On an example of the space charge limited conduction breakdown in relation to the current-voltage characteristics of a single layer metal/organic structure

Abstract

The room-temperature current-voltage data of the hole conducting single layer poly-p-phenylene-vinylene indium tin oxide/poly-p-phenylene-vinylene (200 nm)/Al organic structure of Karg et al. [J. Appl. Phys. 82, 1951 (1997)], representing an archetype for (shallow) trap-controlled space charge limited conduction characterized by the current density proportional to the second power of the applied bias, j∝Va2, are used to calculate the spatial dependence of the internal electric field, the internal electric potential, and the total (free and trap) hole charge density within the organic layer. In contrast to the usual space charge limited current results, it is determined that these quantities are linearly distributed throughout the above structure. The breakdown of the Mott–Gurney approach is assigned to the usual, but in this case inappropriate, assumption of the boundary condition at the hole injecting metal/organic junction. It is shown that for the above stated structure the electric field at the anode/organic boundary is nonzero and linearly increases with the forward bias. As a consequence of this fact the product of the hole mobility and the trapping parameter turns out to be considerably larger than the value deduced on the basis of the Mott–Gurney law. The organic bulk differential capacitance is small in magnitude and exhibits a nonlinear decrease with the increasing value of the applied voltage Va.