Temperature dependent electron transport in oligo (3-methylthiophene) derivative molecular devices

Abstract

Addressable molecular junctions based on a thiol-functionalized oligo (3-methylthiophene) derivative incorporated with pyridine unit were fabricated using polymer stamp-printing method. The junction charge transport was measured from 95 to 299 K under both dark and light conditions. Asymmetric current–voltage characteristics with temperature, light, and bias-direction dependence were observed. Simmons tunneling combined with hopping play dominant roles at low bias under both dark and light. The thermionic and Poole–Frankel emissions are also found to affect the charge transport in some cases. Based on the density functional theory in conjunction with the non-equilibrium Green's function method, we investigated the transport properties of a series of single-molecule junctions with different molecular structures, in which negative differential resistance was observed. Density functional theory calculation and transmission spectrum show that the tunneling barrier may depend on the relative energetic position of the frontier molecular orbitals with respect to the metal Fermi level under the effects of bias and temperature.