Silver Nanowire Electrodes Research Articles

Integrated Piezoelectric Vascular Graft for Continuous Real‐Time Hemodynamics Monitoring

AbstractVascular grafts, widely utilized in managing cardiovascular diseases (CVD), are susceptible to postoperative complications. Recent strides in intelligent vascular grafts leveraging flexible bioelectronics enable hemodynamic and vascular health monitoring. However, their practical application faces challenges, notably biomechanical compatibility and endothelialization. Here, an all‐in‐one piezoelectric vascular graft (PVG) constructed by encapsulating a polyvinylidene fluoride (PVDF) nanofiber mat with patterned silver nanowire (AgNW) electrodes between two layers of polycaprolactone (PCL) nanofiber mats is presented. The meticulously optimized PVG, featuring PVDF and PCL nanofibers with average diameters of ≈950 and 250 nm, respectively, showcases remarkable endothelialization and mechanical performance akin to native blood vessels. The exquisite piezoelectric properties of PVDF nanofibers imbue PVG with outstanding mechanical sensing capabilities, boasting a sensitivity of 11 mV kPa−1 and stability exceeding 50 000 cycles, facilitating precise hemodynamic monitoring. Notably, artificial artery model tests demonstrate PVG's ability to diagnose vascular health status accurately based on detected hemodynamic data. Furthermore, the developed PVG exhibits nontoxicity, good hemocompatibility (hemolytic ratio < 1%), and histocompatibility. This pioneering technology, validated through ex vivo and in vivo experiments, represents a significant stride in precise vascular health management, unlocking diverse potential applications.

Flexible Iontronic Tactile Sensors Based on Silver Nanowire Electrode with Sandpaper-Roughened Surface and Ionic Liquid Gel Electrolyte with Porous Foam Structure for Wearable Sensing Applications

Flexible Iontronic Tactile Sensors Based on Silver Nanowire Electrode with Sandpaper-Roughened Surface and Ionic Liquid Gel Electrolyte with Porous Foam Structure for Wearable Sensing Applications

Unraveling the electrical energy loss in silver nanowire electrodes for flexible and Large-Area organic solar cells

Although the transparency and sheet resistance of silver nanowire (AgNW) electrodes are comparable to those of rigid indium-tin-oxide electrodes, flexible organic solar cells (FOSCs) are still less efficient than their rigid counterparts. Herein, by recording the microscopic photocurrent images of AgNW-based FOSCs in operation, it has been revealed that the limited lateral charge collection range of AgNW leads to inevitable electrical energy loss. The regulation of carrier mobility and energy level of adjacent ZnO electron transport layer increases the effective collection range of AgNWs by 1.8 times and uniform the electrical potential distribution in FOSCs. The D18:Y6:PC71BM-based FOSCs achieve a power conversion efficiency of approaching 18%. Moreover, the performance drop of large-area FOSCs is significantly reduced due to the improved charge collection on large area scale. This work provides an intuitive insight into the electrical energy loss mechanism of AgNW electrodes and demonstrates an electric field regulation strategy in FOSCs.

Multiscale Electrical Response Assessment of Metal Nanowire Transparent Electrodes: A Computational Strategy

Transparent electrodes made of random distributions of metal nanowires (NWs) are appealing for optoelectronic devices, solar cells, light emitting diodes, and transparent heaters. While these electrodes are comparable to thin films in terms of electrical conductivity and transparency, their network structure allows limiting the amount of conductive material and makes them suitable for low-cost solution-based deposition methods, contributing to an overall costs reduction. Despite these advantages, an even material utilization at different length scales is difficult to achieve. The homogeneous distribution of electric current (electrical homogeneity) is indeed not guaranteed in nanowire electrodes but is crucial for the stability of the electrode and actually desirable in most applications. Despite the relevance of this feature, it is common practice to perform qualitative assessments at the electrode scale, overlooking local effects. To address this issue, we have developed a computational strategy to aid in the design of nanowire electrodes with improved electrical homogeneity.We present a computational approach that allows an objective, quantitative, and systematic assessment of the electrical homogeneity. The approach enables a multiscale comparison of electrodes with different NW content and material properties. Nanowire electrodes are modeled as two-dimensional networks of stick and junction resistors (with resistance Rw and Rj, respectively) to simulate the electric conduction process. Electrodes are discretized into regular grids of squares and the electrical power of the network contained in each square is computed. The mismatch between the areal power density of the entire electrode and that of the squares provides a quantitative electrical homogeneity evaluation. Repeating the analysis with squares of different size yields an evaluation that spans across length scales. A scalar indicator, coined the homogeneity index, summarizes the results of the multiscale evaluation.Parametric studies are performed by varying nanowire content and nanowire-to-junction resistance ratio Rw/Rj. We show that electrical homogeneity improves as i) NW density increases, and ii) junction resistance reduces. The ideal condition of negligible junction resistance (Rw >> Rj) leads to the best-case scenario and guarantees the highest rate of improvement of electrical homogeneity with NW content. Nevertheless, we observe that under condition Rw ≈ Rj the response of the system approaches the response of a system meeting the ideal condition Rw >> Rj (15% difference at most in terms of homogeneity index). We therefore conclude that reducing the junction resistance excessively (with the aim of achieving Rw/Rj > 1) may not always be a worthwhile strategy, as it results in only a marginal improvement in terms of electrical homogeneity.The proposed strategy is employed to assess the electrical homogeneity of silver nanowire electrodes through the analysis of scanning electron microscopy images. Our results agree with the outcomes of the experimental assessment performed on the same electrodes.

Beyond Flexibility: Transparent Silver Nanowire Electrodes on Patterned Surfaces for Reconfigurable Devices

Silver nanowire (AgNW) emerges as a next‐generation transparent electrode material, offering enhanced flexibility and ease of fabrication compared to traditional transparent electrode materials, such as metallic oxides. In the previous research, the uniform deposition of AgNWs on flat surfaces is demonstrated, exhibiting high conductivity, flexibility, and excellent transmittance. However, the evolution of nano‐electronics technology necessitates the fabrication of transparent electrodes on non‐flat surfaces, such as those found in zenithal bistable devices and reconfigurable Fresnel lenses. In this study, a method is proposed to deposit AgNW material on uneven surfaces using the Mylar‐bar‐coating method, with a polyvinyl chloride (PVC)‐based Fresnel lens serving as the target surface. Additionally, the impact of varying AgNW suspension concentrations on transmittance and sheet resistance is investigated. To further reduce sheet resistance, a layer of conductive polymer, poly(3,4‐ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), is deposited on the AgNWs. The measurements reveal that a 2 mg mL−1 sample exhibits a sheet resistance of 187.83 W W−1 with 87.4% transmittance at 550 nm. After the PEDOT:PSS process, the sheet resistance decreases to 122.84 W W−1 with 84.4% transmittance. In this research, a solution is offered for the uniform deposition of AgNWs on patterned surfaces, paving the way for the next generation of optical devices.

Solution Processed Semi-Transparent Organic Solar Cells Over 50% Visible Transmittance Enabled by Silver Nanowire Electrode with Sandwich Structure.

Photovoltaic windows with easy installation for the power supply of household appliances have long been a desire of energy researchers. However, due to the lack of top electrodes that offer both high transparency and low sheet resistance, the development of high-transparency photovoltaic windows for indoor lighting scenarios has lagged significantly behind photovoltaic windows where privacy issues are involved. Addressing this issue, this work develops a solution-processable transparent top electrode using sandwich structure silver nanowires, realizing high transparency in semi-transparent organic solar cells. The wettability and conducting properties of the electrode are improved by a modified hole-transport layer named HP. The semi-transparent solar cell exhibits good see-through properties at a high average visible transmittance of 50.8%, with power conversion efficiency of 7.34%, and light utilization efficiency of 3.73%, which is the highest without optical modulations. Moreover, flexible devices based on the above-mentioned architecture also show excellent mechanical tolerance compared with Ag electrode counterparts, which retains 94.5% of their original efficiency after 1500 bending cycles. This work provides a valuable approach for fabricating solution-processed high transparency organic solar cells, which is essential in future applications in building integrated photovoltaics.

Large-area, stretchable, ordered silver nanowires electrode by superwetting-induced transfer of ionic liquid@silver nanowires complex

Stretchable transparent electrodes (STEs) are widely used in electronic skin, implantable biomedical devices and wearable devices, which need to meet metal-like conductivity and high transparency while being prepared in a large area. Silver nanowires are the most widely used material to construct conductive networks because of their excellent optoelectrical properties. However, the silver nanowires-based networks prepared by conventional large-area preparation processes are generally composed of disordered silver nanowires, which suffer both high junction resistance and high diffuse reflection. Herein, a large-area, stretchable, ordered silver nanowires electrode is prepared by superwetting-induced transfer of a self-assembled complex composed of ionic liquid (1-ethyl-3-methylimidazolium (bis-trifluoromethane sulfonyl) imide) and silver nanowires onto stretchable substrates. Then, electroless-welding is used to further reduce the junction resistance between silver nanowires. The generated STE shows a low sheet resistance of 26–46 Ω sq−1 and a high transmittance of 84 %–88 % at 550 nm. The STE is successfully applied for transparent heating devices, exhibiting high heating performance and tensile stability. This study provides a new method for the preparation of large-area high-performance STE for the next generation of stretchable devices.

Research on femtosecond laser welding process of silver nanowire transparent electrodes

With the continuous development of flexible transparent electrodes, silver nanowires have been widely used due to their excellent optoelectronic properties and flexibility. However, their progress has been hindered by high contact resistance. In this study, femtosecond laser post-processing was applied to the silver nanowire transparent electrodes, and the effect of laser power density on the welding of silver nanowires was investigated. The results showed that femtosecond laser could achieve welding between silver nanowires, but excessively high laser energy density could cause the melting of the nanowires. When the femtosecond laser energy density reached the critical energy density of approximately 2546 J·m−2, at which nanowires underwent spheroidization, the average sheet resistance of the silver nanowire electrodes was minimized to 18.89 Ω·sq−1, and the figure of merit (FoM) of the electrodes reached its maximum at 126.99, which was close to twice the initial value. Moreover, the non-uniformity factor (NUF) was also small, at 1.6%, indicating good conductivity and uniformity. Additionally, the influence of femtosecond laser irradiation on the transmittance of the silver nanowire transparent electrodes was insignificant, and the number of effective pulses had no obvious effect on the welding efficiency of the silver nanowires.

Silver nanowire electrodes for transparent light emitting devices based on WS2 monolayers

Transition metal dichalcogenide (TMDC) monolayers with their direct band gap in the visible to near-infrared spectral range have emerged over the past years as highly promising semiconducting materials for optoelectronic applications. Progress in scalable fabrication methods for TMDCs like metal-organic chemical vapor deposition (MOCVD) and the ambition to exploit specific material properties, such as mechanical flexibility or high transparency, highlight the importance of suitable device concepts and processing techniques. In this work, we make use of the high transparency of TMDC monolayers to fabricate transparent light-emitting devices (LEDs). MOCVD-grown WS2 is embedded as the active material in a scalable vertical device architecture and combined with a silver nanowire (AgNW) network as a transparent top electrode. The AgNW network was deposited onto the device by a spin-coating process, providing contacts with a sheet resistance below 10 Ω sq−1 and a transmittance of nearly 80%. As an electron transport layer we employed a continuous 40 nm thick zinc oxide (ZnO) layer, which was grown by atmospheric pressure spatial atomic layer deposition (AP-SALD), a precise tool for scalable deposition of oxides with defined thickness. With this, LEDs with an average transmittance over 60% in the visible spectral range, emissive areas of several mm2 and a turn-on voltage of around 3 V are obtained.

Double-Network Protein Hydrogels as Flexible Pressure Sensors for Contactless Delivery

To meet the growing demand for sustainable development and ecofriendliness, hydrogels based on biopolymers have attracted widespread attention for developing flexible pressure sensors. Natural globular proteins exhibit great potential for developing biobased pressure sensors owing to their advantages of high water solubility, easy gelation, biocompatibility, and low production cost. However, realizing globular protein hydrogel-based sensors with interfacial and bulk toughness for pressure sensing and use in wearable devices remains a challenge. This study focuses on developing a high-performance flexible pressure sensor based on a biobased protein hydrogel. Consequently, a flexible protein/polyacrylamide (PAM) hydrogel with a featured double-network (DN) structure linked covalently with hydrogen bonds was first synthesized via a one-pot method based on natural ovalbumin (OVA). The unique DN structure of the as-synthesized OVA/PAM hydrogel affords excellent mechanical performance, flexibility, and adhesion properties. The mechanical properties of the DN hydrogel were enhanced after further cross-linking with Fe3+ and treatment with glycerol. Subsequently, the flexible pressure sensor was constructed by sandwiching a microstructured OVA/PAM dielectric layer between two flexible silver nanowire electrodes. The obtained sensor exhibits a high sensitivity of 2.9 kPa–1 and a short response time of 18 ms, ensuring the ability to monitor physiological signals. Based on its excellent performance, the fabricated sensor was used for monitoring the signals obtained using practical applications such as wrist bending, finger knocking, stretching, international Morse code, and pressure distribution. Particularly, we implemented a contactless delivery system using the fabricated OVA-based pressure sensors linked to unmanned vehicles and global positioning systems, providing a solution for low-risk commodity distribution during Coronavirus disease 2019 (COVID-19).

Quantitative electrical homogeneity assessment of nanowire transparent electrodes.

The homogeneous distribution of electric current (electrical homogeneity) is not guaranteed in nanowire electrodes but is crucial for the stability of the electrode and actually desirable in most applications. Despite the relevance of this feature, it is common practice to perform qualitative assessments at the electrode scale, thus masking local effects. To address this issue, we have developed a computational strategy to aid in the design of nanowire electrodes with improved electrical homogeneity. Nanowire electrodes are modeled as two-dimensional networks of stick and junction resistors (with resistance Rw and Rj, respectively) to simulate the electric conduction process. Electrodes are discretized into regular grids of squares and the electrical power of the network contained in each square is computed. The mismatch between the areal power density of the entire electrode and that of the squares provides a quantitative electrical homogeneity evaluation. Repeating the analysis with squares of different size yields an evaluation that spans across length scales. A scalar indicator, coined the homogeneity index, summarizes the results of the multiscale evaluation. The proposed strategy is employed to assess the electrical homogeneity of silver nanowire electrodes through the analysis of scanning electron microscopy images. Our results agree with the outcomes of the experimental assessment performed on the same electrodes. Parametric studies are performed by varying nanowire content and nanowire-to-junction resistance ratio Rw/Rj. We observe that a significant reduction of contact resistance is not necessary to ensure a high degree of homogeneity. The ideal condition of negligible junction resistance (Rw ≫ Rj) leads to the best-case scenario, a situation which is closely approached if Rw ≈ Rj (15% difference at the most in terms of homogeneity index).

Silver Nanowire Electrodes Integrated in Organic Solar Cells with Thick Active Layer Based on a Low‐Cost Donor Polymer

Transparent electrodes are a key component in the manufacturing of optoelectronic devices such as light‐emitting diodes, touch screens, and solar cells. The transparent electrode commonly used in this field is based on indium tin oxide (ITO). It contains indium, which is an expensive, rare, difficult to extract, and depleting element, hence the need to find an alternative. Silver nanowire (AgNW) electrodes are one of the best alternatives due to their excellent electrical, optical, and mechanical properties. Herein, it is shown that embedding AgNWs between two layers of ZnO nanoparticles (ZnONPs) leads to superior optical and electrical performance. The validation of the ZnONPs/AgNWs/ZnONPs electrode using the reference PF2:PC70BM organic active layer, known to present a long carrier lifetime, in inverted solar cell architectures shows an increased absorption of the active layer. This enhancement is due to the electrical field resulting from plasmonic resonance because the absorption is proportional to the square of the electric field amplitude. Through photoluminescence spectroscopy, a shorter exciton lifetime in PF2 in the presence of AgNWs is also observed. All these processes lead to improved photovoltaic performance compared to ITO‐based reference, with approximately 20% increase in photocurrent and overall power conversion efficiency.

Enhanced scratch resistance of silver nanowire electrodes using a polyether acrylate and silica composite overcoating

• AgNWs were coated with polyether acrylate resin and silica composite (PAR). • PAR coating increased scratch resistance of AgNW electrodes. • No significant degradation of optical and electrical properties of AgNWs was observed. Silver nanowires (AgNWs) are a promising electrode material for next-generation flexible/wearable electronics; however, the industrial use of AgNWs is limited owing to their poor resistance to scratch damage. In this study, a UV-curable polyether acrylate resin and silica composite (PAR) was adopted as an overcoating material on the AgNW electrodes to improve the scratch resistance. The simple formation of PAR overcoating on the AgNW electrodes was possible because of its UV-curable characteristics. In addition, nanoscale silica particles in PAR blocked the penetration of the scratching tip through PAR overcoating, thereby protecting the AgNWs from scratch damage. The PAR-coated AgNW electrodes showed excellent scratch resistance, with no significant degradation in optical transmittance, sheet resistance, and figure of merit. The strategy of using UV-curable PAR composite overcoating will accelerate the actual usage of AgNW electrodes in flexible electronics.

Microwave-Welded and Photopolymer-Embedded Silver Nanowire Electrodes for Skin-like Supercapacitors

Microwave-Welded and Photopolymer-Embedded Silver Nanowire Electrodes for Skin-like Supercapacitors

Highly Reliable Sensitive Capacitive Tactile Sensor with Spontaneous Micron‐Pyramid Structures for Electronic Skins

AbstractIn recent years, it is still challenging to develop a capacitive tactile sensor with low cost, high sensitivity, and controllable morphology. Herein, the flexible capacitive pressure sensor (FCPS) with high sensitivity is fabricated via a one‐step template method to produce spontaneous micron‐pyramid structured polydimethylsiloxane (PDMS) by releasing a four‐way stretched PDMS film treated with ultraviolet ozone exposure. The capacitive sensor is composed of two silver nanowire electrodes coated on polyimide substrate and a patterned PDMS dielectric layer sandwiching in the middle, exhibits an ultrahigh sensitivity of 15.66 kPa−1, an ultralow limit of detection of 0.2 Pa, a fast response time of 42.4 ms, and excellent cycling stability. The finite‐elemental analysis suggests that the uniform micro‐pyramid structures are vital to obtain ultrahigh sensitivity, low detection limit, and fast response. In particular, the FCPS can keep the tactile performance unchanged after 4000 repeated tests, reflecting the high robustness. In conclusion, the significant advantages of the sensor enable it to be well applied in the fields of sign language detection, spatial pressure distribution, and physiological signal monitoring, indicating that FCPS has a potential application prospect in the fields of flexible wearable electronic devices and electronic skins.

Uniform Silver Nanowire Patterned Electrode on Robust PEN Substrate Using Poly(2-hydroxyethyl methacrylate) Underlayer.

Silver nanowire (AgNW) electrodes are among the most essential flexible transparent electrodes (FTEs) emerging as promising alternatives to brittle indium tin oxide (ITO) electrodes. The polymer comprising the plastic substrate to which the AgNWs are applied must also satisfy the mechanical requirements of the final device and withstand the device processing conditions. However, AgNW-based FTEs have some limitations, such as poor adhesion to coated plastic substrates, surface roughness, and difficulty in patterning. This study demonstrates a new strategy for creating AgNW-based patterned flexible poly(ethylene 2,6-naphthalate) (PEN)-based electrodes with appreciable optical and electrical properties. Introducing poly(2-hydroxyethyl methacrylate) on the PEN substrate enhanced the adhesion between the substrate and AgNWs and improved the dispersibility of the AgNWs. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) and a small amount of 2,4-hexadiyne-1,6-diol as a photosensitizer were coated onto the AgNW layer to improve the surface roughness and achieve an effective electrode pattern. By varying the AgNW concentration, we could tune the density and thickness of the AgNWs to optimize the sheet resistance and transmittance. Optimized AgNWs with a sheet resistance of 22.6 Ω/□ and transmittance of 92.3% at 550 nm were achieved. A polymer solar cell (PSC) was fabricated to evaluate the characteristics of the device employing the flexible electrodes. This PSC showed not only a high power conversion efficiency of 11.20%, similar to that of ITO-based devices, but also excellent mechanical stability, which is difficult to achieve in ITO-based flexible devices.

Silver Nanowire Composite Electrode Enabling Highly Flexible, Robust Organic Photovoltaics

Using Ag nanowires (NWs) is a promising approach to make flexible and transparent conducting electrodes for organic photovoltaics (OPVs). However, the roughness of the NWs can decrease device performance. Herein, a Ag NW electrode embedded in a UV‐curable epoxy that uses a simple mechanical lift‐off process resulting in highly planar electrodes is demonstrated. A bimodal blend of Ag NWs with varying aspect ratios is used to optimize the transparency and conductivity of the electrode. In addition, a ZnO layer is coated on the Ag NWs prior to the embedding process to ensure low contact resistance in the OPV cells. The resulting resin‐embedded ZnO‐encapsulated silver nanowire (REZEN) electrode is found to have excellent mechanical stability. REZEN electrode‐based OPV cells exhibit comparable performance with reference devices, achieving maximum power conversion efficiency (PCE) of 13.5% and 13.6% respectively. The REZEN‐based OPV cells are also mechanically robust, retaining 97% of their PCE after 5000 cycles at R = 1.2 mm and 94% PCE after 1000 cycles at R = 0.55 mm. This flexibility is among the highest reported for freestanding devices. Thus, the REZEN electrode is a promising and simple strategy to achieve mechanically robust ITO‐free flexible OPV cells.

Amino‐Terminated Hyperbranched Polymer‐Based Recyclable Elastic Fibers for a Breathable and Antibacterial Triboelectric Nanogenerator

AbstractRealizing recyclable triboelectric active materials with commendable elasticity, breathability, and durable antibacterial performance is significant for the sustainable development of wearables and bioelectronics. A spinnable elastic polymer (MPVA) is developed by modifying polyvinyl alcohol (PVA) with amino‐terminated hyperbranched polymers (HBP‐NH2), demonstrating a junction‐reinforced electrospun nanofiber membrane (MPVA) with lower Young's modulus and improved stretchability, which exhibits robust network structure and tunable air permeability to sustain 50 tensile cycles at 50% strain. Trapped silver nanoparticles (Ag NPs) in the fibers reduced in situ by the terminal groups of HBP‐NH2 demonstrate MPVA/Ag NPs nanofiber membrane with reliable antibacterial capability for both E. coli and S. aureus. By spraying a silver nanowires (Ag NWs) electrode on the antibacterial fiber membrane to serve as a single‐electrode stretchable (≈50% strain) triboelectric nanogenerator (TENG), it is demonstrated that stable triboelectric output can be maintained regardless of resistance change (ΔR/R0) within 50%. Self‐powered identification of contacting objects is demonstrated. The antibacterial breathable fiber membrane can be facilely dissolved in water for regeneration via electrospinning, which is promising for sustainable development of future transient TENGs and bioelectronics.

29‐3: Invited Paper: Ultra‐thin Stretchable LCD Using Deformable Polarizer

We developed the ultra‐thin and stretchable LCD using the deformable polarizer. The LCD has substrate‐less structure formed by direct coating of silver nanowire electrode on the polarizer. The total thickness of the LCD is 23μm and it achieved excellent bending and stretching performances.

Realizing 17.5% Efficiency Flexible Organic Solar Cells via Atomic-Level Chemical Welding of Silver Nanowire Electrodes.

Solution processable flexible transparent electrodes (FTEs) are urgently needed to boost the efficiency and mechanical stability of flexible organic solar cells (OSCs) on a large scale. However, how to balance the optoelectronic properties and meanwhile achieve robust mechanical behavior of FTEs is still a huge challenge. Silver nanowire (AgNW) electrodes, exhibiting easily tuned optoelectronic/mechanical properties, are attracting considerable attention, but their poor contacts at the junction site of the AgNWs increase the sheet resistance and reduce mechanical stability. In this study, an ionic liquid (IL)-type reducing agent containing Cl- and a dihydroxyl group was employed to control the reduction process of silver (Ag) in AgNW-based FTEs precisely. The Cl- in the IL regulates the Ag+ concentration through the formation and dissolution of AgCl, whereas the dihydroxyl group slowly reduces the released Ag+ to form metal Ag. The reduced Ag grew in situ at the junction site of the AgNWs in a twin-crystal growth mode, facilitating an atomic-level contact between the AgNWs and the reduced Ag. This enforced atomic-level contact decreased the sheet resistance, and enhanced the mechanical stability of the FTEs. As a result, the single-junction flexible OSCs based on this chemically welded FTE achieved record power conversion efficiencies of 17.52% (active area: 0.062 cm2) and 15.82% (active area: 1.0 cm2). These flexible devices also displayed robust bending and peeling durability even under extreme test conditions.