Zinc phosphide (Zn3P2) is a promising and earth-abundant alternative to traditional materials (e.g. CdTe, CIGS, a-Si) for thin film photovoltaics. We report the fabrication of Mg/Zn3P 2 Schottky diodes with VOC values reaching 550 mV, J SC values up to 21.8 mA/cm2, and photovoltaic efficiency reaching 4.5%. Previous authors have suggested that Mg impurities behave as n-type dopants in Zn3P2, but combined Hall effect measurements and Secondary Ion Mass Spectrometry (SIMS) show that 10 17 to 1019 cm-3 Mg impurities compensate p-type doping to form highly resistive Zn3P2. Further device work with modified ITO/Mg/Zn3P2 heterojunctions suggests that the ITO capping layer improves a passivation reaction between Mg and Zn3P2 to yield high voltages > 500 mV without degradation in the blue response of the solar cell. These results indicate that at least 8-10% efficiency cell is realizable by the optimization of Mg treatment in Zn3P2 solar cells.