Heterojunction Nanowire Arrays Research Articles

High light utilization of double-layer InxGa1−xN heterojunction nanowire array photocathodes

We propose a photocathode structure based on InxGa1−xN heterojunction nanowire array to enhance solar energy utilization efficiency. Compared with single-component InGaN nanowires, heterojunction nanowires can achieve higher effective quantum efficiency through the introduction of built-in electric field. This means that it has higher actual performance than previous studies. The maximum effective quantum efficiency of 300 nm-300 nm In0.5Ga0.5N-In0.57Ga0.43N heterojunction nanowires can reach 40.8 % when the incident light is obliquely incident at an angle of 70°. In addition, the external electric field can significantly help the heterojunction nanowires maintain higher actual performance over a longer wavelength range. This research is expected to provide theoretical support for the development and performance improvement of high-performance solar photocathode.

A Highly Active and Durable Hierarchical Electrocatalyst for Large-Current-Density Water Splitting.

Designing bifunctional catalysts with high current densities under industrial circumstances is crucial to propelling hydrogen energy with a boost from fundamental to practical application. In this work, heterojunction nanowire arrays consisting of manganese oxide and cobalt phosphide (denoted as MnO-CoP/NF) are designed to meet the industrial demand by regulating the synergic mass transport and electronic structure coupling with numerous nano-heterogeneous interfaces. The optimal MnO-CoP/NF electrode exhibits remarkable bifunctional electrocatalytic performance with overpotentials of 259.5 mV for hydrogen evolution at a large current density of 1000 mA cm-2 and 392.2 mV for oxygen evolution at 1500 mA cm-2. Moreover, the MnO-CoP/NF electrode demonstrates superior durability and an ultralow voltage of 1.76 V at 500 mA cm-2, outperforming that of a commercial RuO2||Pt/C electrode. This work sheds light on the design of metallic heterostructures with optimized interfacial electronic structures and a high abundance of active sites for practical industrial water splitting applications.

Chiral 2D/Quasi‐2D Perovskite Heterojunction Nanowire Arrays for High‐Performance Full‐Stokes Polarization Detection

The realization of Stokes photodetectors accelerates the development of various modern optoelectronic applications. Chiral 2D perovskites with intrinsic chiral optical activity and superior carrier mobility are promising for next‐generation full‐Stokes polarization detection. So far, most of the chiral 2D metal‐halide perovskite‐based photodetectors suffer from limited discrimination of circularly polarized light due to the high exciton recombination rate in single‐phase perovskite, impeding the accurate measurement for Stokes parameters. Here, an on‐chip Stokes photodetector based on chiral 2D/quasi‐2D perovskite lateral heterojunction nanowire (NW) arrays with high polarization selectivity and photoresponsiveness is reported. The highly‐aligned heterojunction NW arrays not only build up a built‐in electric field for enhanced chiral discrimination, but also possess intrinsic anisotropy that enables outstanding linear polarization response. On this basis, the device exhibits reliable ability for polarization detection with a high anisotropy factor of 0.38, an outstanding polarized ratio of 1.5, and an excellent responsivity of 22.14 A W−1. These results will provide useful enlightenment for direct full‐Stokes polarization detection in optoelectronic integrated circuits.

Synergistic Tuning of CoO/CoP Heterojunction Nanowire Arrays as Efficient Bifunctional Catalysts for Alkaline Overall Water Splitting.

Bifunctional electrocatalysts with superior activity and durability are of great importance for electrocatalytic water splitting. Herein, hierarchical structured CoO/CoP heterojunctions are successfully designed as highly efficient and freestanding bifunctional electrocatalysts toward overall water splitting. The unique microstructure combining two-dimensional nanosheets with one-dimensional nanowires enables numerous exposed active sites, shortened ion-diffusion pathways, and enhanced conductivity, significantly improving performance. Such freestanding electrodes achieve high current density over 400mA cm-2 at low overpotentials and have exceptional electrocatalytic activity as well as long-term durability for both hydrogen and oxygen evolution reactions under alkaline conditions. Remarkably, a high current density of 20mA cm-2 is generated at a low cell voltage of 1.56V in an alkaline water electrolyzer, originating from synergistic interactions between CoO and CoP exposing active sites and facilitating charge transfer and enhancing kinetics. This work provides new insight into designing low-cost but high-performance bifunctional electrocatalysts for practical water splitting.

3D hierarchically branched Cu2S/ZnO heterojunction nanowire arrays for enhanced solar water splitting

3D hierarchically branched Cu2S/ZnO heterojunction nanowire arrays for enhanced solar water splitting

Fast-response self-powered flexible transparent ultraviolet photodetectors based on a CuO/ZnO nanowire array heterojunction

A self-powered flexible transparent ultraviolet photodetector based on a CuO/ZnO nanowire array heterojunction is successfully fabricated, which exhibits fast-response speed, high transparency and superior mechanical stability.

A dual-band graphene/silicon nanowire array heterojunction photodetector induced by leaky mode resonances

A leaky mode resonance induced dual-band photodetector is fabricated using graphene/silicon nanowire array heterojunctions, which exhibit two peak responsivities at 430 nm and 660 nm.

Controlling Micro-Architecture in Dendritic Cu-Ni Heterostructures for Energy Storage and Conversion Applications

A simple and innovative technique was developed in this work creating a stable, fully established porous three dimensional (3D) dendritic structure, which can be adopted as electrode for redox supercapacitors and catalytic energy conversion reactions 1,2. By controlling the surfactant and etching chemistry a series of different micro-architectured morphologies was created for Cu-Ni heterostructures (Fig. 1a) during their dendritic growth at suitable electrodeposition potentials. This work examines in detail the effect of the deposition conditions on the mass and chemical composition (Fig. 1b), and morphology (Fig. 1c-d), mass and chemical composition (Fig. 1e) of the deposited Ni/Cu electrodes and the resulting 3D architectures of the dendritic growth. The porosity, architecture, geometric confinement, and the exposed crystallographic facets were found to play crucial roles in the energy storage and catalytic outcomes yielding insightful structure-activity correlations3. Cyclic Voltammetry (CV) studies reveal clear pseudocapacitive nature of the electrodes with the 10 minutes deposited Ni/Cu redox electrode exhibiting very high specific capacitance of 643 F.g−1 at 1 A.g−1 (Fig. 1e-f). The fabricated electrode delivers the capacitance retention of 84% after 5000 consecutive charge discharge cycles (Fig. 1g). These results spotlight the mechanism involved in the electrodeposition and the influence of the observed mass and deposition duration that modifies the electrode content and morphology, as well as its electrochemical activity. Furthermore, the microtraps present in the architectural matrix and the relative composition of Cu to Ni was fine tuned to efficiently direct the reaction pathway towards C2 products during CO2 electroreduction (eCO2R)4. The local confinement of the suitable intermediates and production of CO and H* in proximal sites leads to controlled product tunability towards higher carbon containing hydrogenated products with high faradaic efficiency5. The structure-activity correlations developed here through operando and postmortem analyses corroborated by computational studies, will help guide future material design strategies for enhanced energy storage and catalytic applications. Keywords: electrodeposition, CuNi structures, microtraps, pseudocapacitor, CO2 reductionFig. 1. a) XRD pattern and b) XPS spectrum of Cu-Ni heterostructure, c) and d) SEM micrographs of the micro-architectured morphologies obtained by controlling the surfactant and etching chemistry, e) and f) CV studies of 10 min deposited Ni/Cu redox electrode, and g) Charge-discharge cycles of the fabricated electrode. References Zou, R. et al. Dendritic Heterojunction Nanowire Arrays for High-Performance Supercapacitors. Sci. Reports 2015 51 5, 1–7 (2015).Zang, D., Huang, Y., Li, Q., Tang, Y. & Wei, Y. Cu dendrites induced by the Anderson-type polyoxometalate NiMo6O24 as a promising electrocatalyst for enhanced hydrogen evolution. Appl. Catal. B Environ. 249, 163–171 (2019).Sebastiá n-Pascual, P., Jordã Pereira, I. & Escudero-Escribano, M. Tailored electrocatalysts by controlled electrochemical deposition and surface nanostructuring. Chem. Commun 56, 13261 (2020).Zhuang, T. T. et al. Copper nanocavities confine intermediates for efficient electrosynthesis of C3 alcohol fuels from carbon monoxide. Nat. Catal. 1, (2018).Sebastián‐Pascual, P., Mezzavilla, S., Stephens, I. E. L. & Escudero‐Escribano, M. Structure‐Sensitivity and Electrolyte Effects in CO 2 Electroreduction: From Model Studies to Applications. ChemCatChem 11, 3626–3645 (2019). Figure 1

Self-connected CuO–ZnO radial core–shell heterojunction nanowire arrays grown on interdigitated electrodes for visible-light photodetectors

An original photodetector system based on self-connected CuO–ZnO radial core–shell heterojunction nanowire arrays grown on metallic interdigitated electrodes, operating as visible-light photodetector was developed by combining simple preparation approaches. Metallic interdigitated electrodes were fabricated on Si/SiO2 substrates using a conventional photolithography process. Subsequently, a Cu layer was electrodeposited on top of the metallic interdigitated electrodes. The CuO nanowire arrays (core) were obtained by thermal oxidation in air of the Cu layer. Afterwards, a ZnO thin film (shell) was deposited by RF magnetron sputtering covering the surface of the CuO nanowires. The morphological, structural, compositional, optical, electrical and photoelectrical properties of the CuO nanowire arrays and CuO–ZnO core–shell nanowire arrays grown on metallic interdigitated electrodes were investigated. The performances of the devices were evaluated by assessing the figures of merit of the photodetectors based on self-connected CuO–ZnO core–shell heterojunction nanowire arrays grown on the metallic interdigitated electrodes. The radial p–n heterojunction formed between CuO and ZnO generates a type II band alignment that favors an efficient charge separation of photogenerated electron–hole pairs at the CuO–ZnO interface, suppressing their recombination and consequently enhancing the photoresponse and the photoresponsivity of the photodetectors. The electrical connections in the fabricated photodetector devices are made without any additional complex and time-consuming lithographic step through a self-connecting approach for CuO–ZnO core–shell heterojunction nanowire arrays grown directly onto the Ti/Pt metallic interdigitated electrodes. Therefore, the present study provides an accessible path for employing low dimensional complex structures in functional optoelectronic devices such as photodetectors.

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.

Near-infrared detection in Si/InP core-shell radial heterojunction nanowire arrays

We have explored the photodetection properties of a core-shell nanowire (NW) heterojunction based device consisting of p-Si/n-InP with an aim to provide an alternative to Si based photodetector by integrating a III-V material, viz. InP with silicon. The core is p-Si NWs, prepared by metal assisted chemical etching of p-type Si (100) substrate at room temperature using Ag nanoparticles, whereas n-type InP shells were deposited by metal organic chemical vapor deposition. The current-voltage characteristics of the device resemble that of a p-n junction with good rectification ratio in the dark, and provides photoresponse under visible and near-infrared (NIR) spectral region at low reverse bias condition. In the NIR regime, it shows an on/off ratio of 23 with a rise and fall time of 387 ms and 424 ms, respectively, at a reverse bias voltage of 2 V. The device exhibits a peak responsivity and detectivity of 2.749 A/W and 5.52 × 1011 Jones, respectively, at 920 nm under the same reverse bias voltage. Thus p-SiNW/n-InP core-shell based device could have the potential to be developed as an optoelectronic device beyond the traditional p-n junction exploiting its radial heterojunction based structure.

Construction of CuO/PPy heterojunction nanowire arrays on copper foam as integrated binder-free electrode material for high-performance supercapacitor

Herein, we report a synthesis of 3D CuO/PPy heterojunction nanowire arrays formed on Cu foam via anodizing and electropolymerization. The prepared electrode shows superior performance as a supercapacitor electrode. The CuO NAs are vertically grown on the 3D Cu foam with a diameter of about 200 nm and uniformly coated by conductive polypyrrole (PPy) nanosheets with a length of about 40 nm. The electrodeposition time of PPy also affects the morphology of the material and influences the material's electrochemical properties. The experimental electrochemical results indicate that the CuO/PPy NAs-600 electrode, the optimum electrodeposition time for PPy, could achieve an excellent real-capacitance of 1080 mF cm−2 (675 F g−1) at a current density of 2 mA cm−2. Surprisingly, even at the current density of 20 mA cm−2, the actual capacitance still has 880 mF cm−2, and it could reach 103.57% of the original capacitance after 8000 cycles. Besides, an asymmetric supercapacitor (ASC) using CuO/PPy NAs-600 as positive electrode and activated carbon (AC) as negative electrode can provide an energy density of 0.93 mWh cm−2 at a power density of 1.71 mW cm−2 at a current density of 2 mA cm−2. Furthermore, a 1.8 V LED is lighted for 2 min by three ASC in series. Benefiting from the 3D heterojunction nanowire array structures and the good electronic conductivity between CuO, PPy and Cu foam substrate, the CuO/PPy NAs electrode has potential applications in capacitive energy storage.

Cooling property and application of Au–Bi2Te3 heterojunction nanowire array based on AAO template

In this work, selective radiation material was used to change heat transport of hot side, a novel heterostructure cooler, constructed by gold (Au)—bismuth telluride (Bi2Te3) nanowires array was reported experimentally. The heterostructure was fabricated by electrochemical deposition based on porous anodic alumina template (AAO). The Au nanowire cluster array is used as an infrared selective radiation surface to optimize heat transport of the heat side. And the Bi2Te3 nanowires generate thermoelectromotive force between the two sides of the device due to thermoelectric effect. More interestingly, the Au nanowire ends produce an interface between the metal and semiconductor to enhance the temperature difference, as the interfacial phonon scattering suppresses thermal conductivity. The co-effects create a linear-like relationship between the temperature difference and the applied heating strength to make the heating source hide from infrared detection. At a heating temperature of 170 °C, the radiation temperature difference arrives 16 °C in the Au–Bi2Te3 heterojunction, (increased by 200% to that in Bi2Te3 single phase), given by an intriguing demonstration of infrared camouflage effect. The Au–Bi2Te3 nanowires heterojunction device can not only realize infrared camouflage, but also convert the heat into electrical energy, which provides a new idea for the development of materials.

Investigation of interfacial charge transfer in CuxO@TiO2 heterojunction nanowire arrays towards highly efficient solar water splitting

We investigated the interfacial charge transfer driven by the buried p-n junctions in CuxO@TiO2 nanowires for solar water splitting. The interfacial p-n junctions in the nanowire are constructed by a novel integrating in situ oxidation and thermal annealing method. The interfacial heterojunctions accelerate the transfer of photogenerated charge carriers and provide thickness controllable protective layer for CuxO nanowires suffering from photocorrsion. The optimized CuxO@TiO2 photocathode achieves a remarkable photocurrent density of -2.43 mA•cm−2 at 0 V versus a reversible hydrogen electrode (RHE), which is approximately two times of the bare CuxO photocathode (-1.12 mA•cm−2 at 0 V vs RHE). And the heterojunction photocathode displays a durable cathodic current with a slight decay of 9.3% over 3 h under continuous illumination. The effects of interfacial p-n junctions in CuxO@TiO2 nanowires in improving photogenerated charge carrier transfer were further disclosed by X-ray absorption spectroscopy (XAS) analysis and density functional theory (DFT) calculation. This work might afford a promising insight in understanding the mechanism of interfacial charge transfer towards designing highly efficient photoelectrodes for solar water splitting.

Photodetecting properties of single CuO\u2013ZnO core\u2013shell nanowires with p\u2013n radial heterojunction

CuO–ZnO core–shell radial heterojunction nanowire arrays were obtained by a simple route which implies two cost-effective methods: thermal oxidation in air for preparing CuO nanowire arrays, acting as a p-type core and RF magnetron sputtering for coating the surface of the CuO nanowires with a ZnO thin film, acting as a n-type shell. The morphological, structural, optical and compositional properties of the CuO–ZnO core–shell nanowire arrays were investigated. In order to analyse the electrical and photoelectrical properties of the metal oxide nanowires, single CuO and CuO–ZnO core–shell nanowires were contacted by employing electron beam lithography (EBL) and focused ion beam induced deposition (FIBID). The photoelectrical properties emphasize that the p–n radial heterojunction diodes based on single CuO–ZnO core–shell nanowires behave as photodetectors, evidencing a time-depending photoresponse under illumination at 520 nm and 405 nm wavelengths. The performance of the photodetector device was evaluated by assessing its key parameters: responsivity, external quantum efficiency and detectivity. The results highlighted that the obtained CuO–ZnO core–shell nanowires are emerging as potential building blocks for a next generation of photodetector devices.

Enhanced Photovoltaic Performances of La-Doped Bismuth Ferrite/Zinc Oxide Heterojunction by Coupling Piezo-Phototronic Effect and Ferroelectricity.

Ferroelectric materials have drawn widespread attention due to their switchable spontaneous polarization and anomalous photovoltaic effect. The coupling between ferroelectricity and the piezo-phototronic effect may lead to the design of distinctive photoelectric devices with multifunctional features. Here, we report an enhancement of the photovoltaic performances in the ferroelectric p-type La-doped bismuth ferrite film (BLFO)/n-type zinc oxide (ZnO) nanowire array heterojunction by rationally coupling the strain-induced piezoelectricity in ZnO nanowires and the ferroelectricity in BLFO. Under a compressive strain of -2.3% and a 10 V upward poling of the BLFO, the open-circuit voltage (VOC) and short-circuit current density (JSC) of the device increase by 8.4% and 54.7%, respectively. Meanwhile, the rise (/decay) time is modulated from 153.7 (/108.8) to 61.28 (/74.86) ms. Systematical band diagram analysis reveals that the promotion of photogenerated carriers and boost of the photovoltaic performances of the device can be attributed to the modulated carrier transport behaviors at the BLFO/ZnO interface and the superposed driving forces arising from the adding up of the piezoelectric potential and ferroelectric polarization. In addition, COMSOL simulation results of piezopotential distribution in ZnO nanowire arrays and the energy band structure change of the heterojunction further confirm the mechanisms. This work not only presents an approach to design high-performance ferroelectric photovoltaic devices but also further broadens the research scope of piezo-phototronics.

Self-organized C70/C60 heterojunction nanowire arrays on Si(1 1 0) for Si-based molecular negative differential resistance nanodevices

Periodic organic heterojunction nanowires on Si(110) were successfully constructed through the self-organization of C70 molecules on the nanotemplate of parallel C60-triplet nanowire array on Si(110) at room temperature. Scanning tunneling microscopy images show that the preferential adsorption of three C70 molecules (i.e., C70 triplet) at the bridge site of two C60 triplets makes C70-triplet nanowires grow epitaxially along original C60-triplet nanowires, leading to the formation of parallel-aligned C70-triplet/C60-triplet heterojunction nanowires over a large area on Si(110). Scanning tunneling spectroscopy results show that these C70/C60 heterojunction nanowires on Si(110) exhibit obvious negative differential resistance (NDR) at room temperature. Using first-principles calculations based on density functional theory and non-equilibrium Green’s function formalism, we suggest that the origin of observed NDR of C70/C60 heterojunction nanowires on Si(110) is mainly attributed to the relatively weak interaction between C70 molecules and Si(110) via the spacers of C60 molecules. This controlled organization of mesoscopically-ordered organic heterojunction nanowire array on Si(110) provides a feasible way for molecular engineering of one-dimensional functional Si-based molecular hierarchical nanoarchitectures by deposition of tailored molecules on parallel C60 molecular nanowire arrays on Si(110), realizing the large-scale integration of desired molecular functionalities into Si-based organic nanodevices for applications in nanoelectronics, photovoltaics, and spintronics.

UV Photodetector Based on Vertical (Al, Ga)N Nanowires with Graphene Electrode and Si Substrate

As the key device in a UV warning system, a solid‐state UV photodetector has attracted great attention. Herein, a new UV photodetector structure based on vertical (Al, Ga)N nanowires with graphene electrode and Si substrate is designed and demonstrated. By graphene/vertical (Al, Ga)N nanowire array heterojunction, the rectifying characteristics of I–V curve are formed, and the dark current is 54 nA at −2 V bias. The fabricated device exhibits a responsivity of 0.176 mA W−1 at the bias of −2 V, as well as a stable switching characteristic. It is proposed that the photogenerated electrons and holes can reach positive and negative electrodes by diffusion or tunneling effect, even with thick AlN sections. This method can promote the implementation of low cost for UV photodetector with adjustable detection range nowadays.

Flexible and Self‐Powered Lateral Photodetector Based on Inorganic Perovskite CsPbI3–CsPbBr3 Heterojunction Nanowire Array

AbstractSelf‐powered perovskite photodetectors mainly adopt the vertical heterojunction structure composed of active layer, electron–hole transfer layers, and electrodes, which results in the loss of incident light and interfacial accumulation of defects. To address these issues, a self‐powered lateral photodetector based on CsPbI3–CsPbBr3 heterojunction nanowire arrays is designed on both a rigid glass and a flexible polyethylene naphthalate substrate using an in situ conversion and mask‐assisted electrode fabrication method. Through adding the polyvinyl pyrrolidone and optimizing the concentration of precursors under the pressure‐assisted moulding process, both the crystallinity and stability of perovskite nanowire array are improved. The nanowire array–based lateral device shows a high responsivity of 125 mA W−1 and a fast rise and decay time of 0.7 and 0.8 ms under a self‐powered operation condition. This work provides a new strategy to fabricate perovskite heterojunction nanoarrays towards self‐powered photodetection.

Efficient separation of photoexcited carriers in a g-C3N4-decorated WO3 nanowire array heterojunction as the cathode of a rechargeable Li-O2 battery.

Utilization of solar energy is very important for alleviating the global energy crisis; however, solar-to-electric energy conversion in a compact battery is a great challenge. High charging overpotential of conventional aprotic Li-O2 batteries still restricts their practical application. Herein, we propose a photo-involved rechargeable Li-O2 battery to not only realize direct solar-to-electric energy conversion/storage but also address the overpotential issue. In this photo-involved battery system, the g-C3N4-decorated WO3 nanowire array (WO3@g-C3N4 NWA) heterojunction semiconductor is used as both the photoelectrode and oxygen electrode. Upon charging under visible-light irradiation, the photoexcited holes and electrons are in situ generated on the WO3@g-C3N4 NWA heterojunction cathode. The fabrication of the heterojunction can distinctly reduce the recombination rate between electrons and holes, while photon-generated carriers are effectively and quickly separated and then migrate under a large current density. The discharge product (Li2O2) can be oxidized to O2 and Li+ with a reduced charging voltage (3.69 V) by the abundant photoexcited holes, leading to high energy efficiency, good cycling stability and excellent rate capability. This newly photo-involved reaction scheme could open new avenues toward the design of advanced solar-to-electric energy conversion and storage systems.