Fabrication of ZnO films consisting of densely accumulated mesoporous nanosheets and their dye-sensitized solar cell performance

Nanocrystalline and mesoporous ZnO films approximately 4 μm in thickness were fabricated through a simple chemical deposition of Zn₄CO₃(OH)₆·H₂O in an aqueous solution of zinc nitrate and urea and subsequent pyrolysis at a low temperature of 300 °C. Microscopic observation of the films revealed that they were composed of mesoporous nanosheets accumulating with submicrometer-order spacing between them on conducting glass substrates. Adsorption of N-719 dye onto the ZnO surface, for application to dye-sensitized solar cells, led to dye-loading of 1.1 × 10^− 7 mol/cm² in spite of the relatively small thickness. The resultant ZnO/N-719 photoanode exhibited a short-circuit photocurrent density of 13.8 mA/cm², which is of the highest level ever reported for ZnO. An overall light-to-electricity conversion efficiency of 3.3% was achieved under 1 sun AM1.5 illumination without any optimization in view of the other cell components.