The effects of free volumes on charge carrier transport in polysilanes probed by positron annihilation

Abstract Free volume characteristics were investigated by positron annihilation technique in poly( n -alkylphenylsilane)s with a variety length of n -alkyl chains from methyl (C1) to n -dodecyl (C12). The average radius of free volume: R changes in two steps. An increase in R is observed with an elongation of n -alkyl side-groups from C1 to n -pentyl (C5), followed by an abrupt decrease in R between C5 and n -hexyl (C6), and a gradual increase by further elongation from C6 to C12. The sudden decrease in R at C5 and C6 gives a good interpretation to the reduction of inter-site hopping distances and their fluctuation for the charge carrier (hole) transport estimated by time-of-flight measurements. The values of free volume fraction in the polymers mainly reflect the density of the polymers; however, differences in the microscopic inter-molecular structure are also observed for poly( n -hexylphenylsilane) in the present study.