Low Contact Resistance Research Articles

Aluminum Halide-Based Electron-Selective Passivating Contacts for Crystalline Silicon Solar Cells.

Extensive research has focused on developing wide-bandgap metal compound-based passivating contacts as alternatives to conventional doped-silicon-layer-based passivating contacts to mitigate parasitic absorption losses in crystalline silicon (c-Si) solar cells. Herein, thermally-evaporated aluminum halides (AlX)-based electron-selective passivating contacts for c-Si solar cells are investigated. A low contact resistivity of 60.5 and 38.4 mΩ cm2 is obtained on the AlClx/n-type c-Si (n-Si) and AlFx/n-Si heterocontacts, respectively, thanks to the low work function of AlX. Power conversion efficiencies (PCEs) of 19.1% and 19.6% are achieved on proof-of-concept n-Si solar cells featuring a full-area AlClx/Al and AlFx/Al passivating contact, respectively. By further implementing an ultrathin SiO2 passivation interlayer and a pre-annealing treatment, the electron selectivity (especially the surface passivation) of AlX is significantly enhanced. Accordingly, a remarkable PCE of 21% is achieved on n-Si solar cells featuring a full-area SiO2/AlFx/Al rear contact. AlFx-based electron-selective passivating contacts exhibit good thermal stability up to ≈400 °C and better long-term environmental stability. This work demonstrates the potential of AlFx-based electron-selective passivating contact for solar cells.

Device level assessment of Ni and Ni45Cu55 as electrodes in Mg2(Si,Sn)-based thermoelectric generators

Owing to efficient thermoelectric conversion, non-toxicity, low density and cost, Mg2(Si,Sn)-based solid solutions hold potential for mid-to-high temperature waste heat recovery. Yet, challenges arise from n-Mg2(Si,Sn) degradation at ≥400 °C caused by Mg loss and charge carrier reduction, particularly in Sn-rich compositions. To build a thermoelectric generator (TEG) stable up to 400 °C, we propose binary Mg2Si as the n-type leg. Using Ni45Cu55and Ni yields low electrical contact resistance (<5 µΩ.cm2) without altering the thermoelectric properties of n-Mg2Si. We fabricated two 2×2 leg TE modules with the same electrode/TE combination for the p-type legs and with Ni or Ni45Cu55 for their n-type legs and tested up to 400 °C, allowing for a direct comparison between these twoelectrodes for n-Mg2Si at the device level. Ni45Cu55 outperformed Ni, resulting in a peak power density of 0.79 W/cm2 at ΔT ∼375 K and an efficiency competitive to Mg2(Si,Sn)-only TEG.Comparative simulations using a constant property model revealed a strong reduction of internal losses when using Ni45Cu55as the electrode for n-Mg2Si as the main reason for the high performance. The presented design overcame challenges such as Mg sublimation at targeted application temperature or electrode induced defect formation, resulting in a stable TEG.

Batch Fabrication and Interface Stabilization Accelerate Application of Skutterudite Thermoelectric Module for Power Generation

AbstractTo achieve the commercial application of high‐performance skutterudite (SKD) thermoelectric (TE) devices, breakthroughs in the batch fabrication of TE material and the realization of its stable bonding to the barrier layer are necessary. In this work, the large‐scale SKD bulks with excellent TE performance and decent homogeneity are prepared by melt‐spinning (MS) combined with a hot pressing process. Then, a modified two‐step sintering method is employed to effectively suppress the degree of initial interfacial reaction, resulting in a barrier layer/SKD joint that exhibits low contact resistivity (≈2µΩ·cm2) and high bonding strength (≈30 MPa) with no significant change after aging at 773 K for 30 days. Encouragingly, the joints welded with Mo50Cu50 electrodes also show high stability under the same aging conditions. Finally, the as‐fabricated 8‐pair module shows a highly competitive conversion efficiency of 9% under a temperature difference of 580 K. In addition, during a 360 h aging test with hot‐side temperature of 773 K, the module shows excellent stability. Overall, this work paves the way for batch fabrication of high‐performance SKD using MS and lays a solid foundation for the stable operation of SKD‐based modules.

Lithography‐free fabrication of a local contact interlayer for Si‐based tandem solar cells

AbstractCurrently, the Si solar cell market share is dominated by PERC solar cells. Although the efficiency of PERC solar cells has been steadily increasing, it is expected to reach the practical efficiency limit in the near future. The thin film/PERC Si tandem cell technique can be one of the solutions to overcome the single‐cell efficiency limit. In this study, we developed a novel interlayer fabrication technology for the diffused junction Si solar cells of the PERC and Al BSF cell architectures. We combined laser contact opening (LCO) and laser‐induced forward transfer (LIFT) processes to fabricate local contact opening with low contact resistance while maintaining the high passivation performance of the Si bottom cell. The dielectric‐passivated emitter of the Si solar cell was ablated locally by the LCO process, and subsequently, the Ti nanoparticles were transferred selectively by the LIFT process to the opened emitter region followed by transparent conducting oxide deposition. Laser process parameters were carefully optimized to fabricate low‐loss interlayers. We applied the developed interlayer fabrication technology to the Si bottom cells of Al BSF and PERC cells. Finally, we demonstrated successfully the perovskite/PERC Si tandem cell with an interlayer developed in this study. The developed interlayer fabrication technology does not include a photolithography step and vacuum deposition processes for buffer metals; thus, we expect it may be more compatible with the mass production of thin film/diffused junction Si tandem solar cells.

Submicron Memtransistors Made from Monocrystalline Molybdenum Disulfide.

Multiterminal memtransistors made from two-dimensional (2D) materials have garnered increasing attention in the pursuit of low-power heterosynaptic neuromorphic circuits. However, existing 2D memtransistors tend to necessitate high set voltages (>1 V) or feature defective channels, posing concerns regarding material integrity and intrinsic properties. Herein, we present a monocrystalline monolayer MoS2 memtransistor designed for operation within submicron regimes. Under reverse drain bias sweeps, our experiments reveal memristive behavior within the device, further controllable through modulation of the gate terminal. This controllability facilitates the consistent manifestation of multistate memory effects. Notably, the memtransistor behavior becomes more significant as the channel length diminishes, particularly with channel lengths below 1.6 μm, showcasing an increase in the switching ratio alongside a decrease in the set voltage with the decreasing channel length. Our optimized memtransistor demonstrates the ability to exhibit individual resistance states spanning 5 orders of magnitude, with switching drain voltages of approximately 0.05 V. To elucidate these findings, we investigate hot carrier effects and their interplay with oxide traps within the HfO2 dielectric. This work highlights the importance of memtransisor behavior in highly scaled 2D transistors, particularly those featuring low contact resistances. This understanding holds the potential to tailor memory characteristics essential for the development of energy-efficient neuromorphic devices.

Fabrication of three dimensional graphene/carbon nanotube/copper foam field emitter by electrophoretic deposition and its emission properties

In this paper, the graphene/carbon nanotubes/copper foam (GR/CNTs/CuF) three-dimensional field emitters were prepared by electrophoretic deposition (EPD). For comparison, the graphene/copper foam (GR/CuF) and carbon nanotubes copper foam (CNTs/CuF) field emitters were also prepared by the same way and characterized by the several different methods. The turn on electrical field (Eon) of composite materials of GR/CNTs/CuF was obtained to be 0.85 V/μm. Threshold electric field (Eth) is 1.52 V/μm. The composite of GR/CNTs/CuF have a large contact area, a lower volume resistance and lower contact resistance, which is more easy to electron transport. The root of the CNTs or the fold tip of GR is fixed in the interlaced composite, and the tip or fold forms a stable micro tip emission structure, which enhanced the field strength factor. The field emission performances are significantly better than that of individual GR/CuF or CNTs/CuF field emitter. The GR/CNTs/CuF as 3D field emitters were prepared by EPD method with low cost and easy manipulation, which provided a good way for a large-scale preparation of composite field emitters.

Implementation of Highly Reliable Contacts for RF MEMS Switches.

A contact is the key structure of RF MEMS (Radio Frequency Microelectromechanical System) switches, which has a direct impact on the switch's electrical and mechanical properties. In this paper, the implementation of highly reliable contacts for direct-contact RF MEMS switches is provided. As a soft metal material, gold has the advantages of low contact resistance, high chemical stability, and mature process preparation, so it is chosen as the metal material for the beam structure as well as the contacts of the switch. However, a Pt film is used in the bottom contact area to enhance the reliability of the contact. Three kinds of contacts with various shapes are fabricated using different processes. Particularly, a circular-shaped contact is obtained by dry/wet combined processes. The detailed fabrication process of the contacts as well as the Pt film on the bottom contact area are given. The experimental test shows that the contact shape has little effect on the RF performance of the switches. However, the circular contact shows better reliability than other contacts and can work well even after 1.2 × 109 cycles.

Tailoring ohmic contact of CdZnTe based device using a ZnTe:Cu film interlayer

ZnTe materials exhibit distinctive characteristics that render them exceptionally suitable for the utilization in circumventing the electrode contact issue for the CdZnTe based devices for photoelectric applications. This work employed the co-sputtering technique to fabricate ZnTe:Cu films, probing the influences of Copper (Cu) sputtering power on the film's structural, morphological, optical, and electrical properties. It is disclosed that the sputtering power of the Cu target leads to a proportional increase in CuxTe compounds within the ZnTe:Cu films. Notably, an increase in the sputtering power of the Cu target is found to enhance the carrier concentration of the film, but not decrease the resistivity. This unnormal arose is due to a substantial reduction in carrier mobility at higher Cu target sputtering powers. The ZnTe:Cu film exhibits relatively lower resistivity when the sputtering power of the Cu target is approximately 3 W. The optimized ZnTe:Cu film as a buffer layer for the electrode is favor of remarkable improving the ohmic contact properties between the electrode and the CdZnTe, exhibiting a low contact resistivity of 0.62 Ω cm2. This work offers a promising approach to ameliorate the contact performance for the CdZnTe devices with high performance and high reliability.

Sn‐Doped Nb2O5Films as Effective Hole‐Selective Passivating Contacts for Crystalline Silicon Solar Cells

Carrier‐selective contacts (CSCs) in crystalline silicon (c‐Si) solar cells have attracted great attention due to suppressing contact region recombination and achieving higher conversion efficiency. Among transition metal oxides for CSCs, niobium oxide (Nb2O5) is considered as an attractive candidate for electron‐selective contact due to its excellent passivation properties and small conduction band offsets with c‐Si. Nevertheless, the performance of c‐Si solar cells employing Nb2O5contact layer has not been explored yet. Herein, the carrier selectivity of solution‐processed Nb2O5films is investigated for c‐Si. Interestingly, Nb2O5exhibits high electron‐blocking performance and low contact resistivities with p‐Si. The ultra‐thin SiOxinterlayer formed by UV–O3pretreatment further reduces the contact resistivities and increases minority carrier lifetime due to the improved contact interface. The Sn4+doping improves the work function of Nb2O5to induce larger upward band bending at c‐Si surface, thus enhancing the hole selectivity. As a result, p‐type c‐Si solar cells with solution‐processed Nb2O5hole‐selective contact layer have achieved the highest power conversion efficiency of 18.4%, with a high‐thermal stability superior to the typical hole transport layers. This work first demonstrates the exceptional hole selectivity of Nb2O5, which shows very promising applications in high‐efficiency c‐Si solar cells.

Synthesis of Nb‐Doped‐WS2–NbS2: A Degenerate‐Semiconductor–Metal Heterostructure

AbstractThe synthesis of semiconductor–metal (S–M) heterostructures comprising semiconducting (S)‐transition metal dichalcogenides (TMDs) and metallic (M)‐TMDs via chemical vapor deposition (CVD) has emerged as a highly promising avenue for achieving low contact resistance in TMD‐based devices. However, CVD‐grown S–M heterostructures are mainly focused on non‐degenerate semiconductors, despite degenerate semiconductors also being essential for semiconductor technology, such as negative differential resistance (NDR) device. In this study, a degenerate‐S–M heterostructure, Nb‐doped‐WS2–NbS2, is synthesized via CVD with a liquid‐metal precursor. Optimizing the growth parameters, such as growth temperature, precursor ratio, and H2 content in the mixture gas, affords the desirable degenerate‐Nb‐doped‐WS2–NbS2 heterostructure. Raman and photoluminescence spectroscopies, transmission electron microscopy, and energy‐dispersive spectroscopy clearly clarify the doping signal and layer structure of the heterostructure. A growth mechanism has been proposed using in‐plane and vertical models based on structural analysis. Electrical transport measurements reveal degenerate p‐type behavior in the Nb‐doped‐WS2. In the Nb‐doped‐WS2–NbS2 degenerate‐S–M heterostructure, the device flows about twice as much on‐state current as that by an Nb‐doped‐WS2/Cr contact.

Effect of Silver Powder Microstructure on the Performance of Silver Powder and Front-Side Solar Silver Paste.

Silver powder, as the primary component of solar silver paste, significantly influences various aspects of the paste's performance, including printing, sintering, and conductivity. This study reveals that, beyond the shape and size of the silver powders, their microstructure is a critical factor influencing the performance of both silver powders and silver pastes in solar cell applications. The growth process leads to the formation of either polycrystalline aggregated silver powder or crystal growth silver powder. Analyzing the performance characteristics of these different microstructures provides guidance for selecting silver powders for silver pastes at different sintering temperatures. Polycrystalline aggregated silver powder exhibits higher sintering activity, with a sintering initiation temperature around 450 °C. The resulting silver paste, sintered at 750 °C, demonstrates a low sheet resistance of 2.92 mΩ/sq and high adhesion of 2.13 N. This silver powder is suitable for formulating silver pastes with lower sintering temperatures. The solar cell electrode grid lines have a high aspect ratio of 0.37, showing poor uniformity. However, due to the high sintering activity of the silver powder, the glass layer dissolves and deposits more silver, resulting in excellent conductivity, a low contact resistance of the silver electrode, a low series resistance of the solar cell of 1.23 mΩ, and a high photoelectric conversion efficiency of 23.16%. Crystal growth silver powder exhibits the highest tap density of 5.52 g/cm3. The corresponding silver paste shows improved densification upon sintering, especially at 840 °C, yielding a sheet resistance of 2.56 mΩ/sq and adhesion of 3.05 N. This silver powder is suitable for formulating silver pastes with higher sintering temperatures. The solar cell electrode grid lines are uniform with the highest aspect ratio of 0.40, resulting in a smaller shading area, a high fill factor of 81.59%, and a slightly higher photoelectric conversion efficiency of 23.17% compared to the polycrystalline aggregated silver powder.

Phase-separated stretchable conductive nanocomposite to reduce contact resistance of skin electronics

Skin electronics, facilitating a high-quality interface between external devices and human skin for recording physiological and/or electrophysiological signals as well as delivering external electrical and/or mechanical energy into the human body, has shown significant progress. However, achieving mechanically conformal contact and electrically low contact resistance at the device-skin interface remains challenging. Here, we propose a material strategy to potentially address such an issue by using phase separation of silver nanowires and silver nanoparticles (Ag NWs and Ag NPs) within a stretchable conductive nanocomposite (NC). This phase-separated NC ensures low contact resistance and high conductivity, which are key requirements in skin electronics, while maintaining excellent mechanical contact with the skin. To achieve phase separation, we hydrophobically treated the surfaces of Ag NWs and Ag NPs. Then, as the NC solidified, the solvent contained in the NC was slowly evaporated to sufficiently precipitate Ag NPs within the NC. As a result, the phase-separated NC exhibited high conductivity (~ 18,535 S cm−1), excellent stretchability (~ 80%), and low contact resistance on both the top and bottom NC surfaces (average ~ 0.132 Ω). The phase-separated NC has enabled implementation of high performance skin-mounted devices, including strain sensors, electrophysiological sensors, and a wearable heater.

Open package form-stable phase change microspheres with low thermal contact resistance for the thermal management of electronic devices

Thermal contact resistance (TCR) is a key factor that affects the rapid heat transfer process based on thermal interface materials (TIMs). Phase change TIMs have the property of thermally induced solid–liquid phase change, which is an advantage to improve the contact state and reduce TCR. However, the contradiction between form-stable and wettability must be solved during the application of phase change TIMs. In this work, a flexible, form-stable and low TCR phase change TIMs of graphene/acrylic polymer foamed microspheres/polyethylene glycol (G/APM/PEG) has been successfully prepared by “open package”. APM is light and the surface are covered with micropores, which can be adsorbed a large amount of liquid phase PEG to prevent leakage and retain good wettability. Furthermore, the thermal properties of G/APM/PEG were systematically studied. The TCR results between “open package” method and “closed package” method were compared. The critical thickness value in all measure conditions were calculated. The thermal conductivity of G/APM/PEG filled with graphene (4 wt%) is 230% higher than that of APM/PEG. The TCR of G/APM/PEG is 0.5～0.9 K∙cm2/W at 65 °C (40 Psi), which is far lower than that of TIMs from “closed package” (3.5～5.3 K∙cm2/W). This is because the G/APM/PEG from “open package” exposes part of the surface of PEG to air, greatly improving the contact state. In addition, the maximum critical thickness is about 0.3 mm for all G/APM/PEG under different measure conditions. It confirms that the TCR is relatively small in all measure conditions and the thermal conductivity resistance is dominant.

Uniform Synthesis of Bilayer Hydrogen Substituted Graphdiyne for Flexible Piezoresistive Applications.

Graphdiyne (GDY) has garnered significant attention as a cutting-edge 2D material owing to its distinctive electronic, optoelectronic, and mechanical properties, including high mobility, direct bandgap, and remarkable flexibility. One of the key challenges hindering the implementation of this material in flexible applications is its large area and uniform synthesis. The facile growth of centimeter-scale bilayer hydrogen substituted graphdiyne (Bi-HsGDY) on germanium (Ge) substrate is achieved using a low-temperature chemical vapor deposition (CVD) method. This material's field effect transistors (FET) showcase a high carrier mobility of 52.6cm2V-1s-1 and an exceptionally low contact resistance of 10Ωµm. By transferring the as-grown Bi-HsGDY onto a flexible substrate, a long-distance piezoresistive strain sensor is demonstrated, which exhibits a remarkable gauge factor of 43.34 with a fast response time of ≈275ms. As a proof of concept, communication by means of Morse code is implemented using a Bi-HsGDY strain sensor. It is believed that these results are anticipated to open new horizons in realizing Bi-HsGDY for innovative flexible device applications.

Low voltage cold and hot switching in nanoswitches cleaned by in situ oxygen plasma can achieve low stable contact resistance

Reliable nanoswitch operation requires low contact voltages and stable electrical contact resistance (ECR). Surface cleanliness is crucial to prevent nanomechanical switch failure, which can occur due to the presence of insulating adventitious hydrocarbon films. In situ O2 plasma cleaning is effective but oxidizes metal surfaces. Here, the noble metal Pt, which forms PtOx, is employed to form electrodes. Previous studies report on PtOx electrical resistivity, but the effects of PtOx evolution at contacting interfaces due to electrical and mechanical stimuli have not been explored. This study investigates the impact of PtOx on ECR at low contact voltages under hot switching, cold switching, and mechanical cycling conditions. An increase in ECR upon plasma cleaning indicates the presence of a resistive PtOx layer. After hot and cold switch cycling at applied voltages of 300 mV or less, a low stable ECR is achieved. A higher contact voltage accelerates ECR stabilization. The results are consistent with PtOx film volatilization, which is primarily due to Joule heating rather than mechanical rupture. This investigation advances the understanding of interface evolution in plasma-cleaned nanoswitches.

Silicon implantation and annealing in β-Ga2O3: Role of ambient, temperature, and time

Optimizing thermal anneals of Si-implanted β-Ga2O3 is critical for low resistance contacts and selective area doping. We report the impact of annealing ambient, temperature, and time on the activation of room temperature ion-implanted Si in β-Ga2O3 at concentrations from 5 × 1018 to 1 × 1020 cm−3, demonstrating full activation (&amp;gt;80% activation, mobilities &amp;gt;70 cm2/V s) with contact resistances below 0.29 Ω mm. Homoepitaxial β-Ga2O3 films, grown by plasma-assisted molecular beam epitaxy on Fe-doped (010) substrates, were implanted at multiple energies to yield 100 nm box profiles of 5 × 1018, 5 × 1019, and 1 × 1020 cm−3. Anneals were performed in an ultra-high vacuum-compatible quartz furnace at 1 bar with well-controlled gas compositions. To maintain β-Ga2O3 stability, pO2 must be greater than 10−9 bar. Anneals up to pO2 = 1 bar achieve full activation at 5 × 1018 cm−3, while 5 × 1019 cm−3 must be annealed with pO2 ≤ 10−4 bar, and 1 × 1020 cm−3 requires pO2 &amp;lt; 10−6 bar. Water vapor prevents activation and must be maintained below 10−8 bar. Activation is achieved for anneal temperatures as low as 850 °C with mobility increasing with anneal temperatures up to 1050 °C, though Si diffusion has been reported above 950 °C. At 950 °C, activation is maximized between 5 and 20 min with longer times resulting in decreased carrier activation (over-annealing). This over-annealing is significant for concentrations above 5 × 1019 cm−3 and occurs rapidly at 1 × 1020 cm−3. Rutherford backscattering spectrometry (channeling) suggests that damage recovery is seeded from remnant aligned β-Ga2O3 that remains after implantation; this conclusion is also supported by scanning transmission electron microscopy showing retention of the β-phase with inclusions that resemble the γ-phase.

Post-annealing-free BaOxFy/LiF-based stack electron-selective contacts for high efficiency crystalline silicon solar cells featuring ultra-low contact resistivity

In silicon heterojunction and tunnel oxide passivating contact crystalline silicon (c-Si) solar cells based on successful passivating contacts technologies, an annealing activation step is indispensable to achieve a suitably low contact resistivity (ρc), which is a costly and non-ideal process. Here, combined with a calcium aluminium (Ca:Al) alloy electrode, a low work function barium oxide and lithium fluoride (BaOxFy/LiF) stack electron-selective contact (ESC) without an annealing activation step on c-Si solar cells clinches an ultra-low ρc of 1.4 mΩ·cm2 delivering a power conversion efficiency (PCE) of 20.5 %. The BaOxFy/LiF/Ca:Al stack structure is built by BaOx/LiF/Ca/Al hybrid structure via a facile continuous thermal evaporation process. As a proof of concept, the stacked BaOxFy/LiF/Ca:Al/Al contact is applied to the rear side of c-Si solar cells, achieving a PCE of 20.5 % with an open-circuit voltage of 625.7 mV, an impressive fill factor of 83.5 % and a short-circuit current density of 39.2 mA/cm2. With the aid of a transient photovoltage setup, the carrier recombination mechanism of the stacked BaOxFy/LiF/Ca:Al structure is explored. This work demonstrates an alternative idea for undoped ESCs, showing potential for next-generation cost-effective ultrathin-slice c-Si solar cells (∼80 μm) with high efficiency, and low-parasitic light absorption losses.

Investigation of Interface Interactions Between Monolayer MoS2 and Metals: Implications on Strain and Surface Roughness.

Achieving a low contact resistance has been an important issue in the design of two-dimensional (2D) semiconductor-metal interfaces. The metal contact resistance is dominated by interfacial interactions. Here, we systematically investigate 2D semiconductor-metal interfaces formed by transferring monolayer MoS2 onto prefabricated metal surfaces, such as Au and Pd, using X-ray photoelectron spectroscopy (XPS), atomic force microscopy, and Raman spectroscopy. In contrast to the MoS2/HOPG interface, the interfaces of MoS2/Au and MoS2/Pd feature the formation of weak covalent bonds. The XPS spectra reveal distinct peak positions for S-Au and S-Pd, indicating a higher doping concentration at the S-Au interface. This difference is a key factor in understanding the electronic interactions at the metal-MoS2 interfaces. Additionally, we observe that the metal surface roughness is a critical determinant of the adhesion behavior of transferred monolayer MoS2, resulting in different strains and doping concentrations. The strain on transferred MoS2 increases with an increase in substrate roughness. However, the strain is released when the roughness of metal surface surpasses a certain threshold. The dependence of the contact material and the influence of the substrate roughness on the contact interface provide critical information for improving 2D semiconductor-metal contacts and device performance.

Effect of optimal rapid thermal alloying of ohmic contacts to microwave pseudomorphic HEMTs

Gallium Arsenide (GaAs) pseudomorphic High Electron Mobility Transistors (pHEMTs) are currently used as active devices in manufacturing Monolithic Microwave Integrated Circuits (MMICs) for microwave and millimetre wave applications like Transmit-Receive (T/R) modules in Radars and communication. Low contact resistances (Rc) of pHEMT devices are necessary to obtain low access resistances to the device channel, for enhancement of transconductance and cut-off frequency. Devices formed by optimal and suboptimal conditions of rapid thermal alloying by infra-red optical radiation are investigated using cross-section transmission electron microscopy (XTEM), backside secondary ion mass spectrometry (backside SIMS) and thermal imaging techniques to understand the role of optimal alloy formation and its role in enhancement of device parameters.

One-step hydrothermal synthesis of a Ni3S2-FeMoO4 nanowire-nanosheet heterostructure array for synergistically boosted oxygen evolution reaction.

A key factor for boosting oxygen evolution reaction (OER) is the design of heterostructures with steerable defects and interfaces, which can optimize the surface electronic structures and achieve efficient water splitting to produce hydrogen fuel. Herein, we propose a novel one-step hydrothermal approach to fabricate hierarchical Ni3S2 nanowires with an S-doped FeMoO4 nanosheet heterostructure array in situ on Ni-Fe foam (NFF) as a self-standing electrode for synergistically boosted OER. The metalloid Ni3S2 nanowires with good conductivity support the FeMoO4 nanosheets and act as high-speed paths for the charge transfer. Numerous ultrathin S-doped FeMoO4 nanosheets are uniformly distributed on each Ni3S2 nanowire to form heterostructures with larger specific surface area and more revealable active sites, and a strong synergistic effect is created at the heterostructure interfaces to further promote the OER dynamics. Additionally, the NFF serves as the conductive support substrate and simultaneously provides the Ni and Fe sources for the self-growing Ni3S2-FeMoO4, leading to a structurally-integrated electrode with low contact resistance, fast mass transfer, and good stability. Therefore, the Ni3S2-FeMoO4/NFF electrode offers a low overpotential of 331 mV to achieve 500 mA cm-2 and long-term stability at 100 mA cm-2 level for more than 40 h. This work provides insight into the heterostructure of molybdate and sulfide, and a deep understanding of the significance of the synergism in OER operation.