Hydrothermal synthesis of oriented ZnO nanorod–nanosheets hierarchical architecture on zinc foil as flexible photoanodes for dye-sensitized solar cells

ZnO nanorods–nanosheets (NR–NS) hierarchical architecture consisted of long nanorod backbones and thin nanosheet branches have been synthesized on zinc foil substrate via a two-step hydrothermal growth process for dye-sensitized solar cells application. The SEM observation showed that the smooth surfaces of nanorods were surrounded by nanosheets, resulting in the enhancement of internal surface area. The photovoltaic results indicated that short-circuit current density of the ZnO NR–NS hierarchical architecture based DSSC significantly increased as compared to that of nanorods based DSSC, which was ascribed to higher dye loading and superior light scattering within the NR–NS hierarchical architecture photoanode. As a result, the conversion efficiency (η) of the ZnO NR–NS hierarchical architecture based DSSC increased by 90% compared with that of the nanorods based DSSC. The electron transport properties were further investigated by means of open-circuit voltage decay (OCVD) and electrochemical impedance spectroscopy (EIS), showing higher electron recombination in NR–NS hierarchical photoanode.