Nanoscale photocurrent distribution in ultra-thin films of zinc oxide nanoparticles and their hybrid with reduced graphene oxide

The electrical properties of ultra-thin films of ZnO nanoparticles and their hybrid with reduced graphene oxide (rGO), prepared at a liquid/liquid interface, are investigated. The photocurrent distribution in ZnO and rGO-ZnO films at nanoscale under UV irradiation is explored using conducting atomic force microscopy (C-AFM) and compared with the bulk electrical measurements. At the rGO-ZnO interface, ohmic contact is achieved rather than the Schottky junction encountered in bare ZnO with a metal electrode. Enhancement of the photocurrent is observed in both cases and the photoresponse mapping by C-AFM reveals an inhomogeneous current distribution at the nanoscale that is associated with various ZnO nanostructures in the film. While a small population of the nanostructures contributes higher photocurrents in bare ZnO film, the majority of the photoresponsive ZnO nanostructures provide high photoresponse in rGO-ZnO. This nanoscale electrical study gives insights into the local current contribution from individual nanostructures toward bulk electrical properties and can aid in understanding photovoltaic device performances.