NOVELTY - A photoelectric conversion element has positive electrode (2), negative electrode (5), photoelectric conversion layer (4) with poly(N-9"-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)) as p-type organic semiconductor material and fullerene as n-type organic semiconductor material, and buffer layer (3) with molybdenum oxide. Ratio of p-type organic semiconductor material in region (R1) which is in contact with buffer layer, is more than ratio of p-type organic semiconductor material in whole photoelectric conversion layer.    USE - Photoelectric conversion element is used for bulk heterojunction-type organic thin-film solar cell.    ADVANTAGE - The element has high photoelectric conversion efficiency. The solar cell containing the element has improved curve factor.    DETAILED DESCRIPTION - A photoelectric conversion element has a positive electrode (2), a negative electrode (5), a photoelectric conversion layer (4) containing poly(N-9"-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)) as a p-type organic semiconductor material, and fullerene or fullerene derivative as n-type organic semiconductor material, and a buffer layer (3) provided between the positive electrode and the photoelectric conversion layer. The layer (3) contains molybdenum oxide. The ratio of the p-type organic semiconductor material in photoelectric conversion layer region (R1) which is in contact with the buffer layer, is more than the ratio of the p-type organic semiconductor material in the whole photoelectric conversion layer. The ratio of the p-type organic semiconductor material in photoelectric conversion layer region (R2) which is closer to the negative electrode than the region (R1) is lower than the ratio of the p-type organic semiconductor material in the whole photoelectric conversion layer. An INDEPENDENT CLAIM is included for manufacture of photoelectric conversion element.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the photoelectric conversion element. (Drawing includes non-English language text)    Substrate (1)    Positive electrode (2)    Buffer layer (3)    Photoelectric conversion layer (4)    Negative electrode (5)