Hole Depletion Research Articles

Interpretation of the degradation and trends in the performance of heterojunction silicon solar cells at low temperature

A compact model that combines numerical simulations using AFORS-HET and accurate equivalent circuit modelling is proposed and used to interpret the origins of the degradation and anomality's in the performance of the a-Si:H/c-Si heterojunction solar cells and its parameters at low temperature. The interpretations are applied to several trends reported on real cells. It is shown that as T decreases the a-Si:H(i) layer is depleted gradually from holes and that the cell operation fails once the layer is totally depleted and becoming intrinsic. The failure is caused by a substantial and sharp increase in the cell series resistance causing the collapse of the fill factor and of the cell current. It is found that at low temperature the open circuit voltage is significantly affected and its temperature dependence strongly distorted by hole depletion in the a-Si:H(i) spacer especially when the TCO work function is not appropriate. It is aslo shown that the S-shape in the cell I-V characteristics under illumination is closely linked to the TCO barrier reverse saturation current which explains its higher probability of appearnce at low temperature. Finally, it is concluded that the HJT cell would perform optimally down to the low 200 K range when the a-Si:H(p) is heavily doped and the front contact is ideally ohmic. Failing to satisfy such conditions the temperature range in which the HJT cell is useful is very limited.

1T/2H MoSe2 modified ZnIn2S4 with modulating internal electric field to boost efficient performance of photocatalytic H2 evolution and epoxide alcoholysis

Herein, the extended layer spacing 1T MoSe2 coupled with ZnIn2S4 nanosheets through in-situ growth, and ultimately obtained 1T /2H MoSe2/ZnIn2S4 photocatalysts with S-scheme heterojunction. This rational structure enables photogenerated carriers to rapidly transfer to MoSe2 via Mo-S bond. In order to further address the problem of wasted oxidative half-reaction, we rely on the dehydrogenation of benzyl alcohol as a carrier for hole depletion. Notably, optimized 1T/2H MoSe2/ZnIn2S4 has superior H2 evolution ability, reaching up to 11.271 mmol·g−1·h−1 and the apparent quantum efficiency at 420 nm is 10.3 %. Meanwhile, the conversion rate of benzyl alcohol to high value-added benzaldehyde is 60.60 %. In addition, the Zn acidic sites can achieve polarization of epoxides and precise cleavage C-O bond. Thus, it also has the ability to high selectivity and efficient photocatalytic epoxide alcoholysis. This work proposes a new insight for enhancing photocatalytic properties via regulating IEF to fabricate S-scheme heterostructure.

Direct imaging of the magnetoelectric coupling in multiferroic BaTiO3/La0.9Ba0.1MnO3

We report the direct imaging of the magnetic response of a 4.8 nm La0.9Ba0.1MnO3 film to the voltage applied across a 5 nm BaTiO3 film in a BaTiO3/La0.9Ba0.1MnO3 multiferroic heterostructure using x-ray photoemission electron microscopy (XPEEM). Specifically, we have written square ferroelectric domains on the BaTiO3 layer with an atomic force microscope in contact mode and imaged the corresponding magnetic contrast through the x-ray circular dichroic effect at the Mn L-edge with high spatial lateral resolution using XPEEM. We find a sudden decrease in the magnetic contrast for positive writing voltages above +6 V associated with the switching of the ferroelectric polarization of the BaTiO3, consistent with the presence of a magnetoelectric effect through changes in the hole carrier density at the BaTiO3/La0.9Ba0.1MnO3 interface. Temperature-dependent measurements show a decrease in the Curie temperature and magnetic moment in the areas where a positive voltage above +6 V was applied, corresponding to the hole depletion state and suggesting the onset of a spin-canted state of bulk La0.9Ba0.1MnO3. Our results are the first direct imaging of magnetoelectric coupling in such multiferroic heterostructure.

Plasmon-induced hot carrier distribution in a composite nanosystem: role of the adsorption site.

The generation of hot carriers (HCs) through the excitation of localized surface plasmon resonance (LSPR) in metal nanostructures is a fascinating phenomenon that fuels both fundamental and applied research. However, gaining insights into HCs at a microscopic level has posed a complex challenge, limiting our ability to create efficient nanoantennas that utilize these energized carriers. In this investigation, we employ real-time time-dependent density functional theory (rt-TDDFT) calculations to examine the creation and distribution of HCs within a model composite system consisting of a silver (Ag) nanodisk and a carbon monoxide (CO) molecule. We find that the creation and distribution of HCs are notably affected by the CO adsorption site. Particularly, when the CO molecule adsorbs onto the hollow site of the Ag nanodisk, it exhibits the highest potential among various composite systems in terms of structural stability, enhanced orbital hybridization, and HC generation and transfer. Utilizing a Gaussian laser pulse adjusted to match the LSPR frequency, we observe a marked buildup of hot electrons and hot holes on the C and O atoms. Conversely, the region encompassing the C-O bond exhibits a depletion of hot electrons and hot holes. We believe that these findings could have significant implications in the field of HC photocatalysis.

Deciphering migraine pain mechanisms through electrophysiological insights of trigeminal ganglion neurons

Migraine is a complex neurological disorder that affects millions of people worldwide. Despite extensive research, the underlying mechanisms that drive migraine pain and related abnormal sensation symptoms, such as hyperalgesia, allodynia, hyperesthesia, and paresthesia, remain poorly understood. One of the proposed mechanisms is cortical spreading depression (CSD), which is believed to be involved in the regulation of trigeminovascular pathways by sensitizing the pain pathway. Another mechanism is serotonin depletion, which is implicated in many neurological disorders and has been shown to exacerbate CSD-evoked pain at the cortical level. However, the effects of CSD and serotonin depletion on trigeminal ganglion neurons, which play a critical role in pain signal transmission, have not been thoroughly studied. In this study, we aimed to investigate the association between CSD and serotonin depletion with peripheral sensitization processes in nociceptive small-to-medium (SM) and large (L) -sized trigeminal ganglion neurons at the electrophysiological level using rat models. We divided the rats into four groups: the control group, the CSD group, the serotonin depletion group, and the CSD/serotonin depletion group. We induced CSD by placing KCl on a burr hole and serotonin depletion by intraperitoneal injection of PCPA (para-chlorophenoxyacetic acid). We then isolated trigeminal ganglion neurons from all groups and classified them according to size. Using patch-clamp recording, we recorded the excitability parameters and action potential (AP) properties of the collected neurons. Our results showed that in SM-sized trigeminal ganglion neurons, the CSD-SM and CSD/serotonin depletion groups had a higher positive resting membrane potential (RMP) than the control-SM group (p = 0.001 and p = 0.002, respectively, post-hoc Tukey’s test). In addition, the gap between RMP and threshold in the CSD-SM group was significantly narrower than in the control-SM group (p = 0.043, post-hoc Tukey’s test). For L-sized neurons, we observed prolongation of the AP rising time, AP falling time, and AP duration in neurons affected by CSD (p < 0.05, pairwise comparison test). In conclusion, our study provides new insights into the underlying mechanisms of migraine pain and abnormal somatosensation. CSD and serotonin depletion promote the transmission of pain signals through the peripheral sensitization process of nociceptive small-to-medium-sized trigeminal ganglion neurons, as well as nociceptive and non-nociceptive large-sized trigeminal ganglion neurons.

Self‐Assembled Junctions of 2D Single‐Layer Semiconductors: A Potential Way toward Advanced Photocatalysis

Self‐Assembled Junctions of <scp>2D</scp> Single‐Layer Semiconductors: A Potential Way toward Advanced Photocatalysis

Single-Atom Iridium on Hematite Photoanodes for Solar Water Splitting: Catalyst or Spectator?

Single-atom catalysts (SACs) on hematite photoanodes are efficient cocatalysts to boost photoelectrochemical performance. They feature high atom utilization, remarkable activity, and distinct active sites. However, the specific role of SACs on hematite photoanodes is not fully understood yet: Do SACs behave as a catalytic site or as a spectator? By combining spectroscopic experiments and computer simulations, we demonstrate that single-atom iridium (sIr) catalysts on hematite (α-Fe2O3/sIr) photoanodes act as a true catalyst by trapping holes from hematite and providing active sites for the water oxidation reaction. In situ transient absorption spectroscopy showed a reduced number of holes and shortened hole lifetime in the presence of sIr. This was particularly evident on the second timescale, indicative of fast hole transfer and depletion toward water oxidation. Intensity-modulated photocurrent spectroscopy evidenced a faster hole transfer at the α-Fe2O3/sIr/electrolyte interface compared to that at bare α-Fe2O3. Density functional theory calculations revealed the mechanism for water oxidation using sIr as a catalytic center to be the preferred pathway as it displayed a lower onset potential than the Fe sites. X-ray photoelectron spectroscopy demonstrated that sIr introduced a mid-gap of 4d state, key to the fast hole transfer and hole depletion. These combined results provide new insights into the processes controlling solar water oxidation and the role of SACs in enhancing the catalytic performance of semiconductors in photo-assisted reactions.

Enhanced ethanol sensing abilities of fiber-like La1−xCexCoO3(0 ≤x ≤ 0.2) perovskites based-sensors at low operating temperatures

Herein, a nanofiber network of La1−xCexCoO3 (x = 0, 0.05, 0.1 and 0.2) was prepared using the electrospinning-calcination method. X-ray diffraction patterns revealed the appearance of CeO2 with increasing Ce-substitution. The gas sensing measurements established that the combination of the nanofiber morphology and catalytic effect of Ce imparts greater ethanol sensing performance, particularly for the highest Ce-substitution level of La0.8Ce0.2CoO3 with enhanced response of 83.4, coupled with great selectivity, along with swift response and recovery time of 17 and 32 s at a low operating temperature of 100 °C. The particle-interconnected nanofiber morphology as observed from scanning electron microscopy presented exceptional large hole depletion layers (HAL) which allowed for HAL overlapping with each other thus promoting greater resistance changes. Furthermore, the Ce-substitution caused a deviation from the stoichiometry and increased the surface oxygen defects that created more active surface area which promoted a more advanced gas and surface interaction. This work demonstrates the potential ethanol sensing capabilities of La1−xCexCoO3 induced by Ce-partial substitution on the La-site.

Extraction of Dynamic Threshold Voltage in Resistive Load Hard Switching Operation of Schottky-Type p-GaN Gate HEMT

Threshold voltage (VTh) drift of Schottky-type p-GaN gate high-electron mobility transistor (HEMT) was analyzed under high-voltage and hard switching conditions with a resistive load (R-Load). To overcome the distortion in the drain current (ID) – gate voltage (VG) curve caused by the internal drain capacitance (IDisp) charging current during the switching transients, a method is presented to accurately measure dynamic VTh through appropriate correction of IDisp. The dynamic variation of VTh was tracked with a gate-drive rise/fall times of 200 ns. During the switching operation, VTh increases rapidly at the beginning and then saturates at a stable value. This is attributed to the gate forward current during turn-on that increases the hole depletion of the p-GaN gate through the AlGaN barrier. The dynamic VTh increases linearly at a rate of 40% with the increase of gate turn-on voltage. VTh is independent of duty cycle but minorly increases with frequency at high voltages, suggesting that channel hot electrons be injected into the AlGaN barrier and p-GaN.

Plasmon-induced hole-depletion layer on p-n heterojunction for highly efficient photoelectrochemical water splitting

The photoelectrocatalytic (PEC) water splitting efficiency of semiconductor photoelectrodes is mainly limited by the effective separation and transfer of photogenerated charges. Zinc indium sulfide-cuprous oxide (ZnIn2S4-Cu2O) p-n heterojunction is constructed to enhance the PEC properties of ZnIn2S4. The nickel hydroxide iron oxide (NiFeOOH) layer on the surface of the heterojunction can be used as a hole depletion layer under the induction of plasmon resonance of the most surface silver (Ag) (the holes transferred from Cu2O valence band to NiFeOOH layer can be excited by Ag to produce hot electron consumption, which makes the last remaining hot holes participate in the water oxidation reaction) to further promote the carrier separation and transfer. The results exhibit that ZnIn2S4/Cu2O/NiFeOOH/Ag photoelectrode with dramatically enhanced photocurrent density of 1.22 mA/cm2 at 1.23 V versus the reversible hydrogen electrode (VRHE), which is 9.4 times higher than the pure ZnIn2S4. This work provides a promising concept to design photoelectrodes efficiently in PEC water splitting.

A Comparative Study of CoNi-LDH/ZnO Film for Photocathodic Protection Applications in the Marine Environment

In this study, two kinds of Co–Ni-layer double hydroxide (LDH)/ZnO films were prepared with different morphologies by a simple electrochemical method. The properties of the films were investigated by SEM, XRD, UV–Vis DRS, XPS, and electrochemical techniques. It was found that Co–Ni-LDH-modified ZnO films exhibited excellent photocathodic properties in a scavenger-free environment. This is mainly due to the absorption of visible light by LDH, the formation ofp–nheterojunction, and the depletion of photo-generated holes by the cycling process of Co (II)/Co (III). Compared with CoNi-LDH/ZnO nanorods, CoNi-LDH/ZnO nanoclusters showed better photocathodic protection performance and physical barrier effect. Under illumination conditions, the rough surface of ZnO nanoclusters and the deposition of a large amount of LDH can provide more photoelectrochemical active sites, thus improving the light absorption capacity and photocathodic protection performance of CoNi-LDH/ZnO nanoclusters. Under dark conditions, the physical barrier effect of CoNi-LDH/ZnO nanoclusters was also enhanced by the dense ZnO nanoclusters and thick CoNi-LDH layers.

Enhanced Carrier Injection in AlGaN-Based Deep Ultraviolet Light-Emitting Diodes by Polarization Engineering at the LQB/p-EBL Interface

The external quantum efficiency (EQE) of AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) is still far from satisfactory due to the main issues of electron leakage and insufficient hole injection. The positive sheet charges generated by polarization at the interface between the last quantum barrier (LQB) and the p-type electron blocking layer (p-EBL) can induce electron accumulation and hole depletion in the vicinity of this interface, leading to electron leakage and hindering the hole injection. In this paper, we propose an Al-composition-increasing AlGaN layer (ACI-AlGaN) inserted between the LQB and p-EBL to enhance the carrier injection ability of DUV LEDs via modulating the sheet charges generated by polarization at the LQB/EBL interface and the underlying mechanism was analyzed by numerical calculation. The inserted structure can eliminate the positive sheet charges at the p-side interface of LQB and induce hole accumulation in the vicinity of the n-side interface of p-EBL, which can subsequently reduce electron leakage and favor hole injection respectively. The proposed DUV LED structure with an ACI-AlGaN layer exhibited enhanced EQE by 45.7% and its forward voltage maintained undegraded. This design scheme can provide an alternative way to promote the performance of DUV LEDs with a variety of applications.

In‐Plane Field‐Driven Excitonic Electro‐Optic Modulation in Monolayer Semiconductor

Abstract2D semiconductors are attractive candidates for on‐chip electro‐optic modulators due to their ease of integration and rich exciton‐mediated phenomena. While electrostatic doping and out‐of‐plane field effect have been extensively studied, in‐plane field‐induced phenomena remain largely unexplored. Here electro‐optic response of monolayer WSe2 subject to modulating in‐plane electric fields probed by electroabsorption and electroreflectance spectroscopy is reported. The devices are found to exhibit spatially varying response near exciton resonance, which cannot be explained by predicted effects such as Pockels and excitonic Stark effect. It is shown that the modulation signal is dominated by exciton linewidth broadening and narrowing associated with local accumulation and depletion of free holes. The field and frequency dependence of the devices is distinct from those of charge modulation devices. The observed behavior is ascribed to elastic scattering of excitons with field‐driven intrinsic free carriers.

Construction of S-scheme CdS/g-C3N4 nanocomposite with improved visible-light photocatalytic degradation of methylene blue

Within moderate band gap, g-C3N4 and CdS are both promising visible light driven photocatalysts. However, their intrinsic high recombination rate of photo-induced electron-hole pairs along with the poor susceptibility in photocorrosion of CdS is main limitations hindering their practical application. In this study, the CdS/g-C3N4 composites with various weight ratios of CdS to g-C3N4 were solvothermal prepared from the dispersion of components, g-C3N4 and CdS, in ethanol. The physicochemical characterizations demonstrate the success in the fabrication of well-dispersed CdS nanoparticles in the g-C3N4 matrix. The enhanced photocatalytic activity of the g-C3N4/CdS composite over the degradation of methylene blue under visible light was ascribed to the effective photo-induced electron-hole separation via the step scheme (S-scheme) pathway in which the main contribution of high oxidative hydroxyl radicals (•OH) was demonstrated. Furthermore, via S-scheme model, we also clarify the depletion of photo-induced holes on CdS which is ascribed as the reason for improvement in resistance to photocorrosion of composites.

Direct evidence for metallic mercury causing photo-induced darkening of red cinnabar tempera paints

Photo-induced darkening of red cinnabar (HgS) has attracted the interest of many researchers as it drastically impacts the visual perception of artworks. Darkening has commonly been related to metallic mercury (Hg0) formation in the presence of chlorides. Based on the study of UV-aged cinnabar pigment and tempera paint we propose an alternative pathway for the blackening reaction of cinnabar, considering its semiconductor properties and pigment-binder interactions. We demonstrate that darkening is caused by the oxidation of cinnabar to mercury sulfates and subsequent reduction to Hg0 via photo-induced electron transfer without the involvement of chlorides, and provide direct evidence for the presence of Hg0 on UV-aged tempera paint. Photooxidation also affects the organic binder, causing a competing depletion of photo-generated holes and consequently limiting but not impeding mercury sulfate formation and subsequent reduction to Hg0. In addition, organics provide active sites for Hg0 sorption, which is ultimately responsible for the darkening of cinnabar-based paint.

Electric field-induced grain boundary degradation mechanism in yttria stabilized zirconia

The degradation mechanism of flash sintering 8 mol% yttria stabilized zirconia, which results in poor densification and crumbling of the samples under direct current, was investigated. Microstructure analysis revealed highly strained grain boundaries and nanopore formation at the grain boundaries after flash sintering with a direct current. A higher current density experiment gave a varied microstructure with internal grain dimpling near the negative electrode, a highly porous “swiss-cheese” like microstructure in the pellet interior, and melting and recrystallization near the positive electrode. These characteristics were not observed under an alternating current. Phase field simulations predicted an oxygen vacancy buildup and potential reduced phases along the grain boundaries, which lead to the depletion of free holes and dramatic increase of free electrons. This results in high tensile stresses at the grain boundaries, which explains the degradation along the grain boundaries after flash sintering under direct current.

Reducing the polarization mismatch between the last quantum barrier and p-EBL to enhance the carrier injection for AlGaN-based DUV LEDs

In this work, we report an AlGaN-based ∼275 nm deep ultraviolet light-emitting diode (DUV LED) that has AlGaN based quantum barriers with a properly large Al composition. It is known that the increased conduction band barrier height helps to enhance the electron concentration in the active region. However, we find that the promoted hole injection efficiency is also enabled for the proposed DUV LED when the Al composition increases. This is attributed to the reduced positive polarization charge density at the last quantum barrier (LQB) and p-type electron blocking layer (p-EBL) interface, which can suppress the hole depletion effect in the p-EBL. Thus, the hole concentration in the p-EBL gets promoted, which is very helpful to reduce the hole blocking effect caused by the p-EBL. Therefore, thanks to the improved carrier injection, the proposed DUV LED increases the optical power and reduces the forward voltage when compared with the conventional DUV LED.

Electric Field-Induced Grain Boundary Degradation Mechanism in Yttria Stabilized Zirconia

The degradation mechanism of flash sintering 8 mol% yttria stabilized zirconia, which results in poor densification and crumbling of the samples under direct current, was investigated. Microstructure analysis revealed highly strained grain boundaries and nanopore formation at the grain boundaries after flash sintering with a direct current. A higher current density experiment gave a varied microstructure with dimpling similar to metallic microvoid coalescence near the negative electrode, a highly porous “swiss-cheese” like microstructure in the pellet interior, and melting and recrystallization near the positive electrode. These characteristics were not observed under an alternating current. Phase field simulations predicted an oxygen vacancy buildup and potential reduced phases along the grain boundaries, which lead to the depletion of free holes and dramatic increase of free electrons. This results in high tensile stresses at the grain boundaries, which explains the degradation along the grain boundaries after flash sintering under direct current.

A Robust Netrosophic Clustering Based Raven Routing Optimization to Alleviate Void Hole and Energy Depletion in IoT WSN

Wireless Sensor Networks (WSNs) find extensive utilisation in diverse domains, including but not limited to environmental monitoring, industrial control, and healthcare. Wireless Sensor Networks (WSNs) have a crucial function in gathering and relaying information from sensor nodes to a central node or sink in various applications. Wireless Sensor Networks (WSNs) encounter various obstacles that can have a significant impact on their performance and lifespan. These challenges include but are not limited to limited battery life, void holes, and energy depletion.&#x0D; Several routing algorithms have been suggested in scholarly works to tackle these concerns, such as clustering-based routing, data-centric routing, and location-based routing. Nonetheless, a majority of these algorithms possess constraints and may not be appropriate for every situation.&#x0D; The present study introduces a methodology called Rncrro (Robust Netrosophic Clustering Based Raven Routing Optimisation) that aims to mitigate the issues of void holes and energy depletion in Wireless Sensor Networks (WSNs). The proposed approach utilises Netrosophic Clustering and Raven Optimisation algorithms in tandem to enhance the efficacy and resilience of the routing mechanism.&#x0D; The significance of this study is rooted in its capacity to surmount the constraints of current routing algorithms and furnish a superior and dependable resolution for Wireless Sensor Networks (WSNs). The proposed methodology has the potential to enhance the performance and longevity of Wireless Sensor Networks (WSNs) by mitigating void holes and energy depletion. This, in turn, can result in more efficient and dependable data collection and transmission across diverse applications.

Highly Efficient InGaN Nanorods Photoelectrode by Constructing Z-scheme Charge Transfer System for Unbiased Water Splitting.

Unbiased photoelectrochemical water splitting for the promising InGaN nanorods photoelectrode is highly desirable, but it is practically hindered by the serious recombination of charge carrier in bulk and surface of InGaN nanorods. Herein, an unbiased Z-scheme InGaN nanorods/Cu2 O nanoparticles heterostructured system with boosted interfacial charge transfer is constructed for the first time. The introduced Cu2 O nanoparticles pose double-sided effect on photoelectrochemical (PEC) performance of InGaN nanorods, which enables a robust hybrid structure and induces weakened light absorption capability simultaneously. As a result, the optimized InGaN/Cu2 O-1.5C photoelectrode with the uniform morphology exhibits an enhanced photocurrent density of ≈170 µA cm-2 at 0 V versus Pt, with 8.5-fold enhancement compared with pure InGaN nanorods. Comprehensive investigations into experimental results and theoretical calculations reveal that the electrons accumulation and holes depletion of Cu2 O facilitate to form a typical Z-scheme band alignment, thus providing a large photovoltage to drive unbiased water splitting and enhancing the stability of Cu2 O. This work provides a novel and facile strategy to achieve InGaN nanorods and other catalyst-based PEC water splitting without external bias, and to relieve the bottlenecks of charge transfer dynamics at the electrode bulk and electrode/electrolyte interface by constructing Z-scheme heterostructure.