Showing papers on "Heterojunction published in 2019"
TL;DR: In this paper, an ultrathin 2D/2D WO3/g-C3N4 step-like composite composite heterojunction photocatalysts were fabricated by electrostatic self-assembly of ultra-thin tungsten trioxide (WO3) and graphitic carbon nitride (g)-nodes.
Abstract: The appropriate interfacial contact of heterojunction photocatalysts plays a critical role in transfer/separation of interfacial charge carriers. Design of two-dimensional (2D)/2D surface-to-surface heterojunction is an effective method for improving photocatalytic activity since greater contact area can enhance interfacial charge transfer rate. Herein, ultrathin 2D/2D WO3/g-C3N4 step-like composite heterojunction photocatalysts were fabricated by electrostatic self-assembly of ultrathin tungsten trioxide (WO3) and graphitic carbon nitride (g-C3N4) nanosheets. The ultrathin WO3 and g-C3N4 nanosheets were obtained by electrostatic-assisted ultrasonic exfoliation of bulk WO3 and a two-step thermal-etching of bulk g-C3N4, respectively. The thickness of ultrathin WO3 and g-C3N4 nanosheets are 2.5–3.5 nm, which is equivalent to 5–8 atomic or molecular layer thickness. This ultrathin layered heterojunction structure can enhance surface photocatalytic rate because photogenerated electrons and holes at heterogeneous interface more easily transfer to surface of photocatalysts. Therefore, the obtained ultrathin 2D/2D WO3/g-C3N4 step-scheme (S-scheme) heterojunction photocatalysts exhibited better H2-production activity than pure g-C3N4 and WO3 with the same loading amount of Pt as cocatalyst. The mechanism and driving force of charge transfer and separation in S-scheme heterojunction photocatalysts are investigated and discussed. This investigation will provide new insight about designing and constructing novel S-scheme heterojunction photocatalysts.
1,440 citations
TL;DR: In this paper, the authors reported the observation of multiple emergent peaks around the original WSe2 A exciton resonance in the absorption spectra, and they exhibit gate dependences that are distinct from that of the A excitons in WSe 2/WS 2 heterostructures with large twist angles.
Abstract: Moire superlattices enable the generation of new quantum phenomena in two-dimensional heterostructures, in which the interactions between the atomically thin layers qualitatively change the electronic band structure of the superlattice. For example, mini-Dirac points, tunable Mott insulator states and the Hofstadter butterfly pattern can emerge in different types of graphene/boron nitride moire superlattices, whereas correlated insulating states and superconductivity have been reported in twisted bilayer graphene moire superlattices1-12. In addition to their pronounced effects on single-particle states, moire superlattices have recently been predicted to host excited states such as moire exciton bands13-15. Here we report the observation of moire superlattice exciton states in tungsten diselenide/tungsten disulfide (WSe2/WS2) heterostructures in which the layers are closely aligned. These moire exciton states manifest as multiple emergent peaks around the original WSe2 A exciton resonance in the absorption spectra, and they exhibit gate dependences that are distinct from that of the A exciton in WSe2 monolayers and in WSe2/WS2 heterostructures with large twist angles. These phenomena can be described by a theoretical model in which the periodic moire potential is much stronger than the exciton kinetic energy and generates multiple flat exciton minibands. The moire exciton bands provide an attractive platform from which to explore and control excited states of matter, such as topological excitons and a correlated exciton Hubbard model, in transition-metal dichalcogenides.
796 citations
University of Sheffield1, University of Manchester2, National Autonomous University of Mexico3, Indian Institute of Technology Madras4, Ulsan National Institute of Science and Technology5, University of Oxford6, Dongguk University7, University of Warsaw8, National Institute for Materials Science9, Henry Royce Institute10
TL;DR: It is demonstrated that excitonic bands in MoSe2/WS2 heterostructures can hybridize, resulting in a resonant enhancement of moiré superlattice effects, which underpin strategies for band-structure engineering in semiconductor devices based on van der Waals heterostructure.
Abstract: Atomically thin layers of two-dimensional materials can be assembled in vertical stacks that are held together by relatively weak van der Waals forces, enabling coupling between monolayer crystals with incommensurate lattices and arbitrary mutual rotation1,2. Consequently, an overarching periodicity emerges in the local atomic registry of the constituent crystal structures, which is known as a moire superlattice3. In graphene/hexagonal boron nitride structures4, the presence of a moire superlattice can lead to the observation of electronic minibands5–7, whereas in twisted graphene bilayers its effects are enhanced by interlayer resonant conditions, resulting in a superconductor–insulator transition at magic twist angles8. Here, using semiconducting heterostructures assembled from incommensurate molybdenum diselenide (MoSe2) and tungsten disulfide (WS2) monolayers, we demonstrate that excitonic bands can hybridize, resulting in a resonant enhancement of moire superlattice effects. MoSe2 and WS2 were chosen for the near-degeneracy of their conduction-band edges, in order to promote the hybridization of intra- and interlayer excitons. Hybridization manifests through a pronounced exciton energy shift as a periodic function of the interlayer rotation angle, which occurs as hybridized excitons are formed by holes that reside in MoSe2 binding to a twist-dependent superposition of electron states in the adjacent monolayers. For heterostructures in which the monolayer pairs are nearly aligned, resonant mixing of the electron states leads to pronounced effects of the geometrical moire pattern of the heterostructure on the dispersion and optical spectra of the hybridized excitons. Our findings underpin strategies for band-structure engineering in semiconductor devices based on van der Waals heterostructures9. Excitonic bands in MoSe2/WS2 heterostructures can hybridize, resulting in a resonant enhancement of moire superlattice effects.
667 citations
TL;DR: In this paper, a metal-free heterostructure photocatalyst constructed by boron nitride quantum dots (BNQDs) and ultrathin porous g-C3N4 (UPCN) was successfully developed for overcoming these defects.
Abstract: Graphitic carbon nitride (g-C3N4) has enormous potential for photocatalysis, but only possesses moderate activity because of excitonic effects and sluggish charge transfer. Herein, metal-free heterostructure photocatalyst constructed by boron nitride quantum dots (BNQDs) and ultrathin porous g-C3N4 (UPCN) was successfully developed for overcoming these defects. Results showed that the BNQDs loaded UPCN can simultaneously promote the dissociation of excitons and accelerate the transfer of charges owing to the negatively charged functional groups on the surface of BNQDs as well as the ultrathin and porous nanostructure of g-C3N4. Benefiting from the intensified exciton dissociation and charge transfer, the BNQDs/UPCN (BU) photocatalyst presented superior visible-light-driven molecular oxygen activation ability, such as superoxide radical ( O2−) generation and hydrogen peroxide (H2O2) production. The average O2− generation rate of the optimal sample (BU-3) was estimated to be 0.25 μmol L−1 min−1, which was about 2.3 and 1.6 times than that of bulk g-C3N4 and UPCN. Moreover, the H2O2 production by BU-3 was also higher than that of bulk g-C3N4 (22.77 μmol L−1) and UPCN (36.13 μmol L−1), and reached 72.30 μmol L−1 over 60 min. This work reveals how rational combination of g-C3N4 with BNQDs can endow it with improved photocatalytic activity for molecular oxygen activation, and provides a novel metal-free and highly efficient photocatalyst for environmental remediation and energy conversion.
512 citations
TL;DR: The constructed heterostructure can selectively extract photogenerated charge carriers and impede the loss of decomposed components from soft perovskites, thereby reducing damage to the organic charge-transporting semiconductors.
Abstract: Here we report a solution-processing strategy to stabilize the perovskite-based heterostructure. Strong Pb–Cl and Pb–O bonds formed between a [CH(NH2)2]x[CH3NH3]1−xPb1+yI3 film with a Pb-rich surface and a chlorinated graphene oxide layer. The constructed heterostructure can selectively extract photogenerated charge carriers and impede the loss of decomposed components from soft perovskites, thereby reducing damage to the organic charge-transporting semiconductors. Perovskite solar cells with an aperture area of 1.02 square centimeters maintained 90% of their initial efficiency of 21% after operation at the maximum power point under AM1.5G solar light (100 milliwatts per square centimeter) at 60°C for 1000 hours. The stabilized output efficiency of the aged device was further certified by an accredited test center.
379 citations
TL;DR: In this article, a planar p-n homojunction perovskite solar cell was proposed to promote oriented transport of the photo-induced carriers and reduce recombination, achieving a power conversion efficiency of 21.3%.
Abstract: Perovskite solar cells (PSCs) have emerged as an attractive photovoltaic technology thanks to their outstanding power conversion efficiency (PCE). Further improvement in the device efficiency is limited by the recombination of the charge carriers in the perovskite layer even when employing heterojunction-based architectures. Here, we propose and demonstrate a p-type perovskite/n-type perovskite homojunction whose built-in electric field promotes oriented transport of the photo-induced carriers, thus reducing carrier recombination losses. By controlling the stoichiometry of the perovskite precursors, we are able to induce n-type or p-type doping. We integrate the homojunction structure in a planar PSC combining a thermally evaporated p-type perovskite layer on a solution-processed n-type perovskite layer. The PSC with a MAPbI3 homojunction achieves a PCE of 20.80% (20.5% certified PCE), whereas the PSC based on a FA0.15MA0.85PbI3 homojunction delivers a PCE of 21.38%. We demonstrate that the homojunction structure is an effective approach, beyond existing planar heterojunction PSCs, to achieve highly efficient PSCs with reduced carrier recombination losses. Carrier recombination limits the power conversion efficiency of perovskite solar cells. Here the authors construct a planar p–n homojunction perovskite solar cell to promote the oriented transport of carriers and reduce recombination, thus enabling power conversion efficiency of 21.3%.
350 citations
TL;DR: A highly polarization-sensitive, broadband, self-powered photodetector based on graphene/PdSe2/germanium heterojunction with an ultrahigh polarization sensitivity of 112.2 is achieved, which represents the best result for 2D layered material-based photodtectors.
Abstract: Polarization-sensitive photodetection in a broad spectrum range is highly desired due to the great significance in military and civilian applications. Palladium diselenide (PdSe2), a newly explored air-stable, group 10 two-dimensional (2D) noble metal dichalcogenide with a puckered pentagonal structure, holds promise for polarization-sensitive photodetection. Herein, we report a highly polarization-sensitive, broadband, self-powered photodetector based on graphene/PdSe2/germanium heterojunction. Owing to the enhanced light absorption of the mixed-dimensional van der Waals heterojunction and the effective carrier collection with graphene transparent electrode, the photodetector exhibits superior device performance in terms of a large photoresponsivity, a high specific detectivity, a fast response speed to follow nanosecond pulsed light signal, and a broadband photosensitivity ranging from deep ultraviolet (DUV) to mid-infrared (MIR). Significantly, highly polarization-sensitive broadband photodetection with an ultrahigh polarization sensitivity of 112.2 is achieved, which represents the best result for 2D layered material-based photodetectors. Further, we demonstrated the high-resolution polarization imaging based on the heterojunction device. This work reveals the great potential of 2D PdSe2 for high-performance, air-stable, and polarization-sensitive broadband photodetectors.
344 citations
TL;DR: In this paper, the authors highlight the various roles of these 2D materials, such as enhanced light harvesting, suitable band edge alignment, facilitated charge separation, and stability during the water splitting reaction, in various SC/2D photoelectrode and photocatalytic systems.
Abstract: Hydrogen (H2) production via solar water splitting is one of the most ideal strategies for providing sustainable fuel because this requires only water and sunlight. In achieving high-yield production of hydrogen as a recyclable energy carrier, the nanoscale design of semiconductor (SC) materials plays a pivotal role in both photoelectrochemical (PEC) and photocatalytic (PC) water splitting reactions. In this context, the advent of two-dimensional (2D) materials with remarkable electronic and optical characteristics has attracted great attention for their application to PEC/PC systems. The elaborate design of combined 2D layered materials interfaced with other SCs can markedly enhance the PEC/PC efficiencies via bandgap alteration and heterojunction formation. Three classes of 2D materials including graphene, transition metal dichalcogenides (TMDs), and graphitic carbon nitride (g-C3N4), and their main roles in the photoelectrocatalytic production of H2, are discussed in detail herein. We highlight the various roles of these 2D materials, such as enhanced light harvesting, suitable band edge alignment, facilitated charge separation, and stability during the water splitting reaction, in various SC/2D photoelectrode and photocatalytic systems. The roles of emerging 2D nanomaterials, such as 2D metal oxyhalides, 2D metal oxides, and layered double hydroxides, in PEC H2 production are also discussed.
338 citations
TL;DR: In this article, the authors demonstrate that in semiconducting heterostructures built of incommensurate MoSe2 and WS2 monolayers, excitonic bands can hybridise, resulting in the resonant enhancement of the moire superlattice effects.
Abstract: Atomically-thin layers of two-dimensional materials can be assembled in vertical stacks held together by relatively weak van der Waals forces, allowing for coupling between monolayer crystals with incommensurate lattices and arbitrary mutual rotation. A profound consequence of using these degrees of freedom is the emergence of an overarching periodicity in the local atomic registry of the constituent crystal structures, known as a moire superlattice. Its presence in graphene/hexagonal boron nitride (hBN) structures led to the observation of electronic minibands, whereas its effect enhanced by interlayer resonant conditions in twisted graphene bilayers culminated in the observation of the superconductor-insulator transition at magic twist angles. Here, we demonstrate that, in semiconducting heterostructures built of incommensurate MoSe2 and WS2 monolayers, excitonic bands can hybridise, resulting in the resonant enhancement of the moire superlattice effects. MoSe2 and WS2 are specifically chosen for the near degeneracy of their conduction band edges to promote the hybridisation of intra- and interlayer excitons, which manifests itself through a pronounced exciton energy shift as a periodic function of the interlayer rotation angle. This occurs as hybridised excitons (hX) are formed by holes residing in MoSe2 bound to a twist-dependent superposition of electron states in the adjacent monolayers. For heterostructures with almost aligned pairs of monolayer crystals, resonant mixing of the electron states leads to pronounced effects of the heterostructure's geometrical moire pattern on the hX dispersion and optical spectrum. Our findings underpin novel strategies for band-structure engineering in semiconductor devices based on van der Waals heterostructures.
326 citations
TL;DR: In this article, the authors studied electroluminescence in two-dimensional atomic double layers of transition metal chalcogenides and showed that the interlayer tunnelling current depends only on the exciton density.
Abstract: A Bose–Einstein condensate is the ground state of a dilute gas of bosons, such as atoms cooled to temperatures close to absolute zero1. With much smaller mass, excitons (bound electron–hole pairs) are expected to condense at considerably higher temperatures2–7. Two-dimensional van der Waals semiconductors with very strong exciton binding are ideal systems for the study of high-temperature exciton condensation. Here we study electrically generated interlayer excitons in MoSe2–WSe2 atomic double layers with a density of up to 1012 excitons per square centimetre. The interlayer tunnelling current depends only on the exciton density, which is indicative of correlated electron–hole pair tunnelling8. Strong electroluminescence arises when a hole tunnels from WSe2 to recombine with an electron in MoSe2. We observe a critical threshold dependence of the electroluminescence intensity on exciton density, accompanied by super-Poissonian photon statistics near the threshold, and a large electroluminescence enhancement with a narrow peak at equal electron and hole densities. The phenomenon persists above 100 kelvin, which is consistent with the predicted critical condensation temperature9–12. Our study provides evidence for interlayer exciton condensation in two-dimensional atomic double layers and opens up opportunities for exploring condensate-based optoelectronics and exciton-mediated high-temperature superconductivity13. Condensation of interlayer excitons at temperatures above 100 kelvin is demonstrated in a van der Waals heterostructure consisting of two-dimensional atomic double layers of transition metal chalcogenides.
316 citations
TL;DR: Effective interface engineering in PSCs is reported via a multifunctional chemical linker of 4-imidazoleacetic acid hydrochloride (ImAcHCl) that can provide a chemical bridge between SnO2 and perovskite through an ester bond withSnO2 via esterification reaction and an electrostatic interaction with perovSkite via imidazolium cation in ImAcH Cl and iodide anion in perovkite.
Abstract: Chemical interaction at a heterojunction interface induced by an appropriate chemical linker is of crucial importance for high efficiency, hysteresis-less, and stable perovskite solar cells (PSCs). Effective interface engineering in PSCs is reported via a multifunctional chemical linker of 4-imidazoleacetic acid hydrochloride (ImAcHCl) that can provide a chemical bridge between SnO2 and perovskite through an ester bond with SnO2 via esterification reaction and an electrostatic interaction with perovskite via imidazolium cation in ImAcHCl and iodide anion in perovskite. In addition, the chloride anion in ImAcHCl plays a role in the improvement of crystallinity of perovskite film crystallinity. The introduction of ImAcHCl onto SnO2 realigns the positions of the conduction and valence bands upwards, reduces nonradiative recombination, and improves carrier life time. As a consequence, average power conversion efficiency (PCE) is increased from 18.60% ± 0.50% to 20.22% ± 0.34% before and after surface modification, respectively, which mainly results from an enhanced voltage from 1.084 ± 0.012 V to 1.143 ± 0.009 V. The best PCE of 21% is achieved by 0.1 mg mL-1 ImAcHCl treatment, along with negligible hysteresis. Moreover, an unencapsulated device with ImAcHCl-modified SnO2 shows much better thermal and moisture stability than unmodified SnO2 .
TL;DR: In this article, a three-dimensional microspheres mediator-free Z-scheme Ag3VO4/BiVO4 heterojunction photocatalyst was successfully obtained for the first time.
Abstract: A A novel three-dimensional microspheres mediator-free Z-scheme Ag3VO4/BiVO4 heterojunction photocatalyst was successfully obtained for the first time. The photocatalytic performance of the as-prepared photocatalyst was systematically examined via the photocatalytic reduction of Cr6+ and oxidation of Bisphenol S under visible-light irradiation. Among these samples, 0.24-Ag3VO4/BiVO4 exhibits the highest photocatalytic performances, the photocatalytic reduction and oxidation efficiency of 74.9 and 94.8%, respectively, can be achieved. The enhanced photocatalytic performance is attributed to the build-in electric field assisted charge transfer between the Ag3VO4 and BiVO4, and the increasing lifetime of the charge carrier confirmed by the results of time-resolved fluorescence spectra and photoelectrochemical measures. Moreover, based on the results of free radical scavenging activity test, and EPR experiments, it has been verified that the Ag3VO4/BiVO4 heterostructures follow a typical Z-scheme charge transfer mechanism rather than conventional type-II heterojunction charge transfer mechanism. Furthermore, the theoretical understanding of the underlying mechanism was also supported, while the energy band structure, and Fermi level were systematically calculated using the density functional theory approach. The results show that a built-in electric field directed from Ag3VO4 to BiVO4 surface was established as an equalized Fermi level was reached, which benefits the separation of photogenerated charge carriers in the way of a Z-scheme charge transfer mechanism. The strategy to form the three-dimensional microspheres Z-scheme heterojunction photocatalyst may offer new insight into the Z-scheme charge transfer mechanism for applications in the field of solar energy conversion.
TL;DR: Zhao et al. fabricate heterojunctions of colloidal perovskite quantum dots with different composition using layer-by-layer deposition and demonstrate improved photovoltaic performance with enhanced photocarrier harvesting.
Abstract: Metal halide perovskite semiconductors possess outstanding characteristics for optoelectronic applications including but not limited to photovoltaics. Low-dimensional and nanostructured motifs impart added functionality which can be exploited further. Moreover, wider cation composition tunability and tunable surface ligand properties of colloidal quantum dot (QD) perovskites now enable unprecedented device architectures which differ from thin-film perovskites fabricated from solvated molecular precursors. Here, using layer-by-layer deposition of perovskite QDs, we demonstrate solar cells with abrupt compositional changes throughout the perovskite film. We utilize this ability to abruptly control composition to create an internal heterojunction that facilitates charge separation at the internal interface leading to improved photocarrier harvesting. We show how the photovoltaic performance depends upon the heterojunction position, as well as the composition of each component, and we describe an architecture that greatly improves the performance of perovskite QD photovoltaics.
TL;DR: In this paper, a review of the latest researches on enhancing the photoelectric performance of photodetectors based on metal oxide semiconductors via chargecarrier engineering is presented.
Abstract: Semiconductor-based photodetectors (PDs) convert light signals into electrical signals via the photoelectric effect, which involves the generation, separation, and transportation of the photoinduced charge carriers, as well as the extraction of these charge carriers to external circuits. Because of their specific electronic and optoelectronic properties, metal oxide semiconductors are widely used building blocks in photoelectric devices. However, the compromise between enhancing the photoresponse and reducing the rise/ decay times limits the practical applications of PDs based on metal oxide semiconductors. As the behaviors of the charge carriers play important roles in the photoelectric conversion process of these PDs, researchers have proposed several strategies, including modification of light absorption, design of novel PD heterostructures, construction of specific geometries, and adoption of specific electrode configurations to modulate the charge-carrier behaviors and improve the photoelectric performance of related PDs. This review aims to introduce and summarize the latest researches on enhancing the photoelectric performance of PDs based on metal oxide semiconductors via chargecarrier engineering, and proposes possible opportunities and directions for the future developments of these PDs in the last section.
TL;DR: This work provides a facile and effective method for the in situ preparation of PVK-MD heterojunctions, which may significantly stimulate the synthesis of various perovskite-based hybrid materials and their further optoelectronic applications.
Abstract: Heterojunction engineering has played an indispensable role in the exploitation of innovative artificial materials with exceptional properties and has consequently triggered a new revolution in achieving high-performance optoelectronic devices. Herein, an intriguing halide perovskite (PVK) and metal dichalcogenide (MD) heterojunction, i.e., a lead-free Cs2SnI6 perovskite nanocrystal/SnS2 nanosheet hybrid, was fabricated in situ for the first time. Comprehensive investigations with experimental characterizations and theoretical calculations demonstrate that cosharing of the Sn atom enables intimate contact in the Cs2SnI6/SnS2 hybrid together with a type II band alignment structure. Additionally, ultrafast carrier separation between SnS2 and Cs2SnI6 has been observed in the Cs2SnI6/SnS2 hybrid by transient absorption measurements, which efficiently prolongs the lifetime of the photogenerated electrons in SnS2 (from 1290 to 3080 ps). The resultant spatial charge separation in the Cs2SnI6/SnS2 hybrid evidenced by Kelvin probe force microscopy (KPFM) significantly boosts the photocatalytic activity toward CO2 reduction and the photoelectrochemical performance, with 5.4-fold and 10.6-fold enhancements compared with unadorned SnS2. This work provides a facile and effective method for the in situ preparation of PVK-MD heterojunctions, which may significantly stimulate the synthesis of various perovskite-based hybrid materials and their further optoelectronic applications.
TL;DR: A hierarchical cable-like TiO2 @Fe3 O4 @PPy is fabricated by a sequential process of solvothermal treatment and polymerization that validates the distinct charge distribution and magnetic coupling and sheds light on novel structures for functional core@shell composites.
Abstract: Core@shell structures have been attracting extensive attention to boost microwave absorption (MA) performance due to the unique interfacial polarization. However, it still remains a challenge to synthesize sophisticated 1D semiconductor-based materials with excellent MA competence. Herein, a hierarchical cable-like TiO2 @Fe3 O4 @PPy is fabricated by a sequential process of solvothermal treatment and polymerization. The complex permittivity of ternary composites can be optimized by tunable PPy coating thickness to improve the loss ability. The maximum reflection loss can reach -61.8 dB with a thickness of 3.2 mm while the efficient absorption bandwidth can achieve over 6.0 GHz, which involves the X and Ku band at only a 2.2 mm thickness. Importantly, the heterojunction contacts constructed by PPy-Fe3 O4 and Fe3 O4 -TiO2 contribute to the enhanced polarization loss. Besides, the configuration of magnetic Fe3 O4 sandwiched between dielectric TiO2 and PPy facilitates the magnetic stray field to radiate into the TiO2 core and out of the PPy shell, which significantly promotes magnetic-dielectric synergy. Electron holography validates the distinct charge distribution and magnetic coupling. The new findings might shed light on novel structures for functional core@shell composites and the design of semiconductor-based materials for microwave absorption.
TL;DR: Wang et al. as mentioned in this paper proposed a method for efficient removal of gaseous chlorinated-volatile organic compounds (VOCs) under simulated sunlight irradiation by using Ag nanoparticles.
Abstract: Ag decorated WO3/Bi2WO6 hybrid heterojunction with a direct Z-scheme band structure has been synthesized by a novel method for efficient removal of gaseous chlorinated-volatile organic compounds (VOCs) under simulated sunlight irradiation. Bismuth atoms were inserted into the [WO6] layers of tungstate acid to form [Bi2O2] layers toward the formation of a Bi2WO6 crystal phase, which results in Z-scheme WO3/Bi2WO6 heterojunction. Ag nanoparticles (NPs) were further introduced and uniformly anchored on the surface of the WO3/Bi2WO6 for improving visible-light absorption and adjusting behavior of photoinduced charge carriers in the heterostructure through surface plasmon resonance (SPR). In comparison with pristine Bi2WO6 and WO3/Bi2WO6, Ag/WO3/Bi2WO6 exhibits a better photocatalytic activity for removal of gaseous chlorobenzene under simulated sunlight irradiation. The conversion efficiency of 2% Ag/WO3/Bi2WO6 heterojunction is 2.5 and 1.9 times higher than those of the pristine Bi2WO6 and WO3/Bi2WO6 samples, respectively. The improved photocatalytic activity is mainly attributed to the formation of three-component heterojunction with the Z-scheme structure and SPR effect of Ag NPs, which could not only increase absorption of visible light, but also promote the separation efficiency of photogenerated electrons and holes in the hybrids.
TL;DR: The onset potential and charge separation of bismuth vanadate photoanode water splitting performances are improved by work function tuning and heterojunction engineering.
Abstract: We herein demonstrate the unusual effectiveness of two strategies in combination to enhance photoelectrochemical water splitting. First, the work function adjustment via molybdenum (Mo) doping significantly reduces the interfacial energy loss and increases the open-circuit photovoltage of bismuth vanadate (BiVO4) photoelectrochemical cells. Second, the creation and optimization of the heterojunction of boron (B) doping carbon nitride (C3N4) and Mo doping BiVO4 to enforce directional charge transfer, accomplished by work function adjustment via B doping for C3N4, substantially boost the charge separation of photo-generated electron-hole pairs at the B-C3N4 and Mo-BiVO4 interface. The synergy between the above efforts have significantly reduced the onset potential, and enhanced charge separation and optical properties of the BiVO4-based photoanode, culminating in achieving a record applied bias photon-to-current efficiency of 2.67% at 0.54 V vs. the reversible hydrogen electrode. This work sheds light on designing and fabricating the semiconductor structures for the next-generation photoelectrodes. While photoelectrodes represent a promising solar-to-fuel conversion technology, material challenges limit performances. Here, authors improve the onset potential and charge separation of bismuth vanadate photoanode water splitting performances by work function tuning and heterojunction engineering.
TL;DR: In this article, a modified electrospinning method utilizing three assisted electrodes for nanofiber collection was proposed to achieve uniformly aligned and millimeter-long ZnO and NiO arrays (more than 90% of nanofibers aligned to within ±4° of the desired direction).
Abstract: Uniformly aligned electrospun nanofiber arrays are important building blocks for high-performance functional devices and device arrays. However, it remains a challenge to prepare perfectly aligned and large area nanofiber arrays using common electrospinning. In this work, a modified electrospinning method utilizing three assisted electrodes for nanofiber collection was proposed to achieve uniformly aligned and millimeter-long ZnO and NiO nanofiber arrays (more than 90% of nanofibers aligned to within ±4° of the desired direction), which were further fabricated into ZnO/NiO heterojunction arrays with a density of 106 cm−2. Photodetectors (PDs) based on the as-prepared ZnO/NiO heterojunction arrays exhibited excellent ultraviolet (UV) selective and self-powered detection properties because of the properly matched energy bands of ZnO and NiO. A maximum responsivity of 0.415 mA W−1 and a short rise/decay time of 7.5 s/4.8 s at 0 V bias of the device markedly outstripped the reference ZnO nanofiber array device. The three-assisted-electrode electrospinning method of this work offers new chances in novel nanostructure design and high-performance device fabrication.
TL;DR: The 3D g-C3N4/TiO2 heterojunction photocatalyst with separation free can facilitate the potential application in the treatment of water pollution.
TL;DR: This work provides a guide for exploration of perovskite materials in next-generation optoelectronics, such as photoelectric detectors or photocatalyst, and demonstrates increased photocurrent generation in response to visible light and X-ray illumination.
Abstract: All-inorganic CsPbX3 (X = Cl, Br or I) perovskite nanocrystals have attracted extensive interest recently due to their exceptional optoelectronic properties. In an effort to improve the charge separation and transfer following efficient exciton generation in such nanocrystals, novel functional nanocomposites were synthesized by the in situ growth of CsPbBr3 perovskite nanocrystals on two-dimensional MXene nanosheets. Efficient excited state charge transfer occurs between CsPbBr3 NCs and MXene nanosheets, as indicated by significant photoluminescence (PL) quenching and much shorter PL decay lifetimes compared with pure CsPbBr3 NCs. The as-obtained CsPbBr3/MXene nanocomposites demonstrated increased photocurrent generation in response to visible light and X-ray illumination, attesting to the potential application of these heterostructure nanocomposites for photoelectric detection. The efficient charge transfer also renders the CsPbBr3/MXene nanocomposite an active photocatalyst for the reduction of CO2 to CO and CH4. This work provides a guide for exploration of perovskite materials in next-generation optoelectronics, such as photoelectric detectors or photocatalyst.
TL;DR: In this article, a 2D/2D hierarchical structure of CuInS2/g-C3N4 composite was developed to enlarge the contact region in the heterojunction interface and provide more active reaction sites.
TL;DR: The cutting‐edge research progress in 2D/2D heterojunctions and heterostructures is highlighted with a specific emphasis on synthetic strategies, reaction mechanism, and applications in catalysis (photocatalysis, electrocatalysis, and organic synthesis).
Abstract: 2D layered materials with atomic thickness have attracted extensive research interest due to their unique physicochemical and electronic properties, which are usually very different from those of their bulk counterparts. Heterojunctions or heterostructures based on ultrathin 2D materials have attracted increasing attention due to the integrated merits of 2D ultrathin components and the heterojunction effect on the separation and transfer of charges, resulting in important potential values for catalytic applications. Furthermore, 2D/2D heterostructures with face-to-face contact are believed to be a preferable dimensionality design due to their large interface area, which would contribute to enhanced heterojunction effect. Here, the cutting-edge research progress in 2D/2D heterojunctions and heterostructures is highlighted with a specific emphasis on synthetic strategies, reaction mechanism, and applications in catalysis (photocatalysis, electrocatalysis, and organic synthesis). Finally, the key issues and development perspectives in the applications of 2D/2D layered heterojunctions and heterostructures in catalysis are also discussed.
TL;DR: In this paper, a flexible and conducting photocatalyst based on NwO3/Ce2S3 nanotube bundles was synthesized and successfully immobilized on a carbon textile, resulting in a flexible photocatalytic degradation of organic pollutants.
Abstract: The availability of robust, versatile, and efficient photocatalysts is the main bottleneck in practical applications of photocatalytic degradation of organic pollutants. Herein, N‐WO3/Ce2S3 nanotube bundles (NBs) are synthesized and successfully immobilized on a carbon textile, resulting in a flexible and conducting photocatalyst. Due to the large interfacial area between N‐WO3 and Ce2S3, the interwoven 3D carbon architecture and, more importantly, the establishment of a heterojunction between N‐WO3 and Ce2S3, the resultant photocatalyst exhibits excellent light absorption capacity and superior ability to separate photoinduced electron–hole pairs for the photocatalytic degradation of organic compounds in air and water media. Theoretical calculations confirm that the strong electronic interaction between N‐WO3 and Ce2S3 can be beneficial to the enhancement of the charge carrier transfer dynamics of the as‐prepared photocatalyst. This work provides a new protocol for constructing efficient flexible photocatalysts for application in environmental remediation.
TL;DR: In this article, twisted bilayer tungsten diselenide (tWSe2), a semiconducting transition metal dichalcogenide (TMD), the authors observed correlated states over a continuum of angles, spanning 4 degree to 5.1 degree.
Abstract: Emergent quantum phases driven by electronic interactions can manifest in materials with narrowly dispersing, i.e. "flat", energy bands. Recently, flat bands have been realized in a variety of graphene-based heterostructures using the tuning parameters of twist angle, layer stacking and pressure, and resulting in correlated insulator and superconducting states. Here we report the experimental observation of similar correlated phenomena in twisted bilayer tungsten diselenide (tWSe2), a semiconducting transition metal dichalcogenide (TMD). Unlike twisted bilayer graphene where the flat band appears only within a narrow range around a "magic angle", we observe correlated states over a continuum of angles, spanning 4 degree to 5.1 degree. A Mott-like insulator appears at half band filling that can be sensitively tuned with displacement field. Hall measurements supported by ab initio calculations suggest that the strength of the insulator is driven by the density of states at half filling, consistent with a 2D Hubbard model in a regime of moderate interactions. At 5.1 degree twist, we observe evidence of superconductivity upon doping away from half filling, reaching zero resistivity around 3 K. Our results establish twisted bilayer TMDs as a model system to study interaction-driven phenomena in flat bands with dynamically tunable interactions.
TL;DR: In this paper, a brief overview of CoFe2O4 as a semiconductor photocatalyst is presented and ferromagnetic behaviour of co-feathers is also discussed.
TL;DR: In this paper, a low-bandgap tin-lead iodide perovskite heterojunction is used to extract holes and the hole transport layer is removed to avoid a reaction with the most popular hole contact.
Abstract: Low bandgap tin–lead iodide perovskites are key components of all-perovskite tandem solar cells, but can be unstable because tin is prone to oxidation. Here, to avoid a reaction with the most popular hole contact, we eliminated polyethylenedioxythiophene:polystyrenesulfonate as a hole transport layer and instead used an upward band offset at an indium tin oxide–perovskite heterojunction to extract holes. To suppress oxidative degradation, we improved the morphology to create a compact and large-grained film. The tin content was kept at or below 50% and the device capped with a sputtered indium zinc oxide electrode. These advances resulted in a substantially improved thermal and environmental stability in a low bandgap perovskite solar cell without compromising the efficiency. The solar cells retained 95% of their initial efficiency after 1,000 h at 85 °C in air in the dark with no encapsulation and in a damp heat test (85 °C with 85% relative humidity) with encapsulation. The full initial efficiency was maintained under operation near the maximum power point and near 1 sun illumination for over 1,000 h. Low bandgap tin–lead perovskites are crucial to making efficient all-perovskite tandem solar cells but have so far shown poor stability. By removing the hole transport layer and improving film morphology, Prasanna et al. demonstrate a low-gap perovskite solar cell that is stable for 1,000 h under heat, light and atmospheric conditions.
TL;DR: In this article, a high photoresponsivity of ∼42.1 AW-1 (at 10.6 μm) was demonstrated, which is an order of magnitude higher than the current record of platinum diselenide.
Abstract: A long-wavelength infrared photodetector based on two-dimensional materials working at room temperature would have wide applications in many aspects in remote sensing, thermal imaging, biomedical optics, and medical imaging. However, sub-bandgap light detection in graphene and black phosphorus has been a long-standing scientific challenge because of their low photoresponsivity, instability in the air, and high dark current. In this study, we report a highly sensitive, air-stable, and operable long-wavelength infrared photodetector at room temperature based on PdSe2 phototransistors and their heterostructure. A high photoresponsivity of ∼42.1 AW-1 (at 10.6 μm) was demonstrated, which is an order of magnitude higher than the current record of platinum diselenide. Moreover, the dark current and noise power density were suppressed effectively by fabricating a van der Waals heterostructure. This work fundamentally contributes to establishing long-wavelength infrared detection by PdSe2 at the forefront of long-IR two-dimensional-materials-based photonics.
TL;DR: Ag bridged 2D/2D Bi5FeTi3O15/ultrathin g-C3N4 Z-scheme heterojunction photocatalyst with powerful interfacial charge transfer has been synthesized via a facile ultrasound method coupled with photo-reduction strategy for efficiently photocatalytic degradation of antibiotics.
Abstract: Heterojunction photocatalysts have attracted widespread interest in photocatalysis because of their high-efficiency interfacial charge-transfer characteristics of nanoarchitectures. In this study, ...