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 °C in a solution containing zinc nitrate and sodium acetate, followed by the pyrolysis of the film at 300 °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 cm2) with the photoanode, consisting of the double-layer film, under 100 mW/cm2 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 © 2012 John Wiley & Sons, Ltd.