Anomalous transition in charge transport behavior of polysilane

Anomalous transition of the dispersion parameter α was observed for the first time in poly( n -butyl- n -pentylsilane) (PBPS). Time-of-flight photocurrent ( I ) of PBPS was measured. The photocurrent transient was dispersive: I ∝ t -(1-α) . The dispersion parameter α dropped around the glass transition temperature T g with increasing temperature, and became temperature-independent above T g . The mobility was described within the framework of a formalism based on disorder due to Bässler and coworkers. Both the diagonal disorder parameter σ, the variance of the density of states, and the off-diagonal disorder parameter Σ, the degree of positional disorder, decreased around T g . Nevertheless the ratio of the off-diagonal disorder parameter Σ to the diagonal disorder parameter σ was found to increase above the transition temperature. This anomalous transition is rationalized by the assumption that the off-diagonal disorder dominates charge transport in PBPS above T g .