Metal nanogrids, nanowires, and nanofibers for transparent electrodes

Sputtered transparent electrodes for optoelectronic devices: Induced damage and mitigation strategies

The next generation of electronic devices will require low cost materials and processing techniques that are fully compatible with flexible substrates and large area applications. Silver nanowires are promising candidates for many applications and can be processed by various solution‐based large area deposition techniques. In this work, high aspect ratio silver nanowires were synthesized via a polyol reduction of silver nitrate in the presence of a metal‐salt and a capping agent. The grown nanowires were spray coated and simply planarized with inkjet printed PEDOT:PSS to produce smooth and high performance nanocomposite electrodes suitable for industrial applications. The nanocomposite electrodes exhibit figure of merit values (σDC/σOP) of about 60, higher than the values required for industrial use (>35). High conductivity with high optical transparency was achieved by controlling the aspect ratio of the nanowires and their concentration in the films. The highly conductive and transparent electrodes were utilized to fabricate organic light emitting diodes, which exhibited high luminance (∼ 7 × 103 cd m−2) and performance comparable to a “benchmark” ITO electrode. The results show that the combination of the nanocomposite materials, together with the solution based techniques could pave the way towards flexible, solution processable, low cost, and large area device applications.ITO‐free OLEDs fabricated using solution processed Ag NW/PEDOT:PSS nanocomposites as transparent conductive electrode. Improving the aspect ratio of the grown nanowires along with controlling their density in the films allow for highly conductive and transparent nanocomposite electrodes. These nanocomposite samples are utilized as a direct replacement for ITO in OLEDs.

Conventional organic solar cell’s (OSC) architectures, including rigid transparent substrate (Glass), conductive electrode (Indium tin oxide, ITO) and small working areas, are widely utilized in organic photovoltaic fields. However, such a structure as well as conventional spin-coating method obviously restrict their industrial application. In this article, we report the deposition of silver nanowires (AgNWs) on the flexible substrate by slot-die printing. The obtained AgNWs films exhibited a high transmittance and a low resistance, and were further used as the transparent conductive electrode of OSCs. A typical conjugated polymer, poly[(2,5-bis(2-hexyldecyloxy)phenylene)-alt-(5,6-difluoro-4,7-di(thiophen-2-yl)benzo[c] [1,2,5]thiadiazole)] (PPDT2FBT), was used as the active material to fabricate large-area (7 cm2 solar cells by a slot-die coating process. The power conversion efficiency (PCE) could reach 1.87% initially and further increased to 3.04% by thermal annealing. Compared to the performance of reference cell on ITO substrate, the result indicated that the AgNWs could be developed as an alternative substitute of conductive electrode to fabricate the large-area flexible OSCs by roll-to-roll printing.

Mechanically and thermally stable, transparent electrodes with silver nanowires encapsulated by atomic layer deposited aluminium oxide for organic optoelectronic devices

Solution-processed transparent conducting electrodes with graphene, silver nanowires and PEDOT:PSS as alternative to ITO

Silver nanowires (AgNWs) have gained much attention owing to their optoelectronic and mechanical properties and are therefore potential candidates to tackle intrinsic drawbacks of currently applied transparent electrodes in various (opto)electronic devices. In order for AgNWs to be justifiably considered as viable, it is necessary to address their insufficient stability by coupling them with another constituent into a nanocomposite. For this purpose, ZnO was chosen because of its low cost, solution processability and barrier properties. In this paper, a fully solution processed AgNW/ZnO TE film was investigated in order to understand the effect of ZnO coating on the electrical stability of AgNWs, including the mechanism of degradation during their exposure to high electrical current densities. The nanocomposite transparent electrode was processed with ZnO coatings to determine their effect on its optoelectronic properties and electrical stability, where the ZnO triple coated AgNW demonstrated the best combination of optoelectronic properties and stability at the highest working voltage.

In this research, we have succeeded in making thin-films for flexible, transparent, and conductive (FTC) electrodes based on silver nanowires. The synthesis of silver nanowires is carried out at low temperatures, namely at 60 to 130 oC. The materials used in the synthesis of AgNWs are polyvinyl pyrrolidone (PVP) as a capping agent and Iron (III) chloride hexahydrate (FeCl3”¢6H2O) as a precursor to controlling the size of silver nanowires. Furthermore, the silver nanowires colloid then created a thin layer over the polycarbonate (PC) substrate by the roll to roll process. The Result shows that the formation of silver nanowires occurred at low temperatures of about 90 °C. The optimum condition of silver nanowires has obtained synthesis at the temperature of 110 °C with the average diameter of (100 ± 20) nm and length (30 ± 15) μm. The silver nanowires will increase in length and diameter at low-temperature and decrease at high temperatures .The transmittance of FTC film silver nanowires about 76-95% at a wavelength of 550 nm. The absorbance coefficient of FTC film silver nanowires has increased from 2.7 to 29.2 cm-1 at wavelength range 400 to 700 nm. The sheet resistance of the FTC film by varying the number of layers obtained of 905.2, 340.7, 21.9, and 3.4 Ω.sq-1 with the transmittance obtained at 76.7 to 95.8%. The number of layers of silver nanowires will increase the sheet resistance and decrease the optical transmittance of the FTC film.

Transparent flexible electrodes (TFEs) are extremely crucial for expanding flexible and wearable electronic devices. Silver nanowires (AgNWs) have been extensively investigated as an alternative to replace Indium Tin Oxide (ITO) as a commercial TFE due to their high conductivity, transparency, and flexibility. AgNWs have replaced ITO-based electrodes as the preferred approach in flexible, transparent, and conductive electrodes (FTCE). AgNWs outperform other materials, such as Reduced Graphene Oxide (RGO), ceramic material, Carbon Nanotubes (CNT), and conductive polymers, in terms of electrical conductivity, transmittance, flexibility, and low sheet resistance. Numerous techniques, including as electrospinning, spray coating, spin coating, and doctor blades, are used to use AgNWs as flexible substrates. Seed-based growth and template-assisted synthesis are two fundamental synthesis techniques that could be used to generate AgNWs. However, poor adhesiveness, and thermal and electrical stability, begin to be bottlenecks for AgNWs as high deployment in a variety of devices. So AgNWs synthesis process began to shift to other methods, such as wet chemical and polyol. In this paper, short and clear summary of various advances including post-treatment methods such as UV radiation, microwave, sonication, quenching, and so on is conducted to be one step forward to test mechanical properties and to improve AgNWs performance.

Graphene/silver nanowire composite films have great potential as transparent conductive electrodes in the field of optoelectronic devices. So far, antioxidant and reducing the junction resistance are two major parameters in the silver nanowire electrode studies. In this paper, a pseudo-biological inspired structure for transparent electrodes was proposed by combining hybrid diameters silver nanowire network with the chemical vapor deposition-grown (CVD-grown) graphene as a passivation layer. Compared with the traditional structure, the silver nanowire network with this novel structure of human vascular tissue network greatly reduced the sheet resistance. An environmentally friendly liquid, deionized water, was selected for the generation of capillary forces at the liquid bridge, thereby improving the wire junction problem. After welding with the capillary force, the increase in the value of the figure of merit (FoM = σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> /σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OP</sub> ) acted a pivotal part in improving conductivity with excellent optical performance. In addition, graphene was chosen as an encapsulation layer to protecting silver nanowires from oxidation while improving electrical properties. Compared with the silver nanowire films with a diameter of 20 nm, the σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DC</sub> /σ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OP</sub> of the graphene/silver nanowire composite film increased by 69.6 % with a sheet resistance of 26.4 Ω/sq. More importantly, graphene is supposed to protect silver nanowires from oxidation and moisture, which makes the composite films promising as electrodes for underwater optoelectronic devices or a possible development in high humidity environments.

As one of the most important conductive materials, silver nanowires have recently attracted a lot of attention for potential applications such as electrically conductive adhesives, transparent electrodes, and conductive ink. In this paper, silver nanowires with a diameter of 200–570 nm and a length of 20–100 μm were synthesized by a polyol process. The electrically conductive adhesives (ECAs) composed of an epoxy-based binder containing silver nanowire were prepared and the curing behaviors and electrical properties of ECAs were investigated. The in situ monitoring of the variation in electrical resistance of the ECAs explore that silver nanowires impact on the curing behavior of the ECAs. The resistance of the ECAs filled with 40 wt% silver nanowires reaches to 0.59 Ω heated to 11 min from the room temperature to 164 °C. Silver nanowires significantly improve the electrical conductivity of the ECAs, and the resistivities of the ECAs filled with 35 and 40 wt% silver nanowires is 9.48 × 10−4 and 1.42 × 10−4 Ω cm after cured at 168 °C, respectively. The reasons for the effects of silver nanowires on the curing behavior and the electrical properties were also discussed in terms of the morphology and higher activity of silver nanowires.

We demonstrate a flexible, transparent, and conductive composite electrode comprising silver nanowires (Ag NWs), and indium-doped zinc oxide (IZO) layers. IZO is sputtered onto an Ag NW layer, with the unique structural features of the resulting composite suitable as a flexible, transparent, conductive electrode. The IZO buffer layer prohibits surface oxidation of the Ag NW, and is thereby effective in preventing undesirable changes in electrical properties. The newly designed composite electrode is a promising alternative to conventional ITO films for the production of flexible and transparent electrodes to be applied in next-generation flexible electronic devices.

Silver nanowires (Ag NWs) can be used in future conductive transparent electrodes to replace indium tin oxide (ITO) thin films. Welding between Ag NWs is required to achieve lower electrical resistance, and an appropriate heating mechanism. In this study, microwave-assisted welding was introduced in order to simultaneously improve the transmittance and electrical conductivity of Ag NWs, through a simple, selective, and rapid process. This method includes only two steps. First, Ag NWs dispersed in a solvent were coated onto polymer substrates by spin coating. The Ag NW-coated substrates were exposed to microwave radiation. Next, the resulting optical transmittances and electrical conductivities are compared between the samples. Ag NWs electrode showed high electrical conductivity with a low sheet resistance of 20 Ω sq−1 at 87% transmittance (at 550 nm). Bending tests were also performed to examine the suitability of the welded Ag NWs for flexible substrates. We found that the transmittance and conductivity were preserved after repeated bending tests. Consequently, the sheet resistance was reduced by 40% using microwave heating, and these welded Ag NWs had good mechanical strength even after bending. These highly flexible and transparent electrodes can be mounted onto non-planar surfaces for use in various future flexible electronics.

Simultaneously improved conductivity and adhesion of flexible AgNW networks via a simple hot lamination process

Simple and versatile method of layer-by-layer deposition is used to coat silver nanowire on a cellulose film to fabricate a flexible and transparent strain sensor. Strain-sensing behaviors of such a simply fabricated cellulose film are analyzed in both stretching and bending modes. When 0.01 wt% silver nanowire is coated on the cellulose film, 70% transmittance is maintained with 2.4 kΩ/sq of sheet resistance, which is applicable for transparent electrode of the strain sensor. Conductivity of the transparent electrode is maintained after mechanical stretching, which demonstrates that the silver nanowire coating is securely adhered on the surface of cellulose film. The strain sensor shows high strain sensitivity and good gauge factor maintaining good transparency at low silver nanowire concentration, which might be associated with the tunneling resistance change in the silver nanowire. The morphology of the silver nanowire–coated cellulose strain sensor is investigated using an atomic force microscopy with an increase in silver nanowire concentration.

In this work, silver nanowire inks with hydroxypropyl methylcellulose (HPMC) binders were coated on polyethylene terephthalate (PET) substrates and welded via flash white light and ultraviolet C (UV-C) irradiation to produce highly conductive transparent electrodes. The coated silver nanowire films were firmly welded and embedded into PET substrate successfully at room temperature and under ambient conditions using an in-house flash white light welding system and UV-C irradiation. The effects of light irradiation conditions (light energy, irradiation time, pulse duration, and pulse number) on the silver nanowire networks were studied and optimized. Bending fatigue tests were also conducted to characterize the reliability of the welded transparent conductive silver nanowire films. The surfaces of the welded silver nanowire films were analyzed via scanning electron microscopy (SEM), while the transmittance of the structures was measured using a spectrophotometer. From the results, a highly conductive and transparent silver nanowire film with excellent reliability could be achieved at room temperature under ambient conditions via the combined flash white light and UV-C irradiation welding process.