Metal oxide semiconductors have long been utilized in various optoelectronic applications, including solar cells, photocatalysis, and Schottky diodes. However, these materials often encounter challenges, prompting the exploration of alternative thin-film structures composed of non-toxic and cost-effective materials. One such promising system is the Coupled Oxide Systems (COS), exemplified by CuO-ZnO (CZO). Despite the potential of COS, comprehensive studies on their synthesis and optimization remain limited. Here, we investigate the physical and optical properties of CZO thin films, confirming successful synthesis and highlighting their potential as alternatives to conventional materials like CIGS and CdTe. In the second part, we explore a novel solar cell structure, FTO/ZnO/X/CuO-ZnO/Mo, with various buffer layer options (CdS, ZnS, Zn0.38Ge0.62O, SnS2, and [Al0.025Ga0.975]2O3). Our results reveal that the solar cell with CdS as the buffer layer exhibits the highest efficiency. This work not only summarizes the fundamental principles governing the optoelectronic properties of materials but also elucidates critical strategies for fabricating high-efficiency solar cells. Furthermore, we have conducted a comparative analysis involving 70 different solar cell structures. Additionally, we discuss potential strategies for the next generation of solar cells to further enhance power conversion efficiency (PCE).