Hole transport in polysilanes with diverse side-chain substituents

Abstract

The hole drift mobilities in polysilanes with diverse substituents and different molecular weights have been measured by the conventional time-of-flight technique. Depending on the kind of substituents, hole drift mobilities varied by more than one order of magnitude; poly(?henyltrimethyldisilane) gave the highest room temperature hole drift mobility, 6·0 × 10⁻⁴cm²V⁻¹s⁻¹ at a field of 2 × 10⁵ V cm⁻¹, of all the polysilanes reported so far.

The electric field and temperature dependences of the hole drift mobilities in polysilanes were analysed in the framework of Gill's expression and Bässler's consideration. Polysilanes with an aromatic side group exhibited a zero-field activation energy E ₀ of ca. 0·35 eV compared to E ₀ = 0·22-0·26 eV obtained for polysilanes with non-aromatic groups, while poly(phenyltrimethyldisilane), with one aromatic side group at every two Si atoms, manifested E ₀ = 0·26 eV, a value which may be categorized in the latter group with non-aromatic substituents. The effects of the substituents on drift mobility are further discussed in terms of the disorder in the energy and position of the hopping sites in the particular polysilanes.