2D Atomic Templating for the Large-Scale Synthesis of Metastable CuInS₂ and Its Heterojunctions

CuInS₂ has emerged as a promising material for sustainable energy technologies due to its combination of attractive electronic, economic, and ecological properties. However, current synthesis routes exhibit limited phase uniformity and degraded optoelectronic performance due to the complex Cu-In-S phase diagram. In this work, we report a synthesis strategy that overcomes these limitations and can produce CuInS₂ with a singular crystalline phase. An atomic templating approach is described that retains the structural order of a two-dimensional (2D) transition-metal monochalcogenide host to realize phase-pure wurtzite CuAu-type CuInS₂. Structural and spectroscopic characterization confirms the exclusive formation of this metastable phase and provides insights into its electronic properties. The transformation proceeds via a strain-mediated layer-by-layer cation-exchange mechanism, enabling precise control over its extent and interfaces. This approach establishes a generalizable route for synthesizing complex 2D heterostructures, and we demonstrate the direct growth of ternary 2D heterojunctions at large scale. The potential of this capability was highlighted through the realization of optoelectronic and thermoelectric devices with enhanced performance.