Abstract
We compare the generation and decay dynamics of charges and excitons in a model polymer semiconductor (MEH-PPV) in solution and drop-cast thin films, by recording the sub-ps transient complex conductivity using time-domain spectroscopy. The results show that the quantum efficiency of charge generation is two orders of magnitude smaller in solution than in the solid film . The proximity of neighboring chains in the films apparently facilitates (hot) exciton dissociation, presumably by allowing the electron and hole to separate on different polymer strands. For both samples, photoexcitation leads to the predominant formation of bound charge pairs (excitons) that can be detected through their polarizability. Surprisingly, the polarizability per absorbed photon is a factor of 3 larger in solution than in the film, suggesting that interchain interactions in the film do not result in a substantial delocalization of the exciton wave function.
- Received 20 August 2004
DOI:https://doi.org/10.1103/PhysRevB.71.125201
©2005 American Physical Society