Solution-derived ZnO nanoflowers based photoelectrodes for dye-sensitized solar cells

Abstract

Flower-like ZnO nanostructures, composed of hexagonal nanorods were manipulated, via a low temperature hydrothermal method from an aqueous solution using polyethyleneimine (PEI) as a surfactant in the seed sole. It was found that the PEI in the seed sole not only affected the geometrical shape of ZnO flowers but also changed the length and spacing of the petals. These flower-like nanostructures were used as photoelectrodes in dye-sensitized solar cells. Compared to rod-like flowers (sample X1), the blade-like flowers (sample X2) nanostructures demonstrate increased power conversion efficiency (η) of about 106%. Meanwhile, short-circuits current density (JSC), open-circuit voltage (VOC), and fill factor (FF) are all substantially improved. The enhancement of η, VOC and FF in the blade-like-flower photoelectrodes were mainly ascribed to the enlargement of internal surface area between the blades for higher dye loading and the improved light harvesting from efficient light scattering. The band gap energies were 3.31eV and 3.27eV for rod-like flowers and blade-like flowers respectively. The decrease in the optical band gap with the increase of film roughness was due to decrease of lattice defects.