Semiconductor Heterojunctions Research Articles

Mixed-Dimensional Semiconductors-Based Ternary Circuits with Tunable Negative Transconductance Characteristics.

Multivalued logic (MVL) systems, in which data are processed with more than two logic values, are considered a viable solution for achieving superior processing efficiency with higher data density and less complicated system complexity without further scaling challenges. Such MVL systems have been conceptually realized by using negative transconductance (NTC) devices whose channels consist of van der Waals (vdW) heterojunctions of low-dimensional semiconductors; however, their circuit operations have not been quite ideal for driving multiple stages in real circuit applications due to reasons such as a reduced output swing and poorly defined logic states. Herein, we demonstrate ternary inverter circuits with near rail-to-rail swing and three distinct logic states by employing vdW p-n heterojunctions of single-walled carbon nanotubes (SWCNT) and MoS2 where the SWCNT layer completely covers the MoS2 layer. In particular, SWCNTs are inkjet printed to form heterojunctions with MoS2 grown by chemical vapor deposition (CVD), and both inkjet printing and CVD are fully scalable device fabrication methods for low-dimensional materials. In addition, the NTC characteristics of heterojunction field-effect transistors (H-FETs) are explained based on the electrical characteristics of individual SWCNT and MoS2 channels. By adjustment of the p-channel characteristics in H-FETs by exploiting the advantages of the inkjet printing technology, the widths of the NTC regions are easily adjusted accordingly. The extended NTC region enables stable middle logic state operations of low-dimensional semiconductors-based ternary inverters over a sufficiently wide input voltage range.

High rectification and gate-tunable photoresponse in 1D-2D lateral van der waals heterojunctions

<p>The self-passivating surfaces and reduced tunneling leakage current enable the creation of ideal Schottky contacts in van der Waals (vdW) semiconductor heterojunctions. However, simultaneously achieving high rectification ratios, low reverse leakage currents, and rapid photoresponse remains challenging. Here, we present a one-dimensional (1D)/two-dimensional (2D) mixed-dimensional heterostructure photodiode to address these challenges. The significant valence band offset and minimal electron affinity difference in this structure ensure high rectification ratios and efficient charge collection. Additionally, the dimensional disparity between the 1D and 2D materials, characterized by a smaller contact area and significant thickness difference, results in low reverse leakage current and a high current on-off ratio. Moreover, it enables gate-tunable band structure transitions. Our device exhibits an exceptional rectifying ratio of 4.7 × 10<sup>7</sup> and a high on-off ratio of 5 × 10<sup>7</sup> (<i>V</i><sub>ds</sub> = 2 V and, <i>V</i><sub>g</sub> = 30 V) at room temperature. Under a gate voltage of 20 V, the photodiode achieves a specific detectivity (<i>D</i><sup><i>*</i></sup>) of 4.9 × 10<sup>14</sup> Jones, a rapid response time of 14 μs, and an extended operational wavelength approaching to <styled-content style-type="number">1550</styled-content> nm. The strategic combination of mixed-dimensional design and band engineering yields a 1D-2D p-n heterojunction photodiode with remarkable sensitivity, repeatability, and fast response, underscoring the potential of vdW semiconductors for advanced optoelectronic applications.</p>

Direct and Indirect Interfacial Electron Transfer at a Plasmonic p-Cu7S4/CdS Heterojunction.

Plasmonic semiconductors exhibit significant potential for harvesting near-IR solar energy, although their mechanisms of plasmon-induced hot electron transfer (HET) are poorly understood. We report a transient absorption study of plasmon-induced HET in p-Cu7S4/CdS type II heterojunctions. Near-IR excitation of the p-Cu7S4 plasmon band at ∼1400 nm leads to ultrafast HET into the CdS conduction band with a time constant of <150 fs and a quantum efficiency of ∼0.054%. The injected hot electrons remain in CdS with an amplitude-weighted average lifetime of 1.9 ± 0.5 ns, significantly longer than that in Au/CdS heterostructures, suggesting that plasmonic semiconductors can slow down charge recombination due to the presence of a bandgap. The excited near-IR plasmon does not decay by coupling to the interfacial charge transfer transition, likely due to its energy mismatch. This study provides a detailed mechanistic understanding and possible directions for improving plasmonic HET in plasmonic semiconductor heterojunctions.

Self‐Rectifying Switching Memory Based on HfOx/FeOx Semiconductor Heterostructure for Neuromorphic Computing

AbstractSneak‐path current is one of the biggest barriers for large‐scale passive memristor array integration. An ideal self‐rectifying resistance random access memory (SR‐RRAM) is a desirable solution but it has not been demonstrated today for optimizing comprehensive indexes for neuromorphic computing. The HfOx/FeOx semiconductor heterojunction SR‐RRAM with a robust self‐rectifying switching behavior featured by an average rectifying ratio (≈104), high resistance ratio (&gt;106), high cycling endurance (&gt;104 cycles), high computing precision (&gt;6 bits) and synaptic plasticity such as paired‐pulse facilitation (PPF) and the spike‐timing‐dependent plasticity (STDP) for artificial intelligence recognition is developed using the unidirectional conductivity feature of p‐n junction. The electron hopping, tunneling, and blocking in this semiconductor heterojunction that is verified by the energy band mode based on UV photoelectron spectroscopy (UPS) technology and low‐energy inverse photoelectron spectroscopy (LEIPS) and in situ high resolution transmission electron microscopy (HR‐TEM) observation plays a dominant role in the self‐rectifying analog switching behaviors. This work provides energy‐band engineering for the large‐scale memristor array integration, representing a significant advancement in hardware for neuromorphic computing.

Heterojunction semiconductor nanocatalysts as cancer theranostics.

Cancer nanotechnology is a promising area of cross-disciplinary research aiming to develop facile, effective, and noninvasive strategies to improve cancer diagnosis and treatment. Catalytic therapy based on exogenous stimulus-responsive semiconductor nanomaterials has shown its potential to address the challenges under the most global medical needs. Semiconductor nanocatalytic therapy is usually triggered by the catalytic action of hot electrons and holes during local redox reactions within the tumor, which represent the response of nontoxic semiconductor nanocatalysts to pertinent internal or external stimuli. However, careful architecture design of semiconductor nanocatalysts has been the major focus since the catalytic efficiency is often limited by facile hot electron/hole recombination. Addressing these challenges is vital for the progress of cancer catalytic therapy. In recent years, diverse strategies have been developed, with heterojunctions emerging as a prominent and extensively explored method. The efficiency of charge separation under exogenous stimulation can be heightened by manipulating the semiconducting performance of materials through heterojunction structures, thereby enhancing catalytic capabilities. This review summarizes the recent applications of exogenous stimulus-responsive semiconducting nanoheterojunctions for cancer theranostics. The first part of the review outlines the construction of different heterojunction types. The next section summarizes recent designs, properties, and catalytic mechanisms of various semiconductor heterojunctions in tumor therapy. The review concludes by discussing the challenges and providing insights into their prospects within this dynamic and continuously evolving field of research.

Surface properties of MOCVD grown (Al1−xGax)2O3 thin films on c-plane sapphire via scanning Kelvin probe microscopy

We report on the surface properties of aluminum-gallium-oxide [(AlxGa1−x)2O3] thin films grown on c-plane sapphire substrates, which form the building block of heterojunction semiconductor devices, by metal–organic chemical vapor deposition (MOCVD). The (AlxGa1−x)2O3 films with aluminum mole fraction (composition) ranging from x = 0 to x = 0.36 were analyzed using x-ray diffraction (XRD) and atomic force microscopy (AFM). The increase in the aluminum composition resulted in the shift in XRD peaks to larger 2θ angles due to the decrease in the lattice constants and broadening due to the degradation in crystallinity. By utilizing the AFM in scanning Kelvin probe microscopy (SKPM) configuration, we report the surface work function of (AlxGa1−x)2O3 decreased from 6.13 to 5.62 eV as aluminum composition increased from 0% to 36%. Direct measurements of epitaxial surface potential in (AlxGa1−x)2O3 thin films show downward band bending ranging from 1.19 to 0.65 eV. The SKPM measurements with trap filling under UV illumination suggest the presence of a relatively high density of donor surface states in (AlxGa1−x)2O3 samples. By modeling the surface states as a spatially localized and energetically discrete level in the bandgap, the density of surface states is found to be ∼2 × 1012 to ∼4 × 1013 cm−2.

Interface structure of PN junctions in NiO–WO3–FTO photoelectrode for efficient DSSCs and enhanced photoresponses

In the current global energy crisis, dye-sensitized solar cells (DSSCs) with excellent performance and loaded with P/N type semiconductor heterojunctions (PN junctions) has attracted huge attention in renewable energy research. This study reports the unique energy level structure and synergistic effect of the PN junction interfaces in response to light. Photoelectrodes containing NiO–WO3 nano-powder (NPs) layers were synthesized on fluorine-doped tin oxide (FTO) substrates by a simple method, which can respond to full-spectrum absorption of sunlight. In this study, the carrier densities in the P-type and N-type semiconductor heterojunctions at a light intensity of 2 SUN (2000 W/m2) were 1.38 × 1028 m−3 and 4.27 × 1028 m−3, respectively. These values are 2.7 and 1.9 times higher than those in dark conditions, indicating that the electrode excels in converting light into electrical energy, outperforming other reported results. Although PN junctions are often used in applications such as DSSCs and energy storage devices, the photoresponses of the heterojunction energy band structure still need to be elucidated. In this work, the analysis of the charge depletion region width revealed the electron transfer mechanism during the charge and discharge process under light illumination. Additionally, the electrochemical experiment demonstrated the impact of space charge at the interface on the energy levels. Furthermore, by studying the energy level structure of the PN junction, it was confirmed that the internal resistance decreases and the photocurrent increases under light conditions. The design and application flexibility of the PN junctions were verified based on these results and the possible applications of this photoelectrode in solar cells were elucidated.

Recent Advances in Metal Oxide Semiconductor Heterojunctions for the Detection of Volatile Organic Compounds

The efficient detection of volatile organic compounds (VOCs) is critically important in the domains of environmental protection, healthcare, and industrial safety. The development of metal oxide semiconductor (MOS) heterojunction gas-sensing materials is considered one of the most effective strategies to enhance sensor performance. This review summarizes and discusses the types of heterojunctions and their working principles, enhancement strategies, preparation methodologies, and applications in acetone and ethanol detection. To address the constraints pertaining to low sensitivity, sluggish response/recovery times, and elevated operating temperatures that are inherent in VOC sensors, several improvement methods are proposed, including doping with metals like Ag and Pd, incorporating additives such as MXene and polyoxometalates, optimizing morphologies through a fine design, and self-doping via oxygen vacancies. Furthermore, this work provides insights into the challenges faced by MOSs heterojunction-based gas sensors and outlines future research directions in this field. This review will contribute to foundational theories to overcome existing bottlenecks in MOS heterojunction technology while promoting its large-scale application in disease screening or agricultural food quality assessments.

(Invited) Extending the Success of Halide Perovskites to Photoelectrochemical and Photocatalytic Solar Fuel Production

To address the pressing global energy demands with clean and sustainable methods, solar-powered photoelectrochemical and photocatalytic transformations of water and carbon dioxide present viable solutions. Achieving this requires the development of cost-effective photoelectrodes and photocatalysts capable of efficiently harnessing solar light and promoting charge transfer to drive water and carbon dioxide reactions. In this presentation, I will outline the advances my team has made in the field, focusing on novel halide perovskites like CsPbBr3, Cs2AgBiBr3, and Cs3Bi2Br9 and bulk heterojunctions of organic semiconductors. These materials exhibit high solar light absorption and outstanding optoelectronic properties, making them excellent candidates for photoelectrochemical and photocatalytic uses. We have developed innovative approaches to enhance their stability in aqueous environments, such as encapsulating halide perovskites and organic bulk heterojunctions within carbon layers modified with Ni nanopyramids and NiFeOOH, a water-oxidation catalyst. This approach exploits different carbon allotropes, from mesoporous carbon to graphite, glassy carbon and boron-doped diamond, in order of chemical and mechanical stability. The use of layers and sheets of these carbon allotropes has led to the creation of photoanodes with low onset potentials and high photocurrents, efficiently translating excellent photocurrents and photovoltages from solar cells to photoelectrodes. For example, organic bulk heterojunction devices result in 25 mA/cm2 photocurrents in three-electrode systems and unassisted 5% solar to hydrogen in two-electrode systems Our approaches significantly extend the lifespan of photoanodes, maintaining for example a projected operation of months with CsPbBr3. In the field of photocatalysts, we have employed mechanochemical synthesis and antisolvent crystallization to create innovative composites like CsPbBr3/Cu-RGO, Cs2AgBiBr3/Cu-RGO, Cs2AgBiBr3/bismuthene, and Cs3Bi2Br9/RGO/g-C3N4, demonstrating efficient activity in converting CO2 into CO and CH4. Through thorough material characterization, we have shed light on their structural and charge-transfer properties, laying a solid foundation for their ongoing development and practical application.Daboczi, M.; Eisner, F.; Luke, J.; Yuan, S.W.; Al Lawati, N.; Müller, J.S.; Kim, J.S. Nelson, J.; Eslava, S. under reviewZhu, Daboczi, Chen, Xuan, Liu and Eslava, Nat. Commun. 2024, 2791.Daboczi, M.; Cui, J.; Temerov, F.; Eslava, S. Adv. Mater. 2023, 2304350Baghdadi, Y.; Temerov, F.; Cui, J. Daboczi, M.; Rattner, E.; Sena, M.S.; Eslava, S. Chem. Mater. 2023, 35, 20, 8607Sena, M.S.; Cui, J.; Baghdadi, Y.; Rattner, E.; Daboczi, M.; Lopes-Moriyama, A.L.; dos Santos, A.G.; Eslava, S. ACS Appl. Energy Mater. 2023, 6, 10193.Kumar, S.; Hassan, I.; Regue, M.; Gonzalez-Carrero, S.; Rattner, E.; Isaacs, M.A.; Eslava, S. J. Mater. Chem. A 2021, 9, 12179

A novel g-C3N4/TiO2 heterojunction for ultrasensitive detection of bisphenol A residues

Semiconductor heterojunction with functional integration can be used as an excellent matrix for the ultrasensitive detection of bisphenol A (BPA) with low molecular affinity. Here, a simple, low-cost and sensitive surface-enhanced Raman scattering (SERS) strategy using g-C3N4/TiO2 heterojunction as substrate was presented for detection of BPA residues in foods. The g-C3N4/TiO2 achieved specific chemisorption for target analyte by the formation of intermolecular H-bond between g-C3N4 and BPA. And, a high-efficiency carrier separation in TiO2 induced by heterostructure could be achieved for charge transfer between the substrate and molecule by a “donor-bridge-acceptor” charge-transfer mode. Due to the synergistic/collaborative contributions of two monomers in heterojunction, the SERS enhancement factor was as high as 3.77 × 107. The detection limit of BPA residues in foods (milk, juice and drinking water) was as low as 10−9 mol·L−1, far below the EU standard. The developed substrate also exhibited excellent stability and anti-interference capability.

P-doped g-C3N4/BiOCl Z-type heterojunction with N and O double vacancies and synergistically enhanced photocatalytic activity under sunlight irradiation

The use of inexhaustible natural sunlight is a highly effective method for wastewater treatment. In this study, P-doped g-C3N4/BiOCl Z-type heterojunction semiconductor photocatalyst with N and O double vacancies was constructed through calcination and coprecipitation. The obtained results revealed that the degradation rate of Rhodamine B (Rh B) reached 0.05642 min −1 within 60 min under visible light irradiation with a 300 W xenon lamp (λ≥400 nm), which was 73 and 8 times that of pure CN and BiOCl, respectively. Under natural sunlight irradiation, Rh B was almost completely degraded within 6 min, and its degradation rate reached 0.95641 min−1, which was 17 times that of Rh B simulated by visible light in the laboratory. The doping of non-metallic P and construction of a heterojunction significantly improved the photocatalytic activity of P-doped g-C3N4/BiOCl, which could be attributed to the synergistic effect of N, O vacancies and heterojunction structure interfaces on the composite material surface, which apparently expanded the light absorption range, promoted the transfer of charge, increased the quantity of active sites for the light-induced reaction, and improved the redox ability of the catalyst. The heterojunction semiconductor with surface defects prepared in this study provides a green approach for future wastewater treatment applications.

High-Performance Self-Powered Dual-Mode Ultraviolet Photodetector Based on (PEA)2PbI4/GaN Heterojunction.

Wide-bandgap semiconductors like GaN, known for their superior photoresponse and detection capabilities in the ultraviolet range, represent a foundational component in the design of advanced photodetectors, where the integration of materials with distinct spectral sensitivities into heterojunctions is pivotal for next-generation device innovation. A high-performance self-powered dual-mode ultraviolet photodetector based on a (PEA)2PbI4/GaN heterojunction was fabricated via spin coating. The device exhibits outstanding UV sensitivity under both positive and negative bias, achieving a responsivity of 1.39 A/W and a detectivity of 8.71 × 1010 Jones under 365 nm UV illumination. The built-in electric field at the heterojunction interface enables self-powered operation, achieving a rapid rise time of 46.9 ms and a decay time of 55.9 ms. These findings offer valuable insights into the development and application of perovskite and wide-bandgap semiconductor heterojunctions in optoelectronic devices.

Piezoelectric effect promotes photoelectrochemical properties of 2D-3D ZnIn2S4/β-CdS strongly coupled interface

In the process of photoelectrochemical (PEC) hydrodecomposition, it is important to design photoelectrode materials with low cost, high charge separation efficiency and low charge recombination rate. Herein, 2D-3D strongly coupled ZnIn2S4/β-CdS nanocomposites were prepared by a two-step hydrothermal method. Meanwhile, the piezoelectric polarization was used to induce its generation of built-in electric field, which suppressed the secondary compounding of photogenerated charge carriers caused by the interfacial structural defects of the semiconductor heterojunction. The results show that ZnIn2S4/β-CdS has better photoelectrochemical decomposition ability of water under ultrasound, and its photocurrent density increases with the increase of ultrasound frequency, reaching a maximum value of 0.46 mA·cm−2 at 1.23 VRHE, which is 3.5 times higher than that before ultrasound. In addition, by comparing the significant increase of photocurrent conversion efficiency under the applied bias voltage before and after ultrasound, it can be concluded that the enhanced catalytic activity of ZnIn2S4/β-CdS is attributed to the efficient coupling effect between ZnIn2S4 and β-CdS under ultrasound conditions. This coupling effect enables the fast electron transfer at the interface between ZnIn2S4 and β-CdS. Consequently, this strongly coupled nanocomposite will provide inspiration for further construction of nanocomposites for photocatalytic decomposition of water.

Three-Dimensional Semiconductor Network as Regulators of Energy Metabolism Drives Angiogenesis in Bone Regeneration.

Insufficient vascularization is a primary cause of bone implantation failure. The management of energy metabolism is crucial for the achievement of vascularized osseointegration. In light of the bone semiconductor property and the electric property of semiconductor heterojunctions, a three-dimensional semiconductor heterojunction network (3D-NTBH) implant has been devised with the objective of regulating cellular energy metabolism, thereby driving angiogenesis for bone regeneration. The three-dimensional heterojunction interfaces facilitate electron transfer and establish internal electric fields at the nanoscale interfaces. The 3D-NTBH was found to noticeably accelerate glycolysis in endothelial cells, thereby rapidly providing energy to support cellular metabolic activities and ultimately driving angiogenesis within the bone tissue. Molecular dynamic simulations have demonstrated that the 3D-NTBH facilitates the exposure of fibronectin's Arg-Gly-Asp peptide binding site, thereby regulating the glycolysis of endothelial cells. Further evidence suggests that 3D-NTBH promotes early vascular network reconstruction and bone regeneration in vivo. The findings of this research offer a promising research perspective for the design of vascularizing implants.

Geometrical stability, electrical contact and optical properties for ZrX2(X = Cl, Br, I) /Zr2Cl2 semiconductor-metal heterojunctions

Exploring metal–semiconductor electrical contact behaviors is highly desirable for developing high-performance new devices. Here, transition metal halide ZrX2 (X = Cl, Br, I)/Zr2Cl2 vdW heterojunctions are constructed by semiconducting ZrX2 and metallic Zr2Cl2 monolayers. Our calculations reveal that such metal–semiconductor heterojunctions possess very high energetic, thermal, dynamic and mechanical stability, with p-type Schottky contacts in the intrinsic state, and their Schottky barrier height (SBH) decreases with the atom number of haloid elements increased. Particularly, ZrI2/Zr2Cl2 heterojunction exhibits a very low p-type SBH, 0.18 eV, favorably to design high-performance Schottky devices. Their electronic and electrical contact properties can also be modulated by physical field coupling effects. For example, p-type SBH decreases continuously to obtain quasi-Ohmic contact under applied compressive strain, and the p-type Schottky contact can be transformed to p-type Ohmic contacts under suitable positive external electric field for all heterojunctions. Particularly, ZrI2/Zr2Cl2 heterojunction achieves Ohmic contact by a relatively low positive electric field, 0.15 V/Å. It is also shown that all heterojunctions possess high intrinsic light absorption capability. The light absorption performance of ZrBr2/Zr2Cl2 heterojunction would undergo a significant enhancement under electric field. Therefore, these suggested heterojunctions hold promising application potentials for developing electronic and optoelectronic devices.

Charge Separated ZnNb2O6/SnO2 Type‐II Heterojunction Photocatalyst for Enhanced Degradation of Emerging Contaminants

AbstractZnNb2O6 and a heterojunction ZnNb2O6/SnO2 have been synthesized, characterized, and studied for its photocatalytic activity against organic and pharmaceutical pollutants under UV irradiation. The characterization techniques include X‐ray Diffraction (XRD), ultraviolet‐visible reflectance spectroscopy (UV–vis DRS), field emission scanning electron microscopy (FESEM), photoluminescence spectra (PL), and X‐ray photoelectron spectroscopy (XPS). XRD confirms single phase formation. The particles sizes of ZnNb2O6 and ZnNb2O6/SnO2 heterojunction are in range of 170–200 nm and 110–140 nm, respectively. Bandgaps as revealed by UV–vis DRS spectra are in the range 3.14–3.71 eV. The n‐n type semiconductor heterojunction ZnNb2O6/SnO2 shows enhanced photocatalytic activity than the individual components for degradation of pollutants due to more effective charge carrier separation. The rate of degradation by the heterojunction is twice that of the individual components. Methyl orange degradation pathways have been proposed using HRMS analysis. This is the first report of pharmaceutical antibiotic pollutants degradation by ZnNb2O6.

Enhancing Photo electrocatalytic Water Splitting Efficiency Using Bi2O2CO3@Ni(OH)2 Composite with Flower-Like Morphology

The rational design of semiconductor heterojunctions is pivotal in enhancing photoelectrochemical (PEC) water-splitting performance. In this study, we synthesized Bi2O2CO3 (BOC) nanosheets, Ni(OH)2 (NH) nanosheets, and their composite Bi2O2CO3@Ni(OH)2 (BOC-NH) separately using a hydrothermal process. The BOC-NH composite displays a distinct 3D flower-like structure with cross-linked petals of 21.82 nm, substantially enhancing the surface area and facilitating effective heterojunction formation between BOC and NH. This synergistic effect enhances charge separation and transport, leading to superior PEC water oxidation performance. The BOC-NH photoanode achieved a remarkable photocurrent density of 5.87 mA/cm2, 4.48 times higher than pure BOC and 1.75 times that of NH, along with a reduced onset potential of 0.464 V. Transient photocurrent measurements demonstrated excellent stability, while electrochemical impedance spectroscopy (EIS) revealed a significantly lower solution resistance (11.06 Ω), and charge transfer resistance (5.27 Ω) compared to the individual BOC and NH photoanodes. The applied bias photon-to-current efficiency (ABPE) of BOC, NH, and BOC-NH was 0.21%, 0.36%, and 0.58%, respectively, with the composite showing the highest efficiency under light illumination. Long-term stability tests over 7200 seconds showed sustained photoactivity, with the photocurrent density rising from 0.26 to 0.53 mA/cm2, highlighting the durability of the composite. This work presents a robust strategy for improving PEC water splitting through heterojunction engineering and morphological optimization.

Coupling of tribovoltaic effect and tribo-electrostatic effect at dynamic semiconductor heterojunction interfaces

Tribovoltaic effect at the dynamic semiconductor interface is of great fundamental and practical importance for developing a variety of functional devices; yet, it can be coupled with a series of different physical effects, such as the contact-electrification induced electrostatic effect and mechanical wearing effect, and the coupling mechanisms are still remained to be elucidated. Herein, we investigated the coupling between tribovoltaic and tribo-electrostatic effects at the dynamic heterojunctions of two wide-bandgap semiconductors: zinc oxide (ZnO) and gallium nitride (GaN). It is found that, in the contact-separation mode, the direct-current outputs from tribovoltaic effect can be clearly distinguished from the alternating-current outputs from tribo-electrostatic effect. Then, humidity, external load resistance and pressure force are found to reveal the coupling characteristics of these two effects, that tribovoltaic outputs are less affected by humidity, show smaller matched impedance and are more sensitive to high pressure force, diverging from the tribo-electrostatic outputs. Lastly, we demonstrate that the mechanical wearing effect can be inhibited in contact-separation mode, achieving long-term stability over 50,000 cycles. Therefore, this work provides insights to the mechanism of tribovoltaic effects and practical guidance for high-performances tribovoltaic devices.

Preparation and Photocatalytic Performance of In2O3/Bi2WO6 Type II Heterojunction Composite Materials.

Bismuth-based photocatalytic materials have been widely used in the field of photocatalysis in recent years due to their unique layered structure. However, single bismuth-based photocatalytic materials are greatly limited in their photocatalytic performance due to their poor response to visible light and easy recombination of photogenerated charges. At present, constructing semiconductor heterojunctions is an effective modification method that improves quantum efficiency by promoting the separation of photogenerated electrons and holes. In this study, the successful preparation of an In2O3/Bi2WO6 (In2O3/BWO) II-type semiconductor heterojunction composite material was achieved. XRD characterization was performed to conduct a phase analysis of the samples, SEM and TEM characterization for a morphology analysis of the samples, and DRS and XPS testing for optical property and elemental valence state analyses of the samples. In the II-type semiconductor junction system, photogenerated electrons (e-) on the In2O3 conduction band (CB) migrate to the BWO CB, while holes (h+) on the BWO valence band (VB) transfer to the In2O3 VB, promoting the separation of photoinduced charges, raising the quantum efficiency. When the molar ratio of In2O3/BWO is 2:6, the photocatalytic degradation degree of rhodamine B (RhB) is 59.4% (44.0% for BWO) after 60 min illumination, showing the best photocatalytic activity. After four cycles, the degradation degree of the sample was 54.3%, which is 91.4% of that of the first photocatalytic degradation experiment, indicating that the sample has good reusability. The XRD results of 2:6 In2O3/BWO before and after the cyclic experiments show that the positions and intensities of its diffraction peaks did not change significantly, indicating excellent structural stability. The active species experiment results imply that h+ is the primary species. Additionally, this study proposes a mechanism for the separation, migration, and photocatalysis of photoinduced charges in II-type semiconductor junctions.

Synthesis of ZnPc/BiVO4 Z-Scheme Heterojunction for Enhanced Photocatalytic Degradation of Tetracycline Under Visible Light Irradiation

The construction of semiconductor heterojunctions is an effective strategy to improve the photocatalytic degradation efficiency of organic pollutants. Herein, ZnPc/BiVO4 Z-scheme heterojunction was synthesized via a physical mixing method and was used for the photocatalytic degradation of tetracycline (TC) under visible light irradiation. Compared with BiVO4 and ZnPc, the 15ZnPc/BiVO4 sample exhibited improved light absorption capacity, and the electron-hole separation efficiency and redox capacity were enhanced due to the formation of the Z-scheme heterojunction. The 15ZnPc/BiVO4 composite exhibited an optimal TC degradation rate of 83.1% within 120 min. Additionally, 15ZnPc/BiVO4 exhibited excellent stability in cycling experiments, which maintained a high TC degradation rate of 79.5% after four cycles. Free radical trapping experiments indicated that superoxide radicals (O2−) were the main active substances in the photocatalytic degradation of TC.