Charge Storage in Conducting Polymers: Solitons, Polarons, and Bipolarons

摘要

The results of a series of experiments demonstrate that solitons are the important excitations in trans-(CH)x and that the properties of these nonlinear excitations can be directly studied during photoexcitation or after doping. The importance of these concepts in the more general context of conducting polymers is addressed. Although the two-fold degenerate ground state of trans-(CH)x is quite special, the relevant concepts have been generalized to confined soliton pairs (bipolarons). Experimental results which demonstrate electron-hole symmetry and weak confinement in poly(thiophene) make this polyheterocycle a nearly ideal example of a model system in which the ground state degeneracy has been lifted. In the dilute doping regime, in situ absorption spectroscopy data (during electrochemical doping) are in detailed agreement with charge storage via bipolarons with confinement parameter gamma approx. 0.1 - 0.2. These results on polythiophene demonstrate that a quantitative fundamental understanding is possible even for relatively complex systems.