Robust reproducible large-area molecular rectifier junctions

Stable rectifying molecular junctions have been obtained by sandwiching self-assembled monolayer films containing "push-pull" donor-pi-acceptor (D-pi-A) moieties between Au and poly(3,4-ethylenedioxythiophene) electrodes. These D-pi-A moieties possess moderate molecular dipoles, but assemble into films with nearly zero dipole moment due to adoption of high average tilt angles. Nevertheless reproducible and well-behaved rectifications (ratio up to 3.3) in the expected polarity were obtained. At low biases, the current-voltage characteristics follow Simmon's tunneling theory with reasonable barrier heights and an effective tunnel mass of similar to 0.5m(e). This suggests that asymmetric tunneling, and not carrier injection, is the origin of the rectification. (c) 2008 American Institute of Physics.