Phase control and its mechanism of CuInS2 nanoparticles

CuInS2 nanoparticles (NPs) usually take chalcopyrite-(CP) structure. Recently, CuInS2 NPs with pseudo-wurtzite (WZ) structure, which is thermodynamically less favored, have been synthesized. However, the formation mechanism of this metastable-phase has not been understood yet. In this report, the key issue of phase selectivity of CuInS2 (CIS) NPs has been investigated using various metal sources and ligands. Experimental results suggested that the crystalline structure and morphology of CIS NPs were decided by the stability of indium ligand complex; the active ligand reduces the precipitation rate of In2S3, resulting in pre-generation of Cu2S seed NPs. Crystallographic analogy and superionic conductivity of Cu2S remind us that the formation of WZ CIS NPs is attributed to the pre-generation of Cu2S seed NPs and the following cation exchange reaction. In order to confirm this hypothesis, Cu2–xS seed NPs with various structures have been annealed in indium–ligand solution. This experiment revealed that the crystalline structure of CIS NP was determined by that of pre-generation Cu2–xS NPs. Our results provide the important information for the phase control and synthesis of ternary chalcogenide NPs with a novel crystalline structure.

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► The phase selectivity of CuInS2 nanoparticles (CIS NPs) has been investigated.
► The pre-generation of Cu2S seed NPs leads to the formation of wurtzite CIS NPs.
► In3+ ion disperses into Cu2–xS NPs to form CIS NPs.
► The crystal structure of CIS NP could be tuned by that of seed NP.
► Cation exchange method can provide chalcopyrite NPs with a novel crystal structure.