Doping effects and electronic states in C-60-polymers

Band structures of Cao-polymers are studied changing conjugation conditions and the electron number. We use a Su-Schrieffer-Heeger type semiempirical model. In the neutral C-60-polymer, electronic structures change among direct-gap insulator and the metal, depending on the degree of conjugations. The C-60-polymer doped with one electron per one molecule is always a metal. The energy difference between the highest-occupied state and the lowest-unoccupied state of the neutral system becomes smaller upon doping owing to the polaron effects. The C-60-polymer doped with two electrons per one C-60 changes from an indirect-gap insulator to the direct-gap insulator, as the conjugations become stronger.