Concentration dependence of the activation energy for the hole drift mobility of 9-ethylcarbazole-3-carbaldehyde diphenylhydrazone dispersed in polycarbonate

The concentration dependence of the activation energy for charge transport in 9-ethylcarbazole-3-carbaldehyde diphenyl-hydrazone (ECH) dispersed in polycarbonate is reported. The activation energy gradually decreased with increasing ECH concentration in the region of relatively low concentrations of ECH, but became nearly constant (0.4 eV) in the region of relatively high concentrations of ECH. This behavior contrasts with that for the 4-diphenylaminobenzaldehyde diphenylhydrazone system. Specific intermolecular interactions between ECH molecules having a planar carbazole moiety at relatively high concentrations are suggested to be responsible for this concentration dependence of the activation energy.