Electron-hole Pairs Research Articles

A flower-like g-C3N4/CDs/Bi2WO6 hierarchical structure for enhanced photocatalytic degradation of tetracycline

Tetracycline (TC), as one of antibiotic emerging pollutants, has posed potential threats to ecological environment and human health because it is hardly biodegradable and prone to be accumulated in water. In this study, g-C3N4/CDs/Bi2WO6 S-scheme heterojunction with flower-like hierarchical structure was synthesized by hydrothermal method. The optimized composite demonstrates significantly enhanced photocatalytic activity with a TC degradation efficiency of 90.1% after 120 min of visible light irradiation and good reusability up to four consecutive cycles. This can be attributed to the improved light capture capability and efficient separation of photo-generated electron-hole pairs in the constructed S-scheme heterojunction. The introduced carbon dots (CDs) can be served as an efficient carrier transport highway, providing a superior photogenerated carrier separation efficiency and an expanded absorption spectrum. As a result, the strongest redox potentials of the CBCN and VBBWO can be retained for participating the photocatalytic reaction. Free radical capture and electron spin resonance experiments indicate that ·O2- and h+ are the principal active species in the g-C3N4/CDs/Bi2WO6 system. This work provides new strategy for the development of advanced materials in the field of photocatalytic treatment of wastewater.

Excitonic properties and solar harvesting performance of Cs2ZnY2X2 as quasi-2D mixed-halide perovskites

Due to their low toxicity and high-temperature stability, lead-free quasi-2D metal halide perovskites (MHPs) are promising materials for optoelectronic applications. However, understanding their structural and optoelectronic properties, especially excitonic effects (electron-hole pair, e-h), is challenging due to their quantum well topology. We propose an efficient protocol for band gap correction of Cs2ZnX (X = Cl4, Br2Cl2, and I2Cl2) and Cs2PbI2Cl2 (used as a benchmark) quasi-2D MHPs. This protocol is based on a relativistic quasiparticle approach (DFT-1/2) using density functional theory (DFT). We first examined the hybrid contributions of the halide alloys, leading to excitonic characterization using the Bethe–Salpeter equation within the maximally localized Wannier functions tight-binding method. This method provides a cost-effective approach for describing e-h quasiparticle effects. Additionally, we analyzed the crystal structure, thermodynamic stability, and optoelectronic properties of the newly synthesized Zn-based systems, focusing on their structural stability mechanisms. We found a correlation between the allocation of Cs+ cations in the crystal structure and the formation of two distinct stabilization patterns, influenced by the radii of the metal (Zn or Pb) and halide components. The relativistic correction of the band gap energies yielded results within 10 % of the experimental values. Furthermore, incorporating e-h quasiparticle effects for Cs2PbI2Cl2 resulted in an exciton binding energy of 0.160 eV, in excellent agreement with experimental data. This work represents a significant advance in the optoelectronic characterization of Cs2ZnX systems, previously unexplored for their excitonic properties.

Nanostructured hexagonal S-doped CeO2 for effective Rh-B and MB dye degradation

The photocatalytic efficiency of CeO2−xSx (x = 0.05, 0.1, 0.2, 0.3, 0.5) hexagonal nanoparticles (HNPs) prepared through the hydrothermal method were tested by performing the degradation of Rhodamine-B and Methylene blue dyes under UV light irradiation. These compounds were thoroughly characterised using XRD, FESEM, EDX, HRTEM, XPS, ESR, FTIR, Raman, UV–vis DRS, BET and PL techniques. XRD analysis verified the cubic crystal structure of S-doped and pure CeO2 HNPs. HRTEM images clearly affirmed that S-doped CeO2 is made from HNPs. Over 94 % of Rh-B and 72 % of MB dyes were degraded by S-doped CeO2 for 180 min under UV light exposure, demonstrating its efficacy towards the photocatalytic activity (PCA). S-doped CeO2 HNPs have enhanced the PCA due to the reduction in the recombination rate of photo-generated electron-hole pairs, the rise in oxygen vacancy (Ov) and the narrowed optical band-gap. The photoluminescence findings clearly validated the increased PCA of S-doped CeO2. The scavenger tests confirmed the OH• and •O2− radicals participation in the quick degradation of both Rh-B and MB dyes.

Synthesis of MoS2@MoO3/(Cu+/g-C3N4) ternary composites with double S-scheme heterojunction for peroxymonosulfate activation exposing to visible light

The construction of semiconductor heterojunction is an effective way for charge separation in photocatalytic degradation of pollutants. In this study, a novel MoS2@MoO3/(Cu+/g-C3N4) ternary composites (MMCCN) was prepared via a simple calcination method. The as-prepared composites exhibited exceptional performance in activating peroxymonosulfate (PMS) for the degradation of rhodamine B (RhB). The activity testing results indicated that 99.41 % of RhB (10 mg·L−1, 10 mL) was effectively removed by the synergistic effect of composites photocatalyst (0.1 g·L−1) and PMS (0.1 g·L−1) under visible light irradiation for 40 min. Its reaction rate constant exceeded that of Cu+/g-C3N4, MoO3 and MoS2 by a factor of 3.56, 17.30 and 11.73 times, respectively. The crystal structure, band gap and density of states (DOS) of the semiconductors were calculated according to the density functional theory (DFT). Free radical trapping tests and electron spin resonance spectroscopy validated that 1O2, O2− and h+ are primary reactive species participating in the decomposition of RhB. The ternary composites demonstrated good stability and maintained excellent degradation efficiency even across four reaction cycles. Furthermore, the activation mechanism and the intermediates produced during the decomposition course of RhB by MMCCN/PMS/vis system were analyzed and elucidated. A double S-scheme heterojunctions was responsible for efficient separation of photo-induced electron-hole pairs. This work presents a novel method in the construction of double S-scheme heterojunctions for PMS activation which is expected to find wide applications in wastewater treatment and environmental remediation.

An endogenous oxygen self-supplied nanoplatform with GSH-depleted and NIR-II triggered electron-hole separation for enhanced photocatalytic anti-tumor therapy.

The use of artificial enzymes and light energy in photocatalytic therapy, a developing drug-free therapeutic approach, can treat malignant tumors in vivo. However, the relatively deficient oxygen concentration in the tumor microenvironment (TME) restrains their further tumor treatment capability. Herein, a novel nanoplatform with Cu7S4@Au nanocatalyst coated by MnO2 was successfully designed. After 1064 nm light irradiation, the designed nanocatalyst can promote the separation of light generated electron-hole pairs, resulting in ROS generation and tumor cell apoptosis. The MnO2 shelled nanoplatform can function as a TME-responsive oxygen self-supplied producer to improve photocatalyst treatment and GSH depletion. In summary, the designed novel nanoplatform shows efficient inhibition of tumor growth via GSH depletion and synergistic photocatalytic therapy, which is of great significance for improving the clinical tumor treatment effect.

Effects of MOF-MoO3-x derivatives synthesis and oxygen defect engineering on photocatalytic CO2 reduction

Photocatalytic conversion of CO2 into valuable fuels is considered a promising approach for the development of sustainable and renewable energy sources. In this study, we utilized Mo-MOF as a precursor to obtain MoO3 by pyrolytic derivatization and treated it to obtain MOF-MoO3-x containing oxygen vacancies as a catalyst for the photocatalytic reduction of CO2 to CO. MOF derivatization altered the morphology of the MoO3, which made the formation of oxygen vacancies easier and facilitated the separation of electron-hole pairs. Meanwhile, the increased specific surface area and the appearance of surface oxygen vacancies enhanced the CO2 adsorption and activation capabilities of MOF-MoO3-x. As a result, MOF-MoO3-x demonstrated a significant enhances in the photoreduction activity of CO2. Its CO yield was 29.1 μmolg−1h−1, which was 3.7 times higher than that of MOF-MoO3 and 2.4 times higher than that of H-MoO3-x. This innovative strategy may provide a new avenue for improving the comprehensive performance of photocatalysts and developing renewable energy sources.

Enhanced Visible-Light-Assisted Photocatalytic Removal of Tetracycline Using Co/La@g-C3N4 Ternary Nanocomposite and Underlying Reaction Mechanisms

Graphitic carbon nitride (g-C3N4) is a promising material for photocatalytic applications. However, it suffers from poor visible-light absorption and a high recombination rate of photogenerated electron–hole pairs. Here, Co/La@g-C3N4 with enhanced photocatalytic activity was prepared by co-doping Co and La into g-C3N4 via a facile one-pot synthesis. Co/La@g-C3N4 displayed better performance, achieving 94% tetracycline (TC) removal within 40 min, as compared with g-C3N4 (BCN, 65%). It also demonstrated promising performance in degrading other pollutants, which was ~2–4-fold greater relative to BCN. The improved photocatalytic activity of Co/La@g-C3N4 was associated with improved photogenerated charge separation, reduced charge transfer resistance, a built-in electric field arising from the p-n-p heterojunction, and the synergistic effect of ternary components for the separation and transfer of the photogenerated charge carriers. Superoxide radicals are suggested to be the most notable reactive species responsible for the photocatalytic reaction. Environmental factors, including the pollutant concentration, catalyst dosage, solution pH, inorganic salts, water matrices, and mixture with dyes, were considered in the photocatalytic reactions. Co/La@g-C3N4 showed good reusability for five cycles of the photocatalytic degradation of TC. The facile one-pot co-doping of Co and La in g-C3N4 formed a p-n-p heterojunction with boosted photocatalytic activity for the highly efficient removal of TC from various water matrices.

First-principles study of the electronic, optical adsorption, and photocatalytic water-splitting properties of a strain-tuned SiC/WS2 heterojunction

Heterojunction is widely acknowledged as a potent strategy as an effective means for achieving quality electronic, optical adsorption, and photocatalytic water-splitting properties. Strain also can regulate these properties effectively. In this study, we have fabricated and studied a heterojunction comprised SiC and WS2. Utilizing a first-principles method, we systematically investigated the SiC/WS2 heterojunction's structure, stability, electronic, and optical properties, as well as its photocatalytic water splitting characteristics under strain engineering. Our calculations reveal that the SiC/WS2 heterojunction is a type-II heterostructure with two stable structures, which exhibits a direct bandgap and well performance in the visible light region, facilitating efficient separation of photogenerated electron-hole pairs. We have explored and discussed the impacts of biaxial strain on the various properties. The bandgaps of System-A and B are 1.778 eV and 1.820 eV, respectively, without strain. Under strain from −6% to 10%, they initially rise, peak at 1.858 eV and 1.899 eV respectively at −2% strain, then decline. Without strain, effective mass mh/me for both structures are 1.642 and 1.673. Under positive strain, they increase, decrease, then increase again, peaking at 6% with 2.116 and 2.260. At −2% strain, values drop to 0.901 and 0.910 for A and B, respectively. Our calculations also demonstrate that the SiC/WS2 heterostructure qualifies as a promising photocatalytic material, fulfilling the criteria for water splitting under strain conditions of −4%, −2%, and 0%. And the heterojunction with System-B under −4% strain has the optimal performance in photocatalytic water splitting. At a strain of −4%, System-B achieves the maximum η′STH of 16.91%. In conclusion, our study not only offers fundamental insights into the utilization of SiC/WS2 heterojunctions for photocatalytic water splitting, but also provides the foundational design principles of heterojunctions.

Ti[sbnd]F bridged IL-CuCQDs-F/TiO2 inverse opal composite for boosting CO2 visible-photo reduction via slow photon effect

Photocatalytic reduction of CO2 exhibits unsatisfactory photocatalytic performance owing to the inefficient separation of photogenerated electron-hole pairs, low CO2 capture efficiency and limited visible light absorption on most photo-catalysts. Herein, TiF bridged IL-CuCQDs-F/TiO2 inverse opal composite (IO-CFTi) was constructed for boosting CO2 visible-photo reduction via slow photo effect. In this work, ethylenediaminetetraacetic acid (EDTA(Cu)) and imidazole ionic liquid 1-(2-Hydroxyethyl)-3-methylimidazolium tetrafluoroborate ([HOEtMIM][BF4]) were employed to confine grow of IL-CuCQDs-F within TiO2 inverse opal supporter via TiF bonds connection. Unique IL-CuCQDs-F efficiently expended light absorption towards visible region, and the confined growth of IL-CuCQDs-F within the TiO2 inverse opal cavity achieved the photoelectric conversion and efficient CO2 capture. Moreover, their TiF bonding interface of IO-CFTi assisted photogenerated electron transportation from TiO2 to CO2 for its reduction in this system. Consequently, IO-CFTi achieved a substantially increased CO production rate of 78.1 μmol·h−1·g−1 with 98 % selectivity. This improved performance in CO2 photoreduction positions the nanocomposite as a promising material for preservation of the environment and conversion of energy.

One-pot construction of α-Fe2O3/ZnNiFe2O4 heterojunction by incomplete sol/gel-self-propagating method with choline chloride-ethylene glycol media and its photo-degradation performance

A magnetic α-Fe2O3/ZnNiFe2O4 composite photocatalyst was synthesized through a one-pot reaction employing choline chloride-ethylene glycol deep eutectic solvents and an incomplete sol-gel self-propagating method. The photocatalytic performance was assessed by removing methylene blue (MB) under 40 W visible light. With a 1.0 g/L catalyst dosage, 10 mg/L MB concentration, and pH levels of 6 and 12, removal rates of 97 % and 99 % were achieved within 90 min, respectively. The composite also demonstrated effective degradation of methyl orange (MO) and malachite green (MG). Stability tests revealed minimal reduction in photocatalytic activity after four cycles. Active species analysis identified ·O2⁻ and ·OH as the primary agents in the photocatalytic process. XRD, XPS, UV–VIS DRS, HRTEM, PL, and EIS analyses confirmed the formation of a Z-scheme heterojunction between ZnNiFe2O4 and α-Fe2O3, which enhanced the specific surface area, electron transport capacity, and narrowed the band gap. This heterojunction improved the separation efficiency of photogenerated electron-hole pairs, resulting in enhanced photocatalytic activity and stability. This study presents a novel approach for preparing Z-scheme heterojunction photocatalysts through a one-pot reaction.

Sustainable photodegradation of pharmaceuticals: KOH-impregnated palm oil mill effluent sludge biochar-BiOBr nanocomposite for wastewater treatment

Biochar has explored in the search of a cost-effective and environmentally friendly photocatalyst for the efficient degradation of CIP antibiotic pollutants. Biochar (BC) produced from palm oil mill sludge was used as a base to fabricate biochar-based BiOBr composites by varying the mass ratio of biochar and BiOBr via a hydrothermal route. The optimized composites BBC-1:1 has exhibited the formation of crystal struvture as tetragonal BiOBr with a a significant specific surface of 267 m2/g (BBC-1:1) while incorporating different mass ratios of BC with BiOBr. This composite facilitates the band gap of BiOBr from 2.87 to 2.42 eV and is consistent with the decreasing recombination rate of electron-hole pairs as suggested by UV-Vis DRS and photoluminescence (PL), respectively. Consequently, the synergistic effect of biochar BiOBr leads to a higher degradation efficiency of CIP showing the highest efficiency (97.49 %) and that of pure BiOBr being 55.66 % under optimized conditions. The degradation rate of the BBC-1:1 composite which observed to be 0.0156 min−1 is 3.25 times that of BiOBr (0.0048 min−1). Furthermore, the scavenging experiments confirmed the significant contribution of the active radicals h+ and O2- as the main photoactive species in the photocatalytic degradation of CIP. Consequently, the photocatalytic degradation mechanism was discussed and the reusability test confirmed the high stability of the BBC composites up to 77 % for the seventh cycles. These results show that the BBC composite is suitable for large-scale practical applications as a green photocatalyst.

WO3/Cu2O-CuO and WO3/Au/Cu2O-CuO heterojunctions photocatalysts for self-cleaning and photocatalytic degradation of organic pollutants applications

In this work, a high-performance WO3/Au/Cu2O-CuO heterojunctions was deposited via dc reactive magnetron sputtering, which displayed superhydrophilicity conversion and superior photocatalytic performance for the degradation of methylene blue. WO3, WO3/Cu2O-CuO, WO3/Au and WO3/Au/Cu2O-CuO heterojunctions were sputtered on precleaned glass and Si(100) substrates. The chemical composition, crystal structure, surface morphology, optical absorption, water contact angle and photocatalytic activities of the prepared single and multilayers films were examined to elucidate the correlation between structure and other properties. SEM revealed tiny small nanoparticles for WO3 film, close-packed nanoparticles for WO3/Cu2O-CuO multilayers and nanoparticles with more open structure for WO3/Au/Cu2O-CuO heterojunctions. The WO3/Au/Cu2O-CuO heterojunctions had the highest optical absorption. The estimated band gap values were 3.16, 3.08, 2.97 and 2.65 eV for WO3, WO3/Cu2O-CuO, WO3/Au and WO3/Au/Cu2O-CuO, respectively. The WO3/Cu2O-CuO, WO3/Au and WO3/Au/Cu2O-CuO became superhydrophilic after UV illumination. The remarkable photocatalytic activities of WO3/Au/Cu2O-CuO is attributed to the enhanced efficiency of separation for photogenerated hole–electron pairs.

Quasi-passive modulation for monolithic GaN photoelectronic circuit

Due to the overlap between the electroluminescence spectrum and spectral responsivity curve, gallium nitride (GaN)-based multi-quantum well (MQW) diodes can modulate and detect light emitted by another diode with the same MQW structure. This enables the realization of a monolithic integrated GaN optoelectronic circuit, integrating an MQW-based transmitter, waveguide, modulator, and receiver on a tiny GaN chip. It is well known that the active region of MQW absorbs high-energy photons within the plane, generating electron-hole pairs and forming photogenerated carriers. The change in free carrier concentration causes variations in the refractive index and absorption characteristics of the waveguide, thereby manipulating light propagation within the waveguide. Based on this physical phenomenon, a quasi-passive modulation scheme is proposed for a monolithic GaN photoelectronic circuit. This scheme achieves optical modulation by connecting a variable resistor between the modulator electrodes, avoiding the need for high-precision external electric fields and complex control circuits. The performance of the quasi-passive modulation was tested through on-chip data transmission and real-time audio signal transmission. The results indicate that quasi-passive modulation is highly feasible in optoelectronic systems and shows great promise as a competitive core module for future large-scale photonic integrated circuits.

Two-Dimensional Atomically Thin Piezoelectric Nanosheets for Efficient Pyroptosis-Dominated Sonopiezoelectric Cancer Therapy.

Sonopiezocatalytic therapy is an emerging therapeutic strategy that utilizes ultrasound irradiation to activate piezoelectric materials, inducing polarization and energy band bending to facilitate the generation of reactive oxygen species (ROS). However, the efficient generation of ROS is hindered by the long distance of charge migration from the bulk to the material surface. Herein, atomically thin Bi2O2(OH)(NO3) (AT-BON) nanosheets are rationally engineered through disrupting the weaker hydrogen bonds within the [OH] and [NO3] layer in the bulk material. The ultrathin structure of AT-BON piezocatalytic nanosheets shortens the migration distance of carriers, expands the specific surface area, and accelerates the charge transfer efficiency, showcasing a natural advantage in ROS generation. Importantly, the non-centrosymmetric polar crystal structure grants the nanosheets the ability to separate electron-hole pairs. Under ultrasonic mechanical stress, Bi2O2(OH)(NO3) nanosheets with the remarkable piezoelectric feature exhibit the desirable in vivo antineoplastic outcomes in both breast cancer model and liver cancer model. Especially, the AT-BON-induced ROS bursts lead to the activation of the Caspase-1-driven pyroptosis pathway. This study highlights the beneficial impact of bulk material thinning on enhancing ROS generation efficiency and anti-cancer effects.

Amorphous Strategy and Doping Copper on Metal-Organic Framework Surface for Enhanced Photocatalytic CO2 Reduction to C2H4.

Amorphous photocatalysts are characterized by numerous grain boundaries and abundant unsaturated sites, which enhance reaction efficiency from both kinetic and thermodynamic perspectives. However, amorphization strategies have rarely been used for photocatalytic CO2 reduction. Doping copper onto a metal-organic framework (MOF) surface can regulate the electronic structure of photocatalysts, promote electron transfer from the MOF to Cu, and improve the separation efficiency of electron-hole pairs. In this study, an amorphous photocatalyst MOFw-p/Cu containing highly dispersed Cu (0, I, II) sites was designed and synthesized by introducing a regulator and in situ copper species during the nucleation process of MOF (UiO-66-NH2). Various characterizations confirmed that the Cu species were anchored to the organometallic skeleton of the surface amorphization MOF structure. The synergistic effect of Cu doping and surface amorphization in MOFw-p/Cu can significantly enhance the CO and CH4 yields while promoting the formation of the multicarbon product C2H4. The approach holds promise for developing novel, highly efficient MOFs as photocatalysts for CO2 photoreduction, enabling the production of high-value-added C2 products.

Scalable fabrication of high surface area g-C3N4 nanotubes for efficient photocatalytic hydrogen production

In this research, we present a novel facile, scalable, and template-free technique of synthesizing graphitic carbon nitride (g-C3N4) nanotubes for generating hydrogen through photocatalysis. The hybrid technique involves a two-fold mixing of the precursor materials melamine (M) and cyanuric acid (CA), involving ball milling followed by solution mixing. By varying the M:CA molar ratios, different compositions of g-C3N4 nanotubes were fabricated. The study focused on examining the surface characteristics and the photocatalytic hydrogen evolution performance of these nanotubes. Nanotubes with high specific surface area of 206 m2 g−1 for M:CA molar ratio of 1:3 and 178 m2 g−1 for M:CA molar ratio of 1:5 were produced, with H2 evolution rates of 543 μmol h−1 g−1 and 740 μmol h−1 g−1 respectively, which were an increase of 4 and 5-fold, respectively, in comparison to the pristine sample. The enhanced efficiency of hydrogen production through photocatalysis by nanotubes, when contrasted with pristine material, can be ascribed to their high crystallinity, superior specific surface areas, decreased recombination rates of electron-hole pairs generated during light exposure, and improved dynamics of charge carriers. This hybrid technique provides a new pathway for cost-effective fabrication of g-C3N4 nanotubes with substantial surface areas and high yield photocatalysts on an industrial scale, without the use of templates and hydrothermal processes for efficient hydrogen generation.

Intercalation of novel Ocimum Sanctum leaves derived carbon dots between g-C3N4/CoFe2O4 Z-scheme heterojunction system for boosting the radicals’ generation in photo-Fenton degradation and synchronized electrochemical sensing of sulfamethoxazole antibiotic

Deeming about incessant consumption and disposal of pharmaceutical antibiotics in natural water bodies, this study demonstrates the synthesis of a novel Tulsi leaves (Ocimum Sanctum) derived carbon dots modified Z-scheme g-C3N4/CoFe2O4 heterojunction system. Characterization techniques namely XRD, FT-IR, XPS, FE-SEM, HR-TEM and EDX supported composite formation. Fabricated catalysts presented excellent photocatalytic performance towards removal of sulfamethoxazole (SMX). UV–vis DRS, PL and EIS findings suggested the augmented visible light absorption capability, suppression of electron-hole pairs recombination and effective separation of charge carriers which were accountable for degradation process. Probable mechanistic pathway for SMX removal was photo-Fenton assisted with Z-scheme separated electron-hole pairs via activation of H2O2, where hydroxyl radicals (•OH) were main reactive species. Additionally, the prepared material was employed as electrochemical sensor for individual as well as simultaneous detection of SMX and trimethoprim with quite impressive detection limits of 0.042 µM and 0.047 µM, respectively.

Realizing enhanced photoresponse for self-powered broadband photodetector with asymmetric contacts based MoTe2/WSe2 van der Waals heterostructure

Self-powered photodetectors constructed by two-dimensional (2D) materials are significant in advanced science and technology with the growing focus on green and energy-efficient solutions. The built-in electric field in photodetector drives efficient separation and transfer of photogenerated electron–hole pairs. However, traditional metal-2D material-metal structures have more interface defects and larger Schottky barrier to hinder carrier transport. In this work, an asymmetric electrode material structure is constructed by adding graphene to provide a more efficient transport channel for photogenerated carriers. Graphene electrodes can play a variety of roles in efficient separation and collection of photogenerated carriers, reducing the barrier and improving the contact quality. Compared with the device using symmetric gold electrodes, the device prepared with asymmetric contacts show optimized performance. The MoTe2/WSe2 heterostructure exhibits brilliant self-powered photoresponse (a responsivity of 268 mA/W and a detectivity of 7.48*1011 Jones). And the rise/decay times are up to 145μs/125μs. Additionally, the detector has a broadband detection capability from visible light to near-infrared. These results provide a promising and simple way to fabricate a MoTe2/WSe2 self-powered broadband photodetector with high performance

2D Gr/WSe2/MoTe2 vertical heterojunction for self-powered photodiode with ultrafast response and high sensitivity

Two-dimensional materials without lattice constraints can be combined into form heterojunctions via van der Waals forces, providing opportunities for the future development of novel high-performance photodetectors. In non-vertical heterojunction devices with long carrier transport channels, SRH recombination due to defect and interface states in the heterojunction and Langevin recombination due to Coulomb interactions induce large amounts of photogenerated carrier recombination, leading to low quantum efficiencies of the heterojunction. At the same time, defect and interface trap states, as well as the long channel of the non-vertical heterojunction device, lead to a slow response speed of the device. In this work, a 2D WSe2/MoTe2 vertical heterojunction photodiode with a transparent graphene top electrode has been designed to simultaneously achieve high sensitivity and fast response speed of photodetectors. Benefiting from the vertical device structure, high-quality interface and low contact resistance, the photogenerated electron-hole pairs can be efficiently separated and transported. The photodiode exhibits remarkable rectification characteristics with a rectification ratio as high as 1.4 × 104, and provides a broadband and self-powered photodetection from the visible to NIR bands (405–1064 nm) with a maximum responsivity of 0.33 A/W at 785 nm. In particular, the photodiode achieves an ultra-fast rise/fall time of 6.49/6.22 μs at 0 V and a further reduction of the response time to 1.68/1.2 μs at a reverse bias of −1 V. This ultra-fast response allows the photodiode to detect switching signals with a cutoff frequency of more than 70 kHz and 200 kHz at 0 V and −1 V, respectively. This work opens up new opportunities for the development of integrated 2D photodetectors with low power consumption, high sensitivity, and high speed.

Structural, optoelectronic, mechanical and thermoelectric properties of ZrO2 via band engineering with Nb doping

The study investigates the structural, mechanical, optoelectronic, and thermoelectric properties of pure and doped ZrO2 using WIEN2k. The goal is to evaluate their potential contribution to future thermoelectric and photovoltaic systems. Thermodynamic stability is confirmed through molecular dynamic simulations, while mechanical stability is confirmed through mechanical features. The electronic characteristics are determined using the GGA-PBE functional. For pristine, 25 % doped, and 50 % doped ZrO2, the measured band gaps were 3.10, 2.92, and 2.73eV, respectively. Significant absorption and conductivity are found in the examined optical properties, together with decreased reflectance and optical loss, which points to a lower rate of electron-hole pair recombination. At lower temperatures, the thermoelectric properties show a noteworthy ZT. As a result, these materials may efficiently transform thermal energy into useful electrical power and offer a considerable potential for optoelectronic technology.