It has been attempted to utilize plastic substrates for electrodes, instead of conventional glass substrates, to fabricate flexible, lightweight, and low-cost dye-sensitized solar cells (DSSCs). We examined a pyrolysis method by which preformed layered hydroxide zinc acetate (LHZA: Zn5(OH) 8(CH3COO)2·2H2O) films were converted into ZnO films at temperatures below 120 °C. Since the pyrolyzed films still contained zinc acetate compounds, they were immersed in hot water aiming at removing such the impurities. This hot water treatment influenced the film morphology to a large extent. The energy conversion efficiency of 3.41% was obtained for the cell using an N719/ZnO electrode fabricated on an indium tin oxide-coated polyethylene naphthalate (ITO-PEN) substrate through the present pyrolysis method.