Photoelectronic Properties of Acid-Doped Poly (N-Vinylcarbazole): o-Dinitrobenzene Charge Transfer Complex Films

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Abstract
The light intensity dependence of the buildup and the dark decay of the current through the poly(N‐vinylcarbazole):o‐dinitrobenzene charge transfer complex doped with trichloroacetic acid has been studied at room temperature. The weight ratio of these components was (24:1:1). We find that the buildup and decay of the current can be described by Is tanhβt and the second order rate law, Is/(αt+1), respectively, where Is is the saturation current and t the time. α and β depend upon the square root of the light intensity whereas Is increases in a manner roughly proportional to it. The acid greatly enhances Is, and reduces the second order decay constant α by orders of magnitude as compared to acid free systems. It is shown that the slow dark decay of the current is closely associated with the presence of a photogenerated radical species which gives rise to an ESR signal. Experiments on multilayer films indicate that the current measured following illumination arises predominantly from hole flow. The carrier generation rate is found to depend only weakly upon the applied field. A kinetic model is presented which successfully accounts for the experimental findings.

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