Silver Nanowire Thin Films Research Articles

Robust ZTO-reinforced Ag nanowire hybrid transparent conductive thin films with absorption-enhanced electromagnetic interference shielding property

Technological advances have accelerated the pursuit of transparent conducting thin films (TCFs) with superior mechanical properties, durability, efficient optoelectrical performance and substrate compatibility as a pivotal focus in the realm of flexible transparent electronics. Against this background, this work investigates the fabrication of multilayer silver nanowire (AgNW) thin films reinforced by zinc tin oxide (ZTO) thin film encapsulation on polycarbonate substrates by a combination of sputtering and spin-coating techniques. An investigation of the influence of AgNW percolation networks on the optoelectrical properties of ZTO/AgNW/ZTO hybrid thin films was carried out. The impact of ZTO protective layers on the enhancement of electrical properties, adhesivity, flexibility and environmental stability of the multilayer TCF was elucidated. Additionally, to explore the compatibility of the fabricated TCF in integrated device and stealth applications, its electromagnetic interference shielding properties were investigated. The hybrid TCF showed 99.47% EMI shielding efficiency with an absorption-dominant EMI shielding effectiveness of 22.7 dB in the x-band region.

Encapsulation of locally welded silver nanowire with water-free ALD-SbOx for flexible thin-film transistors

Transparent conductive electrodes are essential in the application of flexible electronics. In this work, we successfully demonstrated a novel strategy for improving mechanical/electrical properties of indium tin oxide (ITO)-free flexible silver nanowire (Ag NW) thin films. To reduce the contact resistance of Ag NWs, an ethanol-mist was used to weld the cross junction of wires at room temperature. The nano-welded Ag NWs (W-Ag NWs) were then coated with an aluminum-doped ZnO (AZO) solution, which significantly reduce the roughness of the Ag NW thin film. Finally, an ultrathin SbOx thin film of 2 nm was deposited on the film surface using a water-free low-temperature atomic layer deposition technique to protect the W-Ag NW/AZO layer from water or oxygen degradation. The treated Ag NWs have a high transmittance of 87% and a low sheet resistance of about 15 Ω/sq, which is comparable with the ITO electrode's property. After 1000 cycles of bending testing, the W-Ag NW/AZO/SbOx film practically retains its initial conductivity. Furthermore, the samples were immersed in a solution with pH values ranging from 3 to 13 for 5 min. When compared to untreated Ag NWs or those coated with AlOx thin films, W-Ag NW/AZO/SbOx had superior electrical stability. The W-Ag NW/AZO/SbOxlayer was integrated as a gate electrode on low-power operating flexible Ti-ZnO thin film transistors (TFTs). The 5% Ti-ZnO TFT has a field-effect mobility of 19.7 cm2 V s−1, an Ion/Ioff ratio of 107, and a subthreshold swing of 147 mV decade−1.

Hybrid PEDOT:PSS to obtain high-performance Ag NW-based flexible transparent electrodes for transparent heaters

Silver nanowire (Ag NW) networks are remarkable components that may be able to replace indium tin oxide (ITO) as transparent electrodes. In this paper, the Ag NW based flexible transparent electrodes are prepared via PEDOT:PSS sol–gel transition without vacuum process, provides very high figure of merit by minimizing junction resistance, and also exhibit excellent mechanical robustness against bending. The sheet resistance of the flexible Ag NW-based films reduces from 1000 to 9.4 Ω/sq. at transmittance of ~ 90%. The conduction mechanism involves Ag NWs to PEDOT:PSS carrier injection prior to the formation of a continuous metal conduction pathway. Calculations of figure of merit display a large value of 340, which is superior to that obtained from the flexible ITO, carbon nanotube, graphene, copper nanowire, and other silver nanowire and hybrid thin films. Meanwhile, the sheet resistance does not show great change after tape test due to the effect of PEDOT:PSS. Finally, the successful implementation of the prepared Ag NWs-based transparent electrodes into a flexible transparent heater is demonstrated, verifying the applicability of the electrodes. It is believed that our study is the key step toward realizing the practical use of NW flexible transparent electrodes in various flexible electronic devices.

Optical Property Change of Silver Nanowire Thin Films in Laser Patterning Process

Silver nanowire thin films are attractive materials for flexible electrodes as an alternative for conventional tin-doped indium oxide films. An appropriate patterning process is required to apply nanowire-based transparent electrodes into the optoelectronic devices. In this paper, we report the optical property change in silver nanowire transparent electrodes during laser ablation process. We discovered that, when silver nanowires were patterned by nanosecond pulsed lasers at infrared wavelength, their optical properties were changed. The change of optical properties was caused by nanoresidues remaining on the surface. It was analyzed that the color and transparency of thin films were changed because the residual nanoparticles absorbed the visible light wavelengths where silver nanoparticles possess their peak values in the absorption spectra. The nanoparticles were derived from insufficient vaporization of silver nanowires during infrared laser ablation. In the case of using an excimer laser for patterning, the nanoparticles were not left more on the surface due to complete removal of silver nanowires, since silver has higher absorption coefficient at the wavelength of excimer laser. As a result, high-quality patterning of silver nanowire thin films could be obtained without any deterioration of optical properties in transparent electrodes.

Rapid Electrochemical Cleaning Silver Nanowire Thin Films for High-Performance Transparent Conductors.

Silver nanowire (Ag-NW) thin films are of considerable interest for next-generation transparent conductors (TCs). However, their carrier transport properties are largely plagued by the residual polyvinylpyrrolidone (PVP) ligands on surface that were introduced during the synthesis of the Ag-NWs. Here we report a rapid electrochemical cleaning strategy to thoroughly remove the surface PVP ligands and greatly improve the carrier transport properties of the Ag-NW thin films while not affecting their transmittance. In particular, we show a negative electrochemical potential near the hydrogen adsorption/evolution regime can effectively displace all PVP ligands from the Ag-NW surface in 5-15 s, producing ultraclean interfaces between Ag-NW/Ag-NW junctions or Ag-NW film/active layer junction in a stacked optoelectronic device. We show that the removal of the PVP ligands can substantially reduce the sheet resistance of the Ag-NW thin film from 49 to 13 ohm/sq (with 90.91% transmittance at 550 nm) and reduce the interfacial resistance at the Ag-NW film/active layer interface by 94.3%. Such improved Ag-NW thin films can greatly enhance the sensitivity of the wearable strain sensor and the current collection efficiency of the vertically stacked devices constructed from the sandwiched thin films. These results demonstrate that the electrochemical cleaning approach is highly effective in removing surface ligands and improving both the in-plane and the out-of-plane carrier transport properties of the Ag-NW thin films, greatly facilitating their applications in electronic and optoelectronic devices.

Force sensor fabrication by AgNWs film using 532 nm pulses laser

This current study investigated the effects of laser direct writing (LDW) on the capacitance force sensor of a poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) film mixer with silver nanowire thin films by using a 532-nm laser system. The technique was combined with various scanning speeds (i.e., 800, 1000, and 1200 mm s−1) to investigate the effectiveness of the force sensor. During interdigitated electrode fabrication, the laser fluence and laser pulse repetition frequency were fixed at 5.42 J/cm2 and 40 kHz, respectively. Nonloading force and various loading force states were used to test the function of the electrode under different LDW conditions. A best correlation coefficient of approximately 0.88 confirmed a linear functional dependence between the square of the pattern width and capacitance under the micromachining speed of 1000 mm s−1. Moreover, in the nonloading force state, the capacitance value increased with the increase in the electrode pattern width under a micromachining speed of 800 mm s−1. Regarding the loading force status, the capacitance increased when the loading force increased from 18 to 90 g. When the interdigitated pattern line width was 500 μm and electrode micromachining speed was 800 mm s−1, the maximum capacitance value was 71.5 pF under a loading force of 90 g.

Fabrication of flexible indium tin oxide-free polymer solar cells with silver nanowire transparent electrode

Flexible indium tin oxide (ITO)-free poly(3-hexylthiophene):[6,6]-phenyl C61-butyric acid methyl ester (P3HT:PC61BM) solar cells with a spin-coated silver nanowire transparent electrode are demonstrated. The solution-processed silver nanowire thin film not only exhibits high transmission (∼87%), but also shows low sheet resistance Rs (∼25 Ω/sq). For solar cells with a conventional structure, the power conversion efficiency (PCE) of devices based on silver nanowires can reach around 2.29%. For the inverted structure, the PCE of devices can reach 3.39%. Conventional and inverted flexible ITO-based P3HT:PC61BM solar cells are also fabricated as a reference for comparison. For both types of solar cells, the PCE of ITO-free devices is very close that of an ITO-based polymer solar cell.

Communication—Fabrication of Imprinted ITO-Free Perovskite Solar Cells

Solution-processed silver nanowire (AgNW) thin films were designed to function as transparent electrode to replace indium tin oxide (ITO) electrode. Various times spin-coated AgNW films on substrate were fabricated and optimized according to transmission and sheet resistance Rs of electrode film. The optimized solution-processed AgNWs were further transferred and imprinted on flexible substrate (PEN) which can improve elastic modulus and mechanical properties of the electrode. Moreover, the modified AgNW electrode will possess strong endurance ability against resonant cleaning process and preprocess work. The power conversion efficiency (PCE) of flexible ITO-free perovskite solar cells based on AgNW electrode can reach 9.15%.

Welding Silver Nanowire Junctions for Transparent Conducting Films by a Rapid Electroplating Method.

A simple electrochemical method is developed in this study to weld the contact points in silver nanowire (AgNW) thin films. The AgNW thin film is first fabricated by spray coating and then submerged in a silver plating solution. By applying electrical potential over the AgNW thin films, silver ions in the plating solution are reduced into silver nanoparticles preferentially over nanowires and solder the nanomesh structures. Due to the large current density between silver nanowires, nanoparticles generated in the electroplating reaction mainly appeared at the junction. The electroplated AgNW network not only shows better conductivity with a negligible loss of transmittance, but also exhibit much better mechanical strength in the bending test.

Direct Room Temperature Welding and Chemical Protection of Silver Nanowire Thin Films for High Performance Transparent Conductors.

Silver nanowire (Ag-NW) thin films have emerged as a promising next-generation transparent electrode. However, the current Ag-NW thin films are often plagued by high NW-NW contact resistance and poor long-term stability, which can be largely attributed to the ill-defined polyvinylpyrrolidone (PVP) surface ligands and nonideal Ag-PVP-Ag contact at NW-NW junctions. Herein, we report a room temperature direct welding and chemical protection strategy to greatly improve the conductivity and stability of the Ag-NW thin films. Specifically, we use a sodium borohydride (NaBH4) treatment process to thoroughly remove the PVP ligands and produce a clean Ag-Ag interface that allows direct welding of NW-NW junctions at room temperature, thus greatly improving the conductivity of the Ag-NW films, outperforming those obtained by thermal or plasmonic thermal treatment. We further show that, by decorating the as-formed Ag-NW thin film with a dense, hydrophobic dodecanethiol layer, the stability of the Ag-NW film can be greatly improved by 150-times compared with that of PVP-wrapped ones. Our studies demonstrate that a proper surface ligand design can effectively improve the conductivity and stability of Ag-NW thin films, marking an important step toward their applications in electronic and optoelectronic devices.

Electrothermal silver nanowire thin films for In-Situ observation of thermally-driven chemical processes

We develop a novel device comprised of high optical transmittance thin films containing silver nanowires (AgNWs) in poly(methyl methacrylate) (PMMA) acting as heating elements. The electrothermal control of the AgNWs network allows us to externally trigger and tune the temperature conditions required to run chemical reactions and physicochemical processes. The device was successfully applied for the spectroscopic in-situ observation of three different model reactions: i) the thermal equilibrium of a CoCl2/HCl/H2O complex, ii) the reversible macromolecular phase transition of a pNIPAM solution, and iii) the nucleation and growth of gold nanoparticles (AuNPs). In the first case, the color of the Co2+ complex was reversibly switched from pink to blue when changing the thermal equilibrium condition. In the second one, the optical transmittance of an aqueous solution of carboxylic-terminated pNIPAM polymer was cycled from high to low as the temperature of the solution was below or above the lower critical solubility temperature (LCST) respectively. Finally, the electrothermal control on the device was applied to the study of the nucleation and growth of AuNPs in an organic solution of AuCl3 containing oleylamine acting as both the reducer and the stabilizing agent. The versatility of the electrothermal device provides an easy way to undertake thermally controlled processes and develop optical elements such as smart windows and lab-on-a-chip devices. The AgNWs-PMMA nanocomposite was also applied successfully as an electrothermal ink on the external side walls of a test tube.

Nanowelding and patterning of silver nanowires via mask-free atmospheric cold plasma-jet scanning

Silver nanowire (AgNW) thin film is a promising candidate to replace traditional indium tin oxide in optoelectronics applications. To date however, the widespread application of AgNW thin film is limited by the weak point contacts between individual AgNWs and the lack of facile patterning techniques. Here, we demonstrate a novel and facile method to not only nanoweld AgNW junctions but also pattern AgNW thin films via mask-free cold plasma-jet scanning in ambient conditions. After the plasma-jet nanowelding treatment, the morphology of AgNWs change substantially and the junctions are welded together. The nanowelded AgNWs-based thin film shows enhanced electrical and mechanical properties. On the other hand, after the plasma-jet patterning treatment, the AgNWs are etched and transformed into separated large particles. Different kinds of patterns are produced via this patterning technique. At last, a simple light emitting diode circuit is fabricated to demonstrate the suitability of the nanowelded and patterned AgNW electrodes for flexible electronic devices.

Optical constants of long silver nanowire thin films on glass calculated from the transmission spectra

Silver nanowire thin films are a promising material for an application in optoelectronic and photonic devices. The refractive index is one of the most fundamental optical properties, yet for silver nanowire films it has not been studied so far. In this study, long silver nanowires (L-Ag NWs) were synthesized via a polyol-based thermal method and then spin-coated onto glass substrates. The optical transmittance properties of L-Ag NW thin films were characterized by UV–VIS spectrometry, refractive index, dielectric coefficient of the L-Ag NW films were determined from the transmittance and reflectance data. The results show that the refractive index of the L-Ag NW film remains nearly constant over a wide wavelength range, whereas the extinction coefficient first decreased and then subsequently increased.

Vortex-assisted layer-by-layer assembly of silver nanowire thin films for flexible and transparent conductive electrodes

Silver nanowires (AgNWs) have drawn much attention as potential candidates to replace conventional transparent conductive materials such as indium tin oxide (ITO). AgNWs have advantages over ITO with respect to cost and ease of fabrication, and can be used in flexible electrodes. However, the preparation of homogeneous films from the AgNW colloidal suspension is still a challenge mainly because of the coagulation and sedimentation of AgNWs in aqueous media. In this study, uniform transparent conductive films were prepared by using AgNWs paired with poly(allylamine hydrochloride) (PAH) via the vortex-assisted layer-by-layer (VA-LbL) assembly method. We introduced poly(allylamine hydrochloride) (PAH) to bind the AgNWs to the substrates via coordination bonding. Vortex agitation was also applied during the adsorption of AgNWs to achieve a uniform deposition on the substrate. We systematically examined other experimental conditions such as the concentration of AgNW solution and temperature of the heat treatment to correlate them to the transparency and the conductivity of the films. In addition, AgNW films were prepared on transparent and flexible substrates and these exhibited excellent durability against bending (1000 bending cycles).

A Flexible Capacitive Pressure Sensor for Wearable Respiration Monitoring System

This paper presents the design, fabrication, and characterization of a wearable capacitive pressure sensor for respiration-monitoring systems. For the dielectric layer of the proposed capacitive sensor, Porous Ecoflex with a porosity of ~36% was prepared from a manually made sugar cube via a simple melting process. A polydimethylsiloxane-based silver nanowire and carbon fibers thin films were used for the sensor electrodes. The fabricated flexible pressure sensor exhibited a high sensitivity of 0.161 kPa−1 for low pressure regime (<10 kPa), a wide working pressure range of <200 kPa, and a high durability over 6000 cycles. Since the proposed sensor is flexible and resizable, it can be integrated into clothes and easily placed at any location of the human body. Finally, the practicality of the sensor was successfully demonstrated by integrating the sensor into a waist belt to monitor the real-time respiration signal of the human being. The finding is highly useful to monitor respiration signal for the detection of diseases, such as sleep apnea, asthma, and others.

Infrared, transient thermal, and electrical properties of silver nanowire thin films for transparent heaters and energy‐efficient coatings

In this study, we investigate the infrared and electrical properties as well as the thermal response of transparent silver nanowire (AgNW) based thin‐film heaters, when subjected to Joule heating. Controlling the number of layers and hence the deposition time, our spray‐coating technique allows to modulate the thermal and electrical properties of the thin films in a precise manner. In addition, this technique enables the fabrication of homogeneous and large‐area heaters, which, in terms of their electro‐optical properties, nicely compare to the performances of state‐of‐the‐art AgNW transparent electrodes. The thermal response and the electrical properties are accurately reproduced by a purposely developed physical model, which shows that the temperature dependence of the AgNW film resistance is lowered by a factor of 2 compared to bulk silver, independently of the number of deposited layers. Compared to uncoated glass, the emissivity decreases by 58% at a coverage rate of 58%. At the same time, the AgNW film can sustain a transparency as high as 81.3%. Therefore, AgNW‐based thin films can be used as a low‐emissivity coating, for e.g., energy‐efficient window glazing applications. Finally, we accurately determine the fragmentation temperature of AgNWs, which sets the ultimate limitation of use for heating applications.

Ultrafast laser ablation of transparent conductive silver nanowire thin film on polyethylene terephthalate substrate

In printed electronics, such as organic photovoltaic or organic light-emitting diode display and lighting, a transparent conductive oxide layer has to be designed to delimit the size and shape of the final device. The most commonly used material is indium tin oxide (ITO). ITO has however many downsides such as resource scarcity, expensive processing, and brittleness (especially on flexible substrates). Silver nanowires are a promising alternative to overcome these issues, although optimization is still needed to reach ITO performance in terms of transparency and conductivity. In this study, the laser process has to remove the silver nanowire layer in order to obtain an electrical isolation: no remaining bridges in the scribe due to recast material or incomplete removal can be tolerated. Laser ablation of this transparent conductive thin film deposited on polyethylene terephthalate has been investigated using an ultrafast laser source. Pulse energy and scan speed were varied to determine their influence on depth selectivity and process window. The profiles of the selectively ablated area were studied with optical, confocal, and scanning electron microscopy. Compared to irradiation through the substrate, it was shown that front side irradiation allows a much larger process window. In the latter configuration, a fluence ranging from 0.22 to 15.8 J/cm2 and a scanning speed from 200 to 3000 mm/s, at a fixed frequency of 200 kHz, allowed a clean removal of silver nanowires. Using these parameters, isolated squares were scribed and electrical resistance was measured between the inside and the outside of the squares. A good electrical isolation (&amp;gt;20 MΩ) proved the successful removal of the silver nanowire layer using picosecond laser pulses, at a wavelength of 532 nm.

Direct printed silver nanowire thin film patterns for flexible transparent heaters with temperature gradients

Silver nanowire thin film patterns are printed precisely to form transparent heaters with uniform or gradient temperature distributions.

Highly stretchable and conductive silver nanowire thin films formed by soldering nanomesh junctions.

Silver nanowires (AgNWs) have been widely used for stretchable and foldable conductors due to their percolating network nanostructure. To enhance the mechanical strength of AgNW thin films under extreme stretching conditions, in this study, we utilize a simple chemical reaction to join AgNW network connections. Upon applying a reactive ink over AgNW thin films, silver nanoparticles are preferentially generated over the nanowire junctions and solder the nanomesh structures. The soldered nanostructure reinforces the conducting network and exhibits no obvious change in electrical conductivity in the stretching or rolling process with elongation strains up to 120%. Several examples are also demonstrated to show potential applications of this material in stretchable electronic devices.

Low Cost Scalable Self-Assembly of Silver Nanowire Thin Films for Surface Enhanced Raman Scattering Application

ABSTRACTAssembly of nanowires into ordered macroscopic structures has attracted great scientific interests in the past decade. In this work, we report a rapid low-cost scalable oil-water interfacial self assembly process for fabricating aligned Ag nanowires (AgNWs) films on solid substrates. This process is much simpler than the traditional Langmuir-Blodgett (LB) techniques and allows the assembly of one–dimensional Ag nanowires onto any solid substrates without extra pretreatment of the surface of silver nanowires or the solid substrate. The present aligned AgNW films can serve as robust surface-enhanced Raman scattering (SERS) sensors for chemical and bimolecular detection with improved spectra quality and demonstrated uniformity of SERS signal using R6G dye as probe.