An effective photodetector based on a family of p-type semiconductors with unique properties is still required by current trends in optoelectronics. The purpose of this study is to enhance the performance of p-type copper oxide films by doping them with bismuth. The pure copper oxide films were successfully fabricated with 1, 2, and 3 wt% of Bi by the spin coating method in an air atmosphere. Advanced techniques were used to describe the fabricated non-doped and Bi-doped CuO films to understand their structural, topological, and optical characteristics. X-ray diffraction patterns of non-doped and Bi-doped CuO films have demonstrated that they have polycrystalline structures, with a preference for growth in both (−111) and (200) orientations. Copper oxide film with 2% Bi doping exhibited the most uniform particle size distribution compared to others. While 3% Bi-doped CuO thin film exhibits the highest photon absorption, 2% Bi-doped CuO thin film transmits more photons. The direct band gaps of the non-doped and Bi-doped CuO samples were found between 1.77 and 1.94 eV. Copper oxide thin film with 2% Bi has the lowest refractive index. While the 2% Bi-doped CuO heterojunction photodetector shows the highest photosensitivity, responsivity, and detectivity, its rise and time are the lowest. Since 2% Bi-doped CuO film has a good crystal structure, large crystalline size, low particle boundary numbers, and a more homogeneous particle size distribution, the number of traps and defects in this thin film is low, and the recombination of charge carriers is limited. Thus, this thin-film-based heterojunction exhibited the best photodetector property, and the results of this work give a way to create effective photodetectors and adjust their performance over a broad range.