Fullerene C-60-ethylenediamine adduct particles were solubilized in toluene by the addition of acyl chloride. An inverted-type bulk-heterojunction organic thin-film solar cell using polythiophene and the solubilized C60-ethylenediamine adduct as the photoactive layer was fabricated, and the layer generated a photocurrent via the photoexcitation of polythiophene. The solar-cell performance suggested that the solubilized C-60-ethylenediamine adduct works as an n-type semiconductor for polythiophene.