Electric field assisted dissociation of charge transfer states as a mechanism of photocarrier production

摘要

The lowest chargehyphen;transfer excited state (CT1) of electron donorndash;acceptor crystals or polymers is demonstrated to be a plausible precursor of free charge carriers when such materials are photoexcited. Rate constants for the dissociation of chargendash;transfer states are formulated for two approximate descriptions of CT1: classical ion pair and Wannier exciton. The electric field dependence of the dissociation rate constant is postulated to be given by Onsagerrsquo;s 1934 theory (Ohyphen;34) of ion pair dissociation. This formulation of CT1dissociation obviates the need to invoke electronndash;hole lsquo;lsquo;thermalizationrsquo;rsquo; lengths of 2 to 3 nm in order to explain free charge carrier formation in donorndash;acceptor materials.