Time-varied synthesis of hierarchical ZnO microspheres and their applications in dye-sensitized solar cells

Hierarchically nano-structured ZnO microspheres have been synthesized solvothermally at variable reaction times (6, 12, 36, and 48 h) by using ethylene glycol as a solvent, zinc acetate as precursor, and hexamethylene triamine (HMT) as structure directing agent. The study also focused on the mechanism of time-dependant growth of hierarchical ZnO microspheres and their deployment in dye-sensitized solar cells (DSSCs) as photoanode. Longer reaction times lead to formation of nearly spherical ZnO microspheres. The structural and morphological analysis reveals the formation of a wurtzite hexagonal crystalline structure having a microsphere-like morphology. ZnO hierarchical microspheres synthesized at different reaction times have been used as photoanode in DSSCs which show enhanced light-harvesting properties than the commercial ZnO powders. ZnO microspheres synthesized at 48 h show maximum current density and cell efficiency of 8.51 mA/cm(2) and 3.31%, respectively. This enhancement in photovoltaic parameters could be due to highly porous microspheres which provide more specific surface area for dye loading, retardation of recombination, and better charge transport.