Electrophotographic properties of thiophene derivatives as charge transport material

The authors investigated electrophotographic properties of some substituted thiophenecarboxaldehyde-hydrazones as charge transport materials in layered-type photoreceptors from a viewpoint of molecular design. The values of optical bandgap [Eg(opt)] of the polycarbonate films doped with the hydrazones decrease from 2.9 to 2.4 eV with increasing thiophene rings and, therefore, with increasing (pi) -conjugation length. The Eg(opt) values for the thiophene derivatives are smaller than those for phenyl derivatives. Hole mobilities in the polycarbonate films doped with the hydrazones (50% in weight ratio) fall in the range between 1X10MIN6 and 5X10MIN6 cm(superscript 2/Vsec. Any significant difference was not found between the hole drift mobilities for the thiophene derivatives and those for the phenyl derivatives. Hole mobility and charge injection efficiency of the thiophene derivatives increase with decreasing Eg(opt). The hydrazone derivatives with longer (pi) -conjugation length show higher hole mobility and higher charge injection efficiency. And the thiophene derivative shows higher injection efficiency and larger total carrier quantity than the phenyl derivative. The thiophene derivative is superior to the phenyl derivative as a charge transport dopant.