Sequential toy model for electron transfer in donor-bridge-acceptor systems

TL;DR

This paper develops an analytical model for electron transfer in donor-bridge-acceptor molecular systems, elucidating how energy levels influence rectification current in molecular electronic devices.

Contribution

It introduces a sequential tunneling model incorporating Marcus theory to derive an explicit current formula for donor-bridge-acceptor systems with rectification behavior.

Findings

Rectification current depends on energy level positions relative to electrode Fermi energy.

Derived an analytical expression for current at arbitrary potential drop.

Showed how bias voltage shifts energy levels affecting electron transfer.

Abstract

Sequential tunneling model is used to study electron transport in molecular rectifiers based on structures of donor-bridge-acceptor type. The device is made of two metallic electrodes connected by a molecule, which contains acceptor and donor subunits, separated by insulating bridge. Both subunits are modeled as quantum dots with discrete energy levels, isolated from each other by potential barrier and weakly coupled to both electrodes through tunnel junctions. Intervalence donor-acceptor tunneling process is treated as a superexchange mechanism or equivalently through the use of Marcus theory. Analytic formula for the current is found in the case of the Aviram-Ratner ansatz of rectification and current-voltage characteristic is obtained at an arbitrary strength of the potential drop over the tunneling region. It is shown that rectification current depends on the position of the acceptor's LUMO and donor's HOMO levels with respect to the Fermi energy of the electrodes before bias is applied, and their shift due to the bias voltage.