Conductive transparent fabrics: a rugged ITO alternative

January 27, 2017 // By Julien Happich
Swiss research centre CSEM and precision fabrics specialist Sefar have joined their forces to design novel fabric-based flexible and transparent electrodes that could be produced cheaply, in a roll-to-roll process.

By weaving metal wires about 40µm in diameter with semi-transparent polymer fibres into a precision mesh filled with an optically clear polymer, then coating this substrate with a thin layer of a solution-processed organic conductor such as PEDOT:PSS, the research partners were able to obtain ITO-free flexible electrodes which they used to demonstrate large area OLEDs. The high electrical conductivity of the metal wires in the fabric substrate ensures that the electrode displays high conductivity over large distances, even with an ultra-thin, and hence highly transparent, layer of the conductive polymer.

According to Sefar's literature, the conductive fabric now commercialized under the name SEFAR® TCS Planar exhibits a light transmittance of around 90% throughout the visible and near infrared spectrum, a sheet resistance under 0.1Ω/sq, and can be flexed to a bending radius of 6mm with barely any decrease in conductivity. This makes it an interesting alternative to more expensive and brittle ITO layers typically used as transparent electrodes in many electronic applications, from touch displays to solar cells and OLEDs.

The OLED designed with Sefar's conductive fabric.

The fabrics can be further coated with a transparent polymer to make them impermeable to liquids and gases while remaining conductive from one side, providing a barrier for humidity and oxygen without altering noticeably their transmittance characteristics.

Micrometer-size conductive metal wires and transparent polymer fibres are woven together and embedded into an optically clear filling polymer. The substrate coated with the conductive polymer forms the electrode upon which the light-emitted polymer and the top electrode are processed to complete the OLED device. Not to scale.

As a demonstration, CSEM used the new fabric to build a large area flexible OLED.