Cu 2 ZnSnS 4 (CZTS) is a promising material for solar energy conversion, but synthesis of phase-pure, anisotropic CZTS nanocrystals remains a challenge. We demonstrate that the initial concentration (loading) of cationic precursors has a dramatic effect on the morphology (aspect ratio) and composition (internal architecture) of hexagonal wurtzite CZTS nanorods. Our experiments strongly indicate that Cu is the most reactive of the metal cations; Zn is next, and Sn is the least reactive. Using this reactivity series, we are able to purposely fine-tune the morphology (dots versus rods) and degree of axial phase segregation of CZTS nanocrystals. These results will improve our ability to fabricate CZTS nanostructures for photovoltaics and photocatalysis. KeywordsComposition control, CZTS, precursor loading, shape control ABSTRACT: Cu 2 ZnSnS 4 (CZTS) is a promising material for solar energy conversion, but synthesis of phase-pure, anisotropic CZTS nanocrystals remains a challenge. We demonstrate that the initial concentration (loading) of cationic precursors has a dramatic effect on the morphology (aspect ratio) and composition (internal architecture) of hexagonal wurtzite CZTS nanorods. Our experiments strongly indicate that Cu is the most reactive of the metal cations; Zn is next, and Sn is the least reactive. Using this reactivity series, we are able to purposely fine-tune the morphology (dots versus rods) and degree of axial phase segregation of CZTS nanocrystals. These results will improve our ability to fabricate CZTS nanostructures for photovoltaics and photocatalysis.

Chalcogenide-based semiconductor-metal heterostructures are interesting catalysts for solar-to-chemical energy conversion, but current compositions are impractical due to the relative toxicity and/or scarcity of their constituent elements. To address these concerns, Cu 2 ZnSnS 4 (CZTS) emerged as an interesting alternative to other chalcogenide-based semiconductors; however, the fabrication of CZTS metal heterostructures remains unexplored. In this paper, we systematically explore four methods of synthesizing CZTS-Au heterostructures, specifically: reaction of CZTS nanorods with either a soluble molecular gold precursor (AuCl 3) or preformed gold (Au) nanoparticles, each under thermal (heating in the dark) or photochemical reaction conditions (350 nm lamp illumination at room temperature). We find that using AuCl3 under thermal deposition conditions results in the most well-defined CZTS-Au heterostructures, containing >99% surface-bound 2.1 ± 0.5 nm Au islands along the whole length of the nanorod. These CZTS-Au heterostructures are photocatalytically active, reducing the model compound methylene blue upon irradiation much more effectively than bare CZTS nanorods. We also demonstrate the removal of Au from the CZTS-Au heterostructures by amalgamation. These results open up a new area of greener, CZTS-based photocatalysts for solar-to-chemical energy conversion.

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