**1. Introduction**

Low-dimensional ZnO nanoparticles (NPs), quantum dots (QDs), and ZnO nanowires (NWs) have attracted much attention due to their good crystal quality, chemical stability, and unique optical properties. ZnO nanowire is also expected to play an important role because their manifold properties are interconnected as functional units in the fabrication of electronics, photonics, photocatalysts, and piezotronics with nanoscale dimensions. ZnO QDs and NPs are of great interest because of the three-dimensional confinement of carrier, and phonon leads not only continuous tuning of the optoelectronic properties but also improvement in

device performance. As a wide-bandgap semiconductor, ZnO has been reported as an alternative for dye-sensitized solar cells (DSCs) because ZnO offers a large direct bandgap which is close to TiO2 and even higher electron mobility (155 cm2 V<sup>−</sup><sup>1</sup> s<sup>−</sup><sup>1</sup> ) for the high-quality thin film [1]. ZnO provides a promising alternative for improving the performance of the photoelectrode in DSCs because ZnO can be tailored to various nanostructures. In the present proposal, first, I will present the ZnO nanowire structures via a low-pressure vapor-phase deposition and a simple solvothermal method. The one-dimensional ZnO NWs could simultaneously afford a direct conduction pathway to significantly enhance the overall efficiency of the DSCs [2, 3]. Next, I also will demonstrate how to employ the hierarchical structure of the ZnO NPs, fabricated from sol-gel method, which would promote light scattering through the presence of secondary colloidal spheres, thus, enhancing photon absorption to improve the short-circuit current density and the overall light conversion efficiency.
