ZnO hierarchical aggregates: Solvothermal synthesis and application in dye-sensitized solar cells

ZnO hierarchical aggregates have been successfully synthesized by solvothermal methods through reaction of zinc acetate and potassium hydroxide in methanol solution. The shapes of the aggregates were controlled by varying the ratio of Zn²⁺ and OH^– ions in the reaction system, while the size can be tuned from 2 μm to 100 nm. Oriented attachment was found to be the main mechanism of the three-dimensional assembly of small ZnO nanocrystallites into large aggregates. The performance of these aggregates in dye-sensitized solar cells (DSCs) indicated that hierarchical structured photoelectrodes can increase energy conversion efficiency of DSCs effectively when the sizes of aggregates match the wavelengths of visible light.