Electrochemical synthesis of a double-layer film of ZnO nanosheets/nanoparticles and its application for dye-sensitized solar cells

A double-layer film, consisting of an upper layer of ZnO nanosheets and a lower layer of ZnO nanoparticles (designated as ZnONS/NP), was synthesized for the photoanode of a dye-sensitized solar cell (DSSC) by a one-step potentiostatic electrodeposition on a conducting fluorine-doped tin oxide substrate at 70 degrees C in a solution containing zinc nitrate and sodium acetate, followed by the pyrolysis of the film at 300 degrees C. The growth mechanism of the double-layer nanostructure was studied by monitoring the morphological changes at various periods of electrodeposition. The effects of the concentration of acetate anion on the morphology of the double-layer structure were also studied. The double-layer film of ZnONS/NP showed a better self-established light scattering property, compared with that of a thin film of ZnO nanoparticles, prepared without acetate anion. The concentration of an acetate anion in the electrolyte for the electrodeposition of the double-layer film, the electrodeposition period, and the period for dye adsorption were optimized for obtaining the best performance for a DSSC with a photoanode consisting of the double layer. A metal-free dye, coded as D149, was used in this research. A conversion efficiency of 4.65% was achieved for a DSSC (0.2376 cm(2)) with the photoanode, consisting of the double-layer film, under 100 mW/cm(2) illumination in the wavelength range of 400-800 nm. X-ray diffraction patterns, thermo gravimetric curves, elemental analysis, scanning electron microscopic images, transmission electron microscopic image, transmission spectra, and electrochemical impedance spectra were used to explain observations. Copyright (c) 2012 John Wiley & Sons, Ltd.