Modulation of Rectification in Diblock Co-oligomer Diodes by Adjusting Anchoring Groups for Both Symmetric and Asymmetric Electrodes

The rectifying properties in dipyrimidinyl-diphenyl co-oligomer diodes with asymmetric anchoring groups were investigated using density functional theory combined with the nonequilibrium Green’s function method. Effects of asymmetric interfaces caused by both the anchoring groups and/or contact geometries of electrodes have been investigated. Our results showed that the rectifying behavior of the co-oligomer diode could be reversed or largely enhanced by adjusting asymmetric anchoring groups. Whether the asymmetric contact geometries play a positive or negative role in improving the rectifying behavior is closely related to each molecular diode. The mechanism of modulation was analyzed in terms of molecular projected self-consistent Hamiltonian states and transmission spectra. The theoretical simulations are helpful for understanding recent experimental results [Lee et al. Langmuir2009, 25, 1495 and Hihath et al. ACS Nano2011, 5, 8331]. Moreover, the mechanism of the rectification only due to the electrode asymmetry was explained, and a single-molecule diode with significant rectifying behaviors has been theoretically designed.