Si-based metal-insulator-semiconductor (MIS) Schottky junction solar cells with the basic structure Al/Si/TiO2/Au were fabricated. This structure was modified by the addition of nanostructured porous silicon (nanoPS) layers and silver nanoparticles (AgNPs), resulting in devices with the following structures: Al/Si/nanoPS/TiO2/Au and Al/Si/nanoPS+AgNPs/TiO2/Au. The key performance parameters of the three MIS Schottky junction solar cells were determined, including spectral photocurrent response, short-circuit current density, open-circuit voltage, fill factor, and efficiency. The experimental results show a remarkable enhancement in the overall performance of the solar cells upon the addition of nanoPS and AgNPs layers to the basic structure. An energy band model is proposed for the Si-based MIS Schottky junction solar cells to understand the different photogeneration and conduction mechanisms.