Majority Carrier Type Control of Cobalt Iron Sulfide (CoxFe1–xS₂) Pyrite Nanocrystals

We report the colloidal synthesis, characterization, and electronic property control of compositionally varied Co x Fe 1– x S 2 cubic pyrite nanocrystals (NCs) and thin films formed from solution. Using drop-cast NC thin films, we demonstrate the relationship between the material composition and the majority carrier type of the nanocrystalline thin films. Measurements of the majority carrier type as a function of NC composition indicate that Co x Fe 1– x S 2 NC thin films change from p-type to n-type between x = 0.16 and x = 0.21. Additional characterization to confirm the crystallinity, composition, size, and shape was performed using powder X-ray diffraction, Raman spectroscopy, energy dispersive X-ray spectroscopy, and scanning electron microscopy. The observed n-type behavior which accompanies the substitution of Co for Fe in these cubic pyrite nanostructures agrees with previous reports of n-type behavior occurring at even very low concentration Co doping of iron pyrite. The ability to prepare n- or p-type pyrite NCs and thin films opens the door to property-controlled cobalt iron pyrite nanocrystalline materials for optoelectronic and energy conversion applications.