Emerging transparent electrodes based on thin films of carbon nanotubes, graphene, and metallic nanostructures

Transparent electrodes are a necessary component in many modern devices such as touch screens, LCDs, OLEDs, and solar cells, all of which are growing in demand. Traditionally, this role has been well served by doped metal oxides, the most common of which is indium tin oxide, or ITO. Recently, advances in nano-materials research have opened the door for other transparent conductive materials, each with unique properties. These include CNTs, graphene, metal nanowires, and printable metal grids. This review will explore the materials properties of transparent conductors, covering traditional metal oxides and conductive polymers initially, but with a focus on current developments in nano-material coatings. Electronic, optical, and mechanical properties of each material will be discussed, as well as suitability for various applications.     

High‐Performance Flexible Transparent Electrode with an Embedded Metal Mesh Fabricated by Cost‐Effective Solution Process

A new structure of flexible transparent electrodes is reported, featuring a metal mesh fully embedded and mechanically anchored in a flexible substrate, and a cost‐effective solution‐based fabrication strategy for this new transparent electrode. The embedded nature of the metal‐mesh electrodes provides a series of advantages, including surface smoothness that is crucial for device fabrication, mechanical stability under high bending stress, strong adhesion to the substrate with excellent flexibility, and favorable resistance against moisture, oxygen, and chemicals. The novel fabrication process replaces vacuum‐based metal deposition with an electrodeposition process and is potentially suitable for high‐throughput, large‐volume, and low‐cost production. In particular, this strategy enables fabrication of a high‐aspect‐ratio (thickness to linewidth) metal mesh, substantially improving conductivity without considerably sacrificing transparency. Various prototype flexible transparent electrodes are demonstrated with transmittance higher than 90% and sheet resistance below 1 ohm sq^?1, as well as extremely high figures of merit up to 1.5 × 10⁴, which are among the highest reported values in recent studies. Finally using our embedded metal‐mesh electrode, a flexible transparent thin‐film heater is demonstrated with a low power density requirement, rapid response time, and a low operating voltage.     

Fabrication of high-quality silver nanowire conductive film and its application for transparent film heaters

Here,we report a facile method to produce pure silver nanowires (AgNWs) with high yield.A highly conductive dispersant was used to ensure uniform dispersion of the AgNWs.Without any posttreatment,the AgNW networks,deposited on flexible substrates,showed excellent optoelectrical performance owing to minimal junction resistance between the AgNWs.To explore their potential in flexible optoelectronic devices,a transparent film heater was constructed based on the present AgNW networks.The heater could achieve rapid response at low input voltage and reach a relatively high temperature in a short response time.Since this high-quality AgNW film exhibits relatively low production costs and fast production time,it may have value for future electronic industry applications.     

Polarization and incidence angle-dependent transmittance of transparent nickel electrodes with various thicknesses

The polarization and incidence angle-dependent transmittance of thin nickel film with various thicknesses deposited on glass substrates was first investigated by using a modified UV-Vis spectrometer. The thin nickel films showed relatively high uniform transmittance over a wide range of wavelengths, 300-1100 nm. The thickness-dependent dielectric and optical constants extracted from the experimental transmittance are significantly distinct from those of the thick nickel film. In particular, the p-polarized light transmittance largely increases with larger incidence angle, but the s-polarized light transmittance behavior is opposite from that of p-polarized light. The difference of the polarization-dependent transmittance increases parabolically with the incidence angle.     

一种测量透明薄膜折射率的方法

利用表面粗糙度仪和分光光度计,设计了一种简便可行的测量透明薄膜折射率的方法,并举例进行了说明。     

银纳米线-聚对苯二甲酸乙二醇酯透明导电胶膜

以银纳米线作为导电填料,以聚对苯二甲酸乙二醇酯(PET)为柔性衬底,采用平板热压机通过热压方式制备了银纳米线-PET透明导电胶膜。研究了银纳米线-PET导电胶膜的耐弯曲性能、电学性能以及透光性。结果表明,所制备的银纳米线-PET导电胶膜透光率达到80%以上,表面电阻率达到1×10^-3Ω·cm。银纳米线-PET导电胶膜经过500次的弯曲循环后电阻率未下降。随着银纳米线溶液浓度的增加,银纳米线-PET导电胶膜透光性下降,表面电阻率增加。     

基底厚度小于热渗透深度的石墨烯薄膜热声理论

基于热声效应,对基底厚度小于热渗透深度的石墨烯薄膜发声器进行理论和仿真研究。首先,利用石墨烯薄膜发声器的热功率平衡方程与气体中的热弹性耦合线性方程组推导出了石墨烯薄膜发声器的近/远场声压表达式。将理论计算结果与实验测试值进行对比,二者吻合良好,验证了理论模型的正确性。然后,利用仿真软件对石墨烯薄膜的近远场声压值进行了仿真计算,并将仿真值与理论值进行对比,二者有良好的一致性,验证了仿真计算方法的有效性。研究表明,石墨烯薄膜发声器的远声场为球面波,近声场近似为平面波。在远场低频段,声压级随输出声频率的增加而缓慢增大;在近场高频段,声压级几乎不受输出声频率的影响。研究结果为基底厚度小于热渗透深度情形下的热致发声器提供了理论计算和分析方法,对石墨烯薄膜声源器件的实验研究具有指导意义。     

Exfoliation and dispersion of graphene in ethanol-water mixtures

Graphene has attracted much attention as a new nano-carbon for its unique structure and properties. However, production and dispersion of unfunctionalized graphene are still big challenges. Herein, we demonstrate a simple method for preparation and dispersion of such graphene with low cost and non toxicum. This approach is achieved by exfoliating graphite in an ethanol/water mixture and forming stable dispersion of mono- and few-layer graphenes. The ratio of ethanol/water in the mixture is found to be crucial to both the exfoliation and dispersion processes. Exfoliation in pure water or pure ethanol produces no graphene. This method avoids the conventional use of harsh oxidants and surfactants; therefore, the graphitic structure is well maintained without destruction. Benefiting from the use of ethanol and water, it can be easy to prepare transparent and conductive graphene films by vacuum filtering or spray method, and does not need special post-treatment to remove the impurity, which could be beneficial for potential applications in electronic, optic and energy areas.     

Highly flexible transparent film heaters based on random networks of silver nanowires

We demonstrate a new concept for the fabrication of flexible transparent thin film heaters based on silver nanowires. Thanks to the intrinsic properties of random networks of metallic nanowires, it is possible to combine bendability, transparency and high heating performances at low voltage, typically below 12 V which is of interest for many applications. This is currently not possible with transparent conductive oxide technologies, and it compares well with similar devices fabricated with carbon nanotubes or graphene. We present experiments on glass and poly(ethylene naphthalate) (PEN) substrates (with thicknesses of 125 μm and extremely thin 1.3 μm) with excellent heating performances. We point out that the amount of silver necessary to realize the transparent heaters is very low and we also present preliminary results showing that this material can be efficiently used to fabricate photochromic displays. To our knowledge, this is the first report of metallic nanowire-based transparent thin film heaters. We think these results could be a useful approach for the engineering of highly flexible and transparent heaters which are not attainable by existing processes.      

Transparent and conducting graphene-RNA-based nanocomposites

Ribonucleic acid (RNA) is proposed as a nonionic surfactant for the efficient exfoliation of graphite in thin flakes of few-layer graphene and the subsequent preparation of transparent and conducting thin films. Parameters such as the type of RNA used and the size of starting graphite flakes are demonstrated to be essential for obtaining RNA-graphene thin films of good quality. A model explaining the exfoliation of graphene by RNA in water is suggested. A number of post- and predeposition treatments (including thermal annealing, functionalization of the films, and the preoxidation of graphite) are critical to improve the performance of graphene-RNA nanocomposites as transparent conductors. The study establishes an ideal link between RNA and graphene, the fundamental building blocks for nanobiology and carbon-based nanotechnology.     

以Al2L3／AlN为复合绝缘缓冲层的ZnO—TTFT透过率的研究

采用射频反应磁控溅射的方法，以ITO（铟锡氧化物）玻璃为衬底，在Al2O3／AN复合栅极绝缘层上沉积有源层ZnO薄膜，并以Al作为透明薄膜晶体管器件源极和漏极，通过XRD、透射光谱研究了透明薄膜晶体管的有源层ZnO的结晶情况以及对器件在可见光范围内的透过特性的影响，得出以Al2O3／AlN为复合缓冲层薄膜晶体管，在400℃温度下退火处理后，ZnO有源层有较好的c-axis（002）择优取向，器件在可见光的范围内整体透过率在88%以上，从而实现了ZnO-TFT器件在可见光范围内的透明。     

柔性碳纳米管透明导电薄膜国内外研究进展

综述了碳纳米管透明导电薄膜(CNTs-TCF)的主要制备方法以及存在的优缺点,介绍了碳纳米管(CNTs)的制备、金属性/半导体性、纯度与石墨化以及均匀分散CNTs溶液制备过程对CNTs-TCF电学性能产生的影响及相应的改进方法。最后简单介绍了CNTs-TCF在平板显示器、太阳能电池和触控面板上的应用情况,并对CNTs-TCF下一步研究进行了展望。     

Physical vapor deposition of metal nanoparticles on chemically modified graphene: observations on metal-graphene interactions

The growth of metallic nanoparticles formed on chemically modified graphene (CMG) by physical vapor deposition is investigated. Fine control over the size (down to ～1.5 nm for Au) and coverage (up to 5 × 10(4) μm(-2) for Au) of nanoparticles can be achieved. Analysis of the particle size distributions gives evidence for Au nanocluster diffusion at room temperature, while particle size statistics differ clearly between metal deposited on single- and multilayer regions. The morphology of the nanoparticles varies markedly for different metals (Ag, Au, Fe, Pd, Pt, Ti), from a uniform thin film for Ti to a droplet-like growth for Ag. A simple model explains these morphologies, based only on consideration of 1) the different energy barriers to surface diffusion of metal adatoms on graphene, and 2) the ratio of the bulk cohesive energy of the metal to the metal-graphene binding energy. Understanding these interactions is important for controlling nanoparticle and thin-film growth on graphene, and for understanding the resultant charge transfer between metal and graphene.     

Electrochemical actuator based on polypyrrole/sulfonated graphene/graphene tri-layer film

A tri-layer electrochemical actuator was fabricated by the electrodeposition of polypyrrole (PPy) onto a sulfonated graphene (SG)/reduced graphene oxide (RGO) bi-layer film. In this actuator, PPy and RGO were acted as actuation and conductive inert layers, respectively. The SG layer was used to enhance the interfacial interactions. The tri-layer actuator exhibited high and stable actuating performance for over 1000 actuation cycles, and the lifetime of the actuator was tested to be about 5000 cycles. The bending angle of the actuator is larger than 360° and its movement rate was higher than 150° s^− 1 under a driving potential of 1.0 V versus saturated calomel electrode. Furthermore, the low weight density of graphene based supporting layer greatly lowered the energy or charge consuming of the actuator during electrochemical actuation.     

Flexible,Transparent, Conducting Films of Randomly Stacked Graphene from Surfactant‐Stabilized,Oxide‐Free Graphene Dispersions

Graphite is exfoliated in water to give dispersions of mono‐ and few‐layer graphene stabilized by surfactant. These dispersions can be used to form thin, disordered films of randomly stacked, oxide‐free, few‐layer graphenes. These films are transparent with a direct current conductivity of up to 1.5 × 10⁴ S m^?1. The conductivity is stable under flexing for at least 2000 cycles. The electrical properties are limited by disorder and aggregation suggesting future routes for improvement.