Flexible, transparent and conductive silver line electrodes fabricated using surface energy-directed assembly process on polyethylene naphthalate substrates

Flexible transparent conductive electrodes (FTCEs) are essential components in emerging optoelectronics, including flexible displays, smart glasses/windows, organic solar cells, and electronic skins. The surface energy-directed assembly (SEDA) process, known for its capability to create high-resolution and high-fidelity patterns, has been utilized to fabricate TCEs on rigid glass substrates. However, the fabrication of FTCEs on flexible substrates remains comparatively underexplored. Here, we present the fabrication of silver patterns on polyethylene naphthalate (PEN) substrates using the SEDA process. A surface treatment process has been devised to render the PEN substrates hydrophobic, achieved through coating the substrates with fluorine-containing PyFlon films. This approach yields a significant improvement over silane-based self-assembled monolayer film-coated substrates, as it drastically diminishes surface roughness. Consequently, the contact angle hysteresis of the substrate surface is minimized, enabling the effective dewetting of the nanoparticle suspension. The incorporation of PyFlon films into the SEDA process has proven to be highly successful. Using this approach, we have successfully assembled functional patterns of various geometries and dimensions on PEN substrates, composed of silver nanoparticles, quantum dots, carbon nanotubes, silver nanowires, and gallium indium eutectic, with a high resolution down to 500 nm. The assembled silver line electrodes exhibit excellent transmittance (∼88%), low sheet resistance (7.12 Ω/□), and high mechanical stability, and their application in electroluminescent devices is showcased.