A signal-to-noise ratio (S/N) is an important factor for an organic image sensor. We investigated the doping effect of silole derivative in the green-sensitive organic photoconductive device for improving S/N. The maximum S/N of 12 was achieved when 1,1-dimethyl-2,5-bis(N,N-dimethylaminophenyl)-3,4-diphenylsilole with the lowest ionization potential was used as an active layer. In addition, the graphene oxide (GO) layer was found to be an important role for decreasing the dark current density, resulting in the high S/N. The maximum S/N of approximately 20 was realized by inserting the GO layer between an indium tin oxide (ITO) anode and an active layer.