We use a solution-based bromide anion hot injection method to synthesize stable, phase pure and highly crystalline cubic iron pyrite (FeS2) nanocrystals, with size varying from ∼70 to ∼150 nm.

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.

We describe the application of iron persulfide (pyrite, FeS2) NC thin films as a Cu-free back contact to CdS/CdTe solar cells. We synthesized cubic FeS2 NCs, and prepared NC-FeS2 films by drop-casting to investigate their use in thin film solar cells. Characterization of the FeS2 NC films revealed sub-band-gap optical absorption, holes as the majority carrier, free hole concentration of _10 19 cm-3 , and Hall mobility of �h « 1 cm 2 V-I S-I . CdS/CdTe solar cells completed by depositing hydrazine-treated NC-FeS2 back contacts directly onto CdTe displayed efficiencies comparable to those of standard Cu/Au back contact devices. Our best FeS2 device shows an AM1.5G efficiency of 12.5%, Voe = 0.81 V, Jse = 23.0 mA/cm 2 , and FF = 67%. Temperature dependent studies of solar cells reveal that the 'roll-over' effect observed in standard devices at low temperature is controlled by replacing Cu by hydrazine treated NC-FeS2.

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