Large scale, highly conductive and patterned transparent films of silver nanowires on arbitrary substrates and their application in touch screens

The application of silver nanowire films as transparent conductive electrodes has shown promising results recently. In this paper, we demonstrate the application of a simple spray coating technique to obtain large scale, highly uniform and conductive silver nanowire films on arbitrary substrates. We also integrated a polydimethylsiloxane (PDMS)-assisted contact transfer technique with spray coating, which allowed us to obtain large scale high quality patterned films of silver nanowires. The transparency and conductivity of the films was controlled by the volume of the dispersion used in spraying and the substrate area. We note that the optoelectrical property, σ(DC)/σ(Op), for various films fabricated was in the range 75-350, which is extremely high for transparent thin film compared to other candidate alternatives to doped metal oxide film. Using this method, we obtain silver nanowire films on a flexible polyethylene terephthalate (PET) substrate with a transparency of 85% and sheet resistance of 33 Ω/sq, which is comparable to that of tin-doped indium oxide (ITO) on flexible substrates. In-depth analysis of the film shows a high performance using another commonly used figure-of-merit, Φ(TE). Also, Ag nanowire film/PET shows good mechanical flexibility and the application of such a conductive silver nanowire film as an electrode in a touch panel has been demonstrated.     

Transparente leitfähige Elektroden

Transparent conductive oxides and alternative transparent electrodes for organic photovoltaics and OLEDs Organic, photoactive devices, such as OLEDs or organic solar cells, currently use indium tin oxide (ITO) as transparent electrode. Whereas ITO is industry‐proven for many years and shows very good electrical and optical properties, its application for lowcost and flexible devices might not be optimal. For such applications innovative technologies such as networkbased metal nanowire or carbon nanotube electrodes, graphene, conductive polymers, metal thin‐films and alternative transparent conductive oxides emerge. Although some of these technologies are rather experimental and far from application, some of them have the potential to replace ITO in selected applications.     

Ultra thin nickel transparent electrodes

Transparent electrodes made of ultra thin metals have recently been demonstrated with performances comparable to those offered by transparent conductive oxides (TCOs), which are traditionally used in applications such as photovoltaic cells, light emitting devices, photodetectors and electro-optical modulators. In this work we report highly uniform, optically transparent and electrically conductive nickel films. Their good performance, combined with low cost and simplicity in processing, make ultra thin Ni films highly competitive, even with respect to the latest developments in TCO technology. Nickel films can be easily incorporated into an industrial process flow and could therefore be an attractive alternative to TCOs in many industrial applications.     

Electrochromic modulation of near-infrared light by WO<Subscript>3</Subscript> films deposited on silver nanowire substrates

Silver nanowire (Ag NW) transparent conductive electrodes with high conductivity and optical transmittance are fabricated. Then, WO₃ films are deposited on Ag NW electrodes by an electrochemical deposition method. The WO₃/Ag NW films act as obvious optical modulators in the visible region. More importantly, the WO₃/Ag NW films have distinct advantage on NIR modulation over conventional WO₃/ITO electrode. Meanwhile, the WO₃/Ag NW films own high electrochromic efficiency of 86.9 cm² C^?1 at NIR region of 1100 nm. Furthermore, electrochromic devices (ECDs) based on Ag NW substrates are fabricated in this study, which exhibit excellent cycling stability and distinct modulation of near-infrared light compared with ITO-based ECDs. This work is the first study that reports the application of Ag NW-based electrochromic films and electrochromic devices in modulation of NIR light. It exhibits bright prospects that the electrochromic materials deposited on Ag NW electrodes may find potential application in thermal control and emission detectors for spacecraft.     

纳米线透明导电薄膜的制备及在光电器件中的应用

基于纳米线的透明导电薄膜具有光电性能优异、制备成本低廉以及可用于制备柔性器件等优点,在透明导电薄膜材料领域占据重要地位。文章着眼于阐述纳米线透明导电薄膜的制备及其在光电器件中的应用。首先详细介绍了滴涂、浸渍、抽滤、迈耶棒涂布、旋涂、喷印、印刷等7种制备纳米线透明导电薄膜的方法。光电器件是应用透明导电薄膜的重要领域,文章还介绍了纳米线透明导电薄膜在太阳能电池和电致发光器件中的应用。纳米线透明导电薄膜中,银纳米线和铜纳米线透明导电薄膜最受关注,其制备工艺日趋完善,有望率先在工业应用中取得突破。     

Stretchable,Electrochemically-Stable Electrochromic Devices Based on Semi-Embedded Ag@Au Nanowire Network

Stretchable electrochromic (EC) devices that can adapt the irregular and dynamic human surfaces show promising applications in wearable display, adaptive camouflage, and visual sensation. However, challenges exist in lacking transparent conductive electrodes with both tensile and electrochemical stability to assemble the complex device structure and endure harsh electrochemical redox reactions. Herein, a wrinkled, semi-embedded Ag@Au nanowire (NW) networks are constructed on elastomer substrates to fabricate stretchable, electrochemically-stable conductive electrodes. The stretchable EC devices are then fabricated by sandwiching a viologen-based gel electrolyte between two conductive electrodes with the semi-embedded Ag@Au NW network. Because the inert Au layer inhibits the oxidation of Ag NWs, the EC device exhibits much more stable color changes between yellow and green than those with pure Ag NW networks. In addition, since the wrinkled semi-embedded structure is deformable and reversibly stretched without serious fractures, the EC devices still maintain excellent color-changing stability under 40% stretching/releasing cycles.     

Optical properties of conductive silver-nanowire films with different nanowire lengths

Transparent electrodes made of silver nanowires (Ag NWs) exhibit a higher flexibility than conventional indium tin oxide electrodes.For this reason,Ag NWs may find applications in future flexible electronic and optoelectronic devices.However,different optoelectronic devices have different specific requirements for Ag NWs.For example,the optical transmittance haze is an important but rarely studied aspect of Ag NW films.In this study,the optical transmittance and optical scattering of long (5-50 μm,L-NWs) and short (1-20 μm,S-NWs) Ag NW films were investigated.The L-NWs exhibited better optical transmission than the S-NWs,whereas the S-NWs exhibited better light-scattering properties than the L-NWs.Our results indicate that the L-NWs are suitable for touch-screen displays,whereas the S-NWs are better suited as transparent conductive films for solar cells.We analyzed the scattering ratio of forward-scattered light to backscattered light for both the L-NWs and S-NWs and discovered that the mesh size affected the scattering ratio.For longer wavelengths,a larger mesh yielded a higher backscattering ratio,whereas a smaller mesh yielded a lower backscattering ratio.We formulated an equation for calculating the reflection haze using the total reflection (Ag NWs/glass),R and the reflection of glass,R0.The reflection haze of the S-NWs and L-NWs exhibited different trends in the visible-near-infrared region.An omnidirectional scattering model for the Ag NWs was used to evaluate the Ag NW scattering properties.The results of this study have great significance for the evaluation of the performance of Ag NWs in optoelectronic devices.     

Ag层厚度对AZO/Ag/AZO透明导电薄膜性能的影响

在室温条件下,采用磁控溅射技术在玻璃衬底上生长了AZO/Ag/AZO多层透明导电薄膜。主要研究了Ag层厚度对多层透明导电薄膜结构和性能的影响。研究表明,AZO和Ag分别延(002)面和(111)面高度择优生长,随着Ag层厚度的增加,多层透明导电薄膜的电阻率不断降低,透过率呈现先降低再增加最后再降低的变化趋势,其中Ag层厚度为8nm的样品获得最大品质因子33.1×10^-3Ω^-1,综合性能最佳。     

铜纳米线的合成、优化及其透明电极的应用

随着光伏产业、平板显示技术的发展, 市场对于透明导电材料的需求量迅速增加。传统的透明导电材料氧化铟锡(ITO)面临着资源不足、脆性大的问题, 无法满足市场需求。铜纳米线透明电极导电性好、成本低、柔性好, 是一种有潜力的新一代透明导电材料。近年来, 铜纳米线的合成及其在透明导电领域的应用引起了研究人员的关注, 并取得显著的进展。本文从铜纳米线的合成方法、合成机理, 铜纳米线透明电极的制备方法及后处理手段, 铜纳米线透明电极在光伏器件、电加热元件、柔性可穿戴器件中的应用等方面的研究进展进行了阐述。并对铜纳米线研究及应用前景进行了展望。     

Metal Nanowire Networks: The Next Generation of Transparent Conductors

There is an ongoing drive to replace the most common transparent conductor, indium tin oxide (ITO), with a material that gives comparable performance, but can be coated from solution at speeds orders of magnitude faster than the sputtering processes used to deposit ITO. Metal nanowires are currently the only alternative to ITO that meets these requirements. This Progress Report summarizes recent advances toward understanding the relationship between the structure of metal nanowires, the electrical and optical properties of metal nanowires, and the properties of a network of metal nanowires. Using the structure–property relationship of metal nanowire networks as a roadmap, this Progress Report describes different synthetic strategies to produce metal nanowires with the desired properties. Practical aspects of processing metal nanowires into high‐performance transparent conducting films are discussed, as well as the use of nanowire films in a variety of applications.     

Uniform,highly conductive,and patterned transparent films of a percolating silver nanowire network on rigid and flexible substrates using a dry transfer technique

Silver nanowire films are promising alternatives to tin-doped indium oxide (ITO) films as transparent conductive electrodes. In this paper, we report the use of vacuum filtration and a polydimethylsiloxane (PDMS)-assisted transfer printing technique to fabricate silver nanowire films on both rigid and flexible substrates, bringing advantages such as the capability of patterned transfer, the best performance among various ITO alternatives (10 Ω/sq at 85% transparency), and good adhesion to the underlying substrate, thus eliminating the previously reported adhesion problem. In addition, our method also allows the preparation of high quality patterned films of silver nanowires with different line widths and shapes in a matter of few minutes, making it a scalable process. Furthermore, use of an anodized aluminum oxide (AAO) membrane in the transfer process allows annealing of nanowire films at moderately high temperature to obtain films with extremely high conductivity and good transparency. Using this transfer technique, we obtained silver nanowire films on a flexible polyethylene terephthalate (PET) substrate with a transparency of 85%, a sheet resistance of 10 Ω/sq, with good mechanical flexibility. Detailed analysis revealed that the Ag nanowire network exhibits two-dimensional percolation behavior with good agreement between experimentally observed and theoretically predicted values of critical volume.      

Metallic Nanowire‐Based Transparent Electrodes for Next Generation Flexible Devices: a Review

Transparent electrodes attract intense attention in many technological fields, including optoelectronic devices, transparent film heaters and electromagnetic applications. New generation transparent electrodes are expected to have three main physical properties: high electrical conductivity, high transparency and mechanical flexibility. The most efficient and widely used transparent conducting material is currently indium tin oxide (ITO). However the scarcity of indium associated with ITO's lack of flexibility and the relatively high manufacturing costs have a prompted search into alternative materials. With their outstanding physical properties, metallic nanowire (MNW)‐based percolating networks appear to be one of the most promising alternatives to ITO. They also have several other advantages, such as solution‐based processing, and are compatible with large area deposition techniques. Estimations of cost of the technology are lower, in particular thanks to the small quantities of nanomaterials needed to reach industrial performance criteria. The present review investigates recent progress on the main applications reported for MNW networks of any sort (silver, copper, gold, core‐shell nanowires) and points out some of the most impressive outcomes. Insights into processing MNW into high‐performance transparent conducting thin films are also discussed according to each specific application. Finally, strategies for improving both their stability and integration into real devices are presented.     

The effect of annealing on structural, electrical and optical properties of nanostructured ZnS/Ag/ZnS films

In this paper a ZnS/Ag/ZnS (ZAZ) nano-multilayer structure is designed theoretically and optimum thicknesses of ZnS and Ag layers are calculated at 35 and 17 nm, respectively. Several conductive transparent ZAZ nano-multilayer films are deposited on a glass substrate at room temperature by thermal evaporation method. Changes in the electrical, structural, and optical properties of samples are investigated with respect to annealing in air at different temperatures. High-quality nano-multilayer films with the sheet resistance of 8 Ω/sq and the optical transmittance of 83% at 200 °C annealing temperature are obtained. The figure of merit is applied on the ZAZ films and their performance as transparent conductive electrodes are determined.     

Transparent Plasmonic Nanowire Electrodes via Self‐Organised Ion Beam Nanopatterning

A self‐organised approach for the synthesis of transparent metal nanowire arrays is based on defocused ion beam sputtering. The nanowire arrays, supported on low‐cost dielectric substrates (glass slides), feature a dual functionality: they exhibit anisotropic conductivity, with sheet resistances which are reduced in comparison to those of transparent conductive oxides, and additionally they support localised plasmon resonances. The latter represents an attractive feature in view of plasmon enhanced photon harvesting applications, in which the nanostructured metal electrodes are employed as an alternative to conventional transparent conductive oxides.     

High quality transparent conductive ZnO/Ag/ZnO multilayer films deposited at room temperature

We have fabricated, by simultaneous DC and RF magnetron sputtering, multilayer transparent electrodes having much lower electrical resistance than the widely used transparent conductive oxide electrodes. The multilayer structure consists of three layers (ZnO/Ag/ZnO). Ag films with different film thickness were used as metallic layers. Optimum thicknesses of Ag and ZnO films were determined for high optical transmittance and good electrical conductivity. Several analytical tools such as spectrophotometer, atomic force microscopy, scanning electron microscopy and four-point probe were used to explore the possible changes in electrical and optical properties. A high quality transparent electrode, having resistance as low as 3 Ω/sq and high optical transmittance of 90% was obtained at room temperature and could be reproduced by controlling the preparation process parameters. The electrical and optical properties of ZnO/Ag/ZnO multilayers were determined mainly by the Ag film properties. The performance of the multilayers as transparent conducting materials was also compared using a figure of merit.     

有机-无机透明导电薄膜的研究进展

透明导电膜是一种重要的光电材料,应用广泛.以传统的无机氧化物和导电高分子材料制备的导电薄膜虽然电学性能优良,但综合性能不甚理想.通过有机-无机杂化的透明导电薄膜能够借助各组成材料特性的互补作用使复合材料具有出色的综合性能.介绍了透明导电薄膜的种类、用途和特性,综述了有机-无机杂化导电材料在块体材料和透明导电薄膜方面的应用,并展望了其发展前景.     

Development of new transparent conductors and device applications utilizing a multidisciplinary approach

Transparent and conductive films are key components for optoelectronic devices. They are applied as n-type transparent electrical contacts for inorganic and organic light emitting diodes, solar cells and flat panel displays as well as p- and n-type active semiconductive oxides to setup wide band gap p-n junctions and devices for the emerging field of transparent and radiation hard electronics.The demand for these films is strongly increasing due to the extensive market growth in these areas but the solutions available today only partially fulfill the requirements on low resistivity, high transmittance, large area deposition, low cost manufacturing, and ability for fine patterning, light scattering and precise alignment of the electronic structure to surrounding semiconductors.The cooperation of five Fraunhofer Institutes within the “Fraunhofer Project MAVO METCO” aims towards establishing fundamental knowledge and control about the defect chemistry, structure and morphology of the transparent semiconductive oxides. The goal is to achieve materials with outstanding properties such as n-type transparent conductive oxides with tailored work function and excellent durability, novel delafossite based p-type materials allowing cost effective large area deposition, oxide based p-n heterojunctions and Ag based electrodes to be used for thin film photovoltaics and organic light emitting diodes.Starting from first-principle modelling of the electronic structure, we address the development of new transparent conductive layers by PVD and Sol-Gel ending up with device implementation for OLEDs and organic as well as Si based a-Si:H/µc-Si:H and HIT solar cells.     

Washable,stretchable, and reusable core–shell metal nanowire network-based electronics on a breathable polymer nanomesh substrate

Polymer nanofiber-based porous structures, referred to as “breathable devices,” have been recently developed to minimize user discomfort. Although these devices enable conformal integration to the skin with gas permeability, their performance and durability are significantly lower than those of conventional film-based devices. In this study, an ultradurable embedded Ag–Au core–shell nanowire network (AANN) on a nanomesh substrate is fabricated using the intense pulsed light irradiation and electroplating (IPL-EP) process. The AANN is designed to achieve breathability and durability without sacrificing device performance. It can be used in breathable nanomesh electronics and exhibits a low sheet resistance (1.4 Ω sq⁻¹), cycle stability (above 20,000 cycles), stability in chemicals (water-based solutions and highly corrosive H₂O₂ solution), washability (20 washings), and reusability. Additionally, it is used in reusable conductive electronic textiles, and its applications as a reusable strain sensor for motion detection and wearable heater for thermal therapy are demonstrated. Furthermore, the AANN-based conductive thread exhibits excellent electrical performance (0.3 Ω cm⁻¹) with durability and maintains its electrical characteristics after 50 wash cycles. The proposed process can enable large-scale fabrication of highly durable breathable electronics, electronic textiles, and other biomedical devices.     

银纳米线透明导电薄膜的失效机理研究

银纳米线透明导电薄膜材料作为新兴的无铟电极材料, 以其优越的光电性能和力学柔韧性, 在显示器件、触控面板、太阳能电池、智能加热和电磁屏蔽等领域崭露头角, 吸引越来越多的来自科研界及产业界的关注。然而, 银纳米线透明导电薄膜在应用中面临着较为严重的稳定性问题, 主要表现为容易被痕量含硫气体腐蚀, 在300 ℃以上的温度下纳米线出现断裂和球形化等结构失稳现象, 在紫外光照条件下腐蚀及球形化加剧, 在加载电场条件下出现离子迁移并产生孔洞及断裂现象。本文详细介绍了以上各种失效现象, 分析了失效的微观机制, 介绍了解决各种失效现象的具体措施。银纳米线透明导电薄膜失效行为的研究, 有助于进一步推动该材料的实际应用进程。