Space-charge-limited currents due to large polarons

A model of charge injection from Ohmic contacts in disordered organic materials is presented, where the charge carriers are large (or small) polarons. We find that the space-charge-limited current is exponentially sensitive td the size of the molecules and the width of the polaron. For large molecules, we recover, at high fields, the usual Fowler-Nordheim-like dependence observed in many current-voltage characteristics of polymer light-emitting diodes.