Synthesis of Monoclinic and Tetragonal Chalcocite Nanoparticles by Iron-Induced Stabilization

Infrared absorbing monoclinic and tetragonal chalcocite nanoparticles were synthesized. These metastable copper sulfide phases were obtained by addition of varying amounts of iron to the reaction mixtures. Phases were identified by powder X-ray diffraction (PXRD), and the particles were characterized by UV–vis–NIR absorption spectroscopy (UV–vis–NIR), transmission electron microscopy (TEM), and energy dispersive X-ray spectroscopy (EDS). This synthesis affords monoclinic chalcocite, which is difficult to obtain in nanocrystalline form because of its ready transformation to copper-deficient djurleite. Nanoparticles of the little-studied, high-temperature-stable tetragonal chalcocite form were synthesized for the first time. These particles showed improved phase stability compared to monoclinic chalcocite, while maintaining the optical properties that made monoclinic chalcocite intensely investigated as a light absorber in photovoltaics. Together, these syntheses offer two routes toward managing an impediment to utilization of nanocrystalline chalcocite in photovoltaic applications, the transformation to djurleite, and uncover remarkable methods of nanocrystalline phase control.