Multilayer Transparent Electrodes: Design, Fabrication, Performance, and Applications

Indium tin oxide (ITO) is the benchmark transparent conductor for displays and for electrochemical and optical sensors, but its brittleness, cost, and indium supply risk limit its use in flexible, large-area devices. Oxide/metal/oxide multilayers, namely transparent conducting oxide (TCO)/metal/TCO stacks such as ITO/metal/ITO (IMI) and dielectric–metal–dielectric (DMD) stacks, decouple sheet resistance from transmittance: a ductile ultrathin metal core carries the current, while the outer oxides act as anti-reflection layers. This review compares the design rules, deposition routes, and characterisation of these electrodes. Single-study tables relate architecture, substrate, and processing conditions to electrical, optical, and mechanical performance, and the review explains why reported figures of merit are rarely comparable. Ag-based TCO/metal/TCO stacks are the most mature option for flexible displays, and asymmetric stacks with nucleation-controlled Ag are a promising indium-free route. Open limits include ultrathin-metal growth, metal absorption, Ag/Cu stability, and oxide cracking. No biosensor built on a multilayer electrode has been reported; ITO already enables dual electrochemical and optical readout, so testing multilayers against ITO is the next step. Artificial intelligence (AI)-assisted design of multilayer electrodes is at an early stage.