Space-charge-limited bipolar currents in polymer/C60 diodes

We investigate carrier’s transport for devices formed by a heterojunction of the substituted polythiophene polymer and the C60 molecule, sandwiched between anode of indium-tin oxide/poly(3,4-ethylene dioxythiophene) and cathode of Al, for different thicknesses of the C60. We measure their current-voltage characteristics and find that the forward current is limited by spatial charge of holes in the polymer layer and electrons in the molecule layer. We also find that the effective mobilities of holes in the polymer and of electrons in the C60 are dependent on the different thickness of the layers. By adapting to our systems an electrical analytic model previously used in the literature to study bilayer organic diodes, we are able to explain the experimental results.