Delay photoconductivity in polyaniline films from different solvents

Decay kinetics of photoconductivity induced by the nanosecond laser pulses has been studied for films of polyaniline (PANI) in the emeraldine base form (EB) in the temperature range from 110 to 300 K. The films are prepared by casting solutions of EB in formic acid and N-methyl-2-pyrrolidinone (NMP) on glass plates covered by conducting layer of SnO2. Photocurrent signals were registered up to 40 ms and 20 mu s in the films obtained from formic acid and from NMP, respectively. In both cases the kinetic curves are fitted well by the stretched-exponential function F-1(t) similar to exp[-(t/tau(str))(beta)] with the temperature dependent parameters tau(str) and beta. It was found that the quantum yield of photocharge was equal to 10(-4) for the films obtained from the formic acid solution and to 2.10(-6) for those obtained from the NMP solution. The possible mechanisms accounting for photocurrent characteristics are discussed.