Theoretical and Experimental Studies of Electronic Transport of Dithienothiophene

Electronic transport through metal-dithieno[3,2-b:2′,3′-d]thiophene (DTT) junctions with two interface geometries were studied experimentally by conducting probe atomic force microscopy on a self-assembled monolayer of DTT sandwiched between pairs of Au contacts and studied theoretically by using the fully self-consistent nonequilibrium Green’s function combined with the density functional theory to calculate the transport current in the DTT nanostructures. The experimental and simulation results reveal a similar electrical transport nature of a steplike current−voltage (I−V) curve and negative differential resistance (NDR). The characteristics of the I−V curves were elucidated with evolution of the transmission spectra, and the dependence of transmission peaks on the spatial distribution of renormalized molecular orbitals were further analyzed. In two designed test molecular schemes, the highest occupied molecular orbital (HOMO) is mainly responsible for the transmission resonance at a lower external bias voltage, while the interface states originating from coupling between the electrode surface and DTT molecule are suggested to produce the NDR peak in an asymmetrical metal−DTT junction. The study of electronic transport of monomers at the molecular scale in this work demonstrates a new mechanistic approach to engineer and optimize organic material-based electronic devices.