ZnO/TiO2 composite photoanodes for efficient dye-sensitized solar cells

ZnO/TiO2 composite films composed of a ZnO nanoflowers overlayer and a ZnO/TiO2 composite particulate underlayer were fabricated by a simple hydrothermal process. The as-prepared films were characterized by scanning electron microscopy, transmission electron microscopy (TEM) and diffused reflectance spectroscopy. The performance of dye-sensitized solar cells (DSCs) was investigated by photocurrent-voltage measurements, incident photon-to-current conversion efficiency (IPCE) and electro-chemical impedance spectroscopy. It was found that the ZnO/TiO2 composite film prepared with a 60 min growth time exhibited higher reflectivity than that of pure TiO2 film due to the effective light-scattering of ZnO nanoflowers, resulting in increased J(sc). In the meantime, the open-circuit potential of the device were enhanced from 698 to 826 mV due to the formation of an energy barrier by ZnO at TiO2/electrolyte interface, resulting in a 52% improvement in the power conversion efficiency from 4.64 to 7.06%.