Although C-60 is known as a typical n-type organic semiconductor, Schottky-type cells of an ITO/C-60/Al structure do not show definite photovoltaic effects. Thin metallic interlayers were inserted at the C-60/Al interface to examine enhancement of the power conversion efficiency in the cells. An ITO/C-60/Mg/Al cell showed an efficiency up to 0.15% for AM1.5, which is the largest efficiency in the Schottky-type cells of n-type organic semiconductors. The improvement of the photovoltaic effects seems to be caused by intercalation of Mg into C-60 layer as a dopant.