Photonic post-processing of a multi-material transparent conductive electrode architecture for optoelectronic device integration

Emerging flexible optoelectronic devices require multi-material processing capabilities to fully enable the use of temperature-sensitive substrates and materials. This report demonstrates how photonic sintering enables the processing of materials with very different properties. For example, charge carrier transport/blocking metal-oxides, and transparent conductive silver nanowire-based electrodes ought to be compatible with low-energy and high-throughput processing for integration onto flexible low-temperature substrates. Compared to traditional post-processing methods, we show a rapid fabrication route yielding highly-stable hybrid electrode architectures on polyethylene terephthalate (PET). This architecture consists of an interconnected silver nanowire network encapsulated with a thin crystalline photo-sensitive titanium dioxide (TiO2) coating, allowing both layers to be treated using independent photonic post-processing sintering steps. The first step sinters the nanowires, while the second completes the conversion of the top metal-oxide layer from amorphous to crystalline TiO2. This approach improves on the fabrication speed compared to oven processing, while delivering optical and electrical characteristics comparable to the state of the art. Optimized transparency values reach 85% with haze values down-to 7% at 550 nm, while maintaining a sheet resistance of 18.1 Ω sq.-1. However, this hybrid architecture provides a much stronger resilience to degradation, which we demonstrate through exposure to harsh plasma conditions. In summary, this study shows how carefully-optimized photonic curing post-processing can provide more-stable hybrid architectures while using a multi-material processing technique suitable for high-volume manufacturing on low-temperature substrates.

Multiobjective Optimization of Silver-Nanowire Deposition for Flexible Transparent Conducting Electrodes

Optimizing the spin coating of silver nanowires to form transparent conducting electrodes (TCE) is guided by machine learning (ML). A good TCE has two competing characteristics: high transmittance and high conductance. Optimization using a scalar figure of merit, as often done in the field, cannot satisfy the independent requirements for transmittance and conductance imposed by specific applications. By performing a Pareto front analysis based on ML models, we show that the desired outcomes of transmittance ≥ 75% and sheet resistance ≤ 15 Ω/sq are challenging but can be achieved using processing parameters identified by ML analysis.

Silver-Nanowire-Based Elastic Conductors: Preparation Processes and Substrate Adhesion

The production of flexible electronic systems includes stretchable electrical interconnections and flexible electronic components, promoting the research and development of flexible conductors and stretchable conductive materials with large bending deformation or torsion resistance. Silver nanowires have the advantages of high conductivity, good transparency and flexibility in the development of flexible electronic products. In order to further prepare system-level flexible systems (such as autonomous full-software robots, etc.), it is necessary to focus on the conductivity of the system's composite conductor and the robustness of the system at the physical level. In terms of conductor preparation processes and substrate adhesion strategies, the more commonly used solutions are selected. Four kinds of elastic preparation processes (pretensioned/geometrically topological matrix, conductive fiber, aerogel composite, mixed percolation dopant) and five kinds of processes (coating, embedding, changing surface energy, chemical bond and force, adjusting tension and diffusion) to enhance the adhesion of composite conductors using silver nanowires as current-carrying channel substrates were reviewed. It is recommended to use the preparation process of mixed percolation doping and the adhesion mode of embedding/chemical bonding under non-special conditions. Developments in 3D printing and soft robots are also discussed.

Solution-Processed Flexible Transparent Electrodes for Printable Electronics

Flexible transparent electrodes (FTEs) have been widely witnessed in various printable electronic devices, especially those involving light. So far, solution processes have demonstrated increasing advantages in preparing FTEs not only in their mild operation conditions and high-throughput but also in the diversity in micropatterning conductive nanomaterials into networks. For the FTEs, both high transparency and high conductivity are desirable, which therefore create requirements for the conductive network by considering the trade-off relationship between the coverage and the micropatterns of the network. In addition, the conductive networks also affect the flexibility of FTEs due to the deformation during bending/stretching. Consequently, solution processes capable of micropatterning conductive nanomaterials including nanoparticles, nanowires/polymers, and graphene/MXene play a crucial role in determining the performance of FTEs. Here, we reviewed recent research progress on solution-processed FTEs, including the solution processes, the solution-processable conductive nanomaterials and the substrates for making FTEs, and applications of FTEs in flexible electronics. Finally, we proposed several perspective outlooks of the FTEs, which aim at not only the enhanced performance but also the performances in extreme conditions and in integration. We believe that the review would offer inspiration for developing functional FTEs.

Continuous Patterning of Silver Nanowire-Polyvinylpyrrolidone Composite Transparent Conductive Film by a Roll-to-Roll Selective Calendering Process

The roll-to-roll (R2R) continuous patterning of silver nanowire-polyvinylpyrrolidone (Ag NW-PVP) composite transparent conductive film (cTCF) is demonstrated in this work by means of slot-die coating followed by selective calendering. The Ag NWs were synthesized by the polyol method, and adequately washed to leave an appropriate amount of PVP to act as a capping agent and dispersant. The as-coated Ag NW-PVP composite film had low electronic conductivity due to the lack of percolation path, which was greatly improved by the calendering process. Moreover, the dispersion of Ag NWs was analyzed with addition of PVP in terms of density and molecular weight. The excellent dispersion led to uniform distribution of Ag NWs in a cTCF. The continuous patterning was conducted using an embossed pattern roll to perform selective calendering. To evaluate the capability of the calendering process, various line widths and spacing patterns were investigated. The minimum pattern dimensions achievable were determined to be a line width of 0.1 mm and a line spacing of 1 mm. Finally, continuous patterning using selective calendering was applied to the fabrication of a flexible heater and a resistive touch sensing panel as flexible electronic devices to demonstrate its versatility.

Solution processed high performance perovskite solar cells based on a silver nanowire-titanium dioxide hybrid top electrode

Longer silver nanowires (AgNWs) > 50 μm and even 90 μm in length have been produced via a polyol method by just changing the stirring speed at a temperature of 130 °C. As-synthesized longer AgNWs are further utilized to construct transparent conductive AgNWs films by a facile drop-casting technique that attained a sheet resistance of 14.5 Ω sq-1 and transmittance over 85%, which is higher than ITO film. The use of a AgNWs/TiO2 hybrid electrode decreases the sheet resistance to 8.3 Ω sq-1, which is attributed to the enhancement of connections between AgNWs by filling the empty spaces between nanowires and TiO2 nanoparticles. Transparent perovskite solar cells (PSCs) on the basis of these AgNWs and AgNWs/TiO2 hybrid top electrodes were made and examined. Due to the light scattering nature of TiO2 nanoparticles, optical transmittance of the AgNWs/TiO2 hybrid electrode enhances to some extent after the coating of a TiO2 layer. Both cell efficiencies and stability of the PSCs are enhanced by using the AgNWs/TiO2 top electrode. A power conversion efficiency (PCE) of 10.65% was attained for perovskite devices based on only the AgNW electrode with a sheet resistance of 14.5 Ω sq-1. A PCE of 14.53% was achieved after coating with TiO2 nanoparticles, indicating the layer effect of TiO2 coating.

Fabrication of Flexible Wiring with Intrinsically Conducting Polymers Using Blue-Laser Microstereolithography

Recently, flexible devices using intrinsically conductive polymers, particularly poly(3,4-ethylenedioxythiophene) (PEDOT), have been extensively investigated. However, most flexible wiring fabrication methods using PEDOT are limited to two-dimensional (2D) fabrication. In this study, we fabricated three-dimensional (3D) wiring using the highly precise 3D printing method of stereolithography. Although several PEDOT fabrication methods using 3D printing systems have been studied, few have simultaneously achieved both high conductivity and precise accuracy. In this study, we review the post-fabrication process, particularly the doping agent. Consequently, we successfully fabricated wiring with a conductivity of 16 S cm^-1. Furthermore, flexible wiring was demonstrated by modeling the fabricated wiring on a polyimide film with surface treatment and creating a three-dimensional fabrication object.

Regeneration of interfacial bonding force of waste carbon fibers by light: Process demonstration and atomic level analysis

Although interest in recycling carbon fibers is rapidly growing, practical applications of recycled carbon fibers (rCFs) are limited owing to their poor wettability and adhesion. Surface modification of CFs was achieved through intense pulsed light (IPL) irradiation, which functionalizes surface of rCFs. Surface energy, chemical composition, morphology, and interfacial shear strength (IFSS) of rCFs before and after IPL irradiation were investigated. The rCF IPL-irradiated at 1,200 V improved both polar and dispersive components of surface energy, and the IFSS significantly increased by 2.93 times in relation to that of the pristine rCF and reached 95% of that of high-grade commercial CFs. We proposed a mechanism by which oxygen functional groups on the rCF surface enhance the molecular bonding force with HDPE, and the model was validated from molecular dynamics simulations. IPL irradiation is a rapid and effective surface treatment method that can be employed for the manufacture of rCF-reinforced composites.

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IPL irradiation was utilized for surface modification to control HDPE/rCF interfaces

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The IPL-irradiated rCF showed an increase in oxygen functional groups and roughness

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MD simulation revealed IFSS was enhanced by chemical interaction and interlocking

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Surface treatment using IPL energy facilitates commercialization of rCF composites

Advances in constructing silver nanowire-based conductive pathways for flexible and stretchable electronics

With their soaring technological demand, flexible and stretchable electronics have attracted many researchers' attention for a variety of applications. The challenge which was identified a decade ago and still remains, however, is that the conventional electrodes based on indium tin oxide (ITO) are not suitable for ultra-flexible electronic devices. The main reason is that ITO is brittle and expensive, limiting device performance and application. Thus, it is crucial to develop new materials and processes to construct flexible and stretchable electrodes with superior quality for next-generation soft devices. Herein, various types of conductive nanomaterials as candidates for flexible and stretchable electrodes are briefly reviewed. Among them, silver nanowire (AgNW) is selected as the focus of this review, on account of its excellent conductivity, superior flexibility, high technological maturity, and significant presence in the research community. To fabricate a reliable AgNW-based conductive network for electrodes, different processing technologies are introduced, and the corresponding characteristics are compared and discussed. Furthermore, this review summarizes strategies and the latest progress in enhancing the conductive pathway. Finally, we showcase some exemplary applications and provide some perspectives about the remaining technical challenges for future research.

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.

A review on intense pulsed light process as post-treatment for metal oxide thin films and nanostructures for device application

The intense pulsed light (IPL) post-treatment process has attracted great attention in the device fabrication due to its versatility and rapidity particularly for solution process functional structures in devices, flexible/printed electronics, and continuous manufacturing process. The metal oxide materials inherently have multi-functionality and have been widely used in form of thin films or nanostructures in device application such as thin film transistors, light emitting diodes, solar cells, supercapacitors, etc. The IPL treatment enhances the physical and/or chemical properties of the functional metal oxide through photothermal effects. However, most metal oxides are transparent to most range of visible light and require more energy for post-treatment. In this review, we have summarized the IPL post-treatment processes for metal oxide thin films and nanostructures in device applications. The sintering and annealing of metal oxides using IPL improved the device performances by employing additional light absorbing layer or back-reflector. The IPL process becomes an innovative versatile post-treatment process in conjunction with multi-functional metal oxides in near-future device applications.

Highly sensitive, flexible and biocompatible temperature sensor utilizing ultra-long Au@AgNW-based polymeric nanocomposites

Owing to their excellent sensitivity, stretchability, flexibility and conductivity, polymeric nanocomposites with conductive fillers have shown promise for a wide range of applications in bioelectronics and wearable devices. Herein, we report on the development of a flexible and biocompatible polymeric nanocomposite comprising ultra-long Ag-Au core-sheath nanowires (Au@AgNWs) dispersed in elastomeric media to fabricate a high-resolution wearable temperature sensor. Ultra-long AgNWs with an aspect ratio of about 1500 were synthesized using a Ca²⁺ ion-mediated facile one-pot polyol process. To enhance the biocompatibility and anti-oxidative property of the AgNWs, a 10-20 nm gold (Au) layer was conformably deposited without affecting the original nanowire morphology. The core-sheath structure of Au@AgNWs was characterized using HRTEM and EDS elemental mapping while the biocompatibility and anti-oxidative properties were tested using hydrogen peroxide (H₂O₂) etching in solution phase. Finally, the fabricated nanowires were used to prepare the Au@AgNW-poly-ethylene glycol (PEG)-polyurethane (PU)-based nanocomposite ink which can be printed on interdigitated electrodes to fabricate a thermoresistive temperature sensor with negative temperature coefficient (NTC) of resistance and quick response time (<100 s). The Au@AgNW-PEG-PU nanocomposite was characterized in detail and a novel temperature sensing mechanism based on controlling the internanowire distance of the PEG coated Au@AgNWs percolation by means of capillarity force among the nanowires as a result of the glass transition temperature of thermosensitive PEG was demonstrated. The proposed printable temperature sensor is flexible and biocompatible and shows promise for a range of wearable applications.

Patterning of Metal Nanowire Networks: Methods and Applications

With the advance in flexible and stretchable electronics, one-dimensional nanomaterials such as metal nanowires have drawn much attention in the past 10 years or so. Metal nanowires, especially silver nanowires, have been recognized as promising candidate materials for flexible and stretchable electronics. Owing to their high electrical conductivity and high aspect ratio, metal nanowires can form electrical percolation networks, maintaining high electrical conductivity under deformation (e.g., bending and stretching). Apart from coating metal nanowires for making large-area transparent conductive films, many applications require patterned metal nanowires as electrodes and interconnects. Precise patterning of metal nanowire networks is crucial to achieve high device performances. Therefore, a high-resolution, designable, and scalable patterning of metal nanowire networks is important but remains a critical challenge for fabricating high-performance electronic devices. This review summarizes recent advances in patterning of metal nanowire networks, using subtractive methods, additive methods of nanowire dispersions, and printing methods. Representative device applications of the patterned metal nanowire networks are presented. Finally, challenges and important directions in the area of the patterning of metal nanowire networks for device applications are discussed.

High-performance silver nanowires transparent conductive electrodes fabricated using manufacturing-ready high-speed photonic sinterization solutions

On the long road towards low-cost flexible hybrid electronics, integration and printable solar energy harvesting solutions, there is an urgent need for high-performance transparent conductive electrodes produced using manufacturing-ready techniques and equipment. In recent years, randomly-distributed metallic nanowire-based transparent mesh electrodes have proven highly-promising as they offer a superb compromise between high performances and low fabrication costs. Unfortunately, these high figure-of-merit transparent mesh electrodes usually rely heavily on extensive post-deposition processing. While conventional thermal annealing yields good performances, it is especially ill-suited for deposition on low-temperature substrates or for high-throughput manufacturing solutions. Similarly, laser-induced annealing severely limits the processing time for electrodes covering large surfaces. In this paper, we report the fabrication of ultra high-performance silver nanowires-based transparent conductive electrodes fabricated using optimized manufacturing-ready ultrafast photonic curing solutions. Using conventional indium tin oxide (ITO) as our benchmark for transparent electrodes, we demonstrate a 2.6–2.7 \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\times $$\end{document}× performance gain using two different figure-of-merit indicators. Based on these results, we believe this research provides an ideal manufacturing-ready approach for the large-scale and low-cost fabrication of ultra high-performance transparent electrodes for flexible hybrid electronics and solar-energy harvesting applications.

Flexible, transparent and tough silver nanowire/nanocellulose electrodes for flexible touch screen panels

Flexible touch screen panel (f-TSP) has been emerging recently and metallic nanowire transparent conductive electrodes (TCEs) are its key components. However, most metallic nanowire (MNW) TCEs suffer from weak bonding strength between metal nanowire electrode layers and polymer substrates, which causes delamination of TCEs and produces serious declines in durability of f-TSPs. Here, we introduce AgS bonding and develop tough and strong electrode-substrate bonded MNW TCEs, which can enhance durability of f-TSPs significantly. We used silver nanowires (AgNWs) as metal conductive electrode and thiol-modified nanofibrillated cellulose (NFC-HS) nanopaper as substrates. Because of the existence of Ag from AgNWs and S from NFC-HS, strong AgS bonding was generated and tough TCEs were obtained. The TCEs exhibit excellent electrical stability, outstanding optical and electrical properties. The f-TSP devices integrated with the TCEs illustrate striking durability. This technique may provide a promising strategy to produce flexible and tough TCEs for next-generation high-durability f-TSPs.

Fabricating functional circuits on 3D freeform surfaces via intense pulsed light-induced zinc mass transfer

Deployment of functional circuits on a 3D freeform surface is of significant interest to wearable devices on curvilinear skin/tissue surfaces or smart Internet-of-Things with sensors on 3D objects. Here we present a new fabrication strategy that can directly print functional circuits either transient or long-lasting onto freeform surfaces by intense pulsed light-induced mass transfer of zinc nanoparticles (Zn NPs). The intense pulsed light can locally raise the temperature of Zn NPs to cause evaporation. Lamination of a kirigami-patterned soft semi-transparent polymer film with Zn NPs conforming to a 3D surface results in condensation of Zn NPs to form conductive yet degradable Zn patterns onto a 3D freeform surface for constructing transient electronics. Immersing the Zn patterns into a copper sulfate or silver nitrate solution can further convert the transient device to a long-lasting device with copper or silver. Functional circuits with integrated sensors and a wireless communication component on 3D glass beakers and seashells with complex surface geometries demonstrate the viability of this manufacturing strategy.

Rapid nanowelding of silver nanowires by focused-light-scanning for high-performance flexible transparent electrodes

Silver nanowires (AgNWs) have been considered as one of the most promising flexible transparent electrodes (FTEs) material for next-generation optoelectronic devices. However, the large contact resistance between AgNWs could deteriorate the conductivity of FTEs. In the present work, high-performance AgNWs FTEs were obtained by means of focused-light-scanning (FLS), which could lead to the large-area, rapid and high-quality welding between AgNWs within a short time, forming the reliable and stable AgNWs network. The results of the optoelectronic tests show that after FLS, the sheet resistance of the AgNWs FTEs sharply decreased from 5113 Ω/sq to 7.7 Ω/sq, with maintaining a high transmittance (∼94%). Finally, a high-performance flexible transparent heater was fabricated by using FLS, showing reach a relatively high temperature in a short response time and rapid response at low input voltage. The findings offer an effective pathway to greatly improve the conductivity of AgNWs FTEs.

Flexible and transparent silver nanowires/biopolymer film for high-efficient electromagnetic interference shielding

Flexible and transparent conductive films are highly desirable in some optoelectronic devices, such as smart windows, touch panels, as well as displays and electromagnetic protection field. Silver nanowire (Ag NW) has been considered as the best material to replace indium tin oxide (ITO) to fabricate flexible transparent electromagnetic interference (EMI) shielding films due to its superior comprehensive performance. However, the common substrates supporting Ag NWs require surface modification to enhance the adhesion with Ag NWs. In this work, a flexible and transparent Ag NWs EMI shielding film with sandwich structure through a facile rod-coating method, wherein Ag NWs network were embedded between biodegradable gelatin-based substrate and cover layer. The interfacial adhesion between Ag NWs and gelatin-based layers was enhanced by hydrogen-bonding interaction and swelling effect without any pretreatment. The shielding effectiveness (SE) of the G/Ag NW/G (G represents gelatin-based layer) film reaches 37.74 dB at X band with an optical transmittance of 72.0 %. What's more, the flexible gelatin-based layer and encapsulated structure endow the resultant G/Ag NW/G film integrating excellent mechanical properties, reliable durability, antioxidation, as well as anti-freezing performance. This work paves a new way for fabricating flexible transparent EMI shielding films.

Highly stabilized flexible transparent capacitive photodetector based on silver nanowire/graphene hybrid electrodes

The need for photodetectors in various fields has gradually emerged, and several studies in this area are therefore being conducted. For photodetectors to be used in various environments, their transparency, flexibility, and durability must be ensured. However, the development of flexible photodetectors based on the current measurement techniques of conventional photodetectors has been difficult owing to the limitations of semiconductor materials. In this study, a new type of flexible and transparent capacitive photodetector was fabricated to address the shortcomings of conventional photodetectors. In addition, by introducing graphene electrodes to a new type of manufactured photodetector, devices with excellent overall chemical, thermal, and mechanical durability have been developed. Compared to photodetectors based on pristine Ag nanowire (AgNW) electrodes, AgNW/graphene hybrid electrode-based photodetectors exhibit a 20% higher photosensitivity. Also, the hybrid AgNW/graphene electrode on the dielectric layer exhibited low sheet resistance (~ 8 Ω/sq) and relatively high transmittance (~ 45%).

Laser shock pressing of silver nanowires on flexible substrates to fabricate highly uniform transparent conductive electrode films

Large surface roughness, wire-to-wire junction resistance, and poor adhesion strength of percolated silver nanowire films on polymer substrates are critical issues responsible for low shunt resistance, electron concentration, and thermal damage, resulting in the occurrence of dark spots and damage to flexible electronic devices. Therefore, the fabrication of transparent conductive electrode (TCE) thin films with high surface smoothness and enhanced film properties without the aforementioned problems is essential. Herein, we propose an innovative method to mechanically join silver nanowires on heat-sensitive polymer substrates using a laser-induced shock pressure wave generated by laser ablation of a sacrificial layer. The physical joining mechanism and film properties, that is, sheet resistance, transmittance, adhesion strength, and flexibility, were experimentally analyzed. When a high laser shock pressure was applied to the silver nanowires, plastic deformation occurred; thus, a sintered network film was fabricated through solid-state atomic diffusion at the nanowire junctions. Under optimal process conditions, the sintered films showed high resistance to the adhesion tape test (R/R ₀ = 1.15), a significantly reduced surface roughness less than 6 nm, and comparable electrical conductivity (8 ± 2 [Formula: see text]) and visible transmittance (84% ± 3%) to typical joining methods. Consequently, this work demonstrates that the laser-induced shock pressing technique has strong potential for the production of TCE metal films on heat-sensitive flexible substrates with film properties superior to those of films produced by conventional methods.

Understanding the plasmon-enhanced photothermal effect of a polarized laser on metal nanowires

Improving photothermal efficiency can reduce the melting threshold of metal nanowires. The photothermal efficiency of a polarized laser to Cu nanowires was investigated by numerical simulation and experiment. Our simulation results reveal that the photothermal efficiency of a polarized laser depends on the intensity and distribution area of surface plasmons excited by the laser. As the angle between the polarization direction of the incident laser and the long axis of the Cu nanowire increases, the laser-excited surface plasmons shift from both ends to the sidewall of the Cu nanowire. Such a distribution of surface plasmons was confirmed by the melting behavior of Cu nanowires irradiated by a 450 nm polarized laser. Increasing the laser wavelength will enhance the intensity of the surface plasmons but reduce the distribution area of the surface plasmons. As a result, a higher photothermal efficiency was achieved using a laser with a polarization direction perpendicular to the long axis of the Cu nanowire and a wavelength less than 550 nm. Due to the higher photothermal efficiency, the melting threshold of Cu nanowire irradiated by a laser with polarization perpendicular to the long axis of the Cu nanowire is 32 mW, which is around 20% lower that of Cu nanowire irradiated by a laser with polarization parallel to the long axis of the Cu nanowire.

Silver Nanowire Synthesis and Strategies for Fabricating Transparent Conducting Electrodes

One-dimensional metal nanowires, with novel functionalities like electrical conductivity, optical transparency and high mechanical stiffness, have attracted widespread interest for use in applications such as transparent electrodes in optoelectronic devices and active components in nanoelectronics and nanophotonics. In particular, silver nanowires (AgNWs) have been widely researched owing to the superlative thermal and electrical conductivity of bulk silver. Herein, we present a detailed review of the synthesis of AgNWs and their utilization in fabricating improved transparent conducting electrodes (TCE). We discuss a range of AgNW synthesis protocols, including template assisted and wet chemical techniques, and their ability to control the morphology of the synthesized nanowires. Furthermore, the use of scalable and cost-effective solution deposition methods to fabricate AgNW based TCE, along with the numerous treatments used for enhancing their optoelectronic properties, are also discussed.

Recycling silver nanoparticle debris from laser ablation of silver nanowire in liquid media toward minimum material waste

As silver nanowires (Ag NWs) are usually manufactured by chemical synthesis, a patterning process is needed to use them as functional devices. Pulsed laser ablation is a promising Ag NW patterning process because it is a simple and inexpensive procedure. However, this process has a disadvantage in that target materials are wasted owing to the subtractive nature of the process involving the removal of unnecessary materials, and large quantities of raw materials are required. In this study, we report a minimum-waste laser patterning process utilizing silver nanoparticle (Ag NP) debris obtained through laser ablation of Ag NWs in liquid media. Since the generated Ag NPs can be used for several applications, wastage of Ag NWs, which is inevitable in conventional laser patterning processes, is dramatically reduced. In addition, electrophoretic deposition of the recycled Ag NPs onto non-ablated Ag NWs allows easy fabrication of junction-enhanced Ag NWs from the deposited Ag NPs. The unique advantage of this method lies in using recycled Ag NPs as building materials, eliminating the additional cost of junction welding Ag NWs. These fabricated Ag NW substrates could be utilized as transparent heaters and stretchable TCEs, thereby validating the effectiveness of the proposed process.

The surface plasmonic welding of silver nanowires via intense pulsed light irradiation combined with NIR for flexible transparent conductive films

In this work, surface plasmonic welding of silver nanowires (AgNWs) by intense pulse light (IPL) combined with NIR was investigated. AgNWs were coated on a flexible PET (polyethylene terephthalate) substrate using a bar-coater. The coated AgNW films were welded at room temperature and under ambient conditions by white IPL from a xenon lamp, assisted with light from a UV-C (ultraviolet C) and NIR (near infra-red) lamp using an in-house multi-wavelength IPL welding system. In order to investigate the welding mechanism, in situ monitoring with a Wheatstone bridge electrical circuit was performed. The sheet resistance changes of AgNW films during the welding process were monitored under various IPL conditions (e.g. light energy and on-time) with and without UV-C and NIR light irradiation. The microstructure of the welded AgNW film and the interface between the AgNW film and the PET substrate were observed using a scanning electron microscope (SEM) and transmission electron microscope (TEM). COMSOL multi-physics simulations were conducted and compared with the in situ monitoring results to discuss the in-depth mechanism of the IPL welding of AgNWs and its dependence on the wavelength of light. From this study, the optimal IPL welding conditions and appropriate wavelength were suggested, and the optimized IPL welding process could produce AgNW film with a lower sheet resistance (45.2 Ω sq^-1) and high transparency (96.65%) without damaging the PET substrate.

Highly efficient and stable transparent electromagnetic interference shielding films based on silver nanowires

Transparent electromagnetic interference (EMI) shielding materials with high optical transmittance and outstanding shielding effectiveness (SE) for optoelectronic devices in visual windows are urgently needed. Herein, we demonstrate the preparation of a transparent EMI shielding film based on silver nanowires (Ag NWs) via a facile Mayer-rod coating method. The electrical conductivity and transmittance of Ag NW-based films can be greatly improved through treatment with NaBH₄ and the lamination of poly(diallyldimethyl-ammonium chloride). The coverage of the polymer decreases the surface roughness, with no damage on the uniform mesh of the Ag NWs. The Ag NW/PDDA composite films present a sheet resistance of 22 Ω sq^-1 at a transmittance of 95.5%, better than that of commercial indium tin oxide (ITO). The excellent optoelectrical performance of the Ag NW/PDDA composite film is further ascertained by fitting the transmittance with the resistance, with a figure of merit of 443. The Ag NW/PDDA composite films in this study exhibit greatly improved stability during 25 °C/65% RH aging for 35 days with the assistance of the coverage layer. Moreover, the EMI SE of the Ag NW/PDDA composite films is 28 dB on average at a transmittance of 91.3%, and continuously increases to 31.3 dB while the optical transmittance is still maintained at 86.8%, which is superior to those of most reported transparent EMI shielding materials. Taken together, the excellent optical transmittance and EMI shielding performance of the Ag NW/PDDA composite film make it an outstanding transparent EMI shielding material in optoelectronic devices, such as aerospace equipment, medical devices, communication facilities, and electronic displays.

Synergistic Optimization toward the Sensitivity and Linearity of Flexible Pressure Sensor via Double Conductive Layer and Porous Microdome Array

Recently, wearable pressure sensors have attracted considerable interest in various fields such as healthcare monitoring, intelligent robots, etc. Although artificial structures or conductive materials have been well developed, the trade-off between sensitivity and linearity of pressure sensors is yet to be fully resolved by a traditional approach. Herein, from theoretical analysis to experimental design, we present the novel CPDMS/AgNWs double conductive layer (DCL) to synergistically optimize the sensitivity and linearity of piezoresistive pressure sensors. The facilely fabricated solid microdome array (SDA) is first employed as the elastomer to clarify the unrevealed working mechanism of DCL. Attributed to the synergistic effect of DCL, the DCL/SDA based sensor exhibits ultrahigh sensitivity (up to 3788.29 kPa^-1) in an obviously broadened linearity range (0-6 kPa). We also demonstrated that the synergistic effect of DCL can be regulated with use of porous microdome array (PDA) to further optimize the sensing property. The linearity range can be improved up to 70 kPa while preserving the high sensitivity of 924.37 kPa^-1 based on the interlocked PDA structure (IPDA), which is rarely reported in previous studies. The optimized sensitivity and linearity allow the competitive DCL/IPDA based sensor as a reliable platform to monitor kinds of physiological signals covering from low pressures (e.g., artery pulses), medium pressures (e.g., muscle expansions), to high pressures (e.g., body motions). We believe that the methodology along with the robust sensor can be of great potential for reliable healthcare monitoring and wearable electronic applications in the future.

Ag flake/silicone rubber composite with high stability and stretching speed insensitive resistance via conductive bridge formation

High stability, stretchable speed insensitive properties, high stretchability, and electrical conductivity are key characteristics for the realisation of wearable devices. However, conventional research is mainly focused on achieving only high stretchability and electrical conductivity. Studies on the stability and stretching speed insensitive properties generally require complex fabrication processes, which are in need of further improvement. In this study, we propose a facile formation of a conductive bridge in composites by using surface damage and the viscoelastic property of the polymer. Surface cracks due to repeated stretching cycles formed conductive bridges via stress relaxation of the viscoelastic polymer matrix. The conductive bridge resulted in the conductor having highly stable resistance values at target strains and stretching speed insensitive resistance, even at stretching speeds that were 20 times faster than the minimum.

Control of thermal deformation with photonic sintering of ultrathin nanowire transparent electrodes

Development of electronic devices on ultrathin flexible plastic substrates is of great value in terms of portability, cost reduction, and mechanical flexibility. However, because thin plastic substrates with low heat capacity can be more easily damaged by thermal energy, their use is limited. Highly flexible nanowire (NW) transparent conductive electrodes on ultrathin (∼10 μm) low cost polyethylene terephthalate (PET) substrates are fabricated. The control of intense pulsed light (IPL) irradiation process parameters to induce NW welding for maximum conductivity and minimal thermal damage of the PET substrate is explored. For this purpose, trends in temperature variation of NW thin films irradiated by IPL under various operating conditions are numerically analyzed using commercial software. Simulations indicate that irradiating light operated at a higher voltage and for a shorter time, and use of multiple pulses of low frequency can reduce thermal deformation of the PET substrate. Furthermore, we experimentally confirm that NW transparent electrodes can be successfully fabricated with less thermal deformation of the ultrathin plastic substrate when light is irradiated under well-controlled conditions derived from the simulation. The highly flexible NW transparent conducting electrode exhibits excellent mechanical flexibility to withstand severe deformation and can be successfully implemented in flexible organic light-emitting diodes (OLEDs).

Near-Field Electrospinning for Three-Dimensional Stacked Nanoarchitectures with High Aspect Ratios

Near-field electrospinning (NFES) was developed to overcome the intrinsic instability of traditional electrospinning processes and to facilitate the controllable deposition of nanofibers under a reduced electric field. This technique offers a straightforward and versatile method for the precision patterning of two-dimensional (2D) nanofibers. However, three-dimensional (3D) stacked structures built by NFES have been limited to either micron-scale sizes or special shapes. Herein, we report on a direct-write 3D NFES technique to construct self-aligned, template-free, 3D stacked nanoarchitectures by simply adding salt to the polymer solution. Numerical simulations suggested that the electric field could be tuned to achieve self-aligned nanofibers by adjusting the conductivity of the polymer solution. This was confirmed experimentally by using poly(ethylene oxide) (PEO) solutions containing 0.1-1.0 wt% NaCl. Using 0.1 wt% NaCl, nanowalls with a maximum of 80 layers could be built with a width of 92 ± 3 nm, height of 6.6 ± 0.1 μm, and aspect ratio (height/width) of 72. We demonstrate the 3D printing of nanoskyscrapers with various designs, such as curved "nanowall arrays", nano "jungle gyms," and "nanobridges". Further, we present an application of the 3D stacked nanofiber arrays by preparing transparent and flexible polydimethylsiloxane films embedded with Ag-sputtered nanowalls as 3D nanoelectrodes. The conductivity of the nanoelectrodes can be precisely tuned by adjusting the number of 3D printed layers, without sacrificing transmittance (98.5%). The current NFES approach provides a simple, reliable route to build 3D stacked nanoarchitectures with high-aspect ratios for potential application in smart materials, energy devices, and biomedical applications.

A Flexible and Highly Sensitive Pressure Sensor Based on AgNWs/NRLF for Hand Motion Monitoring

Flexible, highly sensitive, easy fabricating process, low-cost pressure sensors are the trend for flexible electronic devices. Inspired by the softness, comfortable, environmental friendliness and harmless of natural latex mattress, herein, we report an agile approach of constructing a flexible 3D-architectured conductive network by dip-coating silver nanowires (AgNWs) on the natural rubber latex foam (NRLF) substrate that provide the 3D micro-network structure as the skeleton. The variation of the contact transformed into the electrical signal among the conductive three-dimensional random networks during compressive deformation is the piezoresistive effect of AgNWs/NRLF pressure sensors. The resulting AgNWs/NRLF pressure sensors exhibit desirable electrical conductivity (0.45-0.50 S/m), excellent flexibility (58.57 kPa at 80% strain), good hydrophobicity (~128° at 5th dip-coated times) and outstanding repeatability. The AgNWs/NRLF sensors can be assembled on a glove to detect hand motion sensitively such as bending, touching and holding, show potential application such as artificial skin, human prostheses and health monitoring in multifunctional pressure sensors.

Binding Conductive Ink Initiatively and Strongly: Transparent and Thermally Stable Cellulose Nanopaper as a Promising Substrate for Flexible Electronics

For flexible electronics, the substrates play key roles in ensuring their performance. However, most substrates suffer from weak bonding with the conductive ink and need additional aids. Here, inspired by the Ag-S bond theory, a novel cellulose nanopaper substrate is presented to improve the bond strength with the Ag nanoparticle ink through a facile printing method. The substrate is fabricated using thiol-modified nanofibrillated cellulose and exhibits excellent optical properties (∼85%@550 nm), ultra-small surface roughness (3.47 nm), and high thermal dimensional stability (up to at least 90 °C). Most importantly, it can attract Ag nanoparticles initiatively and bind them firmly, which enable the conductive ink to be printed without using the ink binder and form a strong substrate-ink bonding and maintain a stable conductivity of 2 × 10^-4 Ω cm even after extensive peeling and bending. This work may lead to exploring new opportunities to fabricate high-performance flexible electronics using the newly developed nanopaper substrate.

Alloying and Embedding of Cu-Core/Ag-Shell Nanowires for Ultrastable Stretchable and Transparent Electrodes

In this paper, transparent electrodes with dense Cu@Ag alloy nanowires embedded in the stretchable substrates are successfully fabricated by a high-intensity pulsed light (HIPL) technique within one step. The intense light energy not only induces rapid mutual dissolution between the Cu core and the Ag shell to form dense Cu@Ag alloy nanowires but also embeds the newly formed alloy nanowires into the stretchable substrates. The combination of alloy nanowires and embedded structures greatly improve the thermal stability of the transparent electrodes that maintain a high conductivity unchanged in both high temperature (140 °C) and high humidity (85 °C, 85% RH) for at least 500 h, which is much better than previous reports. The transparent electrodes also exhibit high electromechanical stability due to the strong adhesion between alloy nanowires and substrates, which remain stable after 1000 stretching-relaxation cycles at 30% strain. Stretchable and transparent heaters based on the alloyed and embedded electrodes have a wide outputting temperature range (up to 130 °C) and show excellent thermal stability and stretchability (up to 60% strain) due to the alloy nanowires and embedded structures. To sum up, this study proposes the combination of alloying and embedding structures to greatly improve the stability of Cu nanowire-based stretchable transparent electrodes, showing a huge application prospect in the field of stretchable and wearable electronics.

Ultraflexible Transparent Bio-Based Polymer Conductive Films Based on Ag Nanowires

The unstable mechanical properties of flexible transparent conductive films (TCFs) make it difficult for them to meet the requirements for displays or wearable devices. Here, the relationship between the mechanism behind the bending behavior and the electrical properties, which is important for improving the mechanical stability of flexible TCFs, is explored. Flexible TCFs are reported based on silver nanowires (AgNWs) and bio-based poly(ethylene-co-1,4-cyclohexanedimethylene 2,5-furandicarboxylate)s (PECFs), with a low sheet resistance (23.8 Ω sq^-1 at 84.6% transmittance) and superior mechanical properties. The electrical properties of the AgNW/PECFs composite film show almost no change after bending for 2000 times.

High-performance flexible transparent nanomesh electrodes

A cost-effective process for producing high-performance Ag-paste-based flexible transparent nanomesh electrodes (FTNEs) was developed by optimizing their linewidth, pitch, and height. These nanomesh electrodes, with a linewidth of several hundred nanometers and a pitch of 10-200 μm on a PET substrate, achieved wide ranges of transmittance (83.1%-98.8%) and sheet resistance (1.2-30.9 Ω/sq) and a figure of merit (992-1619) superior to those of indium tin oxide and silver nanowire (AgNW) electrodes. Our evaluation of their flexibility (testing up to 50 000 cycles) and their electromagnetic interference shielding effectiveness verifies the applicability of these FTNEs to various flexible optoelectronic devices.

Modeling nanoscale temperature gradients and conductivity evolution in pulsed light sintering of silver nanowire networks

Sintering of metal nanowire (NW) networks on transparent polymers is an emerging approach for fabricating transparent conductive electrodes used in multiple devices. Pulsed light sintering is a scalable sintering process in which large-area, broad-spectrum xenon lamp light causes rapid NW fusion to increase network conductivity, while embedding the NWs in the polymer to increase mechanical robustness. This paper develops a multiphysical approach for predicting evolution of conductivity, NW fusion and nanoscale temperature gradients on the substrate during pulsed light sintering of silver NWs on polycarbonate. Model predictions are successfully validated against experimentally measured temperature and electrical resistance evolution. New insight is obtained into the diameter-dependent kinetics of NW fusion and nanoscale temperature gradients on the substrate, which are difficult to obtain experimentally. These observations also lead to the understanding that NW embedding in intense pulsed light sintering (IPL) can occur below the glass transition temperature of the polymer, and to a new differential thermal expansion-based mechanism of NW embedding during IPL. These insights, and the developed model, create a framework for physics-guided choice of NWs, substrate and process parameters to control conductivity and prevent substrate damage during the process.

Rapid Pulsed Light Sintering of Silver Nanowires on Woven Polyester for personal thermal management with enhanced performance, durability and cost-effectiveness

Fabric-based personal heating patches have small geometric profiles and can be attached to selected areas of garments for personal thermal management to enable significant energy savings in built environments. Scalable fabrication of such patches with high thermal performance at low applied voltage, high durability and low materials cost is critical to the widespread implementation of these energy savings. This work investigates a scalable Intense Pulsed Light (IPL) sintering process for fabricating silver nanowire on woven polyester heating patches. Just 300 microseconds of IPL sintering results in 30% lesser electrical resistance, 70% higher thermal performance, greater durability (under bending up to 2 mm radius of curvature, washing, humidity and high temperature), with only 50% the added nanowire mass compared to state-of-the-art. Computational modeling combining electromagnetic and thermal simulations is performed to uncover the nanoscale temperature gradients during IPL sintering, and the underlying reason for greater durability of the nanowire-fabric after sintering. This large-area, high speed, and ambient-condition IPL sintering process represents an attractive strategy for scalably fabricating personal heating fabric-patches with greater thermal performance, higher durability and reduced costs.

The comprehensive effects of visible light irradiation on silver nanowire transparent electrode

The silver nanowire (AgNW) transparent electrode is one of the promising components for flexible electronics due to its high electrical and thermal conductivity, optical transparency and flexibility. However, the application of the AgNW electrode with an improved performance is generally limited by its poor long-term stability. As the name suggests, the transparent electrode is usually exposed to visible light in various applications. Unlike other electrode materials, AgNWs show unique and complicated behavior under long-term visible light illumination. In this study, the comprehensive effect of visible light irradiation on the AgNW transparent electrode is initially investigated in detail. Light irradiation induces the migration of silver to enhance the nanowire contacts while also leading to the generation and growth of particles and diameter loss in the nanowire. Light irradiation accelerates the sulfidation and oxidation of the AgNWs as well, resulting in the emergence of degradation products on the nanowire surface. All these effects influence the sheet resistance of the AgNW electrode during light illumination. The light-induced change of sheet resistance also relates to the nanowire concentration due to the sensitivity of the wire-wire contact resistance near the percolation threshold. It is believed that this work will be a valuable reference for the design, processing and application of transparent electrodes used in numerous optoelectronic devices.

Selective Wavelength Plasmonic Flash Light Welding of Silver Nanowires for Transparent Electrodes with High Conductivity

In this work, silver nanowires (AgNWs) printed on a polyethylene terephthalate substrate using a bar coater were welded via selective wavelength plasmonic flash light irradiation. To achieve high electrical conductivity and transparent characteristics, the wavelength of the flash white light was selectively chosen and irradiated by using high-pass, low-pass, and band-pass filters. The flash white light irradiation conditions such as on-time, off-time, and number of pulses were also optimized. The wavelength range (400-500 nm) corresponding to the plasmonic wavelength of the AgNW could efficiently weld the AgNW films and enhance its conductivity. To carry out in-depth study of the welding phenomena with respect to wavelength, a multiphysics COMSOL simulation was conducted. The welded AgNW films under selective plasmonic flash light welding conditions showed the lowest sheet resistance (51.275 Ω/sq) and noteworthy transmittance (95.3%). Finally, the AgNW film, which was welded by selective wavelength plasmonic flash light with optical filters, was successfully used to make a large area transparent heat film and dye-sensitized solar cells showing superior performances.

Conductivity enhancement of silver nanowire networks via simple electrolyte solution treatment and solvent washing

As a promising replacement material for indium tin oxide in flexible electronics, silver nanowires (AgNWs) usually need complicated post-treatment to reduce the high contact resistance across the intersections when used as transparent conductive films. In this work, a widely applicable nano-joining method for improving the overall conductivity of AgNW networks with different kinds of electrolyte solutions is presented. By treatment with an electrolyte solution with appropriate ionic strengths, the insulating surfactant layer (polyvinylpyrrolidone, PVP) on the AgNWs could be desorbed, and the AgNW network could be densified. The sheet resistance of the AgNW film on a glass slide is reduced by 60.9% (from 67.5 to 26.4 Ohm sq^-1) with a transmittance of 92.5%. High-resolution transmission electron microscopy analysis indicates that atomic diffusion occurs at the intersection of two AgNWs. Thus, metallurgical bonding on the nanometer scale is achieved across the junctions of the AgNWs, leading to a significant enhancement in the conductivity of the AgNW network.

Reverse-Offset Printed Ultrathin Ag Mesh for Robust Conformal Transparent Electrodes for High-Performance Organic Photovoltaics

Mechanically durable transparent electrodes are needed in flexible optoelectronic devices to realize their long-term stable functioning, for applications in various fields such as energy, healthcare, and soft robotics. Several promising transparent electrodes based on nanomaterials have been previously reported to replace the conventional and fragile indium-tin oxide (ITO); however, obtaining feasible printed transparent electrodes for ultraflexible devices with a multistack structure is still a great challenge. Here, a printed ultrathin (uniform thickness of 100 nm) Ag mesh transparent electrode is demonstrated, simultaneously achieving high conductance, high transparency, and good mechanical properties. It shows a 17 Ω sq^-1 sheet resistance (R_sh ) with 93.2% transmittance, which surpasses the performance of sputtered ITO electrodes and other ultrathin Ag mesh transparent electrodes. The conductance is stable after 500 cycles of 100% stretch/release deformation, with an insignificant increase (10.6%) in R_sh by adopting a buckling structure. Furthermore, organic photovoltaics (OPVs) using our Ag mesh transparent electrodes achieve a power conversion efficiency of 8.3%, which is comparable to the performance of ITO-based OPVs.

Flash-induced nanowelding of silver nanowire networks for transparent stretchable electrochromic devices

Electrochromic devices (ECDs) are emerging as a novel technology for various applications like commercialized smart window glasses, and auto-dimming rear-view mirrors. Recently, the development of low-power, lightweight, flexible, and stretchable devices has been accelerated to meet the growing demand in the new wearable devices market. Silver nanowires (AgNWs) can become new primary transparent conducting electrode (TCE) materials to replace indium tin oxide (ITO) for ECDs. However, issues such as substrate adhesion, delamination, and higher resistance still exist with AgNWs. Herein, we report a high-performance stretchable flash-induced AgNW-network-based TCE on surface-treated polydimethylsiloxane (PDMS) substrates. A Xe flash light method was used to create nanowelded networks of AgNWs. Surface silane treatments increased the adhesion and durability of the films as well. Finally, ECDs were fabricated under the optimal conditions and examined under strained conditions to demonstrate the resistance and mechanical behaviours of the devices. Results showed a flexible and durable film maintaining a high level of conductivity and reversible resistance behaviour, beyond those currently achievable with standard ITO/PET flexible TCEs.

Highly conductive and transparent copper nanowire electrodes on surface coated flexible and heat-sensitive substrates

Copper nanowire (CuNW) based flexible transparent electrodes have been extensively investigated due to their outstanding performances and low price. However, commonly used methods for processing CuNW transparent electrodes such as thermal annealing and photonic sintering inevitably damage the flexible substrates leading to low transmittance. Herein, a surface coating layer was demonstrated to protect the heat-sensitive polyethylene terephthalate (PET) polymer from being destroyed by the instantaneous high temperature during the photonic sintering process. The stable ceramic surface coating layer avoided the direct exposure of PET to intense light, further reduced the heat releasing to the bottom part of the PET, protecting the flexible PET base from destruction and ensuring high transparency for the CuNW transparent electrodes. A CuNW transparent electrode on surface coated PET (C-PET) substrates with a sheet resistance of 33 Ohm sq⁻¹ and high transmittance of 82% has been successfully fabricated by the photonic sintering method using light intensity of 557 mJ cm⁻² within several seconds in ambient conditions. The surface coating layers open a novel method to optimize the rapid photonic sintering technique for processing metal nanomaterials on heat-sensitive substrates.

The optoelectrical property of CuNW transparent electrodes on C-PET substrates was superior to that on N-PET because the surface coatings protected the destruction of PET polymer by the high-energy light during the photonic sintering process.

One-step synthesis of ultra-long silver nanowires of over 100 μm and their application in flexible transparent conductive films

Silver nanowires (AgNWs) >100 μm and even 160 μm in length have been synthesized using a facile and rationally designed solvothermal method by heating preservation at 150 °C. The length of the as-synthesized AgNWs is over 4–5 times longer than those previously reported, while the diameter range is from 40 nm to 85 nm. A transparent conducting film (TCF) was fabricated using hydroxyethyl cellulose (HEC) as the adhesive polymer, and it achieved exceptional and stable optoelectronic properties. Its low sheet resistance of ∼19 Ω sq⁻¹ (on polyethylene terephthalate, PET) and high optical transmittance of ∼88% are superior to that of expensive indium tin oxide (ITO) films. More significantly, the AgNW network demonstrates excellent adhesion to PET substrates. This study indicates that ultra-long silver nanowires can serve as an alternative to ITO, which also demonstrates its potential application in flexible electronic devices.

Ultra-long silver nanowires (100–160 μm) were applied in flexible transparent conductive films showing low sheet resistance and high optical transmittance.

Low thermal emissivity surfaces using AgNW thin films

The properties of silver nanowire (AgNW) films in the optical and infrared spectral regime offer an interesting opportunity for a broad range of applications that require low-emissivity coatings. This work reports a method to reduce the thermal emissivity of substrates by the formation of low-emissivity AgNW coating films from solution. The spectral emissivity was characterized by thermal imaging with an FLIR camera, followed by Fourier transform infrared spectroscopy. In a combined experimental and simulation study, we provide fundamental data of the transmittance, reflectance, haze, and emissivity of AgNW thin films. Emissivity values were finely tuned by modifying the concentration of the metal nanowires in the films. The simulation models based on the transfer matrix method developed for the AgNW thin films provided optical values that show a good agreement with the measurements.

Printable and Flexible Copper-Silver Alloy Electrodes with High Conductivity and Ultrahigh Oxidation Resistance

Printable and flexible Cu-Ag alloy electrodes with high conductivity and ultrahigh oxidation resistance have been successfully fabricated by using a newly developed Cu-Ag hybrid ink and a simple fabrication process consisting of low-temperature precuring followed by rapid photonic sintering (LTRS). A special Ag nanoparticle shell on a Cu core structure is first created in situ by low-temperature precuring. An instantaneous photonic sintering can induce rapid mutual dissolution between the Cu core and the Ag nanoparticle shell so that core-shell structures consisting of a Cu-rich phase in the core and a Ag-rich phase in the shell (Cu-Ag alloy) can be obtained on flexible substrates. The resulting Cu-Ag alloy electrode has high conductivity (3.4 μΩ·cm) and ultrahigh oxidation resistance even up to 180 °C in an air atmosphere; this approach shows huge potential and is a tempting prospect for the fabrication of highly reliable and cost-effective printed electronic devices.

Pathways for Gold Nucleation and Growth over Protein Cages

Proteins are widely utilized as templates in biomimetic synthesis of gold nanocrystals. However, the role of proteins in mediating the pathways for gold nucleation and growth is not well understood, in part because of the lack of spatial resolution in probing the complicated biomimetic mineralization process. Self-assembled protein cages, with larger size and symmetry, can facilitate in the visualization of both biological and inorganic components. We have utilized bacteriophage P22 protein cages of ∼60 nm diameter for investigating the nucleation and growth of gold nanocrystals. By adding a gold precursor into the solution with preexisting protein cages and a reducing agent, gold nuclei/prenucleation clusters form in solution, which then locate and attach to specific binding sites on protein cages and further grow to form gold nanocrystals. By contrast, addition of the reducing agent into the solution with incubated gold precursor and protein cages leads to the formation of gold nuclei/prenucleation clusters both in solution and on the surface of protein cages that then grow into gold nanocrystals. Because of the presence of cysteine (Cys) with strong gold-binding affinity, gold nanocrystals tend to bind at specific sites of Cys, irrespective of the binding sites of gold ions. Analyzing the results obtained using these alternate routes provide important insights into the pathways of protein-mediated biomimetic nucleation of gold that challenge the importance of incubation, which is widely utilized in the biotemplated synthesis of inorganic nanocrystals.

Nanojoint Formation between Ceramic Titanate Nanowires and Spot Melting of Metal Nanowires with Electron Beam

Construction of nanoarchitectures requires techniques like joint formation and trimming. For ceramic materials, however, it is extremely difficult to form nanojoints by conventional methods like merging. In this work, we demonstrate that ceramic titanate nanowires (NWs) can be joined by spot melting under electron beam (e-beam) irradiation (EBI). The irradiation fuses the contacted spot of titanate NWs yielding an intact nanojoint. Nanojoints with different morphologies can be produced. The joint structures consist of titanium dioxide (TiO₂) rutile, anatase, and titanate phases in the direction away from the e-beam melting spot. The titanate binds to anatase via a crystallographic matching coherent interface (the oxygen atoms at the interface are shared by the two phases) and the anatase solidly binds to the rutile joint. The resulting rutile joint is stable at high temperatures. Additionally, it is demonstrated that the heat production from EBI treated rutile can be utilized to break metal NWs (Ag, Cu, and Ni) apart by spot melting. The required e-beam intensity is considerably mild (75 pA/cm²) which allows visual access and control over the NW melting. Direct melting of Ag and Cu is not applicable under EBI due to their high thermal conductivity even with high current density (500 pA/cm²). Our findings reveal that ceramic nanojoint formation and spot melting at nanoscale are applicable if the properties of nanomaterials are understood and properly utilized.