Mg doping and alloying in Zn3P2 heterojunction solar cells

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/Zn₃P₂ Schottky diodes with VOC values reaching 550 mV, JSC 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 10¹⁷ 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.