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@TiO 2 core−shell network embedded in polyimide (PI) substrate through a facile and scalable solution-based process. After being treated with TiO 2 sol, an ultrathin, conformal, and continuous TiO 2 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@TiO 2 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 TiO 2 shell simultaneously increases the electrical and optical properties of the AgNW network. After PI precursors are flowed, dried, and thermally cured, the AgNW@TiO 2 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@ TiO 2 −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@TiO 2 −PI composite FTE is washable, and the relative change in resistance (ΔR/R 0 ) is ∼12% after 100 washing cycles, in which a variety of stress situations occur in combination. KEYWORDS: AgNW@TiO 2 core−shell network, TiO 2 sol, flexible transparent electrodes, peeling off and mechanical stabilities, thermal and washing stabilities

Application of ultrathin TiO2 layers in solar energy conversion devices

“…The growth method of TiO 2 ETL has been adapted to fit different forms of electrode alternatives. [133][134][135][136]…”

“…Moreover, it has been gradually recognized that the transparent conducting oxide (TCO) is not a suitable candidate for the electrode in flexible cell due to its brittleness and poor bending durability, thus stimulating the development of alternative electrode materials such as metal foil or grid, carbon nanotube (CNT) and silver nanowires (Ag NW). The growth method of TiO 2 ETL has been adapted to fit different forms of electrode alternatives 133–136 …”

Highly Stable Ag–Au Core–Shell Nanowire Network for ITO‐Free Flexible Organic Electrochromic Device

“…These materials should be able to form a compact layer and completely eliminate the exposed Ag surface; otherwise oxidation will be inevitable in a long run. Various materials, including ion‐gel film, [ 13 ] TiO 2 , [ 15 ] and graphene, [ 16 ] have been attempted. In most of the reported work, the coated Ag NWs showed enhanced stability against oxidation, but not at the level of withstanding a harsh environment, quite likely due to the incomplete coverage of the coating material.…”

Effects of non-homogeneity and oxide coating on silver nanowire networks under electrical stress: comparison between experiment and modeling

“…[66] Ag-based core-shell nanowires fabricated by sol-gel is another promising way to achieve transparent electrodes with enhanced stability. [67,68] In spite of many experimental efforts devoted to the stability improvement of AgNW-based TCMs, a deep understanding of the main mechanisms leading to network failure is still missing. As experimentally observed, the degradation of the AgNW networks usually initiates with a local defect that subsequently propagates over a larger area.…”