Metal halide perovskites are studied for photodetection applications because of their outstanding optical and electrical properties. A self-powered ultraviolet-to-near infrared broadband photodetector based on a Ag-doped CsPbI3/PEDOT:PSS heterojunction was investigated. The photodetector using a CsPbI3:Ag/PEDOT:PSS heterostructure with a planar photoconductive structure operated over a broad 355-1560 nm wavelength range in self-powered mode. A terahertz signal was modulated with the CsPbI3:Ag/PEDOT:PSS structure at low optical excitation intensity to investigate its photodetection mechanism. The experimentally designed detector can present images of the letters "C", "N" and "U" in the visible and near-infrared wavelengths, indicating a potential broadband imaging application.