Intra-device gating effect in graphene electrode-based organic diodes

Current–voltage characteristics of graphene electrode-based thin-film organic diodes show non-saturating high reverse bias currents, unlike standard indium tin oxide-based devices. We show that this deviation is controlled by the intra-device self-gating electric field on graphene anode from the counter cathode through the organic thin-film device layer. This effect contributes to additional charge dynamics due to the quantum capacitance presented by the semi-metallic graphene in series to the semiconductor capacitance of the organic device layer. This leads to a dynamic workfunction change of the graphene electrode as a function of the applied voltage across the diode. The proposed self-gating phenomenon is captured using an analytical model established using the combination of current–voltage and capacitance–voltage relations in these devices based on drift and diffusion equations. The results of the analytical model agree well with the experimental measurements carried out with fabricated P3HT:PCBM based organic thin-film diodes with graphene anode and aluminum cathode. We further support these results with elaborate self-consistent numerical simulations, all showing an increased reverse bias current contributed by the self-gating effects in graphene devices. Our results, being obtained from fundamental device physics, are applicable to a broad range of other devices like light-emitting diodes, perovskite-based devices, and thin-film a-Si devices.