Currently, the research in absorber films for solar cells is focused on the development of non-toxic, low-cost, and high-available materials. Thus, the CuSbS2 phase of the Cu-Sb-S system is promising due to its attractive optoelectronic properties. Chalcostibite thin films have been deposited by several approaches, however, their synthesis, as a predominant phase, is still challenging. In this work, CuSbS2 films were prepared by a simple immersion of amorphous Sb2S3 into a Cu solution. The effect of the annealing on their microstructure was assessed, too. From energy dispersive, X-ray photoelectron, inductively coupled plasma atomic emission, and Raman spectroscopies results, the formation of CuSbS2 was verified to occur through simultaneous dissolution and cationic exchange reactions. The microstructural evolution of the films goes from amorphous, passing by a chalcostibite phase, which enhances its crystallinity with further temperature increment, and finally, it undergoes a phase transition to tetrahedrite. These transitions have a strong impact on the charge carrier concentration, which generates important changes in their optoelectronic performance. The simplicity together with the demonstrated strong impact of the annealing make this methodology versatile and a powerful tool to prepare high-quality Cu-Sb-S films, as interesting candidates as absorber layers in solar cells and other optoelectronic devices.