Thickness-Dependent Performance of Photosensitive Organic Field-Effect Transistors Based on Palladium Phthalocyanine

In this study, photosensitive organic field-effect transistors (PhOFETs) based on palladium phthalocyanine (PdPc) active layer with different thickness were fabricated and characterized. The photoelectric measurement results demonstrated that the device with 46.7-nm-thick PdPc film exhibited the best photoresponsivity of 1.47 mA/W and the maximum saturation field-effect mobility of 1.88 × 10⁻³ cm²/Vs in all devices. In addition, for drain voltage V_d = −50 V and gate voltage V_g = −50 V, the device photosensitivity of 20-nm-thick PdPc film reached a maximum at 5.77 compared with other devices in the same condition. Herein, we assumed that the different characteristics with a series thickness were dependent on the grain size and contact resistances in PdPc films. For which the grain size in PdPc films increased to a certain thickness around 46.7 nm and exhibited improved PhOFETs performances. Hereafter, the performance declined due to increasing contact resistances with thickness.