Antimony-based thin film solar cells have rapidly developed because of their simple preparation method, abundant raw materials, and stable photoelectric performance. Among them, antimony-based light-absorbing layer materials (antimony sulfide, antimony selenide sulfide, and antimony selenide) have high absorption coefficients; thus, they have considerable application potential in indoor or underwater weak light conditions. In this study, two types of attenuation spectra are constructed to study the photoelectric response of a new antimony-based thin film solar cell under weak light. First, the light absorption capacity of the antimony selenide solar cell is adjusted through thickness. It is inferred that when the light absorber is thin, the photoelectric conversion efficiency of the cell has a significant difference. Moreover, when the light absorber is too thick, the device performance is reduced due to the carrier recombination increase. The conversion efficiency of the antimony selenide solar cell is higher than 16% in both the long- and short-wave attenuation spectra when the thickness of the light absorber is in the appropriate range of 0.4～1.2 μm. Subsequently, the selenium content adjusts the spectral absorption range of the antimony-based solar cell. It is found that the device performance of the antimony-based solar cell is significantly higher than the standard spectrum under the long-wave attenuation spectrum, and the best conversion efficiency is obtained at 20%~40% selenium content. In the short-wave attenuation spectrum, the best performance of the antimony-based solar cells appears when the selenium content is 60%. Therefore, specific spectral characteristics should determine, the optimal selenium content of antimony-based thin film solar cells in weak light conditions. Finally, the spectral response characteristics of antimony sulfide/antimony selenide double junction tandem solar cells are studied under two types of attenuation spectra. It is found that the efficiency of the tandem solar cells increases with the increase in the total thickness under the short-wave attenuation spectrum. However, in the long-wave attenuation spectrum, the best performance of the tandem solar cells can be maintained at a high level. When the total thickness of the tandem solar cell is 2 μm, and the thickness of the antimony sulfide top cell is 0.5～1.2 μm, the devices realize the rational distribution of the spectral energy in the two sub-cells under the two attenuation spectra, which maintains the efficiency of the tandem cell above 20%. Through the reasonable design of the device structure of antimony-based solar cells in this study, the high-performance output of single- and double-junction devices under different weak light conditions can be ensured, and the technical support for the research and development of antimony-based thin film solar cells with high environmental adaptability can be provided.