The roles of polarizabilities and dipole moments in hole transport processes in molecularly-doped polymers

Polarizabilities and dipole moments of hole transport molecules with differ ent; mobilities were measured. The zero-field mobilities of the molecularly -doped polymers increase with increasing polarizabilities and decrease with increasing dipole moments of the dopants. Concerning molecules with simila r dipole moments, mobilities correlate well with polarizabilities. Also con cerning molecules whose polarizabilities are almost equal, the correlation between mobilities and dipole moments is clear. The 3-D plot of the mobilit y as a function of the polarizability and the dipole moment is nearly copla nar. Within a framework of the small polaron formalism, polarizabilities ar e good indices to evaluate the degree of electron cloud extension that affe cts transfer integral J. On the other hand, the magnitude of the polaron bi nding energy E-p is macroscopically influenced mostly by the intramolecular structural relaxation. However, we propose that the E-p has a distribution caused by intermolecular interactions, which is not considered in the smal l polaron formalism. Such distributions, which have recently been discussed within a framework of the disorder formalism, are due to the random intern al field caused by the local charge-dipole interaction. These analyses supp ort the experimental data that the logarithm of mobility is described as a linear combination of the polarizability and the dipole moment.