ZnO Nanostructures Towards Photoanode Of Solar Cells-Synthesis And Properties

As a new generation of solar cells, dye-sensitized solar cells have caused widespread concern in the scientific community. Photoanode materials are decisive on the power conversion efficiency. As the best alternative photoande material of TiO₂, ZnO has a similar band gap with TiO₂, but the smaller dielectric constant, the faster electron mobility and easy to be synthesized into a variety of morphologies.In this paper, different morphologies of ZnO structure, including nanowires, nanobulks, nanotubes, up-flowers-down-tubes, complex structures, were synthesized by hydrothermal and electrochemical etching methods. ZnO nanowires are formed due to the continuous adsorption of HMT on its lateral planes; nanobulks were synthezed by connecting longer and thicker nanowires at higher concentration of reaction solution; nanotubes are prepared by etching polar planes of nanobulks by the OH- hydrolyzed from EDA; a so-called up-flowers-down-tube nanostructure was obtained by etching at higher concertration of OH- ions at high temperature; a complex structure composed of flowers, tubes, and bared substrate was formed at higher temperature and longer time.In order to investigate the properties of different ZnO structures, the nanostructrues were assembled into solar cells and their performances were tested. On the other hand, desorption testing and electrochemical impedance were introduced. The results show that although the dye adsorption of nanowires is weaker and the cell efficiency is poor, it has a maximum dye utilization and minimum resistance of electronic transmission; the structure of up-flowers-down-tubes shows the highest cell efficiency, because it has the largest dye adsorption and smaller transmission resistance; nanobulks and nanotubes have larger impedance, less dye adsorption and lower cell efficiency; the complex structure has higher capability of dye adsorption, but it faces the short-circuit problem, the battery efficiency is very low. In summary, the structure of up-flowers-down-tubes is most suitable for ZnO photoanode, while the nanowires have high potential for the next research.