Cation-exchange and lateral ripening in wurtzite-like CuInSe₂ formation from weissite-like Cu_2-xSe

The formation of metastable wurtzite-like CuInSe₂ nanocrystals remains poorly understood due to the structural complexity of copper selenide intermediates. Here, we demonstrate that weissite-like Cu_2-xSe can serve as a structural template for topotactic cation exchange to wurtzite-like CuInSe₂. Time-resolved XRD and SEM/STEM-EDX analyses reveal progressive In³⁺ incorporation within the preserved hexagonally close-packed Se^2- sublattice, accompanied by displacement and redistribution of Cu⁺ ions. TEM and statistical size analysis show that cation exchange is coupled to an anisotropic Ostwald ripening, driving lateral growth of the nanoplates. Control experiments confirm that growth is mediated by In³⁺ incorporation rather than thermal phase relaxation or digestion. These findings provide mechanistic insight into how hexagonal anion sublattices guide metastable ternary formation, clarifying the interplay between cation exchange and nanoplate growth.