Photoconductivities of poly(N-vinyl carbazoles) containing cation radicals

A study into the photoconductance of poly(N-vinyl carbazole) partly oxidized to introduce cation radicals is described (mole fraction < 4 × 10^?3). These materials are shown to be photoconductors whose response to illumination is time dependent. Their photoconductive behaviour has been studied as a function of extent of oxidation, field strength, temperature, light intensity and irradiating wavelength. The observed response is discussed in terms of a model for the amorphous state in which there are accessible levels in the forbidden gap for interaction with photopromoted electrons or holes. Variation in the role of level as trap or recombination centre with external conditions is shown to form, in part, an adequate model for behaviour. However, light intensity and temperature dependence does indicate that there is a significant change of the distribution of levels in the for-bidden gap as the temperature is reduced to ～ ?20°C, possibly due to a change in structure or mode of motion.