Excitonic and polaron/bipolaronic interactions in fullerene - conducting polymer systems

The processes governing charge transfer (CT) between fullerene and conducting polymer (CP) are analysed from the general point of view. It is suggested that C60 is a special type of a weak dopant due to its extended two-dimensional π-electron system, high symmetry and large size of the molecule, which provides good overlaping with electronic states of polymeric chains leading to fast foreward CT. On the other hand self traping effect on C60, leads to charge storage in string type polarons Pc and bipolarons BPc−2 on C60 overlaping of which with polymer chain may become orientationaly suppresed. This may cause spatially suppressed back CT, resulting in long lived BPc−2, which are suggested to contribute to persistent photoconductivity, observed by us in C60-CP composites. Various types of interactions between excitons (Ex), negative polarons (P−) and solitons (S) of polymeric chains with Pc and neutral C60 are considered, e.g. for interpretation of enhanced electroluminescence quenching observed in C60-CP systems. At the same time for positively charged P+, C60 can play a role of a mediator for interchain hoping, increasing thus P+ mobility and contributing additionally to the effect of enhanced photoconductivity.