Substituent Dependence and Orientation Effect on Carrier Trapping in Polysilane Films

Abstract

Thermally stimulated current measurements for polysilanes with aromatic substituents have been performed to investigate the behavior of trapping and release of charge carriers. Different kinds of the substituents(phenyl, p-tolyl and m-tolyl)with and without the orientation of the main chains are examined. It is found that the trapped carriers are released at some specific temperatures exhibiting the endothermic motion of polysilanes but cannot be released completely in one scan of the measurement. This behavior has been analyzed by introducing a concept of the temperature-dependent lifetime of trapped carriers. It is considered that the aromatic substituents in polysilanes form π-π states to be trapping centers for holes and the trapped holes are released by the endothermic motions of the substituents. The analysis reveals that 1)the substituents examined have two principal holereIease peaks at 215K-219K and 226K-234K, 2)the orientation broadens the peak widths, and 3)the orientation also shifts the peaks to higher temperatures for polysilanes with phenyl and p-tolyl but not for polysilanes with m-tolyl because of its strong steric hindrance.