Heterojunction Arrays Research Articles

Enhanced performance of UV photodetector based on ZnO nanorod arrays via TiO2 as electrons trap layer

As a commonly used substrate and matrix material in the construction of high performance ultraviolet photodetector, ZnO nanorod arrays have attached much attention due to their efficiency electron transmission channels and high stability. However, they also have the problem of slow response speed inevitably. In this work, TiO2/ZnO nanorod arrays heterojunction structure was prepared and used to construct ultraviolet photodetector. The obtained heterojunction photodetector has a higher on/off ratio (>1000) and shorter rise/decay time (6.1/3.7 s) compared with that of photodetector based on ZnO nanorod arrays (on/off ratio ∼10 and decay time >20 s). The enhanced response speed is caused by the traps of the electron in TiO2 layer, which can accelerate the decay of current in the OFF state. The obtained results provide a new sight for the further development of the optoelectronic devices based on ZnO nanorod arrays in future.

Construction of Z-scheme WO3-Cu2O nanorods array heterojunction for efficient photocatalytic degradation of methylene blue

The design of tightly interfacial contact and efficient separation of photogenerated electrons and holes is an effective strategy to improve the activity of heterojunction photocatalysts. Here, a Z-scheme core–shell WO3-Cu2O nanorods array has been synthesized by one-step hydrothermal and electrochemical deposition method for photocatalytic degradation of methylene blue under visible light. The effects of electrodeposition time on the structure, morphology, and photocatalytic performance of the products were investigated in detail. It was found that the optimum Cu2O deposition time was 120 s. The UV–Vis DRS results revealed that the deposited Cu2O nanoparticles onto the surface of WO3 enhance the ability and expand the range of visible light absorption, which inhibit the recombination of photogenerated electrons and holes. Moreover, the photoelectrochemical measurement analyses show that the photocurrent response of heterojunction was significantly enhanced and the interfacial charge-transfer resistance was lowered, which further improve the separation of photogenerated carriers. Also, Z-scheme photocatalytic degradation mechanism was investigated and discussed. In consequence, the WO3-Cu2O-120 s photocatalyst showed the highest reaction rate, which was nearly 2 times than that of pristine WO3. The Z-scheme WO3-Cu2O core–shell heterojunction contribute to efficient spatial charge separation, retained the strong redox ability of photogenerated electrons-holes, which improved the photocatalytic activity.

Epitaxial Topological Insulator Bi2Te3 for Fast Visible to Mid-Infrared Heterojunction Photodetector by Graphene As Charge Collection Medium.

Three dimensional topological insulators have a thriving application prospect in broadband photodetectors due to the possessed topological quantum states. Herein, a large area and uniform topological insulator bismuth telluride (Bi2Te3) layer with high crystalline quality is directly epitaxial grown on GaAs(111)B wafer using a molecular beam epitaxy process, ensuring efficient out-of-plane carriers transportation due to reduced interface defects influence. By tiling monolayer graphene (Gr) on the as-prepared Bi2Te3 layer, a Gr/Bi2Te3/GaAs heterojunction array prototype was further fabricated, and our photodetector array exhibited the capability of sensing ultrabroad photodetection wavebands from visible (405 nm) to mid-infrared (4.5 μm) with a high specific detectivity (D*) up to 1012 Jones and a fast response speed at about microseconds at room temperature. The enhanced device performance can be attributed to enhanced light-matter interaction at the high-quality heterointerface of Bi2Te3/GaAs and improved carrier collection efficiency through graphene as a charge collection medium, indicating an application prospect of topological insulator Bi2Te3 for fast-speed broadband photodetection up to a mid-infrared waveband. This work demonstrated the potential of integrated topological quantum materials with a conventional functional substrate to fabricate the next generation of broadband photodetection devices for uncooled focal plane array or infrared communication systems in future.

One-body style photo-supercapacitors based on Ni(OH)2/TiO2 heterojunction array: High specific capacitance and ultra-fast charge/discharge response

In this work, a type of “one-body” photo-supercapacitors (PSs) with high specific capacitance and ultrafast response of charge/discharge is constructed, in which TiO 2 plays a role of photoelectric conversion material and Ni(OH) 2 serves as the energy storage material. The results show that the discharge specific capacitance of 22.9 mF/cm 2 and the charge and discharge response time of 40 and 30 ms in this type of PSs is prior to that in previous works. The large discharge specific capacitance and ultrafast response mainly attribute to the direct storage and release of charges in loose Ni(OH) 2 structure. This study provides a simple fabrication process of PSs with high performance for the direct storage of solar energy and offers reference for the application of other materials in PSs. • The morphology of Ni(OH) 2 on TiO 2 nanorod arrays could be regulated precisely. • TiO 2 nanorod arrays loaded with flower-like Ni(OH) 2 showed p-n junction effect. • Photo charge and dark discharge can be performed by the same working electrode. • The PSs showed ultrafast response, high specific capacitance and stability.

High performance self-powered UV–visible photodetectors based on TiO2/graphene/ZnIn2S4/electrolyte heterojunctions

TiO2 nanorods (TNRs)/graphene (G)/ZnIn2S4 (ZIS)/electrolyte heterojunction arrays were synthesized via a three-step synthesis method and applied as an ultraviolet (UV)-visible self-powered photodetector (SPPD). At zero bias, the SPPD exhibited high responsivities of 13.79 mA/W for UV light and 0.39 mA/W for visible light, respectively. Under UV irradiation, the SPPD showed a short rise time of 5 ms and a decay time of 10 ms. TNRs offered an effective pathway for electron transport, and the type-II energy band structure formed by ZIS stacking improved the response of TNRs to UV and visible light significantly. Furthermore, the graphene intermediate layer accelerated the separation and transfer of carriers due to excellent charge collection ability. Therefore, the TNRs/G/ZIS/electrolyte heterojunction arrays have great potential for application in UV–visible SPPD.

Capillary-Confinement Crystallization for Monolayer Molecular Crystal Arrays.

Organic single-crystalline semiconductors are highly desired for the fabrication of integrated electronic circuits, yet their uniform growth and efficient patterning is a huge challenge. Here, a general solution procedure named the "soft-template-assisted-assembly method" is developed to prepare centimeter-scale monolayer molecular crystal (MMC) arrays with precise regulation over their size and location via a capillary-confinement crystallization process. It is remarkable that the field-effect mobility of the array is highly uniform, with variation less than 4.4%, which demonstrates the most uniform organic single-crystal arrays ever reported so far. Simulations based on fluid dynamics are carried out to understand the function mechanism of this method. Thanks to the ultrasmooth crystalline orientation surface of MMCs, high-quality p-n heterojunction arrays can be prepared by weak epitaxy growth of n-type material atop the MMC. The p-n heterojunction field-effect transistors show ambipolar characteristics and the corresponding inverters constructed by these heterojunctions exhibit a competitive gain of 155. This work provides a general strategy to realize the preparation and application of logic complementary circuits based on patterned organic single crystals.

Design strategies of ZnO heterojunction arrays towards effective photovoltaic applications

AbstractZnO nanorods (NRs) heterojunction arrays have been widely used in photovoltaic cells owing to the outstanding photoelectrical chracteristics, high stability and low cost. The NRs arrays structure can integrate multiple functional components, so that it can exhibit more excellent physical and chemical properties that even independent components do not possess. The design of heterojunction nanostructures can effectively solve the problems of light absorption and carrier transport. First, the synthesis methods of ZnO NRs and their heterojunction arrays were systematically introduced, including traditional chemical vapor deposition (CVD), electrodeposition, hydrothermal method, and so on, the different structures and properties of ZnO NRs heterojunctions were analyzed. Then, the selected materials could be further processed and assembled into NRs array heterojunction with integrated functions were discussed. The strategies of maximizing energy conversion performance (structure optimization, heterojunction, surface plasmon resonance, and doping) were emphatically summarized. In addition, the research progress of ZnO NRs and their heterojunctions in photoelectric energy conversion system were summarized, and the application potential of combining nanostructure design with solar cells was summarized. Finally, the challenges and future development prospects of ZnO NRs and their heterojunction arrays in photovoltaic conversion were pointed out.

In situ integration of Te/Si 2D/3D heterojunction photodetectors toward UV-vis-IR ultra-broadband photoelectric technologies.

Over the past decade, 2D elemental semiconductors have emerged as an ever-increasingly important group in the 2D material family due to their simple crystal structures and compositions, and versatile physical properties. Taking advantage of the relatively small bandgap, outstanding carrier mobility, high air-stability and strong interactions with light, 2D tellurium (Te) has emerged as a compelling candidate for use in ultra-broadband photoelectric technologies. In this study, high-quality centimeter-scale Te nanofilms have been successfully produced by exploiting pulsed-laser deposition (PLD). By performing deposition on pre-patterned SiO2/Si substrates, a Te/Si 2D/3D heterojunction array is formed in situ. To our delight, taking advantage of the relatively small bandgap of Te, the Te/Si photodetectors demonstrate an ultra-broadband photoresponse from ultraviolet to near-infrared (370.6 nm to 2240 nm), enabling them to serve as important alternatives to conventional 2D materials such as MoS2. In addition, an outstanding on/off ratio of ∼108 and a fast response rate (a response/recovery time of 3.7 ms/4.4 ms) are achieved, which is associated with the large band offset and strong interfacial built-in electric field that contribute to suppressing the dark current and separating photocarriers. Beyond these, a 35 × 35 matrix array has been successfully constructed, where the devices exhibit comparable properties, with a production yield of 100% for 100 randomly tested devices. The average responsivity, external quantum efficiency and detectivity reach 249 A W-1, 76 350% and 1.15 × 1011 Jones, respectively, making the Te/Si devices among the best-performing 2D/3D heterojunction photodetectors. On the whole, this study has established that PLD is a promising technique for producing high-quality Te nanofilms with good scalability, and the Te/Si 2D/3D heterojunction provides a promising platform for implementing high-performance ultra-broadband photoelectronic technologies.

Homologous NiCoP@NiFeP heterojunction array achieving high-current hydrogen evolution for alkaline anion exchange membrane electrolyzers

The homologous heterojunction array was constructed to achieve dual-regulation for charge distribution and mass transport. In a real AEM electrolyzer, our catalysts surpassed RuO2‖Pt/C activity at high current (1000 mA cm−2 @ ∼1.93 V) over 100 h.

Faradaic Heterojunction Arrays Enable Fully Solar-Powered Energy Conversion and Storage via High-Efficiency Interface Charge-Transfer

Faradaic Heterojunction Arrays Enable Fully Solar-Powered Energy Conversion and Storage via High-Efficiency Interface Charge-Transfer

Plasmonic Au-decorated hierarchical p-NiO/n-ZnO heterostructure arrays for enhanced photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting is one of most effective ways for converting solar energy into chemical energy. Single-component semiconductor structures as photoanodes always suffer from poor ability to capture photons and serious recombination of electron-hole pairs, which pose inferior photocurrent performance. In order to increase the photocurrent density, here, a hierarchical heterostructure of p-NiO/n-ZnO decorated with Au nanoparticles (NPs) was designed and prepared as photoanodes. Specifically, a n-ZnO nanorods@nanodisks (NRs@NDs) constructure was completely coated with a thin p-NiO layer to construct a miniature p-n junction arrays, and plasmonic Au NPs were attached on the surface of the thin p-NiO layer. Benefiting from such p-n heterostructure, p-NiO/n-ZnO NRs@NDs heterojunction arrays exhibited excellent rectifying behaviour for their I–V and semi-log I–V curves. Moreover, the photoanode of p-NiO/n-ZnO NRs@NDs had a lower emission intensity than that of n-ZnO NRs@NDs, which indicated the effective inhibition of electron-hole pairs recombination. More importantly, the photocurrent density of Au/p-NiO/n-ZnO NRs@NDs was measured to be as high as 1.78 mA cm −2 , outperforming that of pure n-ZnO NRs@NDs (0.61 mA cm −2 ). This method provides a green, and highly efficient photoanode for the PEC water splitting. • A micro p-NiO/n-ZnO NRs@NDs heterostructure decorated with plasmonic Au NPs was prepared. • p-NiO/n-ZnO NRs@NDs heterojunction arrays exhibited excellent rectifying behaviour. • The synergetic effect of inner electric field of p-n junctions and plasmonic Au effectively inhibit charge recombination. • The photocurrent density increased by approximately 2.9-fold compared to that of pure n-ZnO NRs@NDs.

Low‐temperature synthesis of ZnO/ZnS/CuS heterojunction based on solution‐processed nanosheet array with enhanced photocatalytic activity

AbstractZnO/ZnS/CuS net‐like nanosheet (NS) heterojunction array was fabricated via a simple solution method at a low temperature. Morphology and structure of ZnO/ZnS/CuS NS were characterized by scanning electron microscope (SEM) and Transmission electron microscope (TEM). With tiny particles attaching on the rough surface, the thin ZnO/ZnS/CuS NS grew vertically and arranged regularly on Al substrate, providing large effective illumination area and massive active sites. Elemental composition and valence state were confirmed with energy dispersive X‐ray spectrometry and X‐ray photoelectron spectroscopy (XPS), respectively. The UV–vis absorbance spectra indicated that the absorption range of ZnO NS was expanded to the visible region effectively, and the original absorption intensity in the ultraviolet region was also improved after being coated with ZnS and CuS. Photocatalytic activity tests of ZnO, ZnO/ZnS, and ZnO/ZnS/CuS NS were carried out with methyl orange as a simulated pollutant, in which ZnO/ZnS/CuS heterojunction showed great enhancement when making comparison with pure ZnO and ZnO/ZnS NS. After five reuse cycles, photocatalytic performance could still be maintained well, indicating the good catalytic stability. Finally, a probable photocatalytic mechanism was also discussed.

Conformal MoS2/Silicon Nanowire Array Heterojunction with Enhanced Light Trapping and Effective Interface Passivation for Ultraweak Infrared Light Detection

Abstract2D layered materials have attracted considerable attention for fabricating IR photodetectors. However, performance, especially for weak signal detection, of these IR photodetectors is often limited by the low absorbance of the very thin active materials as well as unsuppressed dark currents. Herein, a photodetector with high sensitivity for ultraweak IR signals based on a conformal MoS2/silicon nanowire array heterojunction with an ultrathin Al2O3 interfacial passivation layer is reported. The conformal light‐trapping nanoarray structure can greatly enhance broadband IR absorption, while the Al2O3 layer can suppress interface carrier recombination effectively and thus lower reverse dark current. The photodetectors exhibit broadband photoresponse ranging from 300 to 1600 nm, low noise current of 0.11 pA Hz−1/2, large responsivity up to 0.61 A W−1 at zero bias voltage, and high specific detectivity of 1011–1012 Jones. Significantly, the devices are capable of detecting ultraweak IR signals (e.g., 100 pW at 808 nm and 3 nW at 1310/1550 nm) with high on–off ratios without applying any external bias. This work proposes a new strategy to enhance light absorption of 2D materials and construct high‐quality junction based on them, which is promising for low‐cost and high‐performance optoelectronic devices.

Fabrication of Z-Scheme TiO2/SnS2/MoS2 ternary heterojunction arrays for enhanced photocatalytic and photoelectrochemical performance under visible light

In the current work, Z-scheme TiO2/SnS2/MoS2 ternary heterojunction arrays were synthesised on a fluorine-doped tin oxide conductive glass by using a facile hydrothermal technique. The microstructures, energy band structures, and photocatalytic performances of TiO2, TiO2/SnS2, and TiO2/MoS2 were investigated. The results revealed that for methylene blue, ternary TiO2/SnS2/MoS2 exhibited considerably enhanced photocatalytic efficiency (∼79%) and the optimal transient current density (∼0.92 ​mA/cm2) under visible-light irradiation; these two values were four and eight times higher than those exhibited by TiO2, respectively. The highly improved photocatalytic and photoelectrochemical performance could be attributed to the unique microstructure and band alignment of TiO2/SnS2/MoS2. These attributes can be explained as follows: (i) the large specific surface area offers numerous active sites, (ii) the modulation of the narrow-band SnS2 and MoS2 broadens visible-light response, and (iii) the Z-scheme heterojunction effectively restricts the bulk recombination and spatially separates the photogenerated electron–hole (e−–h+) pairs.

High‐performance optical noncontact controlling system based on broadband PtTex/Si heterojunction photodetectors for human–machine interaction

AbstractNoncontact interaction systems have attracted considerable research attention in recent years because of convenient operation, sterility, and injury prevention. However, the insufficient sensing distance and weak robustness of noncontact interaction systems for complex environments limit their practical applications. Here, we designed an integrated optical noncontact controlling system (ONCS) based on PtTex/Si optoelectronic heterojunction array. Broadband sensitive photoresponse is realized at zero bias voltage, with excellent detectivity and responsivity, boosting the noncontact sensing distance to at least 150 mm. Consequently, the system can perform noncontact detection, encoding, and control by recognizing shadow‐induced spatiotemporal sequence changes in heterojunction array photocurrents. As a proof of concept, different interactive functions have been demonstrated with good accuracy and robustness by encoding finger movement above the ONCS. This study provides a new perspective for constructing high‐performance noncontact interaction systems. image

Manipulating Hot-Electron Injection in Metal Oxide Heterojunction Array for Ultrasensitive Surface-Enhanced Raman Scattering.

Efficient photoinduced charge transfer (PICT) resonance is crucial to the surface-enhanced Raman scattering (SERS) performance of metal oxide substrates. Herein, we venture into the hot-electron injection strategy to achieve unprecedented enhanced PICT efficiency between substrates and molecules. A heterojunction array composed of plasmonic MoO2 and semiconducting WO3-x is designed to prove the concept. The plasmonic MoO2 generates intense localized surface plasmon resonance under illumination, which can generate near-field Raman enhancement as well as accompanied plasmon-induced hot-electrons. The hot-electron injection in direct interfacial charge transfer and plasmon-induced charge transfer process can effectively promote the PICT efficiency between substrates and molecules, achieving a record Raman enhancement factor among metal oxide substrates (2.12 × 108) and the ultrasensitive detection of target molecule down to 10-11 M. This work demonstrates the possibility of hot-electron manipulation to realize unprecedented Raman enhancement in metal oxides, offering a cutting-edge strategy to design high-performance SERS substrates.

Leaky Mode Resonance-Induced Sensitive Ultraviolet Photodetector Composed of Graphene/Small Diameter Silicon Nanowire Array Heterojunctions.

Ultraviolet photodetectors (UVPDs) based on wide band gap semiconductors (WBSs) are important for various civil and military applications. However, the relatively harsh preparation conditions and the high cost are unfavorable for commercialization. In this work, we proposed a non-WBS UVPD by using a silicon nanowire (SiNW) array with a diameter of 45 nm as building blocks. Device analysis revealed that the small diameter SiNW array covered with monolayer graphene was sensitive to UV light but insensitive to both visible and infrared light illumination, with a typical rejection ratio of 25. Specifically, the responsivity, specific detectivity, and external quantum efficiency under 365 nm illumination were estimated to be 0.151 A/W, 1.37 × 1012 Jones, and 62%, respectively, which are comparable to or even better than other WBS UVPDs. Such an abnormal photoelectrical characteristic is related to the HE1m leaky mode resonance (LMR), which is able to shift the peak absorption spectrum from near-infrared to UV regions. It is also revealed that this LMR is highly dependent on the diameter and the period of the SiNW array. These results show narrow band gap semiconductor nanostructures as promising building blocks for the assembly of sensitive UV photodetectors, which are very important for various optoelectronic devices and systems.

Tuning hydrogen binding energy by interfacial charge transfer enables pH-universal hydrogen evolution catalysis of metal phosphides

Transition metal phosphides (TMPs) are new-generation electrocatalysts for Hydrogen evolution reaction (HER), but the performance is still far less than that of noble-metal catalysts due to the strong interactions between the adsorbed H and the intensely electronegative P. Herein, we propose a controllable phosphorization strategy to construct phosphorus-rich and metal-rich (Fe, Ni)3P/NiCoP heterojunction arrays to tune the hydrogen binding energy. The homologous elements distribution and well defined configuration ensure the low Schottky barriers and effective exposure of the catalytic active sites. Theoretical calculations prove that the interfacial charge transfer can modulate the charge density around the active sites for mediating the hydrogen adsorption energy. As expected, the constructed (Fe,Ni)3P/NiCoP catalysts exhibit extraordinary pH-universal Pt-like activity and high stability, with overpotentials of 50.9, 70.5 and 52.3 mV at a current density of 10 mA cm−2 in acidic, neutral and alkaline electrolytes, respectively. Our finding builds a legible connection between atomic/interface/electronic structure and intrinsic properties for designing high-efficiency catalytic materials.

Interfacial electronic modulation of CoP-CoO p-p type heterojunction for enhancing oxygen evolution reaction

Heterojunction can effectively improve oxygen evolution reaction (OER) activity by regulating the interfacial electronic structure of catalysts. However, p-p type heterojunction OER catalysts have obtained less attention, and the corresponding catalytic mechanisms are unclear either. Herein, the self-supported CoP-CoO p-p type heterojunction arrays are fabricated on carbon cloth substrate (CoP-CoO/CC). Band structure analysis shows that the formation of p-p heterojunction can drive the electrons from CoO to flow into CoP. This electronic modulation contributes to positively charged regions on the CoO and enhances the OH− adsorption during OER, proven by X-ray photoelectron spectroscopy and methanol molecular detection, respectively. As a result, the CoP-CoO/CC electrode only needs 210 mV overpotential to drive a current density of 10 mA cm−2 in an alkaline medium, superior to the most reported OER catalysts. Additionally, the CoP-CoO/CC also exhibits an ideal hydrogen evolution reaction response, and a water splitting system has been successfully constructed which can drive a 10 mA cm−2 within 1.65 V. This study supplies insight for catalytic origins p-p type heterojunctions OER catalyst, which provides a reference value for the efficient and reasonable design of heterojunction catalysts.

Symmetric supercapacitors composed of ternary metal oxides (NiO/V2O5/MnO2) nanoribbon electrodes with high energy storage performance

Supercapacitors with improved specific capacitance, long cycling life, high power density and energy density are fabricated to close the gap between traditional and emerging energy storage. We develop interactive ternary metal oxides nano-ribbon electrodes used to assemble symmetric supercapacitor. The well-aligned vanadium oxide ribbon arrays act as the matrix, growing from nickel oxide/nickel substrate and then being grafted by manganese oxide nanoparticles. These tri-metallic oxides are formed in a cost-effective and green hydrothermal chemistry. The electrodes composed of ribbon arrays retain their crystallographic structure during charging and discharging processes, enabling steadiness at 83.6 % after 10,000 cycles. These as-prepared electrodes demonstrate a specific capacitance of 788 F g−1 at 5 mV s−1. The symmetrical supercapacitors are assembled using triple component electrodes, achieving a high energy density of 138 W h kg−1 at a power density of 450 W kg−1. These binderless single-cell devices are reported with a simplified design showing 10–20 times higher energy density in comparison with reported results of the V2O5-MnO2 system. The nanografting results in reactive interfaces with interpenetrating channels for efficient ion transport and electron conduction. The advances to design nanostructured supercapacitor materials are based on these heterojunction arrays to enhance their supercapacitive performances.