NOVELTY - The method comprises: forming a thin film layer by immersing a base material film (110) in a coating solution (171) containing a transparent conductive substance, a solvent, a hole acceptor, an electron acceptor, a hole transporting substance and metal particles for 1-20 minutes while conveying the base material film by a roll-to-roll method at a speed of 0.01-20 m/min, where an angle formed by a thin film layer-formed surface and a surface of the coating solution is 0-180 degrees when the base material film is submerged into the coating solution and is removed from the coating solution.    USE - The method is useful for producing an organic solar cell (claimed).    ADVANTAGE - The method is capable of easily, economically and efficiently producing the organic solar cell with enhanced service life.    DETAILED DESCRIPTION - The method comprises: forming a thin film layer by immersing a base material film (110) in a coating solution (171) containing a transparent conductive substance, a solvent, a hole acceptor, an electron acceptor, a hole transporting substance and metal particles for 1-20 minutes while conveying the base material film by a roll-to-roll method at a speed of 0.01-20 m/min, where an angle formed by a thin film layer-formed surface and a surface of the coating solution is 0-180 degrees when the base material film is submerged into the coating solution and is removed from the coating solution. A concentration of the coating solution is 0.01-1000 mg/ml. A thickness of the thin film layer is 10-1000 nm. The method further comprises drying the thin film layer at 50-400 degrees C for 1-30 minutes after the thin film layer is formed. The thin film layer is a transparent conductive thin film layer, a metal oxide thin film layer, a photoactive layer, a hole transport layer, or an electrode. An average particle size of the metal oxide is less than or equal to 10 nm.    DESCRIPTION OF DRAWING(S) - The diagram shows a schematic view of a method of producing an organic solar cell.    Base material film (110)    Transparent conductive thin film layer (121)    Coating solution. (171)