Engineering Heterostructured Semiconductor Nanorod Assemblies via Controlled Cation Exchange: Implications for Efficient Optoelectronics

Precise control over the composition of heterostructure nanocrystals and their self-assembly is an emerging research interest. Superstructures of this type are typically enhanced in terms of their collective functionalities. Herein, we developed a practical yet simple approach to synthesize and self-assemble Cu_2-xS/CuYS (Y = In, Sb, and Sn) heterostructured nanorods (NRs) into their vertically standing up assemblies. First NRs come together via depletion-attraction forces, and then partial cation exchange between Cu₃₁S₁₆ NRs and the injected cationic precursor taken in stoichiometric amounts dissolved in trioctylphosphine and oleylamine (Olam) results in heterostructured NRs possessing compositions of Cu_2-xS/CuYS (Y = In, Sb, and Sn). The chemical composition changes lead to surface chemistry modifications as the injected guest cationic part of the NR is either naked or covered with Olam which is quite easy to strip-off from the NC surface at high temperature, resulting in a 2D sheetlike structure of heterostructured vertically oriented NRs in solution. The route to obtaining long-range heterostructured assembled NRs is studied and characterized systematically. This work presents a detailed mechanistic insight into the cation exchange-induced self-assembly of heterostructured NRs, where the particles are coupled, which is of growing importance as a synthesis tool. The complex nanostructures synthesized in the present work may benefit solution-processed optoelectronic applications.