A UV−visible light self-powered photodetector based on p-CuO/n-WO 3 heterojunction structure was prepared by hydrothermal and spin-coating methods. The photoelectrical properties of the detector at room temperature and its electrical properties in the temperature range from room temperature to 200 °C were studied. In particular, it shows extremely sensitive response between 400 and 700 nm, with a sensitivity of 449.5 at room temperature, a rise time of 32.6 ms, a fall time of 31.8 ms, and a maximum responsivity of 4.589 μA/ W. Theoretical simulation reveals detailed information about the behavior of electrons and holes, emphasizing the distribution of the electric field in the steady state of the device. Theoretical simulations indicate that the WO 3 layer, where the electric field is maximized, serves as the pressure-bearing layer, with breakdown primarily occurring in this region. These findings provide a straightforward manufacturing method for self-powered devices.