On Charge Carrier Photogeneration Mechanisms in Organic Molecular Crystals

Abstract

Abstract An extended phenomenological model of photogeneration mechanisms in organic molecular crystals is proposed which describes intermediate and final stages of multi‐step photogeneration processes in terms of a modified Onsager approach. It is shown that the intermediate geminate charge pair (CP) states can be populated through two independent competitive pathways: viz. via autoionization and subsequent hot electron thermalization in terms of a ballistic model and via optical charge transfer (CT) transitions. The thermalization processes and their dependence on photon energy, temperature, and electric field are studied in some detail. It is demonstrated that the threshold spectral dependence of intrinsic photoconductivity quantum efficiency β( hv ) in anthracene‐type crystals is mainly determined by the spectral dependence of dissociation efficiency Ω( hv ) of the intermediate CP‐states and can be approximated by Onsager's formula.