UC Irvine

Iron pyrite (FeS2) is an earth-abundant, non-toxic material that has a suitable band gap of 0.95 eV, a large optical absorption coefficient, and adequate carrier diffusion lengths for use in photovoltaic applications. However, its practical use is limited in part by poor understanding and control of doping. Here, we employ variable temperature Hall effect and conductivity to study, in detail, the impact of three transition metal impurities (cobalt, nickel, and chromium) on the electric properties of ultrapure pyrite single crystals grown in sodium polysulfide. By studying samples as a function of impurity concentration, we conclusively establish that cobalt is a nearly ideal donor in the dilute limit (<500 ppm Co) with a defect state that lies ~70-110 meV above the conduction band minimum, while nickel and chromium act as deep donors that barely affect the carrier concentration. These results establish the basic doping behavior of three elements and provide a pathway for overcoming the key challenges to rational doping in pyrite.