The progress of modern life is largely based on technological developments. This is possible with the development of materials that increase the functionality of electronic devices. In this regard, the present work reports the synthesis of MgO and MgO-graphene (MgO-G) composite materials and their device applications. In the first step, MgO and MgO-G nanomaterials synthesis were carried out and then multiple approaches were used to characterize their structural, optical, and morphological properties as interfacial layer. In the next step, the MgO/n-Si and MgO-G/n-Si device structures were fabricated by using spin coating method. Finally, their diode and photodiode properties were investigated in the dark and under varied light energy. The dark current-voltage (I-V) measurements show that the MgO-G/n-Si exhibits better electrical properties compared to the MgO/n-Si device. Similar results were observed for the photo I-V measurements too, the MgO-G/n-Si diode exhibits excellent self-powered photoresponse characteristics with an optical responsivity of 141 mAW-1, light on/off ratio of ~ 2.2 x 103 and, specific detectivity of 9.84 x 108 Jones at -1 V, which is higher than MgO/n-Si diode (0.541 mAW-1, 28.2 and 6.89 Jones) under the 1 Sun light intensity. The obtained results show that the fabricated MgO-G/n-Si diode has a promising potential for optoelectronic application.