The photoresponse of reversed bilayer organic photovoltaic device based on pentacene and C-60 is examined, and the mechanism of photocurrent generation is shown to be different to that in conventional heterojunction devices, with free charge carriers generated at the electrode-organic interfaces rather than the organic heterojunction. This hypothesis is tested with silver nanoclusters incorporated at the organic heterojunction to quench excitons and facilitate recombination of free charge carriers, which shows a predicted increase in J(sc). The large V-oc in this reversed cell structure is also rationalized in the context of the model proposed.