A Comprehensive Overview on Formulating Silver Nanowire Inks & Achieving High Transmittance

With the evolution of technology and science, the manufacturing of flexible devices is expanding at a rapid pace. Compared to rigid devices, flexible electronic devices and flexible transparent conductive film (FTCF) offer incredible advantages such as longevity, good work efficiency, high conductivity, and excellent stretch ability.

But one of the most vital components and the crux of this technology is Silver Nanowire (AgNWs) conductive inks. Due to its impressive performance on various technological applications, it is gaining immense popularity. It is most likely to be the latest generation of transparent conductive film materials and will be responsible for many breakthroughs in this era.

In this article, we cover the formulation of AgNWs inks, techniques to achieve high conductivity, and its latest applications.

Formulating Silver Nanowire Conductive Inks

Silver Nanowires are first added to the solvent and stirred. The solvent is usually alcohol or water, which is hydrophilic and cannot be combined with non-hydrophilic substrates.

Appropriate additives and binders are then added to the solution. Under normal circumstances, the ink tends to agglomerate and precipitate.

Binders can improve the adhesion between the substrate and AgNWs. It can also adjust the viscosity and surface tension of the ink.

Some common binders include:

  • Hydroxypropyl methylcellulose (HPMC)
  • Hydroxyethylcellulose (HEC)
  • Hydroxyethyl methyl cellulose (HEMC)
  • High electrical conductivity

A surfactant with dispersing AgNWs can increase the durability, wettability, and stability of the ink. A leveling agent can increase the fluidity of ink. This can enhance the stability of the ink. For instance, a stable active AgNWs ink can be composed of hydroxyethyl cellulose adhesive, isopropanolamine silver complex, and a formic acid-reducing agent. This ink can be used to develop flexible electrodes.

Dispersants could also enhance stability and improve the uniformity and dispersion of AgNWs in the solvent. The stabilizing mechanisms of dispersants and dispersing include the electric double layer effect and steric hindrance effect. The steric hindrance effect depends on the polymer that is adsorbed on the surface of AgNWs. This ends up forming a protective layer. The electrical double layer effect largely depends on the electrostatic repulsion in order to maintain a certain level of stability in AgNWs.

For a stable droplet formation, the surface tension and the viscosity of the ink must be tailored carefully. This is because the surface tension and the viscosity of the ink are closely related to the properties and concentrations of additives and AgNWs.

During the drying process, the AgNWs are suspended, and droplets start pinning to the substrate. The capillary flows outwards from the center of the drop, bringing suspended AgNWs to the edge as the evaporation takes place.

Keep in mind, to achieve a high-quality FTCF, the surface tension must be controlled under 7 × 10−2 N/m [1].

Achieving High Conductivity & Light Transmittance

Using ultra-long AgNWs that have a length of 75 μm [1], one can develop inks with simple formulation, excellent mechanical stability, high conductivity (up to 8.32 × 103 s/cm) [1], and can achieve about 80% [1] light transmittance on a polyethylene terephthalate substrate.

AgNWs conductive inks can also be used to create FTCF of high transmittance. Here is how we can achieve that. During Silver Nanowire synthesis, aspect ratios of 2000 and diameters of 20nm must be obtained by adding 2.2 mM Sodium Bromide (NaBr). These Silver Nanowires must then undergo selective precipitation and purification processes to remove any form of contamination. After purification, these Silver Nanowires must then be formulated to create conductive inks, which are then used to create FTCF. This purified AgNWs ink-based FTCF will now have the potential to achieve a transmittance of 99.1% [2].

Applications:
Since Silver has a wide range of characteristics, it can be improved, developed, or adjusted by controlling the particle morphology on the nanometer scale. Also, compared to other metals, it has high thermal and electrical conductivity (6.3 ✕ 107 s/m) [3], making AgNWs ink a strong candidate for flexible circuits and electrical devices.

Due to these properties, AgNWs ink is the perfect replacement for ITO. Since ITO is getting expensive, chemically unstable, brittle, and limited in sources, AgNWs ink is gaining tons of attention as a promising replacement material for ITO.

Let us look at some of the latest applications of AgNWs ink:

  • Solar Cells
  • Transparent Film Heater
  • Optoelectronic Devices such as PLED and OLED
  • Flexible touch panels
  • Light Emitting Diodes (LEDs)
  • Electronic interconnects
  • Cell probes
  • Sensors
  • Transparent electrodes
  • Photonic crystals
  • Plasmonic fibers

Achieve Technological Breakthroughs with Nanorbital!

At Nanorbital, we feature Silver Nanowires with diameters ranging from 30±10 to 120±10. However, our materials are not restricted to these ranges. We also specialize in synthesizing Silver Nanowires with custom ranges. This can help you formulate AgNWs inks with high conductivity and achieve light transmittance of 80% and more.

Our advanced materials are also available to a global customer base, and we offer flexible delivery services, ranging from samples to high volume production.

If you have any queries or are looking for a custom solution, feel free to drop us an email at email@nanorbital.com or call us on +91-93279 08826. Our experts will help you through every step of the way!

Sources:

[1] Xiaoli Wu, “Syntheses of Silver Nanowires Ink and Printable Flexible Transparent Conductive Film: A Review” –  https://www.mdpi.com/2079-6412/10/9/865/htm

[2] Ian E. Stewart, Samuel Alvarez, and Benjamin J. Wiley, “Noble-Metal Nanocrystals with Controlled Shapes for Catalytic and Electrocatalytic Applications” – https://pubs.acs.org/doi/10.1021/acs.chemrev.0c00454

[3] Shohreh Hemmati, University of New Hampshire, Durham, “Synthesis and Characterization of Silver Nanowire Suspensions for Printable Conductive Media” – https://scholars.unh.edu/cgi/viewcontent.cgi?article=3249&context=dissertation

 

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