All-solution-processed foldable transparent electrodes of Ag nanowire mesh and metal matrix films for flexible electronics

In this study, we developed foldable transparent electrodes composed of Ag nanowire (AgNW) networks welded by Ag nanoparticles (AgNPs) reduced from commercial Ag ink. All the processes used were solution-based. Using the Meyer rod method, uniform AgNW networks were roll-to-roll coated on large-area polymer substrates, and the spin-coated AgNPs firmly welded the AgNWs together at junctions and to substrates. The hybrid films consisting of AgNWs and the Ag film matrix exhibited higher electrical conductivity (5.0–7.3 × 10⁵ S/m) than and equivalent transparency (90–95%) to the AgNW networks. Furthermore, the hybrid films showed significantly better bending stability than AgNW networks. During cyclic bending tests to 10,000 cycles at 5 mm bending radius and even when almost folded with r_b of 1 mm, the resistivity changes were negligible because AgNWs were tightly held and adhered to the substrate by Ag films covering wires, thereby hindering fracturing of AgNWs under tension. Because the films were fabricated at a low temperature, there was no oxidation on the surfaces of the films. Hence, flexible organic light-emitting diodes (f-OLEDs) were successfully fabricated on polyethylene terephthalates (PET) coated with the hybrid films. The f-OLED in the bent state was comparable to that in the flat state, validating the potential applications of these transparent hybrid films as electrodes in various flexible electronics.     

A highly conductive and smooth AgNW/PEDOT:PSS film treated by hot-pressing as electrode for organic light emitting diode

A highly conductive, smooth and transparent electrode is developed by coating poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS) over silver nanowires (AgNWs) followed by a hot-pressing method. The hot-pressed AgNW/PEDOT:PSS film shows a low sheet resistance of 12 Ω/square, a transmittance of 83% at 550 nm and a smooth surface. The improvement of the conductivity and smoothness are ascribed to the fusion of nanowires resulted from the mechanical hot-pressing. The AgNW/PEDOT:PSS film on polyethylene naphthalate (PEN) substrate exhibits higher conductive stability against the bending test than commonly used indium tin oxide (ITO). Using the hot-pressed AgNW/PEDOT:PSS film as the anode, we have fabricated ITO-free organic light emitting diode with a maximum current efficiency of 58.2 cd/A, which is higher than the device with ITO anode. This proves that such AgNW/PEDOT:PSS film treated by hot-pressing is a promising candidate for flexible optoelectronic devices.     

Uniformly Interconnected Silver‐Nanowire Networks for Transparent Film Heaters

The fabrication and design principles for using silver‐nanowire (AgNW) networks as transparent electrodes for flexible film heaters are described. For best practice, AgNWs are synthesized with a small diameter and network structures of the AgNW films are optimized, demonstrating a favorably low surface resistivity in transparent layouts with a high figure‐of‐merit value. To explore their potential in transparent electrodes, a transparent film heater is constructed based on uniformly interconnected AgNW networks, which yields an effective and rapid heating of the film at low input voltages. In addition, the AgNW‐based film heater is capable of accommodating a large amount of compressive or tensile strains in a completely reversible fashion, thereby yielding an excellent mechanical flexibility. The AgNW networks demonstrated here possess attractive features for both conventional and emerging applications of transparent flexible electrodes.     

Ice-Templated,Large-Area Silver Nanowire Pattern for Flexible Transparent Electrode

Flexible transparent electrodes are critically important for the emerging flexible and stretchable electronic and optoelectronic devices. To this end, transparent polymer films coated with silver nanowires (AgNWs) have been intensively studied in the past decade. However, it remains a grand challenge to achieve both high conductivity and transmittance in large-area films, mainly due to the poor alignment of AgNWs and their high junction resistance. Here, the successful attempt to realize large-area AgNW patterns on various substrates by a 2D ice-templating approach is reported. With a relatively low dosage of AgNWs (4 µg·cm⁻²), the resulted flexible electrode simultaneously achieves high optical transmittance (≈91%) and low sheet resistance (20 Ω·sq⁻¹). In addition, the electrode exhibits excellent durability during cyclic bending (≈10 000 times) and stretching (50% strain). The potential applications of the flexible transparent electrode in both touch screen and electronic skin sensor, which can monitor the sliding pressure and direction in real-time, are demonstrated. More importantly, it is believed that the study represents a facile and low-cost approach to assemble various nanomaterials into large-area functional patterns for advanced flexible devices.     

Production of Flexible Transparent Conducting Films of Self‐Fused Nanowires via One‐Step Supersonic Spraying

Scalable and economical manufacturing of flexible transparent conducting films (TCF) is a key barrier to widespread adoption of low‐cost flexible electronics. Here, a simple, robust, and scalable method of flexible TCF formation using supersonic kinetic spraying is demonstrated. Silver nanowire (AgNW) suspensions are sprayed at supersonic speed to produce self‐sintered films of AgNWs on flexible substrates. These films display remarkably low sheet resistance, <10 Ω sq^?1, combined with high transmittance, >90%. These electrically conducting, transparent, and flexible coatings can be deposited over a 100 cm² area in ≈30 s. Theoretical analysis reveals the underlying physical mechanism behind self‐sintering, showing that self‐sintering is enabled by the high velocity of impact in supersonic spraying.     

Electrical performance of the embedded-type surface electrodes containing carbon and silver nanowires as fillers and one-step organosoluble polyimide as a matrix

Embedded-type surface electrodes with silver nanowire (AgNW) and carbon nanotube (CNT) as conductive fillers and organosoluble polyimide (PI) as a matrix were investigated for their electrical conductivity and electrical durability under cyclic bending. The chosen polyimide was constituted with 4,4′-oxydiphthalic dianhydride and 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane through a one-step process. Two types of surface electrodes of CNT/PI and AgNW/PI were prepared at 90 °C. The flexible CNT/PI and AgNW/PI surface electrodes not only had high electrical conductivities of 6.3 and 100 S/cm, respectively, after 30 spraying cycles but also kept electrical durability after 1200-time bending tests. The ITO-coated ITO/PI and ITO/AgNW/PI electrodes, for a comparative purpose, had severe electrical failure under cyclic bending.     

A Sensing and Stretchable Polymer-Dispersed Liquid Crystal Device Based on Spiderweb-Inspired Silver Nanowires-Micromesh Transparent Electrode

Polymer-dispersed liquid crystal (PDLC) devices are truly promising optical modulators for information display, smart window as well as intelligent photoelectronic applications due to their fast switching, large optical modulation as well as cost-effectiveness. However, realizing highly soft PDLC devices with sensing function remains a grand challenge because of the intrinsic brittleness of traditional transparent conductive electrodes. Here, inspired by spiderweb configuration, a novel type of silver nanowires (AgNWs) micromesh-based stretchable transparent conductive electrodes (STCEs) is developed to support the realization of soft PDLC device. Benefiting from the embedding design of AgNWs micromesh in polydimethylsiloxane (PDMS), the STCEs can maintain excellent electrical conductivity and transparency even in various extreme conditions such as bending, folding, twisting, stretching as well as multiple chemical corrosion. Further, STCEs with the embedded AgNWs micromesh endow the assembled PDLC device with excellent photoelectrical properties including rapid switching speed (<1 s), large optical modulation (69% at 600 nm), as well as robust mechanical stability (bending over 1000 cycles and stretching to 40%). Moreover, the device displays the pressure sensing function with high sensitivity in response to pressure stimulus. It is conceivable that AgNWs micromesh transparent electrodes will shape the next generation of related soft smart electronics.     

Well‐Ordered and High Density Coordination‐Type Bonding to Strengthen Contact of Silver Nanowires on Highly Stretchable Polydimethylsiloxane

Recently, Ag nanowires (AgNWs) has had a great interest as a conducting material for flexible and transparent devices, but it still shows several problems such as the ultimate detachment of AgNWs from substrate and a high contact resistance on AgNW junctions. Therefore, the novel concept to enhance permanent and closed attachment of AgNWs by silane modification to polydimethylsilaoxane (PDMS) substrate well known as high stretchable film with extremly low adhesive is suggested. According to this experiment, higher sigma (σ)‐donating ability and hydrophilicity indicate better electrical and mechanical properties in real device. Especially, densely amine self‐assembled PDMS surface exhibits the strongest contact force to the AgNWs, especially for junction side, and the longest maintenance of hydrophilicity by coordination‐type bonding. In addition, AgNWs adhere permanently to stretchable substrates while simultaneously maintaining high transparency (87%) and high conductivity (27 Ω sq^–1). Consequently, the resulting AgNW film shows excellent mechanical durability which includes enhanced performance of both flexibility and stretchability.     

Ultrasmooth,highly conductive and transparent PEDOT:PSS/silver nanowire composite electrode for flexible organic light-emitting devices

The next generation of optoelectronic devices requires transparent conductive electrodes to be flexible, inexpensive and compatible with large scale manufacturing processes. We report an ultrasmooth, highly conductive and transparent composite electrode on a flexible photopolymer substrate by employing a template stripping method. A random silver nanowire (AgNW) network buried in poly(3,4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) film constituted the composite electrode. Besides the effectively decreased surface roughness, its sheet resistance and transmittance are comparable to those of conventional PEDOT:PSS electrode. As a result, the efficiency of the OLEDs based on the composite electrode exhibited 25% enhancement compared to the OLEDs with conventional PEDOT:PSS electrode. Moreover, the performance of the flexible OLEDs remains stable after over one hundred bending cycles.     

All‐Solution‐Processed Indium‐Free Transparent Composite Electrodes based on Ag Nanowire and Metal Oxide for Thin‐Film Solar Cells

Fully solution‐processed Al‐doped ZnO/silver nanowire (AgNW)/Al‐doped ZnO/ZnO multi‐stacked composite electrodes are introduced as a transparent, conductive window layer for thin‐film solar cells. Unlike conventional sol–gel synthetic pathways, a newly developed combustion reaction‐based sol–gel chemical approach allows dense and uniform composite electrodes at temperatures as low as 200 °C. The resulting composite layer exhibits high transmittance (93.4% at 550 nm) and low sheet resistance (11.3 Ω sq^‐1), which are far superior to those of other solution‐processed transparent electrodes and are comparable to their sputtered counterparts. Conductive atomic force microscopy reveals that the multi‐stacked metal‐oxide layers embedded with the AgNWs enhance the photocarrier collection efficiency by broadening the lateral conduction range. This as‐developed composite electrode is successfully applied in Cu(In_1‐x,Ga_x)S₂ (CIGS) thin‐film solar cells and exhibits a power conversion efficiency of 11.03%. The fully solution‐processed indium‐free composite films demonstrate not only good performance as transparent electrodes but also the potential for applications in various optoelectronic and photovoltaic devices as a cost‐effective and sustainable alternative electrode.     

纳米银线柔性透明导电薄膜研究进展

随着时代的发展,柔性电子产品的应用越来越广。柔性透明导电薄膜是柔性电子器件中的重要组成部分,由于氧化铟锡并不适合应用到柔性电子器件中,寻找新一代材料引起了研究者的广泛关注。纳米银线作为一种新型的纳米材料,在纳米尺度上有很多新奇的性能,其优良的导电性及良好的光学性能被认为是替代氧化铟锡的最佳材料。本文主要综述了纳米银线柔性导电薄膜的研究进展,主要包括纳米银线导电油墨的物化性能、纳米银线柔性透明导电薄膜的常用制备方法以及主要应用领域。此外,还结合国内外纳米银线柔性透明导电膜的研究现状,指出该研究方向仍存在的一些挑战。     

High Power Conversion Efficiency of 13.61% for 1 cm2 Flexible Polymer Solar Cells Based on Patternable and Mass-Producible Gravure-Printed Silver Nanowire Electrodes

With the aim of developing high-performance flexible polymer solar cells, the preparation of flexible transparent electrodes (FTEs) via a high-throughput gravure printing process is reported. By varying the blend ratio of the mixture solvent and the concentration of the silver nanowire (AgNW) inks, the surface tension, volatilization rate, and viscosity of the AgNW ink can be tuned to meet the requirements of gravure printing process. Following this method, uniformly printed AgNW films are prepared. Highly conductive FTEs with a sheet resistance of 10.8 Ω sq⁻¹ and a high transparency of 95.4% (excluded substrate) are achieved, which are comparable to those of indium tin oxide electrode. In comparison with the spin-coating process, the gravure printing process exhibits advantages of the ease of large-area fabrication and improved uniformity, which are attributed to better ink droplet distribution over the substrate. 0.04 cm² polymer solar cells based on gravure-printed AgNW electrodes with PM6:Y6 as the photoactive layer show the highest power conversion efficiency (PCE) of 15.28% with an average PCE of 14.75 ± 0.35%. Owing to the good uniformity of the gravure-printed AgNW electrode, the highest PCE of 13.61% is achieved for 1 cm² polymer solar cells based on the gravure-printed FTEs.     

Neutral-pH PEDOT:PSS as over-coating layer for stable silver nanowire flexible transparent conductive films

The silver nanowire (AgNW) mesh film with poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) as the over-coating layer is a promising flexible transparent conductive film technology. In this work, experimental studies show that the hygroscopic and acid properties of the common PEDOT:PSS lead to poor stabilities of the composite films, due to the conductivity degradation of PEDOT:PSS by the water absorption and the acid corrosion of AgNWs by PEDOT:PSS. By using the modified PEDOT:PSS of neutral pH as the over-coating layer, the long term shelf-life time, thermal and current stressing stabilities are all significantly improved without sacrifice of transparency, electrical conductivity and mechanical flexibility. Under both cases of thermal aging test at 210 °C for 20 min and 12 h continuous current stressing at a current density of 30 mA/cm², no obvious change of the conductivity is observed. The results clearly demonstrate that using the neutral-pH PEDOT:PSS as an over-coating layer can help to achieve flexible AgNW transparent conductive films with superior stability for flexible optoelectronic devices.     

Orthogonally weaved silver nanowire networks for very efficient organic optoelectronic devices

We demonstrate a simple but effective method to control the orientation of silver nanowires (AgNWs). Shear-flow-induced AgNW preferable orientation is realized by judiciously controlling the process parameters in the bar-coating method. This controllability of the NW direction enables the formation of AgNW cross-linking networks for transparent conductive electrode (TCE) applications. We experimentally demonstrate that the orthogonally weaved AgNW networks possess predominant advantages of lower percolation limit, higher transmission, and lower sheet resistance compared with the randomly orientated AgNW counterparts. The phenomenon is also confirmed with theoretical calculation by the Monte Carlo method. These high-quality AgNW TCEs exhibit a high transmittance of ∼94% with a sheet resistance of ∼20 Ω/sq, which meet the requirements of modern optoelectronic devices. Very efficient organic light-emitting diodes (OLEDs) and organic solar cells (OSCs) prepared by these AgNW TCEs are demonstrated. The OLED exhibits exceptionally high luminance efficiency, power efficacy, and external quantum efficiency of 92 cd/A, 111 lm/W, and 26.8%, respectively. The OSCs also deliver a high power conversion efficiency of up to 7.5%.     

Inverted Layer‐By‐Layer Fabrication of an Ultraflexible and Transparent Ag Nanowire/Conductive Polymer Composite Electrode for Use in High‐Performance Organic Solar Cells

A highly flexible and transparent conductive electrode based on consecutively stacked layers of conductive polymer (CP) and silver nanowires (AgNWs) fully embedded in a colorless polyimide (cPI) is achieved by utilizing an inverted layer‐by‐layer processing method. This CP‐AgNW composite electrode exhibits a high transparency of >92% at wavelengths of 450–700 nm and a low resistivity of 7.7 Ω ?^?1, while its ultrasmooth surface provides a large contact area for conductive pathways. Furthermore, it demonstrates an unprecedentedly high flexibility and good mechanical durability during both outward and inward bending to a radius of 40 μm. Subsequent application of this composite electrode in organic solar cells achieves power conversion efficiencies as high as 7.42%, which represents a significant improvement over simply embedding AgNWs in cPI. This is attributed to a reduction in bimolecular recombination and an increased charge collection efficiency, resulting in performance comparable to that of indium tin oxide‐based devices. More importantly, the high mechanical stability means that only a very slight reduction in efficiency is observed with bending (<5%) to a radius of 40 μm. This newly developed composite electrode is therefore expected to be directly applicable to a wide range of high‐performance, low‐cost flexible electronic devices.     

Conductive nonwetting flexible substrate

In this paper an easy method to prepare flexible conductive substrates has been demonstrated. The substrates are mainly PET (PolyEthyleneTerephthalate), on which AgNW (silver nanowire) were deposited by spin casting method. For adhesion purpose a common cosmetic material has been utilized. The material provides versatile features to these coated substrates, including robustness, hydrophobicity with transparent bracing of nanowires (NW) with the flexible substrate. Four probe conductivity measurement shows the resistivity is 12 Ω/cm and is comparable to that of commercially available indium tin oxide (ITO) coated substrates. This method is cheap, easy and can be used for different objectives like flexible thin film photovoltaic, light emitting diodes, photosensors etc.     

纳米银线-环氧树脂复合导电薄膜的制备及其在柔性触控上的应用

纳米银线透明导电薄膜具有优异的光电性能和机械性能,有望取代传统的氧化铟锡材料应用于柔性光电器件中。为解决纳米银线的黏附性、柔韧性和稳定性问题,结合转印法和烷基硫醇修饰法制备了纳米银线-环氧树脂复合导电薄膜。在此过程中,首先应用十八烷基三氯硅烷对转移衬底进行疏水化处理以提升透明电极转印的良率;接着,对转印后的纳米银线进行烷基硫醇分子的自组装修饰,以进一步提升纳米银线透明导电薄膜的稳定性;最后在此基础上制备了柔性投射式电容触控屏。所制备的透明导电薄膜具有优异的综合性能:品质因数约为300(Rs=29.7Ω/□,T=96.2%);薄膜经过100次胶带测试后,电阻变化小于25%;在1 000次弯曲(弯曲半径为1mm)测试后,电阻几乎不发生变化;高温高湿下老化一个月,电阻变化小于20%。本文结合转印工艺以及分子修饰技术开发的纳米银线-环氧树脂复合导电薄膜以及柔性触控工艺,有望推广应用至其他柔性电子元件中。     

Intense-pulsed-light irradiation of Ag nanowire-based transparent electrodes for use in flexible organic light emitting diodes

Silver nanowire (AgNW) based transparent electrodes are inherently coarse and therefore typically are only ever weakly bonded to a substrate. A remarkable improvement in the characteristics of a AgNW network film has, however, been achieved through a simple and short process of irradiating it with intense pulsed light (IPL). This not only avoids any severe deterioration in the optical characteristics of the AgNW film, but also significantly improves its electrical conductivity, adhesion to a polymeric substrate, and ability to endure bending stress. Most important of all, however, is the finding that the surface roughness of AgNW networks can also be improved by radiation. In a series of measurements made of organic light emitting diodes fabricated using these treated electrodes, it was revealed that the leakage current can be notably reduced by IPL treatment.     

Flexible transparent conductive film based on silver nanowires and reduced graphene oxide

Silver nanowires (AgNWs) with diameter of 90—150 nm and length of 20—50 μm were successfully synthesized by a polyol process. Graphene oxide (GO) was prepared by Hummers method, and was reduced with strong hydrazine hy-drate at room temperature. The flexible transparent conductive films (TCFs) were fabricated using the mixed cellulose eater (MCE) as matrix and AgNWs and reduced graphene oxide (rGO) as conductive fillers by the improved vacuum fil-tration process. Then, the optical, electrical and mechanical properties of the AgNWs-rGO films were investigated. The results show that for the AgNWs-rGO film produced with the deposition densities of AgNWs and rGO as 110 mg·m-2 and 55 mg·m-2, the optical transmission at 550 nm is 88.4% with Rs around 891 Ω·sq-1, whereas the optical transmission for the AgNWs-rGO film with deposition densities of AgNWs and rGO of 385 mg·m-2 and 55 mg·m-2 is 79.0% at 550 nm with Rs around 9.6 Ω·sq-1. There is little overt increase in Rs of the AgNWS-rGO film after tape tests for 200 times. The bending test results indicate that the change in Rs of AgNWs-MCE film is less than 2% even after 200 cycles of compressive or tensile bending. The excellent mechanical properties of the AgNWs-rGO film can be attributed to the burying of AgNWs and rGO at the surface of MCE     

Ag Nanowire Reinforced Highly Stretchable Conductive Fibers for Wearable Electronics

Stretchable conductive fibers have received significant attention due to their possibility of being utilized in wearable and foldable electronics. Here, highly stretchable conductive fiber composed of silver nanowires (AgNWs) and silver nanoparticles (AgNPs) embedded in a styrene–butadiene–styrene (SBS) elastomeric matrix is fabricated. An AgNW‐embedded SBS fiber is fabricated by a simple wet spinning method. Then, the AgNPs are formed on both the surface and inner region of the AgNW‐embedded fiber via repeated cycles of silver precursor absorption and reduction processes. The AgNW‐embedded conductive fiber exhibits superior initial electrical conductivity (σ₀ = 2450 S cm^?1) and elongation at break (900% strain) due to the high weight percentage of the conductive fillers and the use of a highly stretchable SBS elastomer matrix. During the stretching, the embedded AgNWs act as conducting bridges between AgNPs, resulting in the preservation of electrical conductivity under high strain (the rate of conductivity degradation, σ/σ₀ = 4.4% at 100% strain). The AgNW‐embedded conductive fibers show the strain‐sensing behavior with a broad range of applied tensile strain. The AgNW reinforced highly stretchable conductive fibers can be embedded into a smart glove for detecting sign language by integrating five composite fibers in the glove, which can successfully perceive human motions.