Influence of Solvent Reducing Ability on Copper Sulfide Crystal Phase

Copper sulfide particles across a wide range of stoichiometries are obtained depending on the ratio of cosolvents from which they are grown. Copper sulfides are abundant, low-cost materials with phase-dependent properties relevant to solar energy conversion and (opto)electronic devices. For this reaction, the reducing ability of dodecanethiol versus oleic acid affects the speciation of the precursors, as determined using UV-vis absorption spectroscopy. The ratio of dodecanethiol to oleic acid in the synthetic medium affects the solid-state structure and stoichiometry, as determined by powder X-ray diffraction, X-ray photoelectron spectroscopy, energy-dispersive X-ray spectroscopy, and detailed investigation of the band edge positions and plasmon behavior using visible-NIR optical absorption spectroscopy and cyclic voltammetry. A range of phases was obtained, including monoclinic chalcocite, tetragonal chalcocite, digenite, and covellite. The thermodynamic relationships between these phases were elucidated using equilibration experiments, revealing methods for postsynthetic property alteration. Particle size and morphology were also affected by solvent ratio, as shown using scanning or transmission electron microscopy. Oleic acid accelerated particle growth and resulted in particles with an unusual faceted shape.