Silicon nanowires (SiNWs) combined with a conducting polymer are studied to constitute a hybrid organic / inorganic solar cell. This type of cell shows a particularly high interfacial area between SiNWs and the polymer so that interfacial control and interface optimization are required. For that purpose we terminated the SiNW surfaces with well selected functional groups (molecules) such as native oxide (hereinafter SiO2-SiNW), hydrogen (hereinafter H-SiNW) and methyl (hereinafter CH3-SiNW). A radial hetero-junction solar cell is formed and the cell parameters with and without interface control by functionalization.