We report the experimental investigations on space charge limited current (SCLC) and injection limited current (ILC) in copper phthalocyanine (CuPc), sandwiched between two metal electrodes. Thickness dependence of current-voltage characteristics of SCLC and ILC is accurately reproduced by the electric field and temperature dependent charge carrier mobility, without invoking charge density dependent mobility. These results are interpreted using a consistent description of SCLC and ILC, based on a unified model of hopping transport within Gaussian density of states in CuPc.

We report an electric-field-induced conductance transition from an insulating state to a conducting state in a thin layer of Alq3 sandwiched between two metal electrodes. Field-induced switching behavior with a high on-off ratio of ∼105 is observed in the devices, in which the cathode electrode is Al and the anode electrode is varied including Al, Au, and indium tin oxide. The switching behavior is absent in devices in which both electrodes have a high work function, indicating that efficient electron injection has an important role in the electric-field-induced switching behavior of Alq3-based single-layer devices.

Systematic studies of current injection from different metal electrodes to metal/3,4,9,10 perylenetetracarboxylic dianhydride (PTCDA) interfaces have been carried out. It has been observed that the barrier for carrier injection cannot be explained by simple vacuum alignment scheme. Moreover, injection barrier is almost independent of metal work function. These observations are explained by the changes of barrier height due to interface dipole barrier which compensate for the difference of work function of PTCDA and metals, leading to metal independent injection barrier and Fermi level pinning at metal/PTCDA interfaces.

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