High-Performance Molecular Diodes in the 2020s: From Single Molecules to Self-Assembled Monolayers

Molecular diodes exemplify rectification at the molecular scale, serving as fundamental components of molecular electronics with the potential to enable low-power logic functions and highly integrated circuit architectures. In this review, we summarize recent advances reported in the 2020s, with particular emphasis on junctions achieving rectification ratios exceeding ∼10 2 . We highlight diverse measurement platforms─including scanning tunneling microscope break junctions, cross-plane junctions, and eutectic gallium–indium alloy (EGaIn)-based large-area junctions─and discuss how molecular design strategies such as donor–acceptor engineering, supramolecular assembly, frontier-orbital gating, Fermi-level pinning, redox switching, ion insertion, and coupling to two-dimensional electrodes have enabled high rectification performance. Representative molecular diode structures include boron-doped van der Waals junctions, quantum interference-controlled single-molecule diodes, supramolecular assemblies, and self-assembled monolayers (SAMs) incorporating ferrocene or other metal complexes. Collectively, these studies reveal that high rectification can be achieved through a multifaceted design strategy combining molecular orbital control, interfacial engineering, and redox-active motifs. Looking forward, further exploration of mixed SAM architectures, integration of 2D electrodes, and systematic studies of environmental factors such as humidity and temperature will be essential to translate molecular-scale rectifiers into robust device architectures. Continued efforts to couple molecular design with scalable fabrication and stability testing are expected to advance molecular diodes toward practical applications in next-generation nanoelectronic circuits.