Electron-hole Research Articles

Fabrication of Polydopamine/hemin/TiO2 Composites with Enhanced Visible Light Absorption for Efficient Photocatalytic Degradation of Methylene Blue

With the rapid progression of industrialization, water pollution has emerged as an increasingly critical issue, especially due to the release of organic dyes such as methylene blue (MB), which poses serious threats to both the environment and human health. Developing efficient photocatalysts to effectively degrade these pollutants is therefore of paramount importance. In this work, titanium dioxide (TiO2) was modified with the photosensitizer hemin and the hydroxyl-rich polymer polydopamine (PDA) to enhance its photocatalytic degradation performance. Hemin and PDA function as photosensitizers, extending the light absorption of TiO2 into the visible spectrum, reducing its bandgap energy, and effectively promoting separation of photogenerated electron–hole pairs through conjugated structures. Additionally, the strong adhesion of PDA enabled the rapid transfer and effective utilization of photogenerated electrons, while its abundant phenolic hydroxyls increased MB adsorption on the photocatalyst’s surface. Experimental results demonstrated a significant enhancement in photocatalytic activity, with the 1%PDA/3%hemin/TiO2 composite achieving degradation rates of 91.79% under UV light and 71.53% under visible light within 120 min, representing 2.22- and 2.05-fold increases compared to unmodified TiO2, respectively. This research presents an effective modification approach and provides important guidance for designing high-performance TiO2-based photocatalysts aimed at environmental remediation.

Bi4Ti3O12-V/Ag Composite with Oxygen Vacancies and Schottky Barrier with Photothermal Effect for Boosting Nizatidine Degradation

Piezo-photocatalysis is a promising solution to address both water pollution and the energy crisis. However, the recombination of electron–hole pairs often leads to poor performance, rendering current piezoelectric photocatalysts unsuitable for industrial water treatment. To overcome this issue, oxygen vacancies (V) and Ag nanoparticles (NPs) are introduced into Bi4Ti3O12 (BTO) nanosheets, forming Schottky junctions (BTO-V/Ag). These 2D/3D structures offer more exposed active sites, shorter carrier separation distances, and improved piezo-photocatalytic performance. Additionally, the photothermal effect of Ag NPs supplies additional energy to counteract adsorption changes caused by active species, promoting the generation of more active species. The rate constant of the optimized BTO-V/Ag-2 in the piezo-photocatalytic degradation of nizatidine (NZTD) was 4.62 × 10−2 min−1 (with a removal rate of 98.34%), which was 4.32 times that of the initial BTO. Moreover, the composite catalyst also showed good temperature and pH response. This study offers new insights into the regulatory mechanisms of piezo-photocatalysis at the Schottky junction.

Ultrasonic Activation of Au Nanoclusters/TiO2: Tuning Hydroxyl Radical Production Through Frequency and Nanocluster Size

This study explores the sonocatalytic activity of gold nanoclusters (Au NCs) combined with titanium dioxide (TiO2) nanoparticles, forming Au NCs/TiO2 composites. The hybrid material significantly enhances hydroxyl radical (•OH) generation under ultrasonic conditions, attributed to high-energy cavitation bubbles formed during ultrasonication. The effects of frequency (200, 430, and 950 kHz) and power were systematically evaluated on Au144/TiO2 composites, identifying 430 kHz as optimal for •OH production due to its efficient cavitation energy. Au144 NCs function as electron traps, reducing electron–hole recombination in ultrasonically activated TiO2, thereby improving charge separation and enhancing •OH generation. Size-dependent effects were also studied, showing an efficiency trend of Au144 > Au25 > plasmonic Au nanoparticles > bare TiO2. These findings highlight the importance of ultrasonication frequency and Au NC size in optimizing sonocatalytic performance in the Au NCs/TiO2 composites, providing valuable insights for designing advanced sonocatalysts with applications in chemical synthesis, environmental remediation, and biomedical fields.

Core–Shell Composite GaP Nanoparticles with Efficient Electroluminescent Properties

Gallium-based light-emitting diodes (LEDs), including AlGaInP and GaN, have become the most widely used light-emitting devices in modern scientific research and practical applications. However, structures like carrier injection layers, active layers, and quantum well layers ensure the high luminescence efficiency of LEDs but also limit their applications at the micro- and nanoscale. Although the next generation of micrometer-scale light-emitting diodes (Micro-LEDs) has alleviated these issues to some extent, challenges such as edge effects and etching damage caused by size reduction lead to lower luminous efficiency and shorter lifetimes. Inspired by LED structure, this study designed and synthesized core–shell composite GaP:Zn/GaP/GaInP and GaP:Te/GaP nanoparticles using a thermal injection method. After high-temperature annealing, these composite materials demonstrated efficient electroluminescent performance under electric field excitation through band-edge transitions and the ZnGa-OP recombination mechanism. Experimental results show that the GaP:Zn/GaP/GaInP-GaP:Te/GaP composite samples with doping concentrations of 15%Zn-8%Te, a core–shell precursor ratio of 1:1:1, and reaction times of 1 h:20 min:20 min exhibit the best electron–hole injection efficiency and bound-recombination efficiency. Under excitation by an external electric field, they demonstrated optimal electroluminescence performance, with a relative luminous intensity of 11,109.21 at 600 nm, approximately 15 times higher than that of the initial condition samples. In addition, this study systematically investigated the structure, morphology, and elemental composition of the composite materials using various characterization techniques, including X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and X-ray photoelectron spectroscopy (XPS). These GaP-doped nanoparticles with a core–shell composite structure, inspired by LED design, exhibited outstanding electroluminescent performance, providing new insights into the development of novel micro- and nanoscale electroluminescent materials.

Engineering Nonvolatile Polarization in 2D α-In2Se3/α-Ga2Se3 Ferroelectric Junctions

The advent of two-dimensional (2D) ferroelectrics offers a new paradigm for device miniaturization and multifunctionality. Recently, 2D α-In2Se3 and related III–VI compound ferroelectrics manifest room-temperature ferroelectricity and exhibit reversible spontaneous polarization even at the monolayer limit. Here, we employ first-principles calculations to investigate group-III selenide van der Waals (vdW) heterojunctions built up by 2D α-In2Se3 and α-Ga2Se3 ferroelectric (FE) semiconductors, including structural stability, electrostatic potential, interfacial charge transfer, and electronic band structures. When the FE polarization directions of α-In2Se3 and α-Ga2Se3 are parallel, both the α-In2Se3/α-Ga2Se3 P↑↑ (UU) and α-In2Se3/α-Ga2Se3 P↓↓ (NN) configurations possess strong built-in electric fields and hence induce electron–hole separation, resulting in carrier depletion at the α-In2Se3/α-Ga2Se3 heterointerfaces. Conversely, when they are antiparallel, the α-In2Se3/α-Ga2Se3 P↓↑ (NU) and α-In2Se3/α-Ga2Se3 P↑↓ (UN) configurations demonstrate the switchable electron and hole accumulation at the 2D ferroelectric interfaces, respectively. The nonvolatile characteristic of ferroelectric polarization presents an innovative approach to achieving tunable n-type and p-type conductive channels for ferroelectric field-effect transistors (FeFETs). In addition, in-plane biaxial strain modulation has successfully modulated the band alignments of the α-In2Se3/α-Ga2Se3 ferroelectric heterostructures, inducing a type III–II–III transition in UU and NN, and a type I–II–I transition in UN and NU, respectively. Our findings highlight the great potential of 2D group-III selenides and ferroelectric vdW heterostructures to harness nonvolatile spontaneous polarization for next-generation electronics, nonvolatile optoelectronic memories, sensors, and neuromorphic computing.

Field–particle energy transfer during chorus emissions in space

Chorus waves are some of the strongest electromagnetic emissions naturally occurring in space and can cause radiation that is hazardous to humans and satellites1, 2–3. Although chorus waves have attracted extreme interest and been intensively studied for decades4, 5, 6–7, their generation and evolution remain highly debated7. Here, in contrast to the conventional expectation that chorus waves are governed by planetary magnetic dipolar fields5,7, we report observations of repetitive, rising-tone chorus waves in the terrestrial neutral sheet, where the effects of the magnetic dipole are absent. Using high-cadence data from NASA’s MMS mission, we present ultrafast measurements of the wave fields and three-dimensional electron distributions within the waves, which provides evidence for chorus–electron interactions and the development of electron holes in the wave phase space. We found that the waves are associated with resonant currents antiparallel to the wave magnetic field, as predicted by nonlinear wave theory. We estimated the nonlinear field–particle energy transfer inside the waves, finding that the waves extract energy from local thermal electrons, in line with the positive growth rate of the waves derived from an instability analysis. Our observations may help to resolve long-standing controversies regarding chorus emissions and in gaining an understanding of the energy transport observed in space and astrophysical environments.

Electric Control of Quasiparticle Band Gap and Electron–Hole Excitation in the Bilayer of Janus Structure MoSeS

Electric Control of Quasiparticle Band Gap and Electron–Hole Excitation in the Bilayer of Janus Structure MoSeS

Reactions of Hydrogen-Passivated Silicon Vacancies in α-Quartz with Electron Holes and Hydrogen.

We used density functional theory with a hybrid functional to investigate the structure and properties of [4H]Si (hydrogarnet) defects in α-quartz as well as the reactions of these defects with electron holes and extra hydrogen atoms and ions. The results demonstrate the depassivation mechanisms of hydrogen-passivated silicon vacancies in α-quartz, providing a detailed understanding of their stability, electronic properties, and behaviour in different charge states. While fully hydrogen passivated silicon vacancies are electrically inert, the partial removal of hydrogen atoms activates these defects as hole traps, altering the defect states and influencing the electronic properties of the material. Our calculations of the hydrogen migration mechanisms predict the low energy barriers for H+, H0, and H-, with the lowest barrier of 0.28 eV for neutral hydrogen migration between parallel c-channels and a similar barrier for H+ migration along the c-channels. The reactions of electron holes and hydrogen species with [4H]Si defects lead to the breaking of O-H bonds and the formation of non-bridging oxygen hole centres (NBOHCs) within the Si vacancies. The calculated optical absorption energies of these centres are close to those attributed to individual NBOHCs in glass samples. These findings can be useful for understanding the role of [4H]Si defects in bulk and nanocrystalline quartz as well as in SiO2-based electronic devices.

Combining Cocatalyst and Oxygen Vacancy to Synergistically Improve Fe2O3 Photoelectrochemical Water Oxidation Performance

Considering the poor conductivity of Fe2O3 and the weak oxygen evolution reaction associated with it, surface hole accumulation leads to electron hole pair recombination, which inhibits the photoelectrochemical (PEC) performance of the Fe2O3 photoanode. Therefore, the key to improving the PEC water oxidation performance of the Fe2O3 photoanode is to take measures to improve the conductivity of Fe2O3 and accelerate the reaction kinetics of surface oxidation. In this work, the PEC performances of Fe2O3 photoanodes are synergistically improved by combining loaded an FeOOH cocatalyst and oxygen vacancy doping. Firstly, amorphous FeOOH layers are successfully prepared on Fe2O3 nanostructures through simple photoassisted electrodepositon. Then oxygen vacancies are introduced into FeOOH-Fe2O3 through plasma vacuum treatment, which reduces the content of Fe-O (OL) and Fe-OH (-OH), jointly promoting the generation of oxygen vacancies. Oxygen vacancy can increase the concentration of most carriers in Fe2O3 and form photo-induced charge traps, promoting the separation of electron holes and enhancing the conductivity of Fe2O3. The other parts of -OH act as oxygen evolution catalysts to reduce the reaction obstacle of water oxidation and promote the transfer of holes to the electrode/electrolyte interface. The performance of FeOOH-Fe2O3 after plasma vacuum treatment has been greatly improved, and the photocurrent density is about 1.9 times higher than that of the Fe2O3 photoanode. The improvement in the water oxidation performance of PEC is considered to be the synergistic effect of the cocatalyst and oxygen vacancy. All outstanding PEC response characteristics show that the modification of the cocatalyst and oxygen vacancy doping represent a favorable strategy for synergistically improving Fe2O3 photoanode performance.

A comprehensive SCAPS-1D simulation study on the photovoltaic properties and efficiency enhancement of CH3NH3PbCl3 perovskite solar cells

Abstract Recent progress in lead (Pb) halide perovskites has inspired much research into economical solar cells, focusing on critical issues of stability and toxicity. This study investigates the performance of perovskite solar cells (PSCs) by simulating the impact of a methylammonium lead chloride (CH3NH3PbCl3) layer as the absorber material using the SCAPS-1D simulator. The first comprehensive study of this material examines the role and configuration of the Electron Transport Layer (ETL) and Hole Transport Layer (HTL), as well as the absorber layer, on solar cell performance. The ETLs used in the device optimization are ZnO, SnO2, IGZO, and CdS; the HTL is CuO; and the front and back contacts are Au and Ni, respectively. The study highlights CuO as the optimal HTL for CH3NH3PbCl3, delivering power conversion efficiencies (PCEs) of 16.10%, 16.06%, 16.05%, and 14.41% with ZnO, SnO2, IGZO, and CdS as ETLs, respectively. The performance of these device architectures is significantly influenced by factors such as defect density, absorber layer thickness, ETL thickness, and the combination of different ETLs and CuO HTLs. Furthermore, this study elucidates the impact of absorber and HTL thickness on key photovoltaic parameters, such as VOC, JSC, FF, and PCE. Also, we have discussed the VBO, and CBO for different ETLs. Additionally, we examine the effects of series and shunt resistance, operating temperature, quantum efficiency (QE), capacitance-voltage characteristics, generation and recombination rates, and current density-voltage (J-V), analysis of absorption data, and impedance analysis behavior on achieving the highest efficiency of the device. This comprehensive study provides critical insights into designing cost-effective, high-performance PSCs, and advancing the development of next-generation photovoltaic technologies.

Healing Trap States of Anomalous Antisite Defects via Surface Passivation in Lead Iodide Perovskites: A First-Principles Study.

Undesirable loss of open-circuit voltage and current of metal halide perovskite (MHP) solar cells are closely associated with defects, so theoretical calculations have been often performed to scrutinize the nature of defects in bulk of MHPs. Yet, exploring the properties of defects at surfaces of MHPs is severely lacking given the complexity of the surface defects with high concentrations. In this study, IPb (PbI) antisite defects, namely one Pb (I) site being occupied by one I (Pb) atom at the surfaces of the FAPbI3 (FA = CH(NH2)2) material, are found to create electron (hole) traps when the surfaces with IPb (PbI) antisite defects are negatively (positively) charged. These are in sharp contrast to the conventional viewpoint that electron (hole) traps are induced by positively (negatively) charged defects. The reasons are discovered through Bader charge analysis, suggesting that there is deficient (excessive) electron charge in the vicinity of the IPb (PbI) defects with respect to the case in pristine surface of FAPbI3 material. Such understanding is then used as guidelines for effectively healing the anomalous IPb (PbI) antisite defects according to Lewis acid-base chemistry, which is exampled by passivating theophylline (C60) molecules on defective surfaces of the FAPbI3 material.

Dual MOF and CuInS2-Constructed Dual Z-Scheme Heterojunctions for Enhanced Photocatalytic Hydrogen Production and Methylene Blue Degradation

A novel dual Z-scheme heterojunction photocatalyst was constructed by introducing the narrow-bandgap semiconductor CuInS2 (CIS) into the dual metal-organic framework (MOF) system of UiO-66(Zr) and NH2-MIL-101(Fe). This structure effectively overcomes the limitations of conventional photocatalysts in terms of light absorption range and the separation efficiency of photogenerated charge carriers. The prepared ternary catalyst, (UiO-66(Zr))-(NH2-MIL-101(Fe))/CuInS2, exhibited excellent photocatalytic performance under visible light irradiation, achieving a hydrogen production rate of 888 μmol g−1 h−1 and a methylene blue (MB) degradation efficiency of up to 95.03%. The significant enhancement in performance is attributed to the material’s porous structure, extended light absorption range, and optimized electron transfer pathways. Additionally, the construction of the dual Z-scheme heterojunction further promotes the separation and migration of photogenerated charge carriers, suppressing electron–hole recombination. This study demonstrates the great potential of dual Z-scheme heterojunctions in improving photocatalytic efficiency and provides an important theoretical foundation and design strategy for the development of efficient photocatalysts.

G-C3N4 Modified with Metal Sulfides for Visible-Light-Driven Photocatalytic Degradation of Organic Pollutants.

Graphitic carbon nitride (g-C3N4) proved to be a promising semiconductor for the photocatalytic degradation of various organic pollutants. However, its efficacy is limited by a fast electron hole recombination, a restricted quantity of active sites, and a modest absorption in the visible range. To overcome these limitations, g-C3N4-Bi2S3 and g-C3N4-ZnS composites were effectively produced utilizing a starch-assisted technique. The findings from FT-IR, XRD, EDX, XPS, BET, SEM, and TEM demonstrated that the enhanced photocatalytic activity of g-C3N4-Bi2S3 and g-C3N4-ZnS composites was primarily due to their improved photocarrier separation and transfer rates. The photocatalyst facilitated the aerobic photocatalytic degradation of colorless contaminants such as coumarin and para-nitrophenol (4-NP). For the decomposition of 4-NP, g-C3N4-Bi2S3 exhibited a maximum efficiency of 90.86% in UV light and 16.78% in visible light, with rate constants of 0.29 h-1 and 0.016 h-1, respectively. In contrast, g-C3N4-ZnS demonstrated a maximum efficiency of 100% in UV light and 15.1% in visible light, with rate constants of 0.57 h-1 and 0.018 h-1, respectively. The bioinspired synthesis combined with the modification with metal sulfides proved to considerably enhance the photocatalytic activity of g-C3N4, increasing its potential for practical applicability in environmentally friendly water treatment systems for the efficient removal of recalcitrant organic contaminants.

Coating MOF Layer on Fe3O4 Nanoparticles Towards Enhancing Photocatalysis Activation of Peroxydisulfate via Layer Thickness Control

ABSTRACTAs the photocatalytic layer, metal organic frameworks (MOFs) with thickness control were coated on the surface of Fe3O4 nanoparticles to investigate the influence of photocatalysis on the activation of peroxydisulfate to degrade antibiotic pollutants. A suitable thickness of MOF layer can not only enhance the adsorption of the substrate molecules on the composite catalyst but also provide optimized electron transfer distance and path, which is conducive to improving the efficiency of electron–hole separation, thereby enhancing the activation of peroxydisulfate and the degradation efficiency of pollutants.

A Versatile Ionic Liquid Additive for Perovskite Solar Cells: Surface Modification, Hole Transport Layer Doping, and Green Solvent Processing.

Hole-transport layers (HTL) in perovskite solar cells (PSCs) with an n-i-p structure are commonly doped by bis(trifluoromethane)sulfonimide (TFSI) salts to enhance hole conduction. While lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) dopant is a widely used and effective dopant, it has significant limitations, including the need for additional solvents and additives, environmental sensitivity, unintended oxidation, and dopant migration, which can lead to lower stability of PSCs. A novel ionic liquid, 1-(2-methoxyethyl)-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide (MMPyTFSI), is explored as an alternative dopant for 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenylamino)-9,9'-spirobifluorene (spiro-OMeTAD). MMPy ions act as a surface passivator, reducing defects on the perovskite surface, while TFSI ions facilitate p-type doping. MMPyTFSI functions as an efficient dopant, maintaining excellent performance even when tetrahydrofuran (THF) is utilized as a solvent in place of chlorobenzene (CB), while significantly reducing the environmental impact of the process. The optimized PSC achieves a power conversion efficiency (PCE) of 23.10% and demonstrates enhanced long-term stability in all aging tests for over 1000 h in a humid atmosphere, at high temperature, and under simulated sunlight illumination. These results demonstrate that MMPyTFSI is an effective and environmentally friendly dopant for producing stable and efficient PSCs.

Nanostructured Fe2O3/Cu x O heterojunction for enhanced solar redox flow battery performance.

Solar redox flow batteries (SRFB) have received much attention as an alternative integrated technology for simultaneous conversion and storage of solar energy. Yet, the photocatalytic efficiency of semiconductor-based single photoelectrodes, such as hematite, remains low due to the trade-off between fast electron hole recombination and insufficient light utilization, as well as inferior reaction kinetics at the solid/liquid interface. Herein, we present an α-Fe2O3/Cu x O p-n junction, coupled with a readily scalable nanostructure, that increases the electrochemically active sites and improves charge separation. Thanks to light-assisted scanning electrochemical microscopy (photo-SECM), we elucidate the morphology-dependent carrier transfer process involved in the photo-oxidation reaction at an α-Fe2O3 photoanode. The optimized nanostructure is then exploited in the α-Fe2O3/Cu x O p-n junction, achieving an outstanding unbiased photocurrent density of 0.46 mA cm-2, solar-to-chemical (STC) efficiency over 0.35% and a stable photocharge-discharge cycling. The average solar-to-output energy efficiency (SOEE) for this unassisted α-Fe2O3-based SRFB system reaches 0.18%, comparable to previously reported DSSC-assisted hematite SRFBs. The use of earth-abundant materials and the compatibility with scalable nanostructuring and heterojunction preparation techniques offer promising opportunities for cost-effective device deployment in real-world applications.

Fabrication of a high-efficiency hydrogen generation Pd/C3N5-K,I photocatalyst through synergistic effects of planar and spatial carrier separation

Non-metallic I heteroatoms and metal Pd nanoparticles construct the charge transfer pathways within and across the CN layers, enhancing electron–hole separation.

Rational design of a carbon nitride photocatalyst with in-plane electron delocalization for photocatalytic hydrogen evolution

Introducing B doping into the π-conjugated system of CN not only induces electron delocalization but enhances the separation and transfer of photoinduced electron–hole pairs. This leads to a 8.6-fold improvement in the photocatalytic H2 evolution.

Interfacial polarization charge engineering with co-designed LQB and EBL for enhanced EQE of AlGaN DUV LEDs

Abstract In this paper, we propose to modulate the polarization charges at the interface between the last quantum barrier (LQB) and the electron blocking layer (EBL) via strategically adjusting the Al composition in the LQB and EBL simultaneously. With appropriate design of the linear gradient profile in Al composition, the original positive polarization charges at the LQB/EBL interface can be diminished or converted into negative charges, which helps to reduce the positive electric field in EBL, thus adjusting the energy band near the LQB/EBL interface. Enhanced effective barrier height for electrons, decreased effective barrier height for holes, and accumulation of a large number of holes at the LQB/EBL interface are obtained, resulting in improved electron leakage and hole injection. In comparison with the reference deep ultraviolet light-emitting diode (DUV LED), an enhanced external quantum efficiency by 37.5% at an injection current density of 100 A cm−2 is achieved for the device with negative polarization charges. The modulation strategy of polarization charges at the LQB/EBL interface via co-designing the linear gradient of Al composition in LQB and EBL can be a feasible approach for obtaining high-performance DUV LEDs.

Exploring Intrinsic and Extrinsic p-Type Dopability of Atomically Thin β-TeO2 from First Principles.

Two-dimensional (2D) β-TeO2 has gained attention as a promising material for optoelectronic and power device applications, thanks to its transparency and high hole mobility. However, the mechanisms driving its p-type conductivity and dopability remain elusive. In this study, we investigate the intrinsic and extrinsic point defects in monolayer and bilayer β-TeO2, the latter of which has been experimentally synthesized, using the Heyd-Scuseria-Ernzerhof (HSE) + D3 hybrid functional. Our results reveal that most intrinsic defects are unlikely to contribute to p-type doping in 2D β-TeO2. Moreover, Si and H contamination could further impair p-type conductivity. Since the point defects do not contribute to p-type conductivity, we suggest two possible mechanisms for hole conduction: hopping conduction via localized impurity states, and substrate effects. We also explored substitutional p-type doping in 2D β-TeO2 with 10 trivalent elements. Among these, the Bi dopant is found to exhibit a relatively shallow acceptor transition level. However, all the dopants introduce deep localized states, where hole polarons are trapped by the lone pairs of Te atoms. Interestingly, monolayer β-TeO2 shows potential advantages over bilayers due to reduced self-compensation effects for p-type dopants. These findings provide valuable insights into defect engineering strategies for future electronic applications involving 2D β-TeO2.