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.