Mechanisms of Phase Evolution in the Cu–Sb–S System Controlled by the Incorporation of Cu in Sb₂S₃ Thin Films

Ongoing research in metal chalcogenide semiconductors aims to develop alternative materials for optoelectronic devices. However, due to cost and environmental considerations, there is an increasing emphasis on utilizing green materials. This shift toward sustainable materials and processing is expected to become essential in materials research. In this work, we report the microstructural evolution of thin films of the Cu-Sb-S (CAS) system. The films were obtained by annealing amorphous Sb₂S₃ precursor films previously immersed in a copper solution with variable residence time. Our main findings demonstrate that varying the residence time in immersion together with the annealing and crystallization of the precursor films leads to a controlled incorporation/distribution of Cu into the films, which promotes the formation of films with phases spanning from a mixture between Sb₂S₃ and CuSbS₂ to a pure Cu₁₂Sb₄S₁₃ phase, which represents a significant variation in optoelectronic properties. The phase transition mechanisms were investigated using first-principles calculations and correlated with the structural, morphological, and optoelectronic characterization. Results indicate that vacancies serve as nucleation sites for copper incorporation. Subsequently, interstitial sites are occupied during the phase transformation from Sb₂S₃ to CuSbS₂, whereas the transition from CuSbS₂ to Cu₁₂Sb₄S₁₃ proceeds via a substitutional mechanism. This study contributes to understanding the fundamental phenomena underlying our proposed methodology. These results could promote the development of CAS-based semiconductors with predetermined properties by manipulating simple process parameters, such as the residence time in a copper solution.