NOVELTY - Manufacturing a buffer layer (40) of a photoelectric conversion device (1), comprises: preparing a reaction solution which includes a component (Z) of at least one kind of zinc source, a component (S) of at least one kind of sulfur source, a component (C) of at least one kind of citrate compound, a component (N) of at least one kind selected from ammonia and ammonium salt, and water; and film forming step for forming a zinc (Zn) compound layer consisting primarily of Zn(S, O) and/or Zn(S, O, OH) by a liquid phase method with a reaction temperature of 70-95 degrees C.    USE - The methods are useful for manufacturing a buffer layer of a photoelectric conversion device; for preparing a reaction solution used in manufacturing a Zn compound layer; and for manufacturing a photoelectric conversion device (all claimed).    ADVANTAGE - The methods efficiently provide a Zn system buffer layer manufacturing method capable of forming a film well covering an underlayer at a practical reaction speed without essentially requiring a fine particle layer that functions as the nucleation site or the growing site of or catalyst for crystal growth.    DETAILED DESCRIPTION - Manufacturing a buffer layer (40) of a photoelectric conversion device (1) having a stacked structure in which a lower electrode (20), a photoelectric conversion semiconductor layer (30) that generates a current by absorbing light, the buffer layer (40), a translucent conductive layer (60), and an upper electrode (70) are stacked on a substrate (10), the method comprises: a preparation step for preparing a reaction solution which includes a component (Z) of at least one kind of zinc source, a component (S) of at least one kind of sulfur source, a component (C) of at least one kind of citrate compound, a component (N) of at least one kind selected from ammonia and ammonium salt, and water, where: the concentration of the component (C) is 0.001-0.25 M; the concentration of the component (N) is 0.001-0.40 M; and the pH before the start of reaction is 9.0-12.0; and a film forming step for forming a zinc (Zn) compound layer consisting primarily of Zn(S, O) and/or Zn(S, O, OH) by a liquid phase method with a reaction temperature of 70-95 degrees C. INDEPENDENT CLAIMS are:    (1) a method of preparing a reaction solution used in manufacturing a Zn compound layer consisting primarily of Zn(S, O) and/or Zn(S, O, OH) included in a buffer layer (40) of a photoelectric conversion device (1) having a stacked structure in which a lower electrode (20), a photoelectric conversion semiconductor layer (30), the buffer layer (40), a translucent conductive layer (60), and an upper electrode (70) are stacked on a substrate (10), the method comprising: preparing a mixed solution by mixing a component (Z) of at least one kind of zinc source, a component (S) of at least one kind of sulfur source, a component (C) of at least one kind of citrate compound, and water; and mixing a component (N) of at least one kind selected from ammonia and ammonium salt in the mixed solution, where each component is mixed through concentration control so that the concentration of the component (C) becomes 0.001-0.25 M, the concentration of the component (N) becomes 0.001-0.40 M, and the pH becomes 9.0-12.0 in the reaction solution; and    (2) a method of manufacturing a photoelectric conversion device (1) having a stacked structure in which a lower electrode (20), a photoelectric conversion semiconductor layer (30), a buffer layer (40), a translucent conductive layer (60), and an upper electrode (70) are stacked on a substrate (10), where the buffer layer (40) is manufactured by the method above.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic cross-sectional view of a photoelectric conversion device.    Photoelectric conversion device (1)    Substrate (10)    Lower electrode (20)    Photoelectric conversion semiconductor layer (30)    Buffer layer (40)    Window layer (50)    Translucent conductive layer (60)    Upper electrode (70)