Formation of Ion Pairs and Carrier Transport in Undopedand Dye-Doped Poly(N-Vinylcarbazole) Films

Dark conductivities σ d of undoped and dye-doped poly(N-vinylcarbazole) (PVK) films have been measured at 298, 276, and 208 K over a wide range of static electric field E =10 4 ∼10 6 V/cm. The observed field dependence of σ d follows apparently the E 0.6 -power law, rather than the E 1/2 -power law of the well-known Poole-Frenkel (PF) type expression. Based on these experimental results, we have discussed the field-induced carrier generation processes from “ion pairs” (bound holes-charged acceptors) that are formed by an electron transfer between carbazole-rings and acceptors involved. Here we have taken into account the Onsager “dissociation-association” model to account for the observed electric field dependence of σ d , in which the dissociation of the ion pairs is enhanced by an applied field.