Electrical conduction behaviour of diphenylthiocarbazone doped cellulose acetate

Abstract

Current–voltage (I–V) characteristics of diphenylthiocarbazone (DPh)-doped cellulose acetate grown from solution have been studied as a function of temperature, thickness and voltage in a metal–polymer–metal sandwich con-figuration. The role of the dopant molecular concentration in the polymer matrix and the modification of the conduction characteristics are studied. Initially, the conductivity increases as a function of dopant concentration, but at higher concentrations, it begins to decrease. The dopant molecules act as additional trapping centres at lower concentration, while at optimum concentration they provide a link between polymer molecules, leading to the formation of a charge transfer complex. The decrease in conductivity with higher concentration of doping is due to the onset of the increase in heterogeneity, which can increase the trapping sites for charge carriers. The variation of current for doped films with temperature shows different regions with different activation energies. This behaviour is explained in terms of the type of conduction mechanism operating in the material. At low voltages, Ohm’s law is followed, while at higher voltages space charge limited current is observed. It was also noted that a Richardson–Schottky emission is responsible to some extent for the transport of charge carriers. Quantitative information about the transport parameters is derived. ©1998 Society of Chemical Industry