Antimony sulfide selenide thin film solar cells have drawn great interest in the field of photovoltaic due to their advantages of simple preparation method, abundant raw materials, non-toxic and stable photoelectric properties. After the development in recent years, the photoelectric conversion efficiency of antimony sulfide selenide solar cells has exceeded 10%, which has great development potential. In this work, the carrier recombination near n/i interface in antimony sulfide selenide solar cells is studied. It is found that the characteristics of the n/i interface are affected by the interfacial electron mobility and energy band structure. The improvement of the interface electron mobility can make the electrons more effectively transferred to the electron transport layer, and realize the effective improvement of the short circuit current density and fill factor of the device. Moreover, the introduction of ZnO/Zn_1–xMg_xO double electron transport layer structure can further optimize the performance of antimony sulfide selenide solar cells. The change of Zn_1–xMg_xO energy level position can adjust the energy level distribution of the interface and light absorption layer simultaneously. When the conduction band energy level of Zn_1–xMg_xO is –4.2 eV and the corresponding Mg content is 20%, the effect of restraining the carrier recombination is the most obvious, and the antimony sulfide selenide solar cell also obtains the best device performance. Finally, under the ideal condition of removing the defect state, the antimony sulfide selenide solar cells with 600 nm in thickness can achieve 20.77% theoretical photoelectric conversion efficiency. The research results provide theoretical and technical support for further optimizing and developing the antimony sulfide selenide solar cells.