Schottky type photodiodes have gained great interest due to their fast response to light. Various materials have been used to improve their efficiency behaviors as interlayers or electrodes. In this study, we synthesized Cu- and Mn-centered nicotinamide/nicotinic acid complexes and used them for Schottky type photodiode as interfacial layer. Thus, Al/Cu-complex/p-Si and Al/Mn-complex/p-Si metal semiconductor heterojunctions were fabricated by Al metal and p-Si semiconductor. The I–V and I-t analyses were employed to identify the fabricated devices under various light power intensities. The devices were evaluated according to various diode parameters such as series resistance, ideality factor and barrier height values obtained by I–V characteristics data from thermionic emission theory, Cheung and Norde techniques. Furthermore, various parameters of photodetection such as specific detectivity, photosensitivity and responsivity were calculated from the I-t measurements. The results reveal that heterojunctions can be employed for photodiode applications.