Graphene’s high carrier mobility and ambipolar nature has the potential to improve electronic devices. The absence of a band-gap necessitates heterostructure devices. Schottky-barrier devices consisting of an interface between graphene and a semiconductor represent the simplest heterostructure. Despite its simplicity, graphene-based Schottky barrier devices are not well understood and exhibit low injection efficiencies. We here investigate the impact of graphene/metal interaction on the properties of the Schottky-barrier. Besides the commonly employed Au/graphene we use Pt/graphene contacts. We find that the injection efficiency for Pt is 5x higher than for Au and systematically study the origin of this behavior. We identify a large difference in Richardson’s constant due to changes in the density of surface states. The demonstrated ability to increase the injection current was applied to improve the efficiency of graphene-based Schottky solar cells by 13x.