This article describes the performance analysis of the fabricated visible photodetector based on the Pd/pentacene/ZnO/ITO/PET structure. Hydrothermal and thermal vacuum deposition techniques deposited the ZnO and pentacene films, and FESEM images examined the topology of the deposited films. The I-V characteristics of a device were assessed in both dark and light environments throughout a voltage range of −5 to 5 V. With the help of Cheung's method and the standard thermionic emission theory, electrical performance parameters in the dark mode were extracted. The barrier height and ideality factor for the thermionic emission test were 0.784 eV and 2.19, respectively. In contrast, the barrier height and ideality factor for the Cheung technique was found to be 0.77 eV and 1.4, respectively. This research demonstrates Cheung's approach, which accounts for series resistance 692.46 Ω. The proposed photodetector exhibits a high gain of 579 and responsivity of 279 A/W.