Designing Stretchable Devices and Displays with Transparent Electrodes

May 14, 2020 by Luke James

Researchers from the Korea Institute of Science and Technology (KIST) have developed a process for the fabrication of large-area, highly transparent, and stretchable electrodes from silver nanowires.

According to the research team, these electrodes can be used as a stretchable display, and by using their technology, the team can fabricate a large area (larger than an A4-sized piece of paper) wavy silver nanowire network of the electrode. 

The research team released its research paper in Advanced Functional Materials and described their technology and its use to form the structurally stretchable nanowire network.


Operating Reliably at 50% Stretching

Designed for use in stretchable electronic displays—the new electronics were reportedly demonstrated to operate reliably even when stretched to 50% of their original size, or when they were twisted and rolled. 

This proof of concept consisted of the KIST logo patterned as a transparent AC-driven electroluminescent device, made from wavy Ag nanowire-based stretchable electrodes that connect the two sides of the electroluminescent layer placed on an elastomeric substrate.


Mitigating Frictional Resistance via Solvent Annealing 

To create the stretchable electrode, the research team first spread a random network of straight nanowires on a pre-stretched sheet of polydimethylsiloxane (PDMS). The research team then got the nanowires wet with solvents, which reduces the frictional resistance between the individual nanowires in the nanowire networks as they get wet.

Each silver nanowire in the network can be worked in with water and rearranged into a curved structure with a large curvature radius, allowing the structure to be reliably stretched and bent. Since the nanowires do not experience any unstable conditions, there is no fracturing when the material is stretched and subsequently relaxes. 


A schematic image of a stretchable-electroluminescent device.

A schematic image of the team's proof of concept–a logo patterned stretchable electroluminescent device stretched to 50% of its original size. Image used courtesy of KIST


Stretchable and Transparent Nanowires

By fabricating the nanowire network in this way, the KIST team was able to stretch the substrate and its nanowires to at least 50% of its initial size while reportedly maintaining transparency and conductivity for 5,000 stretching-relaxing cycles. The team also claims an environmentally friendly production process can be used to fabricate this type of material by using ethanol and water for solvent annealing. 

"The stretchable and transparent electrodes made using wavy silver nanowire networks developed through this research have a high degree of electrical conductivity that is not changed by any deformation." said Dr. Sang-Soo Lee at KIST.


A Boon for Wearable Devices?

Transparent electrodes are essential for touchscreen-based displays like those found on smartphones and wearable devices. Currently, indium tin oxide-based electrodes are used for this purpose, but they are fragile due to the thin layers of metallic oxides found in them. This means that they are not very flexible. 

However, with stretchable devices expected to become mainstream in the next few years, there are already some examples of 'foldable' devices—the race is on to develop an electrode that boasts stretchability as one of its features. 


Commercializing the Product 

Should the KIST team's product be commercialized, it could transform markets like consumer electronics and medical technology where wearables are already widely used. With flexible screens, for example, we may see smartwatches with larger screens that contort to the wearer's wrist or medical monitoring devices that can be attached to the skin and move with it.

 "Since the technology can be used for mass production, it is expected to have a great impact on markets related to wearable electronic devices, such as high-performance smart wear, and the medical equipment field", said KIST's Dr. Jeong Gon Son.