Transport of carriers in a semiconductor polymer random chain: a renormalization approach

Abstract

We present a theoretical study for the quantum transport of carriers in a random semiconductor polymer poly(p-phenylene vinylene) (PPV) chain with the benzoid rings partially replaced by quinoid rings. A renormalization approach maps the polymeric chain into an effective one-dimensional lattice and the transmission coefficient as a function of energy is computed by transfer matrix techniques. In the case of randomly-distributed quinoid rings the spectrum shows narrow peaks in the conduction and the valence bands which indicate the presence of special resonant electron and holes states, lying within a larger fraction of localized states. The obtained density of states (DOS) shows a bandgap smaller than the transmission gap between the electron and the hole resonance peaks, which implies that an electric voltage larger than the band gap is required to inject electrons and holes into the polymer. This could explain why the operating voltage of PPV light-emitting diodes (LEDs) is larger than the semiconductor gap, in sharp contrast to conventional semiconducting LEDs.