Increasing the band gap of iron pyrite by alloying with oxygen.

Systematic density functional theory studies and model analyses have been used to show that the band gap of iron pyrite (FeS(2)) can be increased from ~1.0 to 1.2-1.3 eV by replacing ~10% of the sulfur atoms with oxygen atoms (i.e., ~10% O(S) impurities). O(S) formation is exothermic, and the oxygen atoms tend to avoid O-O dimerization, which favors the structural stability of homogeneous FeS(2-x)O(x) alloys and frustrates phase separation into FeS(2) and iron oxides. With an ideal band gap, absence of O(S)-induced gap states, high optical absorptivity, and low electron effective mass, FeS(2-x)O(x) alloys are promising for the development of pyrite-based heterojunction solar cells that feature large photovoltages and high device efficiencies.