ELECTRON-TRANSPORT IN VAPOR-DEPOSITED MOLECULAR GLASSES

Electron mobilities are measured in a series of vapor deposited 1,-1-dioxo-4-(dicyanomethylidene)thiopyran glasses. The results are described within the framework of a formalism based on disorder, due to Bassler and coworkers. The formalism is based on the assumption that charge transport occurs by hopping through a manifold of localized states with superimposed energetic and positional disorder. The key parameters of the formalism are sigma, the energy width of the hopping site manifold, mu(0), a prefactor mobility, and Sigma, a parameter that describes the degree of positional disorder. Experimental values of sigma are approximately 0.123 eV for al compounds. The width of the hopping site manifold can be described by arguments based on dipolar disorder, if it is assumed that the hopping site energies are determined by group dipole moments associated with the cyano and sulfone functionalities. The prefactor mobilities are between 1 and 4 x 10(-2) cm(2)/Vs. A comparison of these results with literature values for molecular glasses suggests that the prefactor mobilities may be dependent upon the dipole moment. Values of the positional disorder parameter Sigma are approximately 2.0 and attributed to packing constraints.