Ternary CuInX₂ (X= S, Se) nanocrystals (NCs) have attracted increasing attention as promising alternatives for CdX and PbX NCs due to their low toxicity, large absorption cross-sections across a broad spectral range, and unparalleled photoluminescence tunability, spanning a spectral window that extends from the green to the NIR (~550 to ~1100 nm for X= S). To achieve properties that are inaccessible to single component NCs (such as high PL quantum yields, spatial charge carrier separation, etc.), researchers have been synthesizing colloidal CuInX₂-based hetero-NCs (HNCs) (e.g., CuInS₂/ZnS concentric core/shell HNCs, CuInSe₂/CuInS₂ dot-in-rod HNCs). Anisotropic CuInX₂-based HNCs are particularly interesting, since they are expected to exhibit novel properties, such as polarized NIR photoluminescence (PL) and spatial charge separation, which are attractive for many applications (e.g., polarized LEDs, photocatalysis and artificial photosynthesis, luminescent solar concentrators, solar cells). Nevertheless, reports on the synthesis of anisotropic CuInX₂-based HNCs are scarce. 

In this work, we report a novel two-step pathway that yields CuInS₂/ZnS dot core/ rod shell heteronanorods. The wurtzite CuInS₂ NCs used as seeds are obtained by cation exchange in template Cu_2-xS NCs. The CuInS₂ NC seeds are injected together with the S precursor into a hot solution of the Zn precursor and suitable coordinating ligands, which leads to heteroepitaxial growth of ZnS primarily on the cation-rich polar facet of the seeds, as demonstrated by high-angle annular dark-field scanning transmission electron microscopy and electron tomography. The colloidal wurtzite CuInS₂/ZnS dot-in-rod heteronanorods have large molar extinction coefficients, and photoluminescence in the NIR (~800 nm) with PLQYs ~20%. Moreover, they exhibit multi-exponential PL decay that is initially rather fast (a few ns), and then slows down to several hundreds of ns, similar to the behavior previously reported for both chalcopyrite and wurtzite isotropic CuInS₂/ZnS core/shell HNC, which has been attributed to radiative recombination of a conduction band electron with a hole localized at a Cu ion. The slow radiative recombination dynamics are potentially beneficial for photovoltaic and photocatalytic applications, since long carrier lifetimes are of great importance for effectively extracting charge carriers.