Space charge influenced photocurrent transients in fluid solution

Abstract

The dependence of space charge influenced current transients on the spatial distribution of photogenerated carriers in the bulk of a conductivity cell was investigated with the aim of correlating the observed time evolution of the currents with carrier properties such as mobilities and recombination constant. Approximate analytical solutions for the limiting cases of sheet and full interelectrode illumination show how experimental transients result from the competition between the dynamically interdependent processes: interionic recombination, charge carrier migration and discharge at the electrodes, and space charge buil-up. The voltage dependence of the time at which the secondary photocurrent maxima are observed yield mobilities of 2.0 × 10 −4 and 2.8 × 10 −3 cm 2 V −1 s −1 respectively for the pyrene cation and the solvated electron in tetrahydrofuran at room temperature. A bimolecular recombination rate constant of 2.3 × 10 −9 cm 3 s −1 is shown to be consistent with the space charge densities present after total separation of the positive and negative carriers for various periods of charge carrier recombination.