Energy disorder in polysilanes

Abstract

The absorption spectra (T=295 K), photoluminescence spectra (T=5–295 K), and thermally stimulated luminescence curves (T=5–295 K) of poly(di-n-hexylsilane) (PDHS), poly(methyl-n-hexylsilane) (PMHS), poly(methylcyclohexylsilane) (PMCHS), and poly(methylphenylsilane) (PMPS) films are measured. The results obtained are analyzed within the model of random hoppings of excitons and charge carriers over sites with a Gaussian distribution of the density of states. It is established that the variance parameters of the density-of-state functions of excitons and charge carriers characterize the energy disorder and depend on the chemical nature of side groups of the polymer, the conformation of segments of the main chain of the polymer macromolecule, and the temperature. At room temperature, the energy disorder in crystalline regions of the PDHS film is explained in terms of fluctuations in the number of monomer units in chain segments. In polymers with nonsymmetric side groups (such as PMHS, PMCHS, and PMPS), the disorder is more pronounced due to the formation of conformers in which silicon atoms occupy different positions in the chain. In the PMPS polymer, the disorder occurs through one more mechanism associated with fluctuations of the angle between the plane of the phenyl ring and the axis of the polymer segment due to mixing of σ-and π-electron states.