Current Density-voltage Characteristics Research Articles

Exploration of the structural and electrical characteristics and solar cell applications of an electrolyte membrane derived from acacia gum

The natural and eco-friendly solid-state electrolytes were prepared using varying concentrations (wt%) of ZnSO4.7H2O salt and pure acacia gum through the solution cast method. Multiple analytical methods were employed to characterize the resulting acacia gum electrolyte samples. XRD analysis confirmed the increased presence of the amorphous phase with the introduction of salt. FTIR analysis explored the formation of interlinking bands and their complex nature upon salt incorporation. The ionic conductivity was found from room temperature (RT) to 100 °C range. The optimized high ionic conductivity value was found to be 1.11 × 10−4 S/cm at 100 °C for the electrolyte composed of 70 wt% acacia gum and 30 wt% ZnSO4.7H2O, while at RT it was 1.06 × 10−5 S/cm for the same composition. Activation energy values fell within the 0.6–0.92 eV range for all samples. Complex dielectric (real and imaginary) and complex electric modulus analyses were conducted. Dielectric permittivity and electrical modulus analyses revealed a significant interaction between the segmental movements of acacia gum and salt ions. Ionic relaxation processes were explored in terms of conductivity relaxation time using the electrical modulus. The presence of a long tail in the complex dielectric modulus study indicated that the acacia-based solid electrolyte displayed favorable capacitance properties. Further, the Solar Cell (dye-sensitized solar cell) device was fabricated with (Acacia gum + ZnSO4.7H2O) electrolyte. The current density-voltage (J-V) characteristics of the prepared device were investigated. The outstanding results were optimized in the present work, Voc = 0.81 V, Jsc = 9.56 mA/cm2, Fill Factor of 0.67, and optimum power conversion efficiency ƞ = 5.17 % for the electrolyte composed of 70 wt% acacia gum and 30 wt% ZnSO4.7H2O device.

Effects of transparent conducting electrodes and hole transport layers on the performance of MAPbI3 solar cells fabricated on PET substrates

This study investigates how the performance of perovskite solar cells (PSCs) made on polyethylene terephthalate (PET) substrates depends on transparent conducting electrodes (TCEs) and hole transport layers (HTLs). We fabricated PSCs using commercially available PET/TCEs and compared their performance with PSCs manufactured on Glass/indium tin oxide (ITO) substrates. Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) with varying levels of acidity and NiO nanoparticles were used as HTLs. The current density-voltage characteristics of PSCs made on PET/TCEs were found to be significantly lower when highly acidic PEDOT:PSS was used as the HTL. However, this was not observed for PSCs made on Glass/ITO. To investigate the interaction between HTL and TCE, atomic force microscopy was carried out after dipping the TCEs in PEDOT:PSS solutions of different acidity. X-ray photoelectron spectroscopy measurements further revealed differences in the chemical composition between ITO film on PET vs. on glass. Our results indicate that the performance of PSCs depends both on the TCE substrates and HTLs, which can be explained by their chemical interaction.

Aqueous PEIE Soaking on ZnO for Ultraviolet Light Activation-Free Organic Photovoltaic Modules.

Ultraviolet (UV) light is typically needed to activate inverted organic photovoltaics (OPVs) with zinc oxide (ZnO) as electron transporting layer (ETL)for higher efficiency. However, UV light is a major cause for the degradation of organic active layers in OPVs. This is a contradiction that UV light activation enhances the efficiency but UV illumination deteriorates the stability. It is important to solve this contradiction to develop UV light activation-free OPV devices. Herein, a method of aqueous polyethylenimine ethoxylated (PEIE) soaking on ZnO is reported to realize UV light activation-free OPV devices. The S-shape in current density-voltage (J-V) characteristics of devices tested without UV light activation is eliminated through the treatment of aqueous PEIE soaking on ZnO. The treatment reduces the oxygen adsorbates, which is confirmed by Kelvin probe and X-ray photoelectron spectroscopy. A 10.08 cm2 organic photovoltaic module with the treated ZnO asETL showed high photovoltaic performance: VOC = 5.68 V, JSC = 2.7 mAcm-2, FF = 75.1%, and POutput = 11.5 mWcm-2 tested with the UV filter (light intensity of 0.788 sun). UV light activation is not needed for the modules to obtain high efficiency.

Impact of Temperature Optimization of ITO Thin Film on Tandem Solar Cell Efficiency.

This study examined the impact of temperature optimization on indium tin oxide (ITO) films in monolithic HJT/perovskite tandem solar cells. ITO films were deposited using magnetron sputtering at temperatures ranging from room temperature (25 °C) to 250 °C. The sputtering target was ITO, with a mass ratio of In2O3 to SnO2 of 90% to 10%. The effects of temperature on the ITO film were analyzed using X-ray diffraction (XRD), spectroscopic ellipsometry, and sheet resistance measurements. Results showed that all ITO films exhibited a polycrystalline morphology, with diffraction peaks corresponding to planes (211), (222), (400), (440), and (622), indicating a cubic bixbyite crystal structure. The light transmittance exceeded 80%, and the sheet resistance was 75.1 Ω/sq for ITO deposited at 200 °C. The optical bandgap of deposited ITO films ranged between 3.90 eV and 3.93 eV. Structural and morphological characterization of the perovskite solar cell was performed using XRD and FE-SEM. Tandem solar cell performance was evaluated by analyzing current density-voltage characteristics under simulated sunlight. By optimizing the ITO deposition temperature, the tandem cell achieved a power conversion efficiency (PCE) of 16.74%, resulting in enhanced tandem cell efficiency.

Non-Equilibrium Long-Wave Infrared HgCdTe Photodiodes: How the Exclusion and Extraction Junctions Work Separately.

The cooling requirement for long-wave infrared detectors still creates significant limitations to their functionality. The phenomenon of minority-carrier exclusion and extraction in narrow-gap semiconductors has been intensively studied for over three decades and used to increase the operating temperatures of devices. Decreasing free carrier concentrations below equilibrium values by a stationary non-equilibrium depletion of the device absorber leads to a suppression of Auger generation. In this paper, we focus on analyzing exclusion and extraction effects separately, based on experimental and theoretical results for a HgCdTe photodiode. To carry out an experiment, the n+-P+-π-N+ heterostructure was grown by metal organic chemical vapor deposition on CdTe-buffered GaAs substrate. In order to separate the extraction and exclusive junctions, three different devices were evaluated: (1) a detector etched through the entire n+-P+-π-N+ heterostructure, (2) a detector made of the P+-π photoconductive junction and (3) a detector made of the π-N+ photodiode junction. For each device, the dark current density-voltage characteristics were measured at a high-temperature range, from 195 K to 300 K. Next, the carrier concentration distribution across the entire heterostructure and individual junctions was calculated using the APSYS simulation program. It was shown that when the n+-P+-π-N+ photodiode is reverse biased, the electron concentration in the π absorber drops below its thermal equilibrium value, due to the exclusion effect at the P+-π junction and the extraction effect at the π-N+ junction. To maintain the charge neutrality, the hole concentration is also reduced below the equilibrium value and reaches the absorber doping level (NA), leading to the Auger generation rate's reduction by a factor of 2ni/NA, where ni is the intrinsic carrier concentration. Our experiment conducted for three separate detectors showed that the exclusion P+-π photoconductive junction has the most significant effect on the Auger suppression-the majority of the hole concentration drops to the doping level not only at the P+-π interface but also deep inside the π absorber.

Observation of negative capacitance in silicon heterojunction solar cells: role of front contact in carrier depopulation

The origin of the low-frequency inductive loop in the Nyquist plot of the Ag/indium tin oxide (ITO)/p-a-Si:H/intrinsic hydrogenated amorphous silicon (i-a-Si:H)/c-Si/i-a-Si:H/n-a-Si:H/ITO/Al heterojunction (SHJ) solar cells and their effect on the device performance are investigated by adopting impedance spectroscopy under dark and light. The negative capacitance/low-frequency inductive loop originates from the depopulation of injected charge carriers due to a transport barrier at the p-a-Si:H/ITO interface. The p-a-Si:H hole-selective SHJ device with a low-frequency inductive loop also has shown an S-shape and associated performance degradation in the light current density–voltage characteristics due to the opposing field type transport barrier present at the p-a-Si:H/ITO interface, which was overcome after vacuum annealing at ∼200 °C. However, the NiO x -based hole-selective contact Ag/ITO/NiO x /i-a-Si:H/c-Si/i-a-Si:H/n-a-Si:H/ITO/Al SHJ cells have not shown any low-frequency inductive loop or corresponding S-shape and associated performance degradation due to the optimised contact (minimum resistance) between the NiOx and ITO layers.

Beginner's Guide to Visual Analysis of Perovskite and Organic Solar Cell Current Density–Voltage Characteristics

AbstractThe current density–voltage characteristic (J–V) is a critical tool for understanding the behavior of solar cells. This study presents an overview of the key aspects of J–V analysis and introduces a user‐friendly flowchart that facilitates the swift identification of the most probable limiting process in a solar cell, based mainly on the outcomes of light‐intensity‐dependent J–V measurements. The flowchart is developed through extensive drift‐diffusion simulations and a rigorous review of the literature, with a specific focus on perovskite and organic solar cells. Moreover, the flowchart proposes supplementary experiments that can be conducted to obtain a more precise prediction of the primary performance losses. It therefore serves as an optimal starting point to analyse performance losses of solar cells.

Investigating of novel inorganic cubic perovskites of A3BX3 (A=Ca, Sr, B[dbnd]P, As, X=I, Br) and their photovoltaic performance with efficiency over 28%

Inorganic halide perovskite-based compounds of A3BX3 have been gaining huge attention during the development of high-efficiency solar cells (SC) in recent years. This paper, investigating the physical and chemical properties could unveil its further potential to be used as absorber materials in advanced multijunction photovoltaics. The structural, optical, and electronic characterization of different compositional compounds of A3BX3 (A=Ca/Sr, BP/As, X=I/Br) perovskites are examined thoroughly to be used as absorber in high performance photovoltaics. The DFT study reveals direct bandgaps of 1.93 (2.60) eV, 1.58 (2.14) eV, 1.96 (2.63) eV, 1.58 (2.16) eV, 1.52 (2.30) eV, 1.26 (1.94) eV, 1.53 (2.32) eV, and 1.26 (1.96) eV at Γ for the Ca3AsBr3, Ca3AsI3, Ca3PBr3, Ca3PI3, Sr3AsBr3, Sr3AsI3, Sr3PBr3, and Sr3PI3 perovskites using PBE (HSE) methods with optical absorption of (2−5)x104 (a. u.) in the optical region (< 3.2 eV). Subsequently, the potential of the A3BX3 absorber has been investigated and analyzed at varying layer thickness, defect densities, and doping concentrations with SnS2 electron transport layer (ETL) layer using FTO/SnS2/A3BX3/Ni heterostructure with current density-voltage (J-V) characteristics and corresponding quantum efficiency (QE) observation. The power conversion efficiency (PCE) of 13.52, 20.88, 13.66, 22.47, 20.83, 28.16, 20.77, and 27.32% were achieved in Ca3AsBr3, Ca3AsI3, Ca3PBr3, Ca3PI3, Sr3AsBr3, Sr3AsI3, Sr3PBr3, and Sr3PI3 absorber-based heterojunction SC. Notably, the highest PV performance revealed a PCE over 28% with a VOC of 0.913 V, JSC of 35.75 mA/cm−3, and FF of 86.26% obtained in the Sr3AsI3 absorber SCs. Thus, these detailed studies on the physical and optoelectronic properties of eight (8) different possible absorber-based configurations including their PV applications unveil the huge potential of A3BX3 (i.e., Sr3AsI3) and provide resources for the practical cell development of inorganic perovskites-based high efficiency SC over 28%.

Analysis of Charge Transport in Polymer: Non-Fullerene Blend: Evidence for the Absence of Correlated Disorder

Recently, rapid development of non-fullerene acceptors has attracted considerable attention to theirs charge transport. In this paper, charge transport and spatial correlations between the site energies in the blend of polymer PBDB-T derivative PM6 and non-fullerene acceptor Y6 are investigated. From an analysis of the temperature dependence of current density-voltage (J – V ) characteristics of hole-only and electron-only devices based on PM6:Y6 blend, it is found that consistent descriptions with equal quality are obtained using both the improved extended Gaussian disorder model (IEGDM) and the extended correlated disorder model (ECDM), within which spatial correlations between the transport site energies are absent and are included, respectively. By comparing model parameters with the typical values of organic materials, we view more realistic intersite distance obtained using the IEGDM compared to the value obtained using the ECDM as an indication that in PM6:Y6 blend correlations between the transport site energies are absent or play a minor role. Furthermore, it is found that energetic disorder is larger for hole than for electron in PM6:Y6 blend, and electron transport is intrinsically superior to hole transport.

Resonant Tunnelling and Intersubband Optical Properties of ZnO/ZnMgO Semiconductor Heterostructures: Impact of Doping and Layer Structure Variation.

ZnO-based heterostructures are up-and-coming candidates for terahertz (THz) optoelectronic devices, largely owing to their innate material attributes. The significant ZnO LO-phonon energy plays a pivotal role in mitigating thermally induced LO-phonon scattering, potentially significantly elevating the temperature performance of quantum cascade lasers (QCLs). In this work, we calculate the electronic structure and absorption of ZnO/ZnMgO multiple semiconductor quantum wells (MQWs) and the current density-voltage characteristics of nonpolar m-plane ZnO/ZnMgO double-barrier resonant tunnelling diodes (RTDs). Both MQWs and RTDs are considered here as two building blocks of a QCL. We show how the doping, Mg percentage and layer thickness affect the absorption of MQWs at room temperature. We confirm that in the high doping concentrations regime, a full quantum treatment that includes the depolarisation shift effect must be considered, as it shifts mid-infrared absorption peak energy for several tens of meV. Furthermore, we also focus on the performance of RTDs for various parameter changes and conclude that, to maximise the peak-to-valley ratio (PVR), the optimal doping density of the analysed ZnO/Zn88Mg12O double-barrier RTD should be approximately 1018 cm-3, whilst the optimal barrier thickness should be 1.3 nm, with a Mg mole fraction of ~9%.

Bismuth sulfide/carbon black: as a pt free and efficient counter electrode in DSSC

A hydrothermal method was utilized to synthesize microstructures of bismuth sulfide (Bi2S3) across a range of reaction temperatures, spanning from 140 to 180 °C. The impact of varying reaction temperatures on the structural, morphological, and optical properties of the deposited Bi2S3 material was thoroughly examined. The x-ray diffraction (XRD) patterns confirmed the presence of an orthorhombic crystal structure. The formation of intricate three-dimensional Bi2S3 microstructures was evident under field emission scanning electron microscopy (FESEM), with the reaction temperature playing a pivotal role in this process. Furthermore, Bi2S3-carbon black composites were employed as the counter electrode in dye-sensitized solar cell (DSSC) applications. The current density–voltage characteristics of the DSSCs revealed a clear correlation between photoconversion efficiency and the reaction temperature. Notably, the Bi2S3-carbon black film with a 1:1 ratio achieved a peak photoelectric conversion efficiency of 4.37 ± 0.01%. It also exhibited a short-circuit current density of 10.29 mA cm−2 and an open-circuit potential of 0.70 V. Future studies should explore the broader implications of Bi2S3-carbon black composites in various optoelectronic and photocatalytic devices. Secondly, while our findings provide valuable insights, a more in-depth understanding of the underlying mechanisms governing the enhanced photoconversion efficiency, especially with the 1:1 ratio of Bi2S3-carbon black, requires further exploration.

Effects of alkali metals or Cu+ addition to α-FAPbI3 perovskite crystals on electronic structures and photovoltaic properties

A monovalent copper ion (Cu+) with the same valence as formamidinium is focused on the present work, and the effects of A-site inorganic cations on the electronic structures and device performance are discussed from the experiments and the first-principles calculations. The addition of inorganic cations increased the conversion efficiencies, and the copper-doped device showed the highest conversion efficiency. In particular, the hysteresis of current density–voltage characteristics was significantly suppressed by the addition of Cu+, which would be due to suppression of iodine ion (I−) diffusion by electrostatic interaction between Cu+ and I−. The addition of rubidium or cesium contributed to the increase in short-circuit current density by suppressing decomposition of perovskite crystals and formation of PbI2.

Boosting efficiency above 30 % of novel inorganic Ba3SbI3 perovskite solar cells with potential ZnS electron transport layer (ETL)

The inorganic Ba3SbI3 perovskite has emerged as a promising, stable absorber material for efficient and cost-effective solar cells, owing to its intriguing compositional, structural, electrical, and optical properties. This study delves into the potential of Iodide-based Ba3SbI3 perovskites, known for their relative stability, as absorbers in conjunction with a ZnS electron transport layer (ETL) to create a high-performance solar cell heterostructure. Using the SCAPS-1D simulator, we first estimate the absorption spectrum and bandgap of the Ba3SbI3 absorber layer through density functional theory (DFT). This obtained spectrum serves as a crucial input for device simulation. We further optimize the work function of the rear electrode to enhance the photovoltaic (PV) performance of the ZnS/Ba3SbI3 heterostructure solar cell. Various parameters including doping density, absorber thickness, and bulk/interface defect density are carefully considered. Additionally, we investigated generation and recombination rates, current density-voltage (J-V) characteristics, and corresponding quantum efficiency (QE). Under optimized conditions, our study achieves a remarkable maximum power conversion efficiency (PCE) of 30.49 %, accompanied by a photocurrent density (JSC) of 54.63 mA/cm2, fill factor (FF) of 83.75 %, and open circuit voltage (VOC) of 0.67 V in the ITO/ZnS/Ba3SbI3/Ni structure. This comprehensive analysis offers valuable insights and methodologies for the experimental design of high-performance and stable photovoltaic devices based on Ba3SbI3 perovskite.

Organic heterostructures based on thermal evaporated phthalocyanine and porphyrin as mixed (ZnPc:TPyP) or stacked (ZnPc/TPyP) films

A metallic phthalocyanine (zinc phthalocyanine - ZnPc) and a non-metallic porphyrin (10,15,20-tetra(4-pyridyl)21H,23H-porphyne -TPyP) were used to deposit mixed and stacked organic thin films by vacuum thermal evaporation method. The obtained layers were analyzed in a comparative manner from optical, structural, morphological and electrical point of view. The ultraviolet-visible spectra of the deposited layers showed that both organic components have absorption bands in the visible part of the solar spectrum, which means that the acceptor TPyP also contributes to absorption together with the donor. The photoluminescence spectra revealed only the emission bands associated to the porphyrin, especially in the single and stacked layers, while a quenching effect of the photoluminescence was noted in the mixed ones. The X-ray diffraction showed that the prepared layers are in general amorphous. The constituent materials in the single layers and the ratio between the two organic components in the mixed layers affect the morphology of the deposited films as was emphasized by scanning electron microscopy and atomic force microscopy analysis. The current density-voltage characteristics plotted under illumination revealed that the highest short-circuit current value was achieved in the case of the structure based on the layer showing the lowest roughness and thickness emphasizing the significant role played by these parameters of the layers considered for possible applications in the optoelectronic device area.

Charge carrier transport mechanism in plasma polymerized methyl acrylate thin films

Plasma-polymerized methyl acrylate thin films (PPMA) of thicknesses 115 to 290 nm were prepared using a capacitively coupled glow discharge plasma reactor. The current density-voltage (J-V) characteristics of the Aluminum/PPMA/Aluminum sandwich configuration were studied between 0.1 and 75 V over the temperature region from 298 K to 398 K for various thicknesses of PPMA thin films. J-V curves show that the conduction current follows Ohm's law in the low voltage area, but that in the high voltage range, the behavior is attributed to be space charge-limited conduction (SCLC) in PPMA thin films. The free carrier density, the trap density and carrier mobility have been determined to be around 1.77 × 1023 to 5.86 × 1023 m−3, 2.84 × 1024 to 3.77 × 1024 m−3, and 3.87 × 10−18 to 69.7 × 10−18 m2V−1s−1, respectively for various thicknesses of PPMA thin films. For the higher temperature and lower temperature areas, the activation energies were found in the range from 0.60 to 0.84 eV and 0.28 to 0.40 eV, respectively for 5 V in Ohmic region and from 0.61 to 0.98 eV and 0.27 to 0.34 eV, respectively for 60 V in SCLC (Non-Ohmic) region, respectively. It is observed that SCLC mechanism in PPMA thin films is dominated by a single dominant trap level/discrete trap level distribution. The PPMA thin films are promising candidates in manufacturing optoelectronic devices.

Improving Performance of Organic Photodetectors by Using TCNQ Doped Copper Thiocyanate as the Anode Interfacial Layer

AbstractThe responsivity and specific detectivity are critical figures of merits for organic photodetectors; however, it remains challenging to simultaneously enhance two such parameters, since enhancing external quantum efficiency corresponding to responsivities will inevitably increase leakage current and noises, resulting in decreased specific detectivity. To address such a trade‐off, an effective anode interfacial layer of 7,7,8,8‐tetracyanoquinodimethane (TCNQ) doped copper thiocyanate (CuSCN) is developed herein, which can enhance shunt resistance, increase depletion width, enhance hole extraction efficiency, as well as reduce trap density of states of organic photodetectors. The organic photodetectors based on doped CuSCN present a very low dark current density of 4.4 × 10−11 A cm−2 and an impressively high specific detectivity of 1.1 × 1014 Jones. As evidenced by X‐ray photoelectron spectroscopy and ultraviolet photoelectron spectroscopy measurements, the energy levels of the doped CuSCN:TCNQ film are deepened, associated with the occurrence of dopant bonding and charge transfer. In addition, it is found that increasing the delay time can suppress the hysteresis effects of current density–voltage characteristics of organic photodetectors and make the minimum dark current density obtainable at 0 V. These findings demonstrate the great potential of using molecular doping to adjust the anode interfacial layer for developing high‐performance organic photodetectors.

Effect of Diffusion on Charge Transport in Organic Photovoltaic Blends

Charge transport is one of the key factors in the operation of organic photovoltaic devices. Non-fullerene acceptor materials have recently attracted significant attention in organic photovoltaics due to their great potential to realize high power conversion efficiencies. In this paper, we investigate the effect of diffusion on charge transport in a variety of binary and ternary organic photovoltaic materials, including both polymer: fullerene and polymer:non-fullerene blends. It is shown that the temperature dependent current density-voltage characteristics from the drift-diffusion simulations incorporating the extended Gaussian disorder model (EGDM) are more consistent with experimental data in comparison with those obtained from the only drift model for all these material systems. Furthermore, it is found that the effect of diffusion on charge transport is more pronounced at low voltages and seems to be negligible when the applied voltage exceeds 1 V. The deviation of calculated curves from experimental measurements gradually increases with increasing temperature. It is of great importance to the influence of diffusion effect on charge transport in both polymer:fullerene and polymer:non-fullerene blends.

Effect of Water Vapor and Hydrogen Concentration on Power Generation Characteristics of Protonic Ceramic Fuel Cell

The proton and hole conductivities of BaZrO3-based perovskites depend on partial pressures of oxygen and water vapor. These conductivities affect the power generation characteristics of Proton Ceramic Fuel Cells (PCFCs) using the perovskite as an electrolyte. In this study, the effect of humidification conditions on the power generation characteristics of an anode-supported PCFCs was investigated.The configuration of the anode-supported PCFC was La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode/BaZr0.8Yb0.2O3-δ(BZYb) electrolyte/Ni-BZYb anode. The diameter of the effective cathode area was approx. 10 mm. The cathode gas composition was fixed at 97% concentration of air and 3% concentration of water vapor. The concentration of water vapor in the anode gas was controlled to be 3-69%. The current density-voltage characteristics and AC impedance were measured by Bio-Logic SP-150.In all water vapor concentration conditions, the cell showed the highest OCV (approximately 1 V) at 3% concentration of water vapor. However, the maximum power density was highest at 30% concentration of water vapor (346 mW/cm2). The highest maximum power density at 30% concentration of water vapor can be explained by the following reason. The OCV values decrease with increasing the concentration of water vapor because of decreasing the concentration of hydrogen. On the other hand, from the results of impedance measurements, the ohmic resistance of the cell decrease with increasing the concentration of water vapor because of increase of proton conductivity of the cell. Thus, the increase of cell voltage by increase of proton conductivity should be higher than the decrease of OCV values.【Acknowledgements】This presentation is the result of the research and development of ultra-efficient proton-conducting ceramic fuel cell devices, JPNP20003, funded by the New Energy and Industrial Technology Development Organization (NEDO), Japan. We would like to express our gratitude to all parties involved.

Effect of Water Vapor and Hydrogen Concentration on Power Generation Characteristics of Protonic Ceramic Fuel Cell

To investigate the effect of water vapor in the feed gas on the power generation characteristics of PCFCs, the water vapor concentration was changed to 3%, 15%, 30%, and 50%, while the hydrogen concentration in the gas fed to the anode was fixed at 50%. The impedance measurements showed that the ohmic resistance decreased with increasing water vapor concentration, which was attributed to the increase in the proton conductivity of the electrolyte. The measured current density-voltage characteristics showed that the power output increased with increasing water vapor concentration, which was attributed to the decrease in ohmic overvoltage caused by the increase in proton conductivity. In addition, as a more practical condition, the power generation characteristics were measured when the water vapor concentration was varied while the hydrogen concentration was varied in an anode gas consisting only of hydrogen and water vapor.

Tuning the Interfacial Electrical Field of Bipolar Membranes with Temperature and Electrolyte Concentration for Enhanced Water Dissociation

A coupled experimental and numerical study was performed for a fundamental understanding of the impact of operating conditions, i.e., temperature and electrolyte concentration, as well as interfacial abruptness, on the bipolar membrane (BPM) performance. A comprehensive multiphysics-based model was developed to optimize the operation condition and interfacial properties of BPM, and the model was used to guide the design and engineering of high-performing BPMs. The origin of the enhanced BPM performance at a high temperature was identified, which was attributed to the intrinsic reaction rate enhancement as well as the increase in electrolyte ionic conductivity. The experimentally demonstrated current density–voltage characteristics of BPMs clearly exhibited three distinctive regions of operation: ion-crossover region, water dissociation region, and water-limiting region, which agreed well with the multiphysics simulation results. In addition, the model revealed that a sharper interfacial abruptness led to improved BPM performance due to the enhanced interfacial electric field at the water dissociation region. The decrease of the electrolyte concentration, which increased the dielectric constant of the electrolyte, enhanced the interfacial electric field, leading to improved electrochemical performances. The present study offers an in-depth perspective to understand the species transport as well as water dissociation mechanism under various operation conditions and membrane designs, providing the optimal operation conditions and membrane designs for maximizing the BPM performance at high current densities.