Electrode Engineering for Advanced Organic Semiconductor Devices

Electrodes are fundamental determinants of performance in semiconductor devices, governing the critical processes of charge injection, extraction, and interfacial transport. As device architectures transition from rigid, large-scale systems toward miniaturized, flexible, and biointegrated platforms, the requirements for electrode design have evolved into a complex, multiobjective optimization challenge. This review provides a comprehensive overview of the recent advances in electrode materials and engineering strategies using organic field-effect transistors (OFETs) as a primary model system to illustrate broader semiconductor design principles that are universally applicable to organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), and other organic semiconductor electronics. We first establish a multidimensional framework for ideal electrode evaluation, encompassing electrical properties, fabrication processability, environmental stability, and the burgeoning demands for mechanical and biological compatibility. A systematic comparison is provided between traditional metallic electrodes and emerging alternatives, including conducting polymers, carbon-based nanomaterials, and doped organic electrodes (DOEs). Special attention is given to the "conductivity threshold" in organic electronics, suggesting that interfacial compatibility often outweighs bulk conductivity in determining device efficacy. Finally, by outlining a roadmap toward multifunctional, green, and biocompatible electrode technologies, this review aims to provide a cornerstone for the next generation of ubiquitous and human-centric semiconductor electronics.