Controlled colloidal synthesis of anisotropic mixed-metal chalcohalides: insights into morphology and phase evolution

Mixed-metal chalcohalides have recently emerged as promising semiconductor materials for optoelectronic applications owing to their tunable bandgaps, earth-abundant composition, stability, and relatively low toxicity. Despite these advantages, the synthesis of quaternary chalcohalides remains challenging due to their complex phase chemistry and the thermodynamic preference for binary and ternary secondary by-products, which frequently compete with the preferred quaternary phase formation. In this work, we report the colloidal synthesis of Sn₂SbS₂I₃ microcrystals via a dual hot-injection method. Our approach yields uniform, crystalline microrods with well-defined morphology and a direct optical band gap of 1.74 eV, placing them within the ideal range for photovoltaic and photodetection applications. By systematically monitoring the reaction mixture during synthesis, we elucidate the growth pathway of Sn₂SbS₂I₃. The process initiates with the formation of Sb₂S₃ seeds, which subsequently undergo compositional transformation through incorporation of Sn²⁺ and I^- in their structure. This progressive substitution and intercalation drive the conversion toward the quaternary Sn₂SbS₂I₃ phase, highlighting a seed-mediated growth mechanism.