Controlled synthesis of ZnO branched nanorod arrays by hierarchical solution growth and application in dye-sensitized solar cells

We demonstrate the controlled synthesis of ZnO branched nanorod arrays on fluorine-doped SnO₂-coated glass substrates by the hierarchical solution growth method. In the secondary growth, the concentration of Zn(NO₃)₂/hexamethylenetetramine plays an important role in controlling the morphology of the branched nanorod arrays, besides that of diaminopropane used as a structure-directing agent to induce the growth of branches. The population density and morphology of the branched nanorod arrays depend on those of the nanorod arrays obtained from the primary growth, which can be modulated though the concentration of Zn(NO₃)₂/hexamethylenetetramine in the primary growth solution. The dye-sensitized ZnO branched nanorod arrays exhibit much stronger optical absorption as compared with its corresponding primary nanorod arrays, suggesting that the addition of the branches improves light harvesting. The dye-sensitized solar cell based on the optimized ZnO branched nanorod array reaches a conversion efficiency of 1.66% under the light radiation of 1000 W/m². The branched nanorod arrays can also be applied in other application fields of ZnO.