THE ESTIMATION OF TRAP-FREE SPACE-CHARGE-LIMITED CURRENT MAGNITUDES IN MOLECULARLY DOPED POLYMERS

The transient current response of molecularly doped polymers has been numerically simulated for the situation in which a step potential is a pplied to an ideal injecting contact. Calculated trap-free space-charg e-limited currents (TFSCLCs) are found to approach a steady-state magn itude which may be used to construct the single-carrier current-voltag e characteristics. The exact TFSCLC response is compared with a modifi ed analytical expression which is commonly applied to analyse experime ntal data in insulators where the mobility of injected carriers is fie ld dependent. Current-voltage characteristics generated using the exac t and modified analytical approaches are found to agree within predete rmined accuracy limits over a restricted range of applied electric fie ld. It is demonstrated that the latter field range is dictated by the underlying field dependence of the injected carrier mobility. In this range, the modified analytical expression continues to approximate the exact TFSCLC response in the presence of anomalous carrier diffusion and is successfully used to interpret experimental data for a hydrazon e-doped polyester having gold contacts.