ELECTRON-TRANSPORT IN VAPOR-DEPOSITED MOLECULAR GLASSES

Electron mobilities are measured in a series of vapor deposited 1,-1-d ioxo-4-(dicyanomethylidene)thiopyran glasses. The results are describe d within the framework of a formalism based on disorder, due to Bassle r and coworkers. The formalism is based on the assumption that charge transport occurs by hopping through a manifold of localized states wit h superimposed energetic and positional disorder. The key parameters o f the formalism are sigma, the energy width of the hopping site manifo ld, mu(0), a prefactor mobility, and Sigma, a parameter that describes the degree of positional disorder. Experimental values of sigma are a pproximately 0.123 eV for al compounds. The width of the hopping site manifold can be described by arguments based on dipolar disorder, if i t is assumed that the hopping site energies are determined by group di pole moments associated with the cyano and sulfone functionalities. Th e prefactor mobilities are between 1 and 4 x 10(-2) cm(2)/Vs. A compar ison of these results with literature values for molecular glasses sug gests that the prefactor mobilities may be dependent upon the dipole m oment. Values of the positional disorder parameter Sigma are approxima tely 2.0 and attributed to packing constraints.