Abstract [60]Fullerene assembly films consisting of C60 and 1,2-diaminoethane (ethylenediamine) were easily fabricated on an amino-group-modified substrate by an alternate immersion process. The C60-assembly film was characterized after confirming the film formation using transmission absorption spectroscopy, transmission electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy. An inverted-type organic solar cell was fabricated by using the C60-assembly film as the acceptor layer in the photoactive layer of the solar cell. The resultant photoelectric conversion performances of the solar cells were evaluated using the photocurrent and photovoltage via the photoexcitation of polythiophene. The results suggested that the fabricated C60-assembly film works as an n-type semiconductor for polythiophene.