In the present study, we investigated the electrical, optical, and photoresponse characteristics of aluminum 8-hydroxyquinoline (Alq3)/silicon heterojunctions. The Alq3 thin film was successfully coated using the spin coating method on p-type Si. In order to determine the energy band gap diagram, the highest occupied molecular orbital-lowest unoccupied molecular orbital energy diagram was simulated with the density functional theory program. The quality of the coating and morphological properties of the Alq3 thin film were characterized using atomic force microscopy and scanning electron microscopy. The optical characteristics of the organic layer were investigated using ultraviolet-visible spectrophotometry. A reference diode was also fabricated with an Alq3/pSi photodiode to obtain a better understanding of the electrical and optical properties of the device. The photodiode and diode parameters comprising the saturation current, ideality factor, barrier height, short circuit current, open circuit voltage, fill factor, and power conversion efficiency were obtained from the current-voltage measurements. These measurements were performed in the dark and under different illumination conditions at room temperature. The experimental results showed that the properties of the photodiode device were improved by using organic Alq3 microdots, and thus the device may have optoelectronic and photovoltaic applications.