Fabrication of layered hydroxide zinc nitrate films and their conversion to ZnO nanosheet assemblies for use in dye-sensitized solar cells

• Layered hydroxide zinc nitrate (LHZN) films were fabricated by a liquid method.
• The LHZN films were converted to porous LHZN/ZnO nanosheet-assembly films.
• The pyrolyzed films generated relatively high open-circuit voltages in DSSCs.
• The film on the plastic substrate showed a conversion efficiency of 2.08%.

Layered hydroxide zinc nitrate (LHZN; Zn5(NO3)2(OH)8·xH2O) films were fabricated on glass or plastic substrates by a chemical bath deposition method combined with a homogeneous precipitation in methanolic solutions. High- or low-temperature pyrolytic decomposition of the LHZN films having two-dimensional morphology was attempted to obtain porous ZnO nanosheet-assembly films. The LHZN films were converted into porous ZnO films by pyrolyzing at temperatures above 400 °C, while porous LHZN/ZnO hybrid films were obtained by pyrolyzing at a lower temperature of 120 °C without morphological changes. The pyrolyzed ZnO films were applied to dye-sensitized solar cells (DSSCs), resulting in the generation of relatively high open-circuit voltages. The low-temperature pyrolysis enabled us to fabricate the LHZN/ZnO film even on the plastic substrate. Actually a cell using the LHZN/ZnO film on an indium tin oxide-coated polyethylene naphthalate substrate showed an energy conversion efficiency of 2.08% with a high open-circuit voltage around 0.70 V.