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In conventional photosensitive organic field-effect transistors (FETs) (OFETs) (photo-OFETs) based on p-type organic semiconductors, high work function metals such as Au are generally used as source/drain electrodes, whose photosensitivity is generally low. We report on the performance improvements of photo-OFETs based on palladium phthalocyanine (PdPc) by using Al as source and drain electrodes. It is concluded that the dark currents of the photo-OFET based on PdPc with Al as source and drain electrodes (denoted as Al-PdPc device) are about only one-thousandth of that of the photo-OFET based on PdPc with Au as source and drain electrodes (denoted as Au-PdPc device). This tremendous decrease of dark current results in about a three-order-of-magnitude increase for photosensitivity at the gate and drain voltages of -50 V. The enormous decrease of dark current is ascribed to the Schottky contacts between the Al source/drain electrodes and PdPc. In addition, the Al-PdPc devices show also larger photoresponsivity compared with the Au-PdPc devices.