Junction Scale Governs Rectification Magnitude and Probability in Molecular Diodes

Determining the extent to which molecular tunneling performance is an intrinsic property of a molecule versus a consequence of junction architecture remains a central challenge in molecular electronics. In this study, the two-dimensional junction scale is treated as a statistical variable, and rectification is mapped across three junction regimes that differ by orders of magnitude in the number of molecules sampled, namely single-molecule, small-area, and large-area junctions. Using a single family of molecular diodes, SC n BIPY ( n = 11, 5, 1), it is revealed that apparent function depends strongly on scale. Specifically, long-chain SC 11 BIPY rectifies robustly in monolayer-based large-area junctions (| r | ≈ 10 2 ), whereas shorter analogues show little or no significant rectification at ensemble scales, despite recovering pronounced rectification in the single-molecule limit (| r | ≈ 50–70). Importantly, junction scale modulates not only rectification magnitude but also its reliability, as quantified by f r, the fraction (estimated probability) of working junctions that exhibit significant rectification (| r | ≥ 10). These findings show that lateral scaling can act as a statistical filter that amplifies or suppresses disorder-sensitive functionality, providing a unified framework to reconcile cross-platform discrepancies in molecular diode behavior, and highlighting junction dimensionality as a design parameter for robust molecular-scale device functions.