We use the contact potential (Kelvin probe) method to evaluate the electrostatic potential profile across the transparent conductive oxide/p/i junction in hydrogenated amorphous silicon photovoltaic cells. Si films are deposited using reactive magnetron sputter deposition; the atomic H flux to the growth surface is controlled by changing the rate of H-2 injection. H tailoring can be used to minimize the chemical reduction of SnO2, to optimize the contact potential with ZnO, to maximize the doping efficiency of the p(+)-layer, and to minimize the defect density at the p(+)/i interface. These methods should improve the built-in potential and thus raise the output voltage of amorphous silicon photovoltaic cells.