ETL, whilst maintaining almost maximum current collection for this device architecture.

CoMnS@rGO nanocomposite grown on NF for high-performance supercapacitor-battery hybrid device and advancing electrochemical sensitivity

The co-electrodeposition approach has been widely used to synthesize the transition metal sulfides/oxides because of remarkable performance of the energy storage devices. In this research, cobalt manganese sulfide (CoMnS) binary compounds are synthesized using the co-electrodeposition approach. The main objective is to investigate the optimal number of depositing periods in cyclic voltammetry while maintaining a constant scan rate. The electrodes without binders are produced using a rapid synthesis approach, which involves assessing binary metal sulfide to achieve a significantly enhanced energy storage capacity. Further, the rGO is incorporated into the CoMnS to enhance the electrochemical properties. The CoMnS@rGO electrode showed the specific capacitance (Cs) of 2357 F/g because of the small equivalent series resistance values as determined through electrochemical impedance spectroscopy (EIS) measurement, indicating a higher level of conductivity. The hybrid electrode showed high values of energy and power densities of 50.8 Wh/kg and 3440 W/kg, respectively. Besides, the nanocomposite electrode is used as a chemical sensor and precisely detects the multiple elements. The estimated value of R2 is 0.994 because of the high sensitivity. The hybrid electrode showed a signal-to-noise ratio (S/N) of 5. Furthermore, based on four observations, the comparative standard deviation (RSD) is calculated to be 1.9 %. The device showed high electrochemical glucose detection sensitivity. The nanocomposite-based electrodes provide a platform for designing novel multifunctional devices.

A series resistance extraction method for health evaluation of photovoltaic modules

Photovoltaic (PV) modules must be monitored and evaluated in real-time during long-term operations to maintain a high performance, and series resistance is a critical component of this process. However, existing series resistance extraction methods may have either low accuracy or a very complex solution process. Worth mentioning, the size of this series resistance depends on environmental conditions, and the extraction results under different environments cannot be mutually referenced and compared. In this study, an analytical method for series resistance was derived, and a correction method for I–V curves that differs from the IEC 60891 standard was proposed, based on the derivative of the I–V characteristic curve of PV modules. The proposed analytical method was compared with three other methods for PV modules with three varied materials, and the influence of the ideality factor on parameter accuracy was also assessed. The obtained results showed that the proposed method can achieve high accuracy through an analytical expression. In addition, the I–V curves of a PV module operating for more than 6 years were corrected to fit the expected environmental conditions via the proposed correction method. Upon the calculated average value of the series resistance, the results indicated that the PV module has slightly aged, which verifies the effectiveness of the recommended method.

DC current–voltage and impedance spectroscopy characterization of nCdS/pZnTe HJ

This paper describes the electrical and dielectric behavior of the nCdS/pZnTe HJ by current–voltage, capacitance–voltage characteristics, and impedance spectroscopy in a temperature interval 220–350 K. A microcrystalline p-ZnTe layer and n-CdS were grown on glass/ZnO substrate by closed space sublimation method. As frontal contact to CdS, the transparent ZnO and as a back contact to ZnTe, silver conductive paste (Ag) treated at 50 °C in vacuum were used. The current–voltage results of nCdS/pZnTe HJ show a rectifying behavior. The junction ideality factor, barrier height, and series resistance values were extracted from the rectifying curves at different temperatures. The built-in voltage, carrier concentration and depletion width were obtained from the capacitance–voltage measurements. Analysis of the J–V–T and C–V–T characteristics shows that the thermionic emission and recombination current flow mechanisms dominate in the nCdS/pZnTe HJ. The dielectric study reveals that the experimental values of the AC conductivity, dielectric constant, dielectric loss, the imaginary part of the electric modulus are found to be very sensitive to frequency and temperature. The dielectric constant and dielectric loss are observed to be high at the low frequency region. The increase in the values of electric modulus with the frequency implies an increase in the interfacial polarization at the interface of nCdS/pZnTe HJ. Jonscher’s universal power law shows that with increasing frequency, AC conductivity increased. The results conductivity show that the ionic conductivity and interfacial polarization are the main parameters affecting the dielectric properties of the device when the temperature changes.

Modeling temperature dependent Ni/β-Ga2O3 Schottky barrier diode interface properties

A TCAD simulator is used to model measured current–voltage characteristics of Ni/β-Ga2O3 Schottky barrier diode (SBD), deposited by E-beam evaporation, at room temperature. A good fit was obtained when the Ni workfunction, Ni/β-Ga2O3 interface traps concentrations and Si-doped β-Ga2O3 surface electron affinity variation were taken into consideration. Temperature dependent J-V characteristics were investigated and a good agreement at low voltage was obtained. However, the simulated current at high voltage (series resistance domain) was higher than measurement while both series resistance (Rs) and on-resistance (Ron) for measurements were higher than their simulations counterparts. In order to overcome this disagreement, the effect of Si-doped β-Ga2O3 surface electron affinity on the SBD at each temperature was studied. This is due to the fact that the electron affinity can be affected by trap levels located above conduction band maximum (CBM) as reported in the literature. The surface electron affinity decreased with increasing temperature because trap levels located above CBM were activated. A better agreement was achieved.

High Efficiency Flat-Type GaN-Based Light-Emitting Diodes with Multiple Local Breakdown Conductive Channels.

We investigated a flat-type p*-p LED composed of a p*-electrode with a local breakdown conductive channel (LBCC) formed in the p-type electrode region by applying reverse bias. By locally connecting the p*-electrode to the n-type layer via an LBCC, a flat-type LED structure is applied that can replace the n-type electrode without a mesa-etching process. Flat-type p*-p LEDs, devoid of the mesa process, demonstrate outstanding characteristics, boasting comparable light output power to conventional mesa-type n-p LEDs at the same injection current. However, they incur higher operating voltages, attributed to the smaller size of the p* region used as the n-type electrode compared to conventional n-p LEDs. Therefore, despite having comparable external quantum efficiency stemming from similar light output, flat-type p*-p LEDs exhibit diminished wall-plug efficiency (WPE) and voltage efficiency (VE) owing to elevated operating voltages. To address this, our study aimed to mitigate the series resistance of flat-type p*-p LEDs by augmenting the number of LBCCs to enhance the contact area, thereby reducing overall resistance. This structure holds promise for elevating WPE and VE by aligning the operating voltage more closely with that of mesa-type n-p LEDs. Consequently, rectifying the issue of high operating voltages in planar p*-p LEDs enables the creation of efficient LEDs devoid of crystal defects resulting from mesa-etching processes.

Impact of Electrochemical Impedance Spectroscopy Dataset Curation on Solid Oxide Cell Degradation Assessment

Electrochemical impedance spectroscopy (EIS) has become a standard measurement technique for detecting degradation in single cells and stacks of solid oxide cells (SOCs). Depending on the experimental setup and test equipment, instabilities and unexpected results can be observed in EIS measurements. For example, in the low-frequency range, instabilities can be induced by feed gas flow fluctuations. Another phenomenon are parasitic, inductive impedances that degrade the high-frequency range. To compensate for such influences in large EIS data sets, we propose a specially developed EIS data curation pipeline. Based on the results of its application, we demonstrate the impact on the quantitative and qualitative attribution of electrochemical processes from EIS using equivalent circuit modeling and distribution of relaxation times. Furthermore, the substantial differences in the temporal evolution of the latter during long-term experiments are highlighted for EIS measurements obtained at the SOC stack and single cell level. In addition, the significant misestimation of aging rates, especially with respect to the fuel electrode and the high-frequency series resistance, is shown when comparing EIS measurements, few of which exhibit a parasitic inductive impedance.