Hierarchical ZnO nanowire-nanosheet architectures for high power conversion efficiency in dye-sensitized solar cells

We present a two-step synthesis process to produce hierarchical ZnO nanoarchitectures that involves the preparation of ZnO nanosheet arrays by the pyrolysis of the precursor Zn₅(OH)₈Cl₂ electrodeposited on conductive glass substrates, followed by the aqueous chemical growth (ACG) of dense ZnO single-crystalline nanowires on the surfaces of the primary ZnO nanosheets. The dye-sensitized solar cell (DSSC) based on the hierarchical ZnO nanowire-nanosheet architectures showed a power conversion efficiency of 4.8%, which is nearly twice as high as that of the DSSC constructed using a photoanode of bare ZnO nanosheet arrays. The better photovoltaic performance of hierarchical ZnO nanoarchitecture DSSC was due to a better dye loading and light harvesting as a consequence of the enlargement of the internal surface area within the photoanode. Moreover, the improved performance for the DSSC with the hierarchical ZnO nanowire-nanosheet architectures may be also ascribed to more light scattering behavior through extending the optical path length within the photoanode so as to increase the light harvesting. The results demonstrate potential application of the hierarchical ZnO nanoarchitectures derived from ZnO nanosheet arrays for highly efficient DSSCs.