Low‐Temperature Annealed Cu/Al Bilayer Architecture for Highly Stable Flexible Metal‐Mesh Transparent Electrodes

ABSTRACT Flexible transparent electrodes (FTEs) are essential for next‐generation optoelectronics, yet indium tin oxide (ITO) is limited by brittleness and high cost. Copper metal meshes are promising alternatives but suffer from rapid oxidation. Here, we report a Cu/Al bilayer strategy in which an ultrathin Al overlayer self‐passivates into a compact Al 2 O 3 barrier, effectively suppressing Cu degradation while preserving optoelectronic performance. Low‐temperature vacuum annealing (≤125°C) further reduces defect induced scattering and improves interfacial conformity, yielding a 36% reduction in sheet resistance (0.196 to 0.125 Ω/□). The resulting Cu/Al films exhibit excellent environmental stability, with negligible resistance change after 168 h of damp‐heat aging (85°C/85% RH). Photolithographically patterned hexagonal Cu/Al meshes on PET achieve 4.58 Ω/□ at ≈81% visible transmittance, show only a 12% resistance increase after 150 days of natural aging (vs 42% for Cu), and maintain stable conductivity after 1000 bending cycles at 135°. Integrated into a touch sensor, the meshes demonstrate reliable touch, proximity, and force sensing. This scalable bilayer‐and‐anneal strategy enables oxidation‐resistant, high‐performance, ITO‐free transparent electrodes for flexible electronics.