The present invention provides a 3-dimensional P-N junction solar cell composed of a base board coated with a back plate on the upper face of the same; a P type semiconductor thin film formed on the top side of the back plate which has a 3-dimensional porous structure and is composed of P type semiconductor crystal grains; a N type buffer layer formed on the surface of the crystal grains of the said P type semiconductor thin film with playing a role of coating the thin film; and a transparent electrode formed on the surface of the crystal grains of the P type semiconductor thin film on which the N type buffer layer is formed. The solar cell of the present invention is a P-N junction solar cell including a 3-dimensional photo catalytic thin film, which can provide an improved photoelectric conversion efficiency, compared with the conventional P-N junction solar cell, owing to the formation of the N-type buffer layer on the surface of the crystal grains of the 3-dimensional P type semiconductor thin film.
