Bias-induced orbital hybridization in diblock co-oligomer diodes

Abstract

We investigate current rectification in diblock co-oligomer diode molecules on the basis of the Su-Schrieffer-Heeger model [Phys. Rev. B 22, 2099 (1980)] combined with the nonequilibrium Green’s function formalism. The current rectification observed in experiment [M. K. Ng et al., J. Am. Chem. Soc 124, 11862 (2002)] is well explained by the mechanism of bias-induced asymmetric hybridization of molecular orbitals. The positive bias tends to delocalize molecular orbitals through the hybridization, which produces a sharp increase in current at the threshold voltage; while the negative bias enhances the mismatch of energy levels and has no effect on the hybridization and the current.