Initial spatial distribution of geminate charge carriers photogenerated in doped conjugated polymers

- Vibrationally relaxed exciton dissociates into a geminate pair of charges on a charge transfer center.
- Charge transfer center consists of the conjugated segment and dopant molecule.
- A hole executes a diffusion motion along the conjugated segment, in which it has been generated.
- The spatial distribution of trapped holes is found by solving a diffusion equation.
- Effective temperature of pretrapped holes is evaluated at about 1200 K.

A diffusion model of the charge carrier photogeneration in doped conjugated polymers is suggested. A dissociation of a vibrationally relaxed exciton into a Coulombically bound geminate pair of charges occurs at a charge transfer center which consists of a conjugated segment of a polymer chain and a nearby dopant molecule. A photogenerated hole executes one-dimensional diffusion motion along the conjugated segment in the on-chain potential well formed by the Coulomb and external electric fields. Holes are assumed to become localized in trapping sites. It is shown that the spatial distribution of trapped holes is determined mainly by effective temperature of pretrapped holes and external electric field. The model is consistent with experimental data on photoconduction of a copolymer of a phenyl-substituted poly-phenylenevinylene doped with trinitrofluorenone, which have been reported by Weiter et al. (2004). Effective temperature of holes is evaluated at about 1200 K.

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