Determinants of electron transport at asymmetric metal/molecule/metal contacts

Single–molecule electronic devices offer the ultimate pathway to transcend post–Moore scaling limits. However, developing molecular diodes remains paralyzed by trial–and–error, as classical transport models fail at complex hybrid interfaces involving both strong covalent and weak non–covalent interactions. Here, we establish a unified theoretical model enabling precise quantitative prediction of electron transport across highly asymmetric metal/molecule/metal contacts. By screening 144 diverse molecular junctions—including classic donor–acceptor architectures—we uncover the microscopic mechanisms driving charge rectification: asymmetric anchoring groups induce pronounced electronic polarization, while dynamic adsorption–state changes dictate spatial coupling. This interplay is fundamentally governed by a deep synergy between interfacial bond dipoles and effective tunneling widths. We derive a composite descriptor bridging quantum tunneling and thermal excitation, achieving >93% predictive accuracies across monostable and bistable regimes. Guided by this, we identify optimal configurations yielding an intrinsic rectification ratio of 19.25 at 0.12 V, drastically outperforming conventional D–π–A systems. The development of molecular diodes has been hindered by trial-and-error approaches due to the breakdown of classical transport models at the metal–molecule interface. Su et al. investigate 144 molecular junctions and introduce a descriptor that achieves over 93% predictive accuracy in rectification ratio.