Hierarchical rhombus-shaped ZnO array: Synthesis, formation mechanism and solar cell application

Abstract A simple synthesis route was designed to fabricate a novel hierarchical nanostructure consisting of a zinc hydroxide fluoride [Zn(OH)F] nanorod core with a shell of porous wrinkle textured zinc carbonate hydroxide [Zn 5 (CO 3 ) 2 (OH) 6 ]. By adding two precipitating agents, ammonium fluoride (NH 4 F) and urea [(NH 2 ) 2 CO], the one-pot reactions realized sequential decomposition of the precipitating agents following a temperature ramp and the onset of a conformal shell of Zn 5 (CO 3 ) 2 (OH) 6 to succeed the formation of a preferentially oriented Zn(OH)F nanorod forest. Single phase Zn(OH)F nanorods and Zn 5 (CO 3 ) 2 (OH) 6 microspheres were also obtained in the absence of one of the precipitating agents. These two precursors in three configurations were transformed by calcination to porous ZnO nanostructures with the original morphologies and pore structures retained. Chemical reactions and the formation mechanisms are proposed and discussed for both of the precursors and the resulting products from the calcination. The ZnO nanostructures were successfully employed in dye-sensitized solar cells. The light-to-electricity conversion shows that the hierarchical ZnO transformed from core/shell structured Zn(OH)F/Zn 5 (CO 3 ) 2 (OH) 6 exhibits significant enhancement to the short-circuit current density due to its large specific surface area and high growth density compared with the nanorod and microsphere counterparts, respectively.