ELECTRICAL-CONDUCTIVITY IN IODINE-DOPED ETHYL CELLULOSE

The electrical conductivity of solution-grown ethyl cellulose (EC) films, 5-30 mum thick, has been studied in the sandwich configuration (metal-EC-metal) as a function of iodine concentration from 0.5 to 5.0 wt% ratio. The studies were conducted in the temperature range 333-383 K, while the field was varied over the range (3.0-5.5) x 10(4) V/cm. Aluminium was used as the lower electrode, while the upper electrode was of Al, Ag, Cu, Au or Sn. Certain transient effects such as a large burst of current immediately after the application of field were observed. An attempt was made to identify the nature of the current by comparing the observed dependence on electric field, electrode material and temperature with the respective characteristic features of the existing theories of electrical conduction. The results show that the electrical conduction follows Ohm's law at lower fields, while at higher fields, space-charge limited current (SCLC) was observed. It was also found that Richardson-Schottky emission was responsible, to some extent, for the transport of charge carriers in the polymer. The conductivity of the films increased on doping with iodine. The dopant molecules are considered to act as additional trapping centres and provide links between the polymer molecules in the amorphous region, thus resulting in the formation of charge transfer complexes.