Polarons in conducting polymers

Yu, Lu, Solitons and Polarons in Conducting Polymers, World Scientific, River Edge, N.J., 1988. 

In addition to the movement of bipolarons (and polarons) in conducting polymers, the counterion movement must be taken into account in certain circumstances. For electronic conductivity measurements in the dry state, there is no movement of the counterions in steady state since they are blocked at the electrodes. Oxidation in an electrolyte involves the... 

A polaron is a fermion quasi-particle consisting of an anion (or cation) defect with an associated polarized Gegenion (= counterion) atmosphere or polarization this is an excited state of the system, with energy intermediate between the valence band and the conduction band. Its mobility within the lattice is due to the fact that there is a low energy barrier for the polarization to move from one site to the next. Polarons are the dominant excitations in conducting polymers. 

Conwell EM, Mizes HA (1995) Photogeneration of Polaron Pairs in Conducting Polymers. Phys Rev B 51(11) 6953—6958... 

Bredas JL, Street GB (1985) Polarons, Bipolarons, and Solitons in Conducting Polymers. Accounts of Chemical Research 18( 10) 309—315... 

In conducting polymers with a non-degenerate ground state (such as for example poly(p-phenylene), polypyrrole or polythiophene) the charge introduced upon doping can be stored in a form of polarons and bipolarons. Taking polythiophene as an example, polaron and bipolaron can be visualized as follows (Scheme 4.7). 

In solid state physics, polarons are electrostatically induced local lattice distortions caused by an electron in a ionic crystal. In conducting polymers radical cations (lone electrons associated with positively charged holes) have a similar effect. 

The concept of the polaronic metal has been applied to polyaniline as well, and may be a more general feature of the metallic state in conducting polymers. In the context of the discussions presented in Section I through Section IV, the polaronic metal is indeed a "metal" and the analysis given is appropriate. In particular, the importance of the selforganization of the doped polymer (to avoid counter-ion scattering) and the need to avoid localization etc. are of clear importance. 

The nature of the charge carriers in conducting polymers is not very well understood. It is believed that intrinsic excitations, such as solitons, polarons and bipolarons, do play the role of charge carriers [23,24]. Considerable theoretical and experimental work has been carried out in this area [25-27]. The properties of these excitations are discussed in detail in the following sections. 

As discussed in previous sections, the mechanisms for the formation of metallic state and charge conduction in conducting polymers have been the subject of intensive study since the occurrence of an insulator to metal transition was reported upon doping. It is proposed that non linear defects such as polarons, solitons and bipolarons have a major role in these systems [36, 95-97]. In earlier synthesised conducting polymers, inhomogeneities often dominated the transport properties, and metallic island models were proposed to... 

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