Subgap Absorption Spectra in Polysilane Films

The subgap absorption spectra of polysilane films have been measured by photothermal deflection spectroscopy using the deflection medium 1,4-butanediol. It has been revealed that poly(methylphenylsilane) (PMPS) films have a band tail with an exponential distribution rather than a Gaussian distribution and a low density of states in the midgap. The Urbach energy is estimated to be 30 meV. The photodegradation of PMPS films increases the subgap absorption, indicating defect generation. The defects are generated from the photoscission of σ bonds, which has a stretched exponential time dependence. The doping of C60 to PMPS sensitizes the absorption in the visible region. The absorption increases proportionally to the doping ratio of C60 in a range of three orders of magnitude. The absorption spectrum of the PMPS and C60 mixture shows no interaction between the two ground states.