Synergistic Stabilization of Ultrathin Ag Films via Ga Alloying and Controlled Oxidation for Robust and Flexible Oxide-Metal-Oxide Transparent Electrodes

Ultrathin Ag films are attractive embedded layers for oxide/metal/oxide (OMO) transparent conducting electrodes (TCEs), but their strong tendency to agglomerate below the percolation threshold severely degrades the optical and electrical performance. Here, we demonstrate that combining Ga alloying with oxidizing sputter deposition effectively suppresses agglomeration in ultrathin Ag-based films embedded in ITO/metal/ITO OMO-type TCEs on colorless polyimide substrates. By tuning the embedded metal composition, thickness, and oxygen flow ratio Φ, we identify an optimized condition in which a 5 nm Ag–Ga layer (Φ = 6%) forms a continuous, void-free conduction path, achieving a visible transmittance of 86–88% at 550 nm and a sheet resistance of 15.8 Ω sq–1. TEM/STEM–EDS and XPS analyses reveal that Ga alloying, interfacial Ga segregation, and controlled Ag/Ga oxidation act together to lower effective surface and interface energies and stabilize ultrathin Ag–Ga layers against agglomeration. As a result, the optimized ITO/Ag–Ga/ITO OMO-type TCE exhibits a high figure of merit, excellent mechanical flexibility, and strong resistance to high-temperature, high-humidity degradation and operates as a transparent heater, reaching application-relevant temperatures under modest bias.