Density-controlled ZnO nanorod arrays (ZNAs) were prepared on pre-treatment substrates by a hydrothermal approach under different conditions. The effect of substrate pre-treatment conditions on controlling the density of ZNAs was systematically studied by scanning electron microscopy and x-ray diffraction. It is demonstrated that the substrate pre-treatment conditions such as the concentration of the ZnO colloid, spin coating times, and substrate annealing treatment have their respective influence on controlling the density of the ZNAs. The introduction of a ZnO nanoparticle layer on the substrate not only helps to control the nanorod density but also has a strong impact on the orientation of the nanorod arrays. Although controlling the spin coating process has a similar mechanism to controlling the concentration of colloid, it offers a convenient method to prepare a series of ZNAs with variable density. An annealing treatment of the substrate can influence the microstructure of the ZnO seed layer and then influence the density of the ZNAs.

We present a two-step electrochemical deposition process to synthesize hierarchical zinc oxide (ZnO) nanorod-nanosheet structures on indium tin oxide (ITO) substrate, which involves electrodeposition of ZnO nanosheet arrays on the conductive glass substrate, followed by electrochemical growth of secondary ZnO nanorods on the backbone of the primary ZnO nanosheets. The formation mechanism of the hierarchical nanostructure is discussed. It is demonstrated that annealing treatment of the primary nanosheets synthesized by the first-step deposition process plays a key role in synthesizing the hierarchical nanostructure. Photovoltaic properties of dye-sensitized solar cells (DSSCs) based on hierarchical ZnO nanostructures are investigated. The hierarchical ZnO nanorod-nanosheet DSSC exhibits improved device performance compared to the DSSC constructed using photoelectrode of bare ZnO nanosheet arrays. The improvement can be attributed to the enhanced dye loading, which is caused by the enlargement of internal surface area within the nanostructure photoelectrode. Furthermore, we perform a parametric study to determine the optimum geometric dimensions of the hierarchical ZnO nanorod-nanosheet photoelectrode through adjusting the preparation conditions of the first- and second-step deposition process. By utilizing a hierarchical nanostructure photoelectrode with film thickness of about 7 μm, the DSSC with an open-circuit voltage of 0.74 V and an overall power conversion efficiency of 3.12% is successfully obtained.

No abstract

No abstract