Current Density-voltage Measurements Research Articles

Investigation of current density and temperature distribution characteristics under transient conditions based on a 108 cm2 segmented proton exchange membrane fuel cell

Visualizing the electrochemical and temperature distribution characteristics inside proton exchange membrane fuel cell (PEMFC) should greatly contribute to the product development and performance optimization. In the study, a customized 27-segment 108 cm2 fuel cell was fabricated based on the printed circuit board methodology to achieve the local current density and local voltage measurement. In addition, 27 thermocouples were embedded in the segmented cathode graphite gas flow plate for local temperature measurement. Detailed information of fuel cell core components, multi-channel data acquisition system, external temperature control system, and uncertainty analysis was presented. According to the test results of 4000 s current rising conditions and 2400 s current decreasing conditions, the measurement deviation of total current between data acquisition system and TOYO test station is 2.4%–3.2%. Meanwhile, the deviation of output voltage ranges from 0.1% to 2.6%. To quantify the degree of distribution non-uniformity, the range and standard deviation of local parameter values as well as contour map are demonstrated. The non-uniformity of local current density and local temperature becomes more significant under higher operating current conditions. Furthermore, the degree of parameter non-uniformity is more noticeable under current rising conditions compared with current decreasing conditions. The transient increase of operating current leads to the sudden overshoot phenomena of local current range, and the change of local current density among all segments is instantaneously finished. However, the range of current demonstrates relatively smooth transition trends when reactant flow rate rises. Higher temperature area appears in the middle of membrane electrode assembly, especially in the position with higher local current density. The parameter distribution and transition characteristics could provide helpful guidance for fuel cell optimization and diagnosis.

Thymus schimperi Ronniger plant flower extract dye-sensitized solar cells

The demand for energy is greatly increasing due to the world’s population growth and technological advancement. Natural dye-sensitized solar cells are attracting research as an alternative and renewable energy source due to their simple preparation technique, availability, cost effectiveness and environmental friendliness. In the present work, we have successfully fabricated dye-sensitized solar cells (DSSCs) from Thymus schimperi Ronniger plant flowers for the first time. The solvents used for extraction of the flower dye were deionized water and its mixture with ethanol. The T. schimperi Ronniger flower extract dye solutions and sensitized photoanodes were characterized by Fourier transform infrared and ultraviolet–visible techniques. The crystallinity of TiO2 films was analyzed by x-ray diffraction, and the films showed pure anatase phase behavior. The photoelectrochemical solar cell performance parameters, such as short circuit current density, open circuit voltage, fill factor and efficiency, were evaluated from current density–voltage measurements using a Keithley 2450 source meter. DSSCs sensitized with dye solution extracted by a mixture of water and ethanol showed better performance (1.37%) than those sensitized with dye solution extracted by deionized water alone (1.02%).

Influence of surface passivation by MgO on photovoltaic performance of SnO2 based dye-sensitized solar cells

The study highlights effect of surface modification of SnO2 photoelectrode by MgO coating on photovoltaic properties of dye-sensitized solar cells (DSSCs). A thin coating of MgO on SnO2 photoelectrode was prepared using sol-gel-derived dip coating technique. The bare SnO2 and MgO coated SnO2 composite photoanodes was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS) and UV–vis spectrophotometer. The optical absorption study revealed that the modification in SnO2 by MgO coating caused an increase in absorption by photoanode in visible region. The solar cell was demonstrated by preparing FTO|SnO2|Dye|MgO|Electrolyte|Pt coated FTO device structure and tested with current density-voltage (J-V) measurement. The effect of precursor concentration of MgO coating on the performance of DSSCs were investigated. It was found that, optimized coating of MgO for 90 seconds on SnO2 improved all photovoltaic parameters, resulting in enhancement in efficiency by 42% compared to that of DSSC with bare SnO2 photoanode. The coating of MgO would have reduced the trap states and suppressed interfacial recombination losses by preventing back electron transfer from the conduction band of the semiconductor to HOMO of dye molecule or redox species.

Optical and electronic properties of MgPc-Ch-diisoQ blend organic thin film as an active layer for photovoltaic cells.

Organic photovoltaic cells are a promising technology for generating renewable energy from sunlight. These cells are made from organic materials, such as polymers or small molecules, and can be lightweight, flexible, and low-cost. Here, we have created a novel mixture of magnesium phthalocyanine (MgPc) and chlorophenyl ethyl diisoquinoline (Ch-diisoQ). A coating unit has been utilized in preparing MgPc, Ch-diisoQ, and MgPc-Ch-diisoQ films onto to FTO substrate. The MgPc-Ch-diisoQ film has a spherical and homogeneous surface morphology with a grain size of 15.9 nm. The optical absorption of the MgPc-Ch-diisoQ film was measured, and three distinct bands were observed at 800-600 nm, 600-400 nm, and 400-250 nm, with a band gap energy of 1.58 eV. The current density-voltage and capacitance-voltage measurements were performed to analyze the photoelectric properties of the three tested cells. The forward current density obtained from our investigated blend cell is more significant than that for each material by about 22%. The photovoltaic parameters (Voc, Isc, and FF) of the MgPc-Ch-diisoQ cell were found to be 0.45 V, 2.12 μA, and 0.4, respectively. We believe that our investigated MgPc-Ch-diisoQ film will be a promising active layer in organic solar cells.

Investigation of the Absorption Spectrum of InAs Doping Superlattice Solar Cells.

InAs doping superlattice-based solar cells have great advantages in terms of the ability to generate clean energy in space or harsh environments. In this paper, multi-period InAs doping superlattice solar cells have been prepared.. Current density-voltage measurements were taken both in the dark and light, and the short-circuit current was estimated to be 19.06 mA/cm2. Efficiency improvements were achieved with a maximum one sun AM 1.5 G efficiency of 4.14%. Additionally, external quantum efficiency and photoluminescence with different temperature-dependent test results were taken experimentally. The corresponding absorption mechanisms were also investigated.

The Role of PbCoS Quantum Dots in Improved Photovoltaic Efficiency

<p>The quest for efficient, sustainable solar energy solutions has propelled the exploration of novel materials with enhanced photovoltaic properties. This study delves into the synthesis, characterization, and photovoltaic application of cobalt-doped lead sulfide (PbCoS) quantum dots (QDs) deposited on titanium dioxide (TiO2) substrates. Employing a hot-injection method, we synthesized PbCoS QDs and characterized their structural, compositional, and optical properties using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and UV-Visible absorption spectroscopy. The QDs demonstrated a cubic crystal structure with an average size of 20.12 nm and exhibited a direct band gap of 1.91 eV, indicative of quantum confinement effects and improved absorption in the visible spectrum. The photovoltaic performance of quantum dot-sensitized solar cells (QDSSCs) incorporating PbCoS QDs was assessed through current density-voltage (J-V) measurements, revealing a power conversion efficiency (PCE) of 2.17%. This efficiency highlights the potential of PbCoS QDs to enhance the performance of QDSSCs, partly attributed to the impact of cobalt doping on the electronic structure and photovoltaic properties of the material. The study identifies gaps in current research, such as the optimization of cobalt doping levels and the exploration of interface engineering between QDs and substrates, pointing towards future directions for enhancing the efficiency and applicability of PbCoS-based photovoltaic devices.</p>

Analyzing the synergistic effect of Ag and Ge co-incorporation on Cu2ZnSnSe4 thin-film solar cells

At present, the large number of inherent CuZn anti-site defects and harmful [2CuZn + SnZn] defect clusters in the CZTSe film layer limit the further progress of device efficiency. In this paper, Ag and Ge double cations were introduced into the CZTSe film layer, and (CuAg)2ZnSnGeSe4 (CAZTGSe) films were synthesized successfully by the sol-gel method to cut down the above defects and defect clusters to obtain high-efficiency devices. The influences of double cation substitution on CZTSe by partly replacing Cu with Ag and Sn with Ge were developed. The role of Ag, Ge, and Ag + Ge substitution was researched by X-ray diffraction, scanning electron microscopy, current density-voltage (J-V), and external quantum efficiency measurements. By incorporating 5% Ag and 20% Ge double cations into the CZTSe film, the device demonstrated the highest efficiency of 10.12%. In addition, the open circuit voltage (VOC) of 503.57 mV, the short circuit current density (JSC) of 31.36 mA/cm2, and the fill factor (FF) of 64.1% were obtained.

High electric field characteristics of GaAsSb photodiodes on InP substrates

Low noise avalanche photodiodes (APDs) detecting 1550 nm wavelength play a crucial role in optical communication and LiDAR systems. These APDs utilize a separate absorption, charge, and multiplication (SACM) architecture with an absorber for 1400–1650 nm detection and a low noise, high gain multiplier that can be independently optimized for a high signal-to-noise ratio. Recently, GaAs0.5Sb0.5/Al0.85Ga0.15As0.56Sb0.44 SACM APDs have demonstrated ultra-high gain and extremely low noise, possibly improving sensitivity over Si and InGaAs/InP commercial APDs. This accomplishment was achieved using a GaAsSb absorber instead of a conventional InGaAs absorber, mitigating band discontinuities between the absorber and the multiplier. However, further optimization is required to reduce noise due to tunneling and impact ionization from the GaAsSb absorber, which occurs at a high electric field region. This paper focuses on the study of the high-field characteristics of GaAsSb photodiodes (PDs). The tunneling phenomenon is analyzed through current density-voltage measurements, and the impact ionization behavior is evaluated by measuring the multiplication of p-i-n GaAsSb PDs. The result suggests that when designing a SACM APD with a GaAsSb absorber, the electric field in the absorber can be increased to 175 kV/cm without the detrimental effects of ionization occurring in the absorber. The findings from this investigation will assist in optimizing GaAsSb-based SACM APDs and promoting further advancements in the 1550 nm APD technology.

Electrical properties and energy band alignments of p-Si/n-Ga2O3 and p+-Si/n-Ga2O3 heterostructures fabricated by surface-activated bonding

We fabricated p-Si/n-Ga2O3 and p+-Si/n-Ga2O3 heterostructures by surface-activated bonding (SAB) and investigated their electrical properties. Current density–voltage measurement was performed before and after thermal annealing at 450 °C. The current density substantially increased after annealing, which was attributed to thinning of an intermediate layer formed by the bonding process. Distinctive two-stage capacitance–voltage characteristics were observed for p-Si/n-Ga2O3 heterostructures, which were well reproduced by numerical calculation considering the effect of two-dimensional electron gas formed at the heterointerface. These results indicate that Ga2O3-based p–n heterostructures with good interface properties and large-area uniformity can be fabricated using SAB.

Cost effective lithography based PEDOT: PSS, platinum counter electrodes for dye sensitized solar cells

Counter electrodes (CEs) for dye-sensitized solar cell (DSSC) was prepared by Marker pen lithography coating using poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate (PEDOT:PSS) and platinum (Pt) solution with high transparency and high adhesion on a conducting FTO glass substrate. The surface morphology and surface roughness of the PEDOT:PSS-MPL and Pt-MPL CEs were observed using scanning electron microscopy (SEM), and atomic force microscopic (AFM), for conformation test Electrochemical impedance spectroscopy (EIS), cyclic-voltammetry (CV) was measured .The performance of the device were carried out using currentdensity-voltage (J-V) measurement system. As prepared CEs compared with dip coated PEDOT:PSS-DC and Pt-DC CEs. The test devices fabricated with Pt-MPL and PEDOT:PSS-MPL CEs accomplished a power conversion efficiency (PCE) of 4.25%, 3.00% respectively.

Achievement of high infrared photoresponse in n-MoO3/p-Si heterostructure photodiode prepared via the thermal oxidation method, the influence of oxygen flow rate

For the first time, the molybdenum oxide (MoO3) thin films were deposited on a p-type Si substrate to create a heterojunction infrared (IR) photodiode via the simple thermal oxidation technique, while the oxygen flow rate was varied from 20 to 80 sccm. The XRD diffractograms confirmed the formation of an orthorhombic structure (α-MoO3 phase) in all the synthesized layers, consistent with their Raman spectra. The FESEM images showed that the prepared samples have similar flat flakes on top and nano-spherical particles underneath with a thickness of 220 ± 20 nm. The current density-voltage (J-V) measurements showed that with increasing O2 flow rate, the overall rectification ratio (IF/IR) of the samples is increased, with a maximum of 43.60 for the one fabricated at 60 sccm O2 flow rate. Also compared to other layers, this sample with the highest oxygen vacancies, i.e., MoO2.84, showed this property led this sample to achieve the highest photoresponse ratio (ILight/IDark) of 17 to the 835 nm IR radiation.

Improve the efficiency of organic light-emitting diodes using a novel hole injection layer with triple-layer gradually doped structure

In this study, we reported the fabrication of an organic light-emitting diodes (OLED) using the metal oxide Nb-doped ZnO (NZO) and the common hole transport layer of N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB) to form a novel hole injection layer with gradually-doped triple-layer structure (HITL). The comparison between the stepwise doped double-layer and uniformly doped device showed that the HITL structure could effectively improve the current efficiency of the OLED device. The results of both current density-voltage measurement by hole-only device (HOD) and the UV photoelectron spectroscopy (UPS) confirmed that the highest occupied molecular orbital (HOMO) energy level could help to improve the hole injection performance. In addition, the non-destructive analysis method of capacitance-voltage was used to observe the movement of charge carriers during the operation of the device. The comparison study indicated that by the stepwise doped double-layer injection layer, the influence of the doping gradient on the carrier injection was confirmed, and a smaller doping gradient was found to show the better performance of carrier injection. Based on the results obtained from this study, the maximum luminance and current efficiency of OLED device with HITL was found to be enhanced by approximately 2.48 times and 32.6% respectively when compared with the device without hole injection layer. Various measurements carried out in this study showed that the HITL structure could effectively improve the characteristics of hole carriers, and thereby the better charge balance effect and a more stable current efficiency performance could be achieved by reducing the current efficiency roll-off effect. • In this study, we demonstrated the performances of Alq 3 -based OLED using a novel hole injection layer with triple-layer gradually-doped structure (HITL). • The HITL structure can effectively improve the characteristics of hole carriers, thereby obtaining a better charge balance effect, reducing the efficiency roll-off effect, and obtaining a more stable efficiency performance. • Compared with the double-layer stepwise doped injection layer, the influence of the doping gradient on the carrier transport is confirmed, and a smaller doping gradient has a better performance of carrier injection and transport.

Study of Single Diode Model of DSSC Based on Reduced Graphene Oxide as Counter Electrode

We studied the characteristic of reduced graphene oxide (RGO) as a counter electrode (CE) in Pt-free dye-sensitized solar cell (DSSC) using single diode model equation based on current density-voltage (J-V) measurement. The electrical characteristics of DSSC was investigated by electrochemical impedance spectroscopy (EIS) in order to knowing the catalytic properties of RGO as counter electrode. The RGO thin film as CE was deposited on fluorine-doped tin oxide (FTO) substrate and stacked with FTO/TiO2/ruthenium dye/mosalyte/RGO/FTO DSSC structure. The RGO film was obtained from GO (graphene oxide) film that was thermally reduced at 200°C for one hour under argon flow. The performance of DSSC with RGO as CE was characterized by current-voltage measurement and the interface between each layer was observed by Electrochemical Impedance Spectroscopy (EIS). The device efficiency (η) of DSSC that used GO and RGO film as CE are 0.09% and 3.43%, respectively. DSSC parameters such as series resistance (RS) shunt resistance (RSH), and ideality factor (n) were obtained from J-V curve which analyzed using single diode model equation. All samples have a Rs value of 2 indicates that all devices have a good ohmic contact. The RSH of device using RGO-1mg/ml is increase (from 2850 to 3670 Ω.cm2) compared with GO indicate that thermal reduction is successes. The RGO film shows a comparable performance to Pt-conventional CE thus it is a good candidate as alternative of DSSC counter electrode.

Synergistically designed antireflective cover for improving wide-angle photovoltaic efficiencies.

We demonstrated that a well-designed nanopatterned cover improves photovoltaic efficiency across a wide range of incident angles (θ). A nanopatterned cover was created using an integrated ray-wave optics simulation to maximize the light absorption of the surface-textured Si photovoltaic device. A hexagonally arranged nanocone array with a 300 nm pitch was formed into a polymer using nanoimprinting, and the nanostructured polymer was then attached to a glass cover with an index-matching adhesive. Angle-resolved current density-voltage measurements on Si photovoltaic devices showed that the nanopatterned glass cover yielded a 2-13% enhancement in power conversion efficiency at θ = 0-60°, which accounted for its broadband antireflective feature. We performed all-season-perspective simulations based on the results of the integrated ray-wave optics simulations and solar altitude database of South Korea, which validated the sustainability of the developed nanopatterned cover during significant seasonal fluctuations.

Preparation of TiO2/ZrO2 Composite as Photoanode of Ruthenium-Based Dye-Sensitized Solar Cells

Photoanode of dye-sensitized solar cell (DSSC) is an inorganic semiconductor layer with a nanoporous structure that has a function as a charge carrier transport layer and dye storage. Oxide semiconductor material such as titanium dioxide (TiO2) is widely used as a photoanode because of its wide band gap (3.2 eV) and high active surface area (80 m2/g), but TiO2 has low electron diffusion with high recombination (electron-hole pair pairing). To improve the electron diffusion and reduce recombination, TiO2 was modified with zirconia (ZrO2). The synthesis process was carried out using sol-gel method with variations of ZrO2 concentrations at 5 mol%, 10 mol%, and 15 mol%. Composite of TiO2/ZrO2 was then applied as a photoanode of DSSC. XRF results show that in all variations of ZrO2, the composites of TiO2/ZrO2 has been formed. Based on the results of UV-Vis spectroscopy, it was shown that the energy gap of TiO2/ZrO2 decreased as the increasing of ZrO2 concentration. The current density-voltage measurement was done to investigate the effect of ZrO2 addition to the TiO2 photoanode using light irradiation with power intensity of 100 mW/cm2. There is an increasing of photocurrent from 1.63 mA/cm2 of DSSC with TiO2 photoanode to 2.79 mA/cm2 of DSSC with TiO2/ZrO2 10 mol% photoanode. The highest efficiency obtained from DSSC with TiO2/ZrO2 photoanode is 1.15%. It was found that the presence of ZrO2 in the composite of TiO2/ZrO2 increased electron transport and reduced charge recombination to improve the photocurrent of DSSC.

Measurement of ion transport properties in ion exchange membranes for photoelectrochemical water splitting

Photoelectrochemical (PEC) water-splitting systems have the unique ability to produce renewable hydrogen directly from sunlight, independent of the electrical grid. These systems are therefore appealing technological options for resilient long-term energy storage. Ion selective membranes, such as monopolar and bipolar membranes, are a vital component of PEC water-splitting systems. These membranes allow for ionic conduction between the cathode and anode chambers, separation of products, and improved catalyst environments for reactions. In order to measure key properties and to study the performance of these ion exchange membranes, it is imperative to develop a robust testing protocol that can be used across the field. This paper introduces two standard electrochemical cells designed to directly measure ion transport properties in monopolar and bipolar membranes. The first electrochemical cell uses commercially available Pt disk electrodes to preform electrochemical impedance spectroscopy (EIS) and reliably measure through-plane conductivity of monopolar membranes. The second electrochemical cell uses four-point measurements with Luggin capillaries and a series of membrane configurations to perform current density-voltage and Faradaic efficiency (FE) measurements for water dissociation (WD) reactions on bipolar membranes. The cell designs and techniques laid out below allow for accurate measurement of ion transport parameters in ion exchange membranes, direct comparison of membranes being developed across the field, and in turn, greater advancements in ion exchange membranes and PEC water-splitting systems.

Characterization of NO2 gas sensing for ZnO nanostructure grown hydrothermally on porous silicon

ZnO nanostructures have lately been deemed an effective material for fabricating gas sensors, As a result, ZnO nanoparticles are commonly utilized to make effective gas sensors for detecting a variety of hazardous and poisonous chemicals. The current review article focuses on nitrogen dioxide (NO2) gas sensor advances based on ZnO nanoparticles, X-ray diffraction confirmed the wurtzite structure, Surface roughness, layer homogeneity, and morphological structural analysis are studied using Atomic Force Microscopy (AFM). UV–vis and photoluminescence spectra were used to study the optical characteristics of the as-prepared ZnO nanostructures, The electrical properties such as the current density-voltage (J-V) measurements, Finally, the effects of adjusting operating temperature of NO2 gas sensor made from the prepared samples on sensor's sensitivity, recovery time and response time have been explored.

Magnesium doped TiO2 as an efficient electron transport layer in perovskite solar cells

Perovskite solar cells (PSCs) are rapidly emerging as efficient solar cells due to the efficient photovoltaic and physiochemical properties. Ideally, the absorber layer in PSCs is sandwiched between highly conductive electron transport layer (ETL) and highly stable hole transport layer (HTL). The interfaces between these layers highly affect the performance of PSCs. In this study Magnesium (Mg) doped TiO2 based ETL is systematically investigated to enhance the optical and morphological properties of the layer and the interface. It was observed that with Mg doping in mesoporous TiO2, morphology of TiO2 based ETL film was significantly improved thereby providing an interface for the growth of absorber layer. Optoelectronic studies suggested that band gap was effectively reduced with the addition of Mg and absorption range was also enhanced. Electrical analysis yielded, Mg doped TiO2 based ETL showed enhanced conduction and better sheet carrier mobility as compared to undoped films. Thermal studies indicate fabrication of a thermally stable ETL material for PSCs. Moreover, Current density-Voltage (J-V) measurements indicated more than two-fold increase in photovoltaic efficiency of 3 wt% Mg.

Persistent electrical energy generation from organic diodes under constant pressure: Toward organic gravity nanogenerators

SummaryHere it is demonstrated that electricity can be continuously generated by pressing organic diodes with the poly(3-hexylthiophene) (P3HT) layers which are sandwiched between indium-tin oxide and aluminum (Al) electrodes. The optimized single devices with the 150-nm-thick P3HT layers are able to generate 60 μV and 45 μA by pressing, while persistent voltage (50 μV) and current (45 μA) generations are achieved by continuous pressing for 7 days. The charge generation by pressing of organic diodes is supported by the current density-voltage and capacitance measurements, while the friction of pi-orbital electrons in the P3HT chains upon pressing is proposed for the mechanism of persistent electricity generation. Organic diode modules with 14 sub-cells in series deliver ca. 0.4 V and ca. 20 μW. The present technology is expected to pave the way for next-generation energy conversion devices, organic gravity nanogenerators that enable continuous electricity generation by gravitational forces.

Effect of substrate temperature on the charge transport property of Ta2O5 cathode buffer layer in inverted polymer solar cells

Charge extraction ability in inverted polymer solar cells (IPSCs) can be enhanced using thermally evaporated compact Ta2O5 as cathode buffer layer (CBL) deposited onto indium tin oxide (ITO) substrate by varying the substrate temperature from 200 °C to 250 °C. The deposited polycrystalline films exhibit granular morphology with high optical transmittance around 500 nm and significant variation in defects with respect to ITO substrate temperature. Current density–voltage measurements show improvement in power conversion efficiency from 2.8% to 3.1% with ratio/percentage enhancement of 10.7% when substrate temperature is increased from 200 °C to 250 °C.