Dry and wet sliding wear of ITO-coated PET components used in flexible optoelectronic applications

Polyethylene terephthalate (PET) coated with indium tin oxide (ITO) is a common electrode component used in numerous flexible optoelectronic devices including flexible displays and solar cells. The advantages of such components include excellent optical transparency, mechanical flexibility and light weight. However, there is little research reported to date on the wear characteristics of the ITO film. Wear of the ITO can be a critical reliability parameter in devices where repetitive user–device interactions and extreme handling are present. The aim of this work is to investigate the wear of an ITO flat surface in contact with an ITO flat counterface under dry, and wet, sliding conditions. Tests were conducted under a moderate normal load for up to a few thousand sliding cycles. Flat-on-flat contact under pure dry, and wet, sliding conditions was used by means of a custom-built reciprocating wear tester. Wet sliding experiments were conducted using acrylic acid solutions. Acrylic acid, contained in many pressure-sensitive adhesives that are in contact with the ITO layer in optoelectronic stacks, can cause corrosion. Wear was determined from weight measurements. The ITO electrical resistance was monitored in situ in order to provide an insight into the wear development. Microscopy was conducted using optical microscopy, scanning electron microscopy (SEM) and atomic force microscopy (AFM). Wear mechanisms of ITO surfaces include cohesive failure within the film, adhesive wear between ITO film and PET substrate, underlying plastic deformation of the PET substrate and abrasive wear of the ITO film. The results, including weight losses and wear mechanisms for ITO-coated PET, can help the understanding of such systems and aid the design of more reliable optoelectronic devices.