Ultrathin Transparent Conductive Polyimide Foil Embedding Silver Nanowires

Metallic nanowires are among the most promising transparent conductor (TC) alternatives to widely used indium tin oxide (ITO) because of their excellent trade-off between electrical and optical properties, together with their mechanical flexibility. However, they tend to suffer from relatively large surface roughness, instability against oxidation, and poor adhesion to the substrate. Embedding in a suitable material can overcome these shortcomings. Here we propose and demonstrate a new TC comprising silver nanowires (AgNWs) in an ultrathin polyimide foil that presents an optical transmission in the visible larger than ITO (>90%), while maintaining similar electrical sheet resistance (15 ohm/sq). The polyimide protects the Ag against environmental agents such as oxygen and water and, thanks to its deformability and very small thickness (5 μm), provides an ideal mechanical support to the NW's network, in this way ensuring extreme flexibility (bending radius as small as at least 1 mm) and straightforwardly removing any adhesion issue. The initial AgNWs' roughness is also reduced by a factor of about 15, reaching RMS values as low as 2.4 nm, suitable for the majority of applications. All these properties together with the simple fabrication technique based on all-solution processing put the developed TC in a competitive position as a lightweight, mechanically flexible and inexpensive substrate for consumer electronic and optoelectronic devices.