Copper antimony selenides are of interest for a variety of applications including their use in solar cells and thermoelectrics. Developing finely tunable syntheses of technologically relevant materials remains a challenge in the field. Solution-phase nanoparticle synthesis allows control over particle shape and size, though phase purity is often an issue in ternary syntheses. Generally, precursor reactivity must be balanced to avoid binary sinks; however, in the Cu-Sb-Se system the ternaries compete with one another. In this work, we explore the knobs of a hot-injection synthesis in oleylamine that favor specific ternary phases and particle morphologies. Phase composition was determined with X-ray diffraction and particle morphology was characterized with electron microscopy. We determined that stoichiometry, temperature, and time can be manipulated to favor each of the ternary phases. Of particular interest is that reactions targeting the stoichiometry of CuSbSe2 usually form Cu3SbSe3 initially, which decomposes into the more stable CuSbSe2 phase over time. We hypothesized that the initial formation of the metastable copper-rich phase resulted from the active copper complex being more reactive and less stable than antimony complex. Herein, we aimed to control precursor reactivity with the Bronsted bases lithium bis(trimethylsilyl)amide and n-Butyllithium. These bases have been shown to increase metal amide formation, which would be a more reactive Sb complex, and may favor CuSbSe2 formation. Not only did the addition of the bases favor the formation of CuSbSe2 and drastically decrease the required growth time, particle morphology changed as well. While single nanosheets were observed without the base, branched nanosheets are observed in the presence of base. Investigations into the variety of morphologies that can be accessed by tuning base concentration are ongoing. This work sets the stage to develop generalizable principles to control precursor reactivity and thus tune the Cu-Sb-Se phase formation by altering synthetic conditions.

Investigating the effect of metal amide species on Cu-Sb-Se nanoparticle phase and morphology

ACS Spring 2022

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