Injection of Electrons into p‐Chloranil Crystals via Exciton Decay at Metal and Aqueous Electrodes

Abstract

In weakly or non‐luminescing molecular crystals like p‐chloranil, information concerning the exciton dynamics can be derived from injection currents when charge carriers are formed during electron transfer between excitons and an appropriate electron donor‐ or acceptor species in aqueous electrolyte. Due to the slow orientation polarization of water molecules as compared to the hopping frequency of injected charge carriers, image forces can be neglected when aqueous electrodes are applied. Consequently, at external field strengths of 10+ V/cm, steady state saturation currents and space‐charge‐free transients are observed which may yield information as to the kinetics of the electron transfer reaction and the diffusion of excitons (lifetime, diffusion length). In the same field strength region, photocurrents originating from exciton decay at a metal contact are still determined by the action of image forces and by surface recombination of charges. Secondary effects like enhanced trapping of charge carriers within the image potential barrier influence the current rise in space‐charge‐free transients.