TiO₂-Coated Core–Shell Ag Nanowire Networks for Robust and Washable Flexible Transparent Electrodes

Abstract

Silver nanowires (AgNWs) are the most promising materials to fabricate flexible transparent electrodes (FTEs) that are used in next-generation electronics. However, there are several bottlenecks for AgNW-based FTEs to achieve large-scale applications, which include the thermal instability and rough surface topography of AgNWs and the poor interfacial adhesion between AgNWs and the used substrate. To simultaneously address these aforementioned issues, a robust and washable FTE is prepared based on a AgNW@TiO2 core–shell network embedded in polyimide (PI) substrate through a facile and scalable solution-based process. After being treated with TiO2 sol, an ultrathin, conformal, and continuous TiO2 shell is coated on the AgNWs, which can effectively suppress the atomic surface diffusion. In comparison with a pristine AgNW network that breaks into nanorods and nanospheres at 250 °C for 10 min, the AgNW@TiO2 core–shell network is stable at 300 °C, and its resistance just increases by a factor of 11 after being annealed at 400 °C for 1 h. Furthermore, the TiO2 shell simultaneously increases the electrical and optical properties of the AgNW network. After PI precursors are flowed, dried, and thermally cured, the AgNW@TiO2 core–shell network is embedded on the surface of the PI substrate with a surface roughness of 1.9 nm. In addition to high thermal stability, the conductivity of the AgNW@TiO2–PI composite FTE remains almost unchanged after repeated peeling off cycles with 3M tape and mechanical bending cycles. It is also demonstrated that the AgNW@TiO2–PI composite FTE is washable, and the relative change in resistance (ΔR/R0) is ∼12% after 100 washing cycles, in which a variety of stress situations occur in combination.