Preparation And Photoelectrochemical Performance Of Self-Assembly Structure Based ZnO Nanorods

Zinc Oxide (ZnO) is a direct wide band gap compound semiconductor with a band gap of3.37eV and large exciton bounding energy of60meV at room temperature, which make it suitable for many applications such as light-emitting diodes (LEDs), solar cells, nanogenerators, field-effect transistors (FETs), ultraviolet photodetector, piezoelectric device, surface acoustic wave device, gas sensor, photocatalytic degradation and so on. More recently, the preparation and applications of ZnO nanostructures in the photoelectric field have received considerable interest from scientists in the international, which has become a hot spot in the nano-optoelectronic field of the international frontier topics. The dissertation develops the following research on the problems of the growth controlled ZnO nanorods, design and preparation of nano optoelectronic devices based ZnO nanorods:1:By simply heating an aqueous solution containing zinc acetate and ammonium hydroxide, the accumulation of hexagonal ZnO nanorods were successfully prepared at the pH value of11, the Zn2+concentration of0.25 mol/L, the aging temperature of85℃. The results suggest that different morphologies were observed by varing the pH value, the Zn2+concentration and aging temperature. Octahedrally microcrystals of the stable intermediate ε-Zn(OH)2were produced at early stages under these conditions. Transformation from ε-Zn(OH)2to ZnO was observed to occur at various aging times. Transformation from ε-Zn(OH)2to ZnO followed two mechanisms: dissolution-reprecipitation and solid-solid phase transformation mechanism.2:Using the successive ionic layer adsorption and reaction (SILAR), the ZnO seed layer with the size of30nm were successfully prepared onto the FTO substrate under the pH value of10, the Zn2+concentration of0.2mol/L and50cycles. High-density ZnO nanorod arrays with well-defined hexagonal facets (002) were grown vertically on the substrate by the chemical bath deposition, and the diameter and average length of the ZnO nanorod arrays were around150-200nm and1μm. The results show morphology and size of ZnO seed vary with the pH value, the Zn2+concentration and SILAR cycles.The alignment, diameter and density of ZnO nanorod arrays depend on the pH value, the Zn2+concentration, the aging temperature, seed layer and the placement of substrate.3:By simply heating an aqueous solution containing zinc acetate and triethanolamine, ZnO submicrometer-sized aggregates consisting of nanoparticles were successfully synthesized and the size of nanoparticles is around20～30nm.The results show that the the products was changed from layered Zn5(OH)8Ac2·2H2O to ZnO nanoparticles, simultaneously, ZnO nanoparticles assemble into spherical structure until the precursor of Zn5(OH)8Ac2·2H2O completely disappeared with the increase of reactin time. ZnO composite aggregate arrays of nanorods and nanoparticles with a coarse semisphere-like top were obtained by immersing ZnO nanorod arrays into aqueous solution. Obvious absorption peak in the visible region was observed for ZnO composite aggregate arrays of nanorods and nanoparticles, ZnO submicrometer-sized aggregates consisting of nanoparticles. Due to their relatively high surface area, fast electron transport, and enhanced light-scattering capability, solar-to-electric energy conversion efficiency of DSSC based ZnO composite aggregate arrays of nanorods and nanoparticles (3.17%) were much higher than those obtained for the monodisperse aggregate DSSC and ZnO nanorod array DSSC.4:Using hydrothermal method, uniform octahedrons of Cu2O were successfully synthesized in the aqueous solution containing cupric acetate and triethanolamine under the reaction temperture of160℃, reaction time of80min. The results show that Cu2O were converted into Cu crystal under the higher reaction temperture and longer reaction time, different morphology of Cu2O were observed under the addition of surfactant CTAB or alcohol solvent. Dense Cu2O film with thickness of1.5μm were obtained by immersing ZnO nanorod arrays into aqueous solution. The absorption intensity in visible region was enhanced for Cu2O/ZnO heterojunction. Under an AM1.5solar simulator, typical solar cell behavior of the Cu2O/ZnO heterojunction was evaluated, with the short circuit current density (Jsc) of7.8mA/cm2, the open circuit voltage (Voc) of0.36V, and the fill factor (FF) of31%, the photovoltaic conversion effciency (PCE) was found to be0.86%.