Hiearchical ZnO rod-in-tube nano-architecture arrays produced via a two-step hydrothermal and ultrasonication process

Vertically aligned hierarchical ZnO rod-in-tube nano-architecture arrays are produced via a two-step process including an initial hydrothermal reaction followed by ultrasonication growth. The ZnO nanorod arrays grow firstly on FTO glass through a hydrothermal process and then act as templates for the fabrication of rod-in-tube nano-architectures during ultrasonication. The as-prepared ZnO rod-in-tube nano-architectures are assembled by the self-stacking of hexagonal nanorings along with <001> orientation of ZnO nanorod templates. Both hexamethylenetetramine and sodium citrate are found to play key roles in the formation of the novel ZnO rod-in-tube nano-architectures. The power conversion efficiency of dye-sensitized solar cell based on hierarchical ZnO rod-in-tube nano-architectures photoelectrode (0.91%) exhibits a significant improvement (75%) compared to that of ZnO nanorods (0.52%).