Universal strategies have played a transformative role in organic synthesis, offering systematic and mechanistically guided approaches for constructing complex molecules.[1-3] Retrosynthetic analysis and standardized reactions, such as Suzuki coupling and Diels-Alder reactions, utilize well-established mechanisms and predictable kinetic pathways, enabling efficient and reproducible molecular synthesis.[4-6] These synthetic methods have greatly enhanced the reproducibility and scalability of synthetic processes. In this context, there is a growing demand for a universal synthetic approach for colloidal nanocrystals (NCs) to develop reproducible and scalable techniques suitable for a broad range of materials. A robust strategy of this nature would simplify the synthesis process, facilitating precise control over NCs characteristics to meet the needs of various applications. However, achieving such universality in colloidal NCs is hindered by complex reaction chemistry, nucleation kinetics, growth dynamics, and material-specific factors like temperature, solvents, and precursor selection.[8] Surface ligand interactions further complicate standardization, making material-specific generalized protocols a viable alternative.[8, 9] Recently, Cs-based alkali metal chalcogenides have gained interest as promising semiconductors for energy conversion and storage. While theoretical studies highlight their potential, limited nanoscale exploration and high-temperature synthesis constraints impede a deeper understanding of their properties and formation mechanisms.[10]

This study presents a simple and general approach for synthesising ternary Cs-based metal chalcogenides using a metal chalcogenide synthon-based strategy. This method involves the injection of Cs precursor into an in situ-formed metal chalcogenide synthons, resulting in the formation of Cs-M-Se (M = Cu, Bi, Sb, In, Ga) nanostructures with diverse morphologies and shapes. To further demonstrate the versatility of this approach, we extended its application to metal sulfides, synthesizing Cs-M-S (M = Cu, Bi, Sb, In, Ga). Remarkably, this strategy enabled the formation of alkali metal chalcogenides at the nanoscale with a variety of shapes and morphologies while also reporting novel morphologies and shapes in intermediate metal chalcogenide synthons. Furthermore, the study explored the influence of different metal chalcogenide phases on the resulting NC phases. Morever, computational analysis of this phase transition was conducted to clarify the specific phases involved in forming the final ternary product; offering valuable insight into the principles governing this synthetic methodology. In summary, this work establishes a foundation for a scalable, adaptable approach to synthesising alkali metal chalcogenides at the nanoscale.