Tailoring IV Characteristics and Rectification in Single-Molecule Junctions

Asymmetry in the current-voltage characteristics, or current rectification, of nanoscale junctions is a critical property for many optoelectronic and energy conversion applications using nanostructured materials. Here, we compute the conductance, IV characteristics, and bias-dependent rectification of a class of molecular junctions, consisting of donor-acceptor molecules in contact with Au electrodes, using quantitative first-principles calculations [1]. We relate the rectification to the identities of the donor and acceptor moieties through the junction energy level alignment and dipole moments and find, surprisingly, that a large asymmetry in the contact coupling leads to weak rectification. We explain our results with an analytic coherent tunneling model, and suggest concrete strategies for obtaining high rectification in experimentally-achievable systems. [1] Darancet et al. , submitted (2011) .