Charge carriers in conjugated polymers

Both theoretical and experimental evidence suggest that the precise nature of the charge carriers in conjugated polymer systems varies from material to material, and it is still a subject of debate in many cases. A discussion of the various theoretical models for the electronic structure of conjugated polymers is given below, using polyacetylene and poly(paraphenylene) as examples. More detailed information on these materials and the applicability of these theoretical models is given in subsequent sections. 

Neugebauer, H. 2004. Infrared signatures of postive and negative charge carriers in conjugated polymers with low band gaps. / Electroanal Chem 563 153. 

Dyakonov, V., G. Zoriniants, M. Scharber, C.J. Brabec, R.A.J. Janssen, J.C. Hummelen, and N.S. Sariciftci. 1999. Photoinduced charge carriers in conjugated polymer-fullerene composites studied with light-induced electron-spin resonance. Phys Rev B 59 8019. 

Mozer, A.J., G. Dennler, N.S. Sariciftci, M. Westerling, A. Pivrikas, R. Osterbacka, and G. Juska. 2005. Time-dependent mobility and recombination of the photoinduced charge carriers in conjugated polymer/fullerene bulk heterojunction solar cells. Phys Rev B 72 035217. 

CHARGE CARRIERS IN CONJUGATED POLYMERS 2.1. Ground-State Structures... 

Other polyrotaxanes containing a thiophene-based conjugated backbone have been synthesized from the Cu(I)- or Zn(II)-driven assembly between a macrocyclic phenanthroline and a bithiophene-substituted phenanthroline [322] or bipyridine [323, 324]. Swager and co-workers have demonstrated that the contribution of the metal ion to the electronic properties of the polyrotaxane was possible when more electron-rich 3,4-(ethylenedioxy)thio-phene groups were used in place of thiophenes in the polymer backbone [324]. So a 10 -10 -fold increase in the polymer s conductivity was observed after poly(24) was treated with Cu(II) solution. This result was ascribed to the oxidation of the poly(24) backbone by Cu " " ions to generate poly(24,Cu) with charge carriers in the polymer backbone. 

Summarizing the results obtained for charge transport in conjugated polymers, the Poole-Frenkel model seems to be a good description [126,127]. This model of transport assumes the existence of two types of carrier movement, one in conductive states (positive polarons) and the other via traps (negative polarons). 

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