Polarons in conducting polymers

Summary form only given. We have setup an SSH type of hamiltonian for PPV by choosing a set of t/sub 0/, the transfer integral, /spl prop/ (=/spl part/t/sub 0/ / /spl part/u/) and K, the elastic constant, to match the known PPV valence band width, /sp 1/ energy gap and aimerization within 1%. with these parameters, for long chains the polaron level is 0.18 eV form the band edge, the top bipolaron level 0.53 eV from the edge. Interchain coupling should be dominated by the coupling between the 3 C´s that are closest to H´s on the nearest neighbor chain. Determining the parameters for these couplings to match the LDA calculated transverse banwidth, /sub 1/ we find that the polaron is not destabilized by interchain coupling as it is in(CH)/sub x/ for the P2/sub 1/a structure. Studies of picosecond photoinduced absorption (PA) in PPV lead to the conclusion that polaron pairs, P/sub +/ and P/sub -/, are generated in larger numbers than singlet excitons./sub 2/ We have calculated the properties of these pairs using the SSH type hamiltonian described above. The binding energy of air of long chains is /spl tilde/0.35 eV. The peaks of the optical absorption of such found to agree well with the observed PA. We have also calculated the in (CH)/sub x/ and find good agreement with the observed PA for that to single polarons. We suggest that photogeneration of polaron pairs predominates over that of single polarons in conducting polymers, accounting for the paucity of evidence for the photogeneration of single polarons.