Hole mobilities in hydrazone-polycarbonate dispersions

Extensive characterization of the hole mobilities in dispersions of p-diethylamino- benzaldehyde-diphenyl hydrazone (DEH) in polycarbonate has been carried out. We report the effect of varying the electric field E, temperature T, and spacing between DEH molecules on . These data are analyzed by a procedure that allows proper separation of the functional dependencies of the mobility on E, T, and . It is found that ln is proportional to En(T-1-T0-1), where n=0.5 and T0 is a fitted parameter which decreases with increasing , behavior opposite to the dependence of the glass transition temperature on . These experimental results are not yet understood theoretically. Our procedure for separating the and T dependence is applied to data taken on DEH-polycarbonate and to data taken from the literature on another molecularly doped polymer system, N,N diphenyl-N,N-bis (3-methylphenyl)-(1,1-biphenyl)-4,4-diamine (TPD) in polycarbonate. For DEH-polycarbonate, the activation energy is found to be independent of . In contrast, for TPD-polycarbonate the activation energy is strongly dependent on . Our data suggest that small-polaron hopping is occurring in molecularly doped polymers; this different dependence of the activation energy on is consistent with different small-polaron hopping regimes, adiabatic and nonadiabatic, in these two systems. © 1989 The American Physical Society.