Novel Transparent TiO₂/AgNW-Si(NH₂)/PET Hybrid Films for Flexible Smart Windows

The application of flexible indium tin oxide (ITO)-free electrochromic devices (FCDs) has always been a research hotspot in flexible electronics. Recently, a silver nanowire (AgNW)-based transparent conductive film has raised great interest as an ITO-free substrate for FCDs. However, several challenges, such as the weak binding of AgNWs to the substrate, high junction resistance, and oxidation of AgNWs, remain. In this paper, a novel method for surface modification of AgNWs with N-aminoethyl-γ-aminopropyltrimethoxysilane [Si(NH₂)] solution is proposed to enhance the bonding with the flexible substrates and the active materials, thereby inhibiting the delamination of AgNWs from the substrate and reducing the high junction resistance between nanowires. The TiO₂/AgNW-Si(NH₂)/poly(ethylene terephthalate) (PET) films show outstanding mechanical properties, of which the resistance remains almost unchanged after mechanical bending of 5000 cycles (ΔR/R₀ ≈ 3.6%) and repeated peeling off cycles with 3M tape 100 times (ΔR/R₀ ≈ 6.0%). In addition, we found that the oxygen-containing groups on the TiO₂/AgNW-Si(NH₂)/PET surface form hydrogen bonds with the TiO₂ sol, resulting in tight contact between the TiO₂ sol and the AgNWs, which prevents the AgNWs from oxidation. As a result, the TiO₂/AgNW-Si(NH₂)/PET film exhibited long-time aging (ΔR/R₀ ≈ 4.9% in the air for 100 days) stability. A FCD was constructed with the TiO₂/AgNW-Si(NH₂)/PET film, which showed excellent electrochromic performance (94% retention) after 5000 bending cycles, indicating high stability and mechanical flexibility. These results present a promising solution to the transparent conductive films for flexible energy devices.