To advance the development of high-performance organic solar cells, in recent years, the academic community has conducted in-depth research on the design of non-fullerene acceptor materials and the interplay between their structure and properties. Structural modifications of these materials involve optimization of the core structure, side chain engineering, expansion of the conjugated system, and doping with heteroatoms. Focusing on sulfur, due to its outstanding semiconducting properties, it is widely used in the manufacturing of electronic materials and semiconductor devices, especially in the field of organic solar cells. Selenium, as a homologous element of sulfur, not only shares similar chemical and physical properties but also possesses unique characteristics. For instance, compared to sulfur, selenium has a larger atomic radius, which provides additional space within molecules, facilitating charge transfer and improving electron distribution. Moreover, due to its greater mass, selenium atoms have lower vibrational frequencies, a characteristic that enhances light absorption capabilities within the visible spectrum. Therefore, the introduction of selenium atoms is considered a potential approach to enhancing the efficiency of organic solar cells. This review focuses on the impact of the position and ratio of selenium atoms in condensed-ring electron acceptors (such as ITIC and Y6 derivatives) and certain non-condensed ring acceptors on their photovoltaic performance. It also discusses the synergistic effect of selenium atom substitution with other optimization strategies and its comprehensive impact on the performance of various types of organic solar cells (including small molecule, polymer, and all-polymer solar cells).