We demonstrate a high-efficiency graphene/Si Schottky junction solar cell with an easy to fabricate graphene back-contact structure and effective chemical treatments. This device effectively overcame the current challenges associated with reported graphene/Si Schottky solar cell structures. The short-circuit current density for such a device is increased by around 20% due to the increase of the active area of this device, compared to previous graphene/Si Schottky junction solar cell devices. The undesirable s-shaped kink in J-V curves, as found in previous works, have been eliminated by using Formamide treatment for 30 min prior to an annealing process in the forming gas. The fill factor of this device is improved by 40% after this treatment, due to the effective removal of the unwanted PMMA residue. Moreover, volatile oxidant vapour and anti-reflection coating are applied within the fabrication process for this device to further improve solar cell performance. An efficiency of 9.5% has successfully been achieved for the fabricated device using the fabrication techniques developed in this work. Our device presents a viable and achievable approach to preparing low-cost and high-performance graphene/Si Schottky junction solar cells.