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.