A Robust Alloyed Interface of Cu and PET for High Performance Flexible Transparent Conductive Meshes

Flexible transparent conductive electrodes (TCEs) based on copper (Cu) meshes on polyethylene terephthalate (PET) substrates are constrained by critical interfacial weakness and inadequate mechanical durability, which hinder their widespread practical application. This study proposes a robust alloyed interface engineering strategy to address this fundamental challenge. Magnetron sputtering is employed to deposit Cu thin films on PET substrates with intermediate aluminum oxide (Al₂O₃) and nickel-chromium (NiCr) interfacial layers. Systematic comparative analyses reveal that the direct Cu/PET interface exhibits poor adhesion and mechanical fragility, while the incorporation of NiCr interlayers significantly enhances interfacial toughness. Through optimization, the NiCr layer forms a distinct alloyed interface with Cu via interdiffusion, fundamentally reinforcing the Cu/PET interface. Maskless photolithography enables precise patterning of Cu into micrometer-scale meshes, resulting in Cu Mesh/PET electrodes with excellent optoelectronic performance. The optimized electrodes achieve a sheet resistance of ~10.8 Ω/sq with an optical transmittance exceeding 87%, alongside remarkable mechanical robustness under repeated bending cycles. The synergistic toughening mechanism is clarified through interfacial microstructure analysis, which shows that the formation of a gradient alloyed zone effectively mitigates interfacial stress concentrations and suppresses crack propagation. This work provides a viable pathway for the development of next-generation durable flexible electronics.