In this study, the effects of illumination on the electrical properties as well as the structural, optical and photo-electrical properties of organic complex-based photodiodes synthesized with varying amounts of Mn contents were investigated. The thermogravimetric measurement, atomic force microscope images and absorbance measurements were used to determine the structural and optical properties of the produced devices, while current-voltage, capacitance-voltage and transient current measurements were used to determine their electrical properties. From the measurements performed under different light intensities, it is seen that the device has a high sensitivity to light and exhibits photoconductive and photocapacitive behaviors. However, it is another important result obtained that the crucial electrical parameters such as barrier height and ideality factor change with the Mn content and exposed light intensity. In addition, it is seen from the capacitance attributes that the fabricated device is strongly dependent on the frequency and the applied voltage. The band gap value of the synthesized organic complex was determined as 3.82 eV. Atomic force microscope images show that the material has been successfully coated and the roughness on the surface is low. As a result of the experimental studies carried out, the device, in which the manufactured devices are used as the interface layer of the organic complex with Mn content in the ratio of 1: 1, can be used in optoelectronic applications, especially as a photodiode.