An optical energy conversion apparatus 10 includes a first impurity doped semiconductor layer 5, formed on a substrate, and which is of a semiconductor material admixed with a first impurity, an optically active layer 6, formed on the first impurity doped semiconductor layer 5, and which is of a hydrogen-containing amorphous semiconductor material, and a second impurity doped semiconductor layer 7, admixed with a second impurity and formed on the optically active semiconductor layer 6. The second impurity doped semiconductor layer is of a polycrystallized semiconductor material lower in hydrogen concentration than the material of the optically active semiconductor layer 6. The average crystal grain size in the depth-wise direction in an interfacing structure between the optically active semiconductor layer 6 and the second impurity doped semiconductor layer 7 is decreased stepwise in a direction proceeding from the surface of the second impurity doped semiconductor layer towards the substrate 1. By controlling the hydrogen concentration of the second impurity doped semiconductor layer 7, the number of dangling bonds in the second impurity doped semiconductor layer 7 is significantly decreased to exhibit superior crystallinity to improve the conversion efficiency of the apparatus 10.