Tin-doped indium oxide films for highly flexible transparent conducting electrodes

With the recent growing interest in flexible electronics, many studies are being conducted on flexible transparent conducting electrodes (TCE) such as Ag nanowires, Ag nanomeshes, carbon nanotubes, and graphenes. However, it will take time for such technologies to replace Sn-doped In₂O₃ (ITO), which is now widely used, due to challenges with reliability, mass-production, cost, and industry infrastructure. In this study, ITO films with different thicknesses were deposited on a flexible polymer substrate to investigate their optical and electrical properties and flexibility as a function of film thickness. Regardless of thickness, the ITO films' transmittance was about 80% at ~ 550 nm wavelength. The sheet resistances of all films were below 100 Ω/sq although resistance increased with decreasing film thickness. As a result of bending tests, it was found that thinner films had a higher threshold against bending strain. The sheet resistances did not significantly change above a bending radius of ~ 5 mm. In particular, the 50 nm-thick ITO film endured to a bending radius of ~ 3 mm, showing that it is a viable transparent electrode for flexible optoelectronics.