The relatively large bandgaps of the methylammonium lead halide perovskites are the major obstacle to achieving broadband response in the lead-based perovskite photodetectors. Partial or total substitution of lead with tin leads to smaller bandgaps for perovskite materials. Here, we investigated the application of a mixed tin-lead perovskite material, (FASnI3)0.6(MAPbI3)0.4, with small bandgap of 1.24 eV as the absorber material in a perovskite photodetector. The device simulation is performed by using SCAPS simulation software. The effect of different parameters such as absorber layer quality and thickness, interface defects, doping concentration and carrier mobility on the performance of the device is studied. The simulation results clarify that the parameters optimization can result in achieving a self-powered photodetector with broad spectral response from 300 to 1050 nm wavelength, a high responsivity of 0.6 A W-1 at 930 nm, almost flat detectivity of over 1013 Jones and a wide linear dynamic range. We believe this study can provide theoretical guidance for the design of highly sensitive, broadband, mixed tin-lead perovskite photodetectors. Manuscript profile