Polaron and bipolaron excitations in doped polythiophene

Abstract

An energetic study of the excitation spectrum in doped polythiophene is presented within the framework of the H\"uckel approximation. The calculations show that localized states like polarons and bipolarons are produced by doping, the formation of doubly charged bipolarons being energetically more favorable than the formation of two polarons charged singly. It is then shown from the analysis of available magnetic and optical data that the bipolarons are the dominant charge states while the features due to the polarons appear under certain circumstances at low doping levels.