Conductivity, electronic bond alternation defect

The electrical conduction behaviour in doped polymers has been extensively studied and new conduction mechanisms involving coupling of electronic excitations to non-linear conformations have been proposed. The conduction behaviour has been explained by dopant-induced bond-alternation defects such as soli-tons, polarons and bipolarons [1,2,9,11,32-35]. Thermal treatment of organic monomers and polymers results in the formation of extended aromatic structures or planar ladder structures, and hence the heated polymers have considerably smaller bandgaps and higher mobility than unheated ones. They exhibit large... 

The ideal chain-structures employed in theoretical models bear little resemblance to real materials. Disorder has been modelled by either a distribution of conjugation lengths or electron-lattice interactions. Bond length and substitutional disorder has been shown to lead to the disappearance of bond alternation and closure of the band gap, though with a low density of states at the Fermi energy. A simple model has been developed for the influence of defects on the electrical conductivity of doped samples. Pinning of solitons by defects has been discussed, but it is clear that the role of disorder requires further study. ... 

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